Foldable device, foldable substrate and manufacturing method thereof

Abstract

A foldable device includes a foldable substrate foldable about an axis and a substrate thickness defined between a first major surface and a second major surface. The foldable substrate includes a central portion between the first portion and the second portion. The first portion includes a substrate thickness. The central portion includes a central thickness that is less than the substrate thickness. In some embodiments, the width of the central portion is less than or equal to about 45 millimeters. A method of manufacturing a collapsible device includes forming a recess in a first major surface of a collapsible substrate. In some embodiments, a method includes chemically strengthening a foldable substrate.

Description

[0001] This divisional application of a patent for invention is a divisional application of the patent application for "Foldable Device, Foldable Substrate and Manufacturing Method Thereof", with international application number PCT / US2020 / 048507, international filing date of August 28, 2020, and national stage entry application number in China of 202080075558.X.

[0002] Cross - reference to related applications

[0003] This application claims the benefit of priority under 35 U.S.C.§119 to the following applications: U.S. Provisional Application No. 63 / 022748, filed on May 11, 2020; U.S. Provisional Application No. 62 / 914720, filed on October 14, 2019; and U.S. Provisional Application No. 62 / 893291, filed on August 29, 2019. Their respective contents are hereby incorporated by reference in their entireties and made a part of this application. Technical field

[0004] The present disclosure generally relates to foldable devices, foldable substrates, and manufacturing methods thereof. More specifically, it relates to foldable devices and foldable substrates including various parts, and methods for manufacturing foldable devices and foldable substrates. Background art

[0005] Glass - based substrates are commonly used in, for example, display devices such as liquid crystal displays (LCDs), electrophoretic displays (EPDs), organic light - emitting diode displays (OLEDs), plasma display panels (PDPs), etc.

[0006] There is a desire to develop foldable forms of displays and foldable protective cover plates mounted on foldable displays. The foldable displays and cover plates should have excellent impact resistance and puncture resistance. At the same time, the foldable displays and cover plates should have a small minimum bending radius [e.g., about 10 millimeters (mm) or less]. However, plastic displays and cover plates with a small minimum bending radius often have poor impact resistance and / or puncture resistance. Additionally, conventional wisdom suggests that ultra - thin glass substrates with a small minimum bending radius [e.g., a thickness less than or equal to about 75 micrometers (μm or micron)] often have poor impact resistance and / or puncture resistance. Moreover, thicker glass substrates (e.g., greater than 125 micrometers) with excellent impact resistance and / or puncture resistance often have a relatively large minimum bending radius (e.g., greater than or equal to about 30 mm). As a result, there is a need to develop foldable devices with a low minimum bending radius and excellent impact and puncture resistance. Summary of the invention

[0007] This document describes foldable devices, foldable substrates, and methods of manufacturing foldable devices and foldable substrates. The foldable substrate includes a first part and a second part. Each part may include a glass-based and / or ceramic-based portion, which can provide excellent dimensional stability, a reduced incidence of mechanical instability, excellent impact resistance, and / or excellent puncture resistance. The first part and / or the second part may include a glass-based and / or ceramic-based portion that includes one or more regions of compressive stress, which can further increase impact resistance and / or puncture resistance. By providing a substrate that includes a glass-based and / or ceramic-based substrate, the substrate can also provide increased impact resistance and / or increased puncture resistance while enabling excellent folding performance. In some embodiments, the substrate thickness can be large enough [e.g., from about 80 microns (micron or μm) to about 2 millimeters] to provide excellent impact resistance and excellent puncture resistance. The provided foldable substrate includes a central portion that includes a central thickness that is less than the substrate thickness of the first part and / or the second part, thereby enabling a small effective minimum bending radius [e.g., about 10 millimeters (mm) or less] based on the reduced thickness of the central portion. In some embodiments, the central thickness can be small enough (e.g., from about 10 microns to about 125 microns) in the bending region (e.g., the central portion) of the foldable device to provide a low effective bending radius (e.g., less than or equal to about 10 mm, less than or equal to about 9 mm, less than or equal to about 8 mm, less than or equal to about 7 mm, less than or equal to about 6 mm, less than or equal to about 5 mm, less than or equal to about 4 mm, less than or equal to about 3 mm, less than or equal to about 2 mm, or about 1 mm).

[0008] In some embodiments, the foldable substrate may include a first transition portion that attaches the central portion to the first part and / or a second transition region that attaches the central portion to the second part. Providing a transition region with an increasing thickness can reduce stress concentration in the transition region and / or avoid optical distortion. Providing a transition region with a sufficient length (e.g., about 1 mm or greater) can avoid optical distortion that might otherwise exist due to a sudden step change in the thickness of the foldable substrate. Providing a transition region with a sufficiently small length (e.g., less than or equal to about 5 mm) can reduce the amount of the foldable substrate with a medium thickness, and the foldable substrate with a medium thickness can have reduced impact resistance and / or reduced puncture resistance.

[0009] Provide a first portion and / or a second portion, and the first portion and / or the second portion include one or more alkali metals at an average concentration that is close to (e.g., within 100 parts per million, within 10 parts per million based on oxides) the concentration of one or more alkali metals in the central portion, whereby the expansion difference between the first portion and / or the second portion and the central portion due to chemical strengthening can be minimized. Substantially uniform expansion can reduce the incidence of mechanical deformation and / or mechanical instability due to chemical strengthening.

[0010] The ratio of the provided layer depth to the thickness of the first portion and / or the second portion is close to (e.g., within 0.1%, within 0.01%) the corresponding ratio of the central portion, whereby the difference in near-surface expansion between the first portion and / or the second portion and the central portion due to chemical strengthening can be minimized. Minimizing the difference in near-surface expansion can reduce the stress and / or strain in the plane of the first major surface, the second major surface, the first central surface region, and / or the second central surface region, which can further reduce the incidence of mechanical deformation and / or mechanical instability due to chemical strengthening.

[0011] The ratio of the provided compression depth to the thickness of the first portion and / or the second portion is close to (e.g., within 1%, within 0.1%) the corresponding ratio of the central portion, whereby the difference in chemically strengthened-induced strain between the first portion and / or the second portion and the central portion can be minimized. Minimizing the difference in chemically strengthened-induced strain can reduce the incidence of mechanical deformation and / or mechanical instability due to chemical strengthening.

[0012] Minimizing the stress and / or strain on the first major surface, the second major surface, the first central surface region, and / or the second central surface region can reduce stress-induced optical distortion. Moreover, minimizing such stress can increase puncture resistance and / or impact resistance. And, minimizing such stress can be related to a low difference in optical retardation along the centerline (e.g., about 2 nanometers or less). Further, minimizing such stress can reduce the incidence of mechanical deformation and / or mechanical instability due to chemical strengthening.

[0013] The maximum tensile stress at the center of the central tensile stress zone provided in the central portion is greater than the first maximum tensile stress of the first tensile stress zone of the first portion and / or the second maximum tensile stress of the second tensile stress zone of the second portion, whereby fractures caused by impact in the first portion and / or the second portion are low-energy fractures, while excellent folding performance is provided. In some embodiments, the low-energy fracture can be the result of a reduced thickness of the central portion. For a given maximum tensile stress, the central portion with a reduced thickness stores less energy than a thicker glass portion. In some embodiments, the low-energy fracture can be the result of fractures in the first portion and / or the second portion that are remote from the central portion undergoing bending, wherein the first portion and / or the second portion includes a maximum tensile stress lower than that of the central portion. Further, in some embodiments, providing a substantially uniform compression depth associated with the compression stress zone of the foldable substrate simplifies the manufacture of the article by avoiding the use of masking or another non-uniform ion exchange method.

[0014] Providing a neutral stress configuration when the foldable device is in a bent configuration reduces the force required to bend the foldable device to a predetermined parallel plate distance. Further, providing a neutral stress configuration when the foldable device is in a bent state reduces the maximum stress and / or strain experienced by the foldable substrate, the adhesive layer, and / or the polymer-based portion during normal use conditions, which can, for example, increase the durability of the foldable device and / or reduce the fatigue of the foldable device. In some embodiments, the polymer-based portion can include a low (e.g., negative) coefficient of thermal expansion, which can slow down warping caused by volume changes during curing of the polymer-based portion. In some embodiments, the neutral stress configuration can be produced by providing a polymer-based portion that expands upon curing. In some embodiments, the neutral stress configuration can be produced by curing the polymer-based portion in a bent configuration. In some embodiments, the neutral stress configuration can be produced by bending the foldable substrate at an elevated temperature (e.g., when the foldable substrate has a viscosity of from about 10 4 pascal-seconds to about 10 7 pascal-seconds).

[0015] The method of the present disclosure can fabricate a foldable substrate that incorporates one or more of the above-mentioned benefits. For example, disposing a diffusion barrier above the first central surface region and / or the second central surface region can adjust the rate of chemical strengthening of the central portion relative to the first portion and / or the second portion. For example, disposing a paste containing alkali metal ions above the surface region of the first portion and / or the second portion can enable the above-mentioned benefits by promoting the balancing of one or more of the above ratios and / or concentrations of the central portion relative to the first portion and / or the second portion. In some embodiments, the foldable substrate can further undergo chemical strengthening to achieve greater compressive stress without encountering mechanical deformation and / or mechanical instability, and the greater compressive stress can further increase the impact resistance and / or puncture resistance of the foldable substrate.

[0016] Further, the method of the embodiments of the present disclosure can achieve the above-mentioned benefits in a single chemical strengthening step (e.g., heating a paste containing alkali metal ions, immersing the foldable substrate in a solution containing alkali metal ions), which can reduce the time, equipment, space, and labor costs associated with the production of the foldable substrate. For example, the diffusion barrier disposed on the two surfaces of the central portion can include a thickness that can result in the foldable substrate after a single chemical strengthening step. For example, a paste containing alkali metal ions different from the paste containing alkali metal ions applied to the first portion and / or the second portion can be applied to the central portion to produce the foldable substrate after a single chemical strengthening step. In some embodiments, the concentration of one or more alkali metal ions in the paste containing alkali metal ions applied to the first portion and / or the second portion can be greater than the concentration in the different paste containing alkali metals applied to the central portion. In some embodiments, the different paste containing alkali metals applied to the central portion can include one or more alkaline earth metal ions, which can reduce the rate of chemical strengthening of the central portion.

[0017] Some exemplary embodiments of the present disclosure are described below, and it should be understood that any features of the various embodiments can be used alone or in combination with each other.

[0018] Embodiment 1: A foldable device includes a foldable substrate that can be folded about an axis extending in the width direction of the foldable substrate. The foldable substrate further includes a substrate thickness defined between a first major surface and a second major surface opposite the first major surface. The foldable substrate further includes a first portion that includes the substrate thickness, a first surface region of the first major surface, and a first tensile stress region including a first maximum tensile stress. The foldable substrate further includes a second portion that includes the substrate thickness, a third surface region of the first major surface, and a second tensile stress region including a second maximum tensile stress. The foldable substrate further includes a central portion that includes a central thickness defined between a first central surface region and a second major surface opposite the first central surface region. The first central surface region attaches the first surface region to the third surface region. The central thickness is less than the substrate thickness. The central tensile stress region includes a central maximum tensile stress. The central portion is located between the first portion and the second portion in the length direction of the foldable substrate, and the length direction is perpendicular to the width direction of the foldable substrate. The first maximum tensile stress and the second maximum tensile stress are less than the central maximum tensile stress.

[0019] Embodiment 2: The foldable device of Embodiment 1, wherein the first maximum tensile stress is less than or equal to about 100 megapascals. The second maximum tensile stress is less than or equal to about 100 megapascals. The central maximum tensile stress is in the range of about 125 megapascals to about 375 megapascals.

[0020] Embodiment 3: The foldable device of any one of Embodiments 1-2, wherein the first maximum tensile stress is in the range of 10 megapascals to about 100 megapascals. The second maximum central tensile stress is in the range of about 10 megapascals to about 100 megapascals.

[0021] Embodiment 4: The foldable device of any one of Embodiments 1-3, wherein the central portion further includes a first transition portion that attaches the first portion to the central portion. The first transition portion includes a thickness that continuously increases from the central portion to the first portion. The central portion further includes a second transition portion that attaches the second portion to the central portion. The second transition portion includes a thickness that continuously increases from the central portion to the second portion.

[0022] Embodiment 5: The foldable device of any one of Embodiments 1-4, wherein the width of the central portion is in the range of about 3 millimeters to about 45 millimeters.

[0023] Embodiment 6: A foldable device, which includes a foldable substrate. The foldable substrate includes a first main surface extending along a first plane and a second main surface extending along a second plane, and the second plane is parallel to the first plane. The foldable device includes a substrate thickness defined between the first plane and the second plane. The foldable substrate further includes a first portion, which includes a first surface area of the first main surface. The foldable substrate further includes a second portion, which includes a third surface area of the first main surface. The foldable substrate further includes a central portion, which attaches the first portion of the foldable substrate to the second portion of the foldable substrate. The central portion includes a first central surface area located between the first surface area and the third surface area. The central portion includes a central thickness of the foldable substrate defined between the second plane and the first central surface area. The central thickness is less than the substrate thickness. The central portion includes a first transition portion that attaches the first portion to the central portion. The first transition portion includes a thickness that continuously increases from the central portion to the first portion. The central portion includes a second transition portion that attaches the second portion to the central portion. The second transition portion includes a thickness that continuously increases from the central portion to the second portion. The width of the central portion ranges from about 3 millimeters to about 45 millimeters. A recess is defined between the first central surface area of the central portion and the first plane. An adhesive fills the recess.

[0024] Embodiment 7: The foldable device according to Embodiment 6, wherein the first central surface area of the central portion includes a central main surface of the central portion, which extends along a third plane parallel to the second plane.

[0025] Embodiment 8: The foldable device according to any one of Embodiments 4-7, wherein the width of the first transition portion and / or the width of the second transition portion ranges from about 1 millimeter to about 5 millimeters.

[0026] Embodiment 9: The foldable device according to any one of Embodiments 4-8, wherein the thickness of the first transition portion increases at a constant rate from the central portion to the first portion.

[0027] Embodiment 10: The foldable device according to any one of Embodiments 4-9, wherein the thickness of the second transition portion increases at a constant rate from the central portion to the second portion.

[0028] Embodiment 11: The foldable device according to any one of Embodiments 1-10, wherein when the foldable device is in a bent configuration, the foldable device includes a neutral stress configuration.

[0029] Embodiment 12: A foldable device includes a foldable substrate that can be folded about an axis extending in the width direction of the foldable substrate. The foldable substrate further includes a substrate thickness defined between a first major surface and a second major surface opposite the first major surface. The foldable substrate further includes a first portion that includes the substrate thickness and a first surface area of the first major surface. The foldable substrate further includes a second portion that includes the substrate thickness and a third surface area of the first major surface. The foldable substrate further includes a central portion that includes a central thickness defined between a first central surface area and a second major surface opposite the first central surface area. The first central surface area attaches the first surface area to the third surface area. The width of the central portion is less than or equal to about 45 millimeters. The central thickness is less than the substrate thickness. The central portion is located between the first portion and the second portion in the length direction of the foldable substrate, the length direction being perpendicular to the width direction of the foldable substrate. When the foldable device is in a bent configuration, the foldable device includes a neutral stress configuration.

[0030] Embodiment 13: The foldable device of any one of Embodiments 11-12, wherein the foldable device includes a polymer-based portion located in a recess defined between a first central surface area of the central portion and a first plane along which the first major surface extends. The movement of the foldable device from a flat configuration to a neutral stress configuration corresponds to a maximum magnitude of deviatoric strain of the polymer-based portion in the range of about 1% to about 8%.

[0031] Embodiment 14: The foldable device of Embodiment 13, wherein the maximum magnitude of deviatoric strain is in the range of about 2% to about 6%.

[0032] Embodiment 15: The foldable device of any one of Embodiments 5-14, wherein the foldable substrate of the foldable device includes an effective minimum bending radius in the range of about 1 millimeter to about 10 millimeters.

[0033] Embodiment 16: The foldable device of Embodiment 15, wherein the foldable substrate achieves an effective minimum bending radius of 10 millimeters.

[0034] Embodiment 17: The foldable device of Embodiment 15, wherein the foldable substrate achieves an effective minimum bending radius of 5 millimeters.

[0035] Embodiment 18: The foldable device of Embodiment 15, wherein the foldable substrate achieves an effective bending radius of 2 millimeters.

[0036] Embodiment 19: A foldable device according to any one of Embodiments 15-18, wherein the width of the central portion is in the range of about 2.8 times to about 6 times the effective minimum bending radius.

[0037] Embodiment 20: A foldable device according to any one of Embodiments 15-18, wherein the width of the central portion is 4.4 times or more the effective minimum bending radius.

[0038] Embodiment 21: A foldable device according to any one of Embodiments 15-18, wherein the width of the central portion is in the range of about 2.8 mm to about 40 mm.

[0039] Embodiment 22: A foldable device according to any one of Embodiments 1-21, wherein the substrate thickness is in the range of about 80 μm to about 2 mm.

[0040] Embodiment 23: The foldable device of Embodiment 22, wherein the substrate thickness is in the range of about 125 μm to about 200 μm.

[0041] Embodiment 24: A foldable device according to any one of Embodiments 1-23, wherein the central thickness is in the range of about 10 μm to about 125 μm.

[0042] Embodiment 25: The foldable device of Embodiment 24, wherein the range of the central thickness is about 10 μm to about 50 μm.

[0043] Embodiment 26: A foldable device according to any one of Embodiments 1-25, wherein the central thickness is about 0.5% to about 13% of the substrate thickness.

[0044] Embodiment 27: A foldable device according to any one of Embodiments 1-26, wherein the substrate thickness is at least 71 μm greater than about 4 times the central thickness.

[0045] Embodiment 28: A foldable device according to any one of Embodiments 1-27, wherein the first part further includes a first compressive stress zone and a second compressive stress zone, the first compressive stress zone extending from a first surface area of the first main surface to a first compressive depth, and the second compressive stress zone extending from a second surface area of the second main surface to a second compressive depth. The second part further includes a third compressive stress zone and a fourth compressive stress zone, the third compressive stress zone extending from a third surface area of the first main surface to a third compressive depth, and the fourth compressive stress zone extending from a fourth surface area of the second main surface to a fourth compressive depth. The central part further includes a first central compressive stress zone and a second central compressive stress zone, the first central compressive stress zone extending from a first central surface area to a first central compressive depth, and the second central compressive stress zone extending from a second central surface area of the second main surface to a second central compressive depth.

[0046] Embodiment 29: The foldable device of Embodiment 28, wherein the absolute difference between the first compressive depth as a percentage of the substrate thickness and the first central compressive depth as a percentage of the central thickness is less than or equal to about 1%.

[0047] Embodiment 30: The foldable device according to any one of Embodiments 28-29, wherein the absolute difference between the third compressive depth as a percentage of the substrate thickness and the first central compressive depth as a percentage of the central thickness is less than or equal to about 1%.

[0048] Embodiment 31: The foldable device according to any one of Embodiments 28-30, wherein the absolute difference between the second compressive depth as a percentage of the substrate thickness and the second central compressive depth as a percentage of the central thickness is less than or equal to about 1%.

[0049] Embodiment 32: The foldable device according to any one of Embodiments 28-31, wherein the absolute difference between the fourth compressive depth as a percentage of the substrate thickness and the second central compressive depth as a percentage of the central thickness is less than or equal to about 1%.

[0050] Embodiment 33: The foldable device according to any one of Embodiments 28-32, wherein the first central compressive depth is about 10% to about 30% of the central thickness. The second central compressive depth is about 10% to about 30% of the central thickness.

[0051] Embodiment 34: The foldable device according to any one of Embodiments 28-33, wherein the first compressive depth is about 1% to about 10% of the substrate thickness. The second compressive depth is about 1% to about 10% of the substrate thickness.

[0052] Embodiment 35: A foldable device according to any one of Embodiments 28-34, wherein the third compression depth is about 1% to about 10% of the substrate thickness. The fourth compression depth is about 1% to about 10% of the substrate thickness.

[0053] Embodiment 36: A foldable device according to any one of Embodiments 28-35, wherein the first compression depth is substantially equal to the first central compression depth. The third compression depth is substantially equal to the first central compression depth.

[0054] Embodiment 37: A foldable device according to any one of Embodiments 28-36, wherein the second compression depth is substantially equal to the second central compression depth. The fourth compression depth is substantially equal to the second central compression depth.

[0055] Embodiment 38: A foldable device according to any one of Embodiments 28-35, wherein the first central compression depth of the central portion is less than the first compression depth of the first portion of the first surface region away from the first main surface. The first central compression depth of the central portion is less than the third compression depth of the second portion of the second surface region away from the first main surface.

[0056] Embodiment 39: A foldable device according to any one of Embodiments 28-38, wherein the first compression stress zone includes a first maximum compression stress greater than or equal to about 700 megapascals. The second compression stress zone includes a second maximum compression stress, the third compression stress zone includes a third maximum compression stress greater than or equal to about 700 megapascals. The fourth compression stress zone includes a fourth maximum compression stress. The first central compression stress zone includes a first central maximum compression stress greater than or equal to 700 megapascals. The second central compression stress zone includes a second central maximum compression stress.

[0057] Embodiment 40: The foldable device of Embodiment 39, wherein the second maximum compression stress is greater than or equal to about 700 megapascals. The fourth maximum compression stress is greater than or equal to about 700 megapascals. The second central maximum compression stress is greater than or equal to about 700 megapascals.

[0058] Embodiment 41: A foldable device according to any one of Embodiments 28-40, wherein the first portion includes a first average concentration of potassium based on oxide. The second portion includes a second average concentration of potassium based on oxide. The central portion includes a central average concentration of potassium based on oxide. The absolute difference between the first average concentration of potassium and the central average concentration of potassium is about 100 parts per million or less.

[0059] Embodiment 42: The foldable device of Embodiment 41, wherein the absolute difference between the second average concentration of potassium and the central average concentration of potassium is about 100 parts per million or less.

[0060] Embodiment 43: A foldable device according to any one of Embodiments 28-42, wherein the first part includes a first layer depth of one or more alkali metal ions related to a first compression depth and a second layer depth of one or more alkali metal ions related to a second compression depth. The second part includes a third layer depth of one or more alkali metal ions related to a third compression depth and a fourth layer depth of one or more alkali metal ions related to a fourth compression depth. The central part includes a first central layer depth of one or more alkali metal ions related to a first central compression depth and a second central layer depth of one or more alkali metal ions related to a second central compression depth. The absolute difference between the first layer depth as a percentage of the substrate thickness and the first central layer depth as a percentage of the central thickness is less than or equal to about 0.1%.

[0061] Embodiment 44: The foldable device of Embodiment 43, wherein the absolute difference between the third layer depth as a percentage of the substrate thickness and the first central layer depth as a percentage of the central thickness is less than or equal to about 0.1%.

[0062] Embodiment 45: The foldable device according to any one of Embodiments 43-44, wherein the absolute difference between the second layer depth as a percentage of the substrate thickness and the second central layer depth as a percentage of the central thickness is less than or equal to about 0.1%.

[0063] Embodiment 46: The foldable device according to any one of Embodiments 43-45, wherein the absolute difference between the fourth layer depth as a percentage of the substrate thickness and the second central layer depth as a percentage of the central thickness is less than or equal to about 0.1%.

[0064] Embodiment 47: The foldable device according to any one of Embodiments 28-46, further comprising an optical retardation of the central part along the center line exactly in the middle of the first part and the second part. The absolute difference between the maximum value of the optical retardation along the center line and the minimum value of the optical retardation along the center line is less than or equal to about 2 nanometers.

[0065] Embodiment 48: The foldable device according to any one of Embodiments 1-47, wherein the foldable substrate is a glass-based substrate.

[0066] Embodiment 49: The foldable device according to any one of Embodiments 1-47, wherein the foldable substrate is a ceramic-based substrate.

[0067] Embodiment 50: The foldable device according to any one of Embodiments 1-5, wherein the depression defined between the first central surface area defined in the central part and the first plane defined by the first main surface is filled with an adhesive.

[0068] Embodiment 51: A foldable device according to Embodiment 6 or Embodiment 50, wherein the adhesive includes a first contact surface that contacts a first surface region of a first major surface, a second surface region of the first major surface that is opposite to the first surface region, and a first central surface region of a central portion. The adhesive includes a second contact surface that is spaced from the first contact surface of the adhesive.

[0069] Embodiment 52: A foldable device according to any one of Embodiments 50-51, wherein the magnitude of the difference between the refractive index of the foldable substrate and the refractive index of the adhesive is less than or equal to about 0.1.

[0070] Embodiment 53: A foldable device according to any one of Embodiments 50-52, further including a display device attached to the second contact surface of the adhesive.

[0071] Embodiment 54: A foldable device according to any one of Embodiments 50-52, further including a release liner attached to the second contact surface of the adhesive.

[0072] Embodiment 55: A consumer electronic product, including a housing that includes a front surface, a rear surface, and side surfaces. Electrical components are at least partially located within the housing. The electrical components include a controller, a memory, and a display. The display is located at or adjacent to the front surface of the housing. The consumer electronic device includes a cover substrate disposed above the display. At least one of a portion of the housing or the cover substrate includes a foldable device according to any one of Embodiments 1-54.

[0073] Embodiment 56: A method of manufacturing a foldable device, the method including: forming a recess in a first major surface of a foldable substrate, the recess providing a first central surface region that attaches a first portion of the foldable substrate and a second portion of the foldable substrate. The central portion includes a first transition portion that attaches the first portion to the central portion. The thickness of the first transition portion continuously increases from the central portion to the first portion. The central portion includes a second transition portion that attaches the second portion to the central portion. The thickness of the second transition portion continuously increases from the central portion to the second portion. The method includes: chemically strengthening the first central surface region of the central portion of the foldable substrate, the first surface region of the first portion of the first major surface, the third surface region of the second portion of the first major surface, and the second major surface of the foldable substrate. The method includes: applying an adhesive to contact the first surface region of the first major surface, the third surface region of the first major surface, and the first central surface region of the central portion. The adhesive fills the recess.

[0074] Embodiment 57: The method of Embodiment 56, wherein the recess is mechanically formed in the first major surface of the foldable substrate.

[0075] Embodiment 58: The method of any one of Embodiments 56 - 57, further comprising: reducing the thickness of the foldable substrate before chemical strengthening.

[0076] Embodiment 59: The method of Embodiment 58, wherein the thickness reduction occurs after the recess is formed.

[0077] Embodiment 60: The method of any one of Embodiments 58 - 59, wherein reducing the thickness comprises: removing a layer from the second major surface of the foldable substrate.

[0078] Embodiment 61: The method of any one of Embodiments 58 - 60, further comprising: etching the foldable substrate after chemical strengthening and before applying the adhesive.

[0079] Embodiment 62: The method of any one of Embodiments 56 - 61, wherein the chemical strengthening comprises: chemically strengthening a first portion to a first compression depth starting from a first surface region of the first major surface. The chemical strengthening comprises: chemically strengthening a second portion to a third compression depth starting from a third surface region of the first major surface. The chemical strengthening comprises: chemically strengthening a central portion to a first central compression depth starting from a first central surface region of the central portion. The first central compression depth is less than the first compression depth. The first central compression depth is less than the third compression depth.

[0080] Embodiment 63: The method of any one of Embodiments 56 - 62, wherein the chemical strengthening comprises: chemically strengthening a first portion to a second compression depth starting from a second surface region of the second major surface. The chemical strengthening comprises: chemically strengthening a second portion to a fourth compression depth starting from a fourth surface region of the second major surface. The chemical strengthening comprises: chemically strengthening a central portion to a second central compression depth starting from a second central surface region of the second major surface. The second central surface region is located between the second surface region and the fourth surface region. The second central compression depth is less than the second compression depth. The second central compression depth is less than the fourth compression depth.

[0081] Embodiment 64: A method of manufacturing a foldable device, the method comprising: forming a recess in a first major surface of a foldable substrate, the recess forming a first central surface region of a central portion, the first central surface region attaching a first portion to a second portion. The first portion includes a first surface region and a second surface region opposite the first surface region. The second portion includes a third surface region and a fourth surface region opposite the third surface region. The foldable substrate includes a second major surface, the second major surface including the second surface region and the fourth surface region. The foldable substrate includes a first major surface opposite the second major surface. The first major surface includes the first surface region and the third surface region. The method comprises: curing a polymer-based portion disposed between the first portion and the second portion. During curing, the foldable device is in a bent configuration, wherein the movement of the foldable device from a flat configuration to a neutral stress configuration corresponds to a maximum magnitude of deviatoric strain of the polymer-based portion in the range of about 1% to about 8%.

[0082] Embodiment 65: The method of Embodiment 64, further comprising: chemically strengthening the first central surface region of the central portion, the first surface region, the third surface region, and the second major surface.

[0083] Embodiment 66: A method of manufacturing a foldable device, the method comprising: folding a foldable substrate into a bent configuration when the foldable substrate has a viscosity of from about 10 4 Pascal-seconds to about 10 7 Pascal-seconds. The method comprises: curing a liquid to form a polymer-based portion between a first portion of the foldable substrate and a second portion of the foldable substrate.

[0084] Embodiment 67: The method of Embodiment 66, further comprising: forming a recess in the foldable substrate, the recess forming a first central surface region of a central portion of the foldable substrate, the first central surface region attaching a first portion of the foldable substrate to a second portion of the foldable substrate.

[0085] Embodiment 68: The method of any one of Embodiments 66 - 67, further comprising: chemically strengthening the foldable substrate.

[0086] Embodiment 69: The method of any one of Embodiments 66 - 68, wherein the movement of the foldable device from a flat configuration to a neutral stress configuration corresponds to a maximum magnitude of deviatoric strain of the polymer-based portion in the range of about 1% to about 8%.

[0087] Embodiment 70: The method of Embodiment 64, Embodiment 65, or Embodiment 69, wherein the maximum magnitude of deviatoric strain is in the range of about 2% to about 6%.

[0088] Embodiment 71: The method of any one of Embodiments 64 - 70, wherein the polymer-based portion expands due to curing.

[0089] Embodiment 72: A method of manufacturing a foldable device, the method comprising: forming a recess in a first major surface of a foldable substrate, the recess forming a first central surface region of a central portion, the first central surface region attaching a first portion to a second portion. The first portion includes a first surface region and a second surface region opposite the first surface region. The second portion includes a third surface region and a fourth surface region opposite the third surface region. The foldable substrate includes a second major surface, the second major surface including the second surface region and the fourth surface region. The foldable substrate includes a first major surface opposite the second major surface, the first major surface including the first surface region and the third surface region. The method comprises: curing a polymer-based portion disposed within the recess. The polymer-based portion expands due to curing.

[0090] Embodiment 73: The method of Embodiment 72, further comprising: chemically strengthening the first central surface region of the central portion, the first surface region, the third surface region, and the second major surface.

[0091] Embodiment 74: The method of any one of Embodiments 72 - 73, wherein the polymer-based portion includes a negative coefficient of thermal expansion.

[0092] Embodiment 75: The method of Embodiment 74, wherein the polymer-based portion includes particles of one or more of copper oxide, β-quartz, tungstate, vanadate, pyrophosphate, and / or nitinol.

[0093] Embodiment 76: The method of any one of Embodiments 72 - 75, wherein curing the polymer-based portion includes ring-opening metathesis polymerization.

[0094] Embodiment 77: A method of manufacturing a foldable device, the method comprising: forming a recess in a first major surface of a foldable substrate, the recess forming a first central surface region of a central portion, the first central surface region attaching a first portion to a second portion. The first portion includes a first surface region and a second surface region opposite the first surface region. The second portion includes a third surface region and a fourth surface region opposite the third surface region. The foldable substrate includes a second major surface that includes the second surface region and the fourth surface region. The foldable substrate includes a first major surface opposite the second major surface. The first major surface includes the first surface region and the third surface region. The method comprises: curing a polymer-based portion disposed between the first portion and the second portion. During curing, the foldable device is in a bent configuration. The movement of the foldable device from a flat configuration to a neutral stress configuration corresponds to a maximum magnitude of deviatoric strain of the polymer-based portion in the range of about 1% to about 8%.

[0095] Embodiment 78: The method of Embodiment 77, further comprising: chemically strengthening the first central surface region of the central portion, the first surface region, the third surface region, and the second major surface.

[0096] Embodiment 79: The method of any one of Embodiments 77-78, wherein the maximum magnitude of deviatoric strain is in the range of about 2% to about 6%.

[0097] Embodiment 80: A method of manufacturing a foldable device, the method comprising: folding a foldable substrate into a bent configuration when the foldable substrate has a viscosity of from about 10 4 Pascal-seconds to about 10 7 Pascal-seconds. The method comprises: curing a liquid to form a polymer-based portion between a first portion of the foldable substrate and a second portion of the foldable substrate.

[0098] Embodiment 81: The method of Embodiment 80, further comprising: forming a recess in the foldable substrate, the recess forming a first central surface region of a central portion of the foldable substrate, the first central surface region attaching a first portion of the foldable substrate to a second portion of the foldable substrate.

[0099] Embodiment 82: The method of any one of Embodiments 80-81, further comprising: chemically strengthening the foldable substrate.

[0100] Embodiment 83: The method of any one of Embodiments 80-82, wherein the movement of the foldable device from a flat configuration to a neutral stress configuration corresponds to a maximum magnitude of deviatoric strain of the polymer-based portion in the range of about 1% to about 8%.

[0101] Embodiment 84: The method of Embodiment 83, wherein the maximum magnitude of the deviatoric strain is in the range of from about 2% to about 6%.

[0102] Embodiment 86: A method of manufacturing a foldable substrate, the foldable substrate comprising a foldable substrate including a substrate thickness defined between a first major surface and a second major surface. The foldable substrate includes a first portion including the substrate thickness. The foldable substrate includes a second portion including the substrate thickness. The foldable substrate includes a central portion including a central thickness defined between a first central surface region and a second central surface region. The central thickness is less than the substrate thickness. The central portion is located between the first portion and the second portion. The method includes: disposing a first layer over one or more of the first central surface region or the second central surface region. The method includes: after disposing the first layer, chemically strengthening the foldable substrate for a first period of time. The method includes: after chemically strengthening the foldable substrate, removing the first layer.

[0103] As in Embodiment 86: The method of Embodiment 85, wherein the first layer has a thickness of from about 10 nanometers to about 200 nanometers.

[0104] Embodiment 87: The method of any one of Embodiments 85-86, wherein disposing the first layer includes: disposing SiO by physical vapor deposition 2 .

[0105] Embodiment 88: The method of any one of Embodiments 85-87, further comprising: forming a recess in the first major surface of the glass-based substrate to provide the first central surface region, prior to disposing the first layer.

[0106] Embodiment 89: The method of any one of Embodiments 85-88, wherein after chemically strengthening the foldable substrate, the first portion includes a first layer depth of one or more alkali metal ions introduced into the first portion during chemical strengthening from the first major surface. After chemically strengthening the foldable substrate, the central portion includes a first central layer depth of one or more alkali metal ions introduced into the central portion during chemical strengthening from the first central surface region. The absolute difference between the first layer depth as a percentage of the substrate thickness and the first central layer depth as a percentage of the central thickness is less than or equal to about 1%.

[0107] Embodiment 90: The method of Embodiment 89, wherein after chemically strengthening the foldable substrate, the second portion comprises a third layer depth of one or more alkali metal ions introduced into the second portion during chemical strengthening from the first major surface. The absolute difference between the third layer depth as a percentage of the substrate thickness and the first central layer depth as a percentage of the central thickness is less than or equal to about 1%.

[0108] Embodiment 91: The method of any one of Embodiments 89 - 90, wherein the one or more alkali metal ions comprise potassium ions.

[0109] Embodiment 92: The method of any one of Embodiments 85 - 91, wherein after chemically strengthening the foldable substrate, the first portion comprises a first average concentration of potassium based on oxide. After chemically strengthening the foldable substrate, the central portion comprises a central average concentration of potassium based on oxide. The absolute difference between the first average concentration of potassium and the central average concentration of potassium is about 100 ppm or less.

[0110] Embodiment 93: The method of Embodiment 92, wherein after chemically strengthening the foldable substrate, the second portion comprises a second average concentration of potassium based on oxide. The absolute difference between the second average concentration of potassium and the central average concentration of potassium is about 100 ppm or less.

[0111] Embodiment 94: The method of any one of Embodiments 85 - 93, wherein after chemically strengthening the foldable substrate, the first portion comprises a first compressive stress zone extending from the first major surface to a first compressive depth. After chemically strengthening the foldable substrate, the central portion comprises a first central compressive stress zone extending to a first central compressive depth. The absolute difference between the first compressive depth as a percentage of the substrate thickness and the first central compressive depth as a percentage of the central thickness is less than or equal to about 1%.

[0112] Embodiment 95: The method of Embodiment 94, wherein after chemically strengthening the foldable substrate, the second portion comprises a third compressive stress zone extending from the first major surface to a third compressive depth. The absolute difference between the third compressive depth as a percentage of the substrate thickness and the first central compressive depth as a percentage of the central thickness is less than or equal to about 1%.

[0113] Embodiment 96: The method of any one of Embodiments 85 - 88, further comprising: after removing the first layer, further chemically strengthening the foldable substrate for a second time period.

[0114] Embodiment 97: The method of Embodiment 96, wherein the second time period is greater than the first time period.

[0115] Embodiment 98: The method of Embodiment 97, wherein the second time period is in the range of about 103% to about 175% as a percentage of the first time period.

[0116] Embodiment 99: The method of any one of Embodiments 96 - 98, wherein after further chemically strengthening the foldable substrate, the first portion comprises a first layer depth of one or more alkali metal ions introduced into the first portion during chemical strengthening or further chemical strengthening from the first major surface. After further chemically strengthening the foldable substrate, the central portion comprises a first central layer depth of one or more alkali metal ions introduced into the central portion during chemical strengthening or further chemical strengthening from the first central surface region. The absolute difference between the first layer depth as a percentage of the substrate thickness and the first central layer depth as a percentage of the central thickness is less than or equal to about 0.1%.

[0117] Embodiment 100: The method of Embodiment 99, wherein after further chemically strengthening the foldable substrate, there is a third layer depth of one or more alkali metal ions introduced into the second portion during chemical strengthening or further chemical strengthening from the first major surface. The absolute difference between the third layer depth as a percentage of the substrate thickness and the first central layer depth as a percentage of the central thickness is less than or equal to about 0.1%.

[0118] Embodiment 101: The method of any one of Embodiments 99 - 100, wherein the one or more alkali metal ions comprise potassium ions.

[0119] Embodiment 102: The method of any one of Embodiments 96 - 101, wherein after further chemically strengthening the foldable substrate, the first portion comprises a first average concentration of potassium based on oxide. After further chemically strengthening the foldable substrate, the central portion comprises a central average concentration of potassium based on oxide. The absolute difference between the first average concentration of potassium and the central average concentration of potassium is about 100 parts per million or less.

[0120] Embodiment 103: The method of Embodiment 102, wherein after further chemically strengthening the foldable substrate, the second portion comprises a second average concentration of potassium based on oxide. The absolute difference between the second average concentration of potassium and the central average concentration of potassium is about 100 parts per million or less.

[0121] Embodiment 104: The method of any one of Embodiments 96 - 103, wherein, after further chemically strengthening the foldable substrate, the first portion includes a first compressive stress zone extending from the first major surface to a first compressive depth. After further chemically strengthening the foldable substrate, the central portion includes a first central compressive stress zone extending to a first central compressive depth. The absolute difference between the first compressive depth as a percentage of the substrate thickness and the first central compressive depth as a percentage of the central thickness is less than or equal to about 1%.

[0122] Embodiment 105: The method of Embodiment 104, wherein, after further chemically strengthening the foldable substrate, the second portion includes a third compressive stress zone extending from the first major surface to a third compressive depth. The absolute difference between the third compressive depth as a percentage of the substrate thickness and the first central compressive depth as a percentage of the central thickness is less than or equal to about 1%.

[0123] Embodiment 106: A method of manufacturing a foldable substrate, the foldable substrate including a foldable substrate having a substrate thickness defined between a first major surface and a second major surface. The foldable substrate includes a first portion, the first portion including the substrate thickness. The foldable substrate includes a second portion, the second portion including the substrate thickness. The foldable substrate includes a central portion, the central portion having a central thickness defined between a first central surface region and a second central surface region. The central thickness is less than the substrate thickness. The central portion is located between the first portion and the second portion. The method includes: applying a paste containing alkali metal ions to the first portion and the second portion. The method includes: heating the foldable substrate after applying the paste. The method includes: removing the paste after heating the foldable substrate. The method includes: chemically strengthening the foldable substrate after removing the paste.

[0124] Embodiment 107: The method of Embodiment 106, wherein, after chemically strengthening the foldable substrate, the first portion includes a first layer depth of one or more alkali metal ions introduced into the first portion during heating or chemical strengthening from the first major surface. After chemically strengthening the foldable substrate, the central portion includes a first central layer depth of one or more alkali metal ions introduced into the central portion during chemical strengthening from the first central surface region. The absolute difference between the first layer depth as a percentage of the substrate thickness and the first central layer depth as a percentage of the central thickness is less than or equal to about 0.1%.

[0125] Embodiment 108: The method of Embodiment 107, wherein after chemically strengthening the foldable substrate, the second portion comprises a third layer depth of one or more alkali metal ions introduced into the second portion during heating or chemical strengthening from the first major surface. The absolute difference between the third layer depth as a percentage of the substrate thickness and the first central layer depth as a percentage of the central thickness is less than or equal to about 0.1%.

[0126] Embodiment 109: The method of any one of Embodiments 107-108, wherein the one or more alkali metal ions comprise potassium ions.

[0127] Embodiment 110: The method of any one of Embodiments 106-109, wherein after chemically strengthening the foldable substrate, the first portion comprises a first average concentration of potassium based on oxide. After chemically strengthening the foldable substrate, the central portion comprises a central average concentration of potassium based on oxide. The absolute difference between the first average concentration of potassium and the central average concentration of potassium is about 100 ppm or less.

[0128] Embodiment 111: The method of Embodiment 110, wherein after chemically strengthening the foldable substrate, the second portion comprises a second average concentration of potassium based on oxide. The absolute difference between the second average concentration of potassium and the central average concentration of potassium is about 100 ppm or less.

[0129] Embodiment 112: The method of any one of Embodiments 106-111, wherein after chemically strengthening the foldable substrate, the first portion comprises a first compressive stress zone extending from the first major surface to a first compressive depth. After chemically strengthening the foldable substrate, the central portion comprises a first central compressive stress zone extending to a first central compressive depth. The absolute difference between the first compressive depth as a percentage of the substrate thickness and the first central compressive depth as a percentage of the central thickness is less than or equal to about 1%.

[0130] Embodiment 113: The method of Embodiment 112, wherein after chemically strengthening the foldable substrate, the second portion comprises a third compressive stress zone extending from the first major surface to a third compressive depth. The absolute difference between the third compressive depth as a percentage of the substrate thickness and the first central compressive depth as a percentage of the central thickness is less than or equal to about 1%.

[0131] Embodiment 114: A method of manufacturing a foldable substrate, the foldable substrate including a foldable substrate which includes a substrate thickness defined between a first major surface and a second major surface. The foldable substrate includes a first portion which includes the substrate thickness. The foldable substrate includes a second portion which includes the substrate thickness. The foldable substrate includes a central portion which includes a central thickness defined between a first central surface region and a second central surface region. The central thickness is less than the substrate thickness. The central portion is located between the first portion and the second portion. The method includes: applying a first paste containing alkali metal ions to the first portion. The method includes: applying a second paste containing alkali metal ions to the central portion. The method includes: heating the foldable substrate after applying the first paste and the second paste. The method includes: removing the first paste from the first portion after heating the foldable substrate. The method includes: removing the second paste from the central portion after heating the foldable substrate.

[0132] Embodiment 115: The method of Embodiment 114, wherein the concentration of potassium ions in the first paste is greater than the concentration of potassium ions in the second paste.

[0133] Embodiment 116: The method of any one of Embodiments 114 - 115, wherein the second paste further includes one or more alkaline earth metal ions, and based on oxides, the concentration of the one or more alkaline earth metal ions is greater than or equal to about 5 parts per million.

[0134] Embodiment 117: The method of Embodiment 116, wherein the one or more alkaline earth metal ions include calcium in a range from about 10 parts per million to about 1000 parts per million, based on oxides.

[0135] Embodiment 118: The method of any one of Embodiments 114 - 117, wherein after heating the foldable substrate, the first portion includes a first layer depth of one or more alkali metal ions introduced into the first portion during heating from the first major surface. After heating the foldable substrate, the central portion includes a first central layer depth of one or more alkali metal ions introduced into the central portion during heating from the first central surface region. The absolute difference between the first layer depth as a percentage of the substrate thickness and the first central layer depth as a percentage of the central thickness is less than or equal to about 0.1%.

[0136] Embodiment 119: The method of any one of Embodiments 114-118, wherein after heating the foldable substrate, the first portion includes a first average concentration of potassium based on oxide. After heating the foldable substrate, the central portion includes a central average concentration of potassium based on oxide. The absolute difference between the first average concentration of potassium and the central average concentration of potassium is about 100 ppm or less.

[0137] Embodiment 120: The method of Embodiment 119, wherein after further chemically strengthening the foldable substrate, the second portion includes a second average concentration of potassium based on oxide. The absolute difference between the second average concentration of potassium and the central average concentration of potassium is about 100 ppm or less.

[0138] Embodiment 121: The method of any one of Embodiments 114-120, wherein after heating the foldable substrate, the first portion includes a first compressive stress zone extending from the first major surface to a first compressive depth. After heating the foldable substrate, the central portion includes a first central compressive stress zone extending to a first central compressive depth. The absolute difference between the first compressive depth as a percentage of the substrate thickness and the first central compressive depth as a percentage of the central thickness is less than or equal to about 1%.

[0139] Embodiment 122: The method of Embodiment 121, further comprising: applying a first paste containing alkali metal ions to the second portion before heating the foldable substrate. The method further comprises: removing the first paste from the second portion after heating the foldable substrate.

[0140] Embodiment 123: The method of Embodiment 122, wherein after heating the foldable substrate, the second portion includes a third layer depth of one or more alkali metal ions introduced into the second portion during heating from the first major surface. After chemically strengthening the foldable substrate, the central portion includes a first central layer depth of one or more alkali metal ions introduced into the central portion during heating from the first central surface region. The absolute difference between the third layer depth as a percentage of the substrate thickness and the first central layer depth as a percentage of the central thickness is less than or equal to about 0.1%.

[0141] Embodiment 124: The method of Embodiments 122-123, wherein after chemically strengthening the foldable substrate, the second portion includes a second average concentration of potassium based on oxide. After chemically strengthening the foldable substrate, the central portion includes a central average concentration of potassium based on oxide. The absolute difference between the first average concentration of potassium and the central average concentration of potassium is about 100 ppm or less.

[0142] Embodiment 125: The method of Embodiment 124, wherein, after further chemically strengthening the foldable substrate, the second portion comprises a second average concentration of potassium based on oxides. The absolute difference between the second average concentration of potassium and the central average concentration of potassium is about 100 ppm or less.

[0143] Embodiment 126: The method of any one of Embodiments 122-125, wherein, after heating the foldable substrate, the second portion comprises a third compressive stress zone extending from the first major surface to a third compressive depth. After heating the foldable substrate, the central portion comprises a first central compressive stress zone extending from the first central surface to a first compressive depth. The absolute difference between the third compressive depth as a percentage of the substrate thickness and the first central compressive depth as a percentage of the central thickness is less than or equal to about 1%. BRIEF DESCRIPTION OF THE DRAWINGS

[0144] The above and other features and advantages of the embodiments of the present disclosure can be better understood by reading the following detailed description with reference to the accompanying drawings, in which:

[0145] Figure 1 is a schematic diagram of an exemplary foldable device in a flat configuration according to some embodiments, wherein a schematic diagram of the folded configuration can be as Figure 4 shown;

[0146] Figures 2 - 3 is a cross-sectional view of a foldable device along line 2-2 according to other embodiments; Figure 1 of;

[0147] Figure 4 is a schematic diagram of an exemplary foldable device of an embodiment of the present disclosure in a folded configuration, wherein a schematic diagram of the flat configuration can be as Figure 1 shown;

[0148] Figure 5 is a schematic diagram of an exemplary foldable substrate of an embodiment of the present disclosure in a folded configuration for failure mode testing;

[0149] Figure 6 is a cross-sectional view of a test device for determining the effective minimum bending radius of an exemplary modified foldable device along line 6-6 Figure 4 of;

[0150] Figure 7 is a cross-sectional view of another exemplary foldable device along line 6-6 according to some embodiments; Figure 4 of;

[0151] Figure 8is a plan view of an exemplary consumer electronic device according to some embodiments;

[0152] Figure 9 is Figure 8 a perspective view of the exemplary consumer electronic device;

[0153] Figures 10 - 11 is a flowchart illustrating an exemplary method of manufacturing a foldable substrate and / or a foldable device according to embodiments of the present disclosure;

[0154] Figures 12 - 26 schematically illustrates steps in a method of manufacturing a foldable substrate and / or a foldable device;

[0155] Figure 27 is a flowchart illustrating an exemplary method of manufacturing a foldable substrate and / or a foldable device according to embodiments of the present disclosure;

[0156] Figures 28 - 37 schematically illustrates steps in a method of manufacturing a foldable substrate and / or a foldable device;

[0157] Figure 38 schematically illustrates a foldable device similar to Figure 3 and in a neutral stress configuration;

[0158] Figure 39 schematically illustrates a polymer-based portion when the foldable device is in a flat configuration;

[0159] Figure 40 schematically illustrates a polymer-based portion when the foldable device is in a neutral stress configuration.

[0160] Figure 41 is a perspective view of a pen-drop device;

[0161] Figure 42 shows the pen-drop test results of a glass-based substrate, which show the variation of the maximum principal stress on the main surface of the glass-based substrate with the thickness of the glass-based substrate;

[0162] Figure 43 shows the type of mechanical instability observed for a foldable device varying with the substrate thickness and the center thickness; and

[0163] Figure 44 schematically shows the optical retardation measurements of a foldable substrate according to embodiments of the present disclosure.

[0164] In the present disclosure, the drawings are used to emphasize certain aspects. Therefore, unless otherwise explicitly specified, the relative sizes of the different regions, parts, and substrates shown in the figures should not be considered proportional to their actual relative sizes. Detailed implementation manners

[0165] Herein, various implementation manners will be described more completely with reference to the accompanying drawings, in which exemplary implementation manners are given. Whenever possible, the same reference numerals are used in all the drawings to denote the same or similar parts. However, the claims may cover many different aspects of each implementation manner and should not be construed as being limited to the implementation manners presented herein.

[0166] Figures 1 - 4 Views of foldable devices 101 and 301 and / or testable foldable device 602 including a foldable substrate 201 according to embodiments of the present disclosure are illustrated in FIGS. 6 - 7. Unless otherwise indicated, the description of the features of an embodiment of a foldable device may equally apply to the corresponding features of any embodiment of the present disclosure. For example, throughout the present disclosure, the same part numbers may indicate that the identified features are the same as each other in some embodiments, and the description of the identified features of one embodiment may equally apply to the identified features of any other embodiment of the present disclosure, unless otherwise indicated.

[0167] Figures 2 - 3 Exemplary embodiments of foldable devices 101 and 301 including a foldable substrate 201 according to embodiments of the present disclosure in a non - folded (e.g., flat) configuration are schematically illustrated, while Figures 6 - 7 views of testable foldable device 602 and foldable device 301 including a foldable substrate 201 according to embodiments of the present disclosure in a folded configuration are shown respectively. Foldable devices 101 and 301 include a first part 221, a second part 231, and a central part 251 located between the first part 221 and the second part 231. In some embodiments, as Figures 2 - 3 shown, foldable devices 101, 301 may include a foldable substrate 201. In some embodiments, as Figure 2 shown, foldable device 101 may include a release liner 271, but in other embodiments, other substrates (e.g., the glass - based substrate and / or ceramic - based substrate described in this application) may be used instead of the illustrated release liner 271. In some embodiments, as Figure 3 shown, foldable device 301 may include a display device 307. It should be understood that any foldable device of the present disclosure may include additional substrates (e.g., glass - based substrate and / or ceramic - based substrate), release liner 271, and / or display device 307. In some embodiments, as Figures 2 - 3 shown in FIGS. 6 - 7, an adhesive layer 261 (e.g., optically clear adhesive (OCA)) may be disposed above the first major surface 203 of the foldable substrate 201. In other embodiments, as Figure 3 shown in 6As shown in -7, a polymer-based portion may be disposed above the foldable substrate 201 (e.g., as shown in Figure 3 and disposed above the first central surface region 209).

[0168] Throughout this disclosure, reference is made to Figure 1 , the width 103 of the foldable device 101 and / or 301 is considered to be the dimension of the foldable device obtained between opposite edges of the foldable device in the direction 104 of the fold axis 102 of the foldable device, where the direction 104 also includes the direction of the width 103. Additionally, throughout this disclosure, the length 105 of the foldable device 101 and / or 301 is considered to be the dimension of the foldable device 101 and / or 301 obtained between opposite edges of the foldable device 101 and / or 301 in the direction 106 perpendicular to the fold axis 102 of the foldable device 101 and / or 301. In some embodiments, as shown in Figures 1 - 3 , the foldable device of any embodiment of this disclosure may include a folding plane 109 that includes the fold axis 102 and the direction 202 of the substrate thickness 227 (e.g., the first thickness of the first portion 221) when the folding device is in a flat configuration (e.g., see Figure 1 ). In some embodiments, the plane 109 may include a central axis 107 of the foldable device, which may be located at the second major surface 205, as shown in Figures 2 - 3 . In some embodiments, the foldable device may be folded along the direction 111 (e.g., see Figure 1 ) about a fold axis 102 extending in the direction 104 of the width 103 to form a folded configuration (e.g., see Figure 4 and 6 -7). As shown, the foldable device may include a single fold axis to allow the foldable device to include a bifold, where, for example, the foldable device may be folded in half. In additional embodiments, the foldable device may include two or more fold axes, where each fold axis includes a corresponding central portion that is the same or similar to the central portion 251 described herein. For example, providing two fold axes may allow the foldable device to include a trifold, where, for example, the foldable device may be folded into a first portion 221, a second portion 231, and a third portion that is similar or identical to the first or second portion, and having a central portion 251 located between the first portion and the second portion, and another central portion that is similar or identical to the central portion and located between the second portion and the third portion.

[0169] The foldable devices 101 and 301 of the present disclosure may include a foldable substrate 201. In some embodiments, the foldable substrate 201 may include a glass-based substrate and / or a ceramic-based substrate having a pencil hardness greater than or equal to 8H, such as greater than or equal to 9H.

[0170] In some embodiments, the foldable substrate 201 may include a glass-based substrate. As used herein, "glass-based" includes both glass and glass-ceramics, where the glass-ceramics have one or more crystalline phases and an amorphous residual glass phase. Glass-based materials (e.g., glass-based substrates) may include amorphous materials (e.g., glass) and optionally one or more crystalline materials (e.g., ceramics). The amorphous materials and glass-based materials may be strengthened. As used herein, the term "strengthened" may refer to a material that has been chemically strengthened, e.g., by ion-exchanging smaller ions in the surface of the substrate with larger ions, as described below. However, other strengthening methods may also be utilized to form a strengthened substrate, such as thermal tempering, or by using a mismatch in the coefficient of thermal expansion between parts of the substrate to create a compressive stress zone and a central tension zone. Exemplary glass substrates that do not contain or contain lithium oxide include soda-lime glass, alkali metal aluminosilicate glass, alkali metal borosilicate glass, alkali metal aluminoborosilicate glass, alkali metal phosphosilicate glass, and alkali metal aluminophosphosilicate glass. In one or more embodiments, in mole percent (mol %), the glass-based material may include: about 40 mol % to about 80 mol % of SiO 2 , about 5 mol % to about 30 mol % of Al 2 O 3 , 0 mol % to about 10 mol % of B 2 O 3 , 0 mol % to about 5 mol % of ZrO 2 , 0 mol % to about 15 mol % of P 2 O 5 , 0 mol % to about 2 mol % of TiO 2 , 0 mol % to about 20 mol % of R 2 O, and 0 mol % to about 15 mol % of RO. As used herein, R 2 O may refer to an alkali metal oxide, e.g., Li 2 O, Na 2 O, K 2 O, Rb 2 O, and Cs 2 O. As used herein, RO may refer to MgO, CaO, SrO, BaO, and ZnO. In some embodiments, the glass-based substrate may optionally further include various ones of 0 mol % to about 2 mol % of the following: Na 2 SO 4 , NaCl, NaF, NaBr, K2 SO 4 、 KCl, KF, KBr, As 2 O 3 、 Sb 2 O 3 、 SnO 2 、 Fe 2 O 3 、 MnO, MnO 2 、 MnO 3 、 Mn 2 O 3 、 Mn 3 O 4 、 Mn 2 O 7 。 "Glass-ceramics" include materials produced by controlled crystallization of glass. In some embodiments, the glass-ceramics have a crystallinity of about 1% to about 99%. Examples of suitable glass-ceramics can include Li 2 O - Al 2 O 3 - SiO 2 systems (i.e., LAS systems) glass-ceramics, MgO - Al 2 O 3 - SiO 2 systems (i.e., MAS systems) glass-ceramics, ZnO×Al 2 O 3 ×nSiO 2 (i.e., ZAS systems) and / or glass-ceramics comprising a main crystalline phase including β - quartz solid solution, β - spodumene, cordierite, petalite, and / or lithium disilicate. The glass-ceramic substrate can be strengthened using a chemical strengthening process. In one or more embodiments, the glass-ceramic substrate of the MAS system can be strengthened in a Li 2 SO 4 molten salt, whereby an exchange of 2Li + for Mg 2+ can occur.

[0171] In some embodiments, the foldable substrate 201 can include a ceramic-based substrate. As used herein, "ceramic-based" includes both ceramics and glass-ceramics, where the glass-ceramics have one or more crystalline phases and an amorphous residual glass phase. The ceramic-based material can be strengthened (e.g., chemically strengthened). In some embodiments, the ceramic-based material can be formed by heating a glass-based material to form a ceramic (e.g., crystalline) portion. In additional embodiments, the ceramic-based material can include one or more nucleating agents that can promote the formation of the crystalline phase. In some embodiments, the ceramic-based material can include one or more oxides, nitrides, oxynitrides, carbides, borides, and / or silicides. Exemplary embodiments of ceramic oxides include zirconia (ZrO2 ), zirconium silicate (ZrSiO 4 ), alkali metal oxides (e.g., sodium oxide (Na 2 O)), alkaline earth metal oxides (e.g., magnesium oxide (MgO)), titanium dioxide (TiO 2 ), hafnium oxide (Hf 2 O), yttrium oxide (Y 2 O 3 ), iron oxides, beryllium oxide, vanadium oxide (VO 2 ), fused quartz, mullite (a mineral containing a combination of alumina and silica), and spinel (MgAl 2 O 4 ). Exemplary embodiments of ceramic nitrides include silicon nitride (Si 3 N 4 ), aluminum nitride (AlN), gallium nitride (GaN), beryllium nitride (Be 3 N 2 ), boron nitride (BN), tungsten nitride (WN), vanadium nitride, alkaline earth metal nitrides (e.g., magnesium nitride (Mg 3 N 2 ). Exemplary embodiments of oxynitride ceramics include silicon oxynitride, aluminum oxynitride, and SiAlON (e.g., a combination of alumina and silicon nitride and may have the following chemical formulas, e.g., Si 12-m-n Al m+n O n N 16-n , Si 6-n Al n O n N 8-n or Si 2-n Al n O 1+n N 2-n , where m, n, and the resulting subscripts are all non-negative integers). Exemplary embodiments of carbides and carbon-containing ceramics include silicon carbide (SiC), tungsten carbide (WC), iron carbide, boron carbide (B 4 C), alkali metal carbides (e.g., lithium carbide (Li 4 C 3 ), alkaline earth metal carbides (e.g., magnesium carbide (Mg 2 C 3 )) and graphite. Exemplary embodiments of borides include chromium boride (CrB 2 ), molybdenum boride (Mo 2 B 5 ), tungsten boride (W 2 B 5 ), iron boride, titanium boride, zirconium boride (ZrB 2 ), hafnium boride (HfB2 ) Vanadium boride (VB 2 ) Niobium boride (NbB 2 ) and Lanthanum boride (LaB 6 ). Exemplary embodiments of silicides include Molybdenum disilicide (MoSi 2 ), Tungsten disilicide (WSi 2 ), Titanium disilicide (TiSi 2 ), Nickel silicide (NiSi), Alkaline earth metal silicides (e.g., Sodium silicide (NaSi)), Alkali metal silicides (e.g., Magnesium silicide (Mg 2 Si), Hafnium disilicide (HfSi 2 ) and Platinum silicide (PtSi).

[0172] Throughout this disclosure, ASTM D638 is used to determine the tensile strength, ultimate elongation (e.g., failure strain), and yield point of polymeric materials (e.g., adhesives, polymer-based portions) using a tensile testing machine [e.g., Instron 3400 or Instron 6800] at 23 °C and 50% relative humidity with Type I dogbone-shaped specimens. Throughout this disclosure, ISO 527-1:2019 is used to measure the elastic modulus (e.g., Young's modulus) and / or Poisson's ratio. In some embodiments, the foldable substrate 201 may include an elastic modulus of: greater than or equal to about 1 gigapascal (GPa), greater than or equal to about 3 GPa, greater than or equal to 5 GPa, greater than or equal to 10 GPa, less than or equal to about 100 GPa, less than or equal to about 80 GPa, less than or equal to about 60 GPa, or less than or equal to about 20 GPa. In some embodiments, the foldable substrate 201 may include an elastic modulus in the following ranges: about 1 GPa to about 100 GPa, about 1 GPa to about 80 GPa, about 3 GPa to about 80 GPa, about 3 GPa to about 60 GPa, about 5 GPa to about 60 GPa, about 5 GPa to about 20 GPa, about 10 GPa to about 20 GPa, or any range or sub-range therebetween. In additional embodiments, the foldable substrate 201 may include a glass-based portion and / or a ceramic-based portion, and the glass-based portion and / or the ceramic-based portion may include an elastic modulus in the following ranges: about 10 GPa to about 100 GPa, about 40 GPa to about 100 GPa, about 60 GPa to about 100 GPa, about 60 GPa to about 80 GPa, about 80 GPa to about 100 GPa, or any range or sub-range therebetween.

[0173] In some embodiments, the foldable substrate 201 may be optically transparent. As used herein, "optically transparent" or "optically clear" means that the average transmittance through a 1.0 mm thick sheet of the material in the wavelength range of 400 nm to 700 nm is 70% or greater. In some embodiments, the average transmittance of an "optically transparent material" or "optically clear material" through a 1.0 mm thick sheet of the material in the wavelength range of 400 nm to 700 nm may be 75% or greater, 80% or greater, 85% or greater, or 90% or greater, 92% or greater, 94% or greater, 96% or greater. The average transmittance in the wavelength range of 400 nm to 700 nm is calculated by measuring the transmittance at all integer wavelengths from approximately 400 nm to approximately 700 nm and averaging the measured values.

[0174] As Figures 2 - 3 shown in FIGS. 5 and 6 - 7, the foldable substrate 201 may include a first major surface 203 and a second major surface 205 opposite the first major surface 203. As Figures 2 - 3 shown, the first major surface 203 may extend along a first plane 204a. The second major surface 205 may extend along a second plane 204b. In some embodiments, as shown in the figures, the second plane 204b may be parallel to the first plane 204a. As used herein, a substrate thickness may be defined between the first major surface 203 and the second major surface 205, and is defined as the distance between the first plane 204a and the second plane 204b. In some embodiments, the substrate thickness may be greater than or equal to about 10 micrometers (μm), greater than or equal to about 25 μm, greater than or equal to about 40 μm, greater than or equal to about 60 μm, greater than or equal to about 80 μm, greater than or equal to about 100 μm, greater than or equal to about 125 μm, greater than or equal to about 150 μm, less than or equal to about 2 millimeters (mm), less than or equal to about 1 mm, less than or equal to about 800 μm, less than or equal to about 500 μm, less than or equal to about 300 μm, less than or equal to about 200 μm, less than or equal to about 180 μm, or less than or equal to about 160 μm. In some embodiments, the substrate thickness may be in the following ranges: about 10 μm to about 2 mm, about 25 μm to about 2 mm, about 40 μm to about 2 mm, about 60 μm to about 2 mm, about 80 μm to about 2 mm, about 100 μm to about 2 mm, about 100 μm to about 1 mm, about 100 μm to about 800 μm, about 100 μm to about 500 μm, about 125 μm to about 500 μm, about 125 μm to about 300 μm, about 125 μm to about 200 μm, about 150 μm to about 200 μm, about 150 μm to about 160 μm, and any range and sub - range therebetween. Based on the pen - drop test (hereinafter referred to Figure 42As a result of the discussion (discussed elsewhere), by selecting a foldable substrate thickness greater than about 80 micrometers (μm), increased puncture resistance can be achieved. In some embodiments, the puncture resistance of the foldable substrate can be increased when the substrate thickness 227 is greater than or equal to about 80 μm, greater than or equal to about 200 μm, greater than or equal to about 500 μm, less than or equal to about 2 mm, less than or equal to about 1 mm, less than or equal to about 500 μm, or less than or equal to about 300 μm. In some embodiments, the substrate thickness 227 can be in the following ranges: from about 80 μm to about 2 mm, from about 80 μm to about 1 mm, from about 80 μm to about 500 μm, from about 80 μm to about 300 μm, from about 200 μm to about 2 mm, from about 200 μm to about 1 mm, from about 200 μm to about 500 μm, from about 500 μm to about 2 mm, from about 500 μm to about 1 mm, or any range or sub-range therebetween.

[0175] Reference will now be made to Figure 2 the foldable device 101 to describe the first portion 221. It should be understood that, unless otherwise specified, this description of the first portion 221 can also be applied to any embodiment of the present disclosure. For example, Figure 3 and 6 -7, the foldable device 301 and / or the foldable substrate 201 shown in FIG. As Figure 2As shown, the first portion 221 may include a first surface region 223 and a second surface region 225 opposite the first surface region. In some embodiments, as shown, the second surface region 225 of the first portion 221 may include a planar surface. In other embodiments, as shown, the second surface region 225 may be parallel to the first surface region 223. In some embodiments, as shown, the first major surface 203 may include the first surface region 223, and the second major surface 205 may include the second surface region 225. In other embodiments, the first surface region 223 may extend along a first plane 204a. In other embodiments, the second surface region 225 may extend along a second plane 204b. A substrate thickness 227 may be defined between the first plane 204a and the second plane 204b. In some embodiments, the substrate thickness 227 may correspond to the distance between the first surface region 223 of the first portion 221 and the second surface region 225 of the first portion 221. In some embodiments, the substrate thickness 227 may be substantially uniform across the entire first surface region 223. In some embodiments, a first thickness defined between the first surface region 223 and the second surface region 225 may be within one or more of the ranges described above with respect to the substrate thickness. In other embodiments, the first thickness may constitute the substrate thickness 227. In other embodiments, across the entire corresponding length of the foldable device (i.e., in the direction 106 of the length 105 of the foldable device) and / or across the entire corresponding width of the foldable device (i.e., in the direction 104 of the width 103 of the foldable device), the first thickness between the first surface region 223 and the second surface region 225 of the first portion 221 may be substantially uniform.

[0176] As Figures 2 - 3 shown in FIGS. 6-7, the foldable substrate 201 may further include a second portion 231, the second portion 231 including a third surface region 233 and a fourth surface region 235 opposite the third surface region 233. The second portion 231 will now be described with reference to Figure 2 the foldable device 101 of FIGS. 6-7, it should be understood that, unless otherwise stated, the description of the second portion 231 may also apply to any embodiment of the present disclosure, e.g., Figure 3 FIGS. 6The foldable devices 101, 301 and / or the foldable substrate 201 as shown in FIG. -7. In some embodiments, as shown, the third surface region 233 of the second portion 231 may include a planar surface. In additional embodiments, the third surface region 233 of the second surface portion 231 may be coplanar with the first surface region 223 of the first portion 221. In some embodiments, as shown, the fourth surface region 235 of the second portion 231 may include a planar surface. In additional embodiments, as shown, the fourth surface region 235 may be parallel to the third surface region 233. In additional embodiments, the fourth surface region 235 of the second portion 231 may be coplanar with the second surface region 225 of the first portion 221.

[0177] A second thickness 237 may be defined between the third surface region 233 and the fourth surface region 235 of the second portion 231. In some embodiments, the second thickness 237 may be within the range described above for the substrate thickness. In additional embodiments, the second thickness 237 may constitute the substrate thickness. In additional embodiments, as shown, the second thickness 237 may be substantially equal to the first thickness (e.g., the substrate thickness 227). In some embodiments, the second thickness 237 of the second portion 231 may be substantially uniform between the third surface region 233 and the fourth surface region 235.

[0178] As Figures 2 - 3 As shown in FIGS. 6-7, the foldable substrate 201 may include a central portion 251 located between the first portion 221 and the second portion 231. In some embodiments, the central portion 251 may include a first central surface region 209 and a second central surface region 213 opposite the first central surface region 209. In additional embodiments, the central portion 251 may include the first central surface region 209 located between the first surface region 223 and the third surface region 233. In additional embodiments, as shown, the first central surface region 209 may be recessed from the first major surface 203. In additional embodiments, the central portion 251 may include the second central surface region 213 located between the second surface region 225 and the fourth surface region 235. In additional embodiments, as shown, the second major surface 205 may include the second central surface region 213.

[0179] A central thickness 217 of the central portion 251 may be defined between a first central surface region 209 and a second central surface region 213. In some embodiments, the first central surface region 209 may include a central main surface 211 that may extend along a third plane 204c when the foldable devices 101, 301 are in a flat configuration, but in other embodiments, the first central surface region 209 may be provided as a non-planar region. In other embodiments, the third plane 204c may be substantially parallel to the first plane 204a and / or the second plane 204b. By providing the central main surface 211 of the central portion 251 that extends along a third plane 204c parallel to the second plane 204b, a uniform central thickness 217 may extend throughout the central portion 251, which may provide enhanced folding performance at a predetermined thickness of the central thickness 217. By preventing stress concentration, the uniform central thickness 217 over the entire central portion 251 may improve the folding performance, while stress concentration would occur if a part of the central portion 251 is thinner than the remaining central portion 251.

[0180] In some embodiments, such as Figures 2 - 3As shown in FIGS. 6-7, the central thickness 217 can be less than the substrate thickness 227 (e.g., the first thickness of the first portion 221, the second thickness 237 of the second portion 231). In some embodiments, the central thickness 217 can be about 0.5% or more, about 1% or more, about 2% or more, about 5% or more, about 13% or less, about 10% or less, or about 5% or less of the substrate thickness 227 (e.g., the first thickness, the second thickness 237). In some embodiments, as a percentage of the substrate thickness 227 (e.g., the first thickness, the second thickness 237), the central thickness 217 can be in the following ranges: about 0.5% to about 13%, about 0.5% to about 10%, about 0.5% to about 5%, about 1% to about 13%, about 1% to about 10%, about 1% to about 5%, about 2% to about 13%, about 2% to about 10%, about 2% to about 5%, about 5% to about 13%, about 5% to about 10%, or any range or sub-range therebetween. In additional embodiments, the central thickness 217 can be within one or more of the substrate thickness 227 (e.g., the first thickness, the second thickness 237) while being less than the substrate thickness. In additional embodiments, the central thickness 217 can be greater than or equal to about 10 μm, greater than or equal to about 25 μm, greater than or equal to about 50 μm, greater than or equal to about 80 μm, less than or equal to about 220 μm, less than or equal to about 125 μm, less than or equal to about 100 μm, less than or equal to about 80 μm, less than or equal to about 60 μm, or less than or equal to about 40 μm. In additional embodiments, the central thickness 217 can be in the following ranges: about 10 μm to about 220 μm, about 10 μm to about 125 μm, about 10 μm to about 100 μm, about 10 μm to about 80 μm, about 25 μm to about 80 μm, about 25 μm to about 60 μm, about 50 μm to about 60 μm, or any range or sub-range therebetween. Based on the following reference Figure 42For the results of the pen-drop test, increased puncture resistance can be achieved by selecting a center thickness 217 that is less than about 50 micrometers (μm) or greater than about 80 μm. In additional embodiments, the center thickness 217 can be greater than about 80 μm, for example, greater than or equal to about 80 μm, greater than or equal to about 100 μm, greater than or equal to about 125 μm, less than or equal to about 220 μm, less than or equal to about 175 μm, or less than or equal to about 150 μm. In additional embodiments, the center thickness 217 can be in the range of: about 80 μm to about 220 μm, about 80 μm to about 175 μm, about 80 μm to about 150 μm, about 100 μm to about 150 μm, about 125 μm to about 150 μm, or any range or sub-range therebetween. In additional embodiments, the center thickness 217 can be less than about 80 μm, for example, in the range of: about 10 μm to about 80 μm, about 25 μm to about 60 μm, about 10 μm to about 50 μm, about 25 μm to about 50 μm, about 10 μm to about 40 μm, about 25 μm to about 40 μm, or any range or sub-range therebetween.

[0181] As Figure 2 shown, the central portion 251 can include a first transition portion 253. The first transition portion 253 can attach the first portion 221 to a region of the central portion 251 that includes the center thickness 217 (e.g., the region that includes the central major surface 211). The thickness of the first transition portion 253 can be defined between the second plane 204b and the first central surface region 209. As Figure 2 shown, the thickness of the first transition portion 253 can increase continuously from the central major surface 221 (e.g., from the center thickness 217) to the first portion 221 (e.g., to the first thickness, substrate thickness 227). In some embodiments, as shown, from the central major surface 211 to the first portion 221, the thickness of the first transition portion 253 can increase at a constant rate. Although not shown, in some embodiments, compared to the middle of the first transition portion 253, at the location where the central major surface 211 meets the first transition portion 253, the thickness of the first transition portion 253 can increase more slowly. Although not shown, in some embodiments, compared to the middle of the first transition portion 253, at the location where the first portion 221 meets the first transition portion 253, the thickness of the first transition portion 253 can increase more slowly. In some embodiments, as Figure 3 shown, the central portion 251 may not include a first transition portion.

[0182] The central portion 251 can include a second transition portion 255. As Figure 2As shown, the second transition portion 255 may attach the second portion 231 to a region of the central portion 251 that includes the central thickness 217 (e.g., a region that includes the central major surface 211). A thickness of the second transition portion 255 may be defined between the second plane 204b and the first central surface region 209. As Figure 2 shown, the thickness of the second transition portion 255 may increase continuously from the central major surface 211 (e.g., from the central thickness 217) to the second portion 231 (e.g., to the first thickness). In some embodiments, as shown, the thickness of the second transition portion 255 may increase at a constant rate from the central major surface 211 to the second portion 231. Although not shown, in some embodiments, the thickness of the second transition portion 255 may increase more slowly at the location where the central major surface 211 meets the second transition portion 255 as compared to the middle of the second transition portion 255. Although not shown, in some embodiments, the thickness of the second transition portion 255 may increase more slowly at the location where the second portion 231 meets the second transition portion 255 as compared to the middle of the second transition portion 255. In some embodiments, as Figure 3 shown, the central portion 251 may not include the second transition portion.

[0183] As Figure 2 shown, a width 254a of the first transition portion 253 may be defined between the central major surface 211 and the first portion 221 in the direction 106 of the length 105 of the foldable device 101. A width 254b of the second transition portion 255 may be defined between the central major surface 211 and the second portion 231 in the direction 106 of the length 105 of the foldable device 101. In some embodiments, the width 254a of the first transition portion 253 and / or the width 254b of the second transition portion 255 may be large enough (e.g., greater than or equal to 1 mm) to avoid optical distortion that may occur with a stepped transition width or a small transition width (e.g., less than 1 mm) that would otherwise be between the first thickness and the central thickness. Based on the following reference Figure 42The described pen-drop test provides a transition region having a length small enough (e.g., less than or equal to about 5 mm) to reduce the amount of the foldable substrate having a medium thickness, e.g., in the range of about 50 μm to about 80 μm. The foldable substrate having a medium thickness may have reduced impact resistance and / or puncture resistance. In some embodiments, to enhance the puncture resistance of the foldable substrate while avoiding optical distortion, the width 254a of the first transition portion 253 and / or the width 254b of the second transition portion 255 may be greater than or equal to about 1 mm, greater than or equal to about 2 mm, greater than or equal to about 3 mm, less than or equal to about 5 mm, less than or equal to about 4 mm, or less than or equal to about 3 mm. In some embodiments, the width of the first transition portion 253 and / or the width 254b of the second transition portion 255 may be in the following ranges: about 1 mm to about 5 mm, about 1 mm to about 4 mm, about 1 mm to about 3 mm, about 2 mm to about 5 mm, about 2 mm to about 4 mm, about 2 mm to about 3 mm, about 3 mm to about 5 mm, about 3 mm to about 4 mm, or any range or sub-range therebetween.

[0184] If the first layer and / or component is described as "disposed above the second layer and / or component", there may or may not be other layers between the first layer and / or component and the second layer and / or component. Additionally, as used herein, "disposed above" does not refer to the relative position with reference to gravity. For example, when the first layer and / or component is located below, above, or on one side of the second layer and / or component, the first layer and / or component may be considered to be "disposed above the second layer and / or component". As used herein, the first layer and / or component described as "bonded to the second layer and / or component" means that the layers and / or components are bonded to each other, which is achieved by direct contact and / or bonding between the two layers and / or components or by a bonding layer. As used herein, the first layer and / or component described as "in contact with the second layer and / or component" or "contacting the second layer and / or component" refers to direct contact and includes the case where the layers and / or components are bonded to each other.

[0185] As Figures 2 - 3As shown in FIGS. 6 - 7, the foldable device 101 and / or 301 and / or the testable foldable device 602 may include an adhesive layer 261. As shown, the adhesive layer 261 may include a first contact surface 263 and a second contact surface 265 opposite the first contact surface 263. In some embodiments, as shown, the second contact surface 265 of the adhesive layer 261 may include a planar surface. An adhesive thickness 267 of the adhesive layer 261 may be defined between the first contact surface 263 and the second contact surface 265. In some embodiments, the adhesive thickness 267 of the adhesive layer 261 may be greater than or equal to about 1 μm, greater than or equal to about 5 μm, greater than or equal to about 10 μm, less than or equal to about 100 μm, less than or equal to about 60 μm, less than or equal to about 30 μm, or less than or equal to about 20 μm. In some embodiments, the adhesive thickness 267 of the adhesive layer 261 may be in the range of: about 1 μm to about 100 μm, about 5 μm to about 100 μm, about 5 μm to about 60 μm, about 5 μm to about 30 μm, about 10 μm to about 30 μm, about 10 μm to about 20 μm, or any range or sub - range therebetween.

[0186] In some embodiments, as Figure 2 shown, the first contact surface 263 of the adhesive layer 261 may face the first major surface 273 of the release liner 271 (described below). In additional embodiments, as shown, the first contact surface 263 of the adhesive layer 261 may contact the first major surface 273 of the release liner 271. In some embodiments, as Figure 3 and 6 FIGS. 6 - 7 show, the first contact surface 263 of the adhesive layer 261 may face the first major surface 303 of the display device 307. In additional embodiments, as shown, the first contact surface 263 of the adhesive layer 261 may contact the first major surface 303 of the display device 307.

[0187] Reference will now be made to Figure 2 the foldable device 101 to describe the adhesive layer 261. It should be understood that this description of the adhesive layer 261 may also apply to Figure 3 and 6 the foldable device 301 and / or the foldable substrate 201 shown in FIGS. 6 - 7. In some embodiments, as Figure 2As shown, the second contact surface 265 of the adhesive layer 261 may face the first surface area 223 of the first portion 221. In additional embodiments, as shown, the second contact surface 265 of the adhesive layer 261 may contact the first surface area 223 of the first portion 221. In some embodiments, as shown, the second contact surface 265 of the adhesive layer 261 may face the third surface area 233 of the second portion 231. In additional embodiments, as shown, the second contact surface 265 of the adhesive layer 261 may contact the third surface area 233 of the second portion 231.

[0188] In some embodiments, the adhesive layer 261 may include one or more of the following: polyolefins, polyamides, halogen-containing polymers (e.g., polyvinyl chloride or fluoropolymers), elastomers, urethanes, phenolic resins, parylene, polyethylene terephthalate (PET), and polyetheretherketone (PEEK). Exemplary embodiments of polyolefins include low molecular weight polyethylene (LDPE), high molecular weight polyethylene (HDPE), ultra-high molecular weight polyethylene (UHMWPE), and polypropylene (PP). Exemplary embodiments of fluoropolymers include polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), perfluoropolyether (PFPE), perfluorosulfonic acid (PFSA), perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP) polymers, and ethylene tetrafluoroethylene (ETFE) polymers. Exemplary embodiments of elastomers include rubbers (e.g., polybutadiene, polyisoprene, chloroprene, butyl rubber, nitrile rubber) and block copolymers (e.g., styrene-butadiene, high impact polystyrene, poly(dichlorophosphazene)). In additional embodiments, the adhesive layer 261 may include an optically clear adhesive. In additional embodiments, the optically clear adhesive may include one or more optically clear polymers: acrylics (e.g., polymethyl methacrylate (PMMA)), epoxy materials, silicones, and / or polyurethanes. Examples of epoxy materials include: bisphenol-based epoxy resins, novolac-based epoxy materials, cycloaliphatic-based epoxy materials, and glycidylamine-based epoxy materials. In additional embodiments, the optically clear adhesive may include, but is not limited to, acrylic adhesives, e.g., 3M 8212 adhesive, or optically clear liquid adhesives, e.g., LOCTITE optically clear liquid adhesive. Exemplary embodiments of optically clear adhesives include transparent acrylics, epoxy materials, silicones, and polyurethanes. For example, optically clear liquid adhesives may include one or more of the following: LOCTITE AD 8650, LOCTITE AA 3922, LOCTITE EA E-05MR, LOCTITE UK U-09LV, all of which are commercially available from Henkel Corporation.

[0189] As Figure 2 shown, at least a portion of the adhesive layer 261 of the foldable device 101 can be located between the first portion 221 and the second portion 231. In some embodiments, as shown, a recess 219 can be defined between the first central surface region 209 and the first plane 204a. In some embodiments, the recess 219 can be defined between the third plane 204c and the first plane 204a. In some embodiments, as shown, the adhesive layer 261 can be at least partially located in the recess 219. In additional embodiments, as shown, the polymer-based portion 241 can fill the recess 219. In some embodiments, although not shown, the recess may not be completely filled, for example, leaving space for electronic devices and / or mechanical devices.

[0190] As Figure 3 and 6 -7 shown, the polymer-based portion 241 of the foldable device 301 and / or the test foldable device 602 can be located between the first portion 221 and the second portion 231. In some embodiments, as shown, a recess 219 can be defined between the first central surface region 209 and the first plane 204a. In some embodiments, the recess 219 can be defined between the third plane 204c and the first plane 204a. In some embodiments, as shown, the polymer-based portion 241 can be at least partially located in the recess 219. In additional embodiments, as shown, the polymer-based portion 241 can fill the recess 219. In additional embodiments, the polymer-based portion 241 can include the same material as the adhesive layer 261 such that the adhesive layer 261 can fill the recess. Although not shown, in some embodiments, the adhesive layer 261 can extend into the recess to replace the polymer-based portion 241, and / or the adhesive layer 261 can fill the recess. Although not shown, in some embodiments, the recess may not be completely filled, for example, leaving space for electronic devices and / or mechanical devices.

[0191] As Figure 3As shown, the polymer-based portion 241 may include a fourth contact surface 247 opposite the third contact surface 245. In some embodiments, as shown, the fourth contact surface 247 may include a planar surface. In additional embodiments, the fourth contact surface 247 may be substantially coplanar with the first surface region 223 and the third surface region 233 (e.g., extending along a common plane, the first plane 204a). In some embodiments, the third contact surface 245 may include a planar surface. In some embodiments, in addition to the fourth contact surface 247 being substantially coplanar with the first surface region 223 and the third surface region 233, the third contact surface 245 may also be substantially coplanar with the first central surface region 209 (e.g., the central main surface 211) (e.g., extending along a common plane, the third plane 204c). The polymer-based portion 241 may extend in the direction 202 of the substrate thickness 227 (e.g., the first thickness of the first portion 221), the extension being substantially equal to the difference between the substrate thickness 227 (e.g., the first thickness of the first portion 221) and the central thickness 217.

[0192] In some embodiments, the second contact surface 265 of the adhesive layer 261 may face the fourth contact surface 247 of the polymer-based portion 241. In additional embodiments, as shown, the second contact surface 265 of the adhesive layer 261 may contact the fourth contact surface 247 of the polymer-based portion 241. In additional embodiments, as Figure 2 shown, the adhesive layer 261 rather than the polymer-based portion 241 may occupy the recess 219. In some embodiments, although not shown, the adhesive layer 261 may be absent, and instead, the polymer-based portion 241 may occupy the region occupied by the adhesive layer 261.

[0193] In some embodiments, the polymer-based portion 241 comprises a polymer (e.g., an optically transparent polymer). In additional embodiments, the polymer-based portion 241 may comprise one or more optically transparent polymers: acrylics (e.g., polymethyl methacrylate (PMMA)), epoxy materials, silicones, and / or polyurethanes. Examples of epoxy materials include: bisphenol-based epoxy resins, novolac-based epoxy materials, cycloaliphatic-based epoxy materials, and glycidylamine-based epoxy materials. In other embodiments, the polymer-based portion 241 may comprise one or more of the following: polyolefins, polyamides, halogen-containing polymers (e.g., polyvinyl chloride or fluoropolymers), elastomers, urethanes, phenolic resins, parylene, polyethylene terephthalate (PET), and polyetheretherketone (PEEK). Exemplary embodiments of polyolefins include low molecular weight polyethylene (LDPE), high molecular weight polyethylene (HDPE), ultra-high molecular weight polyethylene (UHMWPE), and polypropylene (PP). Exemplary embodiments of fluoropolymers include polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), perfluoropolyether (PFPE), perfluorosulfonic acid (PFSA), perfluoroalkoxy polymer (PFA), fluorinated ethylene propylene (FEP) polymer, and ethylene tetrafluoroethylene (ETFE) polymer. Exemplary embodiments of elastomers include rubbers (e.g., polybutadiene, polyisoprene, neoprene, butyl rubber, nitrile rubber) and block copolymers (e.g., styrene-butadiene, high impact polystyrene, poly(dichlorophosphazene)), e.g., comprising one or more of polystyrene, poly(dichlorophosphazene), and poly(5-ethylidene-2-norbornene). In some embodiments, the polymer-based portion may comprise a sol-gel material. Exemplary embodiments of polyurethanes include thermosetting polyurethanes (e.g., Dispurez 102 from Incorez) and thermoplastic polyurethanes (e.g., KrystalFlex PE505 from Huntsman). In additional embodiments, the second portion may comprise an ethylene acid copolymer. An exemplary embodiment of an ethylene acid copolymer includes SURLYN from Dow (e.g., Surlyn PC-2000, Surlyn 8940, Surlyn 8150). Additional exemplary embodiments of the second portion include Eleglass w802-GL044 from Axalta, which has a crosslinker in an amount of 1 wt% to 2 wt%. In some embodiments, the polymer-based portion 241 may further comprise nanoparticles, e.g., carbon black, carbon nanotubes, silica nanoparticles, or polymer-containing nanoparticles. In some embodiments, the polymer-based portion may further comprise fibers to form a polymer-fiber composite.

[0194] In some embodiments, the polymer-based portion 241 may include a coefficient of thermal expansion (CTE). As used herein, the coefficient of thermal expansion is measured between -20 °C and 40 °C in accordance with ASTM E289-17 using a PICOSCAL Michelson Interferometer. In some embodiments, the polymer-based portion 241 may include particles of one or more of copper oxide, β-quartz, tungstate, vanadate, pyrophosphate, and / or nitinol. In some embodiments, the polymer-based portion 241 may have a CTE that is greater than or equal to about -20x10 -7 1 / °C, greater than or equal to about -10x10 -7 1 / °C, greater than or equal to about -5x10 -7 1 / °C, greater than or equal to about -2x10 -7 1 / °C, less than or equal to about 10x10 -7 1 / °C, less than or equal to about 5x10 -7 1 / °C, less than or equal to about 2x10 -7 1 / °C, less than or equal to about 1x10 -7 1 / °C, or less than or equal to 0 1 / °C. In some embodiments, the polymer-based portion 241 may have a CTE in the following ranges: about -20x10 -7 1 / °C to about 10x10 -7 1 / °C, about -20x10 -7 1 / °C to about 5x10 -7 1 / °C, about -10x10 -7 1 / °C to about -5x10 -7 1 / °C, about -10x10 -7 1 / °C to about 2x10 -7 1 / °C, about -10x10 -7 1 / °C to 0 1 / °C, about -5x10 -7 1 / °C to 0 1 / °C, about -2x10 -7 1 / °C to about 0 1 / °C, or any range or sub-range therebetween. By providing a polymer-based portion having a low (e.g., negative) coefficient of thermal expansion, warping due to volume changes during curing of the polymer-based portion can be mitigated.

[0195] In some embodiments, the polymer-based portion 241 may include a modulus of elasticity that is greater than or equal to about 0.01 megapascals (MPa), greater than or equal to about 1 MPa, greater than or equal to about 10 MPa, greater than or equal to about 20 MPa, greater than or equal to about 100 MPa, greater than or equal to about 200 MPa, greater than or equal to about 1,000 MPa, less than or equal to about 5,000 MPa, less than or equal to about 3,000 MPa, less than or equal to about 1,000 MPa, less than or equal to about 500 MPa, or less than or equal to about 200 MPa. In some embodiments, the polymer-based portion 241 may include a modulus of elasticity in the following ranges: about 0.001 MPa to about 5,000 MPa, about 0.01 MPa to about 3,000 MPa, about 0.01 MPa to about 1,000 MPa, about 0.01 MPa to about 500 MPa, about 0.01 MPa to about 200 MPa, about 1 MPa to about 5,000 MPa, about 1 MPa to about 1,000 MPa, about 1 MPa to about 1,000 MPa, about 1 MPa to about 200 MPa, about 10 MPa to about 5,000 MPa, about 10 MPa to about 1,000 MPa, about 10 MPa to about 200 MPa, about 20 MPa to about 3,000 MPa, about 20 MPa to about 1,000 MPa, about 20 MPa to about 200 MPa, about 100 MPa to about 3,000 MPa, about 100 MPa to about 1,000 MPa, about 100 MPa to about 200 MPa, about 200 MPa to about 5,000 MPa, about 200 MPa to about 3,000 MPa, about 200 MPa to about 1,000 MPa, or any range or sub-range therebetween. In some embodiments, the modulus of elasticity of the polymer-based portion 241 may be in the following ranges: about 1 GPa to about 20 GPa, about 1 GPa to about 18 GPa, about 1 GPa to about 10 GPa, about 1 GPa to about 5 GPa, about 1 GPa to about 3 GPa, or any range or sub-range therebetween. By providing the polymer-based portion 241 with a modulus of elasticity in the range of about 0.01 MPa to about 3,000 MPa (e.g., in the range of about 20 MPa to about 3 GPa), folding of the foldable device without failure can be facilitated. In some embodiments, the adhesive layer 261 includes a modulus of elasticity greater than that of the polymer-based portion 241, and this arrangement provides an improved performance of puncture resistance. In some embodiments, the modulus of elasticity of the polymer-based portion 241 may be less than the modulus of elasticity of the foldable substrate 201. In some embodiments, the adhesive layer 261 may include a modulus of elasticity within the ranges listed prior to this paragraph. In additional embodiments, the adhesive layer 261 may include a modulus of elasticity substantially the same as that of the polymer-based portion 241.In additional embodiments, the elastic modulus of the adhesive layer 261 can be in the following ranges: from about 1 GPa to about 20 GPa, from about 1 GPa to about 18 GPa, from about 1 GPa to about 10 GPa, from about 1 GPa to about 5 GPa, from about 1 GPa to about 3 GPa, or any range or sub-range therebetween. In some embodiments, the elastic modulus of the polymer-based portion 241 can be less than the elastic modulus of the first portion 221. In some embodiments, the elastic modulus of the polymer-based portion 241 can be less than the elastic modulus of the second portion 231.

[0196] In some embodiments, the adhesive layer 261 can include an elastic modulus of: greater than or equal to about 0.001 megapascals (MPa), greater than or equal to about 0.01 MPa, greater than or equal to about 0.1 MPa, less than or equal to about 1 MPa, less than or equal to about 0.5 MPa, less than or equal to about 0.1 MPa, or less than or equal to about 0.05 MPa. In some embodiments, the adhesive layer 261 can include an elastic modulus in the following ranges: from about 0.001 MPa to about 1 MPa, from about 0.01 MPa to about 1 MPa, from about 0.01 MPa to about 0.5 MPa, from about 0.05 MPa to about 0.5 MPa, from about 0.1 MPa to about 0.5 MPa, from about 0.001 MPa to about 0.5 MPa, from about 0.001 MPa to about 0.01 MPa, or any range or sub-range therebetween. In some embodiments, the adhesive layer 261 can include an elastic modulus within one or more of the ranges described above with respect to the elastic modulus of the polymer-based portion 241.

[0197] In some embodiments, such as Figure 2As shown, a coating 281 may be provided above the second major surface 205 of the foldable substrate 201. In additional embodiments, the coating 281 may be provided above the first portion 221, the second portion 231, and the central portion 251. In some embodiments, the coating 281 may include a third major surface 283 and a fourth major surface 285 opposite the third major surface 283. In additional embodiments, the coating 281 (e.g., the third major surface 283) may contact the foldable substrate 201 (e.g., the second major surface 205). In additional embodiments, the coating 281 may include a coating thickness 287 defined between the third major surface 283 and the fourth major surface 285. In additional embodiments, the coating thickness 287 may be greater than or equal to about 0.1 μm, greater than or equal to about 1 μm, greater than or equal to about 5 μm, greater than or equal to about 10 μm, greater than or equal to about 15 μm, greater than or equal to about 20 μm, greater than or equal to about 25 μm, greater than or equal to about 40 μm, greater than or equal to about 50 μm, greater than or equal to about 60 μm, greater than or equal to about 70 μm, greater than or equal to about 80 μm, greater than or equal to about 90 μm, less than or equal to about 200 μm, less than or equal to about 100 μm, or about 50 μm, less than or equal to about 30 μm, less than or equal to about 25 μm, less than or equal to about 20 μm, less than or equal to about 20 μm, less than or equal to about 15 μm, or less than or equal to about 10 μm. In some embodiments, the coating thickness 287 may be in the range of: about 0.1 μm to about 200 μm, about 1 μm to about 200 μm, about 10 μm to about 200 μm, about 50 μm to about 200 μm, about 0.1 μm to about 100 μm, about 1 μm to about 100 μm, about 10 μm to about 100 μm, about 20 μm to about 100 μm, about 30 μm to about 100 μm, about 40 μm to about 100 μm, about 50 μm to about 100 μm, about 60 μm to about 100 μm, about 70 μm to about 100 μm, about 80 μm to about 100 μm, about 90 μm to about 100 μm, about 0.1 μm to about 50 μm, about 1 μm to about 50 μm, about 10 μm to about 50 μm, or any range or sub-range therebetween.In additional embodiments, the coating thickness 287 can be in the range of from about 0.1 μm to about 50 μm, from about 0.1 μm to about 30 μm, from about 0.1 μm to about 25 μm, from about 0.1 μm to about 20 μm, from about 0.1 μm to about 15 μm, from about 0.1 μm to about 10 μm, from about 1 μm to about 30 μm, from about 1 μm to about 25 μm, from about 1 μm to about 20 μm, from about 1 μm to about 15 μm, from about 1 μm to about 10 μm, from about 5 μm to about 30 μm, from about 5 μm to about 25 μm, from about 5 μm to about 20 μm, from about 5 μm to about 15 μm, from about 5 μm to about 10 μm, from about 10 μm to about 30 μm, from about 10 μm to about 25 μm, from about 10 μm to about 20 μm, from about 10 μm to about 15 μm, from about 15 μm to about 30 μm, from about 15 μm to about 25 μm, from about 15 μm to about 20 μm, from about 20 μm to about 30 μm, from about 20 μm to about 25 μm, or any range and sub-range therebetween.

[0198] In some embodiments, the coating 281 can include a polymer hard coating. In additional embodiments, the polymer hard coating can include one or more of an ethylene-acid copolymer, a polyurethane-based polymer, an acrylate resin, and a mercaptoester resin. Exemplary embodiments of ethylene-acid copolymers include ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, and ethylene-acrylic acid-methacrylic acid terpolymers [e.g., Nucrel manufactured by DuPont], ionomers of ethylene-acid copolymers (e.g., Surlyn manufactured by DuPont), and ethylene-acrylic acid copolymer amine dispersions (e.g., Aquacer manufactured by BYK). Exemplary embodiments of polyurethane-based polymers include modified polyurethane aqueous dispersions (e.g., )). Exemplary embodiments of UV-curable acrylate resins include acrylate resins (e.g., resin manufactured by Allnex), cyanoacrylate adhesives (e.g., UV620) and UV free radical acrylic resins (e.g., Ultrabond windshield repair resin, e.g., Ultrabond (45CPS)). Exemplary embodiments of mercaptoester resins include mercaptoester triallyl isocyanurates (e.g., optical adhesive NOA 61 from Norland). In additional embodiments, the polymeric hard coat can include ethylene-acrylic copolymers and ethylene-methacrylic acid copolymers, which can be ionomerized by neutralizing carboxylic acid residues to form ionomer resins, typically using alkali metal ions such as sodium and potassium, and zinc. Such ethylene-acrylic and ethylene-methacrylic acid ionomers can be dispersed in water and coated onto a substrate to form an ionomer coating. Alternatively, such acid copolymers can be neutralized with ammonia, and after coating and drying, the ammonia is released to reform the acid copolymer as a coating. By providing a coating comprising a polymeric coating, the foldable device can include low energy fracture.

[0199] In some embodiments, the coating may include a polymer hard coat, which includes an optically transparent polymer hard coat. Materials suitable for the optically transparent polymer hard coat include, but are not limited to: cured acrylate resin materials, inorganic-organic hybrid polymer materials, aliphatic or aromatic hexa-functional urethane acrylates, silicone-based hybrid materials, and nanocomposites, such as epoxy materials and urethane materials having nanosilicates. In some embodiments, the optically transparent polymer hard coat may consist essentially of one or more of these materials. In some embodiments, the optically transparent polymer hard coat may consist of one or more of these materials. As used herein, "inorganic-organic hybrid polymer material" means a polymer material that contains monomers and has both inorganic and organic components. Inorganic-organic hybrid polymers are obtained by polymerization reactions between monomers having inorganic groups and organic groups. Inorganic-organic hybrid polymers are not nanocomposites that contain separate inorganic and organic components or phases (e.g., inorganic microparticles dispersed in an organic matrix). More specifically, materials suitable for an optically transparent polymer (OTP) hard coat include, but are not limited to, polyimides, polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), organic polymer materials, inorganic-organic hybrid polymer materials, and aliphatic or aromatic hexa-functional urethane acrylates. In some embodiments, the OTP hard coat may consist essentially of an organic polymer material, an inorganic-organic hybrid polymer material, or an aliphatic or aromatic hexa-functional urethane acrylate. In some embodiments, the OTP hard coat may consist of polyimide, an organic polymer material, an inorganic-organic hybrid polymer material, or an aliphatic or aromatic hexa-functional urethane acrylate. In some embodiments, the OTP hard coat may include a nanocomposite. In some embodiments, the OTP hard coat may include at least one of nanosilicates, epoxy materials, and urethane materials. Suitable compositions for such OTP hard coats are described in U.S. Patent Publication No. 2015 / 0110990, which is incorporated herein by reference in its entirety. As used herein, "organic polymer material" means a polymeric material that contains monomers and the monomers have only organic components. In some embodiments, the OTP hard coat may include an organic polymer material manufactured by Gunze Limited and having a hardness of 9H, for example, "High Durability Transparent Film" of Gunze. As used herein, "inorganic-organic hybrid polymer material" means a polymer material that contains monomers and has both inorganic and organic components. Inorganic-organic hybrid polymers are obtained by polymerization reactions between monomers having inorganic groups and organic groups. Inorganic-organic hybrid polymers are not nanocomposites that contain separate inorganic and organic components or phases (e.g., inorganic microparticles dispersed in an organic matrix).In some embodiments, the inorganic-organic hybrid polymer material may include polymerizable monomers containing inorganic silicon-based groups, for example, silsesquioxane polymers. Silsesquioxane polymers may be, for example, those having the following chemical structure (RSiO. 1.5 ) nalkyl-silsesquioxane, aryl-silsesquioxane, or arylalkyl-silsesquioxane, wherein R is an organic group such as, but not limited to, methyl or phenyl. In some embodiments, the OTP hard coat can include a silsesquioxane polymer combined with an organic matrix such as SILPLUS manufactured by Nippon Steel Chemical Co., Ltd. In some embodiments, the OTP hard coat can include 90 wt% to 95 wt% of an aromatic hexa-functional urethane acrylate [e.g., PU662NT (aromatic hexa-functional urethane acrylate) manufactured by Miwon Specialty Chemical Co.] and 10 wt% to 5 wt% of a photoinitiator [e.g., Darocur 1173 manufactured by Ciba Specialty Chemicals Corporation], and has a hardness of 8H or greater. In some embodiments, an OTP hard coat composed of an aliphatic or aromatic hexa-functional urethane acrylate can be formed as a separate layer by spin-coating the layer on a polyethylene terephthalate (PET) substrate, curing the urethane acrylate, and removing the urethane acrylate layer from the PET substrate. The coating thickness of the OTP hard coat (e.g., coating thickness 287) can be in the range of 1 μm to 150 μm, including sub-ranges. For example, the coating thickness (e.g., coating thickness 287) can be in the following ranges: 10 μm to 140 μm, 20 μm to 130 μm, 30 μm to 120 μm, 40 μm to 110 μm, 50 μm to 100 μm, 60 μm to 90 μm, 70 μm, 80 μm, 2 μm to 140 μm, 4 μm to 130 μm, 6 μm to 120 μm, 8 μm to 110 μm, 10 μm to 100 μm, 10 μm to 90 μm, 10 μm, 80 μm, 10 μm, 70 μm, 10 μm, 60 μm, 10 μm, 50 μm, or in the range between any two of these values as endpoints. In some embodiments, the OTP hard coat can be a single integral layer. In some embodiments, the OTP hard coat can be a layer of an inorganic-organic hybrid polymer material or an organic polymer material having a thickness in the range of 80 μm to 120 μm (including sub-ranges). For example, the thickness of the OTP hard coat containing an inorganic-organic hybrid polymer material or an organic polymer material can be 80 μm to 110 μm, 90 μm to 100 μm, or in the range between any two of these values as endpoints. In some embodiments, the OTP hard coat can be a layer of an aliphatic or aromatic hexa-functional urethane acrylate material having a thickness in the range of 10 μm to 60 μm (including sub-ranges).For example, the thickness of the OTP hard coat comprising an aliphatic or aromatic hexa-functional urethane acrylate material can be from 10 μm to 55 μm, from 10 μm to 50 μm, from 10 μm to 40 μm, from 10 μm to 45 μm, from 10 μm to 40 μm, from 10 μm to 35 μm, from 10 μm to 30 μm, from 10 μm to 25 μm, from 10 μm to 20 μm, or within any range bounded by any two of these values as endpoints.

[0200] In some embodiments, if provided, the surface coating 281 may further include one or more of an easy-to-clean coating, a low-friction coating, an oleophobic coating, a diamond-like coating, a scratch-resistant coating, or an abrasion-resistant coating. The scratch-resistant coating may include a nitrogen oxide, for example, aluminum oxynitride or silicon oxynitride, and has a thickness of about 500 microns or greater. In such embodiments, the abrasion-resistant layer may include the same material as the scratch-resistant layer. In some embodiments, the low-friction coating may include a highly fluorinated silane coupling agent, for example, an alkylfluorosilane, wherein a methoxy group is attached to the silicon atom. In such embodiments, the easy-to-clean coating may include the same material as the low-friction coating. In other embodiments, the easy-to-clean coating may include a protonatable group, for example, an amine, for example, an alkylaminosilane, wherein a methoxy group is attached to the silicon atom. In such embodiments, the oleophobic coating may include the same material as the easy-to-clean coating. In some embodiments, the diamond-like coating includes carbon and may be produced by applying a high voltage potential in the presence of a hydrocarbon plasma.

[0201] In some embodiments, as Figure 2As shown, the foldable device 101 may include a release liner 271. However, in other embodiments, other substrates (e.g., the glass-based substrate and / or ceramic-based substrate described in the present application) may be used instead of the illustrated release liner 271. In other embodiments, as shown, the release liner 271 or another substrate may be disposed above the adhesive layer 261. In other embodiments, as shown, the release liner 271 or another substrate may directly contact the first contact surface 263 of the adhesive layer 261. The release liner 271 or another substrate may include a first major surface 273 and a second major surface 275 opposite the first major surface 273. As shown, by attaching the first contact surface 263 of the adhesive layer 261 to the second major surface 275 of the release liner 271 or another substrate, the release liner 271 or another substrate may be disposed on the adhesive layer 261. In some embodiments, as shown, the first major surface 273 of the release liner 271 or another substrate may include a planar surface. In some embodiments, as shown, the second major surface 275 of the release liner 271 or another substrate may include a planar surface. The release liner 271 may include paper and / or polymer. Exemplary embodiments of paper include kraft paper, machine-made paper, polymer-coated paper (e.g., polymer-coated cellophane, siliconized paper), or clay-coated paper. Exemplary embodiments of polymer include polyester (e.g., polyethylene terephthalate (PET)) and polyolefin (e.g., low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP)).

[0202] In some embodiments, as Figure 3 and 7 shown, the foldable device 301 may include a display device 307. In other embodiments, as shown, the display device 307 may be disposed above the adhesive layer 261. In other embodiments, as shown, the display device 307 may contact the first contact surface 263 of the adhesive layer 261. In some embodiments, by removing Figure 2The release liner 271 of the foldable device 101 and attaching the display device 307 to the first contact surface 263 of the adhesive layer 261 enables the production of the foldable device 301. Alternatively, the foldable device 301 can be produced without the step of removing the release liner before attaching the display device 307 to the first contact surface 263 of the adhesive layer 261, for example, when the release liner 271 is not applied to the first contact surface 263 of the adhesive layer 261. The display device 307 can include a first major surface 303 and a second major surface 305 opposite to the first major surface 303. As shown, by attaching the first contact surface 263 of the adhesive layer 261 to the second major surface 305 of the display device 307, the display device 307 can be disposed on the adhesive layer 261. In some embodiments, as shown, the first major surface 303 of the display device 307 can include a planar surface. In some embodiments, as shown, the second major surface 305 of the display device 307 can include a planar surface. The display device 307 can include a liquid crystal display (LCD), an electrophoretic display (EPD), an organic light emitting diode display (OLED), or a plasma display panel (PDP). In some embodiments, the display device 307 can be part of a portable electronic device, such as a consumer electronic product, a smartphone, a tablet computer, a wearable device, or a laptop computer.

[0203] Embodiments of the present disclosure can include consumer electronic products. The consumer electronic products can include a front surface, a rear surface, and side surfaces. The consumer electronic products can further include electrical components at least partially within the housing. The electrical components can include a controller, a memory, and a display. The display can be at or adjacent to the front surface of the housing. The consumer electronic products can include a cover substrate disposed above the display. In some embodiments, at least one of a portion of the housing or the cover substrate includes the foldable device described in the present disclosure.

[0204] The foldable devices disclosed herein can be incorporated into another article, such as an article having a display (or display article) [such as consumer electronics, including mobile phones, tablet computers, computers, navigation systems, wearable devices (such as watches), etc.]; building articles; transportation articles (such as automobiles, trains, aircraft, ships, etc.), appliance articles, or any article that can benefit from a certain degree of transparency, scratch resistance, abrasion resistance, or a combination of the above properties. Figures 8 - 9 Exemplary articles containing any of the foldable devices disclosed herein are shown. Specifically, Figures 8 - 9FIG. 800 shows a consumer electronic device 800, which includes a housing 802 having a front surface 804, a rear surface 806, and side surfaces 808; electrical components (not shown) that are at least partially or fully located within the housing and include at least a controller, a memory, and a display 810, the display 810 being at or adjacent to the front surface of the housing; and a cover substrate 812 that is at or above the front surface of the housing such that the cover substrate is above the display. In some embodiments, at least one of the cover substrate 812 or a portion of the housing 802 may include any of the foldable devices disclosed herein, e.g., a foldable substrate.

[0205] In some embodiments, the foldable devices 101 and 301 and / or the testable foldable device 602 may be substantially symmetric about a plane (e.g., Figures 1 - 3 plane 109 in ). In some embodiments, the plane 109 may include a central axis 107 of the foldable device, which may be located at the second major surface 205 of the foldable substrate 201. As further illustrated, in some embodiments, the plane 109 may include a pivot axis 102 of the foldable device. In some embodiments, the foldable device may be folded about the pivot axis 102 in a direction 111 (e.g., see Figure 1 ) to form a folded configuration (e.g., see Figures 6 - 7 ). As shown, the foldable device may include a single pivot axis to allow the foldable device to include a bifold, where, for example, the foldable device may be folded in half. In additional embodiments, the foldable device may include two or more pivot axes, where each pivot axis includes a corresponding intermediate portion similar or identical to the central portion 251 described above. For example, providing two pivot axes may allow the foldable device to include a trifold, where, for example, the foldable device may be folded into three parts, including a first part 221, a second part 231, and a third part similar or identical to the first or second part.

[0206] In some embodiments, the foldable substrate 201 may include a glass-based substrate and / or a ceramic-based substrate, and the first portion 221, the second portion 231, and / or the central portion 251 may include one or more compressive stress zones. In some embodiments, the compressive stress zones may be established by chemical strengthening. Chemical strengthening may include an ion exchange process in which ions in the surface layer are replaced (or exchanged) with larger ions of the same valence or oxidation state. Methods of chemical strengthening will be discussed below. Without being bound by theory, chemically strengthening the first portion 221, the second portion 231, and / or the central portion 251 can achieve excellent impact resistance and / or puncture resistance (e.g., resistance to failure at a pen drop height greater than or equal to about 15 centimeters (cm), greater than or equal to about 20 cm, greater than or equal to 50 cm). Without wishing to be bound by theory, chemically strengthening the first portion 221, the second portion 231, and / or the central portion 251 can achieve a small (e.g., less than about 10 mm or less) bending radius because the compressive stress from chemical strengthening can counteract the bending-induced tensile stress on the outermost surface of the substrate. The compressive stress zone may extend into a portion of the first and / or second portions to a certain depth, which is referred to as the compressive depth. As used herein, the compressive depth means the depth at which the stress in the chemically strengthened substrate and / or portion described herein changes from compressive stress to tensile stress. Depending on the ion exchange treatment and the thickness of the article being measured, the compressive depth can be measured using a surface stress meter or a scatter light polarimeter (SCALP, where the values reported herein were made using a SCALP-5 manufactured by Glasstress Co., Estonia). If the stress in the substrate and / or portion is generated by exchanging potassium ions into the substrate, the compressive depth is measured using, for example, an FSM-6000 [Orihara Industrial Co., Ltd. (Orihara Sangyo Co., Ltd.), Japan]. Unless otherwise specified, the compressive stress (including surface CS) is measured using a commercially available instrument, such as an FSM-6000 manufactured by Orihara Corporation, through a surface stress meter (FSM). Surface stress measurements rely on the accurate measurement of the stress optical coefficient (SOC), which is related to the birefringence of the glass. Unless otherwise specified, the SOC is measured according to Scheme C (glass disk method) described in ASTM standard C770-16, entitled "Standard Test Method for Measurement of Glass Stress-Optical Coefficient", which is incorporated herein by reference in its entirety. If the stress is generated by exchanging sodium ions into the substrate and the thickness of the article being measured exceeds about 400 μm, the SCALP is used to measure the compressive depth and the central tension (CT).If the stress in the substrate and / or part is created by exchanging both potassium ions and sodium ions into the substrate and / or part, and the thickness of the article being measured exceeds about 400 μm, then the compression depth and CT are measured by SCALP. Without wishing to be bound by theory, the depth of sodium exchange can indicate the compression depth, while the depth of potassium ion exchange can indicate a change in the magnitude of the compressive stress (but not a change from compressive stress to tensile stress). The refraction near field (RNF; the RNF method is described in U.S. Patent No. 8,854,623, titled "Systems and methods for measuring a profile characteristic of a glass sample", which is incorporated herein by reference in its entirety) method can also be used to obtain a graphical representation of the stress distribution. When using the RNF method to obtain a graphical representation of the stress distribution, the maximum central tension value provided by SCALP is used in the RNF method. The graphical representation of the stress distribution obtained by RNF is force balanced and calibrated to the maximum central tension value provided by the SCALP measurement. As used herein, "depth of layer" (DOL) means the depth of ions (e.g., sodium, potassium) exchanged into the substrate and / or part. In the present disclosure, when the maximum central tension cannot be directly measured by SCALP (such as when the article being measured is thinner than about 400 μm), the maximum central tension can be approximated by the product of the maximum compressive stress and the compression depth divided by the difference between the substrate thickness and twice the compression depth, wherein the compressive stress and the compression depth are measured by FSM.

[0207] In some embodiments, a first portion 221 that includes a glass-based portion and / or a ceramic-based portion may include a first compressive stress zone at a first surface region 223, and the first compressive stress zone may extend from the first surface region 223 to a first compressive depth. In some embodiments, a first portion 221 that includes a first glass-based portion and / or a ceramic-based portion may include a second compressive stress zone at a second surface region 225, and the second compressive stress zone may extend from the second surface region 225 to a second compressive depth. In some embodiments, as a percentage of a substrate thickness 227 (e.g., a first thickness), the first compressive depth and / or the second compressive depth may be greater than or equal to about 1%, greater than or equal to about 5%, greater than or equal to about 10%, less than or equal to about 30%, less than or equal to about 25%, or less than or equal to about 20%. In some embodiments, as a percentage of a substrate thickness 227 (e.g., a first thickness), the first compressive depth and / or the second compressive depth may be in a range of: about 1% to about 30%, about 5% to about 30%, about 5% to about 25%, about 5% to about 20%, about 10% to about 30%, about 10% to about 25%, about 10% to about 20%, or any range or sub-range therebetween. In additional embodiments, as a percentage of a substrate thickness 227 (e.g., a first thickness), the first compressive depth and / or the second compressive depth may be less than or equal to about 10%, e.g., about 1% to about 10%, about 1% to about 8%, about 3% to about 8%, about 5% to about 8%, or any range or sub-range therebetween.

[0208] In additional embodiments, the first compressive depth may be substantially equal to the second compressive depth. In some embodiments, the first compressive depth and / or the second compressive depth may be greater than or equal to about 1 μm, greater than or equal to about 10 μm, greater than or equal to about 30 μm, greater than or equal to about 50 μm, less than or equal to about 200 μm, less than or equal to about 150 μm, less than or equal to about 100 μm, or less than or equal to about 60 μm. In some embodiments, the first compressive depth and / or the second compressive depth may be in a range of: about 1 μm to about 200 μm, about 1 μm to about 150 μm, about 10 μm to about 150 μm, about 10 μm to about 100 μm, about 30 μm to about 100 μm, about 30 μm to about 60 μm, about 50 μm to about 60 μm, or any range or sub-range therebetween. By providing a first portion that includes a first glass-based and / or ceramic-based portion, and the first portion includes a first compressive depth and / or a second compressive depth that is about 1% to about 30% of a first thickness, excellent impact resistance and / or puncture resistance can be obtained.

[0209] In some embodiments, the first compressive stress region may include a first maximum compressive stress. In some embodiments, the second compressive stress region may include a second maximum compressive stress. In additional embodiments, the first maximum compressive stress and / or the second maximum compressive stress may be greater than or equal to about 100 megapascals (MPa), greater than or equal to about 300 MPa, greater than or equal to about 500 MPa, greater than or equal to about 600 MPa, greater than or equal to about 700 MPa, less than or equal to about 1,500 MPa, less than or equal to about 1,200 MPa, less than or equal to about 1,000 MPa, or less than or equal to about 800 MPa. In additional embodiments, the first maximum compressive stress and / or the second maximum compressive stress may be in the range of: about 100 MPa to about 1,500 MPa, about 100 MPa to about 1,200 MPa, about 300 MPa to about 1,200 MPa, about 300 MPa to about 1,000 MPa, about 500 MPa to about 1,000 MPa, about 600 MPa to about 1,000 MPa, about 600 MPa to about 1,000 MPa, about 700 MPa to about 1,000 MPa, about 700 MPa to about 800 MPa, or any range or sub-range therebetween. By providing a first maximum compressive stress and / or a second maximum compressive stress of about 100 MPa to about 1,500 MPa, excellent impact resistance and / or puncture resistance can be achieved.

[0210] In some embodiments, the first portion 221 may include a first layer depth of one or more alkali metal ions associated with the first compressive stress region and the first layer depth. In some embodiments, the first portion 221 may include a second layer depth of one or more alkali metal ions associated with the second compressive stress region and the second layer depth. As used herein, the one or more alkali metal ions in the layer depth of the one or more alkali metal ions may include sodium, potassium, rubidium, cesium, and / or francium. In some embodiments, the one or more alkali metal ions in the first layer depth and / or the second layer depth of the one or more alkali metal ions include potassium. In some embodiments, as a percentage of the substrate thickness 227 (e.g., the first thickness), the first layer depth and / or the second layer depth may be greater than or equal to about 1%, greater than or equal to about 5%, greater than or equal to about 10%, less than or equal to about 40%, less than or equal to about 35%, less than or equal to about 30%, less than or equal to about 25%, or less than or equal to about 20%. In some embodiments, as a percentage of the substrate thickness 227 (e.g., the first thickness), the first layer depth and / or the second layer depth may be in the range of: about 1% to about 40%, about 1% to about 35%, about 1% to about 30%, about 1% to about 25%, about 1% to about 20%, about 5% to about 30%, about 5% to about 25%, about 5% to about 20%, about 10% to about 30%, about 10% to about 25%, about 10% to about 20%, or any range or sub-range therebetween. In additional embodiments, as a percentage of the substrate thickness 227 (e.g., the first thickness), the first layer depth of the one or more alkali metal ions and / or the second layer depth of the one or more alkali metal ions may be less than or equal to about 10%, e.g., about 1% to about 10%, about 1% to about 8%, about 3% to about 8%, about 5% to about 8%, or any range or sub-range therebetween. In some embodiments, the first layer depth of the one or more alkali metal ions and / or the second layer depth of the one or more alkali metal ions may be greater than or equal to about 1 μm, greater than or equal to about 10 μm, greater than or equal to about 30 μm, greater than or equal to about 50 μm, less than or equal to about 200 μm, less than or equal to about 150 μm, less than or equal to about 100 μm, or less than or equal to about 60 μm. In some embodiments, the first layer depth of the one or more alkali metal ions and / or the second layer depth of the one or more alkali metal ions may be in the range of: about 1 μm to about 200 μm, about 1 μm to about 150 μm, about 10 μm to about 150 μm, about 10 μm to about 100 μm, about 30 μm to about 100 μm, about 30 μm to about 60 μm, about 50 μm to about 60 μm, or any range or sub-range therebetween.

[0211] In some embodiments, the first portion 221 may include a first tensile stress zone. In some embodiments, the first tensile stress zone may be located between the first compressive stress zone and the second compressive stress zone. In some embodiments, the first tensile stress zone may include a first maximum tensile stress. In additional embodiments, the first maximum tensile stress may be greater than or equal to about 10 MPa, greater than or equal to about 20 MPa, greater than or equal to about 30 MPa, less than or equal to about 100 MPa, less than or equal to about 80 MPa, or less than or equal to about 60 MPa. In additional embodiments, the first maximum tensile stress may be in the range of: about 10 MPa to about 100 MPa, about 10 MPa to about 80 MPa, about 10 MPa to about 60 MPa, about 20 MPa to about 100 MPa, about 20 MPa to about 80 MPa, about 20 MPa to about 60 MPa, about 30 MPa to about 100 MPa, about 30 MPa to about 80 MPa, about 30 MPa to about 60 MPa, or any range or sub-range therebetween. By providing a first maximum tensile stress of about 10 MPa to about 100 MPa, excellent impact resistance and / or puncture resistance can be achieved while providing low energy fracture, as described below.

[0212] In some embodiments, based on oxides, the first portion 221 may include a first average concentration of potassium. As used herein, "based on oxides" means that the measurement of a component is made as if the non-oxygen components in the compound were converted into a specified oxide form or, if no specific oxide is specified, into a fully oxidized oxide, and the calculations are then made accordingly. For example, sodium (Na) based on oxides refers to the amount in terms of sodium oxide (Na 2 O), and potassium based on oxides refers to the amount in terms of potassium oxide (K 2The amount in terms of (O). In this way, the component does not need to be in the actual specified oxide form or fully oxidized oxide form in order for the component to be measured and counted "based on the oxide". Thus, the "based on the oxide" measurement of the specified component includes conceptually converting the substance containing the non-oxygen element of the specified component into the specified oxide form, or if no specific oxide form is specified, into the fully oxidized oxide, and then calculating the concentration based on the oxide. In some embodiments, the first average concentration of potassium based on the oxide can be greater than or equal to about 10 parts per million (10 ppm), greater than or equal to about 50 ppm, greater than or equal to about 200 ppm, greater than or equal to about 500 ppm, greater than or equal to about 1,000 ppm, greater than or equal to about 2,000 ppm, less than or equal to about 300,000, less than or equal to about 100,000 ppm, less than or equal to about 50,000 ppm, less than or equal to about 20,000 ppm, less than or equal to about 10,000 ppm, or less than or equal to about 5,000 ppm. In some embodiments, the first average concentration of potassium based on the oxide can be in the following ranges: about 10 ppm to about 300,000 ppm, about 50 ppm to about 300,000, about 50 ppm to about 100,000, about 200 ppm to about 100,000, about 200 ppm to about 50,000 ppm, about 500 ppm to about 50,000, about 500 ppm to about 20,000 ppm, about 1,000 ppm to about 20,000 ppm, about 2,000 ppm to about 10,000 ppm, about 2,000 ppm to about 5,000 ppm, or any range or sub-range therebetween. Without wishing to be bound by theory, the average concentration of potassium includes the potassium introduced by chemical strengthening and the potassium in the foldable substrate during forming.

[0213] In some embodiments, the second portion 231 that includes the second glass-based and / or ceramic-based portion may include a third compressive stress zone at the third surface region 233, and the third compressive stress zone may extend from the third surface region 233 to a third compressive depth. In some embodiments, the second portion 231 that includes the second glass-based and / or ceramic-based portion may include a fourth compressive stress zone at the fourth surface region 235, and the fourth compressive stress zone may extend from the fourth surface region 235 to a fourth compressive depth. In some embodiments, as a percentage of the substrate thickness 227 (e.g., the second thickness 237), the third compressive depth and / or the fourth compressive depth may be greater than or equal to about 1%, greater than or equal to about 5%, greater than or equal to about 10%, less than or equal to about 30%, less than or equal to about 25%, or less than or equal to about 20%. In some embodiments, as a percentage of the substrate thickness 227 (e.g., the second thickness 237), the third compressive depth and / or the fourth compressive depth may be in the range of: about 1% to about 30%, about 5% to about 30%, about 5% to about 25%, about 5% to about 20%, about 10% to about 30%, about 10% to about 25%, about 10% to about 20%, or any range or sub-range therebetween. In additional embodiments, the third compressive depth may be substantially equal to the fourth compressive depth. In some embodiments, the third compressive depth and / or the fourth compressive depth may be greater than or equal to about 1 μm, greater than or equal to about 10 μm, greater than or equal to about 30 μm, greater than or equal to about 50 μm, less than or equal to about 200 μm, less than or equal to about 150 μm, less than or equal to about 100 μm, or less than or equal to about 60 μm. In some embodiments, the third compressive depth and / or the fourth compressive depth may be in the range of: about 1 μm to about 200 μm, about 1 μm to about 150 μm, about 10 μm to about 150 μm, about 10 μm to about 100 μm, about 30 μm to about 100 μm, about 30 μm to about 60 μm, about 50 μm to about 60 μm, or any range or sub-range therebetween. By providing the second portion that includes the glass-based and / or ceramic-based portion, and the second portion includes a third compressive depth and / or a fourth compressive depth that is about 1% to about 30% of the substrate thickness, excellent impact resistance and / or puncture resistance can be obtained.

[0214] In some embodiments, the third compressive stress zone may include a third maximum compressive stress. In some embodiments, the fourth compressive stress zone may include a fourth maximum compressive stress. In additional embodiments, the third maximum compressive stress and / or the fourth maximum compressive stress may be greater than or equal to about 100 megapascals (MPa), greater than or equal to about 300 MPa, greater than or equal to about 500 MPa, greater than or equal to about 600 MPa, greater than or equal to about 700 MPa, less than or equal to about 1,500 MPa, less than or equal to about 1,200 MPa, less than or equal to about 1,000 MPa, or less than or equal to about 800 MPa. In additional embodiments, the third maximum compressive stress and / or the fourth maximum compressive stress may be in the range of: about 100 MPa to about 1,500 MPa, about 100 MPa to about 1,200 MPa, about 300 MPa to about 1,200 MPa, about 300 MPa to about 1,000 MPa, about 500 MPa to about 1,000 MPa, about 600 MPa to about 1,000 MPa, about 600 MPa to about 1,000 MPa, about 700 MPa to about 1,000 MPa, about 700 MPa to about 800 MPa, or any range or sub-range therebetween. By providing a third maximum compressive stress and / or a fourth maximum compressive stress of about 100 MPa to about 1,500 MPa, excellent impact resistance and / or puncture resistance can be achieved.

[0215] In some embodiments, the second portion 231 may include a third depth of layer of one or more alkali metal ions associated with a third compressive stress region and the third depth of layer. In some embodiments, the second portion 231 may include a fourth depth of layer of one or more alkali metal ions associated with a fourth compressive stress region and a fourth compressive depth. In some embodiments, the one or more alkali metal ions in the third depth of layer and / or the fourth depth of layer of the one or more alkali metal ions include potassium. In some embodiments, as a percentage of the substrate thickness 227 (e.g., the first thickness, the second thickness 237), the third depth of layer and / or the fourth depth of layer may be greater than or equal to about 1%, greater than or equal to about 5%, greater than or equal to about 10%, less than or equal to about 40%, less than or equal to about 35%, less than or equal to about 30%, less than or equal to about 25%, or less than or equal to about 20%. In some embodiments, as a percentage of the substrate thickness 227 (e.g., the first thickness, the second thickness 237), the third compressive depth and / or the fourth compressive depth may be in the range of: about 1% to about 40%, about 1% to about 35%, about 1% to about 30%, about 1% to about 25%, about 1% to about 20%, about 5% to about 30%, about 5% to about 25%, about 5% to about 20%, about 10% to about 30%, about 10% to about 25%, about 10% to about 20%, or any range or sub-range therebetween. In additional embodiments, as a percentage of the substrate thickness 227 (e.g., the first thickness, the second thickness 237), the third depth of layer and / or the fourth depth of layer of the one or more alkali metal ions may be less than or equal to about 10%, e.g., about 1% to about 10%, about 1% to about 8%, about 3% to about 8%, about 5% to about 8%, or any range or sub-range therebetween. In some embodiments, the third depth of layer and / or the fourth depth of layer of the one or more alkali metal ions may be greater than or equal to about 1 μm, greater than or equal to about 10 μm, greater than or equal to about 30 μm, greater than or equal to about 50 μm, less than or equal to about 200 μm, less than or equal to about 150 μm, less than or equal to about 100 μm, or less than or equal to about 60 μm. In some embodiments, the third depth of layer and / or the fourth depth of layer of the one or more alkali metal ions may be in the range of: about 1 μm to about 200 μm, about 1 μm to about 150 μm, about 10 μm to about 150 μm, about 10 μm to about 100 μm, about 30 μm to about 100 μm, about 30 μm to about 60 μm, about 50 μm to about 60 μm, or any range or sub-range therebetween.

[0216] In some embodiments, the second portion 231 may include a second tensile stress zone. In some embodiments, the second tensile stress zone may be located between the third compressive stress zone and the fourth compressive stress zone. In some embodiments, the second compressive stress zone may include a second maximum tensile stress. In additional embodiments, the second maximum tensile stress may be greater than or equal to about 10 MPa, greater than or equal to about 20 MPa, greater than or equal to about 30 MPa, less than or equal to about 100 MPa, less than or equal to about 80 MPa, or less than or equal to about 60 MPa. In additional embodiments, the second maximum tensile stress may be in the range of: about 10 MPa to about 100 MPa, about 10 MPa to about 80 MPa, about 10 MPa to about 60 MPa, about 20 MPa to about 100 MPa, about 20 MPa to about 80 MPa, about 20 MPa to about 60 MPa, about 30 MPa to about 100 MPa, about 30 MPa to about 80 MPa, about 30 MPa to about 60 MPa, or any range or sub-range therebetween. Providing a second maximum tensile stress of about 10 MPa to about 100 MPa can achieve excellent impact resistance and / or puncture resistance while providing low energy fracture, as described below.

[0217] In some embodiments, based on oxides, the second portion 231 may include a second average concentration of potassium. In some embodiments, the second average concentration of potassium based on oxides may be greater than or equal to about 10 parts per million (ppm), greater than or equal to about 50 ppm, greater than or equal to about 200 ppm, greater than or equal to about 500 ppm, greater than or equal to about 1,000 ppm, greater than or equal to about 2,000 ppm, less than or equal to about 300,000 ppm, less than or equal to about 100,000 ppm, less than or equal to about 50,000 ppm, less than or equal to about 20,000 ppm, less than or equal to about 10,000 ppm, or less than or equal to about 5,000 ppm. In some embodiments, the second average concentration of potassium based on oxides may be in the range of: about 10 ppm to about 300,000 ppm, about 50 ppm to about 300,000 ppm, about 50 ppm to about 100,000 ppm, about 200 ppm to about 100,000 ppm, about 200 ppm to about 50,000 ppm, about 500 ppm to about 50,000 ppm, about 500 ppm to about 20,000 ppm, about 1,000 ppm to about 20,000 ppm, about 2,000 ppm to about 10,000 ppm, about 2,000 ppm to about 5,000 ppm, or any range or sub-range therebetween.

[0218] In some embodiments, the first compression depth may be substantially equal to the third compression depth. In some embodiments, the second compression depth may be substantially equal to the fourth compression depth. In some embodiments, the first maximum compression stress may be substantially equal to the third maximum compression stress. In some embodiments, the second maximum compression stress may be substantially equal to the fourth maximum compression stress. In some embodiments, the depth of the first layer of one or more alkali metal ions may be substantially equal to the depth of the third layer of one or more alkali metal ions. In some embodiments, the depth of the second layer of one or more alkali metal ions may be substantially equal to the depth of the fourth layer of one or more alkali metal ions. In some embodiments, the first average concentration of potassium may be substantially equal to the second average concentration of potassium.

[0219] In some embodiments, the central portion 251 including a glass-based portion and / or a ceramic-based portion may include a first central compression stress zone at the first central surface region 209, and the first central compression stress zone may extend from the first central surface region 209 to the first central compression depth. In some embodiments, the central portion 251 including a glass-based portion and / or a ceramic-based portion may include a second central compression stress zone at the second central surface region 213, and the second central compression stress zone may extend from the second central surface region 213 to the second central compression depth. In some embodiments, as a percentage of the central thickness 217, the first central compression depth and / or the second central compression depth may be greater than or equal to about 1%, greater than or equal to about 5%, greater than or equal to about 10%, less than or equal to about 30%, less than or equal to about 25%, or less than or equal to about 20%. In some embodiments, as a percentage of the central thickness 217, the first central compression depth and / or the second central compression depth may be in the following ranges: about 1% to about 30%, about 5% to about 30%, about 5% to about 25%, about 5% to about 20%, about 10% to about 30%, about 10% to about 25%, about 10% to about 20%, or any range or sub-range therebetween. In additional embodiments, as a percentage of the central thickness 217, the first central compression depth and / or the second central compression depth may be greater than or equal to about 10%, for example, about 10% to about 30%, about 10% to about 25%, about 15% to about 25%, about 15% to about 20%, or any range or sub-range therebetween.

[0220] In additional embodiments, the first central compression depth can be substantially equal to the second central compression depth. In some embodiments, the first central compression depth and / or the second central compression depth can be greater than or equal to about 1 μm, greater than or equal to about 10 μm, greater than or equal to about 30 μm, greater than or equal to about 50 μm, less than or equal to about 200 μm, less than or equal to about 150 μm, less than or equal to about 100 μm, or less than or equal to about 60 μm. In some embodiments, the first central compression depth and / or the second central compression depth can be in the range of: about 1 μm to about 200 μm, about 1 μm to about 150 μm, about 10 μm to about 150 μm, about 10 μm to about 100 μm, about 30 μm to about 100 μm, about 30 μm to about 60 μm, about 50 μm to about 60 μm, or any range or sub-range therebetween. By providing a central portion comprising a glass-based and / or ceramic-based portion, and the central portion includes a first central compression depth and / or a second central compression depth that is about 1% to about 30% of the central thickness, excellent impact resistance and / or puncture resistance can be obtained.

[0221] In some embodiments, the first central compression stress zone can include a first central maximum compression stress. In some embodiments, the second central compression stress zone can include a second central maximum compression stress. In additional embodiments, the first central maximum compression stress and / or the second central maximum compression stress can be greater than or equal to about 100 megapascals (MPa), greater than or equal to about 300 MPa, greater than or equal to about 500 MPa, greater than or equal to about 600 MPa, greater than or equal to about 700 MPa, less than or equal to about 1,500 MPa, less than or equal to about 1,200 MPa, less than or equal to about 1,000 MPa, or less than or equal to about 800 MPa. In additional embodiments, the first central maximum compression stress and / or the second central maximum compression stress can be in the range of: about 100 MPa to about 1,500 MPa, about 100 MPa to about 1,200 MPa, about 300 MPa to about 1,200 MPa, about 300 MPa to about 1,000 MPa, about 500 MPa to about 1,000 MPa, about 600 MPa to about 1,000 MPa, about 600 MPa to about 1,000 MPa, about 700 MPa to about 1,000 MPa, about 700 MPa to about 800 MPa, or any range or sub-range therebetween. By providing a first central maximum compression stress and / or a second central maximum compression stress of about 100 MPa to about 1,500 MPa, excellent impact resistance and / or puncture resistance can be achieved.

[0222] In some embodiments, the central portion 251 may include a first central layer depth of one or more alkali metal ions associated with the first central compressive stress region and the first central layer depth. In some embodiments, the central portion 251 may include a second central layer depth of one or more alkali metal ions associated with the second central compressive stress region and the second central layer depth. In some embodiments, the one or more alkali metal ions of the first central layer depth and / or the one or more alkali metal ions of the second central layer depth include potassium. In some embodiments, as a percentage of the central thickness 217, the first central layer depth and / or the second central layer depth may be greater than or equal to about 1%, greater than or equal to about 5%, greater than or equal to about 10%, less than or equal to about 40%, less than or equal to about 35%, less than or equal to about 30%, less than or equal to about 25%, or less than or equal to about 20%. In some embodiments, as a percentage of the central thickness 217, the first central layer depth and / or the second central layer depth may be in the range of: about 1% to about 40%, about 1% to about 35%, about 1% to about 30%, about 1% to about 25%, about 1% to about 20%, about 5% to about 30%, about 5% to about 25%, about 5% to about 20%, about 10% to about 30%, about 10% to about 25%, about 10% to about 20%, or any range or sub-range therebetween. In additional embodiments, as a percentage of the central thickness 217, the first central layer depth of the one or more alkali metal ions and / or the second central layer depth of the one or more alkali metal ions may be less than or equal to about 10%, for example, about 1% to about 10%, about 1% to about 8%, about 3% to about 8%, about 5% to about 8%, or any range or sub-range therebetween. In some embodiments, the first central layer depth of the one or more alkali metal ions and / or the second central layer depth of the one or more alkali metal ions may be greater than or equal to about 1 μm, greater than or equal to about 10 μm, greater than or equal to about 30 μm, greater than or equal to about 50 μm, less than or equal to about 200 μm, less than or equal to about 150 μm, less than or equal to about 100 μm, or less than or equal to about 60 μm. In some embodiments, the first central layer depth of the one or more alkali metal ions and / or the second central layer depth of the one or more alkali metal ions may be in the range of: about 1 μm to about 200 μm, about 1 μm to about 150 μm, about 10 μm to about 150 μm, about 10 μm to about 100 μm, about 30 μm to about 100 μm, about 30 μm to about 60 μm, about 50 μm to about 60 μm, or any range or sub-range therebetween.

[0223] In some embodiments, the first compression depth and / or the third compression depth may be greater than the first central compression depth. In some embodiments, the second compression depth and / or the fourth compression depth may be greater than the second central compression depth. In some embodiments, the first layer depth and / or the third layer depth may be greater than the first central layer depth. In some embodiments, the second layer depth and / or the fourth layer depth may be greater than the second central compression depth.

[0224] In some embodiments, the central portion 251 may include a central tensile stress region. In some embodiments, the central tensile stress region may be located between the first central compressive stress region and the second central compressive stress region. In some embodiments, the central tensile stress region may include a central maximum tensile stress. In additional embodiments, the central maximum tensile stress may be greater than or equal to about 125 MPa, greater than or equal to about 150 MPa, greater than or equal to about 200 MPa, less than or equal to about 375 MPa, less than or equal to about 300 MPa, or less than or equal to about 250 MPa. In additional embodiments, the central maximum tensile stress may be in the range of: about 125 MPa to about 375 MPa, about 125 MPa to about 300 MPa, about 125 MPa to about 250 MPa, about 150 MPa to about 375 MPa, about 150 MPa to about 300 MPa, about 150 MPa to about 250 MPa, about 200 MPa to about 375 MPa, about 200 MPa to about 300 MPa, about 200 MPa to about 250 MPa, or any range or sub-range therebetween. Providing a central maximum tensile stress of about 125 MPa to about 375 MPa enables a low minimum bend radius.

[0225] In some embodiments, the first maximum tensile stress and the second maximum tensile stress may be less than the central maximum tensile stress. Providing a first maximum tensile stress and a second maximum tensile stress that are less than the central maximum tensile stress in the central portion enables low energy fracture while achieving a lower minimum bend radius. In additional embodiments, the first compression depth may be substantially equal to the first central compression depth. In additional embodiments, the third compression depth may be substantially equal to the first central compression depth. In additional embodiments, the second compression depth may be substantially equal to the second central compression depth. In additional embodiments, the fourth compression depth may be substantially equal to the second central compression depth. As described above, the central thickness may be less than the substrate thickness (e.g., in the range of about 0.5% to about 13%), which can cause the central maximum central tension to be greater than the first maximum central tension and the second maximum central tension, even when the compression depths of the first portion, the second portion, and the central portion may be substantially the same.

[0226] In some embodiments, based on the oxide, the second portion 251 may include a central average concentration of potassium. In some embodiments, the central average concentration of potassium based on the oxide may be greater than or equal to about 10 parts per million (10 ppm), greater than or equal to about 50 ppm, greater than or equal to about 200 ppm, greater than or equal to about 500 ppm, greater than or equal to about 1,000 ppm, greater than or equal to about 2,000 ppm, less than or equal to about 300,000, less than or equal to about 100,000 ppm, less than or equal to about 50,000 ppm, less than or equal to about 20,000 ppm, less than or equal to about 10,000 ppm, or less than or equal to about 5,000 ppm. In some embodiments, the central average concentration of potassium based on the oxide may be in the following ranges: about 10 ppm to about 300,000 ppm, about 50 ppm to about 300,000, about 50 ppm to about 100,000, about 200 ppm to about 100,000, about 200 ppm to about 50,000 ppm, about 500 ppm to about 50,000, about 500 ppm to about 20,000 ppm, about 1,000 ppm to about 20,000 ppm, about 2,000 ppm to about 10,000 ppm, about 2,000 ppm to about 5,000 ppm, or any range or sub-range therebetween.

[0227] A foldable substrate (e.g., foldable substrate 201) may be subject to various types of mechanical instabilities. Throughout this disclosure, mechanical instability includes local mechanical instability and system mechanical instability. As used herein, local mechanical instability refers to a deviation (e.g., multiple deviations) from the plane of the surface (e.g., the first central surface region), but the surface does not appear distorted as a whole, such as buckling and / or wrinkling. As used herein, system mechanical instability refers to the distortion of the entire surface from a certain plane, such as warping. As Figure 43 shown, the central axis 4301 (e.g., the x-axis) includes a central thickness (e.g., central thickness 217), and the vertical axis 4303 (e.g., the y-axis) includes the substrate thickness (e.g., the first thickness, second thickness 237). Figure 43The drawn shapes correspond to the type of mechanical instability observed at that location for the center thickness and the substrate thickness. The rhombus 4309 corresponds to buckling. The circle 4307 corresponds to buckling and wrinkling. The triangle 4313 corresponds to warping and wrinkling. The square 4311 corresponds to warping. The curves 4304 and 4305 distinguish the combinations of center thickness and substrate thickness where only extensive instabilities (e.g., warping) occur from the opposite combinations where local instabilities occur. The curve 4305 is the line indicating the local instabilities observable when the substrate thickness is greater than approximately four times the center thickness minus 71 microns. More specifically, the curve 4305 is the line indicating the local instabilities observable when the substrate thickness is greater than approximately 4.1 times the center thickness minus 71.37 microns. The curves 4304 and 4305 indicate that some instabilities (e.g., local mechanical instabilities) encountered by thinner foldable substrates (e.g., above the curves 4304 and / or 4305) can be different from those encountered by thicker foldable substrates (e.g., below the curves 4304 and / or 4305).

[0228] The onset of mechanical instability (e.g., local mechanical instability) can occur when the critical strain (e.g., critical buckling strain) of a portion (e.g., the center portion) of the foldable substrate is exceeded. For example, similar to Figure 3 the foldable substrate 201 shown with a width 252 of 20 mm of its center portion 251, the critical buckling strain of the center portion can be approximated as 10 times the square of the center thickness minus 23 times the center thickness plus 0.0006. For example, without wishing to be bound by theory, similar to 6 the foldable substrate 201 with a center thickness 217 of 30 μm, the critical buckling strain of the center portion can be approximated as 3 x 10 Figure 3 divided by the square of the width 252 of the center portion 251. -7

[0229] ​The chemically strengthened induced compressive strain of the central portion of the foldable substrate obtained by chemically strengthening the foldable substrate can be proportional to the product of the network expansion coefficient (B), the concentration difference (C), and the layer depth of the central portion divided by the difference between the central thickness and the layer depth of the first portion (or the second portion) divided by the substrate thickness. In some embodiments, by minimizing the concentration difference and / or minimizing the difference between the layer depth of the central portion divided by the central thickness and the layer depth of the first portion (or the second portion) divided by the substrate thickness, the compressive strain of the chemically strengthened induced compressive strain of the central portion can be reduced (e.g., reduced to a level below the critical buckling strain). As used herein, the network expansion coefficient refers to how much the volume of the foldable substrate (e.g., the first portion, the second portion, the central portion) expands due to an increase in the concentration of one or more alkali metal ions (e.g., due to chemical strengthening). In some embodiments, the network expansion constant of the first portion and / or the network expansion constant of the second portion can be substantially equal to the network expansion constant of the central portion, for example, if the first portion and / or the second portion and the central portion all comprise the same material before chemical strengthening.

[0230] As used herein, the concentration difference of a portion refers to the difference between the concentration at the surface of the portion and the concentration in the bulk of the portion. Unless otherwise indicated, the concentrations and concentration differences relate to the concentration of one or more alkali metal ions associated with chemical strengthening and / or the compressive stress zone. In some embodiments, based on oxides, the concentration and / or the concentration difference can refer to the concentration of potassium. In some embodiments, the concentration of the bulk of the first portion and / or the concentration of the bulk of the second portion can be substantially equal to the concentration of the bulk of the central portion, for example, if the first portion and / or the second portion and the central portion comprise the same material before chemical strengthening, and / or if the layer depth of a portion is less than about 45% of the thickness of the corresponding portion. In some embodiments, the first average concentration of potassium in the first portion based on oxides can be greater than the concentration of potassium in the bulk of the first portion based on oxides. In some embodiments, the second average concentration of potassium in the second portion based on oxides can be greater than the concentration of potassium in the bulk of the second portion based on oxides. In some embodiments, the central average concentration of potassium in the central portion based on oxides can be greater than the concentration of potassium in the bulk of the central portion based on oxides.

[0231] As used herein, the concentration difference between portions means the difference between one average concentration and another average concentration. Unless otherwise indicated, the concentrations and concentration differences relate to the concentration of one or more alkali metal ions associated with chemical strengthening and / or a compressive stress zone. In some embodiments, based on the oxide, the concentration and / or concentration difference may refer to the concentration of potassium. In some embodiments, the absolute difference between the first average concentration of potassium based on the oxide and the central average concentration of potassium based on the oxide may be greater than or equal to about 1 ppm, greater than or equal to about 10 ppm, greater than or equal to about 20 ppm, greater than or equal to about 50 ppm, about 70 ppm, less than or equal to about 500 ppm, less than or equal to about 200 ppm, less than or equal to about 100 ppm, or less than or equal to about 85 ppm. In some embodiments, the absolute difference between the first average concentration of potassium based on the oxide and the central average concentration of potassium based on the oxide may be in the range of: about 1 ppm to about 500 ppm, about 10 ppm to about 500 ppm, about 10 ppm to about 200 ppm, about 20 ppm to about 200 ppm, about 20 ppm to about 100 ppm, about 50 ppm to about 100 ppm, about 70 ppm to about 100 ppm, about 70 ppm to about 85 ppm, or any range or sub-range therebetween. In some embodiments, the absolute difference between the second average concentration of potassium based on the oxide and the central average concentration of potassium based on the oxide may be greater than or equal to about 1 ppm, greater than or equal to about 10 ppm, greater than or equal to about 20 ppm, greater than or equal to about 50 ppm, about 70 ppm, less than or equal to about 500 ppm, less than or equal to about 200 ppm, less than or equal to about 100 ppm, or less than or equal to about 85 ppm. In some embodiments, the absolute difference between the second average concentration of potassium based on the oxide and the central average concentration of potassium based on the oxide may be in the range of: about 1 ppm to about 500 ppm, about 10 ppm to about 500 ppm, about 10 ppm to about 200 ppm, about 20 ppm to about 200 ppm, about 20 ppm to about 100 ppm, about 50 ppm to about 100 ppm, about 70 ppm to about 100 ppm, about 70 ppm to about 85 ppm, or any range or sub-range therebetween. For example, for a foldable substrate having a central thickness of 30 μm and a central width of 20 mm, when the absolute difference in the average concentration difference is less than or equal to about 75 ppm, the strain induced by chemical strengthening may be less than the critical buckling strain.In some embodiments, the absolute difference between the first average concentration of potassium based on oxides and the central average concentration of potassium based on oxides can be less than 70 ppm, for example, within the following ranges: from about 0.1 ppm to about 50 ppm, from about 0.1 ppm to about 20 ppm, from about 0.5 ppm to about 20 ppm, from about 0.5 ppm to about 10 ppm, from about 1 ppm to about 10 ppm, from about 5 ppm to about 10 ppm, or any range or sub-range therebetween. In some embodiments, the absolute difference between the second average concentration of potassium based on oxides and the central average concentration of potassium based on oxides can be less than 70 ppm, for example, within the following ranges: from about 0.1 ppm to about 60 ppm, from about 0.1 ppm to about 50 ppm, from about 0.1 ppm to about 40 ppm, from about 0.1 ppm to about 30 ppm, from about 0.1 ppm to about 20 ppm, from about 0.5 ppm to about 20 ppm, from about 0.5 ppm to about 10 ppm, from about 1 ppm to about 10 ppm, from about 5 ppm to about 10 ppm, or any range or sub-range therebetween. Providing an absolute difference between the first average concentration and / or the second average concentration of potassium based on oxides and the central average concentration can provide reduced chemically strengthened induced strain (e.g., below the critical buckling strain) and / or reduced occurrence of mechanical instability in the foldable substrate and / or foldable device.

[0232] In some embodiments, the absolute difference between the depth of the first layer divided by the substrate thickness and the depth of the first central layer divided by the central thickness can be greater than or equal to about 0.001%, greater than or equal to about 0.002%, greater than or equal to about 0.005%, less than or equal to about 1%, less than or equal to about 0.2%, less than or equal to about 0.1%, or less than or equal to about 0.05%, less than or equal to about 0.01%, or less than or equal to about 0.008%. In some embodiments, the absolute difference between the depth of the first layer divided by the substrate thickness and the depth of the central layer divided by the central thickness can be in the following ranges: about 0.001% to about 1%, about 0.002% to about 1%, about 0.002% to about 0.2%, about 0.005% to about 0.2%, about 0.005% to about 0.1%, about 0.005% to about 0.1%, about 0.005% to about 0.05%, about 0.005% to about 0.01%, about 0.005% to about 0.008%, or any range or sub-range therebetween. In some embodiments, the absolute difference between the depth of the third layer divided by the substrate thickness and the depth of the first central layer divided by the central thickness can be greater than or equal to about 0.001%, greater than or equal to about 0.002%, greater than or equal to about 0.005%, less than or equal to about 1%, less than or equal to about 0.2%, less than or equal to about 0.1%, or less than or equal to about 0.05%, less than or equal to about 0.01%, or less than or equal to about 0.008%. In some embodiments, the absolute difference between the depth of the third layer divided by the substrate thickness and the depth of the first central layer divided by the central thickness can be in the following ranges: about 0.001% to about 1%, about 0.002% to about 1%, about 0.002% to about 0.2%, about 0.005% to about 0.2%, about 0.005% to about 0.1%, about 0.005% to about 0.1%, about 0.005% to about 0.05%, about 0.005% to about 0.01%, about 0.005% to about 0.008%, or any range or sub-range therebetween.

[0233] In some embodiments, the absolute difference between the depth of the second layer divided by the substrate thickness and the depth of the second center layer divided by the center thickness can be greater than or equal to about 0.001%, greater than or equal to about 0.002%, greater than or equal to about 0.005%, less than or equal to about 1%, less than or equal to about 0.2%, less than or equal to about 0.1%, or less than or equal to about 0.05%, less than or equal to about 0.01%, or less than or equal to about 0.008%. In some embodiments, the absolute difference between the depth of the second layer divided by the substrate thickness and the depth of the second center layer divided by the center thickness can be in the following ranges: about 0.001% to about 1%, about 0.002% to about 1%, about 0.002% to about 0.2%, about 0.005% to about 0.2%, about 0.005% to about 0.1%, about 0.005% to about 0.1%, about 0.005% to about 0.05%, about 0.005% to about 0.01%, about 0.005% to about 0.008%, or any range or sub-range therebetween. In some embodiments, the absolute difference between the depth of the fourth layer divided by the substrate thickness and the depth of the second center layer divided by the center thickness can be greater than or equal to about 0.001%, greater than or equal to about 0.002%, greater than or equal to about 0.005%, less than or equal to about 1%, less than or equal to about 0.2%, less than or equal to about 0.1%, or less than or equal to about 0.05%, less than or equal to about 0.01%, or less than or equal to about 0.008%. In some embodiments, the absolute difference between the depth of the fourth layer divided by the substrate thickness and the depth of the second center layer divided by the center thickness can be in the following ranges: about 0.001% to about 1%, about 0.002% to about 1%, about 0.002% to about 0.2%, about 0.005% to about 0.2%, about 0.005% to about 0.1%, about 0.005% to about 0.1%, about 0.005% to about 0.05%, about 0.005% to about 0.01%, about 0.005% to about 0.008%, or any range or sub-range therebetween. For example, for a foldable substrate having a center thickness of 30 μm and a center width of 20 mm, when the absolute difference between the layer depth divided by the substrate thickness associated with the first or second portion and the layer depth divided by the center thickness associated with the center portion is less than or equal to about 0.075%, the strain induced by chemical strengthening can be less than the critical buckling strain. In some embodiments, the absolute difference between the depth of one of the first layer depth, second layer depth, third layer depth, or fourth layer depth divided by the substrate thickness and the depth of the first center layer or second center layer divided by the center thickness can be less than 0.07%, for example, in the following ranges: about 0.001% to about 0.07%, about 0.01% to about 0.07%, about 0.01% to about 0.05%, about 0.01% to about 0.02%, or any range or sub-range therebetween.Providing the absolute difference between the first layer depth, the second layer depth, the third layer depth, and / or the fourth layer depth divided by the substrate thickness and the first central layer depth and / or the second central layer depth divided by the central thickness (e.g., the layer depth of potassium) can provide reduced chemically strengthened induced strain (e.g., below the critical buckling strain) and / or reduced occurrence of mechanical instability in a foldable substrate and / or a foldable device.

[0234] The compressive depth can be proportional to the corresponding layer depth. In some embodiments, the absolute difference between the first compressive depth divided by the substrate thickness and the first central compressive depth divided by the central thickness can be greater than or equal to about 0.001%, greater than or equal to about 0.002%, greater than or equal to about 0.005%, less than or equal to about 1%, less than or equal to about 0.2%, less than or equal to about 0.1%, or less than or equal to about 0.05%, less than or equal to about 0.01%, or less than or equal to about 0.008%. In some embodiments, the absolute difference between the first compressive depth divided by the substrate thickness and the first central compressive depth divided by the central thickness can be in the range of: about 0.001% to about 1%, about 0.002% to about 1%, about 0.002% to about 0.2%, about 0.005% to about 0.2%, about 0.005% to about 0.1%, about 0.005% to about 0.1%, about 0.005% to about 0.05%, about 0.005% to about 0.01%, about 0.005% to about 0.008%, or any range or sub-range therebetween. In some embodiments, the absolute difference between the third compressive depth divided by the substrate thickness and the first central compressive depth divided by the central thickness can be greater than or equal to about 0.001%, greater than or equal to about 0.002%, greater than or equal to about 0.005%, less than or equal to about 1%, less than or equal to about 0.2%, less than or equal to about 0.1%, or less than or equal to about 0.05%, less than or equal to about 0.01%, or less than or equal to about 0.008%. In some embodiments, the absolute difference between the third compressive depth divided by the substrate thickness and the first central compressive depth divided by the central thickness can be in the range of: about 0.001% to about 1%, about 0.002% to about 1%, about 0.002% to about 0.2%, about 0.005% to about 0.2%, about 0.005% to about 0.1%, about 0.005% to about 0.1%, about 0.005% to about 0.05%, about 0.005% to about 0.01%, about 0.005% to about 0.008%, or any range or sub-range therebetween.

[0235] In some embodiments, the absolute difference between the second compression depth divided by the substrate thickness and the second center compression depth divided by the center thickness can be greater than or equal to about 0.001%, greater than or equal to about 0.002%, greater than or equal to about 0.005%, less than or equal to about 1%, less than or equal to about 0.2%, less than or equal to about 0.1%, or less than or equal to about 0.05%, less than or equal to about 0.01%, or less than or equal to about 0.008%. In some embodiments, the absolute difference between the second compression depth divided by the substrate thickness and the second center compression depth divided by the center thickness can be in the following ranges: about 0.001% to about 1%, about 0.002% to about 1%, about 0.002% to about 0.2%, about 0.005% to about 0.2%, about 0.005% to about 0.1%, about 0.005% to about 0.1%, about 0.005% to about 0.05%, about 0.005% to about 0.01%, about 0.005% to about 0.008%, or any range or sub-range therebetween. In some embodiments, the absolute difference between the fourth compression depth divided by the substrate thickness and the second center compression depth divided by the center thickness can be greater than or equal to about 0.001%, greater than or equal to about 0.002%, greater than or equal to about 0.005%, less than or equal to about 1%, less than or equal to about 0.2%, less than or equal to about 0.1%, or less than or equal to about 0.05%, less than or equal to about 0.01%, or less than or equal to about 0.008%. In some embodiments, the absolute difference between the fourth compression depth divided by the substrate thickness and the second center compression depth divided by the center thickness can be in the following ranges: about 0.001% to about 1%, about 0.002% to about 1%, about 0.002% to about 0.2%, about 0.005% to about 0.2%, about 0.005% to about 0.1%, about 0.005% to about 0.1%, about 0.005% to about 0.05%, about 0.005% to about 0.01%, about 0.005% to about 0.008%, or any range or sub-range therebetween. For example, for a foldable substrate having a center thickness of 30 μm and a center width of 20 mm, when the absolute difference between the compression depth divided by the substrate thickness associated with the first or second portion and the compression depth divided by the center thickness associated with the center portion is less than or equal to about 0.075%, the strain induced by chemical strengthening can be less than the critical buckling strain. In some embodiments, the absolute difference between one of the first compression depth, the second compression depth, the third compression depth, or the fourth compression depth divided by the substrate thickness and the first center compression depth or the second center compression depth divided by the center thickness can be less than 0.07%, for example, in the following ranges: about 0.001% to about 0.07%, about 0.01% to about 0.07%, about 0.01% to about 0.05%, about 0.01% to about 0.02%, or any range or sub-range therebetween.Providing the first compression depth, the second compression depth, the third compression depth, and / or the fourth compression depth divided by the substrate thickness and the absolute difference between the first center compression depth and / or the second center compression depth divided by the center thickness can provide reduced chemically strengthened induced strain (e.g., below the critical buckling strain) and / or reduced occurrence of mechanical instability in a foldable substrate and / or a foldable device.

[0236] In some embodiments, chemically strengthened induced strain and / or stress can be observed in the optical retardation distribution of a foldable substrate. As used herein, the optical retardation distribution is measured using a gray-field polarimeter that detects green LED emission and light passing through the foldable substrate, the light including a light wavelength of about 553 nm. Without wishing to be bound by theory, the spatial difference in optical retardation can correspond to the difference in stress (e.g., in-plane strain) in the foldable substrate, e.g., stress-induced birefringence. In some embodiments, the absolute difference between the maximum value of the optical retardation along the centerline of the center portion midway between the first portion and the second portion and the minimum value of the optical retardation along the centerline can be greater than or equal to about 0.1 nm, greater than or equal to about 0.5 nm, greater than or equal to about 1 nm, less than or equal to about 3 nm, less than or equal to about 2 nm, or less than or equal to about 1.5 nm. In some embodiments, the absolute difference between the maximum value of the optical retardation along the centerline and the minimum value of the optical retardation along the centerline can be in the range of: about 0.1 nm to about 3 nm, about 0.1 nm to about 2 nm, about 0.5 nm to about 2 nm, about 0.5 to about 1.5 nm, about 1 nm to about 1.5 nm, or any range or sub-range therebetween.

[0237] In some embodiments, the maximum difference between the optical retardation of the central portion 251 and the minimum optical retardation of the first portion 221 and / or the second portion 231 can be greater than or equal to about 0.1 nm, greater than or equal to about 0.5 nm, greater than or equal to about 1 nm, greater than or equal to about 2 nm, greater than or equal to about 3 nm, less than or equal to about 8 nm, less than or equal to about 6 nm, less than or equal to about 5 nm, or less than or equal to about 4 nm. In some embodiments, the maximum difference between the optical retardation of the central portion 251 and the minimum optical retardation of the first portion 221 and / or the second portion 231 can be in the following ranges: about 0.1 nm to about 8 nm, about 0.1 nm to about 6 nm, about 0.5 nm to about 6 nm, about 0.5 nm to about 5 nm, about 1 nm to about 5 nm, about 2 nm to about 5 nm, about 2 nm to about 5 nm, about 2 nm to about 4 nm, or any range or sub-range therebetween. For example, when the maximum difference between the optical retardation of the central portion 251 and the minimum optical retardation of the first portion 221 and / or the second portion 231 is less than or equal to about 4.6 nm, a foldable substrate having a central thickness of about 30 μm can avoid mechanical instability. For example, when the maximum difference between the optical retardation of the central portion 251 and the minimum optical retardation of the first portion 221 and / or the second portion 231 is less than or equal to about 5.9 nm, a foldable substrate having a central thickness of about 40 μm can avoid mechanical instability.

[0238] Figure 44 Schematically shows the optical retardation measurement results of a foldable substrate without an adhesive, a polymer-based portion, a release liner, a display device, and a PET sheet. In Figure 44Among them, the horizontal axis 4401 (e.g., the x-axis) is the position along the direction 106 of the length 105, and the vertical axis 4403 (e.g., the y-axis) is the position along the direction 104 of the width 103. The region 4411 corresponding to the maximum optical retardation is located in the central portion 251 along the interface between the central portion 251 and the first portion 221 and / or the second portion 231. The region 4409 is adjacent to the region 4411 in the central portion and corresponds to a slightly smaller optical retardation. The central portion 251 between the regions 4411 includes alternating portions of the regions 4405 and 4407, where the region 4405 includes the lowest optical retardation in the central portion 251, and the region 4407 includes an optical retardation between the optical retardations of the regions 4405 and 4411. The center line will roughly bisect the regions 4405 and 4407 (parallel to the vertical axis 2903), and the region 4405 includes the minimum optical retardation along the center line, while the region 4407 includes the maximum optical retardation along the center line. Without wishing to be bound by theory, local instability may occur when the alternating pattern along the center line is too large. Outside the central portion 251, the region 4413 includes a series of portions that roughly correspond to the alternating pattern between the regions 4405 and 4407. The region 4413 includes an optical retardation similar to that of the region 4409. In the first portion 221 and the second portion 231, the region 4417 includes the lowest optical retardation in the first portion 221 and the second portion 231. The region 4415 includes an optical retardation value between the optical retardations of the regions 4413 and 4417.

[0239] In some embodiments, the polymer-based portion 241 can be optically transparent. The polymer-based portion 241 can include a first refractive index. The first refractive index can be a function of the wavelength of light passing through the optically transparent adhesive. For light of a first wavelength, the refractive index of the material is defined as the ratio of the speed of light in a vacuum to the speed of light in the corresponding material. Without being bound by theory, the refractive index of the optically transparent adhesive can be determined using the ratio of the sine of a first angle to the sine of a second angle, where light of the first wavelength is incident on the surface of the optically transparent adhesive at the first angle from air and is refracted at the surface of the optically transparent adhesive such that the light propagates within the optically transparent adhesive at the second angle. The first angle and the second angle are both measured relative to the normal to the surface of the optically transparent adhesive. As used herein, the refractive index is measured according to ASTM E1967-19, where the first wavelength includes 589 nm. In some embodiments, the first refractive index of the polymer-based portion 241 can be greater than or equal to about 1, greater than or equal to about 1.3, greater than or equal to about 1.4, greater than or equal to about 1.45, greater than or equal to about 1.49, less than or equal to about 3, less than or equal to about 2, or less than or equal to about 1.7, less than or equal to about 1.6, or less than or equal to about 1.55. In some embodiments, the first refractive index of the polymer-based portion 241 can be in the range of: about 1 to about 2, about 1 to about 1.7, about 1.3 to about 1.7, about 1.4 to about 1.7, about 1.4 to about 1.6, about 1.45 to about 1.55, about 1.49 to about 1.55, or any range or sub-range therebetween.

[0240] In some embodiments, the foldable substrate 201 may include a second refractive index. In some embodiments, the second refractive index of the foldable substrate 201 may be greater than or equal to about 1, greater than or equal to about 1.3, greater than or equal to about 1.4, greater than or equal to about 1.45, greater than or equal to about 1.49, less than or equal to about 3, less than or equal to about 2, or less than or equal to about 1.7, less than or equal to about 1.6, or less than or equal to about 1.55. In some embodiments, the second refractive index of the foldable substrate 201 may be in the range of: about 1 to about 3, about 1 to about 2, about 1 to about 1.7, about 1.3 to about 1.7, about 1.4 to about 1.7, about 1.4 to about 1.6, about 1.45 to about 1.55, about 1.49 to about 1.55, or any range or sub-range therebetween. In some embodiments, the absolute value of the difference equal to the difference between the second refractive index of the foldable substrate 201 and the first refractive index of the polymer-based portion 241 may be less than or equal to about 0.1, less than or equal to about 0.07, less than or equal to about 0.05, greater than or equal to about 0.001, greater than or equal to about 0.01, or greater than or equal to about 0.02. In some embodiments, the difference is in the range of: about 0.001 to about 0.1, about 0.001 to about 0.07, about 0.001 to about 0.05, about 0.01 to about 0.1, about 0.01 to about 0.07, about 0.01 to about 0.05, about 0.02 to about 0.1, about 0.02 to about 0.07, about 0.02 to about 0.05, or any range or sub-range therebetween. In some embodiments, the second refractive index of the foldable substrate 201 may be greater than the first refractive index of the polymer-based portion 241. In some embodiments, the second refractive index of the foldable substrate 201 may be less than the first refractive index of the polymer-based portion 241.

[0241] In some embodiments, the adhesive layer 261 may include a third refractive index. In some embodiments, the third refractive index of the adhesive layer 261 may be within one or more of the ranges described above for the first refractive index of the polymer-based portion 241. In some embodiments, the difference equal to the absolute value of the difference between the third refractive index of the adhesive layer 261 and the first refractive index of the polymer-based portion 241 may be less than or equal to about 0.1, less than or equal to about 0.07, less than or equal to about 0.05, greater than or equal to about 0.001, greater than or equal to about 0.01, or greater than or equal to about 0.02. In some embodiments, the difference is in the range of: about 0.001 to about 0.1, about 0.001 to about 0.07, about 0.001 to about 0.05, about 0.01 to about 0.1, about 0.01 to about 0.07, about 0.01 to about 0.05, about 0.02 to about 0.1, about 0.02 to about 0.07, about 0.02 to about 0.05, or any range or sub-range therebetween. In some embodiments, the third refractive index of the adhesive layer 261 may be greater than the first refractive index of the polymer-based portion 241. In some embodiments, the third refractive index of the adhesive layer 261 may be less than the first refractive index of the polymer-based portion 241.

[0242] In some embodiments, the difference equal to the absolute value of the difference between the third refractive index of the adhesive layer 261 and the second refractive index of the foldable substrate 201 may be less than or equal to about 0.1, less than or equal to about 0.07, less than or equal to about 0.05, greater than or equal to about 0.001, greater than or equal to about 0.01, or greater than or equal to about 0.02. In some embodiments, the difference is in the range of: about 0.001 to about 0.1, about 0.001 to about 0.07, about 0.001 to about 0.05, about 0.01 to about 0.1, about 0.01 to about 0.07, about 0.01 to about 0.05, about 0.02 to about 0.1, about 0.02 to about 0.07, about 0.02 to about 0.05, or any range or sub-range therebetween. In some embodiments, the third refractive index of the adhesive layer 261 may be greater than the second refractive index of the foldable substrate 201. In some embodiments, the third refractive index of the adhesive layer 261 may be less than the second refractive index of the foldable substrate 201.

[0243] The foldable device and / or the foldable substrate may have a failure mode that can be described as a low-energy failure or a high-energy failure. Can be used Figure 5A parallel plate device 501 is used to measure the failure mode of a foldable substrate. As described below regarding the effective minimum bending radius, parallel rigid stainless steel plates 503, 505 are moved together at a rate of 50 μm / second until the target parallel plate distance 507 is achieved. The target parallel plate distance 507 is the greater of twice the effective minimum bending radius of the foldable device and / or the foldable substrate or 4 mm. Subsequently, a tungsten carbide sharp contact probe impacts the foldable substrate 201 at the impact location 511, which is at a distance 509 of 30 mm from the outermost periphery of the foldable substrate 201. As used herein, if during fracture, particles are ejected from the foldable substrate 201 at a speed greater than or equal to 1 meter per second (m / s) and the fracture results in more than 2 crack branches, the fracture is high energy. As used herein, if the fracture results in less than or equal to 2 crack branches, or no particles are ejected from the foldable substrate 201 at a speed greater than or equal to 1 m / s during fracture, the fracture is low energy. The average velocity of the ejected particles can be measured by capturing a high-speed video of the foldable device from the time the sharp contact probe contacts the impact location to 5,000 microseconds thereafter.

[0244] Figure 4 and 6 -7 schematically illustrate some embodiments of a test foldable device 602 and / or foldable devices 101 and 301 in a folded configuration according to embodiments of the present disclosure. As Figure 6 shown, the test device 602 is folded such that the second major surface 205 of the foldable substrate 201 is on the inside of the folded test foldable device 602. In Figure 6 the folded configuration shown, the user will view the display device 307 through the foldable substrate 201 rather than the PET sheet 607, and thus, the user will be on the side of the second major surface 205. As Figure 7 shown, the foldable device 301 is folded such that the second major surface 205 of the foldable substrate 201 is on the outside of the folded foldable device 301. In Figure 7 this, the user will view the display device 307 through the foldable substrate 201, and thus, the user will be on the side of the second major surface 205. In some embodiments, although not shown in the folded configuration, the foldable device may include a coating 281 disposed above the polymer-based portion 241 (see Figure 2 ). In additional embodiments, the polymer-based portion 241 may be disposed above another substrate (e.g., a glass-based substrate and / or a ceramic-based substrate rather than above the release liner 271), and this other substrate may be disposed above the display device 307. In additional embodiments, the user will view the display device 307 through the coating 281.

[0245] As defined herein, "foldable" includes the ability to fully fold, partially fold, bend, crease, and multi-fold. As used herein, the terms "fail", "failed", etc. refer to fracture, destruction, delamination, or crack propagation. When a foldable device is maintained at an "X" radius for at least 24 hours at about 85 °C and about 85% relative humidity, if it resists failure, the foldable device achieves an "X" effective bending radius, or has an "X" effective bending radius, or includes an "X" effective bending radius. Similarly, when a foldable device is maintained at an "X" parallel plate distance for 24 hours at about 85 °C and about 85% relative humidity, if it resists failure, the foldable device achieves an "X" parallel plate distance, or has an "X" parallel plate distance, or includes an "X" parallel plate distance.

[0246] As used herein, the "effective minimum bending radius" and "parallel plate distance" of a foldable device are measured using a parallel plate device 601 (see Figure 6 ) by the following test configuration and procedure. The parallel plate device 601 includes a pair of parallel rigid stainless steel plates 603, 605, and the pair of parallel rigid stainless steel plates 603, 605 includes a first rigid stainless steel plate 603 and a second rigid stainless steel plate 605. When measuring the "effective minimum bending radius" or "parallel plate distance", the test adhesive layer 609 has a thickness of 50 μm (e.g., instead of Figures 2 - 3 and the adhesive layer 261 of 7). When measuring the "effective minimum bending radius" or "parallel plate distance", a sheet 607 of 100 μm thick polyethylene terephthalate (PET) is used instead of Figure 2 the release liner 271 of Figure 3 or the display device 307 shown in Figure 2 for the measurement. Thus, during the test for determining the "effective minimum bending radius" or "parallel plate distance" of a foldable device configuration, a test foldable device 602 is produced by using a sheet 607 of 100 μm thick polyethylene terephthalate (PET) instead of Figure 3 the release liner 271 of Figure 2 or the display device 307 shown in Figure 3 . When preparing the test foldable device 602, the sheet 607 of 100 μm thick polyethylene terephthalate (PET) is attached to the test adhesive layer 609 in the same manner as Figures 3 - 4 the release liner 271 is attached to the first contact surface 263 of the adhesive layer 261 shown in Figure 6The configuration for testing on the testable foldable device 602 as shown. The testable foldable device 602 is placed between the pair of parallel rigid stainless steel plates 603, 605 such that, similar to the Figure 6 configuration shown, the foldable substrate 201 will be on the inner side of the bend. To determine the "parallel plate distance", the distance between the parallel plates is decreased at a rate of 50 μm / second until the parallel plate distance 611 is equal to the "parallel plate distance" to be tested. Then, the parallel plates are held at the "parallel plate distance" to be tested for 24 hours at approximately 85 °C and approximately 85% relative humidity. As used herein, the "minimum parallel plate distance" is the minimum parallel plate distance at which the foldable device can withstand the test without failure under the above conditions and configuration. To determine the "effective minimum bend radius", the distance between the parallel plates is decreased at a rate of 50 μm / second until the parallel plate distance 611 is equal to twice the "effective minimum bend radius" to be tested. Then, the parallel plates are held at twice the effective minimum bend radius to be tested for 24 hours at approximately 85 °C and approximately 85% relative humidity. As used herein, the "effective minimum bend radius" is the minimum effective bend radius at which the foldable device can withstand the test without failure under the above conditions and configuration.

[0247] In some embodiments, the foldable device 101 and / or 301 and / or the test foldable device 602 may achieve a parallel plate distance of less than or equal to 200 mm, less than or equal to 100 mm, less than or equal to 50 mm, less than or equal to 20 mm, less than or equal to 10 mm, less than or equal to 5 mm, or less than or equal to 3 mm. In additional embodiments, the foldable device 101 and / or 301 and / or the test foldable device 602 may achieve a parallel plate distance of 50 millimeters (mm), or 20 mm, or 10 mm, or 5 mm, or 3 mm. In some embodiments, the foldable device 101 and / or 301 and / or the test foldable device 602 may include a minimum parallel plate distance of less than or equal to about 40 mm, less than or equal to about 20 mm, less than or equal to about 10 mm, less than or equal to about 5 mm, less than or equal to about 3 mm, less than or equal to about 1 mm, greater than or equal to about 1 mm, greater than or equal to about 3 mm, greater than or equal to about 5 mm, or greater than or equal to about 10 mm. In some embodiments, the foldable device 101 and / or 301, the test foldable device 602, and / or the foldable substrate 201 may achieve a parallel plate distance of 20 mm, 18 mm, 15 mm, 4 mm, 12 mm, 10 mm, 8 mm, 6 mm, 5 mm, 4 mm, and / or 3 mm. In some embodiments, the foldable device 101 and / or 301 and / or the test foldable device 602 may include an effective minimum bending radius within the following ranges: from about 1 mm to about 100 mm, from about 1 mm to about 60 mm, from about 1 mm to about 40 mm, from about 1 mm to about 20 mm, from about 1 mm to about 10 mm, from about 1 mm to about 5 mm, from about 1 mm to about 3 mm, from about 3 mm to about 40 mm, from about 3 mm to about 40 mm, from about 3 mm to about 20 mm, from about 3 mm to about 10 mm, from about 3 mm to about 5 mm, from about 5 mm to about 10 mm, or any range or sub-range therebetween. In some embodiments, the foldable device 101 and / or 301, the test foldable device 602, and / or the foldable substrate 201 may achieve an effective bending radius of 10 mm, 9 mm, 8 mm, 7 mm, 6 mm, 5 mm, 4 mm, 3 mm, 2 mm, and / or 1 mm.

[0248] In some embodiments, in the direction 106 of the length 105, a width 252 of the central portion 251 of the foldable substrate 201 is defined between the first portion 221 and the second portion 231. In some embodiments, the width 252 of the central portion 251 of the foldable substrate 201 may extend from the first portion 221 to the second portion 231. As Figure 2As shown, if present, the width 252 of the central portion 251 may include the width 254a of the first transition portion 253 and / or the width 254b of the second transition portion 255. In some embodiments, the width 252 of the central portion 251 of the foldable substrate 201 defined in the direction 106 of the length 105 between the first portion 221 and the second portion 231 may be about 2.8 times or greater, about 3 times or greater, about 4 times or greater, about 6 times or less, about 5 times or less, or about 4 times or less of the effective minimum bending radius. In some embodiments, as a multiple of the effective minimum bending radius, the width 252 of the central portion 251 may be in the range of: about 2.8 times to about 6 times, about 2.8 times to about 5 times, about 2.8 times to about 4 times, about 3 times to about 6 times, about 3 times to about 5 times, about 3 times to about 4 times, about 4 times to about 6 times, about 4 times to about 5 times, or any range or sub-range therebetween. It should be understood that in some embodiments, the central major surface 211 of the central portion 251 extending along a third plane 204c parallel to the second plane 204b may include a width of about 3 times or greater (e.g., about 3.2 times or greater, about 4.4 times or greater) of the effective minimum bending radius (e.g., bending length) to provide reduced stress concentration and damage in the bending region of the foldable device.

[0249] Without wishing to be bound by theory, the length of the bent portion in a circular configuration between parallel plates may be about 1.6 times (e.g., about 3 times the effective minimum bending radius, about 3.2 times the effective minimum bending radius) of the parallel plate distance 507 or 601. In some embodiments, the width 252 of the central portion 251 of the foldable substrate 201. In some embodiments, the width 252 of the central portion 251 of the foldable substrate 201 may be greater than or equal to about 2.8 mm, greater than or equal to about 6 mm, greater than or equal to about 9 mm, less than or equal to about 60 mm, less than or equal to about 40 mm, or less than or equal to about 24 mm. In some embodiments, the width 252 of the central portion 251 of the foldable substrate 201 may be in the range of: about 2.8 mm to about 60 mm, about 2.8 mm to about 40 mm, about 2.8 mm to about 24 mm, about 6 mm to about 60 mm, about 6 mm to about 40 mm, about 6 mm to about 24 mm, about 9 mm to about 60 mm, about 9 mm to about 40 mm, about 9 mm to about 24 mm, or any range or sub-range therebetween. By providing the width of the central portion between the first portion and the second portion, folding of the foldable device without failure can be facilitated.

[0250] Without wishing to be bound by theory, the length of the curved portion in the elliptical configuration between the parallel plates can be about 2.2 times the parallel plate distance 507 or 601 (e.g., about 4.4 times the effective minimum bending radius). In some embodiments, the width 232 of the central portion 251 of the foldable substrate 201 can be substantially equal to or greater than the bending length of the foldable substrate or foldable device when it is at the effective minimum bending radius. In some embodiments, the width 252 of the central portion 251 of the foldable substrate 201 can be greater than or equal to about 4 mm, greater than or equal to about 10 mm, greater than or equal to about 20 mm, less than or equal to about 45 mm, less than or equal to about 40 mm, or less than or equal to about 30 mm. In some embodiments, the width 252 of the central portion 251 of the foldable substrate 201 can be in the following ranges: about 4 mm to about 45 mm, about 4 mm to about 40 mm, about 4 mm to about 30 mm, about 4 mm to about 20 mm, about 4 mm to about 10 mm, about 10 mm to about 45 mm, about 10 mm to about 40 mm, about 10 mm to about 30 mm, about 10 mm to about 20 mm, about 20 mm to about 45 mm, about 20 mm to about 40 mm, about 20 mm to about 30 mm, about 30 mm to about 45 mm, about 30 mm to about 40 mm, about 40 mm to about 45 mm, or any range or sub-range therebetween.

[0251] The foldable device can have impact resistance, which is the ability of a certain area of the foldable device (e.g., the area including the first portion 221, the area including the second portion 231, the area including the polymer-based portion 241 and / or the central portion 251) to avoid failure at a pen-drop height (e.g., 5 centimeters (cm) or greater, 10 centimeters or greater, 20 cm or greater) when measured according to the "pen-drop test". As used herein, the "pen-drop test" is performed such that the foldable device is tested under a load (i.e., from a pen dropped from a certain height) applied to the main surface (e.g., the second main surface 205 or the first main surface 203 of the foldable substrate 201), and its structure is like that in the parallel plate test, with a 100-μm-thick PET sheet 607 instead of Figure 3 the shown display device 307 attached to a 50-μm-thick test adhesive layer 609. Thus, the PET layer in the pen-drop test is intended to simulate a foldable electronic display device (e.g., an OLED device). During the test, the foldable device combined with the PET layer is placed on an aluminum plate (6063 aluminum alloy, polished to a certain surface roughness with 400-grit paper), and the PET layer is in contact with the aluminum plate. No tape is used on the sample side leaning against the aluminum plate.

[0252] As Figure 41As shown, the pen-drop device 4101 includes a ballpoint pen 4103. The pen used for the pen-drop test is a BIC Easy Glide Pen, a fine pen, which includes a tungsten carbide ballpoint tip 4105 with a diameter of 0.7 mm (0.68 mm), and the weight including the pen cap is 5.73 grams (g) (the weight without the pen cap is 4.68 g). The ballpoint pen 4103 is held at a predetermined height 4109 from the first major surface 203 of the foldable substrate 201. In the pen-drop test, the ballpoint pen 4103 is guided to the first major surface 203 of the foldable substrate 201 using a tube (not shown for clarity), and the tube is placed in contact with the first major surface 203 of the foldable substrate 201 such that the longitudinal axis of the tube is substantially perpendicular to the first major surface 203 of the foldable substrate 201. The outer diameter of the tube is 1 inch (2.54 cm), the inner diameter is nine-sixteenths of an inch (1.4 cm), and the length is 90 cm. For each test, the ballpoint pen 4103 is held at the predetermined height 4109 using an acrylonitrile butadiene ("ABS") spacer. After each drop, the tube is repositioned relative to the foldable substrate 201 to guide the ballpoint pen 4103 to a different impact location on the foldable substrate 201. Although not shown, it should be understood that the pen-drop test can be used for Figures 1 - 4 any of the foldable substrates shown in FIGS. 6-7.

[0253] The tube is used in the pen-drop test to guide the pen to the outer surface of the foldable device. For Figures 2 - 3 the foldable devices 101 and / or 301 and / or the test foldable device 602 shown in FIGS. 6-7, the pen is guided to the second major surface 205 of the foldable substrate 201, and the tube is placed in contact with the second major surface 205 of the foldable substrate 201 such that the longitudinal axis of the tube is substantially perpendicular to the second major surface 205, and the longitudinal axis of the tube extends in the direction of gravity. The outer diameter of the tube is 1 inch (2.54 cm), the inner diameter is nine-sixteenths of an inch (1.4 cm), and the length is 90 cm. For each test, the pen is held at a predetermined height using an acrylonitrile butadiene (ABS) spacer. After each drop, the tube is repositioned relative to the sample to guide the pen to a different impact location on the sample. The pen used for the pen-drop test is a BIC Easy Glide Pen, a fine pen, which includes a tungsten carbide ballpoint tip with a diameter of 0.7 mm (0.68 mm), and the weight including the pen cap is 5.73 grams (the weight without the pen cap is 4.68 g).

[0254] For the pen-drop test, the ballpoint pen 4103 is dropped with the pen cap attached to the top (i.e., the end opposite the tip) such that the ballpoint tip 4105 can interact with the first major surface 203 of the foldable substrate 201. In the drop procedure according to the pen-drop test, one pen-drop is made at an initial height of 1 cm, and then subsequent drops are made in increments of 0.5 cm up to 20 cm. Then, after 20 cm, drops are made in increments of 2 cm until the foldable substrate 201 fails. After each drop, the presence of any observed breakage, failure, or other evidence of damage to the foldable substrate 201 and the specific predetermined height 4109 of the pen-drop are recorded. When using the pen-drop test, multiple foldable substrates (e.g., samples) can be tested according to the same drop procedure to produce an overall improved statistical accuracy. For the pen-drop test, the ballpoint pen 4103 is replaced with a new pen after every 5 drops and for each new foldable substrate 201. Additionally, all pen-drops are made at random locations on the foldable substrate 201 at or near the center of the foldable substrate 201, and the pen does not drop near or on the edge of the foldable substrate 201.

[0255] For the purposes of the pen-drop test, "failure" means the formation of visible mechanical defects in the laminate. Mechanical defects can be cracks or plastic deformations (e.g., surface dents). Cracks can be surface cracks or through-cracks. Cracks can form on the inner or outer surface of the laminate. Cracks can extend through all or part of the foldable substrate 201 and / or the coating 281. The minimum size of a visible mechanical defect is 0.2 mm or greater.

[0256] Figure 42 A curve 4205 is shown of the maximum principal stress 4203 in megapascals (MPa) on the first major surface of a glass-based substrate varying with the thickness 4201 of the glass-based substrate in micrometers, based on a pen-drop height of 2 cm on the second major surface of the glass-based substrate. As Figure 42 shown, the maximum principal stress on the first major surface of the glass-based substrate is maximum at around 65 μm. This suggests that pen-drop performance can be improved by avoiding a thickness of around 65 μm, e.g., by making the thickness less than about 50 μm or greater than about 80 μm.

[0257] In some embodiments, the foldable device can resist pen-drop failure at a pen-drop height of 10 centimeters (cm), 12 cm, 14 cm, 16 cm, or 20 cm in the region including the first part 221 and / or the second part 231. In some embodiments, when the region including the first part 221 or the second part 231 does not fail, the maximum pen-drop height that the foldable device can withstand can be greater than or equal to about 10 cm, greater than or equal to about 12 cm, greater than or equal to about 14 cm, greater than or equal to about 16 cm, less than or equal to about 40 cm, or less than or equal to about 30 cm, less than or equal to about 20 cm, less than or equal to about 18 cm. In some embodiments, when the region including the first part 221 or the second part 231 does not fail, the maximum pen-drop height that the foldable device can withstand can be in the following ranges: about 10 cm to about 40 cm, about 12 cm to about 40 cm, about 12 cm to about 30 cm, about 14 cm to about 30 cm, about 14 cm to about 20 cm, about 16 cm to about 20 cm, about 18 cm to about 20 cm, or any range or sub-range therebetween.

[0258] In some embodiments, in the region including the polymer-based part 241 (such as the central part 251, see Figure 3 ) between the first part 221 and the second part 231, the foldable device can resist pen-drop failure at a pen-drop height of 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, or greater. In some embodiments, when the region including the polymer-based part 241 between the first part 221 and the second part 231 does not fail, the maximum pen-drop height that the foldable device can withstand can be greater than or equal to about 1 cm, greater than or equal to about 2 cm, greater than or equal to about 3 cm, greater than or equal to about 4 cm, less than or equal to about 20 cm, less than or equal to about 10 cm, less than or equal to about 8 cm, or less than or equal to about 6 cm. In some embodiments, when the region including the polymer-based part 241 between the first part 221 and the second part 231 does not fail, the maximum pen-drop height that the foldable device can withstand can be in the following ranges: about 1 cm to about 20 cm, about 2 cm to about 20 cm, about 2 cm to about 10 cm, about 3 cm to about 10 cm, about 3 cm to about 8 cm, about 4 cm to about 8 cm, about 4 cm to about 6 cm, or any range or sub-range therebetween. In some embodiments, when the region including the polymer-based part 241 between the first part 221 and the second part 231 does not fail, the maximum pen-drop height that the foldable device can withstand can be in the following ranges: about 1 cm to about 10 cm, about 1 cm to about 8 cm, about 1 cm to about 5 cm, about 2 cm to about 5 cm, about 3 cm to about 5 cm, about 4 cm to about 5 cm, or any range or sub-range therebetween.

[0259] The smallest force can be used to achieve a predetermined parallel plate distance for a foldable device. As described above, Figure 6 the parallel plate device 601 is used to measure the "closing force" of the foldable device of the embodiments of the present disclosure. The measurement is from a flat configuration (e.g., see Figure 1 ) to the force for a bent (e.g., folded) configuration that includes a predetermined parallel plate distance (e.g., see Figures 6 - 7 ). In some embodiments, the force to bend the foldable device from a flat configuration to a parallel plate distance of 10 mm can be less than or equal to about 20 Newtons (N), less than or equal to 15 N, less than or equal to about 12 N, less than or equal to about 10 N, greater than or equal to about 0.1 N, greater than or equal to about 0.5 N, greater than or equal to about 1 N, greater than or equal to about 2 N, greater than or equal to about 5 N. In some embodiments, the force to bend the foldable device from a flat configuration to a parallel plate distance of 10 mm can be in the following ranges: about 0.1 N to about 20 N, about 0.5 N to about 20 N, about 0.5 N to about 15 N, about 1 N to about 15 N, about 1 N to about 12 N, about 2 N to about 12 N, about 2 N to about 10 N, about 5 N to about 10 N, or any range or sub-range therebetween. In some embodiments, the force to bend the foldable device from a flat configuration to a parallel plate distance of 3 mm can be less than or equal to about 10 N, less than or equal to about 8 N, less than or equal to about 6 N, less than or equal to about 4 N, less than or equal to about 3 N, greater than or equal to about 0.05 N, greater than or equal to about 0.1 N, greater than or equal to about 0.5 N, greater than or equal to about 1 N, greater than or equal to about 2 N, greater than or equal to about 3 N. In some embodiments, the force to bend the foldable device from a flat configuration to a parallel plate distance of 3 mm can be in the following ranges: about 0.05 N to about 10 N, about 0.1 N to about 10 N, about 0.1 N to about 8 N, about 0.5 N to about 8 N, about 0.5 N to about 6 N, about 1 N to about 6 N, about 1 N to about 4 N, about 2 N to about 4 N, about 2 N to about 3 N, or any range or sub-range therebetween.

[0260] In some embodiments, the force per width 103 to bend the foldable device from a flat configuration to a parallel plate distance of 10 mm can be less than or equal to 20 Newtons per millimeter (N / mm), less than or equal to 0.15 N / mm, less than or equal to about 0.12 N / mm, less than or equal to about 0.10 N / mm, greater than or equal to about 0.001 N / mm, greater than or equal to about 0.005 N / mm, greater than or equal to about 0.01 N / mm, greater than or equal to about 0.02 N / mm, greater than or equal to about 0.05 N / mm. In some embodiments, the force per width 103 to bend the foldable device from a flat configuration to a parallel plate distance of 0.10 / mm can be in the range of: about 0.001 N / mm to about 0.20 N / mm, about 0.005 N / mm to about 0.20 N / mm, about 0.005 N / mm to about 0.15 N / mm, about 0.01 N / mm to about 0.15 N / mm, about 0.01 N / mm to about 0.12 N / mm, about 0.02 N / mm to about 0.12 N / mm, about 0.02 N / mm to about 0.10 N / mm, about 0.05 N / mm to about 0.10 N / mm, or any range or sub-range therebetween. In some embodiments, the force per width 103 to bend the foldable device from a flat configuration to a parallel plate distance of 3 mm can be less than or equal to about 0.10 N / mm, less than or equal to about 0.08 N / mm, less than or equal to about 0.06 N / mm, less than or equal to about 0.04 N / mm, less than or equal to about 0.03 N / mm, greater than or equal to about 0.0005 N / mm, greater than or equal to about 0.001 N / mm, greater than or equal to about 0.005 N / mm, greater than or equal to about 0.01 N / mm, greater than or equal to about 0.02 N / mm, greater than or equal to about 0.03 N / mm. In some embodiments, the force per width 103 to bend the foldable device from a flat configuration to a parallel plate distance of 3 mm can be in the range of: about 0.0005 N / mm to about 0.10 N / mm, about 0.001 N / mm to about 0.10 N / mm, about 0.001 N / mm to about 0.08 N / mm, about 0.005 N / mm to about 0.08 N / mm, about 0.005 N / mm to about 0.06 N / mm, about 0.01 N / mm to about 0.06 N / mm, about 0.01 N / mm to about 0.04 N / mm, about 0.02 N / mm to about 0.04 N / mm, about 0.02 N / mm to about 0.03 N / mm, or any range or sub-range therebetween.

[0261] Providing a coating enables a small parallel plate distance to be achieved with low force. Without wishing to be bound by theory, compared to if a glass-based substrate and / or a ceramic-based substrate were used, a coating including a certain modulus and that modulus being less than the modulus of the foldable substrate can shift the neutral axis of the foldable substrate away from the coating (e.g., the user-facing surface). Without wishing to be bound by theory, compared to if a thicker substrate material were used, providing a coating having a thickness less than or equal to about 200 μm can shift the neutral axis of the foldable substrate away from the coating (e.g., the user-facing surface). Without wishing to be bound by theory, the neutral axis of the foldable substrate that is shifted away from the coating (e.g., the user-facing surface) can achieve a small parallel plate distance with low force because this reduces the concentration of tensile stress, and since the tensile stress is distributed over a larger portion of the foldable substrate, deformation of a portion of the foldable substrate due to tensile stress concentration is reduced.

[0262] The foldable device 101 or 301 and / or the test foldable device 602 may include a neutral stress configuration. Throughout this disclosure, the “neutral stress configuration” is measured by the following test configuration and process. When measuring the “neutral stress configuration,” Figure 38 The illustrated test foldable device 3801 includes a test adhesive layer 609 having a thickness of 50 μm between a fifth contact surface 613 and a sixth contact surface 615 of the test adhesive layer 609, and a 100-μm thick sheet 607 of polyethylene terephthalate (PET), and does not include Figure 2 the release liner 271 or Figure 3 and 7 the illustrated display device 307. For example, a foldable device including a foldable substrate 201—such as Figure 38 the illustrated test foldable device 3801 may be similar to Figure 6 the illustrated parallel plate device 601 for measuring the “effective bending radius.” As Figure 38 illustrated, when the test adhesive layer 609 is disposed above a first major surface 203 of the foldable substrate 201, the material (e.g., the polymer-based portion 241) in the recess 219 of the foldable substrate 201 may remain in place. To test the test foldable device 3801, the test foldable device 3801 is placed on its side such that a cross-section perpendicular to the direction of gravity is similar to Figure 38 . The test foldable device 3801 is placed on a surface including SAE grade 304 (e.g., ISO A2) stainless steel, and the arithmetic mean deviation (surface roughness (Ra)) of the surface is less than or equal to 3 μm (e.g., 2.40 μm, finish number 3). As shown, a plane including the direction 202 of the substrate thickness 227 and the direction 106 of the length 105 of the foldable substrate 201 is substantially perpendicular to the direction of gravity, and the direction 104 of the fold axis 102 (seeFigure 1 ) is also the direction of gravity. Next, the test foldable device is relaxed for 1 hour to achieve an equilibrium configuration, as Figure 38 shown.

[0263] In some embodiments, as Figure 38 shown, the neutral stress configuration may include a bent configuration. As used herein, a bent configuration is a non-flat configuration (in contrast to the Figures 1 - 3 flat configuration). In additional embodiments, as Figure 38 shown, the first major surface 203 and / or the second major surface 205 of the foldable substrate 201 may deviate significantly from a planar shape.

[0264] In some embodiments, the magnitude of the maximum deviatoric strain can be used to quantify the deviation of the neutral stress configuration from the flat configuration. As used herein, "deviatoric strain" means the shape change component of the strain tensor (e.g., the strain tensor minus the average of the diagonal components of the strain tensor that are the hydrostatic strain). The strain tensor can be measured by using digital image recognition and / or topological comparison of the shape and dimensions between the flat configuration and the neutral stress configuration of a portion of the folding device (e.g., a polymer-based portion). For example, as Figure 39 shown, which shows an exemplary polymer-based portion 241 in a flat configuration. In this flat configuration, when measured at the third contact surface 245 and the fourth contact surface 247, the length 3901 of the polymer-based portion (e.g., measured in the direction 106 of the length of the foldable device) is substantially equal. For example, as Figure 38 and 40 shown, which shows an exemplary polymer-based portion 241 in a neutral stress configuration. For ease of understanding, Figures 39 - 40 the polymer-based portions 241 in Figure 40 have equal volumes, which would be the case after removing the hydrostatic strain from the shape and dimensions captured digitally of the neutral stress configuration. As Figures 39 - 40 shown, a first length 4003 measured along the third contact surface 245 is different from (e.g., greater than) a second length 4001 measured along the fourth contact surface 247. As used herein, strain means the difference in length between a portion in the flat configuration and the neutral stress configuration divided by the reference length from the flat configuration. For example, the Figures 39 - 40The strain therebetween (e.g., the deviatoric strain when the isostatic strain is removed as described above) will be equal to the difference between the second length 4001 in the neutral stress configuration and the length 3901 in the flat configuration divided by the length 3901 in the flat configuration. As used herein, the magnitude of a numerical value (e.g., a scalar value) is the absolute value of that numerical value. As used herein, the maximum magnitude of a tensor (e.g., a strain tensor, a deviatoric strain tensor) means the component of the tensor (e.g., the deviatoric strain tensor) having the largest value (e.g., the maximum value). As used herein, the maximum magnitude of the deviatoric strain of the polymer matrix portion 241 means the greater value among the maximum magnitudes of the deviatoric strain calculated at the third contact surface 245 and the fourth contact surface 247 of the polymer matrix portion. In some embodiments, the maximum magnitude of the deviatoric strain of the polymer matrix portion 241 may be greater than or equal to about 1%, greater than or equal to about 2%, greater than or equal to about 3%, greater than or equal to about 4%, less than or equal to about 10%, less than or equal to about 8%, less than or equal to about 7%, less than or equal to about 6%, or less than or equal to about 5%. In some embodiments, the maximum magnitude of the deviatoric strain of the polymer matrix portion 241 may be in the following ranges: about 1% to about 10%, about 1% to about 8%, about 1% to about 7%, about 2% to about 7%, about 2% to about 6%, about 2% to about 5%, about 3% to about 5%, about 3% to about 4%, about 2% to about 10%, about 2% to about 8%, about 3% to about 8%, about 4% to about 8%, about 4% to about 7%, about 4% to about 6%, or any range or sub-range therebetween.

[0265] In some embodiments, the deviation of the neutral stress configuration relative to the flat configuration can be quantified using the angle "B", which is measured between a first line extending in the length direction of the first part and a second line extending in the length direction of the second part. For example, referring to Figure 38 , the angle "B" is measured between the first line 3802 and the second line 3804. The first line 3802 is in the length direction 106 of the test foldable device 3801 (e.g., in the length direction 106 of the foldable device 301), at and extending from the first part 221 (e.g., the first surface region 223) of the foldable substrate 201. In some embodiments, as Figure 38 shown, the first line 3802 can extend along the plane along which the first surface region 223 can extend. The second line 3804 is in the length direction 106 of the test foldable device 3801 (e.g., in the length direction 106 of the foldable device 301), at and extending from the second part 231 (e.g., the third surface region 233) of the foldable substrate 201. In some embodiments, as Figure 38As shown, the second line 3804 can extend along the plane along which the third surface region 233 can extend. In some embodiments, the magnitude of the difference between angle "B" in the neutral stress configuration and angle "B" in the flat configuration (e.g., 180°) can be greater than or equal to about 1°, greater than or equal to about 2°, greater than or equal to about 5°, greater than or equal to about 10°, less than or equal to about 40°, less than or equal to about 20°, less than or equal to about 15°, or less than or equal to about 8°. In some embodiments, the magnitude of the difference between angle "B" in the neutral stress configuration and angle "B" in the flat configuration (e.g., 180°) can be in the range of: about 1° to about 40°, about 1° to about 20°, about 2° to about 20°, about 5° to about 20°, about 5° to about 15°, about 10° to about 15°, about 2° to about 15°, about 5° to about 15°, about 5° to about 8°, about 1° to about 8°, about 2° to about 8°, or any range or sub-range therebetween.

[0266] By providing a neutral stress configuration when the foldable device is in a bent configuration, the force required to bend the foldable device to a predetermined parallel plate distance can be reduced. Further, providing a neutral stress configuration when the foldable device is in a bent state can reduce the maximum stress and / or strain experienced by the polymer-based portion during normal use conditions, which can, for example, increase the durability of the foldable device and / or reduce the fatigue of the foldable device. In some embodiments, the neutral stress configuration can be created by providing a polymer-based portion that expands due to curing. In some embodiments, the neutral stress configuration can be created by curing the polymer-based portion in a bent configuration. In some embodiments, the neutral stress configuration can be created by bending the foldable substrate at an elevated temperature (e.g., when the foldable substrate has a viscosity of about 10 4 Pascal-seconds to about 10 7 Pascal-seconds).

[0267] Reference will be made Figures 10 - 11 to the flowcharts of Figures 12 - 26 and 27 and the exemplary method steps illustrated in

[0268] Reference will now be made Figures 12 - 18 to Figure 10The flowchart is used to discuss exemplary embodiments of manufacturing the foldable device 101 and / or 301, the testable foldable device 602 and / or the foldable substrate 201. In the first step 1001 of the disclosed method, the method may start with providing the foldable substrate 201. In some embodiments, the foldable substrate 201 may be provided by purchasing, obtaining the substrate in some other way, or by forming the foldable substrate. In some embodiments, the foldable substrate 201 may include a glass-based substrate and / or a ceramic-based substrate. In additional embodiments, the glass-based substrate and / or the glass-ceramic-based substrate may be provided by forming them using various tape forming processes, such as slit drawing, down-draw, fusion down-draw, up-draw, roll pressing, redrawing, or float process. In additional embodiments, the ceramic-based substrate may be provided by heating the glass-based substrate to crystallize one or more ceramic crystals. The foldable substrate 201 may include a second major surface 205 (see Figure 12 ), which may extend along a certain plane. The second major surface 205 may be opposite to the first major surface 203. In some embodiments, as Figure 34 shown, the foldable substrate 201 may be bent (e.g., including a bent configuration). In additional embodiments, as a result of bending the foldable substrate 201 into a bent configuration, the foldable substrate 201 may include a bent configuration while the foldable substrate 201 includes a viscosity of about 10 4 Pascal-seconds to about 10 7 Pascal-seconds (e.g., within the processing range of the foldable substrate 201, between the softening point and the processing point of the foldable substrate 201).

[0269] In some embodiments, the foldable substrate 201 may include a recess 219 in the first major surface 203 of the foldable substrate 201, which exposes the first central surface region 209. In additional embodiments, the recess 219 may be formed by etching, laser ablation, or machining the first major surface 203. For example, the first major surface 203 may be machined by diamond engraving, thereby generating extremely precise patterns in the glass-based substrate and / or the ceramic-based substrate. As Figure 12As shown, a depression 219 can be created in the first major surface 203 of the foldable substrate 201 using diamond engraving, where a diamond tip probe 1201 can be controlled using a computer numerical control (CNC) machine 1203. Materials other than diamond can also be used for engraving using a CNC machine. Additionally, other methods of forming the depression include photolithography, etching, and laser ablation. For example, etching can include: disposing a mask over the first surface region 223 and the third surface region 233, exposing the first major surface 203 of the foldable substrate 201 to an etchant to form the depression 219, and then removing the mask. Forming the depression 219 in the first major surface 203 can provide a central portion 251 between the first portion 221 and the second portion 231 of the foldable substrate 201. The central portion 251 can include a first central surface region 209, where the depression 219 can be defined between the first central surface region 209 and a first plane 204a, which is Figure 12 the plane along which the first major surface 203 extends in the flat configuration shown. The first central surface region 209 can attach the first portion 221 to the second portion 231. As Figure 2 shown, the central portion 251 can further include a first transition portion 253 that attaches the first portion 221 to the central major surface 211 and a second transition portion 255 that attaches the second portion 231 to the central major surface 211. In some embodiments, the thickness of the first transition portion 253 can continuously increase from the central major surface 211 to the first portion 221. In additional embodiments, the thickness of the second transition portion 255 can continuously increase from the central major surface 211 to the second portion 231. As Figure 12 shown, in some embodiments, the first central surface region 209 can include the central major surface 211 of the central portion 251, which can be planar as shown, but in additional embodiments, a non-planar configuration can be provided. Additionally, the central major surface 211 can be parallel to the first plane 204a and / or the second major surface 205, as Figure 12 shown.

[0270] Although not shown for the Figure 12 device, in some embodiments, step 1001 can further include reducing the thickness of the foldable substrate 201. In additional embodiments, the thickness of the foldable substrate 201 can be reduced by machining (e.g., grinding). In additional embodiments, chemical etching can be employed to reduce the thickness of the foldable substrate 201. In additional embodiments, chemical etching can include: contacting the foldable substrate 201 with an etching solution contained in an etching bath. In additional embodiments, the etching solution can include one or more inorganic acids (e.g., HCl, HF, H 2 SO 4 、HNO3 )。For example, referring to Figure 29 the foldable substrate 201 shown, chemical etching can be used to reduce the thickness of the foldable substrate 201, which can include: contacting the foldable substrate 201 with an etching solution 2903 contained in an etching bath 2901 that includes one or more inorganic acids (e.g., HCl, HF, H 2 SO 4 , HNO 3 ). In some embodiments, the thickness of the foldable substrate 201 can be reduced by removing a layer from the first major surface 203 of the foldable substrate 201 to expose a new first major surface, and the new first major surface can constitute the first major surface 203 as shown in Figures 2 - 3 and FIGS. 5-7. Additionally or alternatively, the thickness of the foldable substrate 201 can be reduced by removing a layer from the second major surface 205 of the foldable substrate 201 to expose a new second major surface, and the new second major surface can constitute the second major surface 205 as shown in Figures 2 - 3 and FIGS. 5-7.

[0271] In some embodiments, the second major surface 205 (e.g., the entire second major surface 205) can be covered with an optional mask (e.g., Figure 29 the mask 2905 in Figures 2 - 3 and FIGS. 5-7) such that the second major surface 205 is not etched and can provide the second major surface 205 as the second major surface 205 described above with respect to Figures 2 - 3 and FIGS. 5-7. Preventing the second major surface 205 from being etched can be beneficial for preserving the original properties of the second major surface 205, which can exist with some processing techniques (e.g., pull-up or pull-down, e.g., by overflow or fusion). Maintaining the original surface can make the second major surface 205 present a particularly smooth surface, and the second major surface can form the outermost surface of the foldable device, and the outermost surface can be for the user of the foldable device to observe and / or touch. Alternatively, the thickness of the foldable substrate 201 can be reduced by removing a layer from the second major surface 205, e.g., removing the surface layer to expose a central layer that is more optically uniform along the length of the foldable substrate 201 (e.g., a glass-based substrate and / or a ceramic-based substrate), as described above. In some embodiments, a layer can be removed from the first major surface 203 to expose a new first major surface, and the new first major surface can constitute Figures 2 - 3and the second major surface 205 shown in FIGS. 5-7. Removing layers from both the first major surface and the second major surface can remove the outer layer of the foldable substrate 201 (e.g., a glass-based substrate and / or a ceramic-based substrate), which may have inconsistent optical properties compared to the underlying inner portion of the foldable substrate 201 (e.g., a glass-based substrate and / or a ceramic-based substrate). As a result, the entire thickness over the entire length and width of the foldable substrate 201 can have more consistent optical properties to provide a consistent optical performance with little distortion over the entire foldable substrate 201 (e.g., a glass-based substrate and / or a ceramic-based substrate).

[0272] In some embodiments, removing a layer from the first major surface 203 can be beneficial for removing surface defects generated during the formation of the recess 219. For example, machining the first major surface 203 (e.g., with a diamond tip probe) to create the recess 219 may generate microcrack surface flaws or other defects, which can present weak points where catastrophic failure of the foldable substrate 201 may occur when folded. Thus, by removing a layer from the first major surface 203, the surface defects generated in the layer during the formation of the recess 219 can be removed, where a new first major surface 203 with fewer surface defects can be presented. Due to the presence of fewer surface defects, a smaller bending radius can be achieved without failure of the foldable substrate. For example, certain processing of the foldable substrate may present different glass-based material properties and / or ceramic-based material properties at the first and second major surfaces of the foldable substrate compared to the central portion of the foldable substrate. For example, during a pull-down process, the properties of the glass-based material and / or ceramic-based material at the major surfaces may be different from those of the central portion. Thus, by removing a layer from the first major surface 203 at the first portion 221 and the second portion 231, the new first major surface 203 of these portions can have the same properties as the first central surface region 209 to provide consistent optical properties over the length of the foldable substrate 201, e.g., if the foldable substrate 201 includes a glass-based substrate and / or a ceramic-based substrate.

[0273] After step 1001, as Figure 13As shown, the method can proceed to step 1003, which includes chemically strengthening the foldable substrate 201. Chemical strengthening of the foldable substrate 201 (e.g., a glass-based substrate, a ceramic-based substrate) can occur through ion exchange when a first cation within the surface depth of the foldable substrate 201 exchanges with a second cation within the molten salt or salt solution 1303 that has a larger radius than the first cation. For example, lithium cations within the depth of the surface of the foldable substrate 201 can exchange with sodium cations or potassium cations in the salt solution 1303. As a result, since the radius of the lithium cations is smaller than the radius of the exchanged sodium cations or potassium cations in the salt solution 1303, the surface of the foldable substrate 201 is in a compressive state and is thus chemically strengthened through the ion exchange process. Chemically strengthening the foldable substrate 201 can include contacting at least a portion of the foldable substrate 201 containing lithium cations and / or sodium cations with a salt bath 1301 containing the salt solution 1303, where the salt solution 1303 contains potassium nitrate, potassium phosphate, potassium chloride, potassium sulfate, sodium chloride, sodium sulfate, sodium nitrate, and / or sodium phosphate, whereby the lithium cations and / or sodium cations diffuse from the foldable substrate 201 into the salt solution 1303 contained in the salt bath 1301. In some embodiments, the temperature of the salt solution 1303 can be greater than or equal to about 300 °C, greater than or equal to about 360 °C, greater than or equal to about 400 °C, less than or equal to about 500 °C, less than or equal to about 460 °C, or less than or equal to about 400 °C. In some embodiments, the temperature of the salt solution 1303 can be in the range of: about 300 °C to about 500 °C, about 360 °C to about 500 °C, about 400 °C to about 500 °C, about 300 °C to about 460 °C, about 360 °C to about 460 °C, about 400 °C to about 460 °C, about 300 °C to about 400 °C, about 360 °C to about 400 °C, or any range or sub-range therebetween. In some embodiments, the foldable substrate 201 can be in contact with the salt solution 1303 for greater than or equal to about 15 minutes, greater than or equal to about 1 hour, greater than or equal to about 3 hours, less than or equal to about 48 hours, less than or equal to about 24 hours, or less than or equal to about 8 hours. In some embodiments, the foldable substrate 201 is in contact with the salt solution 1303 for a time within the range of: about 15 minutes to about 48 hours, about 1 hour to about 48 hours, about 3 hours to about 48 hours, about 15 minutes to about 24 hours, about 1 hour to about 24 hours, about 3 hours to about 48 hours, about 3 hours to about 24 hours, about 3 hours to about 8 hours, or any range or sub-range therebetween.

[0274] Chemically strengthening the foldable substrate 201 may include: chemically strengthening the first central surface region 209, chemically strengthening the first surface region 223 of the first portion 221 of the first major surface 203, chemically strengthening the third surface region 233 of the second portion 231 of the first major surface 203, and chemically strengthening the second major surface 205 of the foldable substrate 201. In some embodiments, chemically strengthening may include: chemically strengthening the first portion 221 to an initial first compressive depth from the first surface region 223 of the first major surface 203, chemically strengthening the second portion 231 to an initial third compressive depth from the third surface region 233 of the first major surface 203, and chemically strengthening the central portion 251 to an initial first central compressive depth from the first central surface region 209. In some embodiments, chemically strengthening the second major surface 205 of the foldable substrate 201 may include: chemically strengthening the second surface region 225 of the first portion 221 of the second major surface 205, chemically strengthening the fourth surface region 235 of the second portion 231 of the second major surface 205, and chemically strengthening the second central surface region 213 of the central portion 251 of the second major surface 205. In some embodiments, chemically strengthening the second major surface 205 may include: chemically strengthening the first portion 221 to an initial second compressive depth from the second surface region 225 of the second major surface 205, chemically strengthening the second portion 231 to an initial fourth compressive depth from the fourth surface region 235 of the second major surface 205, and chemically strengthening the central portion 251 to an initial second central compressive depth from the second central surface region 213 of the second major surface 205.

[0275] After step 1003, as Figures 14 - 15As shown, the method may proceed to step 1005, which includes disposing a layer over the central portion 251. In some embodiments, the layer may include: disposing a material using chemical vapor deposition (CVD) (such as low-pressure CVD, plasma-enhanced CVD), physical vapor deposition (PVD) (such as evaporation, molecular beam epitaxy, ion plating), atomic layer deposition (ALD), sputtering, spray pyrolysis, chemical bath deposition, and / or sol-gel deposition. In some embodiments, the layer may include a material that includes a diffusivity of one or more alkali metal ions. In additional embodiments, the diffusivity of the layer may be less than or equal to the corresponding diffusivity of the foldable substrate. Without wishing to be bound by theory, a layer having a reduced diffusivity relative to the foldable substrate may limit (e.g., reduce) the degree of chemical strengthening of a portion of the foldable substrate over which the layer is disposed, for example, by reducing the concentration of the one or more alkali metal ions at the surface of the foldable substrate relative to another portion of the foldable substrate over which the layer is not disposed. In additional embodiments, relative to the diffusivity of the foldable substrate, the diffusivity of the layer may be greater than or equal to about 5%, greater than or equal to about 10%, greater than or equal to about 20%, greater than or equal to about 25%, less than or equal to about 80%, less than or equal to about 60%, less than or equal to about 50%, less than or equal to about 40%, or less than or equal to about 30%. In additional embodiments, relative to the diffusivity of the foldable substrate, the diffusivity of the layer may be in the range of: about 5% to about 80%, about 5% to about 60%, about 10% to about 60%, about 10% to about 50%, about 20% to about 50%, about 25% to about 50%, about 25% to about 40%, about 25% to about 30%, or any range or sub-range therebetween. In some embodiments, the layer includes titanium dioxide (TiO 2 ), zirconium oxide (ZrO 2 ), tin oxide (SnO 2 ), aluminum oxide (Al 2 O 3 ), silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ) and / or combinations thereof. Exemplary embodiments include: disposing a SiO 2 layer using PVD. Providing a layer having a reduced (but still significant) diffusivity relative to the foldable substrate may reduce chemically strengthened-induced instability while maintaining a low number of required chemical strengthening steps, maintaining reduced processing costs and processing time.

[0276] In some embodiments, as shown, a first layer 1401 or 1501 may be disposed above the first central surface region 209. In additional embodiments, the first layer 1401 or 1501 may contact the first central surface region 209. In additional embodiments, as shown, the first layer 1401 or 1501 may be disposed above the first central surface region 209 but not above the first surface region 223 and / or the third surface region 233. In additional embodiments, the first layer 1401 or 1501 may cover substantially the entire first central surface region 209. In additional embodiments, the first layer 1401 or 1501 may include a first layer thickness 1402 or 1502, which is defined as the average depth of the first layer 1401 or 1501 disposed above the first central surface region 209, and the average depth is from measurements at 5 (five) equally spaced points along the first central surface region 209 in the indicated direction (e.g., Figures 2 - 3 the direction 106 in). In additional embodiments, the first layer thicknesses 1402 and 1502 may be greater than or equal to about 0.5 nm, greater than or equal to about 1 nm, greater than or equal to about 5 nm, greater than or equal to about 10 nm, greater than or equal to about 20 nm, less than or equal to about 250 nm, less than or equal to about 200 nm, less than or equal to about 150 nm, less than or equal to about 100 nm, or less than or equal to about 50 nm. In additional embodiments, the first layer thicknesses 1402 and 1502 may be in the range of: about 0.5 nm to about 250 nm, about 0.5 nm to about 200 nm, about 1 nm to about 200 nm, about 1 nm to about 150 nm, about 5 nm to about 150 nm, about 5 nm to about 100 nm, about 10 nm to about 100 nm, about 10 nm to about 50 nm, about 20 nm to about 50 nm, or any range or sub-range therebetween. In additional embodiments, as Figure 14 shown, the first layer 1401 may include a thickness that is substantially constant over the first central surface region 209 (e.g., in the direction 106 of the length 105 of the foldable device and / or in the direction 104 of the width 103 of the foldable device). In additional embodiments, as Figure 15 shown, the first layer 1501 may include a thickness that varies over the first central surface region 209 (e.g., in the direction 106 of the length 105 of the foldable device and / or in the direction 104 of the width 103 of the foldable device). In additional embodiments, as shown, the thickness of the first layer 1501 near the interface between the central portion 251 and the first portion 221 and / or the second portion 231 may be less than the thickness away from the corresponding interface. Providing a reduced thickness near the interface may reduce stress concentration at the interface due to chemical strengthening.

[0277] In some embodiments, asFigures 14 - 15 As shown, a second layer 1403 or 1503 may be disposed above the second central surface region 213. In additional embodiments, the second layer 1403 or 1503 may contact the second central surface region 213. In additional embodiments, as shown, the second layer 1403 or 1503 may be disposed above the second central surface region 213 but not above the second surface region 225 and / or the fourth surface region 235. In additional embodiments, the second layer 1403 or 1503 may cover substantially the entire second central surface region 213. In additional embodiments, the second layer 1403 or 1503 may include a second layer thickness, which is defined as the average depth of the second layer 1403 or 1503 disposed above the second central surface region 213. In additional embodiments, the second layer thickness may be within one or more of the ranges described above with respect to the first layer thicknesses 1402 and 1502. In additional embodiments, the second layer thickness may be substantially equal to the first layer thicknesses 1402 and 1502. In additional embodiments, as Figure 14 shown, the second layer 1403 may include a thickness that is substantially constant over the second central surface region 213 (e.g., in the direction 106 of the length 105 of the foldable device and / or in the direction 104 of the width 103 of the foldable device). In additional embodiments, as Figure 15 shown, the second layer 1503 may include a thickness that varies over the second central surface region 213 (e.g., in the direction 106 of the length 105 of the foldable device and / or in the direction 104 of the width 103 of the foldable device). In additional embodiments, as shown, the thickness of the second layer 1503 near the interface between the central portion 251 and the first portion 221 and / or the second portion 231 may be less than the thickness away from the corresponding interface. Providing a reduced thickness near the interface may reduce stress concentration at the interface due to chemical strengthening. Further discussion of the method of embodiments of the present disclosure will be illustrated by Figure 14 the first layer 1401 and the second layer 1403 shown, wherein it should be understood that the method may be applied in a similar or identical manner to Figure 15 the first layer 1501 and the second layer 1503 shown.

[0278] After step 1005, as Figure 16 shown, the method may proceed to step 1007, which includes chemically strengthening the foldable substrate 201 for a first period of time. As used herein, the first period of time is the time when at least a portion of the foldable substrate 201 is in contact with one or more alkali metals (e.g., sodium ions, potassium ions) described with respect to the salt solution 1303. In some embodiments, as Figure 16As shown, the chemical strengthening in step 1007 may include: contacting the foldable substrate 201, the first layer 1401, and / or the second layer 1403 containing at least a portion of lithium cations and / or sodium cations with a salt bath 1601 containing a salt solution 1603, which is similar or identical to the salt solution 1303 described above. In some embodiments, the salt solution 1603 may include a certain temperature within one or more of the temperature ranges of the salt solution 1303 described above. In additional embodiments, the temperature of the salt solution 1603 may be substantially the same as the temperature of the salt solution 1303. In some embodiments, the first time period of the chemical strengthening in step 1007 may be within one or more of the time ranges described above for the time of contact with the salt solution 1303 in step 1007. The relationship between the first time period in step 1007 and the time of contact with an alkali metal (e.g., a salt solution) in step 1003 and / or step 1011 will be discussed below.

[0279] After step 1007, as Figure 17 shown, the method may proceed to step 1009, which includes removing the layer disposed above the central portion 251. In some embodiments, removing the layer may include: removing the first layer 1401 disposed above the first central surface region 209 of the central portion 251. In additional embodiments, removing the layer may include: removing the second layer 1403 disposed above the second central surface region 213 of the central portion 251. In additional embodiments, as shown, removing the first layer 1401 and / or the second layer 1403 may include: moving the grinding tool 1701 in the direction 1702 on the surface (e.g., the first central surface region 209, the second central surface region 213). In additional embodiments, using the tool may include: sweeping, scraping, grinding, pushing, etc. In additional embodiments, the first layer 1401 and / or the second layer 1403 may be removed by washing the surface (e.g., the first central surface region 209, the second central surface region 213) with a solvent.

[0280] In some embodiments, after step 1009, as Figure 18As shown, the method may proceed to step 1011, which includes further chemically strengthening the foldable substrate 201. As described herein, this further chemical strengthening of the foldable substrate 201 may continue for a second time period. As used herein, the second time period may be the sum of the times of steps 1003 and 1013 (if present in the method), which is the time that at least a portion of the foldable substrate 201 is in contact with one or more alkali metals (e.g., sodium ions, potassium ions) as described with respect to the salt solution 1303. Thus, the time period during which the foldable substrate 201 is in contact with the one or more alkali metals (e.g., sodium ions, potassium ions) in step 1013 may be less than or equal to the second time period. In some embodiments, the time period during which the foldable substrate 201 is in contact with the one or more alkali metals (e.g., sodium ions, potassium ions) in step 1013 may be within one or more of the ranges described above with respect to step 1003. In some embodiments, the second time period may be greater than the first time period. In additional embodiments, as a percentage of the first time period, the second time period may be greater than or equal to about 103%, greater than or equal to about 110%, greater than or equal to about 120%, greater than or equal to about 135%, less than or equal to about 200%, less than or equal to about 175%, less than or equal to about 160%, or less than or equal to about 150%. In additional embodiments, as a percentage of the first time period, the second time period may be within the following ranges: about 103% to about 200%, about 103% to about 175%, about 110% to about 175%, about 110% to about 160%, about 120% to about 160%, about 120% to about 150%, about 135% to about 150%, or any range or sub-range therebetween.

[0281] In some embodiments, as Figure 18As shown, the further chemical strengthening of the foldable substrate 201 in step 1011 may include: contacting at least a portion of the foldable substrate 201 containing lithium cations and / or sodium cations with a salt bath 1801 containing a salt solution 1803, the salt solution 1803 containing one or more of the alkali metal ions and / or alkali metal-containing compounds described above with respect to steps 1003 and 1007. In some embodiments, the salt solution 1803 may include a certain temperature within one or more of the ranges described above with respect to step 1003. After step 1011, the foldable substrate may include one or more compressive stress zones (e.g., a first compressive stress zone, a second compressive stress zone, a third compressive stress zone, a fourth compressive stress zone, a first central compressive stress zone, and / or a second central compressive stress zone), the compressive stress zones including a compressive depth and / or a related layer depth within one or more of the ranges described above with respect to the corresponding compressive stress zones. In some embodiments where step 1011 is omitted (e.g., following arrow 1004 or 1006), after step 1009, the foldable substrate may include one or more compressive stress zones (e.g., a first compressive stress zone, a second compressive stress zone, a third compressive stress zone, a fourth compressive stress zone, a first central compressive stress zone, and / or a second central compressive stress zone), the compressive stress zones including a compressive depth and / or a related layer depth within one or more of the ranges described above with respect to the corresponding compressive stress zones. In additional embodiments, the absolute difference between the layer depth of one of the first layer depth, the second layer depth, the third layer depth, or the fourth layer depth divided by the substrate thickness and the first central layer depth or the second central layer depth divided by the central thickness may be within one or more of the above ranges. In additional embodiments, the absolute difference between the compressive depth of one of the first compressive depth, the second compressive depth, the third compressive depth, or the fourth compressive depth divided by the substrate thickness and the first central compressive depth or the second central compressive depth divided by the central thickness may be within one or more of the above ranges. In additional embodiments, the absolute difference between the first average concentration of potassium or the second average concentration of potassium and the central average concentration of potassium may be within one or more of the above ranges.

[0282] In some embodiments, step 1011 may further include: after chemically strengthening the foldable substrate 201 (e.g., after the chemical strengthening in step 1007 and / or 1011), chemically etching the foldable substrate 201. In some embodiments, as described below, step 1013 may include: after chemically strengthening the foldable substrate 201 (e.g., after the chemical strengthening in step 1007 and / or 1011), before assembling the foldable device, chemically etching the foldable substrate 201 in step 1013. As described above, the chemical etching may include: bringing the foldable substrate 201 into contact with the etching solution contained in the etching bath. In some embodiments, the first major surface 203 and the first central surface region 209 are etched. In some embodiments, the second major surface 205 is etched. In additional embodiments, the first major surface 203, the first central surface region 209, the second major surface 205, and / or the second central surface region 213 are etched. If present in step 1011 and / or 1013, the chemical etching may be designed to remove surface defects that may remain due to the chemical strengthening of the foldable substrate 201. In fact, chemical strengthening may cause some surface defects, which may affect the strength and / or optical quality of the foldable substrate 201. By etching during step 1011 and / or 1013, the surface defects generated during chemical strengthening can be removed. In some embodiments, such etching may be designed to remove a portion of the layer having a depth of about 1 nm or greater, about 5 nm or greater, about 2 μm or less, about 1 μm or less, about 500 nm or less, about 100 nm or less, about 50 nm or less, or about 10 nm or less. In some embodiments, such etching may be designed to remove a portion of the layer having a depth within the following ranges: about 1 nm to about 2 μm, about 1 nm to about 1 μm, about 5 nm to about 1 μm, about 5 nm to about 500 nm, about 5 nm to about 100 nm, about 5 nm to about 50 nm, about 5 nm to about 10 nm, or any range or sub-range therebetween. Such etching can avoid significantly changing the thickness of the foldable substrate 201 or the surface compression achieved during chemical strengthening.

[0283] After step 1011, the method of the present disclosure may proceed to step 1013, which includes: assembling the foldable device with the foldable substrate 201. As Figure 24 and 26 shown, step 1013 may include: applying an adhesive layer 261 to contact the first surface region 223 of the first major surface 203 and the third surface region 233 of the first major surface 203. As shown, the second contact surface 265 of the adhesive layer 261 may contact the first surface region 223 and the third surface region 233. In some embodiments, asFigure 24 As shown, the adhesive layer 261 may include one or more layers of adhesive material. For example, an integral interface may exist between one or more of the layers that make up the adhesive layer 261, which may reduce (e.g., avoid) optical refraction and / or optical discontinuity when light travels between the layers, since the one or more layers may include substantially the same refractive index in some embodiments. In some embodiments, as Figure 24 shown, the adhesive layer 261 may further fill the recess 219. In additional embodiments, as Figure 24 shown, the second contact surface 265 of the adhesive layer 261 may contact the first central surface region 209. In some embodiments, as Figure 26 shown, step 1013 may include: disposing a polymer-based portion 241 in the recess 219. In additional embodiments, the polymer-based portion 241 may include a third contact surface 245 that may contact the first central surface region 209. In additional embodiments, as Figure 26 shown, the polymer-based portion 241 may include a fourth contact surface 247 that may contact the second contact surface 265 of the adhesive layer 261. Although not shown, in some embodiments, the recess may not be completely filled, for example, leaving space for electronic and / or mechanical devices.

[0284] In some embodiments, as Figure 25 and 32 -33 shown, step 1013 may include: disposing a second liquid 2503 in the recess 219. The second liquid 2503 may then be cured to form a polymer-based portion. In some embodiments, as Figure 25 shown, step 1013 may further include: curing the second liquid 2503 to form a polymer-based portion 241 when the foldable substrate 201 is in a flat configuration. In some embodiments, as Figures 32 - 33 shown, step 1013 may further include: curing the second liquid 2503 to form a polymer-based portion 241 when the foldable substrate 201 is in a bent configuration. In additional embodiments, as Figure 32 shown, in step 1013, the foldable substrate 201 may be in a bent configuration such that the first major surface 203 and the first central surface region 209 are on the outer side of the bend. In additional embodiments, as Figure 33 shown, in step 1013, the foldable substrate 201 may be in a bent configuration such that the second major surface 205 is on the outer side of the bend.

[0285] Curing the second liquid 2503 in step 1013 may form a polymer-based portion 241. In some embodiments, as Figure 25 and 32As shown in FIG. -33, step 1013 may include: disposing a liquid 2503 in the recess 219. In additional embodiments, a catheter (e.g., a flexible tube, a micropipette, or a syringe) may be used to dispose the second liquid 2503 into the recess 219. In additional embodiments, as Figure 25 and 32 shown in FIG. -33, the second liquid 2503 may be disposed in the recess 219 by dispensing the second liquid 2503 from the container 2501 into the recess 219. In some embodiments, disposing the second liquid 2503 in the recess 219 may at least partially (e.g., substantially completely) fill the recess 219. In some embodiments, as shown, disposing the second liquid 2503 in the recess 219 may dispose the second liquid 2503 between the first portion 221 and the second portion 231. In some embodiments, the second liquid 2503 may include one or more precursors of a polymer-based portion and a solvent. In some embodiments, the precursors of the polymer-based portion may include, but are not limited to, one or more of the following: monomers, oligomers, promoters, curing agents, epoxides, polyurethanes (e.g., isocyanates, esters, polyols), mercaptoesters, acrylates, particles (e.g., one or more of copper oxide, β-quartz, tungstate, vanadate, pyrophosphate, nitinol) and / or fibers. In some embodiments, the solvent of the precursor may include polar solvents (e.g., water, alcohols, acetates, acetone, formic acid, dimethylformamide, acetonitrile, dimethyl sulfoxide, nitromethane, propylene carbonate, poly(ether ether ketone)) and / or non-polar solvents (e.g., pentane, 1,4-dioxane, chloroform, dichloromethane, diethyl ether, hexane, heptane, benzene, toluene, xylene). The second liquid 2503 may be cured to form a polymer-based portion 241 as Figure 26 shown. In additional embodiments, curing the second liquid 2503 to form the polymer-based portion 241 may include: heating the second liquid 2503. In additional embodiments, curing the second liquid 2503 to form the polymer-based portion 241 may include: irradiating the second liquid 2503 with ultraviolet (UV) radiation. In additional embodiments, curing the second liquid 2503 to form the polymer-based portion 241 may include: waiting for a predetermined time (e.g., about 30 minutes to 24 hours, about 1 hour to about 8 hours). In some embodiments, the polymer-based portion 241 may include a negative coefficient of thermal expansion, as described above. In some embodiments, the precursor may include cyclic monomers (e.g., norbornene, cyclopentene), wherein curing the precursor includes ring-opening metathesis polymerization, which may cause an increase in volume from the second liquid 2503 to the polymer-based portion 241. In some embodiments, curing the second liquid 2503 may form a polymer-based portion between the first portion 221 and the second portion 231 of the foldable substrate 201.

[0286] In some embodiments, after step 1013 and / or 1015, when the foldable device including the foldable substrate is in a bent configuration, the foldable device may include a neutral stress configuration. In additional embodiments, in the neutral stress configuration, the foldable device may include a maximum amplitude of deviatoric strain of the polymer-based portion within one or more of the ranges described above (e.g., within a range of about 1% to about 8%, within a range of about 2% to about 6%). In additional embodiments, in the neutral stress configuration, the foldable device may include an angle within one or more of the ranges described above. In some embodiments, the neutral stress configuration may correspond to the bent configuration obtained by bending the foldable substrate 201. In some embodiments, the neutral stress configuration may correspond to the bent configuration obtained by curing the second liquid 2503 to form the polymer-based portion 241 when the foldable substrate 201 is bent. In some embodiments, the neutral stress configuration may correspond to the bent configuration obtained because of the volume increase when curing the second liquid 2503 to form the polymer-based portion 241. In some embodiments, the neutral stress configuration may correspond to the bent configuration obtained because the polymer-based portion 241 includes a negative coefficient of thermal expansion.

[0287] In some embodiments, a release liner (e.g., see the release liner 271 of Figure 2 ) or a display device (e.g., see the display device 307 of Figure 3 ) may be disposed on the first contact surface 263 of the adhesive layer 261. In some embodiments, a coating (e.g., see the coating 281 of Figure 2 ) may be disposed on the second major surface of the foldable substrate 201. At Figure 10 the end point 1015 of the flowchart of

[0288] In some embodiments, the method of manufacturing a foldable device according to the embodiments of the present disclosure may proceed sequentially through steps 1001, 1003, 1005, 1007, 1009, 1011, 1013, and 1015 in the flowchart of Figure 10 as described above. In some embodiments, as shown in Figure 10 , step 1003 may be omitted by following arrow 1002 from step 1001, for example, when the folding substrate 201 is not chemically strengthened before step 1007. In some embodiments, step 1011 may be omitted by following arrow 1004 from step 1009 to step 1013, for example, if the foldable substrate 201 already includes a compressive stress zone of the finished foldable substrate. In some embodiments, step 1015 may be followed from step 1009 by following arrow 1006, for example, if the method produces the foldable substrate 201 (e.g., see Figure 5) and when the foldable substrate 201 already includes a compressive stress zone of the finished foldable substrate. In some embodiments, one can follow arrow 1008 from step 1011 to step 1015, for example, if the method results in a foldable substrate 201 (e.g., see Figure 5 ). In some embodiments, the method may include a single chemical strengthening step in step 1007, for example, by following arrow 1002 and following one of arrows 1004 or 1006, while omitting additional chemical strengthening steps. In some embodiments, the method may include two chemical strengthening steps, the two chemical strengthening steps including step 1007 and one of step 1003 or 1011, for example, by following arrow 1002 or one of arrows 1004 or 1006 respectively, while omitting additional chemical strengthening steps. Any of the above options can be combined to manufacture a foldable device according to embodiments of the present disclosure.

[0289] Reference will now be made to Figure 12 、 18 -26 and 32-34 and Figure 11 's flowcharts to discuss exemplary embodiments of manufacturing Figures 2 - 3 and the foldable devices 101 and / or 301, testable foldable device 602 and / or foldable substrate 201 shown in 5-7. In the first step 1101 of the method of the present disclosure, the method can start with providing a foldable substrate 201. In some embodiments, the foldable substrate 201 can be provided by purchasing, or otherwise obtaining, a substrate, or by forming a foldable substrate. In some embodiments, the foldable substrate 201 can include a glass-based substrate and / or a ceramic-based substrate. In additional embodiments, the glass-based substrate and / or glass-ceramic-based substrate can be provided by forming them with various tape forming processes, such as slit drawing, down-draw, fusion down-draw, up-draw, press roll, re-draw, or float process. In additional embodiments, the ceramic-based substrate can be provided by heating the glass-based substrate to crystallize one or more ceramic crystals. The foldable substrate 201 can include a second major surface 205 (see Figure 12 ), which can extend along a certain plane. The second major surface 205 can be opposite to the first major surface 203. In some embodiments, as Figure 34 shows, the foldable substrate 201 can be bent (e.g., including a bent configuration). In additional embodiments, as a result of bending the foldable substrate 201 into a bent configuration, when the foldable substrate 201 includes a viscosity of about 10 4 Pascal-seconds to about 10 7 Pascal-seconds (e.g., within the working range of the foldable substrate 201, between the softening point and the working point of the foldable substrate 201), the foldable substrate 201 can include a bent configuration.

[0290] In some embodiments, the foldable substrate 201 may include a recess 219 in a first major surface 203 of the foldable substrate 201, which exposes a first central surface region 209. In additional embodiments, the recess 219 may be formed by etching, laser ablation, or machining the first major surface 203. For example, the first major surface 203 may be machined by diamond engraving, thereby creating extremely precise patterns in glass-based substrates and / or ceramic-based substrates. As Figure 12 shown, diamond engraving may be used to create the recess 219 in the first major surface 203 of the foldable substrate 201, wherein a diamond tip probe 1201 may be controlled using a computer numerical control (CNC) machine 1203. Materials other than diamond may also be used for engraving using a CNC machine. Additionally, other methods of forming recesses include photolithography, etching, and laser ablation. For example, etching may include: disposing a mask over the first surface region 223 and the third surface region 233, exposing the first major surface 203 of the foldable substrate 201 to an etchant to form the recess 219, and then removing the mask. Forming the recess 219 in the first major surface 203 may provide a central portion 251 between a first portion 221 and a second portion 231 of the foldable substrate 201. The central portion 251 may include a first central surface region 209, wherein the recess 219 may be defined between the first central surface region 209 and a first plane 204a, which is Figure 12 the plane along which the first major surface 203 extends in the flat configuration shown. The first central surface region 209 may attach the first portion 221 to the second portion 231. As Figure 2 shown, the central portion 251 may further include a first transition portion 253 that attaches the first portion 221 to the central major surface 211 and a second transition portion 255 that attaches the second portion 231 to the central major surface 211. In some embodiments, the thickness of the first transition portion 253 may continuously increase from the central major surface 211 to the first portion 221. In additional embodiments, the thickness of the second transition portion 255 may continuously increase from the central major surface 211 to the second portion 231. As Figure 12 shown, in some embodiments, the first central surface region 209 may include the central major surface 211 of the central portion 251, which may be planar as shown, but in additional embodiments, a non-planar configuration may be provided. Additionally, the central major surface 211 may be parallel to the first plane 204a and / or the second major surface 205, as Figure 12 shown.

[0291] Although with respect to Figure 12The device is not shown, but in some embodiments, step 1101 may further include reducing the thickness of the foldable substrate 201. In additional embodiments, the thickness of the foldable substrate 201 may be reduced by machining (e.g., grinding). In additional embodiments, chemical etching may be employed to reduce the thickness of the foldable substrate 201. In additional embodiments, chemical etching may include: contacting the foldable substrate 201 with an etching solution contained in an etching bath. In additional embodiments, the etching solution may include one or more inorganic acids (e.g., HCl, HF, H 2 SO 4 , HNO 3 ). For example, referring to the foldable substrate 201 shown in Figure 29 , chemical etching may be used to reduce the thickness of the foldable substrate 201, which may include: contacting the foldable substrate 201 with an etching solution 2903 contained in an etching bath 2901 that includes one or more inorganic acids (e.g., HCl, HF, H 2 SO 4 , HNO 3 ). In some embodiments, the thickness of the foldable substrate 201 may be reduced by removing a layer from the first major surface 203 of the foldable substrate 201 to expose a new first major surface, and the new first major surface may constitute the first major surface 203 as shown in Figures 2 - 3 and 5-7. Additionally or alternatively, the thickness of the foldable substrate 201 may be reduced by removing a layer from the second major surface 205 of the foldable substrate 201 to expose a new second major surface, and the new second major surface may constitute the second major surface 205 as shown in Figures 2 - 3 and 5-7.

[0292] In some embodiments, the second major surface 205 (e.g., the entire second major surface 205) may be covered with an optional mask (e.g., the mask 2905 in Figure 29 ) such that the second major surface 205 is not etched and may serve as described above with respect to Figures 2 - 3The second major surface 205 as described in FIGS. 5 - 7 is provided to offer the second major surface 205. Preventing the second major surface 205 from being etched can be beneficial for preserving the original nature of the second major surface 205, which can exist with some processing techniques (e.g., pull-up or pull-down, e.g., by overflow or fusion). Maintaining the original surface can make the second major surface 205 present a particularly smooth surface, which can form the outermost surface of the foldable device, and this outermost surface can be available for the user of the foldable device to observe and / or touch. Alternatively, the thickness of the foldable substrate 201 can be reduced by removing a layer from the second major surface 205, e.g., removing the surface layer to expose a central layer with more consistent optical properties along the length of the foldable substrate 201 (e.g., glass-based substrate and / or ceramic-based substrate), as described above. In some embodiments, a layer can be removed from the first major surface 203 to expose a new first major surface, which can constitute Figures 2 - 3 the first major surface 203 as shown in FIGS. 5 - 7, and a layer can be removed from the second major surface 205 to expose a new second major surface, which can constitute Figures 2 - 3 the second major surface 205 as shown in FIGS. 5 - 7. Removing layers from both the first major surface and the second major surface can remove the outer layer of the foldable substrate 201 (e.g., glass-based substrate and / or ceramic-based substrate), which may have inconsistent optical properties compared to the underlying internal portion of the foldable substrate 201 (e.g., glass-based substrate and / or ceramic-based substrate). As a result, the overall thickness across the entire length and width of the foldable substrate 201 can have more consistent optical properties to provide a consistent optical performance with little distortion across the entire foldable substrate 201 (e.g., glass-based substrate and / or ceramic-based substrate).

[0293] In some embodiments, removing a layer from the first major surface 203 can be beneficial for removing surface defects generated during the formation of the recess 219. For example, machining the first major surface 203 (e.g., with a diamond tip probe) to create the recess 219 may generate microcrack surface imperfections or other defects, which can present weaknesses where catastrophic failure of the foldable substrate 201 may occur when folded. Thus, by removing a layer from the first major surface 203, surface defects generated in the layer during the formation of the recess 219 can be removed, where a new first major surface 203 with fewer surface defects can be presented. Since there are fewer surface defects, a smaller bending radius can be achieved without failure of the foldable substrate. For example, certain processing of the tape may present different glass-based material properties and / or ceramic-based material properties at the first and second major surfaces of the foldable substrate than at the central portion of the foldable substrate. For example, during a pull-down process, the properties of the glass-based material and / or ceramic-based material at the major surface may be different from those at the central portion. Thus, by removing a layer from the first major surface 203 at the first portion 221 and the second portion 231, the new first major surface 203 of these portions can have the same properties as the first central surface region 209 to provide consistent optical properties over the length of the foldable substrate 201, such as if the foldable substrate 201 includes a glass-based substrate and / or a ceramic-based substrate.

[0294] After step 1101, as Figure 19 shown, the method of the present disclosure may proceed to step 1103, which includes: applying a paste containing alkali metal ions to the first portion 221 and the second portion 231. In some embodiments, as Figure 19 shown, step 1103 may include: disposing a first salt paste 1003 on the first portion 221 and a fir...

Claims

1. A foldable device, which includes a foldable substrate that can be folded around an axis extending in the width direction of the foldable substrate, and the foldable substrate further includes: a substrate thickness defined between a first main surface and a second main surface opposite to the first main surface; a first part, which includes the substrate thickness, a first surface area of the first main surface, a first compressive stress zone extending from the first surface area of the first main surface to a first compressive depth, a first layer depth of one or more alkali metal ions associated with the first compressive depth, a second compressive stress zone extending from a second surface area of the second main surface to a second compressive depth, a second layer depth of one or more alkali metal ions associated with the second compressive depth, and a first tensile stress zone including a first maximum tensile stress; a second part, which includes the substrate thickness, a third surface area of the first main surface, a third compressive stress zone extending from the third surface area of the first main surface to a third compressive depth, a third layer depth of one or more alkali metal ions associated with the third compressive depth, a fourth compressive stress zone extending from a fourth surface area of the second main surface to a fourth compressive depth, a fourth layer depth of one or more alkali metal ions associated with the fourth compressive depth, and a second tensile stress zone including a second maximum tensile stress; and a central part, which includes a central thickness defined between a first central surface area and the second main surface opposite to the first central surface area, the first central surface area attaching the first surface area to the third surface area, the central thickness being less than the substrate thickness, a first central compressive stress zone extending from the first central surface area to a first central compressive depth, a first central layer depth of one or more alkali metal ions associated with the first central compressive depth, a second central compressive stress zone extending from a second central surface area of the second main surface to a second central compressive depth, a second central layer depth of one or more alkali metal ions associated with the second central compressive depth, and a central tensile stress zone including a central maximum tensile stress, wherein the central part is located between the first part and the second part in the length direction of the foldable substrate, the length direction is perpendicular to the width direction of the foldable substrate, and the absolute difference between the first layer depth as a percentage of the substrate thickness and the first central layer depth as a percentage of the central thickness is less than or equal to about 1%.

2. The foldable device according to claim 1, wherein, the absolute difference between the third layer depth as a percentage of the substrate thickness and the first central layer depth as a percentage of the central thickness is less than or equal to about 1%.

3. The foldable device according to any one of claims 1-2, wherein, the absolute difference between the second layer depth as a percentage of the substrate thickness and the second central layer depth as a percentage of the central thickness is less than or equal to about 1%.

4. The foldable device according to any one of claims 1-2, wherein, the absolute difference between the fourth layer depth as a percentage of the substrate thickness and the second central layer depth as a percentage of the central thickness is less than or equal to about 1%.

5. The foldable device according to any one of claims 1-2, wherein, the first maximum tensile stress and the second maximum tensile stress are less than the central maximum tensile stress.

6. The foldable device according to any one of claims 1-2, wherein, the first maximum tensile stress is less than or equal to about 100 megapascals, the second maximum tensile stress is less than or equal to about 100 megapascals, and the central maximum tensile stress is in the range of about 125 megapascals to about 375 megapascals.

7. The foldable device according to any one of claims 1-2, wherein, the foldable substrate achieves an effective bending radius of 1 millimeter to 10 millimeters.

8. The foldable device according to any one of claims 1-2, wherein, the foldable substrate achieves an effective bending radius of 5 millimeters.

9. The foldable device according to any one of claims 1-2, wherein, the width of the central portion is in the range of about 3 millimeters to about 45 millimeters.

10. The foldable device according to claim 9, wherein, the width of the central portion is in the range of about 2.8 times the effective minimum bending radius to about 6 times the effective minimum bending radius.

11. The foldable device according to any one of claims 1-2, wherein, the central thickness is in the range of about 10 micrometers to about 220 micrometers.

12. The foldable device according to any one of claims 1-11, wherein, the foldable substrate is a glass-based substrate.

13. A method of manufacturing a foldable substrate, the foldable substrate including a substrate thickness defined between a first major surface and a second major surface, a first portion including the substrate thickness, a second portion including the substrate thickness, a central portion including a central thickness, the central thickness being defined between a first central surface region and a second central surface region, the central thickness being less than the substrate thickness, the central portion being located between the first portion and the second portion, the method comprising: disposing a first layer over one or more of the first central surface region or the second central surface region; after disposing the first layer, chemically strengthening the foldable substrate for a first period of time; and after chemically strengthening the foldable substrate, removing the first layer, wherein, after chemically strengthening the foldable substrate, the first portion includes a first layer depth of one or more alkali metal ions introduced into the first portion during chemical strengthening from the first major surface, the central portion includes a first central layer depth of one or more alkali metal ions introduced into the central portion during chemical strengthening from the first central surface region, and the absolute difference between the first layer depth as a percentage of the substrate thickness and the first central layer depth as a percentage of the central thickness is less than or equal to about 1%.

14. The method according to claim 13, wherein, after chemically strengthening the foldable substrate, the second portion includes a third layer depth of one or more alkali metal ions introduced into the second portion during chemical strengthening from the first major surface, and the absolute difference between the third layer depth as a percentage of the substrate thickness and the first central layer depth as a percentage of the central thickness is less than or equal to about 1%.

15. The method according to any one of claims 13 - 14, wherein, the first layer has a thickness of from about 10 nanometers to about 200 nanometers.

16. The method according to any one of claims 13 - 14, further comprising: forming a recess in the first major surface of the foldable substrate before disposing the first layer to provide a first central surface region.

17. The method according to any one of claims 13 - 14, wherein, the foldable substrate achieves an effective bending radius of from 1 millimeter to 10 millimeters.

18. The method according to any one of claims 13 - 14, wherein, the foldable substrate achieves an effective bending radius of 5 millimeters.

19. The method according to any one of claims 13 - 14, wherein, the central thickness is in the range of from about 10 micrometers to about 220 micrometers.

20. The method according to any one of claims 13 - 14, wherein, the foldable substrate comprises a glass-based substrate.

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