Foldable substrate and method of manufacturing the same

Abstract

Foldable substrates include a first outer layer including a first major surface, a second outer layer including a second major surface, and a core layer positioned therebetween. The core layer can include a first central surface region positioned between a first portion and a second portion of the first outer layer, and the core layer includes a second central surface region positioned between a third portion and a fourth portion of the second outer layer. Some foldable substrates include a first portion including a first depth of compression, a first depth of layer, and a first average concentration. The central portion includes a first central depth of compression, a first central depth of layer, and a central average concentration. Methods include chemically strengthening a foldable substrate. Some methods include etching the foldable substrate, and then further chemically strengthening the foldable substrate.

Description

Technical Field

[0001] This disclosure generally relates to foldable substrates and methods of manufacturing the same, and more specifically, to foldable substrates comprising various parts and methods of manufacturing foldable substrates. Background Technology

[0002] 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), or the like.

[0003] There is a need to develop foldable forms of displays and foldable protective covers for mounting on foldable displays. The foldable displays and covers should have good impact and puncture resistance. Simultaneously, the foldable displays and covers should have a small minimum bending radius (e.g., approximately 10 mm or less). However, plastic displays and covers with small minimum bending radii often exhibit poor impact and / or puncture resistance. Furthermore, conventional wisdom suggests that ultra-thin glass-based sheets with small minimum bending radii (e.g., approximately 75 μm thick or less) often exhibit poor impact and / or puncture resistance. Conversely, thicker glass-based sheets with good impact and / or puncture resistance (e.g., greater than 125 μm) often have relatively large minimum bending radii (e.g., approximately 30 μm or greater). Therefore, there is a need to develop foldable devices with low minimum bending radii and good impact and puncture resistance. Summary of the Invention

[0004] This document describes a foldable device comprising a foldable substrate, a foldable substrate, and a method for manufacturing the foldable device and the foldable substrate, the foldable substrate comprising a first portion and a second portion. The portion may comprise a glass-based portion and / or a ceramic-based portion, which provides good dimensional stability, reduced mechanical instability, good impact resistance, and / or good puncture resistance. The first portion and / or the second portion may comprise a glass-based portion and / or a ceramic-based portion, which includes one or more compressive stress regions, further providing increased impact resistance and / or increased puncture resistance. By providing a substrate comprising a glass-based substrate and / or a ceramic-based substrate, the substrate can also provide increased impact resistance and / or puncture resistance, while contributing to good folding performance. In some embodiments, the substrate thickness may be sufficiently large (e.g., from about 80 micrometers (μm) to about 2 millimeters) to further enhance impact resistance and puncture resistance. A foldable substrate that includes a central portion and whose central thickness is less than the thickness of the substrate (e.g., the first thickness of the first portion and / or the second thickness of the second portion) can achieve a small effective minimum bending radius (e.g., about 10 mm or less) based on the reduced thickness in the central portion.

[0005] In some embodiments, the foldable device and / or foldable substrate may include multiple recesses, such as a first central surface region recessed a first distance from a first main surface and a second central surface region recessed a second distance from a second main surface. Providing a first recess opposite to the second recess can provide a central thickness less than the substrate thickness. Additionally, providing a first recess opposite to the second recess can reduce the maximum bending-induced strain of the foldable device, for example, between the central portion and the first and / or second portions, because the central portion containing the central thickness can be closer to the neutral axis of the foldable device and / or foldable substrate than in the case of providing only a single recess. Furthermore, providing a first distance substantially equal to the second distance can reduce the occurrence of mechanical instability in the central portion, for example, because the foldable substrate is planarly symmetrical about the midpoint containing the substrate thickness and the central thickness. Moreover, compared to a single recess having a surface recessed by the sum of the first and second distances, providing a first recess opposite to the second recess can reduce the bending-induced strain of the material located in the first and / or second recess. Providing reduced flexural induced strain to the material positioned in the first and / or second recesses enables the use of a wider range of materials due to reduced strain requirements. For example, a harder and / or more rigid material can be positioned in the first recess, which can improve the impact resistance, puncture resistance, abrasion resistance, and / or scratch resistance of the foldable device. Furthermore, controlling the properties of the first material positioned in the first recess and the second material positioned in the second recess can control the position of the neutral axis of the foldable device and / or foldable substrate, which can reduce (e.g., mitigate, eliminate) mechanical instability, equipment fatigue, and / or equipment failure.

[0006] In some embodiments, the foldable device and / or foldable substrate may include a first transition portion attaching a central portion to a first portion and / or a second transition portion attaching a central portion to a second portion. Providing a transition region with continuously increasing thickness can reduce stress concentration in the transition region and / or avoid optical distortion. Providing a transition region of sufficient length (e.g., about 1 mm or more) can avoid optical distortion that would otherwise exist due to abrupt, stepwise changes in the thickness of the foldable substrate. Providing a transition region of sufficiently short length (e.g., about 5 mm or less) can reduce the amount of foldable device and / or foldable substrate with intermediate thickness, which may have reduced impact resistance and / or reduced puncture resistance. Additionally, providing a first transition portion and / or a second transition portion with a tensile stress region can offset strain between the first or second portion and the first transition portion and / or the second transition portion during folding, the tensile stress region containing a maximum tensile stress greater than the maximum tensile stress in the central tensile stress region of the central portion. Additionally, providing a first transition portion and / or a second transition portion with a tensile stress region can offset the strain between the central portion and the first transition portion and / or the second transition portion during folding, wherein the maximum tensile stress contained in the tensile stress region is greater than the maximum tensile stress in the first tensile stress region of the first portion and / or the second tensile stress region of the second portion.

[0007] The apparatus and methods of embodiments of this disclosure can reduce (e.g., mitigate, eliminate) mechanical instability, equipment fatigue, and / or equipment failure by controlling (e.g., limiting, reducing, equalizing) the difference in expansion between different portions of the foldable device and / or foldable substrate as a result of chemical strengthening. Controlling the difference in expansion between different portions can reduce the chemical strengthening-induced strain between the portions of the foldable device and / or foldable substrate, which can help the foldable device and / or foldable substrate to have a larger folding-induced strain before reaching the critical buckling strain (e.g., the onset of mechanical instability). In addition, reducing mechanical instability and / or the difference between the core layer and the first outer layer and / or the first outer layer, or the difference between the central portion and the first portion and / or the second portion, can reduce optical distortion, for example, caused by strain within the foldable device and / or foldable substrate due to such differences.

[0008] In some embodiments, providing a foldable device and / or foldable substrate comprising laminates allows for control of expansion differences between the first portion, the second portion, and the central portion during a single chemical strengthening process. For example, the properties of the core layer relative to the first and / or second outer layers allow for substantially uniform expansion of the foldable device and / or foldable substrate. In some embodiments, the density of the core layer may be greater than the density of the first and / or second outer layers. In some embodiments, the coefficient of thermal expansion of the core layer may be greater than the coefficient of thermal expansion of the first and / or second outer layers. In some embodiments, the network expansion coefficient of the core layer may be less than the network expansion coefficient of the first and / or second outer layers. Furthermore, providing a core layer having a relationship to the first and / or second outer layers can reduce (e.g., minimize) the forces exerted on folding the foldable device and / or foldable substrate.

[0009] Providing a first and / or second portion containing an average concentration of one or more alkali metals close to that of the central portion (e.g., within 100 to 10 parts per million, based on oxides) minimizes the expansion difference between the first and / or second portions and the central portion due to chemical strengthening. Substantially uniform expansion reduces mechanical deformation and / or mechanical instability caused by chemical strengthening.

[0010] Providing a layer depth ratio close to that of the central portion to the thickness of the first and / or second portions (e.g., within 0.5%, 0.1%, or 0.01%) minimizes the difference in near-surface expansion of the first and / or second portions relative to the central portion due to chemical strengthening. Minimizing this difference in near-surface expansion reduces stress and / or strain in the planes of the first primary surface, second primary surface, first central surface region, and / or second central surface region, which further reduces mechanical deformation and / or mechanical instability due to chemical strengthening.

[0011] Providing a ratio of compression depth to the thickness of the first and / or second portions that is close to (e.g., differing by within 1%, 0.5%, or 0.1%) the center portion minimizes the difference in chemically strengthened induced strain between the first and / or second portions relative to the center portion. Minimizing the difference in chemically strengthened induced strain reduces the occurrence of mechanical deformation and / or mechanical instability due to chemical strengthening.

[0012] Minimizing stress and / or strain in the first primary surface, second primary surface, first central surface region, and / or second central surface region reduces stress-induced optical distortion. Furthermore, minimizing these stresses increases puncture resistance and / or impact resistance. Moreover, minimizing these stresses is associated with low optical hysteresis (e.g., about 2 nanometers or less) along the centerline. Additionally, minimizing these stresses reduces mechanical deformation and / or mechanical instability caused by chemical strengthening.

[0013] The methods of this disclosure enable the manufacture of foldable substrates that incorporate one or more of the benefits mentioned above. In some embodiments, the methods of this disclosure can achieve the benefits mentioned above in a single chemical strengthening step, for example, manufacturing a foldable substrate comprising a laminate, which can reduce the time, equipment, space, and labor costs associated with producing the foldable substrate. In some embodiments, existing recesses (e.g., an existing first central surface area recessed from a first main surface, an existing second central surface area recessed from a second main surface) can be provided or formed prior to any chemical strengthening of the foldable substrate, which can provide the above benefits to foldable devices having recesses that are deeper than could otherwise be achieved (e.g., a larger first distance, a larger second distance). In some embodiments, the above benefits can be provided by chemically strengthening the foldable substrate, etching a central portion of the foldable substrate (e.g., etching an existing first central surface area to form a new first central surface area, etching an existing second central surface area to form a new second central surface area), and then further chemically strengthening the foldable substrate. In another embodiment, the above benefits can be provided by controlling the duration of the chemical strengthening relative to the second time period of the further chemical strengthening, and / or the thickness of the etching from the center portion. Providing the further chemical strengthening to the foldable substrate can 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.

[0014] The following describes some exemplary embodiments of the present disclosure, and it should be understood that any features of the various embodiments may be used alone or in combination with each other.

[0015] Embodiment 1: A foldable substrate includes a substrate thickness defined between a first main surface and a second main surface opposite to the first main surface. The substrate thickness is in the range of about 100 micrometers to about 2 millimeters. The foldable substrate includes a first outer layer comprising the first main surface and a first inner surface opposite to the first main surface. A first outer thickness is defined between the first main surface and the first inner surface. The first outer layer includes a first portion and a second portion separated by a first minimum distance. The first portion includes the first main surface and the first inner surface. The second portion includes the first main surface and the first inner surface. The foldable substrate includes a second outer layer comprising the second main surface and a second inner surface opposite to the second main surface. The second outer layer includes a second outer thickness defined between the second main surface and the second inner surface. The second outer layer includes a third portion and a fourth portion separated by a second minimum distance. The third portion includes the second main surface and the second inner surface. The fourth portion includes the second main surface and the second inner surface. The foldable substrate includes a core layer comprising a third inner surface and a fourth inner surface opposite to the third inner surface. A center thickness is defined between the third inner surface and the fourth inner surface. The center thickness ranges from about 25 micrometers to about 80 micrometers. The core layer is positioned between a first outer layer and a second outer layer. The third inner surface contacts the first inner surface of the first portion and the first inner surface of the second portion. A first center surface region is positioned between the first portion and the second portion of the first outer layer. The fourth inner surface contacts the second inner surface of the third portion and the second inner surface of the fourth portion. A second center surface region is positioned between the third portion and the fourth portion of the second outer layer. The first center surface region is recessed from the first main surface by a first distance. The second center surface region is recessed from the second main surface by a second distance.

[0016] Embodiment 2: The foldable substrate as described in Embodiment 1, wherein the core layer has a core thermal expansion coefficient that is greater than the first thermal expansion coefficient of the first outer layer. The core thermal expansion coefficient is greater than the second thermal expansion coefficient of the second outer layer.

[0017] Embodiment 3: The foldable substrate as described in Embodiment 2, wherein the first coefficient of thermal expansion is substantially equal to the second coefficient of thermal expansion.

[0018] Embodiment 4: A foldable substrate as described in any one of Embodiments 2 to 3, wherein the coefficient of thermal expansion of the core is greater than the first coefficient of thermal expansion by at least about 10 × 10⁻⁶. -7 ℃ -1 Approximately 70×10 -7 ℃ -1 .

[0019] Embodiment 5: A foldable substrate as described in any one of Embodiments 1 to 4, wherein the core density of the core layer is greater than the first density of the first outer layer. The core density is greater than the second density of the second outer layer.

[0020] Embodiment 6: The foldable substrate as described in Embodiment 5, wherein the core density is approximately 0.01 g / cm³ greater than the first density. 3 (Approximately 0.05 g / cm³)

[0021] Embodiment 7: A foldable substrate as described in any one of Embodiments 5 to 6, wherein the first density is substantially equal to the second density.

[0022] Embodiment 8: A foldable substrate as described in any one of Embodiments 1 to 7, wherein the core network expansion coefficient of the core layer is less than the first network expansion coefficient of the first outer layer. The core network expansion coefficient is less than the second network expansion coefficient of the second outer layer.

[0023] Embodiment 9: The foldable substrate as described in Embodiment 8, wherein the first network expansion coefficient is substantially equal to the second network expansion coefficient.

[0024] Embodiment 10: A foldable substrate as described in any one of Embodiments 1 to 9, wherein the first minimum distance is in the range of about 5 mm to about 50 mm.

[0025] Embodiment 11: A foldable substrate as described in any one of Embodiments 1 to 10, wherein the first minimum distance is substantially equal to the second minimum distance.

[0026] Embodiment 12: A foldable substrate as described in any one of Embodiments 1 to 11, wherein the first outer thickness is substantially equal to the second outer thickness.

[0027] Embodiment 13: A foldable substrate as described in any one of Embodiments 1 to 12, wherein the thickness of the substrate is in the range of about 125 micrometers to about 200 micrometers.

[0028] Embodiment 14: A foldable substrate as described in any one of Embodiments 1 to 13, wherein the center thickness is in the range of about 25 micrometers to about 60 micrometers.

[0029] Embodiment 15: A foldable substrate as described in any one of Embodiments 1 to 14, wherein the first outer layer comprises a glass-based substrate.

[0030] Embodiment 16: A foldable substrate as described in any one of Embodiments 1 to 14, wherein the first outer layer comprises a ceramic-based substrate.

[0031] Embodiment 17: A foldable substrate as described in any one of Embodiments 1 to 16, wherein the core layer comprises a glass-based substrate.

[0032] Embodiment 18: A foldable substrate as described in any one of Embodiments 1 to 16, wherein the core layer comprises a ceramic-based substrate.

[0033] Embodiment 19: The foldable substrate as described in any one of Embodiments 1 to 17 further comprises a coating disposed above the first main surface and filling a recess defined between the first central surface region and the first plane defined by the first main surface.

[0034] Embodiment 20: A foldable substrate as described in any one of Embodiments 1 to 19, wherein the first outer layer contains a first average potassium concentration based on oxides, the second outer layer contains a second average potassium concentration based on oxides, and the central portion of the core layer located between the first central surface region and the second central surface region contains a central average potassium concentration based on oxides. The absolute difference between the first average potassium concentration and the central average potassium concentration is about 100 parts per million or less.

[0035] Embodiment 21: The foldable substrate as described in Embodiment 20, wherein the absolute difference between the second average potassium concentration and the central average potassium concentration is about 100 parts per million or less.

[0036] Embodiment 22: The foldable substrate as described in any one of Embodiments 1 to 21 further includes a first compressive stress region extending from the first portion of the first outer layer at the first main surface to a first compression depth. The foldable substrate includes a second compressive stress region extending from the third portion of the second outer layer at the second main surface to a second compression depth. The foldable substrate includes a third compressive stress region extending from the second portion of the first outer layer at the first main surface to a third compression depth. The foldable substrate includes a fourth compressive stress region extending from the fourth portion of the second outer layer at the second main surface to a fourth compression depth. The foldable substrate includes a first central compressive stress region extending from the first central surface region to a first central compression depth. The foldable substrate includes a second central compressive stress region extending from the second central surface region to a second central compression depth.

[0037] Embodiment 23: The foldable substrate as described in Embodiment 22, wherein the absolute difference between the first compression depth as a percentage of the substrate thickness and the first center compression depth as a percentage of the center thickness is about 1% or less.

[0038] Embodiment 24: A foldable substrate as described in any one of Embodiments 22 to 23, wherein the absolute difference between the third compression depth as a percentage of the substrate thickness and the first center compression depth as a percentage of the center thickness is about 1% or less.

[0039] Embodiment 25: A foldable substrate as described in any one of Embodiments 22 to 24, wherein the absolute difference between the second compression depth as a percentage of the substrate thickness and the second center compression depth as a percentage of the center thickness is about 1% or less.

[0040] Embodiment 26: A foldable substrate as described in any one of Embodiments 22 to 25, wherein the absolute difference between the fourth compression depth as a percentage of the substrate thickness and the second center compression depth as a percentage of the center thickness is about 1% or less.

[0041] Embodiment 27: A foldable substrate as described in any one of Embodiments 22 to 26, wherein the first portion comprises a first layer depth of one or more alkali metal ions associated with the first compression depth. The third portion comprises a second layer depth of one or more alkali metal ions associated with the second compression depth. The second portion comprises a third layer depth of one or more alkali metal ions associated with the third compression depth. The fourth portion comprises a fourth layer depth of one or more alkali metal ions associated with the fourth compression depth. The central portion comprises a first central layer depth of one or more alkali metal ions associated with the first central compression depth. The central portion comprises a second central layer depth of one or more alkali metal ions associated with the 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 about 0.5% or less.

[0042] Embodiment 28: The foldable substrate as described in Embodiment 27, wherein the absolute difference between the depth of the third layer as a percentage of the substrate thickness and the depth of the first center layer as a percentage of the center thickness is about 0.5% or less.

[0043] Embodiment 29: A foldable substrate as described in any one of Embodiments 27 to 28, wherein the absolute difference between the second layer depth as a percentage of the substrate thickness and the second center layer depth as a percentage of the center thickness is about 0.5% or less.

[0044] Embodiment 30: A foldable substrate as described in any one of Embodiments 27 to 29, wherein the absolute difference between the depth of the fourth layer as a percentage of the thickness of the substrate and the depth of the second center layer as a percentage of the center thickness is about 0.5% or less.

[0045] Embodiment 31: A foldable substrate as described in any one of Embodiments 1 to 30, wherein the second central surface region is recessed from the second main surface region by a second distance. The second distance is approximately 5% to approximately 20% of the substrate thickness.

[0046] Embodiment 32: The foldable substrate as described in Embodiment 31, wherein the first distance is substantially equal to the second distance.

[0047] Embodiment 33: A foldable substrate comprising a substrate thickness defined between a first main surface and a second main surface opposite to the first main surface. The substrate thickness is in the range of about 100 micrometers to about 2 millimeters. The foldable substrate includes a first portion comprising the substrate thickness. The first portion includes a first compressive stress region extending from the first main surface to a first compression depth. The first portion includes a second compressive stress region extending from the second main surface to a second compression depth. The first portion includes a first layer depth of one or more alkali metal ions associated with the first compression depth. The first portion includes a second layer depth of one or more alkali metal ions associated with the second compression depth. The foldable substrate includes a second portion comprising the substrate thickness. The second portion includes a third compressive stress region extending from the first main surface to a third compression depth. The second portion includes a fourth compressive stress region extending from the second main surface to a fourth compression depth. The second portion includes a third layer depth of one or more alkali metal ions associated with the third compression depth. The second portion includes a fourth layer depth of one or more alkali metal ions associated with the fourth compression depth. The foldable substrate includes a central portion positioned between the first portion and the second portion. The central portion includes a central thickness defined between a first central surface region and a second central surface region opposite to the first central surface region. The central portion includes a first central compressive stress region extending from the first central surface region to a first central compressive depth. The central portion includes a second central compressive stress region extending from the second central surface region to a second central compressive depth. The central portion includes a first central layer depth of one or more alkali metal ions associated with the first central compressive depth. The central portion includes a second central layer depth of the one or more alkali metal ions associated with the second central compressive depth. The central thickness is in the range of about 25 micrometers to about 80 micrometers. The first central surface region is recessed from the first main surface by a first distance. 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 about 0.5% or less.

[0048] Embodiment 34: The foldable substrate as described in Embodiment 33, wherein the absolute difference between the depth of the third layer as a percentage of the substrate thickness and the depth of the first center layer as a percentage of the center thickness is about 0.5% or less.

[0049] Embodiment 35: A foldable substrate as described in any one of Embodiments 33 to 34, wherein the absolute difference between the second layer depth as a percentage of the substrate thickness and the second center layer depth as a percentage of the center thickness is about 0.5% or less.

[0050] Embodiment 36: A foldable substrate as described in any one of Embodiments 33 to 35, wherein the absolute difference between the depth of the fourth layer as a percentage of the thickness of the substrate and the depth of the second center layer as a percentage of the center thickness is about 0.5% or less.

[0051] Embodiment 37: A foldable substrate as described in any one of Embodiments 33 to 36, wherein the first portion contains a first average potassium concentration based on oxides, the second portion contains a second average potassium concentration based on oxides, and the central portion contains a central average potassium concentration based on oxides. The absolute difference between the first average potassium concentration and the central average potassium concentration is about 100 parts per million or less.

[0052] Embodiment 38: A foldable substrate includes a substrate thickness defined between a first main surface and a second main surface opposite to the first main surface. The substrate thickness is in the range of about 100 micrometers to about 2 millimeters. The foldable substrate includes a first portion comprising the substrate thickness. The first portion comprises a first average potassium concentration based on oxides. The first portion includes a first compressive stress region extending from the first main surface to a first compression depth. The first portion includes a second compressive stress region extending from the second main surface to a second compression depth. The foldable substrate includes a second portion comprising the substrate thickness. The second portion comprises a second average potassium concentration based on oxides. The second portion includes a third compressive stress region extending from the first main surface to a third compression depth. The second portion includes a fourth compressive stress region extending from the second main surface to a fourth compression depth. The foldable substrate includes a central portion located between the first portion and the second portion. The central portion includes a central thickness defined between a first central surface region and a second central surface region opposite to the first central surface region. The central portion comprises a central average potassium concentration based on oxides. The central portion includes a first central compressive stress region extending from the first central surface region to a first central compressive depth. The central portion also includes a second central compressive stress region extending from the second central surface region to a second central compressive depth. The central thickness ranges from approximately 25 micrometers to approximately 80 micrometers. The first central surface region is recessed from the first main surface by a first distance. The absolute difference between the first average potassium concentration and the central average potassium concentration is approximately 100 parts per million or less.

[0053] Embodiment 39: A foldable substrate as described in any one of Embodiments 37 to 38, wherein the absolute difference between the second average potassium concentration and the central average potassium concentration is about 100 parts per million or less.

[0054] Embodiment 40: A foldable substrate as described in any one of Embodiments 33 to 39, wherein the absolute difference between the first compression depth as a percentage of the substrate thickness and the first center compression depth as a percentage of the center thickness is about 1% or less.

[0055] Embodiment 41: A foldable substrate includes a substrate thickness defined between a first main surface and a second main surface opposite to the first main surface. The substrate thickness is in the range of about 100 micrometers to about 2 millimeters. The foldable substrate includes a first portion including the substrate thickness. The first portion includes a first compressive stress region extending from the first main surface to a first compression depth. The first portion includes a second compressive stress region extending from the second main surface to a second compression depth. The foldable substrate includes a second portion including the substrate thickness. The second portion includes a third compressive stress region extending from the first main surface to a third compression depth. The second portion includes a fourth compressive stress region extending from the second main surface to a fourth compression depth. The foldable substrate includes a central portion including a central thickness defined between a first central surface region and a second central surface region opposite to the first central surface region. The central portion includes a first central compressive stress region extending from the first central surface region to a first central compression depth. The central portion includes a second central compressive stress region extending from the second central surface region to a second central compression depth. The center thickness ranges from about 25 micrometers to about 80 micrometers. The first center surface region is recessed from the first main surface by a first distance. The center portion is located between the first portion and the second portion. The absolute difference between the first compression depth as a percentage of the substrate thickness and the first center compression depth as a percentage of the center thickness is about 1% or less.

[0056] Embodiment 42: A foldable substrate as described in any one of Embodiments 40 to 41, wherein the absolute difference between the third compression depth as a percentage of the substrate thickness and the first center compression depth as a percentage of the center thickness is about 1% or less.

[0057] Embodiment 43: A foldable substrate as described in any one of Embodiments 40 to 42, wherein the absolute difference between the second compression depth as a percentage of the substrate thickness and the second center compression depth as a percentage of the center thickness is about 1% or less.

[0058] Embodiment 44: A foldable substrate as described in any one of Embodiments 40 to 43, wherein the absolute difference between the fourth compression depth as a percentage of the substrate thickness and the second center compression depth as a percentage of the center thickness is about 1% or less.

[0059] Embodiment 45: A foldable substrate as described in any one of Embodiments 33 to 44, wherein the thickness of the substrate is in the range of about 125 micrometers to about 200 micrometers.

[0060] Embodiment 46: A foldable substrate as described in any one of Embodiments 33 to 45, wherein the center thickness is in the range of about 25 micrometers to about 60 micrometers.

[0061] Embodiment 47: A foldable substrate as described in any one of Embodiments 33 to 46, wherein the foldable substrate comprises a glass-based substrate.

[0062] Embodiment 48: A foldable substrate as described in any one of Embodiments 33 to 46, wherein the foldable substrate comprises a ceramic-based substrate.

[0063] Embodiment 49: A foldable substrate as described in any one of Embodiments 33 to 48, wherein the second central surface region is recessed from the second main surface by a second distance.

[0064] Embodiment 50: The foldable substrate as described in Embodiment 49, wherein the second distance is from about 5% to about 20% of the thickness of the substrate.

[0065] Embodiment 51: A foldable substrate as described in any one of Embodiments 49 to 50, wherein the first distance is substantially equal to the second distance.

[0066] Embodiment 52: A foldable substrate as described in any one of Embodiments 49 to 51, wherein the second main surface includes the second central surface region.

[0067] Embodiment 53: A foldable substrate as described in any one of Embodiments 22 to 52, wherein the first compressive stress region contains a first maximum compressive stress of approximately 700 MPa or greater. The second compressive stress region contains a second maximum compressive stress. The third compressive stress region contains a third maximum compressive stress of approximately 700 MPa or greater. The fourth compressive stress region contains a fourth maximum compressive stress. The first central compressive stress region contains a first central maximum compressive stress of approximately 700 MPa or greater. The second central compressive stress region contains a second central maximum compressive stress.

[0068] Embodiment 54: The foldable substrate as described in Embodiment 53, wherein the second maximum compressive stress is approximately 700 MPa or greater. The fourth maximum compressive stress is approximately 700 MPa or greater. The second central maximum compressive stress is approximately 700 MPa or greater.

[0069] Embodiment 55: The foldable substrate as described in any one of Embodiments 22 to 53 further includes a first tensile stress region located in the first portion between the first compressive stress region and the second compressive stress region. The first tensile stress region includes a first maximum tensile stress. The foldable substrate includes a second tensile stress region located in the second portion between the third compressive stress region and the fourth compressive stress region. The second tensile stress region includes a second maximum tensile stress. The foldable substrate includes a central tensile stress region located in the central portion between the first central compressive stress region and the second central compressive stress region. The central tensile stress region includes a central maximum tensile stress. The absolute difference between the central maximum tensile stress and the first maximum tensile stress is about 10 MPa or less.

[0070] Embodiment 56: The foldable substrate as described in Embodiment 55, wherein the absolute difference between the maximum tensile stress at the center and the second maximum tensile stress is about 10 megapascals or less.

[0071] Embodiment 57: A foldable substrate as described in any one of Embodiments 55 to 56, wherein the first maximum tensile stress is substantially equal to the second maximum tensile stress.

[0072] Embodiment 58: A foldable substrate as described in any one of Embodiments 22 to 57, wherein the central portion further includes a central tensile stress region located between a portion of the first central surface region and a portion of the second central surface region. The central tensile stress region includes a central maximum tensile stress. The central portion includes a first transition portion attaching the first central main surface to the first portion. The first transition portion includes a first transition tensile stress region containing a first transition maximum tensile stress. The central portion includes a second transition portion attaching the first central main surface to the second portion. The second transition portion includes a second transition tensile stress region containing a second transition maximum tensile stress. The first transition maximum tensile stress is greater than the central maximum tensile stress.

[0073] Embodiment 59: The foldable substrate as described in Embodiment 58, wherein the second transition maximum tensile stress is greater than the central maximum tensile stress.

[0074] Embodiment 60: The foldable substrate as described in any one of Embodiments 58 to 59 further includes a first tensile stress region located in the first portion between the first compressive stress region and the second compressive stress region. The first tensile stress region includes a first maximum tensile stress. The first transition maximum tensile stress is greater than the first maximum tensile stress.

[0075] Embodiment 61: The foldable substrate as described in any one of Embodiments 58 to 60 further includes a second tensile stress region located in the second portion between the third compressive stress region and the fourth compressive stress region. The foldable substrate includes the second tensile stress region, which includes a second maximum tensile stress. The second maximum tensile stress is greater than the second maximum tensile stress.

[0076] Embodiment 62: A foldable substrate as described in any one of Embodiments 1 to 61, wherein the first distance is about 20% to about 45% of the thickness of the substrate.

[0077] Embodiment 63: A foldable substrate as described in any one of Embodiments 1 to 62, wherein the thickness of the substrate is at least 71 micrometers greater than about four times the thickness of the center.

[0078] Embodiment 64: A foldable substrate as described in any one of Embodiments 1 to 63, wherein the substrate achieves an effective bending radius of 5 mm.

[0079] Embodiment 65: A foldable device comprising a foldable substrate as described in any one of Embodiments 1 to 64. The foldable device includes an adhesive having a first contact surface and a second contact surface opposite the first contact surface. At least a portion of the adhesive is positioned in a recess defined between the second central surface region and a second plane defined by the second primary surface.

[0080] Embodiment 66: A foldable device comprising a foldable substrate as described in any one of Embodiments 1 to 64. The foldable device includes a polymer-based portion positioned in a recess defined between a second central surface region and a second plane defined by the second main surface. The foldable device includes an adhesive comprising a first contact surface and a second contact surface opposite the first contact surface.

[0081] Embodiment 67: A foldable device as described in Embodiment 66, wherein the polymer-based portion contains a yield strain ranging from about 5% to about 10%.

[0082] Embodiment 68: A foldable device as described in any one of Embodiments 66 to 67, wherein the difference between the refractive index of the foldable substrate and the refractive index of the polymer-based portion is about 0.1 or less.

[0083] Embodiment 69: A foldable device as described in any one of Embodiments 65 to 68, wherein the difference between the refractive index of the substrate and the refractive index of the adhesive is about 0.1 or less.

[0084] Embodiment 70: The foldable device as described in any one of Embodiments 65 to 69 further includes a display device attached to the second contact surface of the adhesive.

[0085] Embodiment 71: A consumer electronic product includes a housing comprising a front surface, a rear surface, and side surfaces. The consumer electronic product includes electrical components at least partially within the housing. The electrical components include a controller, a memory, and a display. The display is located on or adjacent to the front surface of the housing. The consumer electronic product includes a cover substrate disposed above the display. A portion of the housing or at least one of the cover substrates includes a foldable substrate as described in any one of Embodiments 1 to 64.

[0086] Embodiment 72: A method of manufacturing a foldable substrate, the foldable substrate comprising a core layer positioned between and in contact with a first outer layer and a second outer layer. The substrate thickness is defined between a first main surface and a second main surface. The first outer layer defines the first main surface, and the second outer layer defines a second main surface opposite to the first main surface. The method comprises etching a portion of the first main surface to form a first central surface region of the core layer. The method comprises etching a portion of the second main surface to form a second central surface region of the core layer. The central portion comprises a central thickness defined between the first central surface region and the second central surface region. The first central surface region of the core layer in the central portion is positioned between a first portion and a second portion of the first outer layer. The second central surface region of the core layer in the central portion is positioned between a third portion and a fourth portion of the second outer layer.

[0087] Embodiment 73: A method of manufacturing a foldable substrate includes stretching a core layer. The method includes stretching a first outer layer and a second outer layer. The method includes laminating the first outer layer to a third inner surface of the core layer and laminating the second outer layer to a fourth inner surface of the core layer. The first outer layer defines a first main surface, and the second outer layer defines a second main surface opposite to the first main surface. A substrate thickness is defined between the first main surface and the second main surface. During the lamination, the first outer layer includes a first temperature above its softening point, the second outer layer includes a second temperature above its softening point, and the core layer includes a third temperature above its softening point. The method then includes etching a portion of the first main surface to form a first central surface region of the core layer. The method includes etching a portion of the second main surface to form a second central surface region of the core layer. The foldable substrate includes a central portion having a central thickness defined between the first central surface region and the second central surface region. The first central surface region is located between the first portion and the third portion of the first outer layer. The second central surface region is located between the second portion and the fourth portion of the second outer layer.

[0088] Embodiment 74: The method of any one of Embodiments 72 to 73, wherein the first outer layer comprises a first existing average potassium concentration based on oxides. The core layer comprises a core having an existing average potassium concentration based on oxides. The core having an average potassium concentration is approximately 10 parts per million or greater than the first existing average potassium concentration.

[0089] Implementation 75: The method as described in Implementation 74, wherein the second outer layer comprises a second existing average potassium concentration based on oxides, and the core has an average potassium concentration that is approximately 10 parts per million or greater than the second existing average potassium concentration.

[0090] Implementation 76: The method of any one of Implementations 72 to 75, wherein the first outer layer comprises a first existing average lithium concentration based on oxide, the core layer comprises a core existing average lithium concentration based on oxide, and the first existing average lithium concentration is approximately 10 parts per million or greater than the core existing average lithium concentration.

[0091] Embodiment 77: The method of any one of Embodiments 72 to 76 further includes chemically strengthening the foldable substrate after etching the portion of the first main surface and the portion of the second main surface.

[0092] Embodiment 78: A method of manufacturing a foldable substrate, the foldable substrate comprising a core layer positioned between and in contact with a first outer layer and a second outer layer. A substrate thickness is defined between a first main surface of the first outer layer and a second main surface of the second outer layer. The core layer includes a central portion having a central thickness defined between a first central surface region and a second central surface region. The first central surface region of the core layer in the central portion is positioned between a first portion and a second portion of the first outer layer. The second central surface region of the core layer in the central portion is positioned between a third portion and a fourth portion of the second outer layer. The method includes chemically strengthening the foldable substrate.

[0093] Embodiment 79: The method of any one of Embodiments 77 to 78, wherein, prior to the chemical strengthening, the first outer layer comprises a first diffusivity of one or more alkali metal ions. The core layer comprises a core diffusivity of one or more alkali metal ions, and the first diffusivity is greater than the core diffusivity.

[0094] Implementation 80: The method as described in Implementation 79, wherein the first ratio comprises the square root of the first diffusivity divided by the first thickness, the first thickness being defined between the first main surface and the first inner surface of the first outer layer. The core ratio comprises the square root of the core diffusivity divided by the center thickness, and the absolute difference between the first ratio and the core ratio is approximately 0.01s. -0.5 Or smaller.

[0095] Embodiment 81: The method as described in Embodiment 80, wherein the second ratio comprises the square root of the second diffusivity of one or more alkali metal ions of the second outer layer divided by the second thickness defined between the second main surface and the second inner surface of the second portion. The absolute difference between the second ratio and the core ratio is approximately 0.01 s. -0.5 Or smaller.

[0096] Embodiment 82: The method of any one of Embodiments 77 to 81, wherein, after the chemical fortification, the first outer layer comprises a first average potassium concentration based on oxides. The second outer layer comprises a second average potassium concentration based on oxides. The central portion located between the first central surface region and the second central surface region comprises a central average potassium concentration based on oxides. The absolute difference between the first average potassium concentration and the central average potassium concentration is about 100 parts per million or less.

[0097] Embodiment 83: The method of any one of Embodiments 77 to 82, wherein the chemical strengthening includes forming a first compressive stress region extending from a first portion of the first outer layer at the first main surface to a first compression depth. The method includes forming a second compressive stress region extending from a third portion of the second outer layer at the second main surface to a second compression depth. The method includes forming a third compressive stress region extending from a second portion of the first outer layer at the first main surface to a third compression depth. The method includes forming a fourth compressive stress region extending from a fourth portion of the second outer layer at the second main surface to a fourth compression depth. The method includes forming a first central compressive stress region extending from the first central surface region to a first central compression depth. The method includes forming a second central compressive stress region extending from the second central surface region to a second central compression depth.

[0098] Embodiment 84: The method as described in Embodiment 83, wherein the absolute difference between the first compression depth as a percentage of the substrate thickness and the first center compression depth as a percentage of the center thickness is about 1% or less.

[0099] Embodiment 85: The method as described in any one of Embodiments 83 to 84, wherein the absolute difference between the third compression depth as a percentage of the substrate thickness and the first center compression depth as a percentage of the center thickness is about 1% or less.

[0100] Embodiment 86: The method as described in any one of Embodiments 83 to 85, wherein the absolute difference between the second compression depth as a percentage of the substrate thickness and the second center compression depth as a percentage of the center thickness is about 1% or less.

[0101] Embodiment 87: The method as described in any one of Embodiments 83 to 86, wherein the absolute difference between the fourth compression depth as a percentage of the substrate thickness and the second center compression depth as a percentage of the center thickness is about 1% or less.

[0102] Embodiment 88: The method of any one of Embodiments 83 to 87, wherein the first portion comprises a first layer depth of one or more alkali metal ions associated with the first compression depth. The third portion comprises a second layer depth of one or more alkali metal ions associated with the second compression depth. The second portion comprises a third layer depth of one or more alkali metal ions associated with the third compression depth. The fourth portion comprises a fourth layer depth of one or more alkali metal ions associated with the fourth compression depth. The central portion comprises a first central layer depth of one or more alkali metal ions associated with the first central compression depth. The central portion comprises a second central layer depth of one or more alkali metal ions associated with the 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 about 0.5% or less.

[0103] Implementation 89: The method as described in Implementation 88, wherein the absolute difference between the depth of the third layer as a percentage of the thickness of the substrate and the depth of the first center layer as a percentage of the center thickness is about 0.5% or less.

[0104] Embodiment 90: The method as described in any one of Embodiments 88 to 89, wherein the absolute difference between the second layer depth as a percentage of the substrate thickness and the second center layer depth as a percentage of the center thickness is about 0.5% or less.

[0105] Embodiment 91: The method as described in any one of Embodiments 88 to 89, wherein the absolute difference between the depth of the fourth layer as a percentage of the thickness of the substrate and the depth of the second center layer as a percentage of the center thickness is about 0.5% or less.

[0106] Embodiment 92: The method as described in any one of Embodiments 72 to 91, wherein the core layer has a core thermal expansion coefficient that is greater than the first thermal expansion coefficient of the first outer layer. The core thermal expansion coefficient is greater than the second thermal expansion coefficient of the second outer layer.

[0107] Embodiment 93: The method as described in any one of Embodiments 72 to 92, wherein the core density of the core layer is greater than the first density of the first outer layer. The core density is greater than the second density of the second outer layer.

[0108] Implementation 94: The method as described in any one of Implementations 72 to 93, wherein the core network expansion coefficient of the core layer is less than the first network expansion coefficient of the first outer layer. The core network expansion coefficient is less than the second network expansion coefficient of the second outer layer.

[0109] Embodiment 95: A method of manufacturing a foldable substrate, the foldable substrate comprising a substrate thickness defined between a first main surface and a second main surface opposite to the first main surface. The method comprises chemically strengthening the foldable substrate for a first time period. The method then comprises etching a portion of the first main surface to form a first central surface region. The method comprises etching a portion of the second main surface to form a second central surface region. The method further comprises further chemically strengthening the foldable substrate for a second time period. A central portion comprises a central thickness defined between the first central surface region and the second central surface region. The central portion is positioned between the first portion and the second portion. The first central surface region is recessed from the first main surface by a first distance. The second central surface region is recessed from the second main surface by a second distance. After the further chemical strengthening, the foldable substrate comprises a first compressive stress region of the first portion extending from the first main surface to a first compression depth. The foldable substrate comprises a second compressive stress region of the third portion extending from the second main surface to a second compression depth. The foldable substrate includes a third compressive stress region in the second portion, extending from the first main surface to a third compression depth. The foldable substrate includes a fourth compressive stress region in the fourth portion, extending from the second main surface to a fourth compression depth. The foldable substrate includes a first central compressive stress region in the central portion, extending from the first central surface area to a first central compression depth. The foldable substrate includes a second central compressive stress region in the central portion, extending from the second central surface area to a second central compression depth.

[0110] Embodiment 96: A method of manufacturing a foldable substrate, the foldable substrate comprising a substrate thickness defined between a first main surface and a second main surface opposite to the first main surface. The method comprises chemically strengthening the foldable substrate for a first time period. Next, the method comprises etching an existing first central surface region to form a first central surface region. The existing first central surface region is not coplanar with the first main surface. The method comprises etching an existing second central surface region to form a second central surface region. Next, the method further comprises further chemically strengthening the foldable substrate for a second time period. A central portion comprises a central thickness defined between the first central surface region and the second central surface region. The central portion is positioned between the first portion and the second portion. The first central surface region is recessed from the first main surface by a first distance. After the further chemical strengthening, the foldable substrate comprises a first compressive stress region of the first portion extending from the first main surface to a first compression depth. The foldable substrate comprises a second compressive stress region of the third portion extending from the second main surface to a second compression depth. The foldable substrate includes a third compressive stress region in the second portion, extending from the first main surface to a third compression depth. The foldable substrate includes a fourth compressive stress region in the fourth portion, extending from the second main surface to a fourth compression depth. The foldable substrate includes a first central compressive stress region in the central portion, extending from the first central surface area to a first central compression depth. The foldable substrate includes a second central compressive stress region in the central portion, extending from the second central surface area to a second central compression depth.

[0111] Implementation 97: The method as described in Implementation 96, wherein prior to etching the first central surface area, the existing first central surface area is recessed from the first main surface by a first existing distance, the first existing distance ranging from about 10% to about 75% of the substrate thickness.

[0112] Implementation 98: The method of any one of Implementations 96 to 97, wherein the existing second center surface region is substantially coplanar with the second main surface region before the etching of the existing second center surface region.

[0113] Implementation 99: The method of any one of Implementations 96 to 97, wherein prior to etching the existing second central surface area, the existing second central surface area is recessed from the second main surface by a second existing distance ranging from about 1% to about 50%.

[0114] Implementation 100: The method as described in any one of Implementations 96 to 99, wherein the second central surface region is recessed from the second main surface by a second distance.

[0115] Implementation 101: The method as described in any one of Implementations 97 to 98, wherein the existing second center surface region protrudes from the second main surface before the existing second center surface region is etched.

[0116] Implementation 102: The method as described in Implementation 101, wherein after etching the existing second central surface area, the second central surface area is substantially coplanar with the second main surface.

[0117] Implementation 103: The method as described in Implementation 95 or Implementation 100, wherein the first distance is substantially equal to the second distance.

[0118] Embodiment 104: The method as described in Embodiment 95 or Embodiment 100, wherein the second distance is about 5% to about 20% of the thickness of the substrate.

[0119] Embodiment 105: The method of any one of Embodiments 95 to 104, wherein the first distance is about 20% to about 45% of the thickness of the substrate.

[0120] Implementation 106: The method of any one of Implementations 95 to 105, wherein the square root of the ratio of the second time period to the first time period is related to the center thickness divided by the difference between the substrate thickness and the center thickness within 10%.

[0121] Implementation 107: The method as described in Implementation 106, wherein the square root of the ratio of the second time period to the first time period is substantially equal to the center thickness divided by the difference between the substrate thickness and the center thickness.

[0122] Implementation 108: The method as described in any one of Implementations 95 to 107, wherein the second time period is about 2% to about 50% of the first time period.

[0123] Embodiment 109: The method of any one of Embodiments 95 to 108, wherein, after the chemical strengthening but before the further chemical strengthening, the first portion includes a first intermediate compressive stress region extending to a first intermediate compressive depth. The first intermediate compressive depth divided by the substrate thickness is in the range of about 10% to about 20%.

[0124] Embodiment 11: The method of any one of Embodiments 95 to 108, wherein, after the chemical strengthening but before the further chemical strengthening, the first portion includes a first intermediate compressive stress region and a first intermediate layer depth from the first main surface to one or more alkali metal ions introduced during the chemical strengthening. The first intermediate layer depth divided by the substrate thickness is in the range of about 10% to about 20%.

[0125] Embodiment 111: The method of any one of Embodiments 95 to 110, wherein, after the further chemical strengthening of the foldable substrate, the first portion includes a first layer depth from the first main surface of one or more alkali metal ions introduced into the first portion during the chemical strengthening and / or the further chemical strengthening. The central portion includes a first central layer depth from the first central surface region of one or more alkali metal ions introduced into the central portion during the further chemical strengthening. 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 about 0.5% or less.

[0126] Embodiment 112: The method as described in Embodiment 111, wherein, after the further chemical strengthening of the foldable substrate, the foldable substrate further includes a third layer depth from the first main surface of one or more alkali metal ions introduced into the second portion during the chemical strengthening and / or the further chemical strengthening. The absolute difference between the third layer depth as a percentage of the substrate thickness and the first center layer depth as a percentage of the center thickness is about 0.5% or less.

[0127] Embodiment 113: The method of any one of Embodiments 111 to 112, wherein the one or more alkali metal ions include potassium ions.

[0128] Embodiment 114: The method of any one of Embodiments 95 to 113, wherein, after the further chemical strengthening of the foldable substrate, the first portion comprises a first average potassium concentration based on oxides. The central portion comprises a central average potassium concentration based on oxides. The absolute difference between the first average potassium concentration and the central average potassium concentration is about 100 parts per million or less.

[0129] Embodiment 115: The method as described in Embodiment 114, wherein, after the further chemical strengthening of the foldable substrate, the second portion comprises a second average potassium concentration based on oxides. The absolute difference between the second average potassium concentration and the central average potassium concentration is about 100 parts per million or less.

[0130] Embodiment 116: The method of any one of Embodiments 95 to 115, wherein, after the further chemical strengthening of the foldable substrate, the absolute difference between the first compression depth as a percentage of the substrate thickness and the first center compression depth as a percentage of the center thickness is about 1% or less.

[0131] Embodiment 117: The method as described in Embodiment 116, wherein, after the further chemical strengthening of the foldable substrate, the absolute difference between the third compression depth as a percentage of the substrate thickness and the first center compression depth as a percentage of the center thickness is about 1% or less.

[0132] Embodiment 118: The method of any one of Embodiments 95 to 117, wherein after the chemical strengthening, the foldable substrate further includes a first tensile stress region located in the first portion between the first compressive stress region and the second compressive stress region. The first tensile stress region includes a first maximum tensile stress. The foldable substrate further includes a second tensile stress region located in the second portion between the third compressive stress region and the fourth compressive stress region. The second tensile stress region includes a second maximum tensile stress. The foldable substrate further includes a central tensile stress region located in the central portion between the first central compressive stress region and the second central compressive stress region. The central tensile stress region includes a central maximum tensile stress. The absolute difference between the central maximum tensile stress and the first maximum tensile stress is about 10 MPa or less.

[0133] Implementation 119: The method as described in Implementation 118, wherein the absolute difference between the central maximum tensile stress and the second maximum tensile stress is about 10 megapascals or less.

[0134] Embodiment 120: The method as described in any one of Embodiments 118 to 119, wherein the first maximum tensile stress is substantially equal to the second maximum tensile stress.

[0135] Embodiment 121: The method of any one of Embodiments 95 to 120, wherein after the chemical strengthening, the central portion further includes a central tensile stress region located between a portion of the first central surface region and a portion of the second central surface region. The central tensile stress region includes a central maximum tensile stress. The central portion includes a first transition portion attaching the first central surface region to the first portion. The first transition portion includes a first transition tensile stress region containing a first transition maximum tensile stress. The central portion includes a second transition portion attaching the first central surface region to the second portion. The second transition portion includes a second transition tensile stress region containing a second transition maximum tensile stress. The first transition maximum tensile stress is greater than the central maximum tensile stress.

[0136] Implementation 122: The method as described in Implementation 121, wherein the second transition maximum tensile stress is greater than the central maximum tensile stress.

[0137] Embodiment 123: The method of any one of Embodiments 121 to 122, wherein after the chemical strengthening, the foldable substrate further includes a first tensile stress region located in the first portion between the first compressive stress region and the second compressive stress region. The first tensile stress region includes a first maximum tensile stress. The first transition maximum tensile stress is greater than the first maximum tensile stress.

[0138] Embodiment 124: The method of any one of Embodiments 121 to 123, wherein after the chemical strengthening, the foldable substrate further includes a second tensile stress region located in the second portion between the third compressive stress region and the fourth compressive stress region. The second tensile stress region includes a second maximum tensile stress. The second transition maximum tensile stress is greater than the second maximum tensile stress.

[0139] Embodiment 125: The method of any one of Embodiments 78 to 124 further includes providing a coating above the first main surface, the coating filling the depression defined between the first central surface region and the first plane defined by the first main surface.

[0140] Embodiment 126: The method of any one of Embodiments 78 to 125 further includes providing an adhesive above the second main surface of the foldable substrate. The adhesive includes a first contact surface and a second contact surface opposite to the first contact surface.

[0141] Embodiment 127: The method as described in Embodiment 126, wherein at least a portion of the adhesive is positioned in a recess defined between the second central surface region and the second plane defined by the second main surface.

[0142] Embodiment 128: The method as described in any one of Embodiments 126 to 127, wherein the difference between the refractive index of the substrate and the refractive index of the adhesive is about 0.1 or less.

[0143] Embodiment 129: The method of any one of Embodiments 126 to 128 further includes attaching the display device to the second contact surface of the adhesive. Attached Figure Description

[0144] The above features and advantages, as well as other features and advantages, of the embodiments of this disclosure will be better understood when the accompanying drawings are consulted and the following detailed description is read, wherein:

[0145] Figure 1 This is a schematic diagram of an exemplary foldable device in a flat configuration according to some embodiments, wherein the schematic diagram of the foldable configuration is as follows: Figure 9 As shown in the image;

[0146] Figures 2 to 8 According to some embodiments, along Figure 1 A cross-sectional view of the foldable device shown in line 2-2;

[0147] Figure 9 This is a schematic diagram of an exemplary foldable device for implementing the present disclosure in a folded configuration, wherein the schematic diagram of the flat configuration may be as follows: Figure 1 As shown in the image;

[0148] Figures 10 to 11 A cross-sectional view of a test apparatus for determining the effective minimum bending radius of an exemplary modified foldable device;

[0149] Figure 12 A schematic diagram of an exemplary foldable device for implementing the present disclosure in a foldable configuration;

[0150] Figure 13 This is a schematic plan view of an exemplary consumer electronic device according to some embodiments;

[0151] Figure 14 for Figure 13 A schematic perspective view of an exemplary consumer electronic device;

[0152] Figures 15 to 18 A flowchart illustrating an exemplary method for manufacturing a foldable device according to an embodiment of the present disclosure;

[0153] Figures 19 to 52 The schematic diagram illustrates the steps in a method of manufacturing a foldable substrate and / or a foldable device;

[0154] Figure 53 Experimental results of pen drop tests on glass-based substrates are shown, illustrating how the maximum principal stress on the main surface of the glass-based substrate varies with the thickness of the glass-based substrate.

[0155] Figure 54 The types of mechanical instabilities observed for foldable devices vary depending on the substrate thickness and the center thickness.

[0156] Figures 55 to 57 These are curves illustrating the results of some embodiments of this disclosure; and

[0157] Figures 58 to 59 The optical hysteresis measurement of a foldable substrate according to an embodiment of the present disclosure is illustrated schematically.

[0158] Throughout this disclosure, accompanying drawings are used to emphasize certain aspects. Therefore, the relative sizes of the different areas, portions, and substrates shown in the drawings should not be assumed to be proportional to their actual relative sizes, unless otherwise expressly indicated. Detailed Implementation

[0159] The embodiments will now be described more fully with reference to the accompanying drawings, which illustrate exemplary embodiments. Wherever possible, the same reference numerals are used throughout the drawings to refer to the same or similar parts. However, the claims may cover many different aspects of various embodiments and should not be construed as limiting oneself to the embodiments set forth herein.

[0160] Figure 1-9 Image and Figure 11-12 The embodiments of this disclosure illustrate views of foldable devices 101, 301, 401, 501, 601, 701, 801, and 1201 and / or test foldable device 1102 comprising foldable substrates 206, 407, or 807. Unless otherwise indicated, the description of features of one embodiment of a foldable device is equally applicable to corresponding features of any embodiment of this disclosure. For example, the same part numbers throughout this disclosure may indicate that identified features are identical to each other in some embodiments, and unless otherwise indicated, the description of identified features of one embodiment is equally applicable to identified features of any other embodiment of this disclosure.

[0161] Figure 2-3 Figures 6 and 7 schematically illustrate exemplary embodiments of foldable devices 101, 301, and 601 according to embodiments of the present disclosure, comprising a foldable substrate 206, in an undisturbed (e.g., flat) configuration. Figure 11 An exemplary embodiment of a test foldable device 1102 comprising a foldable substrate 206 according to an embodiment of the present disclosure is illustrated in a folded configuration. The foldable substrate 206 comprises a laminate including a core layer 207 positioned between a first outer layer 213 and a second outer layer 215. Figure 4-5 and Figure 7 The illustrations schematically depict exemplary embodiments of foldable devices 401, 501, and 701, according to embodiments of the present disclosure, comprising a foldable substrate 407, in an undisturbed (e.g., flat) configuration. Figure 12 A foldable device 1201 comprising a foldable substrate 407 according to an embodiment of the present disclosure, wherein the device is in a folded configuration. Figure 8 The illustration schematically depicts a foldable device 801 comprising a foldable substrate 807 according to an embodiment of the present disclosure in an undisturbed (e.g., flat) configuration.

[0162] Foldable devices 101, 301, 401, 501, 601, 701, 801, and 1201 include a first portion 221, 421, or 821, a second portion 231, 431, or 831, and a central portion 281, 481, or 881 positioned between the first portion 221, 421, or 821 and the second portion 231, 431, or 831. In some embodiments, such as in Figure 2 and 4 As shown, the foldable device 101 or 401 may include a release liner 271, but in other embodiments, other substrates (e.g., glass-based substrates and / or ceramic-based substrates discussed throughout this application) may be used instead of the release liner 271 illustrated. In some embodiments, such as in Figure 1-5 Image and Figure 11-12 As shown, foldable devices 101, 301, 401, 501, and 1201, or test foldable device 1102, may include a coating 251. In some embodiments, such as in... Figure 1-5 Image and Figure 12 As shown, foldable devices 101, 301, 401, 501, and 1201 may include an adhesive layer 261. In some embodiments, such as in... Figure 2 , 5 As shown in Figures 101, 501, and 1201, foldable devices 101, 501, and 1201 may include a polymer-based portion 241. In some embodiments, such as in... Figure 1-12 As shown, the foldable substrate 206, 407, or 807 may include a first recess 234, 434, or 834. In another embodiment, such as in Figure 1-7 As shown in Figures 10-12, the foldable substrate 206 or 407 may further include a second recess 244 or 444. It should be understood that any of the foldable devices of this disclosure may include a second substrate (e.g., a glass-based substrate and / or a ceramic-based substrate), a release liner 271, a display device 307, a coating 251, an adhesive layer 261, and / or a polymer-based portion 241.

[0163] Throughout this disclosure, see [link / reference] Figure 1The width 103 of the foldable devices 101, 301, 401, 501, 601, 701 and / or 801 is considered to be the size of the foldable device obtained in the direction 104 of the folding axis 102 of the foldable device between the opposing edges of the foldable device, wherein the direction 104 also includes the direction of the width 103. Furthermore, throughout this disclosure, the length 105 of the foldable devices 101, 301, 401, 501, 601, 701, and / or 801 is considered to be the dimension of the foldable devices 101, 301, 401, 501, 601, 701, and / or 801 obtained between their opposing edges in a direction 106 perpendicular to the folding axis 102 of the foldable devices 101, 301, 401, 501, 601, 701, and / or 801. In some embodiments, such as in Figure 1-5 As shown in the diagram, any embodiment of the foldable device of this disclosure may include a folding plane 109 including a folding axis 102, and when the foldable device is in a flat configuration (e.g., see...), Figure 1 In some embodiments, plane 109 may include the central axis 107 of the foldable device. In some embodiments, the foldable device may be in direction 111 (e.g., see...). Figure 1 Folding around a folding axis 102 extending in a direction 104 of width 103 to form a folded structure (e.g., see...). Figure 9 and Figure 11-12 As shown, the foldable device may include a single fold axis to allow the foldable device to include a double fold, wherein, for example, the foldable device can be folded in half. In another embodiment, the foldable device may include two or more fold axes, wherein each fold axis includes a corresponding central portion similar to or identical to the central portions 281, 481, or 881 discussed herein. For example, providing two fold axes may allow the foldable device to include a triple fold, wherein, for example, the foldable device can be folded, wherein the first portion 221, 421, or 821, the second portion 231, 431, or 831, and the third portion are similar to the first or second portion having a central portion 281, 481, or 881 respectively positioned between the first and second portions and between the second and third portions, and another central portion (which is similar to or identical to said central portion).

[0164] Foldable devices 101, 301, or 601, including a foldable substrate 206, may include a core layer 207 positioned between a first outer layer 213 and a second outer layer 215. Foldable devices 401, 501, 701, or 801 may include a foldable substrate 407 or 807. In some embodiments, the foldable substrate 407 or 807, the first outer layer 213, the second outer layer 215, and / or the core layer 207 may include a glass-based substrate and / or a ceramic-based substrate having a pencil hardness of 8H or greater (e.g., 9H or greater).

[0165] In some embodiments, the foldable substrate 407 or 807, the first outer layer 213, the second outer layer 215, and / or the core layer 207 may comprise a glass-based substrate. As used herein, “glass-based” includes glass and glass-ceramics, wherein the glass-ceramics have one or more crystalline phases and an amorphous residual glass phase. Glass-based materials (e.g., glass-based substrates) may comprise amorphous materials (e.g., glass) and optionally one or more crystalline materials (e.g., ceramics). Amorphous materials and glass-based materials may be strengthened. As used herein, the term “strengthened” may refer to a chemically strengthened material, for example, via ion exchange between larger and smaller ions on the substrate surface, as discussed below. However, strengthened substrates may be formed using other strengthening methods (e.g., heat tempering, or utilizing the mismatch of thermal expansion coefficients between portions of the substrate to generate compressive stress and a central tension region). Exemplary glass-based materials, which may be free of or contain lithium oxide, include soda-lime glass, alkali aluminosilicate glass, alkali borosilicate glass, alkali aluminoborosilicate glass, alkali phosphosilicate glass, and alkali aluminophosphosilicate glass. In one or more embodiments, the glass-based material may comprise, in molar percentage (mol%), SiO2 in the range of about 40 mol% to about 80%, Al2O3 in the range of about 5 mol% to about 30 mol%, B2O3 in the range of about 0 mol% to about 10 mol%, ZrO2 in the range of about 0 mol% to about 5 mol%, P2O5 in the range of about 0 mol% to about 15 mol%, TiO2 in the range of about 0 mol% to about 2 mol%, R2O in the range of about 0 mol% to about 20 mol%, and RO in the range of about 0 mol% to about 15 mol%. As used herein, R₂O may refer to alkali metal oxides, such as Li₂O, Na₂O, K₂O, Rb₂O, and Cs₂O. As used herein, RO may refer to MgO, CaO, SrO, BaO, and ZnO. In some embodiments, the glass-based substrate may optionally further comprise each of the following in the range of from about 0 mol% to about 2 mol%: Na₂SO₄, NaCl, NaF, NaBr, K₂SO₄, KCl, KF, KBr, As₂O₃, Sb₂O₃, SnO₂, Fe₂O₃, MnO, MnO₂, MnO₃, Mn₂O₃, Mn₃O₄, and Mn₂O₇. “Glass ceramics” include materials produced via controlled crystallization of glass. In some embodiments, the glass ceramics have a crystallinity of from about 1% to about 99%.Suitable examples of glass-ceramics may include Li₂O-Al₂O₃-SiO₂ system (i.e., LAS system) glass-ceramics, MgO-Al₂O₃-SiO₂ system (i.e., MAS system) glass-ceramics, ZnO×Al₂O₃×nSiO₂ (i.e., ZAS system) 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 may be strengthened using a chemical strengthening process. In one or more embodiments, the MAS system glass-ceramic substrate may be strengthened in Li₂SO₄ molten salt, thereby generating 2Li. + With Mg 2+ The exchange.

[0166] In some embodiments, the foldable substrate 407 or 807, the first outer layer 213, the second outer layer 215, and / or the core layer 207 may comprise a ceramic-based substrate. As used herein, "ceramic-based" includes ceramics and glass-ceramics, wherein the glass-ceramic has one or more crystalline phases and an amorphous residual glass phase. The ceramic-based material may be strengthened (e.g., chemically strengthened). In some embodiments, the ceramic-based material may be formed by heating the glass-based material to form a ceramic (e.g., crystalline) portion. In other embodiments, the ceramic-based material may comprise one or more nucleating agents that promote the formation of the crystalline phase. In some embodiments, the ceramic-based material may comprise one or more oxides, nitrides, oxynitrides, carbides, borides, and / or silicides. Exemplary embodiments of ceramic oxides include zirconium oxide (ZrO2), zirconium oxide (ZrSiO4), alkali metal oxides (e.g., sodium oxide (Na2O)), alkaline earth metal oxides (e.g., magnesium oxide (MgO)), titanium oxide (TiO2), hafnium oxide (Hf2O), yttrium oxide (Y2O3), iron oxides, beryllium oxide, vanadium oxide (VO2), fused silica, aluminum-rich andalusite (a mineral comprising a combination of alumina and silicon dioxide), and spinel (MgAl2O4). Exemplary embodiments of ceramic nitrides include silicon nitride (Si3N4), aluminum nitride (AlN), gallium nitride (GaN), beryllium nitride (Be3N2), boron nitride (BN), tungsten nitride (WN), vanadium nitride, alkaline earth metal nitrides (e.g., magnesium nitride (Mg3N2)), nickel nitride, and tantalum nitride. Exemplary embodiments of oxynitride ceramics include silicon oxynitride, aluminum oxynitride, and SiAlON (a combination of aluminum oxide and silicon nitride, and may contain, for example, 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 Aln O 1+n N 2-n The chemical formulas of the compounds are given, 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 (B4C), alkali metal carbides (e.g., lithium carbide (Li4C3)), alkaline earth metal carbides (e.g., magnesium carbide (Mg2C3)), and graphite. Exemplary embodiments of borides include chromium boride (CrB2), molybdenum boride (MO2B5), tungsten boride (W2B5), iron boride, titanium boride, zirconium boride (ZrB2), hafnium boride (HfB2), vanadium boride (VB2), niobium boride (NbB2), and lanthanum boride (LaB6). Exemplary embodiments of silicides include molybdenum disilicide (MoSi2), tungsten disilicide (WSi2), titanium disilicide (TiSi2), nickel disilicide (NiSi), alkaline earth silicides (e.g., sodium silicide (NaSi)), alkali metal silicides (e.g., magnesium silicide (Mg2Si)), hafnium disilicide (HfSi2), and platinum disilicide (PtSi).

[0167] Throughout this disclosure, tensile strength, ultimate elongation (e.g., failure strain), and yield point of polymeric materials (e.g., adhesives, polymer-based components) are determined using a tensile testing machine (e.g., Instron 3400 or Instron 6800) with a type I dog-bone shaped sample at 23°C and 50% relative humidity, using ASTM D638. Throughout this disclosure, the modulus of elasticity (e.g., Young's modulus) and / or Poisson's ratio are measured using ISO 527-1:2019. In some embodiments, the foldable substrate 206, 407, or 807, the first outer layer 213, the second outer layer 215, and / or the core layer 207 may contain a modulus of elasticity of about 1 gigapascal (GPa) or greater, about 3 GPa or greater, about 5 GPa or greater, about 10 GPa or greater, about 100 GPa or less, about 80 GPa or less, about 60 GPa or less, or about 20 GPa or less. In some embodiments, the foldable substrate 206, 407, or 807 may contain an elastic modulus in the range of 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 subrange thereof. In other embodiments, the foldable substrate 206, 407, or 807, the first outer layer 213, the second outer layer 215, and / or the core layer 207 may contain a glass-based portion or a ceramic-based portion containing an elastic modulus in the range of 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 subrange thereof.

[0168] In some embodiments, the foldable substrate 206, 407, or 807, the first outer layer 213, the second outer layer 215, and / or the core layer 207 may be optically transparent. As used herein, "optically transparent" or "optically clear" means an average transmittance of 70% or greater in the wavelength range of 400 nm to 700 nm when passing through a 1.0 mm thick material. In some embodiments, the "optically transparent material" or "optically clear material" may have an average transmittance of 75% or greater, 80% or greater, 85% or greater, or 90% or greater, 92% or greater, 94% or greater, or 96% or greater in the wavelength range of 400 nm to 700 nm when passing through a 1.0 mm thick material. The average transmittance in the wavelength range of 400 nm to 700 nm is calculated by measuring the transmittance at integer wavelengths from about 400 nm to about 700 nm and averaging the measurements.

[0169] As in Figure 2-3 As shown in Figures 6 and 11, foldable devices 101, 301, and 601, and test foldable device 1102, include a foldable substrate 206. The foldable substrate includes a first main surface 203 and a second main surface 205 opposite to the first main surface 203. (As shown in...) Figure 2-3 As shown in Figures 2 and 6, a first main surface 203 may extend along a first plane 204a. A second main surface 205 may extend along a second plane 204b. In some embodiments, as shown, the second plane 204b may be parallel to the first plane 204a. As used herein, the substrate thickness 211 may be defined between the first main surface 203 and the second main surface 205 as the distance between the first plane 204a and the second plane 204b.

[0170] As in Figure 2-3 As shown in Figures 6 and 11, the foldable substrate 206 may include a first outer layer 213. As shown, the first outer layer 213 may include a first main surface 203 and a first inner surface 214 opposite to the first main surface 203. In some embodiments, when the foldable devices 101, 301, and / or 601 are in a flat configuration, the first inner surface 214 may extend along a third plane 204c. As used herein, a first outer thickness 217 of the first outer layer 213 may be defined between the first main surface 203 and the first inner surface 214, as the distance between the first plane 204a and the third plane 204c. In some embodiments, the substrate thickness 211 may be about 10 micrometers (μm) or greater, about 25 μm or greater, about 40 μm or greater, about 60 μm or greater, about 80 μm or greater, about 100 μm or greater, about 125 μm or greater, about 150 μm or greater, about 2 millimeters (mm) or less, about 1 mm or less, about 800 μm or less, about 500 μm or less, about 300 μm or less, about 200 μm or less, about 180 μm or less, or about 160 μm or less. In some embodiments, the substrate thickness 211 may be in the range of 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, or any range or subrange thereof.

[0171] Reference Figure 2The first outer layer 213 is described in the context of a foldable device 101, and it should be understood that unless otherwise stated, this description of the first outer layer 213 is also applicable to any implementation of this disclosure, for example, in... Figure 3 , 6 And the foldable devices 301 and / or 601 shown in Figure 11, the test foldable device 1102 and / or the foldable substrate 206. (As shown in...) Figure 2 As shown, the first outer layer 213 may include a first portion 213a and a second portion 213b. A first minimum distance 210 may be defined between the first portion 213a and the second portion 213b of the first outer layer 213. In some embodiments, the first portion 213a of the first outer layer 213 may include a first surface region 223 of a first main surface 203 and a first inner surface region 214a of a first inner surface 214 opposite to the first surface region 223. In some embodiments, the second portion 213b of the first outer layer 213 may include a third surface region 233 of the first main surface 203 and a second inner surface region 214b of the first inner surface 214 opposite to the third surface region 233. In some embodiments, as shown, the first surface region 223 and the third surface region 233 may extend along a first plane 204a. In some embodiments, as shown, the first inner surface region 214a and the second inner surface region 214b may extend along a third plane 204c. In some embodiments, a first portion 213a of the first outer layer 213 may include a first outer thickness 217. In other embodiments, the first outer thickness 217 may be substantially uniform between the first surface region 223 and the first inner surface region 214a over its corresponding length (i.e., in the direction 106 of the length 105 of the foldable device) and / or its corresponding width (i.e., in the direction 104 of the width 103 of the foldable device). In some embodiments, a second portion 213b of the first outer layer 213 may include the first outer thickness 217. In other embodiments, the first outer thickness 217 may be substantially uniform between the third surface region 233 and the second inner surface region 214b over its corresponding length (i.e., in the direction 106 of the length 105 of the foldable device) and / or its corresponding width (i.e., in the direction 104 of the width 103 of the foldable device).

[0172] As in Figure 2-3As shown in Figures 6 and 11, the foldable substrate 206 may include a second outer layer 215. As shown, the second outer layer 215 may include a second primary surface 205 and a second inner surface 216 opposite to the second primary surface 205. In some embodiments, when the foldable devices 101, 301, and / or 601 are in a flat configuration, the second inner surface 216 may extend along a fourth plane 204d. As used herein, a second outer thickness 237 of the second outer layer 215 may be defined between the second primary surface 205 and the second inner surface 216, as the distance between the second plane 204b and the fourth plane 204d.

[0173] Reference Figure 2 The second outer layer 215 is described in reference to the foldable device 101, and it should be understood that unless otherwise stated, this description of the second outer layer 215 is also applicable to any embodiment of this disclosure, for example, in Figure 3 , 6 And the foldable devices 301 and / or 601 shown in Figure 11, the test foldable device 1102 and / or the foldable substrate 206. (As shown in...) Figure 2As shown, the second outer layer 215 may include a first portion 215a and a second portion 215b. A second minimum distance 220 may be defined between the first portion 215a and the second portion 215b of the second outer layer 215. In some embodiments, the first portion 215a of the second outer layer 215 may include a second surface region 225 of the second main surface 205 and a third inner surface region 216a of the second inner surface 216 opposite to the second surface region 225. In some embodiments, the second portion 215b of the second outer layer 215 may include a fourth surface region 235 of the second main surface 205 and a fourth inner surface region 216b of the second inner surface 216 opposite to the fourth surface region 235. In some embodiments, as shown, the second surface region 225 and the fourth surface region 235 may extend along a second plane 204b. In some embodiments, as shown, the third inner surface region 216a and the fourth inner surface region 216b may extend along a fourth plane 204d. In some embodiments, a first portion 215a of the second outer layer 215 may include a second outer thickness 237. In other embodiments, the second outer thickness 237 may be substantially uniform between the second surface region 225 and the third inner surface region 216a along its corresponding length (i.e., in the direction 106 of the length 105 of the foldable device) and / or its corresponding width (i.e., in the direction 104 of the width 103 of the foldable device). In some embodiments, a second portion 215b of the second outer layer 215 may include the second outer thickness 237. In other embodiments, the second outer thickness 237 may be substantially uniform between the fourth surface region 235 and the fourth inner surface region 216b along its corresponding length (i.e., in the direction 106 of the length 105 of the foldable device) and / or its corresponding width (i.e., in the direction 104 of the width 103 of the foldable device).

[0174] As in Figure 2-3 Figures 6 and 11 show that the foldable substrate 206 may include a core layer 207. As shown, the core layer 207 may include a third inner surface 208 and a fourth inner surface 218 opposite to the third inner surface 208. In some embodiments, the third inner surface 208 may extend along a third plane 204c. In some embodiments, the fourth inner surface 218 may extend along a fourth plane 204d. As used herein, the center thickness 227 of the core layer 207 may be defined between the third inner surface 208 and the fourth inner surface 218, as the distance between the third plane 204c and the fourth plane 204d.

[0175] In some embodiments, the first outer thickness 217, the second outer thickness 237, and / or the center thickness 227 may be about 1 μm or greater, about 5 μm or greater, about 10 μm or greater, about 25 μm or greater, about 40 μm or greater, about 80 μm or greater, about 100 μm or greater, about 125 μm or greater, about 150 μm or greater, about 1 mm or less, about 800 μm or less, about 500 μm or less, about 300 μm or less, about 200 μm or less, about 180 μm or less, or about 160 μm or less. In some embodiments, the first outer thickness 217, the second outer thickness 237, and / or the center thickness 227 may be in the range of about 1 μm to about 1 mm, about 1 μm to about 800 μm, about 5 μm to about 800 μm, about 5 μm to about 500 μm, about 10 μm to about 500 μm, about 10 μm to about 300 μm, about 25 μm to about 300 μm, about 25 μm to about 200 μm, about 40 μm to about 200 μm, about 80 μm to about 200 μm, about 80 μm to about 200 μm, about 100 μm to about 200 μm, about 125 μm to about 200 μm, about 125 μm to about 180 μm, about 125 μm to about 160 μm, about 125 μm to about 150 μm, or any range or subrange thereof. In another embodiment, the center thickness 227 may be about 1 μm or greater, about 5 μm or greater, about 10 μm or greater, about 25 μm or greater, about 40 μm or greater, about 100 μm or less, about 80 μm or less, about 60 μm or less, or about 50 μm or less. In another embodiment, the center thickness 227 may be in the range of about 1 μm to about 100 μm, about 5 μm to about 100 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 40 μm to about 60 μm, or any range or subrange thereof. In some embodiments, the first outer thickness 217 may be substantially equal to the second outer thickness 237. In some embodiments, the first outer thickness 217 may be greater than the second outer thickness 237. In some embodiments, the second outer thickness 237 may be greater than the first outer thickness 217.

[0176] Reference Figure 2 The core layer 207 is described in the context of a foldable device 101, and it should be understood that unless otherwise stated, this description of the core layer 207 is also applicable to any embodiment of this disclosure, for example, in... Figure 3 , 6 And the foldable devices 301 and / or 601 shown in Figure 11, the test foldable device 1102 and / or the foldable substrate 206. (As shown in...) Figure 2As shown, core layer 207 can be positioned between first outer layer 213 and second outer layer 215. In some embodiments, as shown, the third inner surface 208 of core layer 207 can contact the first inner surface region 214a of the first inner surface 214 of the first portion 213a of the first outer layer 213. In some embodiments, as shown, the third inner surface 208 of core layer 207 can contact the second inner surface region 214b of the first inner surface 214 of the second portion 213b of the first outer layer 213. In some embodiments, as shown, the fourth inner surface 218 of core layer 207 can contact the third inner surface region 216a of the second inner surface 216 of the first portion 215a of the second outer layer 215. In some embodiments, as shown, the fourth inner surface 218 of core layer 207 can contact the fourth inner surface region 216b of the second portion 215b of the second outer layer 215.

[0177] As in Figure 2 As shown, the third inner surface 208 may be included in a first central surface region 209 between a first inner surface region 214a of the first inner surface 214 of the first portion 213a of the first outer layer 213 and a second inner surface region 214b of the first inner surface 214 of the second portion 213b of the first outer layer 213. In some embodiments, as shown, the first central surface region 209 of the core layer 207 may be recessed from the first main surface 203 by a first distance, which may be substantially equal to or greater than the first outer thickness 217. A first recess 234 may be defined between the first plane 204a and the first central surface region 209.

[0178] As in Figure 2 As shown, the fourth inner surface 218 may be included in a second central surface region 219 between the third inner surface region 216a of the second inner surface 216 of the first portion 215a of the second outer layer 215 and the fourth inner surface region 216b of the second inner surface 216 of the second portion 231 of the second outer layer 215. In some embodiments, as shown, the second central surface region 219 of the core layer 207 may be recessed from the second main surface 205 by a second distance, which may be substantially equal to or greater than the second outer thickness 237. A second recess 244 may be defined between the second plane 204b and the second central surface region 219.

[0179] The width of the first central surface area 209 may be substantially equal to the first minimum distance 210, and the width of the second central surface area 219 may be substantially equal to the second minimum distance 220. In some embodiments, the first minimum distance 210 and / or the second minimum distance 220 may be about 1 mm or more, about 3 mm or more, about 5 mm or more, about 8 mm or more, about 10 mm or more, about 15 mm or more, about 20 mm or more, about 100 mm or less, about 60 mm or less, about 50 mm or less, about 40 mm or less, about 35 mm or less, about 30 mm or less, or about 25 mm or less. In some embodiments, the first minimum distance 210 and / or the second minimum distance 220 may be within a range of about 1 mm to about 100 mm, about 3 mm to about 100 mm, about 3 mm to about 60 mm, about 5 mm to about 60 mm, about 5 mm to about 50 mm, about 8 mm to about 50 mm, about 8 mm to about 40 mm, about 10 mm to about 40 mm, about 10 mm to about 35 mm, about 15 mm to about 35 mm, about 15 mm to about 30 mm, about 20 mm to about 30 mm, about 20 mm to about 25 mm, or any range or subrange thereof. In some embodiments, the first minimum distance 210 may be substantially equal to the second minimum distance 220. In some embodiments, the first minimum distance 210 may be greater than the second minimum distance 220. In some embodiments, the second minimum distance 220 may be greater than the first minimum distance 210.

[0180] In some embodiments, the first distance (e.g., the first outer thickness 217) of the first central surface region 209 recessed from the first plane 204a as a percentage of the substrate thickness 211 and / or the second distance (e.g., the second outer thickness 237) of the second central surface region 219 recessed from the second plane 204b as a percentage of the substrate thickness 211 can be about 1% or more, about 5% or more, about 10% or more, about 15% or more, about 20% or more, about 25% or more, about 75% or less, about 60% or less, about 50% or less, about 40% or less, about 35% or less, or about 30% or less. In some embodiments, the first distance and / or the second distance, as a percentage of the substrate thickness 211, can be in the range of about 1% to about 75%, about 1% to about 60%, about 5% to about 60%, about 5% to about 50%, about 10% to about 50%, about 10% to about 40%, about 15% to about 40%, about 15% to about 35%, about 20% to about 35%, about 20% to about 30%, about 25% to about 30%, or any range or subrange thereof. In some embodiments, the first distance can be substantially equal to the second distance. Providing a first distance substantially equal to the second distance can further reduce the occurrence of mechanical instability in the central portion, for example, because the foldable substrate is symmetrical about a plane containing the midpoint of the substrate thickness and the central thickness. In some embodiments, the second distance can be greater than the first distance. In some embodiments, the first distance can be greater than the second distance. In another embodiment, the second distance (e.g., the second outer thickness 237) of the second central surface region 219 recessed from the second plane 204b as a percentage of the substrate thickness 211 can be about 1% or more, about 2% or more, about 5% or more, about 10% or more, about 12% or more, about 30% or less, about 25% or less, about 20% or less, about 18% or less, or about 15% or less. In another embodiment, the second distance (e.g., the second outer thickness 237) of the second central surface region 219 recessed from the second plane 204b as a percentage of the substrate thickness 211 can be in the range of about 1% to about 30%, about 1% to about 25%, about 2% to about 25%, about 5% to about 25%, about 5% to about 20%, about 10% to about 20%, about 10% to about 18%, about 12% to about 18%, about 12% to about 15%, or any range or subrange thereof.

[0181] In some embodiments, the center thickness 227 as a percentage of the substrate thickness 211 may be about 0.5% or more, about 1% or more, about 2% or more, about 5% or more, about 6% or more, about 20% or less, about 13% or less, about 10% or less, or about 8% or less. In some embodiments, the center thickness 227 as a percentage of the substrate thickness 211 may be in the range of about 0.5% to about 20%, about 0.5% to about 13%, about 1% to about 13%, about 1% to about 10%, about 2% to about 10%, about 2% to about 8%, about 5% to about 8%, about 6% to about 8%, or any range or subrange thereof.

[0182] The first outer layer 213 may include a first coefficient of thermal expansion, the second outer layer 215 may include a second coefficient of thermal expansion, and the core layer 207 may include a core coefficient of thermal expansion. Throughout this disclosure, the coefficient of thermal expansion of the foldable substrate or a layer of the foldable substrate refers to the linear expansion rate based on temperature and is measured at 25°C according to ASTM E228-17. In some embodiments, the first coefficient of thermal expansion, the second coefficient of thermal expansion, and / or the core coefficient of thermal expansion may be approximately 5 × 10⁻⁶. -7 ℃ -1 Or larger, approximately 10×10 -7 ℃ -1 Or larger, approximately 20×10 -7 ℃ -1 Or larger, approximately 30×10 -7 ℃ -1 Or larger, approximately 40×10 -7 ℃ -1 Or larger, approximately 50×10 -7 ℃ -1 Or larger, approximately 60×10 -7 ℃ -1 Or larger, approximately 500×10 -7 ℃ -1 Or smaller, approximately 300×10 -7 ℃ -1 Or smaller, approximately 200×10 -7 ℃ -1 Or smaller, approximately 150×10 -7 ℃ -1 Or smaller, approximately 100×10 -7 ℃ -1 Or smaller, approximately 90×10 -7 ℃ -1 Or smaller, approximately 80×10 -7 ℃ -1 Or smaller or approximately 70×10 -7 ℃ -1Or smaller. In some embodiments, the first coefficient of thermal expansion, the second coefficient of thermal expansion, and / or the core coefficient of thermal expansion can be from about 5 × 10⁻⁶. -7 ℃ -1 Approximately 500×10 -7 ℃ -1 , approximately 5×10 -7 ℃ -1 Approximately 300×10 -7 ℃ -1 , from approximately 10×10 -7 ℃ -1 Approximately 300×10 -7 ℃ -1 , from approximately 10×10 -7 ℃ -1 Approximately 200×10 -7 ℃ -1 , approximately 20×10 -7 ℃ -1 Approximately 200×10 -7 ℃ -1 , approximately 20×10 -7 ℃ -1 Approximately 100×10 -7 ℃ -1 , approximately 30×10 -7 ℃ -1 Approximately 100×10 -7 ℃ -1 , approximately 30×10 -7 ℃ -1 Approximately 90×10 -7 ℃ -1 , approximately 40×10 -7 ℃ -1 Approximately 90×10 -7 ℃ -1 , approximately 40×10 -7 ℃ -1 Approximately 80×10 -7 ℃ -1 Approximately 50×10 -7 ℃ -1 Approximately 80×10 -7 ℃ -1 Approximately 50×10 -7 ℃ -1 Approximately 70×10 -7 ℃ -1 Approximately 60×10 -7 ℃ -1 Approximately 70×10 -7 ℃ -1Within the range or any range or subrange thereof. In some embodiments, the first coefficient of thermal expansion may be substantially equal to the second coefficient of thermal expansion. In some embodiments, the core coefficient of thermal expansion may be greater than the first coefficient of thermal expansion and / or the second coefficient of thermal expansion. In other embodiments, the core coefficient of thermal expansion may be approximately 5 × 10⁻⁶ greater than the first coefficient of thermal expansion and / or the second coefficient of thermal expansion. -7 ℃ -1 Or larger, approximately 10×10 -7 ℃ -1 Or larger, approximately 20×10 -7 ℃ -1 Or larger, approximately 30×10 -7 ℃ -1 Or larger, approximately 40×10 -7 ℃ -1 Or larger, approximately 50×10 -7 ℃ -1 Or larger, or approximately 100×10 -7 ℃ -1 Or smaller, approximately 80×10 -7 ℃ -1 Or smaller, or approximately 70×10 -7 ℃ -1 Or smaller, or about 60×10 -7 ℃ -1 Or even greater. In another embodiment, the coefficient of thermal expansion of the core may be larger than the first and / or second coefficient of thermal expansion by an amount ranging from approximately 5 × 10⁻⁶. -7 ℃ -1 Approximately 100×10 -7 ℃ -1 , approximately 5×10 -7 ℃ -1 Approximately 80×10 -7 ℃ -1 , from approximately 10×10 -7 ℃ -1 Approximately 80×10 -7 ℃ -1 , from approximately 10×10 -7 ℃ -1 Approximately 70×10 -7 ℃ -1 , approximately 20×10 -7 ℃ -1 Approximately 70×10 -7 ℃ -1 , approximately 20×10 -7 ℃ -1 Approximately 60×10 -7 ℃ -1 , approximately 30×10 -7 ℃ -1 Approximately 60×10 -7 ℃-1 , approximately 30×10 -7 ℃ -1 Approximately 50×10 -7 ℃ -1 , approximately 40×10 -7 ℃ -1 Approximately 60×10 -7 ℃ -1 , approximately 40×10 -7 ℃ -1 Approximately 50×10 -7 ℃ -1 Within or within any range or subrange thereof. As discussed elsewhere herein, controlling the difference between the coefficients of thermal expansion of the core layer relative to the first outer layer and / or the second outer layer, or the central portion relative to the first portion and / or the second portion, can reduce chemically reinforced induced expansion and / or strain between layers and / or portions of the foldable device and / or foldable substrate. This can help in situations where the foldable device and / or foldable substrate requires a large folding induced strain to reach the critical buckling strain (e.g., the onset of mechanical instability), and reduce the occurrence of optical distortion.

[0183] The first outer layer 213 may contain a first density, the second outer layer 215 may contain a second density, and the core layer 207 may contain a core density. Throughout this disclosure, the density is measured at 25°C according to ASTM C693-93 (2019). In some embodiments, the first density, the second density, and / or the core density may be about 2 grams per cubic centimeter (g / cm³). 3 ) or larger, approximately 2.2 g / cm³ 3 Or larger, approximately 2.3 g / cm³ 3 Or larger, approximately 2.4 g / cm³ 3 Or larger, approximately 2.42 g / cm³ 3 Or larger, approximately 2.45 g / cm³ 3 Or larger, approximately 2.47 g / cm³ 3 Or larger, approximately 3g / cm 3 Or smaller, approximately 2.8 g / cm³ 3 Or smaller, approximately 2.7 g / cm³ 3 Or smaller, approximately 2.65 g / cm³ 3 Or smaller, approximately 2.6 g / cm³ 3 Or smaller or approximately 2.58 g / cm³ 3 Or smaller, approximately 2.55 g / cm³ 3 Or smaller, approximately 2.52 g / cm³ 3 Or smaller or about 2.5g / cm³ 3 Or even smaller. In some embodiments, the first density, the second density, and / or the core density can be as low as about 2 g / cm³. 3 Approximately 3g / cm3 , Approximately 2g / cm 3 Approximately 2.8 g / cm³ 3 Approximately 2.2 g / cm³ 3 Approximately 2.8 g / cm³ 3 Approximately 2.2 g / cm³ 3 Approximately 2.7 g / cm³ 3 Approximately 2.3 g / cm³ 3 Approximately 2.7 g / cm³ 3 Approximately 2.4 g / cm³ 3 Approximately 2.7 g / cm³ 3 Approximately 2.42 g / cm³ 3 Approximately 2.7 g / cm³ 3 Approximately 2.42 g / cm³ 3 Approximately 2.68 g / cm³ 3 Approximately 2.45 g / cm³ 3 Approximately 2.68 g / cm³ 3 Approximately 2.45 g / cm³ 3 Approximately 2.65 g / cm³ 3 Approximately 2.48 g / cm³ 3 Approximately 2.65 g / cm³ 3 Approximately 2.48 g / cm³ 3 Approximately 2.52 g / cm³ 3 Approximately 2.48 g / cm³ 3 Approximately 2.5 g / cm³ 3 The core density is within the range of or any range or subrange thereof. In some embodiments, the first density may be substantially equal to the second density. In some embodiments, the core density may be greater than the first density and / or the second density. In other embodiments, the core density may be approximately 0.005 g / cm³ greater than the first density and / or the second density. 3 Or larger, approximately 0.01 g / cm³ 3 Or larger, approximately 0.015 g / cm³ 3 Or larger, approximately 0.02 g / cm³ 3 Or larger, approximately 0.025 g / cm³ 3 Or larger, approximately 0.055 g / cm³ 3 Or even smaller, approximately 0.05 g / cm³ 3 Or even smaller, approximately 0.045 g / cm³ 3 Or even smaller, approximately 0.04 g / cm³ 3 Or smaller, approximately 0.35 g / cm³ 3 Or even smaller or approximately 0.3 g / cm³ 3 Or even smaller. In another embodiment, the core density may be greater than the first density and / or the second density by an amount of approximately 0.005 g / cm³. 3To approximately 0.055 g / cm 3 Approximately 0.005 g / cm³ 3 To approximately 0.05 g / cm 3 Approximately 0.01 g / cm³ 3 To approximately 0.05 g / cm 3 Approximately 0.01 g / cm³ 3 To approximately 0.045 g / cm³ 3 Approximately 0.015 g / cm³ 3 To approximately 0.045 g / cm³ 3 Approximately 0.015 g / cm³ 3 To approximately 0.04 g / cm 3 0.02g / cm 3 To approximately 0.04 g / cm 3 0.02g / cm 3 Approximately 0.035 g / cm³ 3 Approximately 0.025 g / cm³ 3 Approximately 0.035 g / cm³ 3 Approximately 0.025 g / cm³ 3 Approximately 0.03 g / cm³ 3 Within or within any range or subrange thereof. As discussed herein, controlling the density difference between the core layer and the first outer layer and / or the second outer layer, or between the central portion and the first portion and / or the second portion, can reduce chemically reinforced induced expansion and / or strain between layers and / or portions of the foldable device and / or foldable substrate. This can help in situations where the foldable device and / or foldable substrate requires a large folding induced strain to reach critical buckling strain (e.g., the onset of mechanical instability), and reduce the occurrence of optical distortion.

[0184] The first outer layer 213 may include a first network expansion coefficient, the second outer layer 215 may include a second network expansion coefficient, and the core layer 207 may include a core network expansion coefficient. Throughout this disclosure, the network expansion coefficient (e.g., lattice expansion coefficient) refers to the ratio of the increase in volume of a material (e.g., a glass-based material, a ceramic-based material) to the increase in alkali metal ions per mole percent. In some embodiments, the network expansion coefficient may be for potassium based on oxides. In some embodiments, the network expansion coefficient may be for sodium based on oxides. In some embodiments, the first network expansion coefficient, the second network expansion coefficient, and / or the core network expansion coefficient may be approximately 300 × 10⁻⁶. -6 / mol% or greater, approximately 500 × 10 -6 / mol% or greater, approximately 700 × 10 -6 / mol% or greater, approximately 800 × 10 -6 / mol% or greater, approximately 900 × 10 -6 / mol% or greater, approximately 200 × 10⁻⁶ -6 / mol% or less, approximately 1500 × 10 -6 / mol% or less, approximately 1200 × 10 -6 / mol% or less, approximately 1100 × 10 -6 / mol% or less or approximately 1000×10 -6 / molar percentage or less. In some embodiments, the first network expansion factor, the second network expansion factor, and / or the core network expansion factor can be from about 300 × 10⁻⁶. -6 / mol% to approximately 2000×10 -6 / mol%, approximately 300×10 -6 / mol% to approximately 1500×10 -6 / mol%, approximately 500×10 -6 / mol% to approximately 1500×10 -6 / mol%, approximately 500×10 -6 / mol% to approximately 1200×10 -6 / mol%, approximately 700×10 -6 / mol% to approximately 1200×10 -6 / mol%, approximately 700×10 -6 / mol% to approximately 1100 × 10⁻⁶ -6 / mol%, approximately 800×10 -6 / mol% to approximately 1100 × 10⁻⁶ -6 / mol%, approximately 800×10 -6 / mol% to approximately 1000×10 -6 / mol%, approximately 900×10 -6 / mol% to approximately 1000×10 -6 Within the range of / mol% or any range or subrange thereof. In some embodiments, the first network expansion coefficient may be substantially equal to the second network expansion coefficient. In some embodiments, the core network expansion coefficient may be less than the first network expansion coefficient and / or the second network expansion coefficient. As discussed above, controlling the difference between the network expansion coefficients of the core layer relative to the first outer layer and / or the second outer layer, or the central portion relative to the first portion and / or the second portion, can reduce chemically reinforced induced expansion and / or strain between layers and / or portions of the foldable device and / or foldable substrate. This can help reduce the occurrence of optical distortion when the foldable device and / or foldable substrate has a large folding induced strain before reaching the critical buckling strain (e.g., the onset of mechanical instability).

[0185] As in Figure 4-5As shown in Figure 7, the foldable substrate 407 may include a first main surface 403 and a second main surface 405 opposite to the first main surface 403. For example, in... Figure 4-5 As shown in Figure 7, the first main surface 403 may extend along the first plane 404a. The second main surface 405 may extend along the second plane 404b. In some embodiments, as shown, the second plane 404b may be parallel to the first plane 404a. As used herein, the substrate thickness 411 may be defined between the first main surface 403 and the second main surface 405 as the distance between the first plane 404a and the second plane 404b. The substrate thickness 411 may be within one or more of the ranges discussed above with reference to substrate thickness 211.

[0186] As in Figure 4-5 As shown in Figure 7, the foldable substrate 407 may further include a first portion 421, which includes a first surface region 423 and a second surface region 425 opposite to the first surface region 423. References will now be made to... Figure 4 The first part 421 is described in terms of a foldable device 401, and it should be understood that unless otherwise stated, this description of the first part 421 is also applicable to any implementation of this disclosure, for example, in Figure 5 The foldable devices 501 and 701 and / or the foldable substrate 407 are illustrated in Figures 7 and 8. Figure 4As shown, the first portion 421 may include a first surface region 423 and a second surface region 425 opposite to the first surface region 423. In some embodiments, as shown, the second surface region 425 of the first portion 421 may include a planar surface. In other embodiments, as shown, the second surface region 425 may be parallel to the first surface region 423. In some embodiments, as shown, a first main surface 403 may include the first surface region 423, and a second main surface 405 may include the second surface region 425. In other embodiments, the first surface region 423 may extend along a first plane 404a. In other embodiments, the second surface region 425 may extend along a second plane 404b. In some embodiments, the substrate thickness 411 may correspond to the distance between the first surface region 423 and the second surface region 425 of the first portion 421. In some embodiments, the substrate thickness 411 may be substantially uniform over the first surface region 423. In some embodiments, the first thickness defined between the first surface region 423 and the second surface region 425 may be within one or more of the ranges discussed above regarding the substrate thicknesses 211 or 411. In other embodiments, the first thickness may include the substrate thickness 411. In yet another embodiment, the first thickness of the first portion 421 may be substantially uniform between the first surface region 423 and the second surface region 425 over its corresponding length (i.e., in the direction 106 of the length 105 of the foldable device) and / or its corresponding width (i.e., in the direction 104 of the width 103 of the foldable device).

[0187] As in Figure 4-5 As shown in Figure 7, the foldable substrate 407 may also include a second portion 431, which includes a third surface region 433 and a fourth surface region 435 opposite to the third surface region 433. References will now be made to... Figure 4 The second part 431 is described in connection with the foldable device 401, and it should be understood that unless otherwise stated, this description of the second part 431 is also applicable to any implementation of this disclosure, for example, in Figure 5 and 7The foldable device 501 and / or 701 and / or foldable substrate 407 are illustrated in the figure. In some embodiments, as shown, the third surface region 433 of the second portion 431 may include a planar surface. In other embodiments, the third surface region 433 of the second portion 431 may be in a common plane with the first surface region 423 of the first portion 421. In some embodiments, as shown, the fourth surface region 435 of the second portion 431 may include a planar surface. In other embodiments, as shown, the fourth surface region 435 may be parallel to the third surface region 433. In other embodiments, the fourth surface region 435 of the second portion 431 may be in a common plane with the second surface region 425 of the first portion 421. A second thickness may be defined between the third surface region 433 and the fourth surface region 435 of the second portion 431. In some embodiments, the second thickness may be within the range discussed above regarding substrate thicknesses 211 or 411. In other embodiments, the second thickness may include substrate thickness 411. In another embodiment, as shown, the second thickness may be substantially equal to the substrate thickness 411 (e.g., the first thickness). In some embodiments, the second thickness of the second portion 431 may be substantially uniform between the third surface region 433 and the fourth surface region 435.

[0188] As in Figure 4-5 As shown in Figures 7 and 8, the foldable substrate 407 may include a central portion 481 positioned between a first portion 421 and a second portion 431. In some embodiments, the central portion 481 may include a first central surface region 409 and a second central surface region 419 opposite to the first central surface region 409. In other embodiments, the central portion 481 may include a first central surface region 409 positioned between a first surface region 423 and a third surface region 433. In still other embodiments, as shown, the first central surface region 409 may be recessed from the first main surface 403 by a first distance 417. The first distance 417 may be within one or more of the ranges discussed above with respect to the foldable substrate 206 for the first distance (e.g., a first outer thickness 217). In still other embodiments, as shown, when the foldable devices 401, 501, and / or 701 are in a flat configuration, the first central surface region 409 may extend along a third plane 404c, but in other embodiments, the first central surface region 409 may be provided as a non-flat region. The first recess 434 may be defined between the first central surface region 409 (e.g., the third plane 404c) and the first plane 404a. In another embodiment, the third plane 404c may be substantially parallel to the first plane 404a and / or the second plane 404b.

[0189] In some embodiments, the central portion 481 may include a second central surface region 419 positioned between the second surface region 425 and the fourth surface region 435. In other embodiments, as shown, the second central surface region 419 may be recessed from the second main surface 405 by a second distance 437. The second distance 437 may be within one or more of the ranges discussed above with respect to the second distance (e.g., the second outer thickness 237) of the foldable substrate 206. In still other embodiments, as shown, when the foldable devices 401, 501, and / or 701 are in a flat configuration, the second central surface region 419 may extend along the fourth plane 404d, but in other embodiments, the second central surface region 419 may be provided as a non-flat region. A second recess 444 may be defined between the second central surface region 419 (e.g., the fourth plane 404d) and the second plane 404b. As discussed above, providing a first distance from the first main surface that is substantially equal to the second distance from the second main surface recess of the second central surface region can reduce mechanical instability in the central portion, for example, because the foldable substrate is symmetrical about a plane that includes the midpoint of the substrate thickness and the central thickness.

[0190] The center thickness 427 may be defined between the first center surface region 409 and the second center surface region 419, and this thickness may be measured as the distance between the third plane 404c and the fourth plane 404d. In some embodiments, the center thickness 427 may be within one or more of the ranges discussed above for the center thickness 227 of the foldable substrate 206. In some embodiments, the center thickness 427 as a percentage of the substrate thickness 411 may be within one or more of the ranges discussed above for the center thickness 227 as a percentage of the substrate thickness 211 of the foldable substrate 206. The first center surface region 409 of the center portion 481 extending along the third plane 404c is parallel to the second center surface region 419 of the center portion 481 extending along the fourth plane 404d, thereby allowing a uniform center thickness 427 to extend over the center portion 481, which can provide enhanced folding performance at a predetermined thickness of center thickness 427. By preventing stress concentration, a uniform center thickness 427 on the center portion 481 can improve folding performance, while stress concentration will occur if a part of the center portion 481 is thinner than the rest of the center portion 481.

[0191] In some implementations, such as in Figure 4-5 As shown, the transition between the first central surface region 409 and the first surface region 423 and / or the third surface region 433 can be substantially abrupt (e.g., narrow enough to resemble a straight edge perpendicular to the first plane 404a and / or the third plane 404c). In some embodiments, such as in Figures 4 to 5As shown, the transition between the second central surface region 419 and the second surface region 425 and / or the fourth surface region 435 can be substantially abrupt (e.g., narrow enough to resemble a straight edge perpendicular to the second plane 404b and / or the fourth plane 404d). In some embodiments, although not shown, the foldable substrate 407 may include a first transition between the first surface region and the first central surface and / or between the second surface regions and the second central surface region, which may, for example, resemble... Figure 8 The first transition portion 853. In some embodiments, although not shown, the foldable substrate 407 may include a second transition between the third surface region and the first central surface region and / or between the fourth surface region and the second central surface region, which may be, for example, similar to... Figure 8 The second transition section 855.

[0192] In some implementations, such as in Figure 7 As shown, the foldable device 701 may include a foldable substrate 707, which may include a first portion 421 and / or a second portion 431 similar to or identical to a corresponding portion of the foldable substrate 407. In some embodiments, the foldable substrate 707 may include a first transition portion 753 positioned between the first portion 421 and a portion of a central portion 781 including a third plane 404c (e.g., a first central surface region 709). In another embodiment, the first transition portion 753 includes a portion of the first transition portion 753 extending from the first portion 421 with a continuously varying thickness, and a portion extending from the third plane 404c with abrupt changes. In still other embodiments, the abruptly changed transition depth 727 may be about 1 μm or greater, about 5 μm or greater, about 10 μm or greater, about 12 μm or greater, about 50 μm or less, about 30 μm or less, about 25 μm or less, about 20 μm or less, about 18 μm or less, or about 15 μm or less. In a further embodiment, the abruptly changed transition depth 727 may be in the range of about 1 μm to about 50 μm, about 1 μm to about 30 μm, about 2 μm to about 30 μm, about 2 μm to about 25 μm, about 5 μm to about 25 μm, about 5 μm to about 20 μm, about 10 μm to about 20 μm, about 10 μm to about 18 μm, about 12 μm to about 18 μm, about 12 μm to about 15 μm, or any range or subrange thereof. In some embodiments, such as in Figure 7As shown, the foldable substrate 707 may include a second transition portion 755 positioned between the second portion 431 and a portion of a central portion 781 including a third plane 404c (e.g., a first central surface region 709). In another embodiment, the second transition portion 755 includes a portion of the second transition portion 755 extending from the second portion 431 whose thickness continuously changes, and a portion extending from the third plane 404c that can change abruptly. In a further embodiment, the abruptly changed transition depth 727 in the second transition portion may be within one or more of the ranges discussed above regarding the abruptly changed transition depth 727 of the first transition portion. In a further embodiment, the abruptly changed transition depth 727 in the second transition portion may be substantially equal to the abruptly changed transition depth 727 in the first transition portion.

[0193] As in Figure 8 As shown, the foldable device 801 may include a foldable substrate 807. This foldable substrate may include a first main surface 803 and a second main surface 805 opposite to the first main surface 803. (As shown in...) Figure 8 As shown, a first main surface 803 may extend along a first plane 804a. A second main surface 805 may extend along a second plane 804b. In some embodiments, as shown, the second plane 804b may be parallel to the first plane 804a. As used herein, a substrate thickness 811 may be defined between the first main surface 803 and the second main surface 805, as the distance between the first plane 804a and the second plane 804b. The substrate thickness 811 may be within one or more of the ranges discussed above with reference to substrate thicknesses 211 or 411.

[0194] As in Figure 8As shown, the foldable substrate 807 may further include a first portion 821, which includes a first surface region 823 and a second surface region 825 opposite to the first surface region 823. In some embodiments, as shown, the second surface region 825 of the first portion 821 may include a planar surface. In other embodiments, as shown, the second surface region 825 may be parallel to the first surface region 823. In some embodiments, as shown, a first main surface 803 may include the first surface region 823, and a second main surface 805 may include the second surface region 825. In other embodiments, the first surface region 823 may extend along a first plane 804a. In other embodiments, the second surface region 825 may extend along a second plane 804b. In some embodiments, the substrate thickness 811 may correspond to the distance between the first surface region 823 and the second surface region 825 of the first portion 821. In some embodiments, the substrate thickness 811 may be substantially uniform over the first surface region 823. In some embodiments, the first thickness defined between the first surface region 823 and the second surface region 825 may be within one or more of the ranges discussed above regarding the substrate thicknesses 211, 411, or 811. In other embodiments, the first thickness may include the substrate thickness 811. In yet another embodiment, the first thickness of the first portion 821 may be substantially uniform between the first surface region 823 and the second surface region 825 along its corresponding length (i.e., in the direction 106 of the length 105 of the foldable device) and / or its corresponding width (i.e., in the direction 104 of the width 103 of the foldable device).

[0195] like Figure 8As shown, the foldable substrate 807 may also include a second portion 831, which includes a third surface region 833 and a fourth surface region 835 opposite to the third surface region 833. In some embodiments, as shown, the third surface region 833 of the second portion 831 may include a planar surface. In another embodiment, the third surface region 833 of the second portion 831 may be in a common plane with the first surface region 823 of the first portion 821. In some embodiments, as shown, the fourth surface region 835 of the second portion 831 may include a planar surface. In another embodiment, as shown, the fourth surface region 835 may be parallel to the third surface region 833. In another embodiment, the fourth surface region 835 of the second portion 831 may be in a common plane with the second surface region 825 of the first portion 821. The second thickness may be limited between the third surface region 833 and the fourth surface region 835 of the second portion 831. In some embodiments, the second thickness may be within the range discussed above regarding substrate thicknesses 211, 411, or 811. In another embodiment, the second thickness may include the substrate thickness 811. In another embodiment, as shown, the second thickness may be substantially equal to the substrate thickness 811 (e.g., the first thickness). In some embodiments, the second thickness of the second portion 831 may be substantially uniform between the third surface region 833 and the fourth surface region 835.

[0196] As in Figure 8As shown, the foldable substrate 807 may include a central portion 881 positioned between a first portion 821 and a second portion 831. In some embodiments, the central portion 881 may include a first central surface region 809 and a second central surface region 819 opposite to the first central surface region 809. In another embodiment, the central portion 881 may include a first central surface region 809 positioned between a first surface region 823 and a third surface region 833. In a further embodiment, as shown, the first central surface region 809 may be recessed from the first main surface 803 by a first distance 817. The first distance 817 may be within one or more of the ranges discussed above with respect to the foldable substrate 206 for a first distance (e.g., a first outer thickness 217). In a further embodiment, as shown, when the foldable device 801 is in a flat configuration, the first central surface region 809 may extend along a third plane 804c, but in other embodiments, the first central surface region 809 may be provided as a non-planar region. A first recess 834 may be defined between a first central surface region 809 (e.g., a third plane 804c) and a first plane 804a. In another embodiment, the third plane 804c may be substantially parallel to the first plane 804a and / or the second plane 804b. In another embodiment, the central portion 881 may include a second central surface region 819 positioned between the second surface region 825 and the fourth surface region 835. In a further embodiment, as shown, the second main surface 805 may include the second central surface region 819. In a further embodiment, although not shown, a portion of the second central surface region may be recessed from the second plane. In a further embodiment, although not shown, the foldable substrate may include another recess in the second main surface of the foldable substrate that exposes the second central surface region.

[0197] The center thickness 827 of the central portion 881 may be defined between the first center surface region 809 and the second center surface region 819. In some embodiments, when the foldable device 801 is in a flat configuration, the first center surface region 809 may extend along a third plane 804c, but in other embodiments, the first center surface region 809 may be provided as a non-planar region. In other embodiments, the third plane 804c may be substantially parallel to the first plane 804a and / or the second plane 804b. In some embodiments, the center thickness 827 may be within one or more of the ranges discussed above for the center thickness 227 of the foldable substrate 206. In some embodiments, the center thickness 827 as a percentage of the substrate thickness 811 may be within one or more of the ranges discussed above for the center thickness 227 as a percentage of the substrate thickness 211 of the foldable substrate 206. By providing a first central surface region 809 of a central portion 881 extending along a third plane 804c parallel to the second plane 804b, a uniform central thickness 827 can be extended on the central portion 881, which can provide enhanced folding performance at a predetermined thickness of the central thickness 827. The uniform central thickness 827 on the central portion 881 improves folding performance by preventing stress concentration, which would occur if a portion of the central portion 881 were thinner than the rest.

[0198] As in Figure 8 As shown, the central portion 881 may include a first transition portion 853. The first transition portion 853 may attach the first portion 821 to the region of the central portion 881, which includes a central thickness 827. The thickness of the first transition portion 853 may be defined between the second plane 804b and the first central surface region 809. (As shown in...) Figure 8 As shown, the thickness of the first transition portion 853 may increase continuously from the first central surface region 809 (e.g., central thickness 827) to the first portion 821 (e.g., substrate thickness 811). In some embodiments, as shown, the thickness of the first transition portion 853 may increase at a constant rate from the first central surface region 809 to the first portion 821. In some embodiments, although not shown, the thickness of the first transition portion 853 may increase more slowly at the junction of the first central surface region 809 and the first transition portion 853 than in the middle of the first transition portion 853. In some embodiments, although not shown, the thickness of the first transition portion 853 may increase more slowly at the junction of the first portion 821 and the first transition portion 853 than in the middle of the first transition portion 853. In some embodiments, although not shown, the thickness of the first transition portion 853 may increase more slowly at the junction of the first portion 821 and the first transition portion 853 than in the middle of the first transition portion 853. In some embodiments, although not shown, the thickness of the first transition portion 853 may increase more slowly at the junction of the first portion 821 and the first transition portion 853. Figure 8 The image is shown in the middle, but the central part may or may not include the first transition section. Figure 4The central portion 481. In some embodiments, although not shown, the first transition portion 853 may transition from the second surface region to the second central surface region, for example, if the second central surface region is recessed from the second plane. In some embodiments, although not shown, the first transition portion may include a portion whose thickness changes continuously and extends from the first portion, and a portion whose thickness changes abruptly and extends from the third plane 804c (e.g., see...). Figure 7 ).

[0199] The central portion 881 may include a second transition portion 855. For example, in Figure 8 As shown, the second transition portion 855 can attach the second portion 831 to a region including the central portion 881 (e.g., the region including the first central surface region 809) that includes the central thickness 827. The thickness of the second transition portion 855 can be defined between the second plane 804b and the first central surface region 809. Figure 8 As shown, the thickness of the second transition portion 855 can increase continuously from the first central surface region 809 (e.g., central thickness 827) to the second portion 831 (e.g., substrate thickness 811). In some embodiments, as shown, the thickness of the second transition portion 855 can increase at a constant rate from the first central surface region 809 to the second portion 831. In some embodiments, although not shown, the thickness of the second transition portion 855 may increase more slowly at the junction of the first central surface region 809 and the second transition portion 855 than in the middle of the second transition portion 855. In some embodiments, although not shown, the thickness of the second transition portion 855 may increase more slowly at the junction of the second portion 831 and the second transition portion 855 than in the middle of the second transition portion 855. In some embodiments, as shown in... Figure 8 As shown in the diagram, the central portion 881 may include a second transition portion. In some embodiments, although not shown... Figure 8 The image is shown in the middle, but the central part may or may not contain the second transition section. Figure 4 The central portion 481. In some embodiments, although not shown, the second transition portion 855 may transition from the fourth surface region to the second central surface region, for example, if the second central surface region is recessed from the second plane. In some embodiments, although not shown, the second transition portion may include a portion whose thickness changes continuously and extends from the second portion, and a portion whose thickness changes abruptly and extends from the third plane 804c, for example, similar to... Figure 7 The situation shown in the middle.

[0200] As in Figure 8As shown, the width of the first transition portion 853 may be defined in the direction 106 of the length 105 of the foldable device 801 between a portion of the central portion 881 containing the center thickness 827 (e.g., the third plane 804c) and the first portion 821. The width of the second transition portion 855 may be defined in the direction 106 of the length 105 of the foldable device 101 between a portion of the central portion 881 containing the center thickness 827 (e.g., the third plane 804c) and the second portion 831. In some embodiments, the width of the first transition portion 853 and / or the width of the second transition portion 855 may be sufficiently large (e.g., 1 mm or more) to avoid optical distortion that could occur at a stepped transition or a small transition width (e.g., less than 1 mm) between the first thickness and the center thickness. In some embodiments, to enhance the puncture resistance of the foldable substrate while avoiding optical distortion, the width of the first transition portion 853 and / or the width of the second transition portion 855 may be about 1 mm or greater, about 2 mm or greater, about 3 mm or greater, about 5 mm or less, about 4 mm or less, or about 3 mm or less. In some embodiments, the width of the first transition portion 853 and / or the width of the second transition portion 855 may be within the range of 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 subrange thereof.

[0201] As used herein, if a first layer and / or component is described as "located above a second layer and / or component," then there may or may not be other layers between the first layer and / or component and the second layer and / or component. Furthermore, as used herein, "located above" does not refer to a relative position with reference to gravity. For example, when a first layer and / or component is positioned below, above, or to one side of a second layer and / or component, the first layer and / or component may be considered "located above a second layer and / or component." As used herein, a first layer and / or component described as "bonded to" a second layer and / or component means that the layer and / or component is bonded to each other by direct contact and / or bonding between the two layers and / or components or via an adhesive layer. As used herein, a first layer and / or component described as "contacting" a second layer and / or component or "in contact with a second layer and / or component" refers to direct contact and includes cases where the layers and / or components are bonded to each other.

[0202] As in Figure 2-5As shown in Figures 1 and 12, foldable devices 101, 301, 401, 501, and / or 1201 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 to the first contact surface 263. In some embodiments, such as in Figure 2-5 As shown, the second contact surface 265 of the adhesive layer 261 may include a planar surface. In some embodiments, such as in... Figure 2 and 5 As shown, the first contact surface 263 of the adhesive layer 261 may include a planar surface. The adhesive thickness 267 of the adhesive layer 261 can be defined as the minimum distance 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 about 1 μm or greater, about 5 μm or greater, about 10 μm or greater, about 100 μm or less, about 60 μm or less, about 30 μm or less, or about 20 μm or less. 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 subrange thereof.

[0203] In some implementations, such as in Figure 2 and 4 As shown, the second contact surface 265 of the adhesive layer 261 may face the first main surface 273 of the release liner 271 (described below). In another embodiment, as shown, the second contact surface 265 of the adhesive layer 261 may contact the first main surface 273 of the release liner 271. In some embodiments, such as in Figure 3 , 5 As shown in Figure 12, the second contact surface 265 of the adhesive layer 261 may face the first main surface 303 of the display device 307. In another embodiment, as shown, the second contact surface 265 of the adhesive layer 261 may contact the first main surface 303 of the display device 307.

[0204] In some implementations, such as in Figure 2-5 As shown in Figures 1 and 12, the first contact surface 263 of the adhesive layer 261 may face the second surface region 225 or 425 of the first portion 221 or 421. In another embodiment, as shown, the first contact surface 263 of the adhesive layer 261 may contact the second surface region 225 or 425 of the first portion 221 or 421. In some embodiments, such as in Figure 2-5As shown in Figure 12, the first contact surface 263 of the adhesive layer 261 may face the fourth surface region 235 or 435 of the second portion 231 or 431. In another embodiment, as shown, the first contact surface 263 of the adhesive layer 261 may contact the fourth surface region 235 or 435 of the second portion 231 or 431. In some embodiments, such as in Figure 2-5 As shown in Figure 12, the first contact surface 263 of the adhesive layer 261 may face the second central surface area 219 or 419 of the central portion 281 or 481. In another embodiment, as shown in Figure 3-4 As shown, the first contact surface 263 of the adhesive layer 261 can contact the second central surface area 219 or 419 of the central portion 281 or 481. In another embodiment, such as in Figure 3-4 As shown, adhesive layer 261 may extend into the second recess 244 or 444. In some embodiments, although not shown, the second recess may not be completely filled, for example, to leave space for electronic devices and / or mechanical devices. In some embodiments, although not shown, another adhesive layer (e.g., similar to adhesive layer 261) may be disposed above and / or in contact with the first main surface (e.g., the first surface area, the third surface area), and / or extend into the first recess, but the first recess may not be completely filled, for example, to leave space for electronic devices and / or mechanical devices.

[0205] In some embodiments, the adhesive layer 261 may include one or more of the following: polyolefins, polyamides, halogenated polymers (e.g., polyvinyl chloride or fluoropolymers), elastomers, urethanes, phenolic resins, parylene, polyethylene terephthalate (PET), and polyether ether ketone (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), polyvinylidene fluoride (PVF), polyvinylidene fluoride (PVDF), perfluoropolyether (PFPE), perfluorosulfonic acid (PFSA), perfluoroalkoxy polymers (PFA), fluorinated ethylene propylene (FEP) polymers, and ethylene tetrafluoroethylene (ETFE) polymers. Exemplary embodiments of elastomers include rubbers (e.g., polybutadiene, polyisoprene, chloroprene rubber, butyl rubber, nitrile rubber) and block copolymers (e.g., styrene-butadiene, high-impact polystyrene, poly(dichlorophosphazene)). In another embodiment, adhesive layer 261 may include an optically clear adhesive. In another embodiment, 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, phenolic resin varnish-based epoxy materials, cycloaliphatic epoxy materials, and glycidylamine-based epoxy materials. In another embodiment, the optically clear adhesive may include, but is not limited to, acrylic adhesives, such as 3M 8212 adhesive, or optically clear liquid adhesives, such as LOCTITE optically clear liquid adhesive. Exemplary embodiments of optically clear adhesives include transparent acrylics, epoxy materials, silicones, and polyurethanes. For example, optically transparent 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 purchased from Henkel.

[0206] In some embodiments, the adhesive layer 261 may contain an elastic modulus of about 0.001 MPa or greater, about 0.01 MPa or greater, about 0.1 MPa or greater, about 1 MPa or less, about 0.5 MPa or less, about 0.1 MPa or less, or about 0.05 MPa or less. In some embodiments, the adhesive layer 261 may contain an elastic modulus in the range of about 0.001 MPa to about 1 MPa, about 0.01 MPa to about 1 MPa, about 0.01 MPa to about 0.5 MPa, about 0.05 MPa to about 0.5 MPa, about 0.1 MPa to about 0.5 MPa, about 0.001 MPa to about 0.5 MPa, about 0.001 MPa to about 0.01 MPa, or any range or subrange thereof. In some embodiments, the adhesive layer may include an elastic modulus within one or more of the ranges discussed below regarding the elastic modulus of the polymer-based portion 241.

[0207] As in Figure 2 , 5 As shown in Figures 1 and 12, the polymer-based portion 241 of the foldable devices 101, 401, and / or 1201 may be positioned between the first portion 221 or 421 and the second portion 231 or 431. In some embodiments, as shown, the polymer-based portion 241 may be at least partially positioned in the second recess 244 or 444. In other embodiments, as shown, the polymer-based portion 241 may fill the second recess 244 or 444. In some embodiments, although not shown, the second recess may not be completely filled, for example, to leave space for electronic and / or mechanical devices. In some embodiments, although not shown, another polymer-based portion (e.g., similar to polymer-based portion 241) may extend into and / or fill the first recess. Figure 2 , 5 As shown in Figures 1 and 12, the polymer-based portion 241 may include a fourth contact surface 247 opposite to the third contact surface 245. In some embodiments, as shown, the fourth contact surface 247 may include a planar surface. In other embodiments, the fourth contact surface 247 may be substantially coplanar with the second surface region 225 or 425 and the fourth surface region 235 or 435 (e.g., extending along a common plane (second plane 204b or 404b)). 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 second surface region 225 or 425 and the fourth surface region 235 or 435, the third contact surface 245 may also be substantially coplanar with the second central surface region 219 or 419 (e.g., extending along a common plane (fourth plane 204d)). In some embodiments, as in Figure 2 and5 As shown, the first contact surface 263 of the adhesive layer 261 may face the fourth contact surface 247 of the polymer-based portion 241. In another embodiment, as shown, the first contact surface 263 of the adhesive layer 261 may contact the fourth contact surface 247 of the polymer-based portion 241.

[0208] In some embodiments, the polymer-based portion 241 comprises a polymer (e.g., an optically transparent polymer). In other embodiments, the polymer-based portion 241 may comprise one or more of the following optically transparent materials: acrylics (e.g., polymethyl methacrylate (PMMA)), epoxy materials, silicones, and / or polyurethanes. Examples of epoxy materials include: bisphenol-based epoxy resins, phenolic resin varnish-based epoxy materials, cycloaliphatic epoxy materials, and glycidylamine-based epoxy materials. In still other embodiments, the polymer-based portion 241 may comprise one or more of the following: polyolefins, polyamides, halogenated 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), polyvinylidene 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, chloroprene rubber, butyl rubber, nitrile rubber) and block copolymers (e.g., styrene-butadiene, high-impact polystyrene, poly(dichlorophosphazene)), such as one or more of polystyrene, polydichlorophosphazene, and poly(5-ethylidene-2-norbornene). In some embodiments, the polymer-based portion may include 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 other embodiments, the second portion may include an ethylene glycol copolymer. An exemplary embodiment of the ethylene glycol copolymer includes SURLYN (e.g., Surlyn PC-2000, Surlyn 8940, Surlyn 8150) purchased from Dow Chemical Company. Another exemplary embodiment of the second part includes Eleglass w802-GL044 purchased from Axalta Chemical Company, having 1% to 2% by weight of a crosslinking agent. In some embodiments, the polymer-based portion 241 may also include nanoparticles, such as carbon black, carbon nanotubes, silica nanoparticles, or polymer-containing nanoparticles. In some embodiments, the polymer-based portion may also include fibers to form a polymer-fiber composite.

[0209] In some embodiments, the polymer-based portion 241 may contain a coefficient of thermal expansion (CTE). As used herein, the CTE is measured using a PICOSCAL Michelson Interferometer between -20°C and 40°C, according to ASTM E289-17. In some embodiments, the polymer-based portion 241 may contain particles of one or more of copper oxides, β-quartz, tungstates, vanadates, pyrophosphates, and / or nickel-titanium alloys. In some embodiments, the polymer-based portion 241 may contain approximately -20 × 10⁻⁶ particles. -7 1 / ℃ or greater, approximately -10×10 -7 1 / ℃ or greater, approximately -5 × 10 -7 1 / ℃ or greater, approximately -2×10 -7 1 / ℃ or greater, approximately 10 × 10 -7 1 / ℃ or less, approximately 5 × 10 -7 1 / ℃ or less, approximately 2×10 -7 1 / ℃ or less, approximately 1×10 -7 1 / ℃ or less or 0 1 / ℃ or less CTE. In some embodiments, the polymer-based portion 241 may be included from about -20 × 10 -7 1 / ℃ to approximately 10×10 -7 1 / ℃, approximately -20×10 -7 1 / ℃ to approximately 5×10 -7 1 / ℃, approximately -10×10 -7 1 / ℃ to approximately -5×10 -7 1 / ℃, approximately -10×10 -7 1 / ℃ to approximately 2×10 -7 1 / ℃, approximately -10×10 -7 1 / ℃ to 0 1 / ℃, from approximately -5×10 -7 1 / ℃ to 0 1 / ℃, from approximately -2×10 -7 CTE in the range of 1 / ℃ to about 0 1 / ℃ or any range or subrange thereof. By providing a polymer-based portion containing a low (e.g., negative) coefficient of thermal expansion, warping caused by volume change during the curing of the polymer-based portion can be mitigated.

[0210] In some embodiments, the polymer-based portion 241 may include an elastic modulus of about 0.01 megapascals (MPa) or greater, about 1 MPa or greater, about 10 MPa or greater, about 20 MPa or greater, about 100 MPa or greater, about 200 MPa or greater, about 1,000 MPa or greater, about 5,000 MPa or less, about 3,000 MPa or less, about 1,000 MPa or less, about 500 MPa or less, or about 200 MPa or less. In some embodiments, the polymer-based portion 241 may include pressures ranging from about 0.001 MPa to about 5,000 MPa, from about 0.01 MPa to about 3,000 MPa, from about 0.01 MPa to about 1,000 MPa, from about 0.01 MPa to about 500 MPa, from about 0.01 MPa to about 200 MPa, from about 1 MPa to about 5,000 MPa, from about 1 MPa to about 1,000 MPa, from about 1 MPa to about 200 MPa, from about 10 MPa to about 5,000 MPa, and from about 10 MPa. The elastic modulus in the range of about 1,000 MPa, from about 10 MPa to about 200 MPa, from about 20 MPa to about 3,000 MPa, from about 20 MPa to about 1,000 MPa, from about 20 MPa to about 200 MPa, from about 100 MPa to about 3,000 MPa, from about 100 MPa to about 1,000 MPa, from about 100 MPa to about 200 MPa, from about 200 MPa to about 5,000 MPa, from about 200 MPa to about 3,000 MPa, and from about 200 MPa to about 1,000 MPa, and all ranges and subranges therebetween. In some embodiments, the elastic modulus of the polymer-based portion 241 may be in the range of 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 subrange thereof. By providing the polymer-based portion 241 having an elastic modulus in the range of about 0.01 MPa to about 3,000 MPa (e.g., from about 20 MPa to about 3 GPa), it is possible to facilitate folding of the foldable device without failure. In some embodiments, the adhesive layer 261 contains an elastic modulus greater than that of the polymer-based portion 241, and this arrangement provides improved performance in terms of puncture resistance. In some embodiments, the elastic modulus of the polymer-based portion 241 may be less than that of the foldable substrate 206, 407, or 807. In some embodiments, the adhesive layer 261 may contain an elastic modulus within the ranges listed above in this paragraph. In another embodiment, adhesive layer 261 may contain an elastic modulus substantially the same as that of polymer-based portion 241.In another embodiment, the elastic modulus of the adhesive layer 261 may be in the range of 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 subrange thereof. In some embodiments, the elastic modulus of the polymer-based portion 241 may be less than the elastic modulus of the first portions 221, 421, or 821. In some embodiments, the elastic modulus of the polymer-based portion 241 may be less than the elastic modulus of the second portions 231, 431, or 831.

[0211] In some implementations, such as in Figure 2-5 and Figure 11-12As shown, coating 251 may be disposed above a first main surface 203 of foldable substrate 206 or 407. In another embodiment, coating 251 may be disposed above a first portion 221 or 421, a second portion 231 or 431, and a central portion 281 or 481. In some embodiments, coating 251 may include a third main surface 253 and a fourth main surface 255 opposite to the third main surface 253. In another embodiment, coating 251 (e.g., the fourth main surface 255) may contact foldable substrate 206 or 407 (e.g., the first main surface 203 or 403). In another embodiment, at least a portion of coating 251 may be positioned in a first recess 234 or 434. In a further embodiment, coating 251 may fill the first recess 234 or 434. In another embodiment, coating 251 may include a coating thickness 257 defined between the third main surface 253 and the fourth main surface 255. In another embodiment, the coating thickness 257 may be about 0.1 μm or greater, about 1 μm or greater, about 5 μm or greater, about 10 μm or greater, about 15 μm or greater, about 20 μm or greater, about 25 μm or greater, about 40 μm or greater, about 50 μm or greater, about 60 μm or greater, about 70 μm or greater, about 80 μm or greater, about 90 μm or greater, about 200 μm or less, about 100 μm or less, about 50 μm or less, about 30 μm or less, about 25 μm or less, about 20 μm or less, about 20 μm or less, about 15 μm or less, or about 10 μm or less. In some embodiments, the coating thickness 257 can be from about 0.1 μm to about 200 μm, from about 1 μm to about 200 μm, from about 10 μm to about 200 μm, from about 50 μm to about 200 μm, from about 0.1 μm to about 100 μm, from about 1 μm to about 100 μm, from about 10 μm to about 100 μm, from about 20 μm to about 100 μm, from about 30 μm to about 100 μm. The range of μm, from about 40 μm to about 100 μm, from about 50 μm to about 100 μm, from about 60 μm to about 100 μm, from about 70 μm to about 100 μm, from about 80 μm to about 100 μm, from about 90 μm to about 100 μm, from about 0.1 μm to about 50 μm, from about 1 μm to about 50 μm, from about 10 μm to about 50 μm, or any range or subrange thereof.In another embodiment, the coating thickness 257 can be 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 5 μm. Within the range of about 25 μm, about 5 μm to about 20 μm, about 5 μm to about 15 μm, about 5 μm to about 10 μm, about 10 μm to about 30 μm, about 10 μm to about 25 μm, about 10 μm to about 20 μm, about 10 μm to about 15 μm, about 15 μm to about 30 μm, about 15 μm to about 25 μm, about 15 μm to about 20 μm, about 20 μm to about 30 μm, about 20 μm to about 25 μm, or any range or subrange thereof.

[0212] In some embodiments, the polymer-based portion and / or adhesive layer may include a yield strain. Providing a first recess opposite to a second recess can reduce the strain encountered by the polymer-based portion or other materials (e.g., adhesive layer) in the recess (e.g., a reduction of 0% to 50%). Therefore, the yield strain requirement for the polymer-based portion can be relaxed. In some embodiments, the yield strain of the polymer-based portion and / or adhesive layer may be about 3% or greater, about 4% or greater, about 5% or greater, about 6% or greater, about 7% or greater, about 500% or less, about 100% or less, about 50% or less, about 20% or less, about 15% or less, about 10% or less, about 9% or less, or about 8% or less. In some embodiments, the yield strain of the polymer-based portion and / or adhesive layer may be in the range of about 1% to about 500%, about 1% to about 100%, about 2% to about 100%, about 2% to about 50%, about 3% to about 50%, about 3% to about 20%, about 4% to about 20%, about 4% to about 15%, about 5% to about 15%, about 5% to about 10%, about 5% to about 9%, about 6% to about 9%, about 6% to about 8%, about 7% to about 8%, or any range or subrange thereof.

[0213] In some embodiments, coating 251 may comprise a polymeric hard coating. In other embodiments, the polymeric hard coating may comprise one or more of ethylene-acid copolymers, polyurethane-based polymers, acrylate resins, and mercaptoester resins. 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 based on polyurethane polymers include modified polyurethane aqueous dispersions (e.g., Axalta manufactured by Axalta). Exemplary embodiments of UV-curable acrylate resins include acrylate resins (e.g., those manufactured by Allinx). Resins), cyanoacrylate adhesives (e.g., those manufactured by Krayden). UV620) and UV radical acrylic resins (e.g., Ultrabond windshield repair resin, e.g., Ultrabond (45CPS)). Exemplary embodiments of mercaptoester resins include mercaptoester triallyl isocyanuates (e.g., Norland's optical adhesive NOA 61). In another embodiment, the polymeric hard coating may include ethylene-acrylic acid 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 acid 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, foldable devices may include low-energy fracture.

[0214] In some embodiments, the coating may include a polymeric hard coating, including optically transparent polymeric hard coatings. Materials suitable for optically transparent polymeric hard coatings include, but are not limited to: cured acrylate resin materials, inorganic-organic hybrid polymer materials, aliphatic or aromatic hexafunctional urethane acrylates, siloxane-based hybrid materials, and nanocomposites, such as epoxy materials and urethane materials having nanosilicates. In some embodiments, the optically transparent polymeric hard coating may consist primarily of one or more of these materials. As used herein, "inorganic-organic hybrid polymer material" means a polymer material comprising monomers and having inorganic and organic components. Inorganic-organic hybrid polymers are obtained through polymerization reactions between monomers having inorganic and organic groups. Inorganic-organic hybrid polymers are not nanocomposites containing separated inorganic and organic components or phases (e.g., inorganic particles dispersed in an organic matrix). More specifically, materials suitable for optically transparent polymer (OTP) hard coatings include, but are not limited to, polyimide, polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), organic polymer materials, inorganic-organic hybrid polymer materials, and aliphatic or aromatic hexafunctional urethane acrylates. In some embodiments, the OTP hard coating may consist substantially of an organic polymer material, an inorganic-organic hybrid polymer material, or an aliphatic or aromatic hexafunctional urethane acrylate. In some embodiments, the OTP hard coating may consist of polyimide, an organic polymer material, an inorganic-organic hybrid polymer material, or an aliphatic or aromatic hexafunctional urethane acrylate. In some embodiments, the OTP hard coating may include nanocomposite materials. In some embodiments, the OTP hard coating may include at least one of nanosilicates, epoxy materials, and urethane materials. Suitable compositions for such OTP hard coatings 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 comprising monomers, wherein the monomers have only organic components. In some embodiments, the OTP hard coating may comprise an organic polymeric material manufactured by Gunze Ltd. and having a hardness of 9H, such as Gunze’s “High Durability Transparent Film”. As used herein, “inorganic-organic hybrid polymer material” means a polymeric material comprising monomers and having both inorganic and organic components. Inorganic-organic hybrid polymers are obtained through polymerization reactions between monomers having inorganic and organic groups. Inorganic-organic hybrid polymers are not nanocomposites comprising separate inorganic and organic components or phases (e.g., inorganic particles dispersed in an organic matrix).In some embodiments, the inorganic-organic hybrid polymer material may include polymeric monomers containing inorganic silicon-based groups, such as silsesquioxane polymers. Silsesquioxane polymers may, for example, have the following chemical structure (RSiO). 1.5 ) nThe R is an alkyl-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 coating may comprise a silsesquioxane polymer in combination with an organic matrix, such as SILPLUS manufactured by Nippon Steel Chemical Co., Ltd. In some embodiments, the OTP hard coating may comprise 90% to 95% by weight of an aromatic hexafunctional urethane acrylate [e.g., PU662NT (aromatic hexafunctional urethane acrylate) manufactured by Miwon Specialty Chemical Co.] and 10% to 5% by weight 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 coating composed of aliphatic or aromatic hexafunctional urethane acrylates can be formed as a separate layer by spin-coating the layer onto 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 coating (e.g., coating thickness 257) can range from 1 μm to 150 μm, including subranges. For example, the coating thickness (e.g., coating thickness 257) may be in the range of 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 within a range having any two of these values ​​as endpoints. In some embodiments, the OTP hard coating may be a single monolithic layer. In some embodiments, the OTP hard coating may be an inorganic-organic hybrid polymer material layer or an organic polymer material layer having a thickness in the range of 80 μm to 120 μm (inclusive). For example, an OTP hard coating comprising an inorganic-organic hybrid polymer material or an organic polymer material may have a thickness from 80 μm to 110 μm, 90 μm to 100 μm, or in a range having any two of these values ​​as endpoints. In some embodiments, the OTP hard coating may be an aliphatic or aromatic hexafunctional urethane acrylate material layer having a thickness in the range of 10 μm to 60 μm (inclusive).For example, an OTP hard coating comprising an aliphatic or aromatic hexafunctional urethane acrylate material may have a thickness ranging from 10 μm to 55 μm, 10 μm to 50 μm, 10 μm to 40 μm, 10 μm to 45 μm, 10 μm to 40 μm, 10 μm to 35 μm, 10 μm to 30 μm, 10 μm to 25 μm, 10 μm to 20 μm, or having any two of these values ​​as endpoints.

[0215] In some embodiments, if provided, surface coating 251 may further comprise one or more of an easy-clean coating, a low-friction coating, an oleophobic coating, a diamond-like carbon (DLC) coating, a scratch-resistant coating, or an abrasion-resistant coating. The scratch-resistant coating may comprise oxynitrides, such as aluminum oxynitride or silicon oxynitride, and have a thickness of about 500 micrometers or more. In such embodiments, the abrasion-resistant layer may comprise the same material as the scratch-resistant layer. In some embodiments, the low-friction coating may comprise a highly fluorinated silane coupling agent, such as an alkylfluorosilane, wherein an oxymethyl group is side-attached to a silicon atom. In such embodiments, the easy-clean coating may comprise the same material as the low-friction coating. In other embodiments, the easy-clean coating may comprise a protonable group, such as an amine, for example, an alkylaminosilane, wherein an oxymethyl group is side-attached to a silicon atom. In such embodiments, the oleophobic coating may comprise the same material as the easy-clean coating. In some embodiments, the diamond-like carbon coating comprises carbon and may be generated by applying a high-voltage potential in the presence of a hydrocarbon plasma.

[0216] Compared to a single recess having a surface recessed by the sum of a first distance and a second distance, providing a first recess opposite to a second recess reduces the flexural induced strain of the material located in the first and / or the second recess. This reduced flexural induced strain in the material located in the first and / or the second recess allows for the use of a wider range of materials due to reduced strain requirements. For example, a harder and / or more rigid material (e.g., coating 251) can be located in the first recess, which can improve the impact resistance, puncture resistance, abrasion resistance, and / or scratch resistance of the foldable device. Furthermore, controlling the properties of the first material (e.g., coating 251) located in the first recess and the second material located in the second recess can control the position of the neutral axis of the foldable device and / or the foldable substrate, which can reduce (e.g., mitigate, eliminate) mechanical instability, device fatigue, and / or device failure.

[0217] In some implementations, such as in Figure 2 and 4As shown, foldable devices 101 and 401 may include a release liner 271, but in other embodiments, other substrates (e.g., glass-based substrates and / or ceramic-based substrates discussed throughout this application) may be used instead of the release liner 271 illustrated. In another embodiment, as shown, the release liner 271 or another substrate may be disposed above the adhesive layer 261. In a further embodiment, as shown, the release liner 271 or another substrate may directly contact the second contact surface 265 of the adhesive layer 261. The release liner 271 or another substrate may include a first main surface 273 and a second main surface 275 opposite to the first main surface 273. As shown, the release liner 271 or another substrate may be disposed on the adhesive layer 261 by attaching the second contact surface 265 of the adhesive layer 261 to the first main surface 273 of the release liner 271 or another substrate. In some embodiments, as shown, the first primary surface 273 of the release liner 271 or another substrate may comprise a planar surface. In some embodiments, as shown, the second primary surface 275 of the release liner 271 or another substrate may comprise a planar surface. The substrate comprising the release liner 271 may comprise paper and / or a polymer. Exemplary embodiments of paper include kraft paper, machine-processed paper, polymer-coated paper (e.g., polymer-coated paper, cellophane, silicone-treated paper), or clay-coated paper. Exemplary embodiments of polymers include polyesters (e.g., polyethylene terephthalate (PET)) and polyolefins (e.g., low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP)).

[0218] In some implementations, such as in Figure 3 , 5 As shown in Figures 1 and 12, foldable devices 301, 501, and 1201 may include a display device 307. In another embodiment, as shown, the display device 307 may be disposed above the adhesive layer 261. In another embodiment, as shown, the display device 307 may contact a second contact surface 265 of the adhesive layer 261. In some embodiments, foldable devices similar to foldable devices 301, 501, or 1201 can be produced by removing... Figure 2 and 4The foldable device 101 or 401 is achieved by attaching a release liner 271 to the second contact surface 265 of the adhesive layer 261 and attaching the display device 307 to the second contact surface 265 of the adhesive layer 261. Alternatively, the foldable device 301 can be manufactured without the additional step of removing the release liner 271 before attaching the display device 307 to the second contact surface 265 of the adhesive layer 261, for example, when the release liner 271 is not applied to the second contact surface 265 of the adhesive layer 261. The display device 307 may include a first main surface 303 and a second main surface 305 opposite to the first main surface 303. As shown, the display device 307 can be disposed on the adhesive layer 261 by attaching the second contact surface 265 of the adhesive layer 261 to the second main surface 305 of the display device 307. In some embodiments, as shown, the first main surface 303 of the display device 307 may include a planar surface. Display device 307 may 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, display device 307 may be part of a portable electronic device, such as a consumer electronics product, a smartphone, a tablet computer, a wearable device, or a laptop computer.

[0219] Embodiments of this disclosure may include consumer electronic products. The consumer electronic product may include a front surface, a rear surface, and side surfaces. The consumer electronic product may further include electrical components at least partially within the housing. The electrical components may include a controller, memory, and a display. The display may be located on or adjacent to the front surface of the housing. The consumer electronic product may include a cover substrate disposed above the display. In some embodiments, a portion of the housing or at least one of the cover substrates includes a foldable device that extends throughout the scope of this disclosure.

[0220] The foldable devices disclosed herein can be incorporated into another article, such as articles having a display (or display articles) (e.g., consumer electronics, including mobile phones, tablets, computers, navigation systems, wearable devices (e.g., watches), and the like), building articles, transportation articles (e.g., automobiles, trains, airplanes, ships, etc.), electrical articles, or any article that benefits from a certain degree of transparency, scratch resistance, abrasion resistance, or a combination thereof. Illustrative articles of any of the foldable devices disclosed herein are shown in [the document / document]. Figure 13-14 In China. Specifically, Figures 13 to 14A consumer electronic device 1300 is illustrated, comprising: a housing 1302 having a front surface 1304, a rear surface 1306, and a side surface 1308; electrical components (not shown) at least partially or entirely within the housing, including at least a controller, memory, and a display 1310 located on or adjacent to the front surface of the housing; and a cover substrate 1312 located on or above the front surface of the housing, such that it is above the display. In some embodiments, at least one of the cover substrate 1312 or a portion of the housing 1302 may include any of the foldable devices disclosed herein, such as a foldable substrate.

[0221] In some embodiments, the foldable substrate 206, 407, or 807 may comprise a glass-based substrate and / or a ceramic-based substrate, and the first portion 221, 421, or 821, the second portion 231, 431, or 831, and / or the central portion 281, 481, or 881 may comprise one or more compressive stress regions. In some embodiments, the compressive stress regions may be generated by chemical strengthening. Chemical strengthening may include an ion exchange process, wherein ions in the surface layer are replaced by, or exchanged with, larger ions having the same valence or oxidation state. Methods of chemical strengthening will be discussed later. It is not intended to be theoretically constrained, but chemical strengthening of the first portion 221, 421, or 821, the second portion 231, 431, or 831, and / or the central portion 281, 481, or 881 can achieve good impact resistance and / or puncture resistance (e.g., resistance to failure at pen drop heights of approximately 15 cm or greater, approximately 20 cm or greater, or approximately 50 cm or greater). Not wishing to be bound by theory, the chemically strengthened first portion 221, 421, or 821, second portion 231, 431, or 831, and / or central portion 281, 481, or 881 can achieve small (e.g., less than about 10 mm or less) bending radii because the compressive stress from chemical strengthening can offset the bending-induced tensile stress on the outermost surface of the substrate. The compressive stress region can extend into a portion of the first and / or second portions, reaching a depth called the compression depth. As used herein, compression depth means the depth to 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 compression depth can be measured using a surface stress meter or a scattered light polarizer (SCALP, where the values ​​reported herein are SCALP-5 manufactured by Glassstress Co., Estonia). If the stress in the substrate and / or portion is generated by the exchange of potassium ions into the substrate, the compression depth is measured using, for example, an FSM-6000 [Orihara Industrial Co., Ltd., Japan]. Unless otherwise specified, compressive stress (including surface CS) is measured using a surface stress meter (FSM) with a commercially available instrument, such as the FSM-6000 manufactured by Orihara. Surface stress measurement relies on the accurate measurement of the stress optical coefficient (SOC), which is related to the birefringence of the glass. Unless otherwise specified, SOC is measured according to Scheme C (glass disk method) of 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 approximately 400 μm, SCALP is used to measure the depth of compression and center tension (CT). If the stress in the substrate and / or portion is generated by exchanging both potassium and sodium ions into the substrate and / or portion, and the thickness of the article being measured exceeds approximately 400 μm, SCALP is used to measure the depth of compression and CT. Not wishing to be confined to theory, the depth of sodium exchange can indicate the depth of compression, while the depth of potassium ion exchange can indicate a change in the magnitude of compressive stress (but not a change from compressive stress to tensile stress). The refractive near-field (RNF) method (described in U.S. Patent No. 8,854,623 entitled "Systems and methods for measuring a profile characteristic of a glass sample," which is incorporated herein by reference in its entirety) 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 center tension value provided by SCALP is used in the RNF method. The stress distribution graph obtained via RNF is force-balanced and calibrated to the maximum center tension value provided by SCALP measurement. As used herein, “layer depth” (DOL) means the depth to which ions (e.g., sodium, potassium) are exchanged into the substrate and / or portion. In this disclosure, when the maximum center tension cannot be directly measured by SCALP (e.g., when the article being measured is thinner than about 400 μm), the maximum center tension can be approximated by dividing the product of the maximum compressive stress and the compression depth by the difference between the substrate thickness and twice the compression depth, wherein the compressive stress and compression depth are measured by FSM.

[0222] In some embodiments, a first portion 221, 421, or 821 comprising a glass-based portion and / or a ceramic-based portion may include a first compressive stress region at a first surface region 223, 423, or 823, extending from the first surface region 223, 422, or 823 to a first compression depth. In some embodiments, a first portion 221, 421, or 821 comprising a first glass-based and / or ceramic-based portion may include a second compressive stress region at a second surface region 225, 425, or 825, extending from the second surface region 225, 425, or 825 to a second compression depth. In some embodiments, the first compression depth and / or the second compression depth, as a percentage of the substrate thickness 211, 411, or 811, may be about 1% or greater, about 5% or greater, about 10% or greater, about 30% or less, about 25% or less, or about 20% or less. In some embodiments, the first compression depth and / or the second compression depth as a percentage of the substrate thickness 211, 411, or 811 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 subrange thereof. In other embodiments, the first compression depth and / or the second compression depth as a percentage of the substrate thickness 211, 411, or 811 may be about 10% or less, for example, from about 1% to about 10%, from about 1% to about 8%, from about 3% to about 8%, from about 5% to about 8%, or any range or subrange thereof.

[0223] In another embodiment, the first compression depth may be substantially equal to the second compression depth. In some embodiments, the first compression depth and / or the second compression depth may be about 1 μm or greater, about 10 μm or greater, about 30 μm or greater, about 50 μm or greater, about 200 μm or less, about 150 μm or less, about 100 μm or less, or about 60 μm or less. In some embodiments, the first compression depth and / or the second compression 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 subrange thereof. Good impact resistance and / or puncture resistance can be achieved by providing a first portion comprising a first glass-based and / or ceramic-based portion (including a first compression depth and / or a second compression depth ranging from about 1% to about 30% of the first thickness).

[0224] 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 other embodiments, the first maximum compressive stress and / or the second maximum compressive stress may be about 100 MPa or greater, about 300 MPa or greater, about 500 MPa or greater, about 600 MPa or greater, about 700 MPa or greater, about 1,500 MPa or less, about 1,200 MPa or less, about 1,000 MPa or less, or about 800 MPa or less. In another embodiment, the first maximum compressive stress and / or the second maximum compressive stress may be within a range or any sub-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 700 MPa to about 1,000 MPa, about 700 MPa to about 800 MPa, or elsewhere. By providing a first maximum compressive stress and / or a second maximum compressive stress in the range of about 100 MPa to about 1,500 MPa, good impact resistance and / or puncture resistance can be achieved.

[0225] In some embodiments, the first portion 221, 421, or 821 may include a first layer depth of one or more alkali metal ions associated with a first compressive stress region and a first layer depth. In some embodiments, the first portion 221, 421, or 821 may include a second layer depth of one or more alkali metal ions associated with a second compressive stress region and a second layer depth. As used herein, the one or more alkali metal ions in the layer depth may include sodium, potassium, rubidium, cesium, and / or francium. In some embodiments, one or more alkali ions in the first layer depth and / or the second layer depth of one or more alkali ions include potassium. In some embodiments, the first layer depth and / or the second layer depth as a percentage of the substrate thickness 211, 411, or 811 may be about 1% or more, about 5% or more, about 10% or more, about 40% or less, about 35% or less, about 30% or less, about 25% or less, or about 20% or less. In some embodiments, the first layer depth and / or the second layer depth, as a percentage of the substrate thickness 211, 411, or 811, 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 subrange thereof. In other embodiments, the first layer depth of one or more alkali metal ions and / or the second layer depth of one or more alkali metal ions, as a percentage of the substrate thickness 211, 411, or 811, may be about 10% or less, for example, from about 1% to about 10%, from about 1% to about 8%, from about 3% to about 8%, from about 5% to about 8%, or any range or subrange thereof. In some embodiments, the depth of the first layer of one or more alkali metal ions and / or the depth of the second layer of one or more alkali metal ions may be about 1 μm or greater, about 10 μm or greater, about 30 μm or greater, about 50 μm or greater, about 200 μm or less, about 150 μm or less, about 100 μm or less, or about 60 μm or less. In some embodiments, the depth of the first layer of one or more alkali metal ions and / or the depth of the second layer of 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 subrange thereof.

[0226] In some embodiments, the first portion 221, 421, or 821 may include a first tensile stress region. In some embodiments, the first tensile stress region may be located between a first compressive stress region and a second compressive stress region. In some embodiments, the first tensile stress region may include a first maximum tensile stress. In other embodiments, the first maximum tensile stress may be about 10 MPa or greater, about 20 MPa or greater, about 30 MPa or greater, about 100 MPa or less, about 80 MPa or less, or about 60 MPa or less. In another embodiment, 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 subrange thereof. Providing a first maximum tensile stress in the range of about 10 MPa to about 100 MPa achieves good impact resistance and / or puncture resistance while providing low-energy fracture, as discussed below.

[0227] In some embodiments, the first portion 221, 421, or 821 may include a first average potassium concentration based on oxides. As used herein, "based on oxides" means measuring a component as if the non-oxygen component in a compound were converted into a specified oxide form or a fully oxidized oxide (if no specific oxide form is specified). For example, sodium (Na) based on oxides refers to the amount of sodium oxide (Na₂O), while potassium based on oxides refers to the amount of potassium oxide (K₂O). Thus, the component does not need to actually be in a specified oxide form or a fully oxidized oxide form in order to count the component according to an "oxide-based" measurement. Therefore, an "oxide-based" measurement for a specific component involves conceptually converting the material containing the non-oxygen element of the specific component into a specified oxide form or a fully oxidized oxide (if no specific oxide form is specified before calculating the concentration based on oxides). In some embodiments, the first average potassium concentration based on oxides may be about 10 parts per million (10 ppm) or more, about 50 ppm or more, about 200 ppm or more, about 500 ppm or more, about 1,000 ppm or more, about 2,000 ppm or more, about 300,000 or less, about 100,000 ppm or less, about 50,000 ppm or less, about 20,000 ppm or less, about 10,000 ppm or less, or about 5,000 ppm or less. In some embodiments, the first average potassium concentration 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 subrange thereof. It is not intended to be theoretically limited, but the average potassium concentration includes potassium introduced via chemical strengthening and potassium in the newly formed foldable substrate.

[0228] In some embodiments, the second portion 231, 431, or 831 comprising the second glass-based and / or ceramic-based portion may be included in a third compressive stress region at the third surface region 233, 433, or 833, extending from the third surface region 233, 433, or 833 to a third compression depth. In some embodiments, the second portion 231, 431, or 831 comprising the second glass-based and / or ceramic-based portion may be included in a fourth compressive stress region at the fourth surface region 235, 435, or 835, extending from the fourth surface region 235 to a fourth compression depth. In some embodiments, the third compression depth and / or fourth compression depth as a percentage of the substrate thickness 211, 411, or 811 may be about 1% or greater, about 5% or greater, about 10% or greater, about 30% or less, about 25% or less, or about 20% or less. In some embodiments, the third and / or fourth compression depth, as a percentage of the substrate thickness 211, 411, or 811, may be within a range or subrange thereof 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 anywhere in between. In other embodiments, the third compression depth may be substantially equal to the fourth compression depth. In some embodiments, the third and / or fourth compression depth may be about 1 μm or greater, about 10 μm or greater, about 30 μm or greater, about 50 μm or greater, about 200 μm or less, about 150 μm or less, about 100 μm or less, or about 60 μm or less. In some embodiments, the third and / or fourth compression depths may be within 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 subrange thereof. Good impact resistance and / or puncture resistance can be achieved by providing a second portion comprising a glass-based and / or ceramic-based portion (including the third and / or fourth compression depths within a range of about 1% to about 30% of the substrate thickness).

[0229] In some embodiments, the third compressive stress region may include a third maximum compressive stress. In some embodiments, the fourth compressive stress region may include a fourth maximum compressive stress. In other embodiments, the third maximum compressive stress and / or the fourth maximum compressive stress may be about 100 MPa or greater, about 300 MPa or greater, about 500 MPa or greater, about 600 MPa or greater, about 700 MPa or greater, about 1,500 MPa or less, about 1,200 MPa or less, about 1,000 MPa or less, or about 800 MPa or less. In another embodiment, the third and / or fourth maximum compressive stress may be within a range or any sub-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 700 MPa to about 1,000 MPa, about 700 MPa to about 800 MPa, or elsewhere. By providing a third and / or fourth maximum compressive stress in the range of about 100 MPa to about 1,500 MPa, good impact resistance and / or puncture resistance can be achieved.

[0230] In some embodiments, the second portion 231, 431, or 831 may include a third layer depth of one or more alkali metal ions associated with the third compressive stress region and the third layer depth. In some embodiments, the second portion 231 may include a fourth layer depth of one or more alkali metal ions associated with the fourth compressive stress region and the fourth compression depth. In some embodiments, one or more alkali ions in the third layer depth and / or the fourth layer depth of one or more alkali ions comprise potassium. In some embodiments, the third layer depth and / or the fourth layer depth as a percentage of the substrate thickness 211, 411, or 811 may be about 1% or more, about 5% or more, about 10% or more, about 40% or less, about 35% or less, about 30% or less, about 25% or less, or about 20% or less. In some embodiments, the third and / or fourth compression depths as a percentage of the substrate thicknesses 211, 411, or 811 can 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 subrange thereof. In other embodiments, the third layer depth of one or more alkali metal ions and / or the fourth layer depth of one or more alkali metal ions as a percentage of the substrate thicknesses 211, 411, or 811 can be about 10% or less, for example, from about 1% to about 10%, from about 1% to about 8%, from about 3% to about 8%, from about 5% to about 8%, or any range or subrange thereof. In some embodiments, the depth of the third layer and / or the depth of the fourth layer of one or more alkali metal ions may be about 1 μm or greater, about 10 μm or greater, about 30 μm or greater, about 50 μm or greater, about 200 μm or less, about 150 μm or less, about 100 μm or less, or about 60 μm or less. In some embodiments, the depth of the third layer and / or the depth of the fourth layer of 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 subrange thereof.

[0231] In some embodiments, the second portion 231, 431, or 831 may include a second tensile stress region. In some embodiments, the second tensile stress region may be located between a third compressive stress region and a fourth compressive stress region. In some embodiments, the second tensile stress region may include a second maximum tensile stress. In other embodiments, the second maximum tensile stress may be about 10 MPa or greater, about 20 MPa or greater, about 30 MPa or greater, about 100 MPa or less, about 80 MPa or less, or about 60 MPa or less. In another embodiment, 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 subrange thereof. Providing a second maximum tensile stress in the range of about 10 MPa to about 100 MPa achieves good impact resistance and / or puncture resistance while providing low-energy fracture, as discussed below.

[0232] In some embodiments, the second portion 231, 431, or 831 may include a second average potassium concentration based on an oxide. In some embodiments, the second average potassium concentration based on an oxide may be about 10 parts per million (10 ppm) or greater, about 50 ppm or greater, about 200 ppm or greater, about 500 ppm or greater, about 1,000 ppm or greater, about 2,000 ppm or greater, about 300,000 or less, about 100,000 ppm or less, about 50,000 ppm or less, about 20,000 ppm or less, about 10,000 ppm or less, or about 5,000 ppm or less. In some embodiments, the second average potassium concentration 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 subrange thereof.

[0233] 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 compressive stress may be substantially equal to the third maximum compressive stress. In some embodiments, the second maximum compressive stress may be substantially equal to the fourth maximum compressive stress. In some embodiments, the first layer depth of one or more alkali metal ions may be substantially equal to the third layer depth of one or more alkali metal ions. In some embodiments, the second layer depth of one or more alkali metal ions may be substantially equal to the fourth layer depth of one or more alkali metal ions. In some embodiments, the first average potassium concentration may be substantially equal to the second average potassium concentration.

[0234] In some embodiments, the central portion 281, 481, or 881 comprising the glass-based and / or ceramic-based portion may include a first central compressive stress region at a first central surface region 209, 409, or 809, extending from the first central surface region 209, 409, or 809 to a first central compression depth. In some embodiments, the central portion 281, 481, or 881 comprising the glass-based and / or ceramic-based portion may include a second central compressive stress region at a second central surface region 219, 419, or 819, extending from the second central surface region 219, 419, or 819 to a second central compression depth. In some embodiments, the first central compression depth and / or the second central compression depth, as a percentage of the central thickness 227, 427, or 827, may be about 1% or greater, about 5% or greater, about 10% or greater, about 30% or less, about 25% or less, or about 20% or less. In some embodiments, the first and / or second center compression depth as a percentage of the center thickness of 227, 427, or 827 may be within 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 subrange thereof. In other embodiments, the first and / or second center compression depth as a percentage of the center thickness of 227, 427, or 827 may be about 10% or greater, for example, from about 10% to about 30%, from about 10% to about 25%, from about 15% to about 25%, from about 15% to about 20%, or any range or subrange thereof.

[0235] In another embodiment, the first center compression depth may be substantially equal to the second center compression depth. In some embodiments, the first center compression depth and / or the second center compression depth may be about 1 μm or greater, about 10 μm or greater, about 30 μm or greater, about 50 μm or greater, about 200 μm or less, about 150 μm or less, about 100 μm or less, or about 60 μm or less. In some embodiments, the first center compression depth and / or the second center compression 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 subrange thereof. Good impact resistance and / or puncture resistance can be achieved by providing a central portion that includes a glass-based and / or ceramic-based portion (including a first central compression depth and / or a second central compression depth in the range of about 1% to about 30% of the thickness from the center).

[0236] In some embodiments, the first central compressive stress region may include a first central maximum compressive stress. In some embodiments, the second central compressive stress region may include a second central maximum compressive stress. In other embodiments, the first central maximum compressive stress and / or the second central maximum compressive stress may be about 100 MPa or greater, about 300 MPa or greater, about 500 MPa or greater, about 600 MPa or greater, about 700 MPa or greater, about 1,500 MPa or less, about 1,200 MPa or less, about 1,000 MPa or less, or about 800 MPa or less. In another embodiment, the first central maximum compressive stress and / or the second central maximum compressive stress may be within a 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 700 MPa to about 1,000 MPa, about 700 MPa to about 800 MPa, or any range or subrange thereof. By providing a first central maximum compressive stress and / or a second central maximum compressive stress within the range of about 100 MPa to about 1,500 MPa, good impact resistance and / or puncture resistance can be achieved.

[0237] In some embodiments, the central portion 281, 481, or 881 may include a first central layer depth of one or more alkali metal ions associated with a first central compressive stress region and a first central layer depth. In some embodiments, the central portion 281, 481, or 881 may include a second central layer depth of one or more alkali metal ions associated with a second central compressive stress region and a second central layer depth. In some embodiments, one or more alkali ions in the first central layer depth and / or the second central layer depth of one or more alkali ions comprise potassium. In some embodiments, the first central layer depth and / or the second central layer depth as a percentage of the central thickness 227, 427, 827 may be about 1% or greater, about 5% or greater, about 10% or greater, about 40% or less, about 35% or less, about 30% or less, about 25% or less, or about 20% or less. In some embodiments, the first and / or second central layer depths as a percentage of the central thickness of 227, 427, or 827 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 subrange thereof. In other embodiments, the first and / or second central layer depths of one or more alkali metal ions as a percentage of the central thickness of 227, 427, or 827 may be about 10% or less, for example, from about 1% to about 10%, from about 1% to about 8%, from about 3% to about 8%, from about 5% to about 8%, or any range or subrange thereof. In some embodiments, the depth of the first central layer of one or more alkali metal ions and / or the depth of the second central layer of one or more alkali metal ions may be about 1 μm or greater, about 10 μm or greater, about 30 μm or greater, about 50 μm or greater, about 200 μm or less, about 150 μm or less, about 100 μm or less, or about 60 μm or less. In some embodiments, the depth of the first central layer of one or more alkali metal ions and / or the depth of the second central layer of 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 subrange thereof.

[0238] In some embodiments, the first compression depth and / or the third compression depth may be greater than the first center compression depth. In some embodiments, the second compression depth and / or the fourth compression depth may be greater than the second center compression depth. In some embodiments, the first layer depth and / or the third layer depth may be greater than the first center layer depth. In some embodiments, the second layer depth and / or the fourth layer depth may be greater than the second center layer depth.

[0239] In some embodiments, the central portion 281, 481, or 881 may include a central tensile stress region. In some embodiments, the central tensile stress region may be located between a first central compressive stress region and a second central compressive stress region. In some embodiments, the central tensile stress region may include a central maximum tensile stress. In other embodiments, the central maximum tensile stress may be about 125 MPa or greater, about 150 MPa or greater, about 200 MPa or greater, about 375 MPa or less, about 300 MPa or less, or about 250 MPa or less. In another embodiment, the maximum central tensile stress can 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 subrange thereof. Providing a maximum central tensile stress in the range of about 125 MPa to about 375 MPa allows for a low minimum bending radius.

[0240] In some embodiments, the first maximum tensile stress may be substantially equal to the second maximum tensile stress. 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 less than the central maximum tensile stress in the central portion can achieve low-energy fracture and simultaneously enable a lower minimum bending radius. In some embodiments, the absolute difference between the central maximum tensile stress and the first maximum tensile stress and / or the second maximum tensile stress may be about 0 MPa or greater, about 1 MPa or greater, about 5 MPa or greater, about 50 MPa or less, about 20 MPa or less, about 10 MPa or less, or about 8 MPa or less. In some embodiments, the absolute difference between the central maximum tensile stress and the first maximum tensile stress and / or the second maximum tensile stress may be in the range of about 0 MPa to about 50 MPa, about 1 MPa to about 50 MPa, about 1 MPa to about 20 MPa, about 5 MPa to about 20 MPa, about 5 MPa to about 10 MPa, about 5 MPa to about 8 MPa, or any range or subrange thereof.

[0241] In some embodiments, the first compression depth may be substantially equal to the first center compression depth. In further embodiments, the third compression depth may be substantially equal to the first center compression depth. In some embodiments, the second compression depth may be substantially equal to the second center compression depth. In other embodiments, the fourth compression depth may be substantially equal to the second center compression depth. As discussed above, the center thickness may be less than the substrate thickness (e.g., in the range of about 0.5% to about 13%), which allows the maximum center tension to be greater than the first maximum center tension and the second maximum center tension, even if the compression depths of the first portion, the second portion, and the center portion are substantially the same.

[0242] In some embodiments, the first transition portion (e.g., first transition portion 853) and / or the second transition portion may include a transition tensile stress region. This transition tensile stress region may include a maximum transition tensile stress. In other embodiments, the maximum transition tensile stress may be about 125 MPa or greater, about 150 MPa or greater, about 200 MPa or greater, about 500 MPa or less, about 375 MPa or less, about 300 MPa or less, or about 250 MPa or less. In another embodiment, the maximum transition tensile stress may be within the range of about 125 MPa to about 500 MPa, 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 subrange thereof. In another embodiment, the maximum transition tensile stress may be greater than the central maximum tensile stress. In another embodiment, the maximum transition tensile stress may be greater than the first maximum tensile stress and / or the second maximum tensile stress. Providing a maximum transition tensile stress greater than the central maximum tensile stress can offset the strain between the first or second portion and the first transition portion and / or the second transition portion during folding. A transition maximum tensile stress greater than the first maximum tensile stress and / or the second maximum tensile stress is provided to offset the strain between the central portion and the first transition portion and / or the second transition portion during folding.

[0243] In some embodiments, the central portion 281, 481, or 881 may include a central average potassium concentration based on an oxidant. In some embodiments, the central average potassium concentration based on an oxidant may be about 10 parts per million (10 ppm) or more, about 50 ppm or more, about 200 ppm or more, about 500 ppm or more, about 1,000 ppm or more, about 2,000 ppm or more, about 300,000 or less, about 100,000 ppm or less, about 50,000 ppm or less, about 20,000 ppm or less, about 10,000 ppm or less, or about 5,000 ppm or less. In some embodiments, the central average potassium concentration 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 subrange thereof.

[0244] Foldable substrates (e.g., foldable substrates 206, 407, or 807) can withstand various types of mechanical instability. Throughout this disclosure, mechanical instability includes localized mechanical instability as well as systemic mechanical instability. As used herein, localized mechanical instability manifests as deviations (e.g., multiple deviations) from the plane of a surface (e.g., a first central surface region), but the surface as a whole is not distorted, such as buckling and / or wrinkling. As used herein, systemic mechanical instability manifests as distortion of the entire surface from the plane, such as warping. Figure 54 As shown, the horizontal axis 5401 (e.g., the x-axis) includes the center thickness (e.g., center thickness 227, 427, or 827), and the vertical axis 5403 (e.g., the y-axis) includes the substrate thickness 211, 411, or 811. Figure 54The shapes drawn in the figure correspond to the type (or types) of mechanical instability observed for the combination of center thickness and substrate thickness at that location. Rhombus 5409 corresponds to buckling. Circle 5407 corresponds to buckling and wrinkling. Triangle 5413 corresponds to warping and wrinkling. Square 5411 corresponds to warping. Curves 5404 and 5405 distinguish between combinations of center thickness and substrate thickness that only exhibit widespread instability (e.g., warping) and the opposite combinations that exhibit localized instability. Curve 5405 is a line indicating localized instability observable when the substrate thickness is approximately 4 times the center thickness minus 71 micrometers. More specifically, curve 5405 is a line indicating localized instability observable when the substrate thickness is approximately 4.1 times the center thickness minus 71.37 micrometers. Curves 5404 and 5405 indicate that some instabilities encountered by thinner foldable substrates (e.g., localized mechanical instabilities) (e.g., above curves 5404 and / or 5405) may differ from those encountered by thicker foldable substrates (e.g., below curves 2804 and / or 2805).

[0245] When the critical strain (e.g., critical buckling strain) of a portion (e.g., the central portion) of the foldable substrate is exceeded, the onset of mechanical instability (e.g., localized mechanical instability) can occur. For example, similar to Figure 8 The foldable substrate 807 shown has a width of 20 mm for its central portion 881. The critical buckling strain of the central portion can be approximated as 10 times the square of the central thickness. 6 Subtract 23 times the center thickness plus 0.0006. For example, not wanting to be confined to theory, similar to... Figure 8 The foldable substrate 807 with a center thickness of 30 μm (827) has a critical buckling strain in the center portion that can be approximated as 3 x 10⁻⁶. -7 Divide by the square of the width of the central part, 281, which is 252.

[0246] Because the chemically strengthened compressive strain of the central portion of a foldable substrate obtained by chemically strengthening the substrate can be proportional to the network expansion coefficient (B), the concentration difference (C), and the product of the layer depth of the central portion divided by the central thickness and the difference between the layer depth of the first portion (or the second portion) divided by the substrate thickness. In some embodiments, 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) 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. 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 exchanged into the substrate (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 and / or the second portion and the central portion comprise the same material prior to chemical strengthening.

[0247] As used herein, a concentration difference in a portion refers to the difference between the concentration at the surface of that portion and the concentration in the bulk of that portion. Unless otherwise indicated, concentration and concentration difference refer to the concentration of one or more alkali metal ions associated with the chemically strengthened and / or compressive stress region. In some embodiments, concentration and / or concentration difference may refer to potassium concentration based on oxides. In some embodiments, the bulk concentration of the first portion and / or the bulk concentration of the second portion may be substantially equal to the bulk concentration of the central portion, for example, if the first and / or second portions and the central portion comprise the same material prior to 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, a first average potassium concentration in the first portion, based on oxides, may be greater than the potassium concentration in the bulk of the first portion, based on oxides. In some embodiments, a second average potassium concentration in the second portion, based on oxides, may be greater than the potassium concentration in the bulk of the second portion, based on oxides. In some embodiments, a central average potassium concentration in the central portion, based on oxides, may be greater than the potassium concentration in the bulk of the central portion, based on oxides.

[0248] As used herein, concentration differences between portions mean the difference between one average concentration and another average concentration. Unless otherwise indicated, concentration and concentration differences refer to the concentration of one or more alkali metal ions associated with chemically strengthened and / or compressive stress regions. In some embodiments, based on oxides, concentration and / or concentration differences may refer to the concentration of potassium. In some embodiments, the absolute difference between a first average potassium concentration based on oxides and a central average potassium concentration based on oxides 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 potassium concentration based on the oxidant meter and the center average potassium concentration based on the oxidant meter can 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 subrange thereof. In some embodiments, the absolute difference between the second average potassium concentration based on the oxidant meter and the center average potassium concentration based on the oxidant meter can be about 1 ppm or greater, about 10 ppm or greater, about 20 ppm or greater, about 50 ppm or greater, about 70 ppm, about 500 ppm or less, about 200 ppm or less, about 100 ppm or less, or about 85 ppm or less. In some embodiments, the absolute difference between the second average potassium concentration based on oxide and the center average potassium concentration based on oxide can 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 subrange thereof. For example, when the absolute difference between the average concentrations is about 75 ppm or less, for a foldable substrate comprising a center thickness of 30 μm and a center width of 20 mm, the chemically strengthened induced strain can be less than the critical buckling strain.In some embodiments, the absolute difference between the first average potassium concentration based on the oxidant meter and the center average potassium concentration based on the oxidant meter may be less than 70 ppm, for example, in the range of about 0.1 ppm to about 60 ppm, about 0.1 ppm to about 50 ppm, about 0.1 ppm to about 40 ppm, about 0.1 ppm to about 30 ppm, about 0.1 ppm to about 20 ppm, about 0.5 ppm to about 20 ppm, about 0.5 ppm to about 10 ppm, about 1 ppm to about 10 ppm, about 5 ppm to about 10 ppm, or any range or subrange thereof. In some embodiments, the absolute difference between the second average potassium concentration based on the oxidant meter and the center average potassium concentration based on the oxidant meter may be less than 70 ppm, for example, in the range of about 0.1 ppm to about 50 ppm, about 0.1 ppm to about 20 ppm, about 0.5 ppm to about 20 ppm, about 0.5 ppm to about 10 ppm, about 1 ppm to about 10 ppm, about 5 ppm to about 10 ppm, or any range or subrange thereof. Providing an absolute difference between the first and / or second average concentrations of potassium based on oxides and the central average concentration can provide reduced chemical strengthening induced strain (e.g., below the critical buckling strain) and / or reduce the occurrence of mechanical instability in foldable substrates and / or foldable devices.

[0249] In some embodiments, the absolute difference between the depth of the first layer divided by the substrate thickness and the depth of the first center layer divided by the center thickness may be about 0.001% or greater, about 0.002% or greater, about 0.005% or greater, about 1% or less, about 0.2% or less, about 0.1% or less, about 0.05% or less, about 0.01% or less, or about 0.008% or less. In some embodiments, the absolute difference between the depth of the first layer divided by the substrate thickness and the depth of the first center layer divided by the center thickness may 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 subrange thereof. In some embodiments, the absolute difference between the depth of the third layer divided by the substrate thickness and the depth of the first center layer divided by the center thickness may be about 0.001% or greater, about 0.002% or greater, about 0.005% or greater, about 1% or less, about 0.2% or less, about 0.1% or less, about 0.05% or less, about 0.01% or less, or about 0.008% or less. In some embodiments, the absolute difference between the depth of the third layer divided by the substrate thickness and the depth of the first center layer divided by the center thickness may 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 subrange thereof.

[0250] In some embodiments, the absolute difference between the second layer depth divided by the substrate thickness and the second center layer depth divided by the center thickness may be about 0.001% or greater, about 0.002% or greater, about 0.005% or greater, about 1% or less, about 0.2% or less, about 0.1% or less, about 0.05% or less, about 0.01% or less, or about 0.008% or less. In some embodiments, the absolute difference between the second layer depth divided by the substrate thickness and the second center layer depth divided by the center thickness may 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 subrange thereof. 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 may be about 0.001% or greater, about 0.002% or greater, about 0.005% or greater, about 1% or less, about 0.2% or less, about 0.1% or less, about 0.05% or less, about 0.01% or less, or about 0.008% or less. 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 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 subrange thereof. For example, when the absolute difference between the depth of the layer associated with the first or second portion divided by the substrate thickness and the depth of the layer associated with the center portion divided by the center thickness is about 0.075% or less, for a foldable substrate comprising a center thickness of 30 μm and a center width of 20 mm, the chemically strengthened induced strain can be less than the critical buckling strain. In some embodiments, the absolute difference between the depth of one of the first layer, the depth of the second layer, the depth of the third layer, or the depth of the fourth layer divided by the substrate thickness and the depth of the first center layer or the depth of the second center layer divided by the center thickness may be less than 0.07%, for example, in the range of 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 subrange thereof.Providing the absolute difference between the depth of the first layer, the depth of the second layer, the depth of the third layer and / or the depth of the fourth layer divided by the substrate thickness and the depth of the first center layer and / or the depth of the second center layer divided by the center thickness (e.g., the depth of the potassium layer) can provide reduced chemical strengthening induced strain (e.g., below the critical buckling strain) and / or reduce the occurrence of mechanical instability in foldable substrates and / or foldable devices.

[0251] The compression depth can be proportional to the corresponding layer depth. In some embodiments, the absolute difference between the first compression depth divided by the substrate thickness and the first center compression depth divided by the center thickness can be about 0.001% or greater, about 0.002% or greater, about 0.005% or greater, about 1% or less, about 0.2% or less, about 0.1% or less, about 0.05% or less, about 0.01% or less, or about 0.008% or less. In some embodiments, the absolute difference between the first compression depth divided by the substrate thickness and the first center compression depth divided by the center thickness may 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 subrange thereof. In some embodiments, the absolute difference between the third compression depth divided by the substrate thickness and the first center compression depth divided by the center thickness may be about 0.001% or greater, about 0.002% or greater, about 0.005% or greater, about 1% or less, about 0.2% or less, about 0.1% or less, about 0.05% or less, about 0.01% or less, or about 0.008% or less. In some embodiments, the absolute difference between the third compression depth divided by the substrate thickness and the first center compression depth divided by the center thickness may 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 subrange thereof.

[0252] 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 may be about 0.001% or greater, about 0.002% or greater, about 0.005% or greater, about 1% or less, about 0.2% or less, about 0.1% or less, about 0.05% or less, about 0.01% or less, or about 0.008% or less. 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 may 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 subrange thereof. 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 may be about 0.001% or greater, about 0.002% or greater, about 0.005% or greater, about 1% or less, about 0.2% or less, about 0.1% or less, about 0.05% or less, about 0.01% or less, or about 0.008% or less. 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 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 subrange thereof. For example, when the absolute value 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 about 0.075% or less, for a foldable substrate comprising a center thickness of 30 μm and a center width of 20 mm, the chemically strengthened induced strain 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 may be less than 0.07%, for example, in the range of 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 subrange thereof.Providing the absolute difference between 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 first center compression depth and / or the second center compression depth divided by the center thickness can provide reduced chemical strengthening induced strain (e.g., below the critical buckling strain) and / or reduce the occurrence of mechanical instability in foldable substrates and / or foldable devices.

[0253] In some embodiments, chemically reinforced induced strain and / or stress can be observed in the optical hysteresis distribution of the foldable substrate. As used herein, the optical hysteresis distribution is measured using a gray-field polarimeter that detects light emitted by a green LED and passing through the foldable substrate, the light comprising a wavelength of approximately 553 nm. Not wishing to be confined to theory, spatial differences in optical hysteresis can correspond to differences in stress (e.g., in-plane strain) in the foldable substrate, such as stress-induced birefringence. In some embodiments, the absolute difference between the maximum and minimum optical hysteresis along the centerline at the midpoint between the first and second portions can be greater than or equal to approximately 0.1 nm, greater than or equal to approximately 0.5 nm, greater than or equal to approximately 1 nm, less than or equal to approximately 3 nm, less than or equal to approximately 2 nm, or less than or equal to approximately 1.5 nm. In some implementations, the absolute difference between the maximum value of the optical hysteresis along the centerline and the minimum value of the optical hysteresis along the centerline can be within the following ranges: 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 nm to about 1.5 nm, about 1 nm to about 1.5 nm, or any range or subrange therebetween.

[0254] In some embodiments, the maximum difference between the optical hysteresis of the central portion 281, 481 or 881 and the minimum optical hysteresis of the first portion 221, 421 or 821 and / or the second portion 231, 431 or 831 may be about 0.1 nm or greater, about 0.5 nm or greater, about 1 nm or greater, about 2 nm or greater, about 3 nm or greater, about 8 nm or less, about 6 nm or less, about 5 nm or less, or about 4 nm or less. In some embodiments, the maximum difference between the optical hysteresis of the central portion 281, 481, or 881 and the minimum optical hysteresis of the first portion 221, 421, or 821 and / or the second portion 231, 431, or 831 can be within a range of 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 subrange thereof. For example, when the maximum difference between the optical hysteresis of the central portion 281, 481, or 881 and the minimum optical hysteresis of the first portion 221, 421, or 821 and / or the second portion 231, 431, or 831 is about 4.6 nm or less, a foldable substrate with a center thickness of about 30 μm can avoid mechanical instability. For example, when the maximum difference between the optical hysteresis of the central portion 281, 481 or 881 and the minimum optical hysteresis of the first portion 221, 421 or 821 and / or the second portion 231, 431 or 831 is about 5.9 nm or less, a foldable substrate with a central thickness of about 40 μm can avoid mechanical instability.

[0255] In some embodiments, the polymer-based portion 241 may be optically transparent. The polymer-based portion 241 may include a first refractive index. This first refractive index may be a function of the wavelength of light passing through the optically transparent adhesive. For the first wavelength of light, the refractive index of a material is defined as the ratio between the speed of light in a vacuum and the speed of light in the corresponding material. Without being limited to theory, the refractive index of the optically transparent adhesive may be determined using the ratio of the sine of a first angle to the sine of a second angle, wherein light of the first wavelength is incident from air at a first angle on the surface of the optically transparent adhesive and refracted at the surface of the optically transparent adhesive, thereby causing the light to propagate within the optically transparent adhesive at a second angle. Both the first and second angles are 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, wherein the first wavelength includes 589 nm. In some embodiments, the first refractive index of the polymer-based portion 241 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 first refractive index of the polymer-based portion 241 may be within 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 subrange thereof.

[0256] In some embodiments, the foldable substrate 206, 407, or 807 may include a second refractive index. In some embodiments, the second refractive index of the foldable substrate 206, 407, or 807 may be about 1 or greater, about 1.3 or greater, about 1.4 or greater, about 1.45 or greater, about 1.49 or greater, about 3 or less, about 2 or less, about 1.7 or less, about 1.6 or less, or about 1.55 or less. In some embodiments, the second refractive index of the foldable substrate 206, 407, or 807 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 subrange thereof. In some embodiments, the absolute value of the difference between the second refractive index of the foldable substrate 206, 407, or 807 and the first refractive index of the polymer-based portion 241 may be about 0.1 or less, about 0.07 or less, about 0.05 or less, about 0.001 or more, about 0.01 or more, or about 0.02 or more. In some embodiments, this difference falls within 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 subrange thereof. In some embodiments, the second refractive index of the foldable substrate 206, 407, or 807 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 206, 407, or 807 may be less than the first refractive index of the polymer-based portion 241.

[0257] In some embodiments, adhesive layer 261 may include a third refractive index. In some embodiments, the third refractive index of adhesive layer 261 may be within one or more of the range discussed above regarding the first refractive index of polymer-based portion 241. In some embodiments, the difference equal to the absolute value of the difference between the third refractive index of adhesive layer 261 and the first refractive index of polymer-based portion 241 may be about 0.1 or less, about 0.07 or less, about 0.05 or less, about 0.001 or more, about 0.01 or more, or about 0.02 or more. In some embodiments, the difference is within 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 subrange thereof. 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.

[0258] 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 206, 407, or 807 may be about 0.1 or less, about 0.07 or less, about 0.05 or less, about 0.001 or more, about 0.01 or more, or about 0.02 or more. In some embodiments, this 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 subrange thereof. In some embodiments, the third refractive index of the adhesive layer 261 may be greater than the second refractive index of the foldable substrate 206, 407, or 807. In some embodiments, the third refractive index of the adhesive layer 261 may be less than the second refractive index of the foldable substrate 206, 407 or 807.

[0259] In some embodiments, coating 251 may include a fourth refractive index. In some embodiments, the fourth refractive index of coating 251 may be within one or more of the range discussed above regarding the first refractive index of polymer-based portion 241. In some embodiments, the difference equal to the absolute value of the difference between the fourth refractive index of coating 251 and the first refractive index of polymer-based portion 241 may be about 0.1 or less, about 0.07 or less, about 0.05 or less, about 0.001 or more, about 0.01 or more, or about 0.02 or more. In some embodiments, the difference is within 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 subrange thereof. In some embodiments, the fourth refractive index of coating 251 may be greater than the first refractive index of polymer-based portion 241. In some embodiments, the fourth refractive index of coating 251 may be less than the first refractive index of polymer-based portion 241.

[0260] In some embodiments, the absolute value of the difference between the fourth refractive index of coating 251 and the second refractive index of foldable substrate 206, 407, or 807 may be about 0.1 or less, about 0.07 or less, about 0.05 or less, about 0.001 or more, about 0.01 or more, or about 0.02 or more. In some embodiments, this difference falls within 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 subrange thereof. In some embodiments, the fourth refractive index of coating 251 may be greater than the second refractive index of foldable substrate 206, 407, or 807. In some embodiments, the fourth refractive index of coating 251 may be less than the second refractive index of foldable substrate 206, 407 or 807.

[0261] In some embodiments, the difference equal to the absolute value of the difference between the fourth refractive index of coating 251 and the third refractive index of adhesive layer 261 may be about 0.1 or less, about 0.07 or less, about 0.05 or less, about 0.001 or more, about 0.01 or more, or about 0.02 or more. In some embodiments, this 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 subrange thereof. In some embodiments, the fourth refractive index of coating 251 may be greater than the third refractive index of adhesive layer 261. In some embodiments, the fourth refractive index of coating 251 may be less than the third refractive index of adhesive layer 261.

[0262] Foldable devices and / or foldable substrates may have failure modes that can be described as low-energy failures or high-energy failures. They can be used... Figure 10 A parallel plate apparatus 1001 is used to measure the failure modes of the foldable substrate. As described below regarding the effective minimum bending radius, parallel rigid stainless steel plates 1003 and 1005 move together at a rate of 50 μm / s until a target parallel plate distance 1007 is achieved. The target parallel plate distance 1007 is the greater of twice the effective minimum bending radius of the foldable apparatus and / or the foldable substrate, or 4 mm. Next, a tungsten carbide sharp contact probe impacts the foldable substrate 206 at impact location 1011, said impact location 1009 being a distance 509 from the outermost periphery of the foldable substrate 206 of 30 mm. As used herein, if during fracture, particles are ejected from the foldable substrate 206 at a velocity greater than or equal to 1 m / s, and fracture results in more than two crack branches, then the fracture is of high energy. As used herein, fracture is considered low-energy if it results in two or fewer crack branches, or if no particles are ejected from the foldable substrate 206 at a speed greater than or equal to 1 m / s during fracture. The average velocity of the ejected particles can be measured by capturing high-speed video of the foldable device from the point of impact with a sharp contact probe to 5,000 microseconds thereafter.

[0263] Figure 9 and 11 -12 schematically illustrates some embodiments of the test folding device 1102 and / or foldable device 1201 according to embodiments of the present disclosure when in a folded configuration. For example... Figure 11 As shown, the test device 1102 is folded such that the second main surface 205 of the foldable substrate 206 is on the inside of the folded test foldable device 602. Figure 11In the folding structure shown, the user views the display device 307 via the foldable substrate 206, replacing the PET sheet 1107, and thus the user is positioned on the side of the second main surface 205. (As shown in...) Figure 12 As shown, the foldable device 401 is folded to form a folded device 1201, such that the second main surface 405 of the foldable substrate 407 is on the exterior of the folded foldable device 1201. Figure 12 In this configuration, the user will view the display device 307 via the foldable substrate 407, and will therefore be positioned on the side of the second main surface 205. In some embodiments, such as in... Figure 11-12 As shown, the foldable device may include a coating 251 disposed above the test foldable device 1102 or foldable device 1201 (e.g., the first main surface 203 or 403, the first central surface region 209 or 409). In another embodiment, the user will view the display device 307 through the coating. In some embodiments, although not shown, a polymer-based portion 241 and / or an adhesive layer 261 may be disposed above an additional substrate (e.g., a glass-based substrate and / or a ceramic-based substrate, replacing the release liner 271 or the PET sheet 1107), and this additional substrate may be disposed above the display device 307.

[0264] As defined herein, “foldable” includes the ability to fold completely, partially, bend, fold, and fold multiple times. As used herein, the terms “failure,” “failed,” etc., refer to breakage, destruction, delamination, or crack propagation. When a foldable device maintains an “X” radius for at least 24 hours at approximately 85°C and approximately 85% relative humidity, if it resists failure, the foldable device achieves, has, or includes an effective bending radius of “X.” Similarly, when a foldable device maintains a “X” parallel plate distance for 24 hours at approximately 85°C and approximately 85% relative humidity, if it resists failure, the foldable device achieves, has, or includes a parallel plate distance of “X.”

[0265] As used in this article, the "effective minimum bending radius" and "parallel plate distance" of the foldable device use the parallel plate device 1101 (see [link]). Figure 11 The parallel plate device 1101 comprises a pair of parallel rigid stainless steel plates 1103, 1105, measured by the following test construction and process, wherein the pair of parallel rigid stainless steel plates 1103, 1105 comprises a first rigid stainless steel plate 1103 and a second rigid stainless steel plate 1105. When measuring the “effective minimum bending radius” or “parallel plate distance”, the test adhesive layer 1109 comprises a thickness of 50 μm (e.g., alternative to...). Figure 2-5The adhesive layer 261). When measuring the “effective minimum bending radius” or “parallel plate distance”, use a 100 μm thick sheet of polyethylene terephthalate (PET) 1107 instead of Figure 2 and 4 Release lining 271 or Figure 3 and 5 The measurement is performed using the display device 307 shown. Therefore, during the test used to determine the "effective minimum bending radius" or "parallel plate distance" of the foldable device construction, a 100μm thick polyethylene terephthalate (PET) sheet 1102 is used instead of... Figure 2 and 4 Release lining 271 or Figure 3 and 5 The display device 307 shown is used to produce a test foldable device 1102. When preparing the test foldable device 1102, it is used in conjunction with... Figure 2 and 4 The release liner 271 is attached to the second contact surface 265 of the adhesive layer 261, or to... Figure 3 and 5 In the same manner as the display device 307 is attached to the second contact surface 265 of the adhesive layer 261, a 100 μm thick sheet of polyethylene terephthalate (PET) 1107 is attached to the test adhesive layer 1109. For testing... Figure 6-8 The foldable devices 601, 701 and / or 801, the test adhesive layer 609 and the sheet 607 can be similarly used as in Figure 12 The structure is shown in the example installation for testing the test foldable device 1102. The test foldable device 1102 is placed between the pair of parallel rigid stainless steel plates 1103 and 1105, such that it is similar to... Figure 11The configuration shown in the diagram involves foldable substrates 206, 407, or 807 placed inside the bend. To determine the "parallel plate distance," the distance between the parallel plates is decreased at a rate of 50 μm / s until the parallel plate distance 1111 equals the "parallel plate distance" to be tested. The parallel plates are then 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 testing without failure under the aforementioned conditions and configuration. To determine the "effective minimum bending radius," the distance between the parallel plates is decreased at a rate of 50 μm / s until the parallel plate distance 11 equals twice the "effective minimum bending radius" to be tested. The parallel plates are then held at approximately 85°C and approximately 85% relative humidity for 24 hours at twice the effective minimum bending radius to be tested. As used herein, the "effective minimum bending radius" is the minimum effective bending radius at which the foldable device can withstand testing without failure under the aforementioned conditions and configuration.

[0266] In some embodiments, foldable devices 101, 301, 401, 501, 601, 701, 801 and / or 1201 and / or test foldable device 1102 can achieve a parallel plate distance of 100 mm or less, 50 mm or less, 20 mm or less, 10 mm or less, 5 mm or less, or 3 mm or less. In other embodiments, foldable devices 101, 301, 401, 501, 601, 701, 801 and / or 1201 and / or test foldable device 1102 can achieve a parallel plate distance of 50 mm, 20 mm, 10 mm, 5 mm, or 3 mm. In some embodiments, foldable devices 101, 301, 401, 501, 601, 701, 801 and / or 1201 and / or test foldable device 1102 may include a minimum parallel plate distance of about 40 mm or less, about 20 mm or less, about 10 mm or less, about 5 mm or less, about 3 mm or less, about 1 mm or less, about 1 mm or more, about 3 mm or more, about 5 mm or more, or about 10 mm or more. In some embodiments, the foldable devices 101, 301, 401, 501, 601, 701, 801 and / or 1201 and / or the test foldable device 1102 may include an effective minimum bending radius in the range of about 1 mm to about 40 mm, about 1 mm to about 20 mm, about 1 mm to about 10 mm, about 1 mm to about 5 mm, about 1 mm to about 3 mm, about 3 mm to about 40 mm, about 3 mm to about 40 mm, about 3 mm to about 20 mm, about 3 mm to about 10 mm, about 3 mm to about 5 mm, about 5 mm to about 10 mm, or any range or subrange thereof.

[0267] In some embodiments, the width of the central portions 281, 481, and / or 881 of the foldable substrate 206, 407, or 807 is defined in the direction 106 of the length 105 between the first portion 221, 421, or 821 and the second portion 231, 431, or 831. In some embodiments, the width of the central portions 281, 481, and / or 881 of the foldable substrate 206, 407, or 807 may extend from the first portion 221, 421, or 821 to the second portion 231, 431, or 831. In some embodiments, the width of the central portions 281, 481, or 881 of the foldable substrate 206, 407, or 807 defined in the direction 106 of length 105 between the first portions 221, 421, or 821 and the second portions 231, 431, or 831 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, the width of the central portions 281, 481, and / or 881, which are multiples of the effective minimum bending radius, 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 subrange thereof. Not wishing to be bound by theory, the length of the bent portion in the circular structure between the parallel plates can be approximately 1.6 times the distance 1111 between the parallel plates (e.g., approximately 3 times the effective minimum bending radius, approximately 3.2 times the effective minimum bending radius). In some embodiments, the width of the central portions 281, 481, and / or 881 of the foldable substrates 206, 407, or 807 can be approximately 2.8 mm or greater, approximately 6 mm or greater, approximately 9 mm or greater, approximately 60 mm or less, approximately 40 mm or less, or approximately 24 mm or less. In some embodiments, the width of the central portions 281, 481, and / or 881 of the foldable substrate 206, 407, or 807 may be within a 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 subrange thereof. By providing a width within the range indicated above for the central portions (e.g., between the first and second portions), folding of the foldable device in a fault-free manner can be facilitated.

[0268] Foldable devices 101, 301, 401, 501, 601, 701, 801, and 1201 may have impact resistance defined by the ability of regions of the foldable device (e.g., the region containing the first portion 221, 421, or 821, the region containing the second portion 231, 431, or 831, the region containing the polymer-based portion 241, and / or the central portion 281, 481, or 881) to avoid failure at a pen drop height (e.g., 5 cm or more, 10 cm or more, 20 cm or more), said pen drop height being measured according to a "pen drop test". As used herein, a "pen drop test" is performed to test the foldable device under a load (i.e., from a pen dropped from a height) applied to the primary surface (e.g., the second primary surface 205, 405, or 805 of the foldable substrate 206, 407, or 807), constructed as in the parallel plate test, using a 100 μm thick PET sheet 1107 instead of... Figure 3 and 5 The display device 307 shown or Figure 2 and 4 The release liner 271 shown is attached to a 50 μm thick test adhesive layer 1109. Therefore, 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 bonded to the PET layer is placed on an aluminum plate (6063 aluminum alloy, polished to a certain surface roughness with 400 grit paper), with the PET layer in contact with the aluminum plate. No tape is used on the sample side resting on the aluminum plate.

[0269] The tube is used for pen drop testing to guide the pen to the outer surface of the foldable device. For Figure 2-8 Foldable devices 101, 301, 401, 501, 601, 701, 801, and 1201 and / or testable foldable device 1102 in 11-12 guide the pen to the second primary surface 205, 405, or 805 of the foldable substrate 206, 407, or 807, and place the tube in contact with the second primary surface 205, 405, or 805 of the foldable substrate 206, 407, or 807 such that the longitudinal axis of the tube is substantially perpendicular to the second primary surface 205, 405, or 805, wherein the longitudinal axis of the tube extends in the direction of gravity. The tube has an outer diameter of 1 inch (2.54 cm), an inner diameter of nine-sixteenths of an inch (1.4 cm), and a length of 90 cm. For each test, an acrylonitrile butadiene (ABS) gasket is used to hold the pen at a predetermined height. After each drop, the tube is repositioned relative to the sample to guide the pen to different impact points on the sample. The pen used in the pen drop test was a BIC Easy Glide pen, a fine pen with a 0.7 mm (0.68 mm) diameter tungsten carbide bead tip, and a weight of 5.73 grams (g) including the cap (4.68 g without the cap).

[0270] For the pen drop test, the pen is dropped with the cap attached to the tip (i.e., the end opposite the tip) so that the bead can interact with the test sample. According to the drop procedure of the pen drop test, a drop is made from an initial height of 1 cm, followed by drops in increments of 0.5 cm until a height of 20 cm is reached. Then, after 20 cm, drops are made in increments of 2 cm until the test sample fails. After each drop, the presence of any observed evidence of breakage, failure, or other damage to the sample, along with the specific drop height, is recorded. When using the pen drop test, multiple samples can be tested according to the same drop procedure to produce a population with improved statistical accuracy. For the pen drop test, a new pen is used after every 5 drops, and for each new test sample. Furthermore, all drops are made at or near the center of the sample, at random locations on the sample, and the pen does not drop near or on the edges of the sample.

[0271] For pen-drop testing purposes, "failure" means the formation of a visible mechanical defect in the laminate. A mechanical defect can be a crack or plastic deformation (e.g., surface dent). A crack can be a surface crack or a through crack. Cracks can form on the internal or external surface of the laminate. Cracks can extend through all or part of the foldable substrate 206, 407, or 807 and / or the coating. The minimum size of a visible mechanical defect is 0.2 mm or greater.

[0272] Figure 53 A graph 5305 shows the variation of the maximum principal stress 5303 (in megapascals (MPa)) on the first principal surface of the glass-based substrate with respect to the micrometer thickness 5301 of the glass-based substrate at a pen drop height of 2 cm on the second principal surface. (See graph 5305 for details on the maximum principal stress 5303 on the first principal surface of the glass-based substrate, as shown in the graph 5305 for ... Figure 53 The study shows that the maximum principal stress on the first principal surface of the glass-based sheet is highest around 65 μm. This indicates that pen stroke performance can be improved by avoiding a thickness of approximately 65 μm, for example, by using a thickness less than approximately 50 μm or greater than approximately 80 μm.

[0273] In some embodiments, the foldable device is resistant to pen drop failure at a pen drop height of 10 cm, 12 cm, 14 cm, 16 cm, or 20 cm in the area containing the first portion 221, 421, or 821 or the second portion 231, 431, or 831. In some embodiments, the maximum pen drop height that the foldable device can withstand without failure in the area containing the first portion 221, 421, or 821 or the second portion 231, 431, or 831 may be approximately 10 cm or greater, approximately 12 cm or greater, approximately 14 cm or greater, approximately 16 cm or greater, approximately 40 cm or less, approximately 30 cm or less, approximately 20 cm or less, or approximately 18 cm or less. In some embodiments, the maximum pen drop height that the foldable device can withstand without failure in the area comprising the first portion 221, 421, or 821 or the second portion 231, 431, or 821 may be within the range of 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 subrange thereof.

[0274] In some embodiments, within the region of polymer-based portion 241 (e.g., central portion 281, 481, or 881) encompassing the first portion 221, 421, or 821 and the second portion 231, 431, or 831, 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, within the region of polymer-based portion 241 encompassing the first portion 221, 421, or 821 and the second portion 231, 431, or 831, the maximum pen drop height that the foldable device can withstand without failure may be approximately 1 cm or greater, approximately 2 cm or greater, approximately 3 cm or greater, approximately 4 cm or greater, approximately 20 cm or less, approximately 10 cm or less, approximately 8 cm or less, or approximately 6 cm or less. In some embodiments, the maximum pen drop height that the foldable device can withstand without failure in the region of the polymer-based portion 241 contained between the first portion 221, 421, or 821 and the second portion 231, 431, or 831 can be within a range of 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 subrange thereof. In some embodiments, the maximum pen drop height that the foldable device can withstand without failure in the region of the polymer-based portion 241 contained between the first portion 221, 421, or 821 and the second portion 231, 431, or 831 can be within a range of 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 subrange thereof.

[0275] The predetermined parallel plate distance can be achieved using minimal force through a foldable device. (The above description...) Figure 11 The parallel plate device 1101 is used to measure the "closing force" of the foldable device according to embodiments of the present disclosure. Measurement is performed from a flat structure (e.g., see...). Figure 1 ) becomes a curved (e.g., folded) structure containing a predetermined parallel plate distance (e.g., see Figure 9 and 11-12) of force. In some embodiments, the force required to bend the foldable device from a flat structure to a parallel plate distance of 10 mm can be about 20 Newtons (N) or less, 15 N or less, about 12 N or less, about 10 N or less, about 0.1 N or more, about 0.5 N or more, about 1 N or more, about 2 N or more, or about 5 N or more. In some embodiments, the force required to bend the foldable device from a flat structure to a parallel plate distance of 10 mm can be in the range of 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 subrange thereof. In some embodiments, the force required to bend the foldable device from a flat structure to a parallel plate distance of 3 mm can be about 10 N or less, about 8 N or less, 6 N or less, about 4 N or less, about 3 N or less, about 0.05 N or more, about 0.1 N or more, about 0.5 N or more, about 1 N or more, about 2 N or more, or about 3 N or more. In some embodiments, the force required to bend the foldable device from a flat structure to a parallel plate distance of 3 mm can be in the range of 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 subrange thereof.

[0276] In some embodiments, the force per width 103 of the foldable device that bends the foldable device from a flat construction to a parallel plate distance of 10 mm can be about 20 Newtons per millimeter (N / mm) or less, 0.15 N / mm or less, about 0.12 N / mm or less, about 0.10 N / mm or less, about 0.001 N / mm or more, about 0.005 N / mm or more, about 0.01 N / mm or more, about 0.02 N / mm or more, or about 0.05 N / mm or more. In some embodiments, the force per width 103 of the foldable device that bends the foldable device from a flat construction 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 subrange thereof. In some embodiments, the force per width 103 of the foldable device that bends the foldable device from a flat construction to a parallel plate distance of 3 mm can be about 0.10 N / mm or less, about 0.08 N / mm or less, about 0.06 N / mm or less, about 0.04 N / mm or less, about 0.03 N / mm or less, about 0.0005 N / mm or more, about 0.001 N / mm or more, about 0.005 N / mm or more, about 0.01 N / mm or more, about 0.02 N / mm or more, or about 0.03 N / mm or more. In some embodiments, the force per width 103 of the foldable device that bends the foldable device from a flat construction 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 subrange thereof.

[0277] Providing a coating enables low forces to achieve a small parallel plate distance. It is not desirable to be theoretically constrained that a coating with a modulus smaller than that of the foldable substrate can result in a foldable substrate neutral axis that shifts away from the coating (e.g., the user-facing surface) compared to when using glass-based and / or ceramic-based substrates. It is not desirable to be theoretically constrained that providing a coating with a thickness of approximately 200 μm or less can result in a foldable substrate neutral axis that shifts away from the coating (e.g., the user-facing surface) compared to when using a thicker substrate. It is not desirable to be theoretically constrained that shifting the neutral axis of the foldable substrate portion away from the coating (e.g., the user-facing surface) enables low forces to achieve a small parallel plate distance because it reduces the concentration of tensile stress and the resulting deformation of a portion of the foldable substrate (since tensile stress is distributed over a larger portion of the foldable substrate).

[0278] Embodiments of the method for manufacturing foldable devices and / or foldable substrates according to the embodiments of this disclosure will be referred to. Figure 15-18 The flowchart and in Figure 19-52 The exemplary method steps shown in the figure will be used for discussion.

[0279] Reference Figure 19-24 and Figures 50-52 and Figure 15 The flowchart in the text is used to discuss manufacturing. Figure 2-3 Exemplary embodiments of the foldable devices 101, 301, 601 and / or 1201, the test foldable device 1102 and / or the foldable substrate 206 illustrated in Figures 6 and 11-12 are described. In the first step 1501 of the method of this disclosure, the method may begin by providing the foldable substrate 206. In some embodiments, the foldable substrate 206 may be provided by purchasing or otherwise obtaining the substrate or by forming the foldable substrate. As discussed above, the foldable substrate 206 may include a core layer 207 positioned between a first outer layer 213 and a second outer layer 215. In some embodiments, the core layer 207, the first outer layer 213 and / or the second outer layer 215 of the foldable substrate 206 may include a glass-based substrate and / or a ceramic-based substrate. In another embodiment, the glass-based substrate and / or the ceramic-based substrate can be provided by forming them using various strip forming processes (e.g., slot drawing, down drawing, fusion down drawing, up drawing, roll forming, heavy drawing, or float forming). In another embodiment, the ceramic-based substrate can be provided by heating the glass-based substrate to crystallize one or more ceramic crystals. The foldable substrate 206 may include a second main surface 205 that can extend along a plane (see...). Figure 20-21 The second main surface 205 may be opposite to the first main surface 203.

[0280] For example, such as in Figure 19As shown, a lamination and fusion drawing apparatus 1901 can be used to produce a foldable substrate 206. As shown, the lamination and fusion drawing apparatus 1901 may include an upper forming device 1902 positioned above a lower forming device 1904. In some embodiments, as shown, the upper forming device 1902 may include a first groove 1910 configured to receive a first molten material 1906, and the lower forming device 1904 may include a second groove 1912 configured to receive a second molten material 1908. In some embodiments, the second molten material 1908 may overflow from the second groove 1912 and flow through corresponding outer forming surfaces 1916 and 1918 of the lower forming device 1904. In another embodiment, as shown, the outer forming surfaces 1916 and 1918 may converge at the root 1920 of the lower forming device 1904 to form a core molten layer 1932 that can be cooled to form a core layer 207. In some embodiments, the first molten material 1906 may overflow the first groove 1910 and flow on the corresponding outer surfaces 1922 and 1924 of the upper forming device 1902. In another embodiment, the first molten material 1906 may be deflected by the upper forming device 1902 such that when the second molten material flows to the corresponding outer forming surfaces 1916 and 1918 of the lower forming device 1904, the first molten material 1906 flows around the lower forming device 1904 and contacts the second molten material 1908. In a further embodiment, the first molten material 1906 may form a first molten outer layer 1934 that can be cooled to form a first outer layer 213, and the first molten material 1906 may form a second molten outer layer 1936 that can be cooled to form a second outer layer 215. In yet another embodiment, as shown, the core molten layer 1932 may be positioned below the root 1920, between the first molten outer layer 1934 and the second molten outer layer 1936. In another embodiment, the temperature of the first molten material 1906 forming the first molten outer layer 1934 and the second molten outer layer 1936 at the root 1920 can be higher than the softening point of the first molten material 1906 forming the first molten outer layer 1903 and the second molten outer layer 1936. In another embodiment, the temperature of the second molten material 1908 forming the core molten layer 1932 at the root 1920 can be higher than the softening point of the second molten material 1908 forming the core molten layer 1932. In yet another embodiment, the first molten outer layer 1934 can be laminated onto the core molten layer 1932 (for example, the first outer layer 213 can be laminated onto...). Figure 2-3 and the third inner surface 208 of the core layer 207 in 6), and / or the second molten outer layer 1936 may be laminated to the core molten layer 1932 (for example, the second outer layer 215 may be laminated to Figure 2-3 and the fourth inner surface 218 of the core layer 207 in 6, to form Figure 20-21 The foldable substrate 206 shown in the image.

[0281] In some embodiments, the density of the core layer 207 may be greater than the first density of the first outer layer 213 and / or the second density of the second outer layer 215. In some embodiments, the network expansion coefficient of the core layer 207 may be less than the network expansion coefficient of the first outer layer 213 and / or the network expansion coefficient of the second outer layer 215. In some embodiments, the coefficient of thermal expansion of the core layer 207 may be greater than the coefficient of thermal expansion of the first outer layer 213 and / or the coefficient of thermal expansion of the second outer layer 215.

[0282] In some embodiments, in step 1501, the foldable substrate 206 may have a first recess 234 in the first main surface 203 of the foldable substrate 206 exposing the first central surface region 209 of the core layer 207, and / or a second recess 244 in the second main surface 205 of the foldable substrate 206 exposing the second central surface region 219 of the core layer 207. In other embodiments, the recesses (e.g., the first recess 234, the second recess 244) may be formed by etching, laser ablation, or machining of the first main surface 203 and / or the second main surface 205. For example, the etching process may be similar to steps 1503, 1505, and 1507 discussed below. For example, machining the foldable substrate 206 may be similar to step 1517 discussed below.

[0283] Following step 1501, in some embodiments, core layer 207 may include an existing average potassium concentration based on oxides and / or an existing average lithium concentration based on oxides. In some embodiments, first outer layer 213 may include a first existing average potassium concentration based on oxides and / or a first existing average lithium concentration based on oxides. In some embodiments, second outer layer 215 may include a second existing average potassium concentration based on oxides and / or a second existing average lithium concentration based on oxides. In some embodiments, the existing average potassium concentration in the core layer may be approximately 10 parts per million or greater than the first existing average potassium concentration and / or the second existing average potassium concentration. In some embodiments, the first existing average lithium concentration and / or the second existing average lithium concentration may be approximately 10 parts per million or greater than the existing average lithium concentration in the core layer. It is not desirable to be theoretically constrained, but providing a larger existing average potassium concentration in the core layer will reduce the expansion of the core layer due to the chemical strengthening process, and / or reduce the extent of chemical strengthening of the core layer relative to the first outer layer and / or the second outer layer. It is not desirable to be bound by theory that providing a larger existing average lithium concentration in the first outer layer and / or the second outer layer would reduce the extent of chemical strengthening and / or increase the expansion of the corresponding layer relative to the core layer due to the chemical strengthening process.

[0284] In some embodiments, after step 1501 (e.g., before step 1509, which includes the chemically reinforced foldable substrate 206), the core layer may contain a core diffusivity of one or more alkali metal ions. In some embodiments, the first outer layer may contain a first diffusivity of one or more alkali metal ions. In some embodiments, the second outer layer may contain a second diffusivity of one or more alkali metal ions. In some embodiments, the first and / or second diffusivity may be greater than the core diffusivity. In some embodiments, the diffusivity may relate to sodium ions. In some embodiments, the diffusivity may relate to potassium ions. It is not desirable to be theoretically constrained, but providing a first and / or second outer layer with a diffusivity of one or more alkali metal ions having a diffusivity less than that associated in the core layer may increase the extent of chemical reinforcement in the first and / or second outer layers relative to the core layer. In another embodiment, the first ratio may be defined as the square root of the first diffusivity divided by the first thickness of the first outer layer 213 (e.g., the first outer thickness 217). In another embodiment, the second ratio can be defined as the square root of the second diffusivity divided by the second thickness of the second outer layer 215 (e.g., the second outer thickness 237). In another embodiment, the core ratio can be defined as the square root of the core diffusivity divided by the center thickness of the core layer 207 (e.g., the center thickness 227). In another embodiment, the difference between the first ratio and the core ratio can be approximately 0.01s. -0.5 Or even smaller. In a further embodiment, the first ratio may be substantially equal to the core ratio. In another embodiment, the difference between the second ratio and the core ratio may be approximately 0.01s. -0.5 Or smaller. In a further embodiment, the second ratio may be substantially equal to the core ratio. In another embodiment, the difference between the first ratio and / or the second ratio and the core ratio may be approximately 0.00001s. -0.5 Or larger, approximately 0.0001s -0.5 Or larger, approximately 0.001s -0.5 Or larger, approximately 0.003s -0.5 Or larger, approximately 0.1s -0.5 Or even smaller, approximately 0.05s -0.5 Or even smaller, approximately 0.02s -0.5 Or even smaller, approximately 0.01s -0.5 Or even smaller, or approximately 0.008s -0.5 Or even smaller. In another embodiment, the difference between the first ratio and / or the second ratio and the core ratio may be from approximately 0.00001s. -0.5 From approximately 0.1s -0.5 0.0001s -0.5 From approximately 0.05s -0.5 0.001s -0.5 From approximately 0.02s -0.50.001s -0.5 From approximately 0.01s -0.5 0.003s -0.5 From approximately 0.01s -0.5 0.003s -0.5 From approximately 0.005s -0.5 Within or within any range or subrange of the range. It is not desirable to be theoretically constrained that the layer depth from chemical strengthening is proportional to the square root of the diffusivity divided by the corresponding thickness. Providing a first ratio, a second ratio, and / or a core ratio can provide substantially equal layer depths as a percentage of the corresponding thickness, which can reduce chemical strengthening-induced strain in foldable substrates.

[0285] In step 1501, in some embodiments, the method may continue to step 1517, including forming a first recess 234 and / or a second recess 244 by machining the first main surface 203 and / or the second main surface 205 of the foldable substrate 206. The first recess 234 may be formed in the first main surface 203 of the foldable substrate 206, exposing a first central surface region 209 of the core layer 207. The second recess 244 may be formed in the second main surface 205 of the foldable substrate 206, exposing a second central surface region 219 of the core layer 207. For example, the first main surface 203 and / or the second main surface 205 may be machined by diamond engraving to create very precise patterns in glass-based and / or ceramic-based substrates. Figure 20 As shown, a first recess 234 can be created in a first main surface 203 of a foldable substrate 206 using diamond engraving, wherein a computer numerical control (CNC) machine 2003 can be used to control a diamond tip probe 2001. Materials other than diamond can be used for engraving by the CNC machine. In some embodiments, although not shown, a similar process can be used to form a second recess 244 that may be opposite the first recess 234. It should be understood that other methods for forming the recess, such as photolithography and laser ablation, can be used.

[0286] Following step 1501, in some embodiments, the method may continue to step 1503, including providing a mask over one or more portions of the foldable substrate 206. In some embodiments, such as in Figure 21As shown, step 1503 may include applying a first liquid 2107 over one or more portions of the foldable substrate 206. In another embodiment, as shown, a container 2101 (e.g., a pipe, flexible tube, micropipette, or syringe) may be used to apply the first liquid 2107 over one or more portions of the foldable substrate 206. In another embodiment, as shown, the first liquid 2107 may be applied as a first liquid deposit 2103 over a first surface region 223 and as a second liquid deposit 2105 over a third surface region 233. Although not shown, it should be understood that similar liquid deposits may be formed over a second surface region and / or a fourth surface region. In another embodiment, the liquid deposit (e.g., Figure 21 The first liquid deposit 2103 and the second liquid deposit 2105 shown in the image can be cured to form a mask (e.g., Figure 22 The first mask 2205 and the third mask 2209 are shown in the diagram. Curing the first liquid may include heating the first liquid 2107, irradiating the first liquid 2107 with ultraviolet (UV) radiation, and / or waiting for a predetermined amount of time (e.g., from about 30 minutes to 24 hours, from about 1 hour to about 8 hours). In some embodiments, another method (e.g., chemical vapor deposition (CVD) (e.g., low-pressure CVD, plasma-enhanced CVD), physical vapor deposition (PVD) (e.g., evaporation, molecular beam epitaxy, ion plating), atomic layer deposition (ALD), sputtering, spray pyrolysis, chemical bath deposition, sol-gel deposition) may be used to form the masks (e.g., masks 2205, 2207, 2209, and 2211). Figure 22 As shown, the result of step 1503 may include a first mask 2205 disposed above the first surface region 223, a second mask 2207 disposed above the second surface region 225, a third mask 2209 disposed above the third surface region 233, and / or a fourth mask 2211 disposed above the fourth surface region 235. In some embodiments, the mask material may include titanium dioxide (TiO2), zirconium oxide (ZrO2), tin oxide (SnO2), aluminum oxide (Al2O3), silicon dioxide (SiO2), silicon nitride (Si3N4), and / or combinations thereof, but in other embodiments other materials may be used for the mask.

[0287] After step 1503, as in Figure 22As shown, the method can proceed to step 1505, which includes etching the foldable substrate 206. In some embodiments, as shown, etching may include exposing the foldable substrate 206 to an etchant 2203. In other embodiments, as shown, the etchant 2203 may be a liquid etchant contained in an etchant bath 2201. In still other embodiments, the etching solution may contain one or more inorganic acids (e.g., HCl, HF, H2SO4, HNO3). In some embodiments, as shown, etching may include etching a central portion 281 of the first primary surface 203 to form a first central surface region 209. In other embodiments, as shown, the first central surface region 209 may include a portion of a third inner surface 208. In other embodiments, as shown, etching may form a first recess 234 between the first plane 204a and the first central surface region 209. In some embodiments, the depth of the first recess 234 may be substantially equal to the first outer thickness 217 of the first outer layer 213 (see...). Figure 2-3 (Figures 5). In some embodiments, although not shown, the depth of the first recess may be greater than the first thickness of the first outer layer. In some embodiments, as shown, etching may include etching the central portion 281 of the second primary surface 205 to form a second central surface region 219. In other embodiments, as shown, the second central surface region 219 may include a portion of the fourth inner surface 218. In other embodiments, as shown, etching may form a second recess 244 between the second plane 204b and the second central surface region 219. In some embodiments, the depth of the second recess 244 may be substantially equal to the second outer thickness 237 of the first outer layer 213 (see Figure 5). Figure 2-3 (and 5). In some embodiments, although not shown, the depth of the second recess may be greater than the second thickness of the second outer layer.

[0288] After step 1505, as in Figure 23 As shown, the method can proceed to step 1507, which includes removing the mask. In some embodiments as shown, removing the mask (e.g., masks 2205, 2207, 2209, and 2211) may include moving a polishing tool 2301 on a surface (e.g., a third surface region 233) in direction 2302. In further embodiments, using the tool may include sweeping, scraping, polishing, pushing, etc. In other embodiments, the mask (e.g., masks 2205, 2207, 2209, and 2211) may be removed by washing the surface (e.g., a first surface region 223, a second surface region 225, a third surface region 233, and a fourth surface region 235) with a solvent. In some embodiments, removing the mask may include removing masks 2205, 2207, 2209, and 2211 from the first surface region 223, the second surface region 225, the third surface region 233, and the fourth surface region 235, respectively.

[0289] Alternatively, steps 1501, 1507, or 1517 may include removing a sublayer from the second main surface 205 of the foldable substrate 206 to expose a layer that may be contained within the substrate. Figure 2-3 The thickness of the foldable substrate 206 is reduced by a new second primary surface 205 illustrated in Figures 6 (e.g., by machining, etching, photolithography, or ablation). Removing sublayers from both the first and second primary surfaces removes an outer sublayer of the foldable substrate 206, which may have optical properties inconsistent with the underlying internal portion of the corresponding layer of the foldable substrate 206. Therefore, the entire thickness of the corresponding layer throughout the length and width of the foldable substrate 206 can have more consistent optical properties to provide consistent optical performance with minimal or no distortion across the entire foldable substrate 206. Removing sublayers from the first primary surface 203 and / or from the second primary surface 205 can help remove surface defects generated during the formation of the first recess 234 and / or the second recess 244. For example, machining the first primary surface 203 and / or the second primary surface 205 (e.g., by means of a diamond-tipped probe) to create the first recess 234 and / or the second recess 244 can produce microcracks or other defects that can present weaknesses, at which catastrophic failure of the foldable substrate 206 can occur after folding. Therefore, by removing sublayers from the first primary surface 203 and from the second primary surface 205, surface defects generated in the sublayers during the formation of the first recess 234 and / or the second recess 244 can be removed, resulting in new first and / or second primary surfaces with fewer surface defects. Because of the fewer surface defects, a smaller bending radius can be achieved without failure of the foldable substrate. For example, a certain processing of the foldable substrate can present differences in glass-based and / or ceramic-based material properties at the first and second primary surfaces of the foldable substrate compared to those at the central portion of the foldable substrate. For example, during the pull-down process, the properties of the glass-based and / or ceramic-based materials on the main surface may differ from those in the central portion.

[0290] After steps 1501, 1507, or 1517, if in Figure 24As shown, the method can proceed to step 1509, which includes chemically strengthening the foldable substrate 206. Chemical strengthening of the foldable substrate 206 by ion exchange can occur when a first cation at a depth within the surface of the foldable substrate 206 exchanges with a second cation having a larger radius in the molten salt or salt solution 2403 (e.g., a glass-based substrate and / or a ceramic-based substrate for the first outer layer, second outer layer, and / or core layer). For example, lithium cations at a depth within the surface of the foldable substrate 206 can exchange with sodium or potassium cations in the salt solution 2403. Therefore, the surface of the foldable substrate 206 is compressed and thus chemically strengthened by the ion exchange process because the lithium cations have a smaller radius than the exchanged sodium or potassium cations in the salt solution 2403. The chemically reinforced foldable substrate 206 may include contacting at least a portion of the foldable substrate 206 containing lithium cations and / or sodium cations with a salt bath 2401 containing a salt solution 2403 (containing potassium nitrate, potassium phosphate, potassiu...

Claims

1. A foldable substrate comprising: The substrate thickness is defined between a first main surface and a second main surface opposite to the first main surface, and the substrate thickness is in the range of 100 micrometers to 2 millimeters. The first portion includes the thickness of the substrate, the first portion including a first average potassium concentration based on oxides, a first compressive stress region extending from the first main surface to a first compression depth, and a second compressive stress region extending from the second main surface to a second compression depth, wherein... The first part includes a first concentration difference between a first potassium concentration at a first main surface of the first part and a potassium concentration in the body of the first part. The second portion includes the thickness of the substrate, the second portion includes a second average potassium concentration based on oxides, a third compressive stress region extending from the first main surface to a third compressive depth, and a fourth compressive stress region extending from the second main surface to a fourth compressive depth, wherein the second portion includes a second concentration difference between the second potassium concentration at the first main surface of the second portion and the potassium concentration in the body of the second portion. A central portion is located between the first portion and the second portion, the central portion including a central thickness defined between a first central surface area and a second central surface area opposite to the first central surface area, a central average potassium concentration based on oxides, a first central compressive stress region extending from the first central surface area to a first central compressive depth, the central portion also including a second central compressive stress region extending from the second central surface area to a second central compressive depth, wherein the central portion includes a central concentration difference between a third potassium concentration at the first central surface area and a potassium concentration in the body of the central portion, wherein the central thickness is in the range of 25 micrometers to 80 micrometers, wherein the first central surface area is recessed from the first main surface by a first distance, and the absolute difference between the first average potassium concentration and the central average potassium concentration is 100 parts per million or less, wherein the potassium concentration in the body of the first portion and the body of the second portion is equal to the potassium concentration in the body of the central portion.

2. The foldable substrate of claim 1, wherein the absolute difference between the first compression depth as a percentage of the substrate thickness and the first center compression depth as a percentage of the center thickness is 1% or less.

3. The foldable substrate as described in any one of claims 1-2, wherein the thickness of the substrate is in the range of 125 micrometers to 200 micrometers.

4. The foldable substrate according to any one of claims 1-3, wherein, The second central surface area is recessed from the second main surface by a second distance.

5. The foldable substrate of claim 4, wherein the second distance is 5% to 20% of the substrate thickness.

6. The foldable substrate as claimed in any one of claims 4-5, wherein the first distance is equal to the second distance.

7. The foldable substrate according to any one of claims 1-6, wherein, The first compressive stress region contains a first maximum compressive stress of 700 MPa or greater, the second compressive stress region contains a second maximum compressive stress, the third compressive stress region contains a third maximum compressive stress of 700 MPa or greater, the fourth compressive stress region contains a fourth maximum compressive stress, the first central compressive stress region contains a first central maximum compressive stress of 700 MPa or greater, and the second central compressive stress region contains a second central maximum compressive stress.

8. The foldable substrate of any one of claims 1-7, further comprising a first tensile stress region located in the first portion between the first compressive stress region and the second compressive stress region, the first tensile stress region comprising a first maximum tensile stress; the foldable substrate comprising a second tensile stress region located in the second portion between the third compressive stress region and the fourth compressive stress region, the second tensile stress region comprising a second maximum tensile stress; and the foldable substrate comprising a central tensile stress region located in the central portion between the first central compressive stress region and the second central compressive stress region, the central tensile stress region comprising a central maximum tensile stress, the absolute difference between the central maximum tensile stress and the first maximum tensile stress being 10 MPa or less.

9. The foldable substrate according to any one of claims 1-8, wherein, The central portion further includes a central tensile stress region located between a portion of the first central surface region and a portion of the second central surface region, the central tensile stress region containing a central maximum tensile stress. The central portion includes a first transition portion attaching the first central main surface to the first portion, the first transition portion containing a first transition tensile stress region containing a first transition maximum tensile stress. The central portion includes a second transition portion attaching the first central main surface to the second portion, the second transition portion containing a second transition tensile stress region containing a second transition maximum tensile stress. The first transition maximum tensile stress is greater than the central maximum tensile stress.

10. The foldable substrate of claim 9, wherein, The second maximum tensile stress during the transition is greater than the maximum tensile stress at the center.

11. The foldable substrate as claimed in any one of claims 1-10, wherein the first distance is 20% to 45% of the substrate thickness.

12. The foldable substrate as claimed in any one of claims 1-11, wherein the substrate achieves an effective bending radius of 5 mm.

13. A foldable device comprising a foldable substrate as claimed in any one of claims 1-12, the foldable device further comprising an adhesive having a first contact surface and a second contact surface opposite the first contact surface, wherein... At least a portion of the adhesive is positioned in a recess defined between the second central surface region and the second plane defined by the second main surface.

14. A foldable device comprising a foldable substrate as claimed in any one of claims 1-12, the foldable device further comprising a polymer-based portion positioned in a recess defined between the second central surface region and a second plane defined by the second main surface, wherein, The foldable device includes an adhesive having a first contact surface and a second contact surface opposite to the first contact surface.

15. The device as claimed in claim 14, wherein, The polymer-based portion contains a yield strain in the range of 5% to 10%, and the difference between the refractive index of the foldable substrate and the refractive index of the polymer-based portion is 0.1 or less.

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