Chemically strengthened substrate and method for chemically strengthening substrate

Abstract

The invention relates to a chemically strengthened substrate and a method for chemically strengthening a substrate. A method of chemically strengthening a substrate having a thickness of 10 [mu] m to 100 [mu] m includes contacting the substrate with a molten salt solution maintained at 350 DEG C to 400 DEG C for 10 minutes to 90 minutes. In an aspect, the molten salt solution comprises at least two anions associated with at least two potassium salts. The concentration of the first potassium salt and the second potassium salt is at least 2% by weight of the molten salt solution. In an aspect, a method includes transferring a substrate to a cooling chamber having a temperature decreasing from 4 DEG C / min to 20 DEG C / min. In an aspect, a method includes contacting a substrate with an acidic solution having a pH of 3.5 to 4.5 for 10 seconds to 3.5 minutes. A chemically strengthened substrate having a thickness of 10 [mu] m to 100 [mu] m has a maximum compressive stress of 650 megapascal to 1200 megapascal.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority benefit of Chinese Application No. 202311773622.3, filed on December 21, 2023, the entire content of which is hereby incorporated by reference in its entirety and made a part hereof. Technical field

[0003] The present disclosure generally relates to chemically strengthened substrates and methods for chemically strengthening substrates. More specifically, it relates to chemically strengthened substrates having a thickness of 100 microns or less and methods for chemically strengthening substrates having a thickness of less than 100 microns. Background art

[0004] Glass - based substrates are widely used, for example, in display devices such as liquid crystal displays (LCDs), electrophoretic displays (EPDs), organic light - emitting diode displays (OLEDs), or plasma display panels (PDPs), etc.

[0005] There is a desire to develop foldable versions of displays and foldable protective covers to be mounted on foldable displays. The foldable displays and covers should have good impact resistance and puncture resistance. At the same time, the foldable displays and covers should have a small minimum bending radius (e.g., about 10 millimeters (mm) or less). Plastic displays and covers with a small minimum bending radius tend to have poor impact resistance and / or puncture resistance. In addition, common sense suggests that ultra - thin glass - based sheets (e.g., about 75 microns (μm or micron) thick or thinner) with a small minimum bending radius tend to have poor impact resistance and / or puncture resistance. In addition to this, glass - based sheets with a relatively thick thickness (e.g., greater than 125 microns) having good impact resistance and / or puncture resistance tend to have a relatively large minimum bending radius (e.g., about 30 mm or greater). Therefore, there is a need to develop foldable devices with a low minimum bending radius, good impact resistance, and good puncture resistance. Summary of the invention

[0006] Chemically strengthened substrates (e.g., foldable substrates) and methods for chemically strengthening substrates (e.g., for manufacturing them) are described herein. Providing glass - based substrates and / or ceramic - based substrates can provide good dimensional stability, can reduce the incidence of mechanical instability, and / or can provide good impact resistance and puncture resistance. The methods according to aspects of the present disclosure can increase the drop height that a foldable device and / or foldable substrate can withstand, can increase the survival rate of folding the substrate to a parallel - plate spacing of 5 mm, 3 mm, 2 mm, and / or 1 mm, and / or can increase the foldability of the substrate.

[0007] In aspects, a substrate can be chemically strengthened with a molten salt solution that includes two anions associated with at least a first potassium salt and a second potassium salt. Providing multiple (i.e., two or more) potassium atoms per anion for the first potassium salt can increase the effective concentration and / or activity of potassium in the molten salt solution, which can contribute to an increase in the maximum compressive stress in the resulting chemically strengthened foldable substrate. Providing the first potassium salt in the molten salt solution with a pKa of about 9 or greater and / or a molten salt solution pH of about 9 to 12 can improve the strength and / or foldability of the resulting chemically strengthened foldable substrate, for example, by selectively etching inherent defects in the foldable substrate that might otherwise be amplified due to the chemical strengthening process. As discussed herein with reference to the examples, potassium carbonate (K2CO3) has a more pronounced and unexpected increase in compressive stress compared to other components in the molten salt solution. Further, without being bound by theory, it is believed that the carbonate anion can contribute to the precipitation of other cations (e.g., lithium, sodium) exchanged from the foldable substrate, which can increase the life of the molten salt solution (e.g., by removing components from the solution phase that would otherwise "poison" the molten salt solution). As confirmed by the examples discussed herein, providing a first temperature of the molten salt solution below 400 °C can increase the maximum compressive stress established for a predetermined layer depth and / or compressive depth. Further, for some of the molten salt solutions discussed herein, a temperature of 350 °C or higher can be used to ensure salt melting.

[0008] It has been observed that a foldable substrate having a thickness of about 50 μm or less (e.g., from about 10 μm to about 50 μm or from about 10 μm to about 30 μm) is unexpectedly sensitive to events occurring after removal of the foldable substrate from a molten salt solution. For these thin foldable substrates, even relatively small differences in compressive stress on their surfaces can result in rippling and / or warping, which can create optical deformations that are visually visible to the user of a consumer electronic product that may incorporate the foldable substrate. Accordingly, a controlled temperature in the cooling chamber can contribute to relatively uniform compressive stress on the surface of the foldable substrate. Additionally, providing an initial temperature in the cooling chamber of 180° C. or higher (e.g., 200° C. or higher or 220° C. or higher) can facilitate removal of the remaining portion of the molten salt solution before it solidifies. Without wishing to be bound by theory, the first potassium salt can have a higher melting temperature compared to the second potassium salt, which means that incorporating the first potassium salt in the molten salt solution can increase the viscosity of the molten salt solution and / or can cause the molten salt solution to solidify at a higher temperature compared to a molten salt solution without the first potassium salt. Accordingly, when the molten salt solution contains the first potassium salt, it can be particularly useful to allow the remaining portion of the molten salt solution on the foldable substrate after removal of the foldable substrate from the molten salt solution. Reducing the temperature of the cooling chamber to a final temperature of about 100° C. or lower (e.g., from about 25° C. to about 100° C. or from about 60° C. to about 90° C.) can enable subsequent treatment of the foldable substrate with an aqueous solution (e.g., relatively quickly or immediately) (e.g., rinsing with water or an alkaline detergent solution, contacting with an aqueous acidic solution). Providing a cooling rate of from about 4° C. / minute to about 20° C. / minute can cause the temperature of the cooling chamber (and the foldable substrate) to drop rapidly while maintaining a relatively consistent temperature throughout the cooling chamber (and / or the foldable substrate), e.g., thereby creating relatively uniform compressive stress on the surface of the foldable substrate.

[0009] Providing an etch rate of about 1 μm / minute or less (e.g., about 1.0 μm / minute or less) can facilitate substantially uniform material removal from the surface(s) of the foldable substrate. As discussed above, a foldable substrate having a thickness of about 50 μm or less (e.g., from about 10 μm to about 50 μm or from about 10 μm to about 30 μm) is quite sensitive to differences in compressive stress and thickness variations on its surface. Accordingly, providing an etch rate of about 1 μm / minute can remove relatively uniform thickness and compressive stress portions from the surface(s), thereby reducing the likelihood of rippling and / or warping that can create optical deformations that are visually visible to the user of a consumer electronic product that may incorporate the foldable substrate. Without wishing to be bound by theory, providing an acidic solution at a lower temperature (e.g., from about 20° C. to about 40° C. or from about 20° C. to about 25° C.) can reduce the concentration of the SiF6 - anion, since H2SiF6 combines with 2H + +SiF6- The reaction is endothermic. Reducing the concentration of SiF6 - anions will be associated with a decrease in the deposition (e.g., redeposition) of silica or silica-like materials on the surface, which otherwise would result in a change in the thickness and / or compressive stress on the surface of the foldable substrate. Providing a higher pH (e.g., from about 3.5 to about 4.5, from about 3.6 to about 4.3, or from about 3.7 to about 4.0) will reduce the etching rate, which can help to produce relatively uniform compressive stress and thickness on the foldable substrate. Providing a total concentration of HF and NH4F of about 4.0 wt% or less, about 3.5 wt% or less, about 3.0 wt% or less, about 2.5 wt% or less, or about 2.0 wt% or less (e.g., from about 1.25 wt% to about 4.0 wt%, from about 1.3 wt% to about 3.5 wt%, from about 1.35 wt% to about 3.0 wt%, from about 1.4 wt% to about 2.5 wt%, from about 1.5 wt% to about 2.0 wt%) can provide relatively controlled and uniform etching of the foldable substrate and / or can reduce the deposition of materials (e.g., silica, silica-like materials, ammonium fluoride crystals) on the foldable substrate that would degrade the optical properties of the foldable substrate.

[0010] In an aspect, the substrate thickness of the substrate can be about 50 μm or thicker (e.g., about 50 μm to about 100 μm, about 50 μm to about 90 μm, or any corresponding sub-range therebetween as discussed above) and combined with one or more of the following properties: (1) the compression depth is about 10% to about 30%, about 16% to about 26%, or any corresponding sub-range therebetween as discussed above, based on the percentage of the substrate thickness; (2) the layer depth of potassium (e.g., the first layer depth and / or the second layer depth) ranges from about 3 μm to about 20 μm, about 10 μm to about 15 μm, or any corresponding sub-range as discussed above; and / or (3) the maximum compression stress (e.g., the first maximum compression stress and / or the second maximum compression stress) ranges from about 650 MPa to about 1200 MPa, about 800 MPa to about 1100 MPa, about 850 MPa to about 1200 MPa, or any corresponding sub-range as discussed above. In an aspect, the substrate thickness can be about 50 μm or thinner (e.g., about 10 μm to about 50 μm, about 10 μm to about 30 μm, or any corresponding sub-range therebetween as discussed above) and combined with one or more of the following properties: (1) the compression depth is about 10% to about 30%, about 12% to about 19%, or any corresponding sub-range therebetween as discussed above, based on the percentage of the substrate thickness; (2) the layer depth of potassium ranges from about 3 μm to about 20 μm, about 5 μm to about 9 μm, or any corresponding sub-range as discussed above; and / or (3) the maximum compression stress (e.g., the first maximum compression stress and / or the second maximum compression stress) ranges from about 650 MPa to about 1200 MPa, about 750 MPa to about 1100 MPa, about 750 MPa to about 1,000 MPa, or any corresponding sub-range as discussed above.

[0011] Some exemplary aspects of the present disclosure are described below. It is to be understood that any feature of the various aspects can be used alone or in combination with each other.

[0012] Aspect 1: A method of chemically strengthening a substrate, the substrate including a thickness of 10 micrometers to 100 micrometers defined between a first existing major surface and a second existing major surface opposite the first existing major surface, the method comprising:

[0013] Contacting the first existing major surface of the substrate with a molten salt solution maintained at a first temperature for a first period of time, the molten salt solution including at least two anions associated with at least a first potassium salt and a second potassium salt, the concentration of the first potassium salt and the concentration of the second potassium salt being 2 wt% or greater of the molten salt solution, the first temperature ranging from about 350 °C to about 400 °C, and the first period of time ranging from about 10 minutes to about 90 minutes.

[0014] Aspect 2: The method of Aspect 1, wherein the first potassium salt comprises two or more potassium atoms per anion, and the pKa of the potassium salt is 9 or greater, and the concentration range of the first potassium salt is from about 2 wt% to about 12 wt% of the molten salt solution.

[0015] Aspect 3: The method of any one of Aspects 1-2, wherein the first potassium salt is potassium carbonate K2CO3, and the concentration range of the first potassium salt is from about 2 wt% to about 12 wt% of the molten salt solution.

[0016] Aspect 4: The method of any one of Aspects 1-3, wherein the concentration range of the first potassium salt is from about 2.5 wt% to about 5.0 wt%.

[0017] Aspect 5: The method of any one of Aspects 1-3, wherein the concentration range of the first potassium salt is from about 5 wt% to about 12 wt%.

[0018] Aspect 6: The method of Aspect 5, wherein the concentration range of the first potassium salt is from about 8 wt% to about 12 wt%.

[0019] Aspect 7: The method of any one of Aspects 3-6, wherein the molten salt solution further comprises from 0 wt% to 5 wt% of a third potassium salt associated with a third anion, the third anion being different from the anions associated with the first potassium salt and the second potassium salt, and the third potassium salt comprises two or more potassium atoms per anion.

[0020] Aspect 8: The method of Aspect 7, wherein the third potassium salt comprises potassium sulfate K2SO4, and the concentration of the third potassium salt is from about 0.5 wt% to about 5 wt%.

[0021] Aspect 9: The method of any one of Aspects 1-8, wherein the second potassium salt is potassium nitrate KNO3, and the concentration range of the second potassium salt is from about 50 wt% to about 98 wt% of the molten salt solution.

[0022] Aspect 10: The method of Aspect 9, wherein the concentration range of the second potassium salt is from about 88 wt% to about 98 wt%.

[0023] Aspect 11: The method of any one of Aspects 1-10, wherein the pH range of the molten salt solution at the first temperature is from about 9 to 12.

[0024] Aspect 12: The method of any one of Aspects 1-11, wherein, relative to the case of immersing the substrate in a comparative molten salt solution having the same composition as the molten salt solution without the first potassium salt, the presence of the first potassium salt increases the compressive stress imparted by contact through the existing first major surface with the molten salt solution by about 5% or more.

[0025] Aspect 13: The method of any one of Aspects 1-12, wherein the thickness range of the substrate is from about 15 μm to about 50 μm.

[0026] Aspect 14: The method of any one of Aspects 1 - 12, wherein the thickness range of the substrate is from about 50 μm to about 90 μm.

[0027] Aspect 15: The method of any one of Aspects 1 - 13, further comprising: heating the substrate in a temperature range of about 250 °C to about 350 °C for a period of about 10 minutes to about 4 hours before the existing first major surface contacts the molten salt solution.

[0028] Aspect 16: The method of any one of Aspects 1 - 13 or 15 (inclusive), further comprising after the existing first major surface contacts the molten salt solution:

[0029] transferring the substrate from the molten salt solution to a cooling chamber and reducing the temperature of the cooling chamber from an initial temperature in the range of about 180 °C to about 300 °C to a final temperature in the range of about 25 °C to about 100 °C at a cooling rate of from about 4 °C / minute to about 20 °C / minute.

[0030] Aspect 17: A method for chemically strengthening a substrate having a thickness of from 10 microns to 50 microns defined between an existing first major surface and an existing second major surface opposite the existing first major surface, the method comprising:

[0031] strengthening the substrate in a molten salt solution maintained at a first temperature for a first period, the first temperature being in the range of about 350 °C to about 400 °C and the first period being in the range of about 10 minutes to about 90 minutes; and

[0032] transferring the substrate from the molten salt solution to a cooling chamber and reducing the temperature of the cooling chamber from an initial temperature in the range of about 180 °C to about 300 °C to a final temperature in the range of about 25 °C to about 100 °C at a cooling rate of from about 4 °C / minute to about 20 °C / minute.

[0033] Aspect 18: The method of any one of Aspects 16 - 17, wherein the final temperature is in the range of about 60 °C to about 90 °C.

[0034] Aspect 19: The method of any one of Aspects 16 - 18, wherein the initial temperature is in the range of about 180 °C to about 220 °C.

[0035] Aspect 20: The method of any one of Aspects 16 - 19, further comprising: after the cooling chamber reaches the final temperature, cleaning the substrate with water, an alkaline detergent solution, or a combination thereof.

[0036] Aspect 21: The method of any one of Aspects 1 - 20, wherein after the existing first major surface is contacted with the molten salt solution, the initial maximum compressive stress of the substrate is from about 800 megapascals to about 1500 megapascals.

[0037] Aspect 22: The method of Aspect 21, wherein the initial maximum compressive stress is from about 900 megapascals to about 1200 megapascals.

[0038] Aspect 23: The method of any one of Aspects 1 - 20, further comprising:

[0039] contacting the existing first major surface with an acidic solution for a second time period to remove an outer layer from the existing first major surface to form a new first major surface, the pH range of the acidic solution is from 3.5 to 4.5, and the second time period is from about 10 seconds to about 3.5 minutes; and then

[0040] washing the new first major surface with water.

[0041] Aspect 24: A method for chemically strengthening a substrate, the substrate comprising a thickness of 10 micrometers to 100 micrometers defined between an existing first major surface and an existing second major surface opposite the existing first major surface, the method comprising:

[0042] chemically strengthening the substrate in a molten salt solution maintained at a first temperature for a first time period, the range of the first temperature is from about 350 °C to about 400 °C, and the range of the first time period is from about 10 minutes to about 90 minutes;

[0043] contacting the existing first major surface with an acidic solution for a second time period to remove an outer layer from the existing first major surface to form a new first major surface, the pH range of the acidic solution is from 3.5 to 4.5, and the second time period is from about 10 seconds to about 3.5 minutes; and then

[0044] washing the new first major surface with water.

[0045] Aspect 25: The method of any one of Aspects 23 - 24, wherein the second temperature of the acidic solution is from about 20 °C to about 40 °C.

[0046] Aspect 26: The method of Aspect 23, wherein the range of the second temperature is from about 20 °C to about 25 °C.

[0047] Aspect 27: The method of any one of Aspects 23 - 26, wherein the acidic solution comprises a buffered HF solution.

[0048] Aspect 28: The method of any one of Aspects 23 - 27, wherein, based on the weight % of the acidic solution, the acidic solution comprises:

[0049] about 0.5 wt% to about 1.5 wt% HF; and

[0050] From about 0.75 wt% to about 2.5 wt% NH4F.

[0051] Aspect 29: The method of aspect 28, wherein the acidic solution comprises, based on the weight % of the acidic solution:

[0052] From about 0.5 wt% to about 0.75 wt% HF; and

[0053] From about 0.9 wt% to about 1.5 wt% NH4F.

[0054] Aspect 30: The method of any one of aspects 23 - 29, wherein the acidic solution removes the outer layer at a rate of about 1.0 micron per minute or less.

[0055] Aspect 31: The method of any one of aspects 23 - 30, wherein the substrate includes an initial maximum compressive stress before contact with the acidic solution, the substrate includes a final maximum compressive stress after contact with the acidic solution, and the final maximum compressive stress is about 10% to about 25% less than the initial maximum compressive stress, based on the percentage of the initial maximum compressive stress.

[0056] Aspect 32: The method of aspect 31, wherein the final maximum compressive stress is about 15% to about 20% less than the initial maximum compressive stress, based on the percentage of the initial maximum compressive stress.

[0057] Aspect 33: The method of any one of aspects 31 - 32, wherein the final maximum compressive stress ranges from about 700 megapascals to about 1200 megapascals.

[0058] Aspect 34: The method of any one of aspects 23 - 33, further comprising cleaning the substrate with water or another acidic solution after the first major surface has contacted the acidic solution.

[0059] Aspect 35: The method of any one of aspects 23 - 34, wherein 95% or more of the substrate samples can withstand a parallel plate spacing of 5 millimeters.

[0060] Aspect 36: The method of any one of aspects 23 - 35, wherein the substrate exhibits a drop threshold height of 10 centimeters or more in a drop test.

[0061] Aspect 37: The method of any one of aspects 23 - 35, wherein the substrate exhibits a drop threshold height of 20 centimeters or more in a drop height.

[0062] Aspect 38: The method of any one of aspects 23 - 37, wherein when the thickness ranges from about 50 microns to about 100 microns, about 30% or more of the substrate samples can withstand a parallel plate spacing of 3 millimeters.

[0063] Aspect 39: The method according to any one of Aspects 23-36, wherein the thickness is from 10 micrometers to 50 micrometers.

[0064] Aspect 40: The method according to Aspect 39, wherein the thickness is from 10 micrometers to 30 micrometers.

[0065] Aspect 41: The method according to any one of Aspects 39-40, wherein 90% or more of the substrate samples are able to withstand a parallel plate spacing of 2 millimeters.

[0066] Aspect 42: The method according to any one of Aspects 39-40, wherein 10% or more of the substrate samples are able to withstand a parallel plate spacing of 1 millimeter.

[0067] Aspect 43: The method according to any one of Aspects 1-42, wherein the substrate is a glass-based substrate.

[0068] Aspect 44: The method according to Aspect 43, wherein the composition of the substrate, in mole % of the substrate, comprises:

[0069] From about 60 mole % to about 70 mole % SiO2;

[0070] From about 8 mole % to about 16 mole % Al2O3;

[0071] From about 12 mole % to about 18 mole % Na2O;

[0072] From about 2 mole % to about 6 mole % MgO; and

[0073] From about 0.1 mole % to about 2.0 mole % CaO.

[0074] Aspect 45: The method according to Aspect 44, wherein the composition, in mole % of the substrate, comprises:

[0075] From about 64 mole % to about 69 mole % SiO2;

[0076] From about 9 mole % to about 15 mole % Al2O3;

[0077] From about 14 mole % to about 17 mole % Na2O;

[0078] From about 2.5 mole % to about 5.5 mole % MgO;

[0079] From about 0.3 mole % to about 1.2 mole % CaO; and

[0080] From 0.0 mole % to about 0.5 mole % K2O.

[0081] Aspect 45: Chemically strengthened substrate, comprising:

[0082] a thickness defined between a first major surface and a second major surface opposite the first major surface, the thickness being from about 10 micrometers to about 100 micrometers; and

[0083] a first compressive stress region extending from the first major surface to a first compressive depth, a first depth of potassium being about 5 micrometers or greater and a maximum first compressive stress being from about 650 megapascals to about 1200 megapascals,

[0084] wherein the chemically strengthened substrate comprises a glass-based material, at least 95% of samples of the chemically strengthened substrate being able to withstand a parallel plate spacing of 5 millimeters, and the substrate exhibiting a scratch threshold height of 10 centimeters or greater in a scratch test.

[0085] Aspect 47: The chemically strengthened substrate of aspect 46, wherein, in mole % of the chemically strengthened substrate, the composition of the chemically strengthened substrate is:

[0086] from about 60 mole % to about 70 mole % SiO2;

[0087] from about 8 mole % to about 16 mole % Al2O3;

[0088] from about 12 mole % to about 18 mole % Na2O;

[0089] from about 2 mole % to about 6 mole % MgO; and

[0090] from about 0.1 mole % to about 2.0 mole % CaO.

[0091] Aspect 48: The chemically strengthened substrate of aspect 47, wherein, in mole % of the chemically strengthened substrate, the composition comprises:

[0092] from about 64 mole % to about 69 mole % SiO2;

[0093] from about 9 mole % to about 15 mole % Al2O3;

[0094] from about 14 mole % to about 17 mole % Na2O;

[0095] from about 2.5 mole % to about 5.5 mole % MgO;

[0096] from about 0.3 mole % to about 1.2 mole % CaO; and

[0097] from 0.0 mole % to about 0.5 mole % K2O.

[0098] Aspect 49: The chemically strengthened substrate of any one of aspects 46 - 48, wherein the maximum first compressive stress is from about 800 megapascals to about 1100 megapascals.

[0099] Aspect 50: The chemically strengthened substrate according to any one of Aspects 46 - 49, wherein 90% or more of the substrate samples can withstand a parallel plate spacing of 3 mm.

[0100] Aspect 51: The chemically strengthened substrate according to any one of Aspects 46 - 50, wherein the thickness is from about 10 μm to about 50 μm.

[0101] Aspect 52: The chemically strengthened substrate according to Aspect 51, wherein the thickness is from about 10 μm to about 30 μm.

[0102] Aspect 53: The chemically strengthened substrate according to any one of Aspects 51 - 52, wherein the maximum first compressive stress is from about 750 MPa to about 1100 MPa.

[0103] Aspect 54: The chemically strengthened substrate according to any one of Aspects 51 - 53, wherein 90% or more of the substrate samples can withstand a parallel plate spacing of 2 mm.

[0104] Aspect 55: The chemically strengthened substrate according to any one of Aspects 51 - 54, wherein 10% or more of the substrate samples can withstand a parallel plate spacing of 1 mm.

[0105] Aspect 56: The chemically strengthened substrate according to any one of Aspects 46 - 50, wherein the maximum first compressive stress is from about 850 MPa to about 1200 MPa.

[0106] Aspect 57: The chemically strengthened substrate according to any one of Aspects 46 - 50, wherein the maximum first compressive stress is from about 1000 MPa to about 1200 MPa.

[0107] Aspect 58: The chemically strengthened substrate according to any one of Aspects 46 - 50 or 56 - 57 (inclusive), wherein about 30% or more of the chemically strengthened substrate samples can withstand a parallel plate spacing of 3 mm.

[0108] Aspect 59: The chemically strengthened substrate according to any one of Aspects 46 - 50 or 56 - 57 (inclusive), wherein about 50% or more of the chemically strengthened substrate samples can withstand a parallel plate spacing of 3 mm.

[0109] Aspect 60: The chemically strengthened substrate according to any one of Aspects 46 - 59, wherein the chemically strengthened substrate exhibits a haze of about 1% or less.

[0110] Aspect 61: The chemically strengthened substrate according to any one of Aspects 46 - 60, wherein the chemically strengthened substrate exhibits a transmittance of 90% to 95%.

[0111] Throughout this disclosure, the accompanying drawings are used to emphasize certain aspects. Thus, unless otherwise explicitly stated, it should be assumed that the relative dimensions of the different regions, portions, and substrates shown in the figures are not in proportion to their actual relative dimensions. BRIEF DESCRIPTION OF THE DRAWINGS

[0112] Referring to the accompanying drawings, read the following detailed description to better understand the above and other features and advantages of the aspects of the present disclosure, wherein:

[0113] Figure 1 is a schematic view of an exemplary foldable device in a flat configuration according to an aspect, wherein a schematic view of the folded configuration can be seen as shown in Figure 5 shown;

[0114] Figure 2 is a cross-sectional view of an exemplary foldable device formed of a foldable substrate along line 2-2 of Figure 1 ;

[0115] Figure 3 is a cross-sectional view of an exemplary foldable device along line 2-2 of Figure 1 ;

[0116] Figure 4 is a schematic view of an exemplary foldable device in a folded configuration according to an aspect of the present disclosure, wherein a schematic view of the flat configuration can be seen as shown in Figure 1 shown;

[0117] Figure 5 is a cross-sectional view of a test device for determining the minimum parallel plate spacing of an exemplary improved foldable device and / or foldable substrate along line 5-5 of Figure 4 ;

[0118] Figure 6 is an elevation schematic view of a writing device;

[0119] Figure 7 is an elevation schematic view of a foldable consumer electronic product;

[0120] Figure 8 is a plan schematic view of an exemplary consumer electronic device according to an aspect;

[0121] Figure 9 is Figure 8 a perspective schematic view of an exemplary consumer electronic device;

[0122] Figure 10 The flowchart shows an exemplary method of chemically strengthening a substrate to form a foldable substrate and / or foldable device according to an aspect of the present disclosure;

[0123] Figure 11Schematically shows that the chemical strengthening method of the substrate includes a step of heating the substrate;

[0124] Figure 12 Schematically shows that the chemical strengthening method of the substrate includes a step of bringing the substrate into contact with a molten salt solution;

[0125] Figure 13 Schematically shows that the chemical strengthening method of the substrate includes a step of lowering the temperature of the cooling chamber and / or causing the molten salt solution to drip from the substrate;

[0126] Figure 14 Schematically shows that the chemical strengthening method of the substrate includes a step of cleaning the substrate;

[0127] Figure 15 Schematically shows that the chemical strengthening method of the substrate includes a step of bringing the substrate into contact with an acidic solution;

[0128] Figure 16 is a cross-sectional view of the foldable device after Figure 12 the steps shown and / or before Figure 15 the steps shown;

[0129] Figure 17 Schematically shows the compressive stress (in megapascals) (vertical axis - y-axis) of Examples 1 - 6 and Comparative Examples AA - DD;

[0130] Figure 18 Schematically shows the layer depth (in micrometers) (vertical axis - y-axis) of Examples 1 - 6 and Comparative Examples AA - DD;

[0131] Figure 19 Schematically shows the functional relationship between the compressive stress (in megapascals) (vertical axis - y-axis) and the concentration of K2CO3 in the molten salt solution (in weight %) (horizontal axis - x-axis);

[0132] Figure 20 Schematically shows the functional relationship between the layer depth (in micrometers) (vertical axis - y-axis) and the concentration of K2CO3 in the molten salt solution (in weight %) (horizontal axis - x-axis);

[0133] Figure 21 Schematically shows the functional relationship between the survival rate (percentage, vertical axis - y-axis) and the parallel plate spacing (in micrometers) (horizontal axis - x-axis);

[0134] Figure 22 Schematically shows the functional relationship between the survival rate (percentage, vertical axis - y-axis) and the parallel plate spacing (in micrometers) (horizontal axis - x-axis);

[0135] Figure 23Schematically shows the survival rate (percent, vertical axis - y-axis) as a function of the parallel plate spacing (in micrometers) (horizontal axis - x-axis);

[0136] Figure 24 Schematically shows the survival rate (percent, vertical axis - y-axis) as a function of the parallel plate spacing (in micrometers) (horizontal axis - x-axis);

[0137] Figure 25 Schematically shows the survival rate (percent, vertical axis - y-axis) as a function of the parallel plate spacing (in micrometers) (horizontal axis - x-axis); and

[0138] Figures 26A - 26C Schematically shows the visually visible reflections from chemically strengthened substrates exhibiting different levels of rippling.

[0139] Throughout this disclosure, the drawings are used to emphasize certain aspects. Thus, unless otherwise explicitly stated, it should be assumed that the relative sizes of the different regions, parts, and substrates shown in the figures are not in proportion to their actual relative sizes. Detailed Description

[0140] Aspects will now be described more fully with reference to the drawings, in which exemplary aspects are shown. Whenever possible, the same reference numerals are used throughout the drawings to refer to the same or like parts. However, the claims may encompass many different aspects of various aspects and should not be construed as limited to the aspects presented herein.

[0141] Figures 1 - 5 Schematic diagrams showing foldable devices 101, 301, and / or 401 that include a foldable substrate 201 according to aspects of the present disclosure. Unless otherwise specified, the discussion of the features of an aspect of a foldable device and / or foldable substrate may be equally applicable to the corresponding features of any aspect of the present disclosure. For example, throughout this disclosure, the same component numbers may indicate that, in some aspects, the features referred to are consistent with each other, and unless otherwise specified, the discussion of the features referred to in one aspect may be equally applicable to the features referred to in any other aspect of the present disclosure.

[0142] As Figures 1 - 3 shown, an exemplary aspect of foldable devices 101 and / or 301 may include a foldable substrate 201 according to the present disclosure in an unfolded (e.g., flat) configuration, while Figure 5 a foldable device 401 according to the present disclosure that includes a foldable substrate 201 is shown in a folded configuration. In an aspect, as Figures 4 - 5 shown, foldable device 401 may include a foldable substrate 201 and / or be formed of a foldable substrate 201. In an aspect, as Figure 3As shown, the foldable device 310 may include a layer (e.g., PET sheet 321) attached to the foldable substrate 201 via an adhesive layer 311. It is understood that other layers (e.g., release layer, display device, additional substrate) may also be used as a supplement or alternative to the shown layer.

[0143] Throughout this disclosure, refer to Figure 1 , the width 103 of the foldable device 101 and / or 301 is regarded as the dimension of the foldable device selected between the opposite edges of the foldable device in the direction 104 of the folding axis 102 of the foldable device, where the direction 104 also includes the direction of the width 103. Additionally, throughout this disclosure, the length 105 of the foldable device 101 and / or 301 is regarded as the dimension of the foldable device 101 and / or 301 selected between the opposite edges of the foldable device 101 and / or 301 in the direction 106 perpendicular to the folding axis 102 of the foldable device. In an aspect, as Figures 1 - 3 shown, the foldable device of any aspect of this disclosure may include a folding plane 109, which includes the folding axis 102 and the direction of the substrate thickness 209 when the foldable device is in a flat configuration (e.g., refer to Figure 2 ). The folding plane 109 may include the central axis 107 of the foldable device, and its position is at, for example, the second major surface 205 of the foldable devices 101 and 301 (refer to Figures 2 - 3 ). In an aspect, the foldable device may be folded in the direction 111 about a folding axis 102 extending in the direction 104 of the width 103 (refer to Figure 1 ), thereby forming a folded configuration (e.g., refer to Figures 4 - 5 ). In an aspect, as Figures 2 - 3 shown, the foldable device 101 and / or 301 and / or the foldable substrate 201 may include a substantially flat first major surface 203 and / or second major surface 205, where the central portion of the foldable device may be indistinguishable from the adjacent portions. As Figures 1 - 5 shown, the foldable device may include a single folding axis, thereby allowing the foldable device to include a bifold, where, for example, the foldable device may be folded in half. In other aspects, the foldable device may include two or more folding axes. For example, each folding axis includes a corresponding central portion similar or identical to the central portion discussed herein. For example, providing two folding axes may allow the foldable device to include a trifold, where, for example, the foldable device may be folded such that the first portion, the second portion, and the third portion, which are similar or identical to the first portion or the second portion, are folded respectively through the central portion and another central portion (which is similar or identical to the central portion placed between the first portion and the second portion and is located between the second portion and the third portion).

[0144] The foldable devices 101 and / or 301 of the present disclosure include a foldable substrate 201. In aspects, the foldable substrate 201 may include a glass-based substrate having a pencil hardness of 8H or higher (e.g., 9H or higher). In aspects, the foldable substrate 201 may include a glass-based substrate. As used herein, "glass-based" includes both glass and glass-ceramics, where the glass-ceramics have: one or more crystalline phases, and an amorphous residual glass phase. Glass-based materials (e.g., glass-based substrates) may contain amorphous materials (e.g., glass) and optionally one or more crystalline materials (e.g., ceramics). The amorphous materials and the glass-based materials may be strengthened. As used herein, the term "strengthened" may refer to a material that has been chemically strengthened, for example, by ion-exchanging smaller ions in the surface of the substrate with larger ions, as discussed below. However, other strengthening methods may also be employed, such as using thermal tempering or a mismatch in the coefficient of thermal expansion between parts of the substrate to create regions of compressive stress and central tension to form a strengthened substrate. Exemplary glass-based materials (which may be lithium oxide-free or contain lithium oxide) include: soda-lime silicate glass, alkaline aluminosilicate glass, alkaline borosilicate glass-containing, alkaline aluminoborosilicate glass-containing, alkaline phosphosilicate glass-containing, and alkaline aluminophosphosilicate glass-containing. In one or more aspects, in mole percentages (mol%), the glass-based material may contain: about 40 mol% to about 80 mol% SiO2, about 5 mol% to about 30 mol% Al2O3, 0 mol% to about 10 mol% B2O3, 0 mol% to about 5 mol% ZrO2, 0 mol% to about 15 mol% P2O5, 0 mol% to about 2 mol% TiO2, 0 mol% to about 20 mol% R2O, and 0 mol% to about 15 mol% RO. As used herein, R2O refers to alkali metal oxides, such as Li2O, Na2O, K2O, Rb2O, and Cs2O. As used herein, RO refers to MgO, CaO, SrO, BaO, and ZnO. In aspects, the glass-based substrate may also optionally contain 0 mol% to about 2 mol% of each of the following: Na2SO4, NaCl, NaF, NaBr, K2SO4, KCl, KF, KBr, As2O3, Sb2O3, SnO2, Fe2O3, MnO, MnO2, MnO3, Mn2O3, Mn3O4, Mn2O7. "Glass-ceramics" includes materials produced by the controlled crystallization of glass. In aspects, the glass-ceramics have a crystallinity of about 1% to about 99%.Examples of suitable glass ceramics can 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 including a primary crystal phase containing β-quartz solid solution, β-spodumene, cordierite, petalite and / or lithium disilicate. The glass ceramic substrate can be strengthened by a chemical strengthening process. In one or more aspects, the MAS system glass ceramic substrate can be strengthened in a Li2SO4 molten salt, so that 2Li can occur. + is replaced by Mg 2+ exchange.

[0145] In an aspect, the glass-based substrate (e.g., the foldable substrate 201) has SiO2 as the largest component, and thus SiO2 is the main constituent component of the glass network formed by the glass-based composition. Pure SiO2 has a relatively low CTE. However, pure SiO2 has a high melting point. Therefore, if the concentration of SiO2 in the glass-based composition is too high, the formability of the glass-based composition may decrease because the higher SiO2 concentration increases the difficulty of melting the glass, which in turn has a negative impact on the formability of the composition. If the concentration of SiO2 in the glass-based composition is too low, the chemical durability of the glass-based material may decrease, and the glass-based material may be prone to surface breakage during the post-forming process. In an aspect, the amount of SiO2 contained in the glass-based substrate can be: 60 mol% or more, 61 mol% or more, 62 mol% or more, 63 mol% or more, 63.5 mol% or more, 64 mol% or more, 70 mol% or less, 69 mol% or less, 68 mol% or less, 67 mol% or less, 66 mol% or less, or 65 mol% or less. In an aspect, the range of SiO2 contained in the glass-based substrate can be: 60 mol% to 70 mol%, 61 mol% to 70 mol%, 62 mol% to 69 mol%, 63 mol% to 69 mol%, 64 mol% to 69 mol%, 65 mol% to 69 mol%, 64 mol% to 68 mol%, 65 mol% to 67 mol%, or any range or sub-range therebetween. In a preferred aspect, the amount of SiO2 contained in the glass-based substrate is 60 mol% to 70 mol% or 64 mol% to 69 mol%.

[0146] The glass-based substrate (e.g., the foldable substrate 201) may include Al2O3. Similar to SiO2, Al2O3 can act as a glass network former. Al2O3 can increase the viscosity of the glass-based composition because it is tetrahedrally coordinated in the glass melt formed from the glass-based composition. When the amount of Al2O3 is too high, the formability of the glass-based composition is reduced. However, when the concentration of Al2O3 is balanced with the concentration of SiO2 and the concentration of basic oxides in the glass-based composition, Al2O3 reduces the liquidus temperature of the glass melt, thereby enhancing the liquidus viscosity and improving the compatibility of the glass-based composition with certain forming processes. Inclusion of Al2O3 in the glass-based composition can achieve high fracture toughness values as described herein. In an aspect, the concentration of Al2O3 included in the glass-based substrate is: 8 mol% or more, 9 mol% or more, 10 mol% or more, 11 mol% or more, 12 mol% or more, 16 mol% or less, 16 mol% or less, 15 mol% or less, 14 mol% or less, or about 13 mol% or less. In an aspect, the amount of Al2O3 included in the glass-based substrate can be in the following ranges: 8 mol% to 16 mol%, 9 mol% to 15 mol%, 10 mol% to 15 mol%, 11 mol% to 14 mol%, 12 mol% to 13 mol%, or any range or sub-range therebetween. In a preferred aspect, the amount of Al2O3 included in the glass-based substrate is 8 mol% to 16 mol% or 9 mol% to 15 mol%.

[0147] The glass-based substrate (e.g., the foldable substrate 201) may include Na2O. Na2O can contribute to the ion-exchangeability of the glass-based composition and can improve formability, thereby improving the manufacturability of the glass-based composition. However, if too much Na2O is added to the glass-based composition, the CTE may be too low and the melting point may be too high. In addition, if too much Na2O is included in the composition relative to the amount of Li2O, the ability of the glass-based substrate to achieve a deep compressive depth when ion-exchanged may be reduced. In an aspect, the amount of Na2O included in the glass-based substrate is: 12 mol% or more, 13 mol% or more, 14 mol% or more, 15 mol% or more, 18 mol% or less, 17 mol% or less, 16 mol% or less, or 15 mol% or less. In an aspect, the amount of Na2O included in the glass-based substrate is in the following ranges: 12 mol% to 17 mol%, 13 mol% to 18 mol%, 14 mol% to 17 mol%, 15 mol% to 16 mol%, or any range or sub-range therebetween. In a preferred aspect, the amount of Na2O included in the glass-based substrate is 12 mol% to 18 mol% Na2O or 14 mol% to 17 mol%.

[0148] A glass-based substrate (e.g., the foldable substrate 201) can include K2O. Including K2O in the glass-based composition increases the potassium diffusivity in the glass-based material, enabling a deeper depth of the compressive stress peak (DOL SP ) to be achieved within a lower amount of ion exchange time. If too much K2O is included in the composition, the amount of compressive stress imparted during the ion exchange process may be reduced. In an aspect, the amount of K2O included in the glass-based substrate can be: 0.0 mol% or more, 0.1 mol% or more, 0.25 mol% or more, 1 mol% or less, 0.75 mol% or less, 0.5 mol% or less, or 0.3 mol% or less. In an aspect, the amount of K2O included in the glass-based substrate can be in the following ranges: 0.0 mol% to 1 mol%, 0.0 mol% to 0.75 mol%, 0.0 mol% to 0.5 mol%, 0.1 mol% to 0.3 mol%, or any range or sub-range therebetween. In a preferred aspect, the amount of K2O included in the glass-based substrate can be in the following ranges: 0.0 mol% to 1 mol% or 0.0 mol% to 0.5 mol%

[0149] A glass-based substrate (e.g., the foldable substrate 201) can include MgO. MgO can reduce the viscosity of the glass, which enhances the formability and manufacturability of the composition. Including MgO in the glass-based composition can also improve the strain point and Young's modulus of the glass-based composition. However, if too much MgO is added to the glass-based composition, the liquidus viscosity may be too low for compatibility with the desired forming technology. Adding too much MgO may also increase the density and CTE of the glass-based composition to an undesirable level. Including MgO in the glass-based composition also helps improve the fracture toughness. In an aspect, the amount of MgO included in the glass-based substrate can be: 2 mol% or more, 2.5 mol% or more, 3.0 mol% or more, 3.2 mol% or more, 3.5 mol% or more, 4.0 mol% or more, 6 mol% or less, 5.5 mol% or less, 5.0 mol% or less, or 4.9 mol% or less. In an aspect, the amount of MgO included in the glass-based substrate can be in the following ranges: 2 mol% to 6 mol%, 2.5 mol% to 5.5 mol%, 3.0 mol% to 5.0 mol%, 3.2 mol% to less than or equal to 4.9 mol%, 3.5 mol% to 4.9, or any range or sub-range therebetween. In a preferred aspect, the amount of MgO included in the composition is 2 mol% to 6 mol% or 2.5 mol% to 5.5 mol%.

[0150] The glass-based substrates described herein (e.g., foldable substrate 201) can include CaO. CaO can reduce the viscosity of the glass, which can enhance formability, strain point, and Young's modulus. However, if too much CaO is added to the glass-based composition, the density and CTE of the glass-based composition may increase to undesirable levels, and the ion-exchangeability of the glass-based substrate may be undesirably hindered. Inclusion of CaO in the glass-based composition also improves fracture toughness. In aspects, the amount of CaO included in the glass-based substrate can be: 0.1 mol% or more, 0.2 mol% or more, 0.3 mol% or more, 0.4 mol% or more, 0.5 mol% or more, 0.7 mol% or more, 2.0 mol% or less, 1.5 mol% or less, 1.2 mol% or less, 1.1 mol% or less, 1.0 mol% or less, or 0.9 mol% or less. In aspects, the amount of CaO included in the glass-based substrate can be in the following ranges: 0.1 mol% to 2.0 mol%, 0.2 mol% to 1.5 mol%, 0.3 mol% to 1.2 mol%, 0.4 mol% to less than or equal to 1.1 mol%, 0.5 mol% to 1.0 mol%, 0.7 mol% to 1.0 mol%, or any range or sub-range therebetween. In a preferred aspect, the amount of CaO included in the glass-based substrate is 0.1 mol% to 2.0 mol% or 0.3 mol% to 1.2 mol%.

[0151] In aspects, the glass-based substrate can be substantially free or free of one or more of the following: P2O5, B2O3, TiO2, ZnO, ZrO2, Ta2O5, HfO2, La2O3, and / or Y2O3. As used herein, the term "substantially free" means that although very small amounts of the component may be present as contaminants in the final glass-based composition (e.g., less than 0.1 mol%), the component is not intentionally added as a component of the batch materials. For example, inclusion of ZrO2 in the glass-based composition may result in the formation of undesirable zirconia in the glass-based material, which is at least partially due to the low solubility of ZrO2 in the glass-based material. Additionally, inclusion of Ta2O5, HfO2, La2O3, and / or Y2O3 may increase the raw material costs associated with the glass-based substrate.

[0152] In an aspect, a glass-based substrate (e.g., foldable substrate 201) can comprise: about 60 mol% to about 70 mol% SiO2, about 8 mol% to about 16 mol% Al2O3, about 12 mol% to about 18 mol% Na2O, about 2 mol% to about 6 mol% MgO, and about 0.1 mol% to about 2.0 mol% CaO. In an aspect, a glass-based substrate (e.g., foldable substrate 201) can comprise: about 64 mol% to about 69 mol% SiO2, about 9 mol% to about 15 mol% Al2O3, about 14 mol% to about 17 mol% Na2O, about 2.5 mol% to about 5.5 mol% MgO, about 0.3 mol% to about 1.2 mol% CaO, and 0.0 mol% to about 0.5 mol% K2O.

[0153] The foldable substrate 201 may include a glass-based substrate, and one or more compressive stress regions may be included in the first major surface 203 and / or the second major surface 205. In aspects, the compressive stress regions may be produced by chemical strengthening. Chemical strengthening may include an ion exchange process in which ions in the surface layer are replaced or exchanged with larger ions having the same valence or oxidation state. The chemical strengthening method will be discussed later. Without wishing to be bound by theory, chemical strengthening of the foldable substrate 201 may achieve good impact resistance and / or puncture resistance (e.g., resistance to failure at a drop height of 20 cm). Without wishing to be bound by theory, chemical strengthening of the foldable substrate 201 may achieve a small (e.g., less than about 10 mm or smaller) bending radius because the compressive stress from chemical strengthening may counteract the bending-induced tensile stress on the outermost surface of the substrate. The compressive stress regions may extend into a portion of the first portion and / or the second portion to a depth referred to as the compressive depth. As used herein, the compressive depth represents the depth at which the stress in the chemically strengthened substrate and / or portion described herein changes from compressive stress to tensile stress. Depending on the ion exchange treatment and thickness of the article being measured, the compressive depth may be measured by a surface stress meter or a scattered light polariscope (SCALP, where the values recorded herein were obtained using a SCALP-5 manufactured by Glasstress Estonia OÜ). When stress is generated in the substrate and / or portion by exchanging potassium ions into the substrate, a surface stress meter (e.g., FSM-6000 (Orihara Industries Co., Ltd. (Japan))) is used to measure the compressive depth. Unless otherwise specified, compressive stress (including surface CS) is measured by a surface stress meter (FSM), using a commercial instrument such as the FSM-6000 manufactured by Orihara Co., for example. Surface stress measurement relies on an accurate measurement of the stress optical coefficient (SOC), which is related to the birefringence of the glass. Unless otherwise specified, the SOC is measured according to Scheme C (the glass disk method) described in ASTM standard C770-16, entitled “Standard Test Method for Measurement of Glass Stress-Optical Coefficient,” the entire text of which is incorporated herein by reference. When stress is generated by exchanging sodium ions into the substrate and the article being measured is thicker than about 400 μm, the SCALP is used to measure the compressive depth and the central tension (CT). When stress is generated in the substrate and / or portion by exchanging both potassium ions and sodium ions into the substrate and the article being measured is thicker than about 400 μm, the compressive depth and CT are measured by the SCALP. Without wishing to be bound by theory, the exchange depth of sodium may represent the compressive depth, while the exchange depth of potassium ions may represent the change in the magnitude of the compressive stress (but not the change in stress from compressive to tensile).The refraction near field (RNF; RNF method) described in U.S. Patent No. 8,854,623, entitled "Systems and methods for measuring a profile characteristic of a glass sample" (the entire text of which is incorporated herein by reference), can also be used to obtain a map representative of the stress distribution. When the RNF method is used to obtain a map representative of the stress distribution, the maximum central tension value provided by SCALP is used in the RNF method. The map representative of the stress distribution obtained by RNF is force balanced and calibrated with the maximum central tension value provided by SCALP measurement. As used herein, "depth of layer" (DOL) represents the depth of ions (e.g., sodium, potassium) exchanged into the substrate and / or portion. In the present disclosure, when the maximum central tension cannot be directly measured by SCALP (when the article being measured is thinner than about 400 μm), the maximum central tension can be approximated by dividing the product of the maximum compressive stress and the compressive depth by the difference between the substrate thickness and twice the compressive stress, wherein the compressive stress and the compressive depth are measured by FSM. Throughout the present disclosure, the absolute value of the compressive stress is recorded as the compressive stress, and the absolute value of the central tensile stress is recorded as the central tensile stress.

[0154] In an aspect, as Figure 2 shown, the first major surface 203 of the foldable substrate 201 may include a first compressive stress region 212 extending from the first major surface 203 to a first compressive depth 216. Although not shown, the first compressive stress region 212 may also include a first depth of layer of one or more alkali metal ions (e.g., potassium) associated with the first compressive stress region. In an aspect, as Figure 2 shown, the second major surface 205 of the foldable substrate 201 may include a second compressive stress region 214 extending from the second major surface 205 to a second compressive depth 218. Although not shown, the second compressive stress region 214 may also include a second depth of layer of one or more alkali metal ions (e.g., potassium) associated with the first compressive stress region. As Figure 2 shown, the dashed lines 213 and 215 correspond to the positions where the stress in the foldable substrate switches from compression to tension (or vice versa), corresponding to the boundaries (i.e., the compressive depths) of the corresponding compressive stress regions. It is to be understood that Figure 2 the first compressive stress region 212 and / or the second compressive stress region 214 of the foldable substrate 201 of the foldable device 101 shown in Figures 3 - 5 may also be present in other foldable devices (e.g., in the foldable devices 301 and / or 401 shown in Figures 3 - 5 although not explicitly labeled therein).

[0155] In aspects, the first compression depth 216 and / or the second compression depth 218, as a percentage of the substrate thickness 209, can be: about 5% or greater, about 10% or greater, about 12% or greater, about 14% or greater, about 16% or greater, about 18% or greater, about 20% or greater, about 30% or less, about 26% or less, or about 22% or less, about 20% or less, about 19% or less, about 18% or less, about 17% or less, or about 16% or less. In aspects, the first compression depth 216 and / or the second compression depth 218, as a percentage of the substrate thickness 209, can be in the following ranges: about 5% to about 30%, about 10% to about 26%, about 12% to about 22%, about 14% to about 20%, about 16% to about 19%, about 16% to about 19%, about 16% to about 18%, or any range or sub-range therebetween. In other aspects, the first compression depth 216 and / or the second compression depth 218, as a percentage of the substrate thickness 209, can be about 15% or greater, such as in the following ranges: about 16% to about 30%, about 16% to about 26%, about 18% to about 24%, about 20% to about 22%, or any range or sub-range therebetween. In an exemplary aspect, the first compression depth 216 and / or the second compression depth 218, as a percentage of the substrate thickness 209, can be in the following ranges: about 10% to about 30%, about 12% to about 19%, or about 16% to about 26%.

[0156] In aspects, the first compression depth 216 and / or the second compression depth 218 can be: about 1 μm or greater, 3 μm or greater, about 4 μm or greater, about 5 μm or greater, about 6 μm or greater, about 7 μm or greater, about 10 μm or greater, about 11 μm or greater, about 12 μm or greater, about 13 μm or greater, about 30 μm or less, about 25 μm or less, about 20 μm or less, about 17 μm or less, about 15 μm or less, about 14 μm or less, about 13 μm or less, about 12 μm or less, about 10 μm or less, about 9 μm or less, about 8 μm or less, or about 7 μm or less. In aspects, the first compression depth 216 and / or the second compression depth 218 can be in the following ranges: about 1 μm to about 30 μm, about 3 μm to about 25 μm, about 3 μm to about 20 μm, about 4 μm to about 17 μm, about 5 μm to about 15 μm, about 6 μm to about 14 μm, about 6 μm to about 13 μm, about 7 μm to about 12 μm, about 7 μm to about 10 μm, or any range or sub-range therebetween. In aspects, the first compression depth 216 and / or the second compression depth 218 can be about 10 μm or less, such as in the following ranges: about 3 μm to about 10 μm, about 5 μm to about 10 μm, about 6 μm to about 9 μm, about 7 μm to about 8 μm, or any range or sub-range therebetween. In aspects, the first compression depth 216 and / or the second compression depth 218 can be about 10 μm or greater, such as in the following ranges: about 10 μm to about 20 μm, about 10 μm to about 17 μm, about 11 μm to about 15 μm, about 12 μm to about 14 μm, about 12 μm to about 13 μm, or any range or sub-range therebetween. In a preferred aspect, the first compression depth 216 and / or the second compression depth 218 can be in the following ranges: about 3 μm to about 20 μm, about 5 μm to about 9 μm, or about 10 μm to about 15 μm.

[0157] In aspects, the depth of the first layer and / or the second layer of one or more alkali metal ions (e.g., potassium), as a percentage of the substrate thickness 209, can be: about 5% or greater, about 10% or greater, about 12% or greater, about 14% or greater, about 16% or greater, about 18% or greater, about 20% or greater, about 30% or less, about 26% or less, or about 22% or less, about 20% or less, about 19% or less, about 18% or less, about 17% or less, or about 16% or less. In aspects, the depth of the first layer and / or the second layer of one or more alkali metal ions (e.g., potassium), as a percentage of the substrate thickness 209, can be in the following ranges: about 5% to about 30%, about 10% to about 26%, about 12% to about 22%, about 14% to about 20%, about 16% to about 19%, about 16% to about 19%, about 16% to about 18%, or any range or sub-range therebetween. In aspects, the depth of the first layer and / or the second layer of one or more alkali metal ions (e.g., potassium), as a percentage of the substrate thickness 209, can be about 15% or greater, such as in the following ranges: about 16% to about 30%, about 16% to about 26%, about 18% to about 24%, about 20% to about 22%, or any range or sub-range therebetween. In preferred aspects, the depth of the first layer and / or the second layer of one or more alkali metal ions (e.g., potassium), as a percentage of the substrate thickness 209, can be in the following ranges: about 10% to about 30%, about 12% to about 19%, or about 16% to about 26%.

[0158] In aspects, the depth of the first layer and / or the depth of the second layer of one or more alkali metal ions (e.g., potassium) can be: about 1 μm or greater, 3 μm or greater, about 4 μm or greater, about 5 μm or greater, about 6 μm or greater, about 7 μm or greater, about 10 μm or greater, about 11 μm or greater, about 12 μm or greater, about 13 μm or greater, about 30 μm or less, about 25 μm or less, about 20 μm or less, about 17 μm or less, about 15 μm or less, about 14 μm or less, about 13 μm or less, about 12 μm or less, about 10 μm or less, about 9 μm or less, about 8 μm or less, or about 7 μm or less. In aspects, the depth of the first layer and / or the depth of the second layer of one or more alkali metal ions (e.g., potassium) can be in the following ranges: about 1 μm to about 30 μm, about 3 μm to about 25 μm, about 3 μm to about 20 μm, about 4 μm to about 17 μm, about 5 μm to about 15 μm, about 6 μm to about 14 μm, about 6 μm to about 13 μm, about 7 μm to about 12 μm, about 7 μm to about 10 μm, or any range or sub-range therebetween. In aspects, the depth of the first layer and / or the depth of the second layer of one or more alkali metal ions (e.g., potassium) can be about 10 μm or less, such as in the following ranges: about 3 μm to about 10 μm, about 5 μm to about 10 μm, about 6 μm to about 9 μm, about 7 μm to about 8 μm, or any range or sub-range therebetween. In aspects, the first compression depth 216 and / or the second compression depth 218 can be about 10 μm or greater, such as in the following ranges: about 10 μm to about 20 μm, about 10 μm to about 17 μm, about 11 μm to about 15 μm, about 12 μm to about 14 μm, about 12 μm to about 13 μm, or any range or sub-range therebetween. In a preferred aspect, the depth of the first layer and / or the depth of the second layer of one or more alkali metal ions (e.g., potassium) can be in the following ranges: about 3 μm to about 20 μm, about 5 μm to about 9 μm, or about 10 μm to about 15 μm.

[0159] In some aspects, the first compressive stress region 212 may include a first maximum compressive stress and / or the second compressive stress region 214 may include a second maximum compressive stress. In other aspects, the first maximum compressive stress may be substantially equal to the second maximum compressive stress. In other aspects, the first maximum compressive stress and / or the second maximum compressive stress may be: about 500 megapascals (MPa) or greater, about 600 MPa or greater, about 650 MPa or greater, about 700 MPa or greater, about 750 MPa or greater, about 800 MPa or greater, about 850 MPa or greater, about 900 MPa or greater, about 950 MPa or greater, about 1,000 MPa or greater, about 1050 MPa or greater, about 1,500 MPa or less, about 1,300 MPa or less, about 1,200 MPa or less, about 1,150 MPa or less, about 1,100 MPa or less, about 1,050 MPa or less, about 1,000 MPa or less, about 950 MPa or less, about 900 MPa or less, about 850 MPa or less, or about 800 MPa or less. In other aspects, the first maximum compressive stress and / or the second maximum compressive stress may be in the following ranges: about 500 MPa to about 1,500 MPa, about 600 MPa to about 1,300 MPa, about 650 MPa to about 1,250 MPa, about 650 MPa to about 1,200 MPa, about 700 MPa to about 1,150 MPa, about 750 MPa to about 1,100 MPa, about 800 MPa to about 1,050 MPa, about 850 MPa to about 1,000 MPa, about 900 MPa to about 950 MPa, or any range or sub-range therebetween. In other aspects, the first maximum compressive stress and / or the second maximum compressive stress may be about 700 MPa or greater, for example, in the following ranges: about 700 MPa to about 1500 MPa, about 700 MPa to about 1300 MPa, about 700 MPa to about 1200 MPa, about 750 MPa to about 1150 MPa, about 800 MPa to about 1100 MPa, about 850 MPa to about 1100 MPa, about 900 MPa to about 1050 MPa, or any range or sub-range therebetween. In other aspects, the maximum first compressive stress and / or the maximum second compressive stress may be about 1000 MPa or greater, for example, in the following ranges: about 1000 MPa to about 1500 MPa, about 1000 MPa to about 1300 MPa, about 1000 MPa to about 1200 MPa, about 1050 MPa to about 1150 MPa, or any range or sub-range therebetween. In a preferred aspect, the first maximum compressive force and / or the second maximum compressive stress may be in the following ranges: about 650 MPa to about 1200 MPa, about 750 MPa to about 1100 MPa, or about 850 MPa to about 1200 MPa.

[0160] In an aspect, the substrate thickness 209 can be about 50 μm or thicker (e.g., about 50 μm to about 100 μm, about 50 μm to about 90 μm, or any corresponding sub-range therebetween as discussed above) and combined with one or more of the following properties: (1) the compression depth (e.g., the first compression depth 216 and / or the second compression depth 218), as a percentage of the substrate thickness 209, is about 10% to about 30%, about 16% to about 26%, or any corresponding sub-range therebetween as discussed above; (2) the layer depth of potassium (e.g., the first layer depth and / or the second layer depth) ranges from about 3 μm to about 20 μm, about 10 μm to about 15 μm, or any corresponding sub-range as discussed above; and / or (3) the maximum compression stress (e.g., the first maximum compression stress and / or the second maximum compression stress) ranges can be about 650 MPa to about 1200 MPa, about 800 MPa to about 1100 MPa, about 850 MPa to about 1200 MPa, or any corresponding sub-range as discussed above. In an aspect, the substrate thickness 209 can be about 50 μm or thinner (e.g., about 10 μm to about 50 μm, about 10 μm to about 30 μm, or any corresponding sub-range therebetween as discussed above) and combined with one or more of the following properties: (1) the compression depth (e.g., the first compression depth 216 and / or the second compression depth 218), as a percentage of the substrate thickness 209, is about 10% to about 30%, about 12% to about 19%, or any corresponding sub-range therebetween as discussed above; (2) the layer depth of potassium (e.g., the first layer depth and / or the second layer depth) ranges from about 3 μm to about 20 μm, about 5 μm to about 9 μm, or any corresponding sub-range as discussed above; and / or (3) the maximum compression stress (e.g., the first maximum compression stress and / or the second maximum compression stress) ranges can be about 650 MPa to about 1200 MPa, about 750 MPa to about 1100 MPa, about 750 MPa to about 1000 MPa, or any corresponding sub-range as discussed above.

[0161] Throughout the present disclosure, ASTM D638 is used with a tensile testing machine (e.g., Instron 3400 or Instron 6800) at 23 °C and 50% relative humidity with a Type I dogbone-shaped sample to determine the tensile strength, ultimate elongation (e.g., failure strain), and yield point of a polymeric material (e.g., an adhesive, a polymer-based part). Throughout the present disclosure, ISO 527-1:2019 is used to measure the elastic modulus (e.g., Young's modulus) and / or Poisson's ratio. Throughout the present disclosure, the resonant ultrasound spectroscopy technique set forth in ASTM E2001-13, entitled "Standard Guide for Resonant Ultrasound Spectroscopy for Defect Detection in Both Metallic and Non-metallic Parts", is used to measure the Young's modulus of glass-based materials and ceramic-based materials. In aspects, the foldable substrate 201 may include an elastic modulus of about 10 gigapascals (GPa) or higher, about 40 GPa or higher, about 60 GPa or higher, about 70 GPa or higher, about 100 GPa or lower, about 80 GPa or lower, about 60 GPa or lower, or about 20 GPa or lower. In other aspects, the foldable substrate 201 may include a glass-based portion that includes 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 80 GPa to about 100 GPa, or any range or sub-range therebetween.

[0162] The transmittance and haze values recorded herein are measured using BYK Haze-Gard Dual (BYK Gardner). In aspects, an "optically clear material" or "optically transparent material" can have: an average transmittance in the wavelength range of 400 nm to 700 nm of 75% or greater, 80% or greater, 85% or greater, or 90% or greater, 92% or greater, 93% or greater, 94% or greater, 95% or greater, 96% or greater, through a 0.7 mm thick sheet of the material. The average transmittance in the wavelength range of 400 nm to 700 nm is calculated by measuring the transmittance at integer wavelengths from approximately 400 nm to approximately 700 nm and averaging the measurements. In aspects, the foldable substrate can be optically clear. In aspects, the foldable substrate 201 can include the following average transmittance (averaged over the optical wavelength of 400 nm to 700 nm): approximately 80% or greater, approximately 90% or greater, approximately 91% or greater, approximately 92.0% or greater, approximately 92.2% or greater, approximately 92.5% or greater, approximately 92.8% or greater, approximately 93.0% or greater, approximately 99% or less, approximately 96% or less, approximately 95% or less, or approximately 94% or less. In aspects, the foldable substrate 201 can include the following range of average transmittance (averaged over the optical wavelength of 400 nm to 700 nm): approximately 80% to approximately 99%, approximately 90% to approximately 96%, approximately 90% to approximately 95%, approximately 91% to approximately 95%, approximately 92.0% to approximately 95%, approximately 92.2% to approximately 94%, approximately 92.5% to approximately 94%, approximately 92.8% to approximately 93%, or any range or sub-range therebetween.

[0163] As used herein, haze refers to transmission haze, which is measured according to ASTM D1003-21 at 0° in a direction normal to the first major surface 203 through the first major surface 203. Haze is measured using BYK Haze-Gard Dual (BYK Gardner). The CIE D65 illuminant is used as the light source for illuminating the foldable substrate 201. The haze values recorded herein are measured through a substrate having a thickness of 0.7 mm, and the light incident on the first major surface 203 is measured as it exits the first major surface 203. In other aspects, the haze of the foldable substrate 201 can be: approximately 5% or less, approximately 2% or less, approximately 1% or less, approximately 0.8% or less, approximately 0.5% or less, or approximately 0.3% or less. In other aspects, the haze of the foldable substrate 201 can be in the following range: approximately 0.01% to approximately 5%, approximately 0.05% to approximately 2%, approximately 0.1% to approximately 1%, approximately 0.1% to approximately 0.8%, approximately 0.2% to approximately 0.5%, or any range or sub-range therebetween.

[0164] As Figures 2 - 3As shown, the foldable substrate 201 can include a first major surface 203 and a second major surface 205 opposite the first major surface 203. In aspects, the first major surface 203 can extend along a first plane, and / or the second major surface 205 can extend along a second plane. In other aspects, the second plane (second major surface 205) can be parallel to the first plane (first major surface 203). As used herein, the substrate thickness 209 of the foldable substrate 201 is defined as the average distance between the first major surface 203 and the second major surface 205 therebetween. In aspects, the foldable substrate 201 can be an ultra-thin substrate, meaning the substrate thickness 209 is about 100 micrometers or less. In aspects, the substrate thickness 209 can be: about 10 micrometers (μm) or thicker, about 15 μm or thicker, about 20 μm or thicker, about 25 μm or thicker, about 30 μm or thicker, about 40 μm or thicker, about 50 μm or thicker, about 60 μm or thicker, about 70 μm or thicker, about 100 μm or thinner, about 95 μm or thinner, about 90 μm or thinner, about 85 μm or thinner, about 80 μm or thinner, about 75 μm or thinner, about 70 μm or thinner, about 60 μm or thinner, about 50 μm or thinner, about 40 μm or thinner, about 30 μm or thinner, or about 25 μm or thinner. In aspects, the range of the substrate thickness 209 can be: about 10 μm to about 100 μm, about 15 μm to about 95 μm, about 20 μm to about 80, about 25 μm to 75 μm, about 30 μm to about 70 μm, about 40 μm to about 60 μm, about 40 μm to about 50 μm, or any range or sub-range therebetween. In aspects, the substrate thickness 209 can be about 50 μm or thicker, which can exhibit better impact resistance and / or puncture resistance and reasonable foldability (e.g., a 5 mm parallel plate spacing discussed below) compared to even thinner foldable substrates, such as the following ranges: about 50 μm to about 100 μm, about 50 μm to about 95 μm, about 50 μm to about 90 μm, about 60 μm to about 80 μm, about 70 μm to about 75 μm, or any range or sub-range therebetween. In aspects, the substrate thickness 209 can be about 50 μm or thinner, which can exhibit increased foldability (e.g., a parallel plate spacing of 3 mm or less or 2 mm or less discussed below) compared to thicker substrates, such as the following ranges: about 10 μm to about 50 μm, about 15 μm to about 50 μm, about 20 μm to about 45 μm, about 25 μm to about 40 μm, about 30 μm to about 40 μm, or any range or sub-range therebetween. In aspects, as shown, on the first major surface 203 and / or the second major surface 205, the local thickness of the foldable substrate 201 can be substantially uniform (e.g., substantially equal to the substrate thickness 209).

[0165] As used herein, if a first layer / or component is described as being “disposed above” a second layer / or component, there may or may not be other layers between the first layer / or component and the second layer / or component. Further, as used herein, “disposed above” does not denote a relative position with reference to gravity. For example, when a first layer and / or component is disposed below, above, or to one side of a second layer and / or component, the first layer and / or component can be considered to be “disposed above” the second layer and / or component. As used herein, describing a first layer / or component as “bonded to” a second layer / or component means the mutual bonding of the layers / or components, which is by direct contact and / or bonding between the two layers / or components and / or via an adhesive layer. As used herein, describing a first layer and / or component as being “in contact with” or “contacting” a second layer and / or component refers to direct contact and includes the case of the mutual bonding of the layers and / or components.

[0166] As Figure 3 shown, the foldable device 301 can include an adhesive layer 311. As shown, the adhesive layer 311 can include a first contact surface 313 and a second contact surface 315 that is opposite to the first contact surface 313. In an aspect, as shown, the first contact surface 313 of the adhesive layer 311 can include a flat surface, and / or the second contact surface 315 of the adhesive layer 311 can include a flat surface. The adhesive thickness 319 of the adhesive layer 311 can be defined as the average distance between the first contact surface 313 and the second contact surface 315. In an aspect, the adhesive thickness 319 of the adhesive layer 311 can be: about 1 μm or thicker, about 5 μm or thicker, about 10 μm or thicker, about 100 μm or thinner, about 60 μm or thinner, about 30 μm or thinner, or about 20 μm or thinner. In an aspect, the adhesive thickness 319 of the adhesive layer 311 can be in the following ranges: about 1 μm to about 100 μm, about 5 μm to about 60 μm, about 10 μm to about 30 μm, about 10 μm to about 20 μm, or any range or sub-range therebetween. In an aspect, as Figure 3 shown, the first contact surface 313 of the adhesive layer 311 can face and / or contact the first major surface 203 of the foldable substrate 201. In an aspect, as Figure 3 shown, the second contact surface 315 of the adhesive layer 311 can face and / or contact another layer (e.g., the PET sheet 321 discussed below).

[0167] In aspects, the adhesive layer 311 can include one or more of the following: polyolefins, polyamides, halogen-containing polymers (such as polyvinyl chloride or fluoropolymers), elastomers, urethanes, phenolic resins, parylene, polyethylene terephthalate (PET), and polyetheretherketone (PEEK). Exemplary aspects of polyolefins include: low molecular weight polyethylene (LDPE), high molecular weight polyethylene (HDPE), ultra-high molecular weight polyethylene (UHMWPE), and polypropylene (PP). Exemplary aspects of fluoropolymers include: polytetrafluoroethylene (PTFE), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), perfluoropolyether (PFPE), perfluorosulfonic acid (PFSA), perfluoroalkoxide (PFA), fluorinated ethylene propylene (FEP) polymer, and ethylene tetrafluoroethylene (ETFE) polymer. Exemplary aspects of elastomers include: rubbers (such as, polybutadiene, polyisoprene, neoprene, butyl rubber, nitrile rubber) and block copolymers (such as, styrene-butadiene, high impact polystyrene, poly(dichlorophosphazene)). In other aspects, the adhesive layer 311 can include an optically clear adhesive. In even other aspects, the optically clear adhesive can include one or more optically transparent polymers: acrylics (such as, polymethyl methacrylate (PMMA)), epoxies, silicones, and / or urethanes. Examples of epoxies include: bisphenol-based epoxy resins, phenol-based epoxies, cycloaliphatic-based epoxies, and glycidylamine-based epoxies. In even other aspects, the optically clear adhesive can include, but is not limited to: acrylic adhesives (such as, 3M's 8212 adhesive) or optically clear liquid adhesives (such as, LOCTITE optically clear liquid adhesive). Exemplary aspects of optically clear adhesives include transparent acrylics, epoxies, silicones, and urethanes. For example, the optically clear liquid adhesive can 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 Corporation.

[0168] In aspects, although not shown, the coating may be disposed over the second major surface 205 of the foldable substrate 201. In even other aspects, the coating thickness of the coating 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, or 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 other aspects, the coating thickness of the coating may be in the following ranges: about 0.1 μm to about 200 μm, about 1 μm to about 100 μm, about 10 μm to about 100 μm, about 20 μm to about 100 μm, about 30 μm to about 100 μm, about 40 μm to about 100 μm, about 50 μm to about 100 μm, about 60 μm to about 100 μm, about 70 μm to about 100 μm, about 80 μm to about 100 μm, about 90 μm to about 100 μm, about 0.1 μm to about 50 μm, about 1 μm to about 50 μm, about 10 μm to about 50 μm, or any range or sub-range therebetween.

[0169] In some aspects, the coating can include a polymer coating. In other aspects, the polymer coating can include one or more of the following: ethylene-acid copolymers, polyurethane-based polymers, acrylate resins, and thiol-ester resins. Exemplary aspects of ethylene-acid copolymers include: ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, and ethylene-acrylic acid-methacrylic acid terpolymers (e.g., Nucrel (DuPont)), ionomers of ethylene-acid copolymers (e.g., Surlyn (DuPont)), and ethylene-acrylic acid copolymer amine dispersions (e.g., Aquacer (BYK)). Exemplary aspects of polyurethane-based polymers include waterborne modified polyurethane dispersions (e.g., Eleglas (Axalta)). Exemplary aspects of acrylate resins that can be UV-curable include: acrylate resins (e.g., Uvekol resin (Allinex)), cyanoacrylate adhesives (e.g., Permabond UV620 (Krayden)), and UV free radical acrylic resins (e.g., Ultrabond windshield repair resin, e.g., Ultrabond (45CPS)). Exemplary aspects of thiol-ester resins include thiol-ester triallyl isocyanurate (e.g., Norland optical adhesive NOA61). In other aspects, the polymer coating can include: ethylene-acrylic acid copolymers and ethylene-methacrylic acid copolymers, which can be ionomerized by neutralization of carboxylic acid residues with typical alkali metal ions (e.g., sodium and potassium) and zinc to form ionomer resins. 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, which releases ammonia after coating and drying to reform the acid copolymer as a coating. By providing a coating that includes a polymer coating, the foldable device can include low-energy rupture.

[0170] In an aspect, the coating can include a polymer coating comprising an optically transparent polymer coating. Suitable materials for the optically transparent polymer coating include, but are not limited to: cured acrylate resin materials, inorganic-organic hybrid polymer materials, aliphatic or aromatic hexa-functional urethane acrylates, silicone-based hybrid materials, and nanocomposites (e.g., epoxy and urethane materials with nanosilicates). In an aspect, the optically transparent polymer coating can consist essentially of one or more of these materials. In an aspect, the optically transparent polymer coating can consist of one or more of these materials. As used herein, "inorganic-organic hybrid polymer material" refers to a polymer material comprising monomers having inorganic and organic components. The inorganic-organic hybrid polymer is obtained by a polymerization reaction between monomers having inorganic groups and organic groups. The inorganic-organic hybrid polymer is not a nanocomposite comprising separate inorganic and organic components or phases (e.g., inorganic particles dispersed in an organic matrix). More specifically, suitable materials for an optically transparent polymer (OTP) coating 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 hexa-functional urethane acrylates. In an aspect, the OTP coating can consist essentially of an organic polymer material, an inorganic-organic hybrid polymer material, or an aliphatic or aromatic hexa-functional urethane acrylate. In an aspect, the OTP coating can consist of polyimide, an organic polymer material, an inorganic-organic hybrid polymer material, or an aliphatic or aromatic hexa-functional urethane acrylate. In an aspect, the OTP coating can include a nanocomposite. In an aspect, the OTP coating can include at least one of nanosilicates, epoxides, and urethane materials. U.S. Patent Publication No. 2015 / 0110990 describes suitable compositions for such OTP coatings, the entire text of which is incorporated herein by reference. As used herein, "organic polymer material" refers to a polymer material comprising monomers having only organic components. In an aspect, the OTP coating can include an organic polymer material with a hardness of 9H manufactured by Gunze Limited, for example, Gunze's "High Durability Transparent Film". As used herein, "inorganic-organic hybrid polymer material" refers to a polymer material comprising monomers having inorganic and organic components. The inorganic-organic hybrid polymer is obtained by a polymerization reaction between monomers having inorganic groups and organic groups. The inorganic-organic hybrid polymer is not a nanocomposite comprising separate inorganic and organic components or phases (e.g., inorganic particles dispersed in an organic matrix). In an aspect, the inorganic-organic hybrid polymer material can include polymerized monomers comprising inorganic silicon-based groups, for example, silsesquioxane polymers.The silsesquioxane polymer can be, for example: alkyl-silsesquioxane, aryl-silsesquioxane, or arylalkyl-silsesquioxane having the following chemical structure (RSiO。 1.5 )n, where R is an organic group, such as but not limited to methyl or phenyl. In an aspect, the OTP coating can include a silsesquioxane polymer combined with an organic matrix, for example, SILPLUS manufactured by Nippon Steel Chemical Co., Ltd. In an aspect, the OTP coating can contain: 90 wt% to 95 wt% of an aromatic hexa-functional urethane acrylate (for example, PU662NT (aromatic hexa-functional urethane acrylate) manufactured by Miwon Specialty Chemicals Co., Ltd.), and 10 wt% to 5 wt% of a photoinitiator (for example, Darocur 1173 manufactured by Ciba Specialty Chemicals), with a hardness of 8H or greater. In an aspect, an OTP coating containing an aliphatic or aromatic hexa-functional urethane acrylate can be formed as a free-standing layer by spin-coating the layer onto a polyethylene terephthalate (PET) substrate such that the urethane acrylate cures, and removing the urethane acrylate layer from the PET substrate. The OTP coating can have a coating thickness range of 1 μm to 150 μm, including sub-ranges; for example: 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 to 80 μm, or any range or sub-range therebetween. In an aspect, the OTP coating can be a monomeric single layer. In an aspect, the OTP coating can be a layer of an inorganic-organic hybrid polymer material or an organic polymer material with a thickness range of 80 μm to 120 μm, including sub-ranges. For example, the OTP coating containing an inorganic-organic hybrid polymer material or an organic polymer material can have a thickness of: 80 μm to 110 μm, 90 μm to 100 μm, or any range or sub-range therebetween. In an aspect, the OTP coating can be a layer of an aliphatic or aromatic hexa-functional urethane acrylate material, having one or more of the thickness ranges discussed in this paragraph or above for the coating thickness.

[0171] In aspects, if provided, the coating can further include one or more of the following: an easy-to-clean coating, a low-friction coating, an oleophobic coating, a diamond-like coating, a scratch-resistant coating, or an abrasion-resistant coating. The scratch-resistant coating can include oxynitrides, such as aluminum oxynitride or silicon oxynitride having a thickness of about 500 μm or more. In such aspects, the abrasion-resistant layer can include the same material as the scratch-resistant layer. In aspects, the low-friction coating can include a highly fluorinated silane coupling agent, such as an alkylfluorosilane having an oxymethyl group side chain on the silicon atom. In such aspects, the easy-to-clean coating can include the same material as the low-friction coating. In other aspects, the easy-to-clean coating can include a protonatable group, such as an amine, such as an alkylaminosilane having an oxymethyl group side chain on the silicon atom. In such aspects, the oleophobic coating can include the same material as the easy-to-clean coating. In aspects, the diamond-like coating contains carbon and can be produced by applying a high voltage potential in the presence of a hydrocarbon plasma.

[0172] In aspects, as Figure 3As shown, a layer (e.g., PET sheet 321) can be disposed above the first major surface 203 of the foldable substrate 201, and / or the layer (e.g., PET sheet 321) can be attached to the foldable substrate 201 via an adhesive layer 311. In other aspects, the layer (e.g., PET sheet 321) can be disposed above and / or in contact with the second contact surface 315 of the adhesive layer 311. In other aspects, as shown, the first surface region 323 of the PET sheet 321 can face the first major surface 203 of the foldable substrate 201, can face the second contact surface 315 of the adhesive layer 311, and / or can be in contact with the second contact surface 315 of the adhesive layer 311. The thickness 329 of the PET sheet 321 is defined as the average distance between the first surface region 323 and the second surface region 325 opposite the first surface region 323. As discussed below with reference to the writing test, the adhesive thickness 319 of the adhesive layer 311 (e.g., optically clear adhesive 8212 purchased from 3M Company) can be 50 μm, and the thickness 329 of the PET sheet 321 can be 100 μm, although other materials and / or thicknesses can also be used in other aspects of the foldable device. For example, in other aspects, the layer (e.g., PET sheet) can include polymer materials (not limited to PET), such as: polyesters (e.g., polyethylene terephthalate (PET)) and polyolefins (e.g., low density polyethylene (LDPE), high density polyethylene (HDPE), polypropylene (PP)). Additionally, in other aspects, the layer (e.g., PET sheet 321) can be replaced by a release liner, which can include paper and / or polymer. Exemplary aspects of paper include: kraft paper, machine finished paper, multi-coated paper (e.g., polymer coated paper, cellophane, silicone paper) or clay coated paper. As a supplement or alternative, the layer can include and / or incorporate a display device, such as: liquid crystal display (LCD), electrophoretic display (EPD), organic light emitting diode (OLED) display or plasma display panel (PDP). The display device can be part of a portable electronic device (e.g., consumer electronics, smartphone, tablet, wearable device or laptop).

[0173] Aspects of the present disclosure may include consumer electronic products. The consumer electronic product may include a front surface, a back surface, and side surfaces. The consumer electronic product may also include electronic components at least partially located within a housing. The electronic components may include a controller, a memory, and a display. The display may be located on or adjacent to the front surface of the housing. The display may include: a liquid crystal display (LCD), an electrophoretic display (EPD), an organic light emitting diode (OLED) display, or a plasma display panel (PDP). The consumer electronic product may include a cover substrate disposed above the display. In an aspect, at least one of the housing or a portion of the cover substrate includes a foldable device discussed throughout the present disclosure. The consumer electronic product may include portable electronic products such as: smartphones, tablets, wearable devices, or laptop computers.

[0174] The foldable devices disclosed herein may be incorporated into another article, such as an article having a display screen (or a display article) (e.g., consumer electronics, including mobile phones, tablets, computers, navigation systems, and wearable devices (such as watches), etc.), building articles, transportation articles (e.g., vehicles, trains, aircraft, marine vessels, etc.), electrical articles, or any article that may benefit from partial transparency, scratch resistance, abrasion resistance, or a combination thereof. Exemplary articles incorporating any of the foldable devices 101 and / or 301 and / or foldable substrates 201 disclosed herein are as Figures 8 - 9 shown. Specifically, Figures 8 - 9 a consumer electronic device 800 is shown, which includes a housing 802 having a front surface 804, a back surface 806, and side surfaces 808. Although not shown, the consumer electronic device may include electronic components at least partially located within or fully located within the housing. For example, the electronic components at least include a controller, a memory, and a display. As Figures 8 - 9 shown, the display 810 may be located on or adjacent to the front surface of the housing 802. The consumer electronic device may include a cover substrate 812 located on or above the front surface of the housing 802 such that it is located above the display 810. In an aspect, at least one of the cover substrate 812 or a portion of the housing 802 may include any of the foldable devices disclosed herein (e.g., foldable substrate 201).

[0175] In addition, Figure 7Schematic elevation view showing a foldable consumer electronic product 701. The consumer electronic product 701 may include a foldable device 101 and / or 301 and / or a foldable substrate 201 according to aspects of the present disclosure. As shown, the consumer electronic product 701 may include a front surface 703 and side surfaces 705. The consumer electronic product 701 may contain electronic components, including a display screen 702 that can be viewed through the front surface 703. In an aspect, as shown, the consumer electronic product 701 may be folded in a direction 712 to form a folded configuration such that a first end 727 and a second end 727 (opposite the first end 737) are closer to each other (compared to the non-folded configuration). Additionally, as shown, the consumer electronic product 701 may be folded such that the front surface 703 and / or the display screen 702 face itself, but the consumer electronic product may also be folded in the opposite direction to 712 such that the front surface 703 is on the outer side of the consumer electronic product in the folded configuration. Figure 15 The illustrated consumer electronic product 701 may be folded about a folding axis 102, where a central portion 781 is located between a first portion 721 including the first end 727 and a second portion 731 including the second end 737. The position of the folding axis 102 will determine a first distance 713 between the first end 727 and the folding axis 102 (e.g., in the direction 106) relative to a second distance 715 between the second end 737 and the folding axis 102 (e.g., in the direction 708). The total length of the consumer electronic product (e.g., Figure 1 the length 105 in) may be the sum of the first distance 713 and the second distance 715. Additionally, as shown, the consumer electronic product is shown in a folded or partially folded configuration, with the front surface 703 forming an angle A about the folding axis 102.

[0176] Throughout the present disclosure, the refractive index is measured according to ASTM E1967-19, where the first wavelength includes 589 nm. In an aspect, the first refractive index of the foldable substrate 201 may be: about 1.4 or greater, about 1.45 or greater, about 1.48 or greater, about 1.49 or greater, about 1.50 or greater, about 1.6 or less, about 1.57 or less, or about 1.55 or less, about 1.53 or less, or about 1.52 or less. In an aspect, the first refractive index of the foldable substrate 201 may be in the following ranges: about 1.4 to about 1.6, about 1.45 to about 1.57, about 1.48 to about 1.55, about 1.49 to about 1.53, about 1.50 to about 1.52, or any range or sub-range therebetween.

[0177] In aspects, the adhesive layer 311 can include a second refractive index within one or more of the ranges discussed above with respect to the first refractive index of the foldable substrate. In aspects, the difference equal to the absolute value of the difference between the second refractive index of the adhesive layer 311 and the first refractive index of the foldable substrate 201 can be: about 0.1 or less, about 0.07 or less, about 0.05 or less, about 0.001 or greater, about 0.01 or greater, or about 0.02 or greater. In aspects, the difference can be in the range of: about 0.001 to about 0.1, about 0.001 to about 0.07, about 0.01 to about 0.07, about 0.01 to about 0.05, about 0.02 to about 0.05, or any range or sub-range therebetween. In aspects, the second refractive index of the adhesive layer 311 can be greater than the first refractive index of the foldable substrate 201. In aspects, the second refractive index of the adhesive layer 311 can be less than the first refractive index of the foldable substrate 201.

[0178] Figure 5 Aspects schematically showing a foldable substrate 201 in accordance with aspects of the present disclosure and / or a foldable device 401 formed of a foldable substrate 201 in accordance with aspects of the present disclosure, in a folded configuration. As Figure 4 shown, the foldable device 401 is folded such that the second major surface 205 of the foldable substrate 201 is on the outer side of the foldable device 401, while the first major surface 203 is on the inner side of the foldable device 401. In the folded configuration, although not shown, if the display device is located on the curved inner side, the user would view the display device through the foldable substrate 201 and would thus be on the side of the second major surface 205. Alternatively, if the display device is located on the curved outer side, the user would view the display device through the foldable substrate 201 and would thus be on the side of the first major surface 203. Alternatively, although not shown, the foldable device can be folded such that the first major surface of the foldable substrate is on the outer side of the folded foldable device, where the user would view the display device through the foldable substrate and would thus be opposite the display device.

[0179] As used herein, "foldable" includes full folding, partial folding, bending, flexing, or multiple folding functions. As used herein, terms such as "failure" and "fault" refer to rupture, breakage, delamination, or crack propagation. A foldable device has achieved, withstood, or has a "X" parallel plate spacing if the foldable device resists failure when maintained at a "X" parallel plate spacing between parallel plates for 10 minutes at about 25 °C and about 50% relative humidity. Similarly, a foldable device has achieved, withstood, or includes a parallel plate spacing of "X" if the foldable device resists failure when maintained at a parallel plate spacing of "X" for 10 minutes at about 50 °C and about 50% relative humidity. In aspects, the foldable substrate and / or foldable device can be rollable. As used herein, a foldable substrate or foldable device is "rollable" if it can achieve a threshold parallel plate spacing over a length greater than 10 mm or 10% of the length of the corresponding foldable substrate and / or foldable device. Throughout the present disclosure, the "survival rate" or % of samples that withstand a parallel plate spacing of X mm refers to the percentage of at least 20 samples that withstand bending to a parallel plate spacing of X mm.

[0180] As used herein, the "parallel plate spacing" of a foldable device and / or foldable substrate is measured using a parallel plate apparatus 501 (see Figure 5 ) with the following test configuration and procedure. The parallel plate apparatus 501 includes a pair of parallel rigid stainless steel plates 503 and 505, which includes a first rigid stainless steel plate 503 and a second rigid stainless steel plate 505. When measuring the "parallel plate spacing", the foldable device or foldable substrate is placed as received (without modification) between the pair of parallel rigid stainless steel plates 503 and 505. For example, as Figure 4 shown, a foldable device 101 formed of a foldable substrate 201 as shown in Figure 2 is placed between the pair of parallel rigid stainless steel plates 503 and 505 without modification, with the second major surface of the foldable substrate 201 contacting the pair of parallel rigid stainless steel plates 503 and 505 as the foldable device 401. To determine the "parallel plate spacing", the spacing between the parallel plates is decreased at a rate of 1 millimeter per second (mm / sec) until the parallel plate spacing 511 equals the "parallel plate spacing" to be tested. Then, at about 85 °C and about 85% relative humidity, the parallel plates are maintained at the "parallel plate spacing" to be tested for 10 minutes. As used herein, the "minimum parallel plate spacing" is the smallest parallel plate spacing that a foldable device can withstand without failure under the conditions and configuration described above.

[0181] In aspects, the foldable devices 101, 301, and / or 401 and / or the foldable substrate 201 can achieve a parallel plate spacing as follows: 20 mm or less, 10 mm or less, 7 mm or less, 5 mm or less, 3 mm or less, 2 mm or less, or 1 mm or less. In aspects, the foldable devices 101, 301, and / or 401 and / or the foldable substrate 201 can include a minimum parallel plate spacing as follows: about 5 mm or less, 4 mm or less, about 3 mm or less, about 2 mm or less, or about 1 mm or less. In aspects, the foldable devices 101, 301, and / or 401 and / or the foldable substrate 201 can include a minimum parallel plate spacing range as follows: about 0.5 mm to about 5 mm, about 0.5 mm to about 4 mm, about 0.5 mm to about 3 mm, about 0.5 mm to about 2 mm, about 1 mm to about 2 mm, or any range or sub-range therebetween.

[0182] In an aspect, at a parallel plate spacing of 5 mm, the foldable substrate 201 can exhibit a survival rate as follows: about 90% or higher, about 92% or higher, about 95% or higher, about 97% or higher, about 98% or higher, about 99% or higher, or about 100% (i.e., about 90% or more, about 92% or more, about 95% or more of the samples of the foldable substrate can withstand a parallel plate spacing of 5 mm, etc.). In an aspect, at a parallel plate spacing of 3 mm, the foldable substrate 201 can exhibit a survival rate as follows: about 90% or higher, about 92% or higher, about 95% or higher, about 97% or higher, about 98% or higher, about 99% or higher, or about 100% (i.e., about 90% or more, about 92% or more, about 95% or more of the samples of the foldable substrate can withstand a parallel plate spacing of 3 mm, etc.). In an aspect, at a parallel plate spacing of 3 mm, the foldable substrate 201 can exhibit a survival rate as follows: about 30% or higher, about 35% or higher, about 40% or higher, about 50% or higher, about 55% or higher, about 60% or higher, about 65% or higher, about 70% or higher, about 75% or higher, about 80% or higher, about 85% or higher, about 90% or higher, about 95% or higher, or about 100% (i.e., about 30% or more, about 35% or more, about 40% or more of the samples of the foldable substrate can withstand a parallel plate spacing of 3 mm, etc.). In an aspect, at a parallel plate spacing of 2 mm, the foldable substrate 201 can exhibit a survival rate as follows: about 90% or higher, about 92% or higher, about 95% or higher, about 97% or higher, about 98% or higher, about 99% or higher, or about 100% (i.e., about 90% or more, about 92% or more, about 95% or more of the samples of the foldable substrate can withstand a parallel plate spacing of 2 mm, etc.). In an aspect, at a parallel plate spacing of 1 mm, the foldable substrate 201 can exhibit a survival rate as follows: about 10% or higher, about 15% or higher, about 20% or higher, about 25% or higher, about 30% or higher, about 40% or higher, or about 50% (i.e., about 10% or more, about 15% or more, about 20% or more of the samples of the foldable substrate can withstand a parallel plate spacing of 1 mm, etc.).

[0183] In aspects, when the foldable substrate 201 includes a substrate thickness 209 of about 50 μm or greater (e.g., about 50 μm to about 100 μm, about 50 μm to about 90 μm, or any corresponding sub-range discussed above), it can exhibit: (1) a survival rate of about 90% or greater, 92% or greater, and / or 95% or greater (e.g., about 90% to about 100%, about 92% to about 99%, about 95% to about 97%) at a parallel plate spacing of 5 mm, and / or (2) a survival rate of about 30% or greater, 35% or greater, or about 40% or greater (e.g., about 30% to about 50%, about 35% to about 45%) at a parallel plate spacing of 3 mm. In aspects, when the foldable substrate 201 includes a substrate thickness 209 of about 50 μm or less (e.g., about 10 μm to about 50 μm, about 10 μm to about 30 μm, or any corresponding sub-range discussed above), it can exhibit: (1) a survival rate of about 90% or greater, 92% or greater, 95% or greater, 97% or greater, 98% or greater, or 99% or greater (e.g., about 90% to about 100%, about 92% to 100%, or about 95% to about 99%) at a parallel plate spacing of 5 mm; (2) a survival rate of about 80% or greater, about 90% or greater, or about 95% or greater (e.g., about 80% to about 100%, about 90% to 100%, or about 95% to about 99%) at a parallel plate spacing of 3 mm; (3) a survival rate of about 90% or greater, about 92% or greater, about 95% or greater, or about 97% or greater (e.g., about 90% to about 100%, about 92% to 100%, about 95% to about 99%, or about 97% to about 99%) at a parallel plate spacing of 2 mm; and / or (4) a survival rate of about 10% or greater, about 15% or greater, or about 20% or greater (e.g., about 10% to about 50%, about 15% to 40%, about 20% to about 30%) at a parallel plate spacing of 1 mm.

[0184] When measured according to the "pen-drop test", the foldable device and / or the foldable substrate can have an impact resistance defined by the ability of the area of the foldable device and / or the foldable substrate to avoid failure at a pen-drop height (e.g., 5 centimeters (cm) or higher, 10 cm or higher, 20 cm or higher). As used herein, the "pen-drop test" is performed as follows: a sample of the foldable device and / or the foldable substrate is tested by causing a load (i.e., a pen dropped from a certain height) to impact the main surface (e.g., the second main surface 205 of the foldable substrate 201 and / or the foldable device 101 and / or 301), and the foldable substrate 201 is constructed as Figure 3As shown, a PET sheet 321 with a thickness 329 of 100 μm is attached to an adhesive layer 311 with a thickness of 50 μm composed of an optically clear adhesive 8212 (purchased from 3M Company) and contacts the first major surface 203 of the foldable substrate 201. Thus, the purpose of the PET sheet in the drop pen test is to simulate a foldable electronic display device (e.g., an OLED device). During the test, the foldable substrate 201 bonded to the PET sheet is placed on an aluminum plate (6063 aluminum alloy, polished to a surface roughness with 400-mesh paper), and the PET sheet 321 contacts the aluminum plate. No strip is used on the side of the sample located on the aluminum plate.

[0185] The drop pen test uses a catheter to guide a pen to the outer surface of the foldable device. For Figures 2 - 3 the foldable devices 101, 301, and / or 401 and / or the foldable substrate 201 (modified as described in the previous paragraph) shown in FIGS. 5, the pen is guided to the second major surface 205 of the foldable substrate 201, and the catheter is placed in contact with the second major surface 205 of the foldable substrate 201 such that the longitudinal axis of the catheter is substantially perpendicular to the second major surface 205, and the longitudinal axis of the catheter extends in the direction of gravity. Refer to Figure 6 , the drop pen device 601 includes a ballpoint pen 603, which is a BIC Easy Glide Pen, Fine (fine tip easy glide pen), includes a tungsten carbide ball tip 605 with a diameter of 0.7 mm (0.68 mm), and the weight including the pen cap is 5.73 grams (g). The ballpoint pen 603 is held at a predetermined height 609 from the outer surface of the sample (e.g., the second major surface 205 of the foldable device 201) (refer to Figure 3 the foldable device 301 shown). A catheter (not shown for clarity) is used as part of the drop pen device 601 to guide the ballpoint pen 603 to the outer surface of the sample (e.g., the second major surface 205 of the foldable substrate 201), and the catheter is placed in contact with the outer surface such that the longitudinal axis of the catheter is substantially perpendicular to the outer major surface, and the longitudinal axis of the catheter extends in the direction of gravity. The catheter has an outer diameter of 1 inch (2.54 cm), an inner diameter of 9 / 16 inch (1.4 cm), and a length of 90 cm. For each test, an acrylonitrile butadiene (“ABS”) spacer (not shown) is used to hold the ballpoint pen 603 at the predetermined height 609. After each drop, the catheter is repositioned relative to the sample so as to guide the pen to a different impact location on the sample.

[0186] For the drop test, the pen is dropped with the cap attached to the tip (i.e., the end opposite the nib) so that the ball tip can interact with the test sample. In the drop sequence for the drop test, one drop is made at an initial height of 1 cm, and then subsequent drops are made at 0.5 cm increments (up to 20 cm), and then after 20 cm, at 2 cm increments until the test sample fails. After each drop, any observable evidence of cracking, failure, or other damage to the sample is recorded, along with the specific drop height. Using the drop test, multiple samples can be tested according to the same drop sequence to produce a group with improved statistical accuracy. For the drop test, the pen is replaced with a new pen after every five drops and for each new sample test. Additionally, all drops are made at random locations on the sample at or near the center of the sample, and no drops are made at or near the edge of the sample.

[0187] For the purposes of the drop test, "failure" means the formation of visible mechanical defects in the laminate. The mechanical defects can be cracks or plastic deformations (e.g., surface indentations). The cracks can be surface cracks or through cracks. Cracks may form on the inner or outer surface of the laminate. The cracks can extend through all or a portion of the foldable substrate 201. Visually observable mechanical defects have a minimum size of 0.2 mm or greater.

[0188] In aspects, the foldable substrate 201 and / or the foldable device 101 and / or 301 resist failure upon a drop from a drop height of 10 centimeters (cm), 12 cm, 14 cm, 16 cm, or 20 cm. In aspects, the maximum drop height that the foldable substrate 201 and / or the foldable device 101 and / or 301 can withstand without failure can be: about 10 cm or greater, about 12 cm or greater, about 14 cm or greater, about 15 cm or greater, about 16 cm or greater, about 18 cm or greater, about 20 cm or greater, about 40 cm or less, or about 30 cm or less, about 25 cm or less, about 20 cm or less, or about 15 cm or less. In aspects, the maximum drop height that the foldable substrate 201 and / or the foldable device 101 and / or 301 can withstand without failure can be in the following ranges: about 10 cm to about 40 cm, about 12 cm to about 40 cm, about 14 cm to about 30 cm, about 16 cm to about 30 cm, about 18 cm to about 30 cm, about 20 cm to about 25 cm, or any range or sub-range therebetween. In aspects, when the substrate thickness 209 of the foldable substrate 201 is about 50 μm or greater (e.g., about 50 μm to about 100 μm, about 50 μm to about 90 μm, or any corresponding sub-range discussed above), the foldable substrate 201 can withstand a drop from a drop height of 15 cm or higher or even 20 cm or higher. In aspects, when the substrate thickness 209 of the foldable substrate 201 is about 50 μm or less (e.g., about 10 μm to about 50 μm, about 10 μm to about 30 μm, or any corresponding sub-range discussed above), the foldable substrate 201 can withstand a drop from a drop height of 10 cm or higher.

[0189] Reference will be made Figure 10 to the flowchart of Figures 12 - 15 and the exemplary method steps shown in Figure 16 and the cross-sectional views shown in Figures 2 - 3 to discuss aspects of the chemical strengthening method of the foldable substrate 201 shown in

[0190] In the first step 1001 of the method of the present disclosure, as Figures 11 - 12As shown, the method can start by providing a foldable substrate 1111. In aspects, the substrate can be obtained by purchase or any other means or by forming a foldable substrate to provide the foldable substrate 1111. In aspects, the foldable substrate 1111 can include a glass-based substrate. In other aspects, the glass-based substrate can be provided by forming through various ribbon forming processes, such as: slot drawing, down-draw, fusion down-draw, up-draw, press roll, redraw, or float process. In other aspects, a glass-based substrate containing one or more ceramic crystals can be provided by heating the glass-based substrate to crystallize to obtain one or more ceramic crystals. The foldable substrate 1111 can include a first existing major surface 1113 and a second existing major surface 1115 opposite the first existing major surface 1113. In other aspects, the initial thickness 1119 of the foldable substrate 1111 (defined as the average spacing between the first existing major surface 1113 and the second existing major surface 1115) can be within one or more of the ranges discussed above and / or can differ from the final thickness (e.g., substrate thickness 209) by within 5 μm (i.e., 0.1 μm to about 5 μm or about 0.5 μm to about 4 μm greater than the final thickness). In other aspects, the first existing major surface 1113 and / or the second existing major surface 1115 can extend along a plane. In aspects, the foldable substrate 1111 can have a composition within one or more of the ranges discussed above with respect to the glass-based substrate (e.g., foldable substrate 201). In aspects, at the end of step 1001, the foldable substrate 1111 will be substantially unstrengthened. As used herein, substantially unstrengthened refers to a substrate that includes: no layer depth, no compressive depth, a layer depth within the range of 0% to about 5% of the substrate thickness, or a compressive depth within the range of 0% to about 5% of the substrate thickness.

[0191] After step 1001, as Figure 11 shown, the method can optionally proceed to step 1003, including heating the foldable substrate 1111 at a predetermined temperature for a predetermined period of time. In aspects, as Figure 11As shown, heating the foldable substrate 1111 can include placing the foldable substrate 1111 in an environment maintained at a predetermined temperature (e.g., oven 1101) for a predetermined period of time. In an aspect, the predetermined temperature can be: about 250 °C or higher, about 270 °C or higher, about 280 °C or higher, about 290 °C or higher, about 300 °C or higher, about 350 °C or lower, about 330 °C or lower, about 320 °C or lower, about 310 °C or lower, or about 300 °C or lower. In an aspect, the predetermined temperature can be in the range of: about 250 °C to about 350 °C, about 270 °C to about 330 °C, about 270 °C to about 320 °C, about 280 °C to about 310 °C, about 280 °C to about 300 °C, or any range or sub-range therebetween. In an aspect, the predetermined temperature can be less than the first temperature maintained by the molten salt solution used in step 1005 (discussed below). In an aspect, the predetermined period of time can be: about 10 minutes or longer, about 20 minutes or longer, about 30 minutes or longer, about 45 minutes or longer, about 1 hour or longer, about 4 hours or shorter, about 2 hours or shorter, about 1.5 hours or shorter, or about 1 hour or shorter. In an aspect, the predetermined period of time can be in the range of: about 10 minutes to about 4 hours, about 20 minutes to about 2 hours, about 30 minutes to about 1.5 hours, about 45 minutes to about 1 hour, or any range or sub-range therebetween. Heating the foldable substrate prior to the chemical strengthening treatment of step 1005 can reduce the thermal shock to the foldable substrate and contribute to a more uniform compressive stress region on the surface of the foldable substrate.

[0192] After step 1001 or 1003, as Figure 12 shown, the method can proceed to step 1005, including at least bringing the existing first major surface 1113 into contact with a molten salt solution 1203 maintained at a first temperature for a first period of time to at least establish an initial compressive stress region. In an aspect, as Figure 12 shown, the molten salt solution 1203 can be contained in a molten salt bath 1201. In an aspect, as Figure 12As described, at least bringing the existing first major surface 1113 into contact with the molten salt solution 1203 may include dipping the foldable substrate 1111 into the molten salt solution 1203. For example, both the existing first major surface 1113 and the existing second major surface 1115 are brought into contact with the molten salt solution 1203. However, in other aspects, only a portion of the foldable substrate (e.g., the existing first major surface) may be in contact with the molten salt solution. When a first cation within the surface depth of the foldable substrate 1111 exchanges with a second cation in the molten salt solution 1203 that has a radius larger than the first cation, the foldable substrate 1111 is chemically strengthened through ion exchange. For example, lithium cations within the surface depth of the foldable substrate 1111 may exchange with sodium cations or potassium cations in the molten salt solution 1203. Similarly, sodium cations within the surface depth of the foldable substrate 1111 may exchange with potassium cations in the molten salt solution 1203 to establish a compressive stress within the foldable substrate 1111. Accordingly, the surface of the foldable substrate 1111 is in compression and thus chemically strengthened through the ion exchange process because the radius of the lithium cation is smaller than the radius of the exchanged sodium cation or potassium cation in the molten salt solution 1203.

[0193] In an aspect, the first temperature of the molten salt solution 1203 may be: about 350 °C or greater, about 360 °C or greater, about 370 °C or greater, about 380 °C or greater, about 400 °C or less, about 390 °C or less, or about 380 °C or less. In an aspect, the first temperature of the molten salt solution 1203 may be in the range of: about 350 °C to about 400 °C, about 360 °C to about 400 °C, about 370 °C to about 390 °C, about 380 °C to about 390 °C, or any range or sub-range therebetween. As demonstrated by the embodiments discussed herein, providing a first temperature of the molten salt solution below 400 °C may increase the maximum compressive stress established for a predetermined layer depth and / or compressive depth. Additionally, for some of the molten salt solutions discussed herein, a temperature of 350 °C or higher may be used to ensure salt melting. Without wishing to be bound by theory, it is believed that lower temperature molten salt solutions (e.g., about 400 °C or less, about 350 °C to about 400 °C) improve the properties of the substrate by preventing stress relaxation and providing a more controlled and uniform compressive stress on the substrate.

[0194] In an aspect, the first time period during which the foldable substrate 1111 (e.g., having a first major surface 1113) is in contact with the molten salt solution 1203 can be: about 10 minutes or longer, about 15 minutes or longer, about 20 minutes or longer, about 30 minutes or longer, about 45 minutes or longer, about 60 minutes or longer, about 90 minutes or shorter, about 75 minutes or shorter, about 60 minutes or shorter, about 45 minutes or shorter, about 30 minutes or shorter, about 20 minutes or shorter, or about 15 minutes or shorter. In an aspect, the first time period during which the foldable substrate 1111 (e.g., having a first major surface 1113) is in contact with the molten salt solution 1203 can be in the following ranges: about 10 minutes to about 90 minutes, about 15 minutes to about 75 minutes, about 20 minutes to about 60 minutes, about 30 minutes to about 45 minutes, or any range or sub-range therebetween. In an aspect, the first time period during which the foldable substrate 1111 (e.g., having a first major surface 1113) is in contact with the molten salt solution 1203 can be about 30 minutes or shorter, such as in the following ranges: about 5 minutes to about 30 minutes, about 10 minutes to about 20 minutes, about 10 minutes to about 15 minutes, or any range or sub-range therebetween.

[0195] In an aspect, the molten salt solution 1203 can include at least two anions associated with different salts. In other aspects, the at least two anions can be associated with different potassium salts, and the molten salt solution 1203 can contain potassium ions in addition to the at least two anions. In even other aspects, the concentration of the first potassium salt and the concentration of the second potassium salt in the molten salt solution 1203 can be 2 wt% or higher (e.g., 2.0 wt% or higher), 2.5 wt% or higher, 3.0 wt% or higher, 4.0 wt% or higher, 5.0 wt% or higher, 7 wt% or higher, 8 wt% or higher, or 10 wt% or higher of the total 100 wt% of the molten salt solution 1203 (i.e., before immersing the foldable substrate 1111). Unless otherwise specified, the composition of the molten salt solution 1203 refers to the composition before immersing the foldable substrate 1111 therein and is based on 100 wt% of the total molten salt solution. It is to be understood that the molten salt solution can include additional components other than the two potassium salt components discussed herein, such as: sodium salts, lithium salts, silicic acid, or combinations thereof. For example, based on the weight % superaddition excluding silicic acid of the molten salt solution, the amount of silicic acid contained in the molten salt solution can be: 0.1 wt% or more, about 0.3 wt% or more, about 0.5 wt% or more, about 1.0 wt% or less, about 0.7 wt% or less, or about 0.5 wt%, such as in the following ranges: about 0.1 wt% to about 1.0 wt%, about 0.3 wt% to about 0.7 wt%, about 0.3 wt% to about 0.5 wt%, or any range or sub-range therebetween.

[0196] In other aspects, the concentration of the first potassium salt in the molten salt solution 1203 can be: about 2 wt% or more (e.g., about 2.0 wt% or more), about 2.5 wt% or more, about 3.0 wt% or more, about 4.0 wt% or more, about 5.0 wt% or more, about 7 wt% or more, about 8 wt% or more, about 10 wt% or more, about 12 wt% or less, about 10 wt% or less, about 8 wt% or less, about 5 wt% or less (e.g., about 5.0 wt% or less), about 4.0 wt% or less, or about 3.0 wt% or less. In other aspects, the concentration of the first potassium salt in the molten salt solution 1203 can be in the following ranges: about 2 wt% to about 12 wt%, about 2.5 wt% to about 10 wt%, about 3.0 wt% to about 8 wt%, about 4.0 wt% to about 5 wt%, or any range or sub-range therebetween. In other aspects, the concentration of the first potassium salt in the molten salt solution 1203 can be about 5 wt% or more, e.g., in the following ranges: about 5 wt% to about 12 wt%, about 7 wt% to about 12 wt%, about 8 wt% to about 10 wt%, or any range or sub-range therebetween. In other aspects, the concentration of the first potassium salt in the molten salt solution 1203 can be about 5.0 wt% or less, e.g., in the following ranges: about 2.0 wt% to about 5.0 wt%, about 2.5 wt% to about 5.0 wt%, about 3.0 wt% to about 4.0 wt%, or any range or sub-range therebetween. In a preferred aspect, (based on 100 wt% of the total molten salt solution before immersing the foldable substrate therein), the concentration of the first potassium salt in the molten salt solution can be: about 2 wt% to about 12 wt%, about 2.0 wt% to about 5.0 wt%, or about 5 wt% to about 12 wt%.

[0197] In other aspects, the first potassium salt can include two or more potassium atoms per anion. Providing multiple (i.e., two or more) potassium atoms per anion for the first potassium salt can increase the effective concentration and / or activity of potassium in the molten salt solution, which can contribute to an increase in the maximum compressive stress in the resulting chemically strengthened foldable substrate. Throughout this disclosure, the pKa of the potassium salt is measured according to OPPTS 830.7370, "Dissociation Constants in Water" (August 1996) of the U.S. Environmental Protection Agency, which is available from the National Center for Environmental Publications and Services. In other aspects, the first potassium salt can include a pKa of about 9 or greater, about 10 or greater, about 10.5 or greater, about 11 or greater, about 20 or less, about 15 or less, about 13 or less, or about 12 or less. In other aspects, the first potassium salt can include a pKa in the range of about 9 to about 20, about 10 to about 15, about 10.5 to about 13, about 11 to about 12, or any range or sub-range therebetween. Providing a pKa of about 9 or greater for the first potassium salt in the molten salt solution can improve the strength and / or foldability of the resulting chemically strengthened foldable substrate, for example, by selectively etching inherent defects in the foldable substrate (which might otherwise be amplified due to the chemical strengthening process). Exemplary aspects of potassium salts having more than two potassium atoms per anion and a pKa of about 9 or greater include potassium carbonate (K2CO3) and potassium phosphate (K3PO4). A preferred aspect of the first potassium salt is potassium carbonate (K2CO3), and the concentration of potassium carbonate (as the first potassium salt) can be within one or more of the corresponding ranges discussed in the previous paragraph (e.g., about 2 wt% to about 12 wt%, about 2.0 wt% to about 5.0 wt%, or about 5 wt% to about 12 wt%). As discussed herein with reference to the examples, potassium carbonate (K2CO3) has a more pronounced and unexpected increase in compressive stress compared to other components in the molten salt solution. Further, without wishing to be bound by theory, it is believed that the carbonate anion can contribute to the precipitation of other cations (e.g., lithium, sodium) exchanged from the foldable substrate, which can increase the lifetime of the molten salt solution (e.g., by removing components from the solution phase that would otherwise "poison" the molten salt solution).

[0198] In other aspects, the molten salt solution includes a second potassium salt associated with the two or more anions, wherein the anion of the first potassium salt is different from the anion of the second potassium salt. In even other aspects, the second potassium salt can be potassium nitrate (KNO3) and / or potassium chloride (KCl) or more. A preferred aspect of the second potassium salt is potassium nitrate (KNO3). In other aspects, the concentration of the second potassium salt (e.g., potassium nitrate) in the molten salt solution can be: about 50 wt% or higher, about 60 wt% or higher, about 70 wt% or higher, about 80 wt% or higher, about 84 wt% or higher, about 88 wt% or higher, about 89 wt% or higher, about 90 wt% or higher, about 91 wt% or higher, about 92 wt% or higher, about 93 wt% or higher, about 94 wt% or higher, about 95.0 wt% or higher (e.g., about 95 wt% or higher), about 96.0 wt% or higher, about 97.0 wt% or higher, about 97.5 wt% or higher, or about 98.0 wt% or higher (e.g., 98 wt% or higher). In other aspects, the concentration of the second potassium salt (e.g., potassium nitrate) in the molten salt solution can be in the following ranges: about 50 wt% to about 98.0 wt%, about 60 wt% to about 98 wt%, about 70 wt% to about 98 wt%, about 80 wt% to about 98 wt%, about 84 wt% to about 98 wt%, about 88 wt% to about 98.0 wt%, about 89 wt% to about 97.5 wt%, about 90 wt% to about 97.0 wt%, about 91 wt% to about 96.5 wt%, about 92 wt% to about 96.0 wt%, about 93 wt% to about 95.5 wt%, about 94 wt% to about 95.0 wt%, or any range or sub-range therebetween. In other aspects, the concentration of the second potassium salt (e.g., potassium nitrate) in the molten salt solution can be about 88 wt% or higher, for example, in the following ranges: about 88 wt% to about 98 wt%, about 88 wt% to about 97.5 wt%, about 88 wt% to about 97.0 wt%, about 88 wt% to about 96.0 wt%, about 88 wt% to about 95.0 wt%, about 88 wt% to about 94.0 wt%, about 88 wt% to about 93.0 wt%, about 88 wt% to about 92.0 wt%, about 89 wt% to about 91 wt%, about 90 wt% to about 91 wt%, or any range or sub-range therebetween. In other aspects, the concentration of the second potassium salt (e.g., potassium nitrate) in the molten salt solution can be about 95.0 wt% or higher, for example, in the following ranges: about 95.0 wt% to about 98.0 wt%, about 95.0 wt% to about 97.5 wt%, about 96.0 wt% to about 97.0 wt%, or any range or sub-range therebetween. In a preferred aspect, the concentration of the second potassium salt (e.g., potassium nitrate) in the molten salt solution can be in the following ranges: about 50 wt% to about 98 wt%, about 88 wt% to about 98 wt%, or about 95 wt% to about 98 wt%.

[0199] In other aspects, the molten salt solution 1203 can include a third potassium salt associated with a third anion of the at least two anions, where the third anion is different from the anions associated with the first potassium salt and the second potassium salt (discussed above). In even other aspects, the third potassium salt can have two or more potassium atoms per anion (similar to the first potassium salt). An exemplary aspect of the third potassium salt is potassium sulfate K2SO4. For example, the molten salt solution 1203 can contain K2CO3 as the first potassium salt, KNO3 as the second potassium salt, and K2SO4 as the (optional) third potassium salt. In even other aspects, the concentration of the third potassium salt (e.g., potassium sulfate) in the molten salt solution can be: 0 wt% or higher, about 0.1 wt% or higher, about 0.3 wt% or higher, about 0.5 wt% or higher, about 0.8 wt% or higher, about 1.0 wt% or higher, about 1.2 wt% or higher, about 1.5 wt% or higher, about 1.8 wt% or higher, about 2.0 wt% or higher, about 2.5 wt% or higher, about 3.0 wt% or higher, about 3.5 wt% or higher, about 4.0 wt% or higher, about 5 wt% or lower (e.g., about 5.0 wt% or lower), about 4.5 wt% or lower, about 4.0 wt% or lower, about 3.5 wt% or lower, about 3.0 wt% or lower, about 2.5 wt% or lower, about 2.0 wt% or lower, about 1.5 wt% or lower, about 1.0 wt% or lower, about 0.8 wt% or lower, or about 0.5 wt% or lower. In even other aspects, the concentration of the third potassium salt (e.g., potassium sulfate) in the molten salt solution can be in the following ranges: about 0 wt% to about 5 wt%, about 0.1 wt% to about 5.0 wt%, about 0.2 wt% to about 5.0 wt%, about 0.5 wt% to about 5.0 wt%, about 0.8 wt% to about 4.5 wt%, about 1.0 wt% to about 4.0 wt%, about 1.2 wt% to about 3.5 wt%, about 1.5 wt% to about 3.0 wt%, about 1.8 wt% to about 2.5 wt%, about 2.0 wt% to about 2.5 wt%, or any range or sub-range therebetween. In even other aspects, the concentration of the third potassium salt (e.g., potassium sulfate) in the molten salt solution can be about 2.0 wt% or lower, such as in the following ranges: about 0 wt% to about 2.0 wt%, about 0 wt% to about 1.5 wt%, about 0.1 wt% to about 1.0 wt%, about 0.1 wt% to about 0.8 wt%, about 0.2 wt% to about 0.5 wt%, or any range or sub-range therebetween.

[0200] Due to the presence of a first potassium salt (e.g., having a pKa of 9 or higher, such as potassium carbonate), in aspects, the molten salt solution 1203 will be alkaline (i.e., pH greater than 7). In other aspects, the pH of the molten salt solution 1203 can be: about 8 or higher, about 9 or higher, about 10 or higher, about 10.5 or higher, about 11 or higher, about 15 or lower, about 13 or lower, or about 12 or lower. In other aspects, the pH of the molten salt solution 1203 can be in the following ranges: about 8 to about 15, about 9 to about 13, about 9 to about 12, about 10 to about 13, about 10.5 to about 12, or any range or sub-range therebetween. In preferred aspects, the pH of the molten salt solution can be in the following ranges: about 9 to 12 or about 10 to 12. Providing a molten salt solution with a pH of about 9 to 12 can improve the strength and / or foldability of the resulting chemically strengthened foldable substrate, for example, by selectively etching inherent defects in the foldable substrate (which may otherwise be amplified due to the chemical strengthening process). Additionally, in aspects, as discussed below and as Figures 13 - 14 and 16 show, the chemical strengthening process of step 1005 can generate an initial first compressive stress region 1212 and / or an initial second initial compressive stress region 1214. For example, the presence of the first potassium salt can cause the compressive stress imparted by contacting the existing first main surface with the molten salt solution 1203 (at least in step 1005) to increase by about 5% or more (e.g., about 10% or more, about 5% to about 20%, about 5% to about 15%, or about 7% to about 10%), as compared to immersing the foldable substrate in a comparative molten salt solution having the same composition as the molten salt solution with and without the first potassium salt.

[0201] In aspects, after step 1005, as Figure 13 shown, the method can proceed to step 1007, including transferring the foldable substrate 1111 to the cooling chamber 1301 and causing the temperature of the cooling chamber to decrease from an initial temperature to a final temperature. In other aspects, as Figure 13 shown, the foldable substrate 1111 will still contain a residual portion of the molten salt solution (shown by droplets 1305) and / or deposits 1303 from the surface (e.g., the existing first main surface 1113) that contacted the molten salt solution during step 1005. In even other aspects, as Figure 13 shown, the foldable substrate 1111 can be suspended in the cooling chamber 1301, for example, to facilitate removal of the residual portion of the molten salt solution (shown by droplets 1305) from the foldable substrate 1111, which will flow away from the foldable substrate 1111 in the direction of gravity (not shown, but assumed to be downward in Figure 13 ).

[0202] In aspects, the initial temperature of the cooling chamber 1301 (e.g., when the foldable substrate 1111 is placed therein) can be: about 300 °C or lower, about 280 °C or lower, about 260 °C or lower, about 240 °C or lower, about 220 °C or lower, about 180 °C or higher, about 190 °C or higher, about 200 °C or higher, about 210 °C or higher, or about 220 °C or higher. In aspects, the initial temperature of the cooling chamber 1301 (e.g., when the foldable substrate 1111 is placed therein) can be in the following ranges: about 180 °C to about 300 °C, about 190 °C to about 280 °C, about 200 °C to about 260 °C, about 210 °C to about 240 °C, about 210 °C to about 220 °C, or any range or sub-range therebetween. In a preferred aspect, the initial temperature of the cooling chamber 1301 can be in the following ranges: about 180 °C to about 300 °C or about 180 °C to about 220 °C. In other aspects, the difference between the first temperature maintained by the molten salt solution 1203 at step 1005 and the initial temperature of the cooling chamber 1301 in step 1007 (i.e., the first temperature minus the initial temperature) can be: about 50 °C or greater, about 75 °C or greater, about 100 °C or greater, about 120 °C or greater, about 140 °C or greater, or about 160 °C or greater. Providing an initial temperature of the cooling chamber lower than the molten salt solution (e.g., lower by about 50 °C or more, about 100 °C or more, or about 140 °C or more) can reduce residual chemical strengthening that occurs due to any remaining portion of the molten salt solution or deposits from the molten salt solution on the foldable substrate after removal from the molten salt solution. Specifically, it has been observed that foldable substrates having a thickness of about 50 μm or less (e.g., about 10 μm to about 50 μm or about 10 μm to about 30 μm) are unexpectedly sensitive to events that occur after removal of the foldable substrate from the molten salt solution. For these thin foldable substrates, even relatively small differences in compressive stress on their surfaces can cause rippling and / or warping, which can result in optical deformations that are visually visible to the user of a consumer electronic product that may incorporate the foldable substrate. Thus, a controlled temperature of the cooling chamber can contribute to relatively uniform compressive stress on the surface of the foldable substrate. Additionally, providing an initial temperature of the cooling chamber of 180 °C or higher (e.g., 200 °C or higher or 220 °C or higher) can facilitate the removal of the remaining portion of the molten salt solution before it solidifies. Without wishing to be bound by theory, the first potassium salt can have a higher melting temperature compared to the second potassium salt, which means that incorporating the first potassium salt in the molten salt solution can increase the viscosity of the molten salt solution and / or can cause the molten salt solution to solidify at a higher temperature compared to a molten salt solution without the first potassium salt. Thus, when the molten salt solution contains the first potassium salt, it can be particularly useful to allow the remaining portion of the molten salt solution on the foldable substrate after removal of the foldable substrate from the molten salt solution.

[0203] In other aspects, the final temperature of the cooling chamber 1301 can be: about 25 °C or higher, about 40 °C or higher, about 60 °C or higher, about 70 °C or higher, about 100 °C or lower, about 90 °C or lower, or about 80 °C or lower, about 70 °C or lower, or about 60 °C or lower. In other aspects, the final temperature of the cooling chamber 1301 can be in the following ranges: about 25 °C to about 100 °C, about 40 °C to about 90 °C, about 60 °C to about 90 °C, about 60 °C to about 80 °C, about 70 °C to about 80 °C, or any range or sub-range therebetween. Reducing the temperature of the cooling chamber to about 100 °C or lower (e.g., about 25 °C to about 100 °C or about 60 °C to about 90 °C) as the final temperature can enable subsequent treatment (e.g., relatively rapid or immediate) of the foldable substrate with an aqueous solution (e.g., rinsing with water or an alkaline detergent solution, contacting with an aqueous acidic solution).

[0204] In other aspects, a sufficiently ventilated and / or circulating environment (e.g., air) can be passed through the cooling chamber to obtain the cooling rate of the temperature of the cooling scheme. In other aspects, the cooling rate of the temperature of the cooling scheme (e.g., from the initial temperature to the final temperature) can be: about 4 °C per minute (°C / min) or greater, about 6 °C / min or greater, about 8 °C / min or greater, about 10 °C / min or greater, about 12 °C / min or greater, about 14 °C / min or greater, about 20 °C / min or less, about 18 °C / min or less, about 16 °C / min or less, about 14 °C / min or less, or about 10 °C / min or less. In other aspects, the cooling rate of the temperature of the cooling scheme (e.g., from the initial temperature to the final temperature) can be in the following ranges: about 4 °C / min to about 20 °C / min, about 6 °C / min to about 18 °C / min, about 8 °C / min to about 16 °C / min, about 10 °C / min to about 14 °C / min, about 12 °C / min to about 14 °C / min, or any range or sub-range therebetween. Providing a cooling rate of about 4 °C / min to about 20 °C / min can cause the temperature of the cooling chamber (and the foldable substrate) to drop rapidly while maintaining a relatively consistent temperature throughout the cooling chamber (and / or the foldable substrate), e.g., thereby creating a relatively consistent compressive stress on the surface of the foldable substrate.

[0205] In an aspect, after step 1005 or 1007, as Figure 14As shown, the method can proceed to step 1009, including (e.g., after removing the foldable substrate from the molten salt solution in step 1005 and / or after the cooling chamber reaches the final temperature) cleaning the foldable substrate 1111 with solution 1403. In other aspects, solution 1403 can be contained in bath 1401 and / or the foldable substrate 1111 can be immersed in solution 1403 (e.g., with the existing first major surface 1113 and the existing second major surface 1115 contacting solution 1403). In other aspects, such as Figure 13 and 14As shown therebetween, solution 1403 can remove (e.g., dissolve and / or replace) deposits 1303 from the molten salt solution remaining on the foldable substrate 1111. In aspects, solution 1403 can be agitated (e.g., ultrasonically) to further facilitate removal of deposits 1303 and / or contaminants on the surface that would interfere with uniform treatment of the surface of the foldable substrate in subsequent steps. In other aspects, solution 1403 can be: water (e.g., purified water, filtered water, deionized water, and / or distilled water), an alkaline detergent solution, or a combination thereof. As used herein, the pH of the solution is measured as a standard solution that extends to a pH of at least 14 at 25 °C according to ASTM E70-90. In even other aspects, the alkaline detergent solution (e.g., solution 1403) can comprise an alkaline detergent and have a pH of: about 11 or greater, about 12 or greater, about 12.5 or greater, about 12.8 or greater, about 14 or less, about 13.5 or less, or about 13.2 or less. In aspects, the alkaline detergent solution (e.g., solution 1403) can have a pH range of: about 11 to about 14, about 12 to about 14, about 12.5 to about 13.5, about 12.8 to about 13.2, or any range or sub-range therebetween. In aspects, the alkaline detergent solution (e.g., solution 1403) can comprise an alkaline detergent at a concentration of: about 0.5 wt% or more, about 1 wt% or more, about 1.5 wt% or more, about 2 wt% or more, about 4 wt% or less, about 3 wt% or less, or about 2.5 wt% or less. In aspects, the alkaline detergent solution (e.g., solution 1403) can comprise an alkaline detergent at a concentration range of: about 0.5 wt% to about 4 wt%, about 1 wt% to about 4 wt%, about 1.5 wt% to about 3 wt%, about 2 wt% to about 3 wt%, about 2.5 wt% to about 3 wt%, or any range or sub-range therebetween. Exemplary aspects of the alkaline detergent solution include SemiClean KG (Yokohama Oil & Fat Co., Ltd.). Exemplary aspects of ultrasonication can include ultrasonication and megasonication. Without wishing to be bound by theory, ultrasonication (e.g., ultrasonication, megasonication) can assist in removing contaminants (e.g., particles, oils) from the surface by forming microscale bubbles on the surface, by increasing the circulation of the alkaline detergent solution via agitation, and / or by loosening the contaminants via direct vibration. In aspects, the alkaline detergent solution and / or water can be substantially free of rheology modifiers. As used herein, a rheology modifier is a component other than the solvent or the listed components (e.g., acids, hydroxide-containing bases, H2SiF6, fluorine-containing compounds) that changes the viscosity or shear-dependent behavior (dilatancy, thixotropy) of the solution.Exemplary aspects of the solution being substantially free of rheology modifiers include one or more of the following: cellulose, cellulose derivatives (e.g., ethyl cellulose, methyl cellulose, and AQUAZOL (poly-2-ethyl-2-oxazine)), hydrophobically modified ethylene oxide urethane modifiers (HUER), and ethylene acrylic acid.

[0206] In other aspects, solution 1403 can include a cleaning temperature and / or contact with the foldable substrate 1111 for a cleaning time period. In other aspects, ultrasound can be applied for at least half of the cleaning time period, such as the entire first time period. In other aspects, the cleaning time period can be: about 2 minutes or longer, about 3 minutes or longer, about 4 minutes or longer, about 5 minutes or longer, about 60 minutes or shorter, about 40 minutes or shorter, about 20 minutes or shorter, about 10 minutes or shorter, about 8 minutes or shorter, or about 6 minutes or shorter. In other aspects, the cleaning time period can be in the range of: about 2 minutes to about 40 minutes, about 2 minutes to about 20 minutes, about 3 minutes to about 20 minutes, about 3 minutes to about 10 minutes, about 4 minutes to about 8 minutes, about 4 minutes to about 6 minutes, or any range or sub-range therebetween. Providing a cleaning time period of at least 2 minutes can effectively remove contaminants and / or deposits from the surface. Providing a cleaning time period of less than 40 minutes can keep the probability of breakage or rupture within an acceptable range. In an aspect, the first temperature can be: about 20°C or higher, about 25°C or higher, about 30°C or higher, about 35°C or higher, about 65°C or lower, about 60°C or lower, about 55°C or lower, or about 45°C or lower. In an aspect, the first temperature can be in the range of: about 20°C to about 65°C, about 25°C to about 60°C, about 30°C to about 55°C, about 35°C to about 45°C, or any range or sub-range therebetween. Providing an alkaline detergent solution can selectively act on surface imperfections (e.g., remove, round, passivate) before removing material from other parts of the surface, which can increase the impact resistance of the substrate without removing an appreciable thickness from the surface of the foldable substrate.

[0207] As Figure 14 and 16As shown, after and / or at the end of steps 1005, 1007, and / or 1009, the chemically strengthened foldable substrate (i.e., foldable substrate 1111) can include (e.g., as a result of the chemically strengthening process described above) an initial first compressive stress region 1212 extending from the existing first major surface 1113 to an initial first compressive depth 1216 and an initial first layer depth of one or more alkali metal ions (e.g., potassium) associated with the initial first compressive stress region 1212, and / or the foldable substrate 1111 can include an initial second compressive stress region 1214 extending from the existing second major surface 1115 to an initial second compressive depth 1218 and an initial second layer depth of one or more alkali metal ions (e.g., potassium) associated with the initial second compressive stress region 1214. In other aspects, the maximum initial first compressive stress of the initial first compressive stress region 1212 and / or the maximum initial second compressive stress of the initial second compressive stress region 1214 can be within one or more of the ranges discussed above with respect to the maximum first compressive stress. In other aspects, the maximum initial first compressive stress of the initial first compressive stress region 1212 and / or the maximum initial second compressive stress of the initial second compressive stress region 1214 can be: about 800 MPa or greater, about 850 MPa or greater, about 900 MPa or greater, about 950 MPa or greater, about 1000 MPa or greater, about 1500 MPa or less, about 1300 MPa or less, about 1200 MPa or less, about 1100 MPa or less, about 1050 MPa or less, about 1000 MPa or less, or about 950 MPa or less. In other aspects, the maximum initial first compressive stress of the initial first compressive stress region 1212 and / or the maximum initial second compressive stress of the initial second compressive stress region 1214 can be in the following ranges: about 800 MPa to about 15000 MPa, about 850 MPa to about 1300 MPa, about 900 MPa to about 1200 MPa, about 950 MPa to about 1100, about 1000 MPa to about 1050 MPa, or any range or sub-range therebetween. In other aspects, the presence of the first potassium salt can cause the compressive stress imparted by contacting the existing first major surface with the molten salt solution 1203 (at least in step 1005) to increase by about 5% or more (e.g., about 10% or more, about 5% to about 20%, about 5% to about 15%, or about 7% to about 10%), as compared to immersing the foldable substrate in a comparative molten salt solution having the same composition as the molten salt solution without the first potassium salt.In other aspects, the maximum initial first compressive stress of the initial first compressive stress region 1212 and / or the maximum initial second compressive stress of the initial second compressive stress region 1214 can be about 5% or more, about 8% or more, about 10% or more, about 12% or more, about 15% or more, about 17% or more, or about 20% or more greater than the obtained maximum first compressive stress and / or the obtained maximum second compressive stress, such as in the following ranges: about 5% to about 30%, about 8% to about 25%, about 10% to about 22%, about 12% to about 20%, about 15% to about 18%, or any range or sub-range therebetween.

[0208] After step 1005, 1007, or 1009, as Figures 15 - 16 shown, the method can proceed to step 1011, including at least contacting the existing first major surface 1113 with an acidic solution 1503 maintained at a second temperature for a second time period to remove an outer layer (e.g., an outer compressive layer extending to a first outer depth 1603 of the initial first compressive stress region 1212 as Figure 16 shown) to form a new first major surface (e.g., first major surface 205) and a first compressive stress region 212. In an aspect, as shown, the existing second major surface 1115 can also be contacted with the acidic solution 1503 to remove an outer layer (e.g., an outer compressive layer extending to a second outer depth 1605 of the initial second compressive stress region 1214 as Figure 16 shown) to form a new second major surface (e.g., second major surface 205) and a second compressive stress region 214. In an aspect, as Figure 15 shown, the acidic solution 1503 can be contained in a bath 1501 and the foldable substrate 1111 can be immersed in the acidic solution 1503, although in other situations in other aspects, the acidic solution can also be contacted with the foldable substrate (e.g., the existing first major surface 1113). In other aspects, as Figure 16 shown, the first outer depth 1603 and / or the second outer depth 1605 of the outer layer removed by the acidic solution 1503 (see Figure 15 ) can be: about 3.5 μm or less, about 3.0 μm or less, about 2.5 μm or less, about 2.0 μm or less, about 1.5 μm or less, about 1.0 μm or less, about 0.8 μm or less, about 0.1 μm or greater, about 0.3 μm or greater, about 0.5 μm or greater, about 0.8 μm or greater, about 1.0 μm or greater, or about 1.5 μm or greater. In other aspects, as Figure 16 shown, the first outer depth 1603 and / or the second outer depth 1605 of the outer layer removed by the acidic solution 1503 (see Figure 15) can be in the following ranges: from about 0.1 μm to about 3.5 μm, from about 0.3 μm to about 3.0 μm, from about 0.5 μm to about 2.5 μm, from about 0.8 μm to about 2.0 μm, from about 1.0 μm to about 1.5 μm, or any range or sub-range therebetween. Thus, as Figure 16 shown, the first outer depth 1603 and / or the second outer depth 1605 are respectively less than the initial first compression depth 1216 and / or the initial second compression depth 1218, and the foldable substrate 201 can include a first compressive stress region 212 and / or a second compressive stress region 214 after contact with the acidic solution 1503 (see Figure 15 ) that have a reduced compressive stress relative to the corresponding initial compression regions. In other aspects, the reduction in compressive stress (i.e., removed by the acidic solution), expressed as a percentage of the maximum initial first compressive stress and / or the maximum initial second compressive stress, can be: about 10% or more, about 12% or more, about 15% or more, about 17% or more, about 20% or more, about 22% or more, about 25% or less, about 22% or less, about 20% or less, about 17% or less, or about 15% or less. In other aspects, the reduction in compressive stress (i.e., removed by the acidic solution), expressed as a percentage of the maximum initial first compressive stress and / or the maximum initial second compressive stress, can be in the following ranges: from about 10% to about 25%, from about 12% to about 22%, from about 15% to about 20%, from about 17% to about 20%, or any range or sub-range therebetween. In other aspects, the resulting compressive stress regions can include corresponding maximum compressive stresses within one or more of the ranges discussed above with reference to the maximum first compressive stress.

[0209] The etching rate of the acidic solution (i.e., the material removal rate from each surface (existing major surface) of the foldable substrate) can be adjusted based on the second temperature, the inclusion of the aqueous solution containing the components, the component concentration, and the pH obtained from the acidic solution. In an aspect, the etching rate of the acidic solution 1503 can be: about 1 μm per minute (μm / min) or less (e.g., about 1.0 μm / min or less), about 0.9 μm / min or less, about 0.8 μm / min or less, about 0.7 μm / min or less, about 0.6 μm / min or less, about 0.5 μm / min or less, about 0.4 μm / min or less, about 0.1 μm / min or greater, about 0.2 μm / min or greater, about 0.3 μm / min or greater, about 0.4 μm / min or greater, about 0.5 μm / min or greater, or about 0.6 μm / min or greater. In an aspect, the etching rate of the acidic solution 1503 can be in the following ranges: about 0.1 μm / min to about 1.0 μm / min, about 0.2 μm / min to about 0.9 μm / min, about 0.3 μm / min to about 0.8 μm / min, about 0.4 μm / min to about 0.7 μm / min, about 0.5 μm / min to about 0.6 μm / min, or any range or sub-range therebetween. Providing an etching rate of about 1 μm / min or less (e.g., about 1.0 μm / min or less) can facilitate substantially uniform material removal from the surface(s) of the foldable substrate. As discussed above, a foldable substrate having a thickness of about 50 μm or less (e.g., about 10 μm to about 50 μm or about 10 μm to about 30 μm) is quite sensitive to differences in compressive stress and thickness variations on its surface. Thus, providing an etching rate of about 1 μm / min can remove a relatively uniform thickness and compressive stress portion from the surface(s), thereby reducing the occurrence probability of ripples and / or warping that can cause optical deformations visually visible to the user of a consumer electronic product that may incorporate the foldable substrate.

[0210] In an aspect, the second temperature of the acidic solution 1503 can be: about 20 °C or higher, about 22 °C or higher, about 25 °C or higher, about 28 °C or higher, about 30 °C or higher, about 40 °C or lower, about 35 °C or lower, about 30 °C or lower, about 28 °C or lower, about 25 °C or lower, or about 23 °C or lower. In an aspect, the second temperature of the acidic solution 1503 can be in the following ranges: about 20 °C to about 40 °C, about 20 °C to about 35 °C, about 20 °C to about 30 °C, about 20 °C to about 28 °C, about 20 °C to about 25 °C, about 22 °C to about 23 °C, or any range or sub-range therebetween. Without wishing to be bound by theory, providing an acidic solution at a lower temperature (e.g., about 20 °C to about 40 °C or about 20 °C to about 25 °C) can reduce SiF6 -The concentration of anions, since the reaction of H2SiF6 with 2H + +SiF6 - is endothermic. Reducing the concentration of SiF6 - anions will be associated with a decrease in the deposition (e.g., redeposition) of silica or silica-like materials on the surface, which otherwise would result in changes in the thickness and / or compressive stress on the surface of the foldable substrate.

[0211] In aspects, the second time period during which the foldable substrate 201 or 1111 (e.g., having a first major surface 1113 or a first major surface 203) is in contact with the acidic solution 1503 can be: about 20 seconds or longer, about 30 seconds or longer, about 45 seconds or longer, about 60 seconds or longer, about 75 seconds or longer, about 90 seconds or longer, about 120 seconds or longer, about 3.5 minutes or shorter, about 3 minutes or shorter, about 2.5 minutes or shorter, about 2 minutes or shorter, about 1.5 minutes or shorter, or about 1.0 minute or shorter. In aspects, the second time period can be in the range of: about 20 seconds to about 3.5 minutes, about 30 seconds to about 3 minutes, about 45 seconds to about 2.5 minutes, about 60 seconds to about 2 minutes, about 75 seconds to about 1.5 minutes, or any range or sub-range therebetween. In aspects, during the second time period, the acidic solution 1503 can be oscillated (e.g., stirred, sonicated). Without wishing to be bound by theory, oscillating the acidic solution can reduce the supersaturation of silica-like compounds near the surface.

[0212] As discussed above, the pH of the solution is measured at 25 °C according to ASTM E70-90. In aspects, the pH of the acidic solution 1503 can be: about 3.5 or higher, about 3.55 or higher, about 3.6 or higher, about 3.65 or higher, about 3.7 or higher, about 3.75 or higher, about 3.8 or higher, about 4.5 or lower, about 4.3 or lower, about 4.0 or lower, about 3.9 or lower, about 3.8 or lower, or about 3.7 or lower. In aspects, the pH of the acidic solution 1503 can be in the range of: about 3.5 to about 4.5, about 3.55 to about 4.3, about 3.6 to about 4.0, about 3.65 to about 3.9, about 3.7 to about 3.8, about 3.75 to about 3.8, or any range or sub-range therebetween. Providing a higher pH (e.g., about 3.5 to about 4.5, about 3.6 to about 4.3, or about 3.7 to about 4.0) will reduce the etching rate, which can help produce relatively uniform compressive stress and thickness on the foldable substrate.

[0213] In aspects, the acidic solution can include a buffered HF solution and / or an aqueous acidic solution. As used herein, buffered HF means the solution contains NH4F or produces F in an acidic solution -Similar compounds of anions. In an aspect, based on the weight percentage of the acidic solution, the amount of HF contained in the acidic solution can be: about 0.5 wt% or more, about 0.55 wt% or more, about 0.6 wt% or more, about 1.5 wt% or less, about 1.25 wt% or less, about 1.0 wt% or less, about 0.75 wt% or less, about 0.7 wt% or less, or about 0.65 wt% or less. In an aspect, based on the weight percentage of the acidic solution, the amount of HF contained in the acidic solution can be in the following range: about 0.5 wt% to about 1.5 wt%, about 0.5 wt% to about 1.25 wt%, about 0.5 wt% to about 1.0 wt%, about 0.5 wt% to about 0.75 wt%, about 0.55 wt% to about 0.70 wt%, about 0.6 wt% to about 0.65 wt%, or any range or sub-range therebetween. In an aspect, based on the weight percentage of the acidic solution, the amount of NH4F contained in the acidic solution can be: about 0.75 wt% or more, about 0.8 wt% or more, about 0.85 wt% or more, about 0.9 wt% or more, about 0.95 wt% or more, about 1.0 wt% or more, about 1.1 wt% or more, about 2.5 wt% or less, about 2.25 wt% or less, about 2.0 wt% or less, about 1.75 wt% or less, about 1.5 wt% or less, about 1.3 wt% or less, about 1.2 wt% or less, about 1.1 wt% or less, or about 1.0 wt% or less. In an aspect, based on the weight percentage of the acidic solution, the amount of NH4F contained in the acidic solution can be in the following range: about 0.75 wt% to about 2.5 wt%, about 0.8 wt% to about 2.25 wt%, about 0.8 wt% to about 2.0 wt%, about 0.85 wt% to about 1.75 wt%, about 0.9 wt% to about 1.5 wt%, about 0.95 wt% to about 1.3 wt%, about 1.0 wt% to about 1.2 wt%, about 1.0 wt% to about 1.1 wt%, or any range or sub-range therebetween. In an exemplary aspect, the acidic solution can contain: about 0.5 wt% to about 1.5 wt% or about 0.5 wt% to about 0.75 wt% HF, and / or about 0.75 wt% to about 2.5 wt% or about 0.9 wt% to about 1.5 wt% NH4F.Providing a total concentration of HF and NH4F of about 4.0 wt% or less, about 3.5 wt% or less, about 3.0 wt% or less, about 2.5 wt% or less, or about 2.0 wt% or less (e.g., from about 1.25 wt% to about 4.0 wt%, from about 1.3 wt% to about 3.5 wt%, from about 1.35 wt% to about 3.0 wt%, from about 1.4 wt% to about 2.5 wt%, from about 1.5 wt% to about 2.0 wt%) can provide relatively controlled and uniform etching of the foldable substrate and / or can reduce the deposition of materials (e.g., silica, silica-like materials, ammonium fluoride crystals) on the foldable substrate that can degrade the optical properties of the foldable substrate.

[0214] In an aspect, after step 1011, the method can further proceed to step 1013, including cleaning the foldable substrate with water, an alkaline detergent solution, or a combination thereof. For example, referring to Figure 12 , step 1013 can include cleaning the foldable substrate (e.g., herein replace the foldable substrate 1111 in Figure 12 with the foldable substrate 201) with the solution 1203 (e.g., an alkaline detergent solution, water) contained in the bath 1201. In other aspects, step 1013 can include: cleaning with an alkaline detergent solution after cleaning with water, the reverse order, or multiple cleanings involving water and / or an alkaline detergent solution. In other aspects, step 1013 can include one or more aspects discussed above with reference to step 1009. For example, providing an alkaline detergent solution in step 1013 can neutralize the residual etchant from step 1011, which can prevent surface defects and / or result in a more uniform foldable substrate thickness. Providing an alkaline detergent solution in step 1013 can neutralize and / or remove the hydrogen (e.g., hydronium ions) enrichment at the surface of the foldable substrate, which otherwise, as a result of stress corrosion during a subsequent chemical strengthening process, may lead to large defects. Providing an alkaline detergent solution can selectively act on surface defects (e.g., removing, rounding, passivating) before removing material from other parts of the surface, which can increase the impact resistance of the substrate without removing a significant thickness from the surface of the foldable substrate.

[0215] In an aspect, after step 1009, 1011, or 1013, the method can proceed to step 1015, including assembling a foldable device from the foldable substrate. In other aspects, step 1015 can include disposing an adhesive layer 311 or a polymer-based part above the foldable substrate 201 (e.g., the first major surface 203). In other aspects, step 1015 can further include the adhesive layer 311 disposed earlier in step 1015 (see Figure 3) or a layer disposed above the polymer-based portion (e.g., a display device, another substrate, PET sheet 321). In other aspects, step 1015 may further include an adhesive layer 311 disposed earlier in step 1015 (see Figure 3 ) or a release liner disposed above the polymer-based portion. In an aspect, step 1015 may include disposing a coating above the foldable substrate (e.g., the second major surface).

[0216] After steps 1009, 1011, 1013, and / or 1015, the method may be completed at step 1017. In an aspect, method 1017 may further include assembling the foldable device, e.g., by disposing a coating opposite the release liner or the display device, or by disposing a release liner or a display device opposite the coating. At the end of steps 1009, 1011, 1013, and / or 1015, the foldable substrate 201 may be in contact with, for example Figures 2 - 3The collapsible substrates 201 shown are similar or identical. In aspects, the method can proceed along the steps discussed above, such as through steps 1001, 1003, 1005, 1007, 1009, 1011, 1013, 1015, and 1017 in sequence. In aspects, if the collapsible substrate 1111 is to be chemically strengthened without preheating, the method can proceed from step 1001 to step 1005 along arrow 1002. In aspects, for example, if the chemically strengthened collapsible substrate is cleaned in step 1009 without placing the collapsible substrate in a cooling chamber with a controlled temperature distribution, the method can proceed from step 1005 to 1009 along arrow 1004. In aspects, for example, if the collapsible substrate is to be chemically strengthened from step 1015 directly to etching with an acidic solution (e.g., without cleaning and / or placing in a cooling chamber with a controlled temperature distribution), the method can proceed from step 1005 to step 1011 along arrow 1006. In aspects, for example, if the collapsible substrate is to be transferred from the cooling chamber to the acidic solution (e.g., without cleaning the collapsible substrate therebetween), the method can proceed from step 1007 to step 1011 along arrow 1008. In aspects, for example, if the method is completed at the end of step 1011, the method can proceed from step 1011 to step 1017 along arrow 1010. In aspects, for example, if the collapsible substrate is to be assembled into a part of the collapsible substrate after etching with the acidic solution (e.g., without cleaning therebetween), the method can proceed from step 1011 to step 1015 along arrow 1012. In aspects, for example, if the method is completed at the end of step 1013, the method can proceed from step 1013 to step 1017 along arrow 1014. In aspects, for example, if the method is completed at the end of step 1009, the method can proceed from step 1009 to step 1017 along arrow 1016. The chemically strengthened collapsible substrates and / or collapsible devices according to aspects of the present disclosure can be manufactured by combining any of the above options.

[0217] In aspects, the method according to aspects of the present disclosure can consist of the steps discussed above. For example, there can be no further processing of the collapsible substrate between one or more (or even all) of the steps described in the flowchart referenced above Figure 10 . Throughout the present disclosure, the phrases "without further processing" or "without additional processing" exclude processing of the first major surface other than contacting with the solution and rinsing with water (e.g., pure water, filtered water, deionized water, distilled water). Exemplary aspects of processing that would be excluded by "without further processing" or "without additional processing" include treatment with additional acidic solutions, basic solutions, fluorine-containing solutions, detergents, and mechanical polishing of the collapsible substrate.

[0218] Example

[0219] The various aspects are further illustrated by the following examples.

[0220] Examples 1-3, 21-24, 29-43, and 48-50 and Comparative Examples AA-BB, II-JJ, MM-NN, QQ, and TT include glass-based substrates having Composition 1 (in mol%, designated as: 68.9 SiO2, 10.1 mol% Al2O3, 4.9 mol% MgO, 0.5 mol% CaO, 15.5 Na2O, and 0.1 mol% SnO2). Examples 1-3 and Comparative Examples AA-BB and QQ include a substrate thickness of 80 μm. Examples 21-24 and 40-43 and Comparative Examples II-JJ include a substrate thickness of 75 μm. Examples 29-39 and 49-50 and Comparative Examples MM-NN include a substrate thickness of 30 μm.

[0221] Examples 4-20, 25-28, 44-47, and 51-74 and Comparative Examples CC-HH, KK-LL, OO-PP, and RR-SS include glass-based substrates having Composition 2 (in mol%, designated as: 65.0 SiO2, 14.1 mol% Al2O3, 3.4 mol% MgO, 1.0 mol% CaO, 16.4 Na2O, and 0.1 mol% SnO2). Examples 4-6 and Comparative Examples CC-DD and RR include a substrate thickness of 80 μm. Examples 14-20 and 25-28 and Comparative Examples GG-HH include a substrate thickness of 75 μm. Examples 44-47 and Comparative Examples KK-LL include a substrate thickness of 70 μm. Examples 7-13 and 51-74 and Comparative Examples EE-FF, OO-PP, and SS include a substrate thickness of 30 μm.

[0222] Table 1-2 and Figures 17 - 18 present the processing conditions and properties of Examples 1-6 and Comparative Examples AA-DD. The remainder of the molten salt solution (after considering the second potassium salt) is potassium nitrate (KNO3) with any silicic acid added to it as an over-addition. For example, Example 1 is 95 wt% KNO3 and 5 wt% K2CO3 with 0.5 wt% over-added silicic acid. In Figure 17 , the vertical axis 1703 (e.g., the y-axis) corresponds to the compressive stress in MPa, and the horizontal axis 1701 (e.g., the x-axis) corresponds to the different examples, with the examples using Composition 1 separated from those using Composition 2 by a dashed line. In Figure 18 , the vertical axis 1803 (e.g., the y-axis) corresponds to the layer depth in μm, and the horizontal axis 1801 (e.g., the x-axis) corresponds to the different examples, with the examples using Composition 1 separated from those using Composition 2 by a dashed line.

[0223] Table 1 presents the properties of Composition 1 (Examples 1-3 and Comparative Examples AA-BB). Comparing Example 1 with Comparative Example AA, further addition of K2CO3 at 420 °C reduced the compression and layer depth (relative to Comparative Example AA). The molten salt solutions of Comparative Example BB and Examples 2-3 were maintained at 380 °C instead of 420 °C. As confirmed by Comparative Example BB, a longer chemical strengthening treatment at a lower temperature (380 °C vs. 420 °C) (69 minutes vs. 30 minutes) can achieve roughly the same (or even slightly higher) compression stress with a reduced layer depth. As discussed above, it is believed that the lower molten salt solution temperature improved the properties of the substrate by preventing stress relaxation and by providing a more controlled and uniform compression stress on the substrate. The addition of a second potassium salt in Examples 2-3 improved the compression stress and (improved or maintained) the layer depth (relative to Examples 1 and Comparative Example BB). In addition, Examples 2-3 improved the compression stress (relative to Comparative Example AA).

[0224] Table 1: Processing Conditions and Properties of Examples 1-3 and Comparative Examples AA-BB (Composition 1 with 80 μm Thickness)

[0225]

[0226] Table 2: Processing Conditions and Properties of Examples 4-6 and Comparative Examples CC-DD (Composition 2 with 80 μm Thickness)

[0227]

[0228] Table 2 presents the results for Composition 2 (Examples 4 - 6 and Comparative Examples CC - DD). Comparing Example 4 with Comparative Example CC, further addition of K2CO3 at 420 °C decreased the compression and layer depth (relative to Comparative Example CC). The molten salt solutions for Comparative Example DD and Examples 5 - 6 were maintained at 380 °C instead of 420 °C. As confirmed by Comparative Example DD, longer chemical strengthening treatment (69 minutes vs. 30 minutes) at a lower temperature (380 °C vs. 420 °C) can achieve higher compression stress with a reduced layer depth. As discussed above, it is believed that the lower molten salt solution temperature improves the properties of the substrate by preventing stress relaxation and by providing more controlled and uniform compressive stress on the substrate. Examples 5 - 6 added a second potassium salt. For Example 6, addition of K2CO3 improved both the compression stress and layer depth (relative to Example 4), and also improved the compression stress (relative to Comparative Examples CC - DD). However, addition of K3PO4 increased the layer depth but decreased the compression stress (relative to Example 4) (and had properties roughly the same as Comparative Example DD). Thus, addition of K3PO4 did not improve the properties of Composition 2 (Example 5 compared to Comparative Example DD, although it did improve the compression stress of Composition 1), while K2CO3 improved the compression stress (and layer depth) for both Composition 1 (Example 3 compared to Comparative Example BB) and Composition 2 (Example 6 compared to Comparative Example DD).

[0229] Tables 3 - 4 and Figures 19 - 20 present the processing conditions and properties for Examples 7 - 20. In Figures 19 - 20 , the vertical axis 1903 or 2003 (e.g., y - axis) corresponds to the compression stress in MPa, and the horizontal axis 1901 or 2001 (e.g., x - axis) corresponds to the weight % of K2CO3 in the molten salt bath.

[0230] Table 3 and Figure 19 present the results for Composition 2 with a substrate thickness of 30 μm. Curve 1907 from left to right corresponds to Comparative Example EE and Examples 7 - 9, which were chemically strengthened at 400 °C for 12 minutes. As shown, for Example 10 with 5 weight % K2CO3, a maximum compression stress of 975 MPa in Curve 1907 was unexpectedly obtained (about 4% or more greater than Comparative Example EE). Based on this result, it is expected that adding about 2 weight % to about 5 weight % (e.g., about 2.5 weight % to about 5.0 weight %) K2CO3 to the molten salt bath will also exhibit an unexpected increase in compression stress (when chemically strengthening a substrate with a thickness less than 50 μm (e.g., about 10 μm to about 50 μm or about 10 μm to about 30 μm) at 400 °C).

[0231] Curve 1909 corresponds from left to right to Comparative Example FF and Examples 10 - 12, which were chemically strengthened at 380 °C for 18 minutes. As shown, for a K2CO3 content of 10 wt% or higher (e.g., 12 wt% or higher or less than 15 wt%), Curve 1909 (380 °C) is higher than Curve 1907 (400 °C). As discussed above, performing chemical strengthening at a lower temperature (e.g., 380 °C instead of 400 °C) achieved the same or greater compressive stress with an additional duration (e.g., 18 minutes instead of 12 minutes). For Curve 1909, for 10 wt% K2CO3 (Example 11), a maximum compressive stress of 984 MPa was unexpectedly observed, although 5 wt% K2CO3 (Example 10) also had a high compressive stress (e.g., about 980 MPa or greater). Based on this result, it is expected that adding about 2 wt% to about 12 wt% (e.g., about 2.5 wt% to about 12 wt%, about 5 wt% to about 12 wt%, or about 8 wt% to about 12 wt%) K2CO3 to the molten salt bath will also exhibit an unexpected increase in compressive stress (when chemically strengthening a substrate with a thickness of less than 50 μm (e.g., about 10 μm to about 50 μm or about 10 μm to about 30 μm) at 380 °C). Figure 19 There is also shown a difference 1917 between the compressive stress of Comparative Example EE (line 1905), which is about 50 MPa (i.e., 47 MPa), and the compressive stress of Example 11 (line 1915), which corresponds to an increase in compressive stress of about 5% or greater from Comparative Example EE to Example 11.

[0232] As shown in Table 3 (but not plotted in Figure 19 ), Example 13 corresponds to Example 11 without silicic acid, and Example 13 still exhibits an increase in compressive stress (relative to Comparative Example EE, but not relative to Comparative Example FF or Example 11). Table 3 also shows the pH measured for a solution prepared by diluting 5 g of the molten salt solution (cooled to ambient temperature) in 100 g of deionized water using the criteria discussed above. As shown, the pH of pure KNO3 (Comparative Example EE) is 7.51, which is approximately neutral. In contrast, the pH of 10 wt% K2CO3 and 90 wt% KNO3 (Examples 11 and 13) is about 11. The pH of the other molten salt baths was not measured. As discussed above, it is believed that the increase in pH for Examples 11 and 13 (relative to Comparative Example EE) can improve the strength and / or foldability of the resulting chemically strengthened foldable substrate, for example, by selectively etching inherent defects in the foldable substrate (which might otherwise be amplified due to the chemical strengthening process).

[0233] As shown in Table 3 (but not drawn), Examples 73 - 74 used lower concentrations (2.5 wt%) of the second potassium salts (K2CO3 and K2SO4 respectively). At 2.5 wt%, K2CO3 (Example 73) produced greater compressive stress and layer depth compared to K2SO4. Comparing 2.5 wt% K2CO3 (Example 73) with 5.0 wt% K2CO3 (Example 10), the compressive stress and layer depth were substantially the same. This confirmed that the concentration of K2CO3 could be reduced from 5 wt% to 2.5 wt% without negatively affecting the stress-related properties of the resulting article.

[0234] Table 3: Processing Conditions and Properties of Examples 7 - 13 and 73 - 74 and Comparative Examples EE - FF (Composition 2 with 30 μm Thickness)

[0235]

[0236]

[0237] * = pH measured by dissolving 5 grams of the molten salt solution cooled to ambient temperature in 100 grams of deionized water -- = not measured

[0238] Table 4: Processing Conditions and Properties of Examples 14 - 20 and Comparative Examples GG - HH (Composition 2 with 75 μm Thickness)

[0239]

[0240]

[0241] Table 4 and Figure 20 presents the results for Composition 2 with a substrate thickness of 75 μm (instead of 30 μm discussed above in Table 3 and Figure 19 ). Curve 2007 corresponds from left to right to Comparative Example GG and Examples 14 - 16, which were chemically strengthened at 400 °C for 12 minutes. As shown, for Example 14 with 5 wt% K2CO3, a maximum compressive stress of 1123 MPa in Curve 2007 was unexpectedly obtained (about 5% or more greater than Comparative Example EE, i.e., 4.75%). Example 15 also exhibited a compressive stress of approximately 1120 MPa. Based on this result, it is expected that adding about 2 wt% to about 12 wt% (e.g., about 2.5 wt% to about 12 wt%, about 5 wt% to about 12 wt%, or even about 2.5 wt% to about 5.0 wt%) K2CO3 to the molten salt bath will also exhibit an unexpected increase in compressive stress (when chemically strengthening a substrate with a thickness greater than 50 μm (e.g., about 50 μm to about 100 μm or about 50 μm to about 90 μm) at 400 °C).

[0242] Curve 2009 corresponds to Comparative Example HH and Examples 17 - 19 from left to right, which were chemically strengthened at 380 °C for 18 minutes. As shown, for a K2CO3 content of approximately 10 wt% (e.g., from about 8 wt% to about 12 wt%), Curve 2009 (380 °C) is higher than Curve 2007 (400 °C). This is different from Figure 19 the trend observed for the thinner substrates in Table 3. For Curve 2009, a maximum compressive stress of 1131 MPa was unexpectedly observed for 10 wt% K2CO3 (Example 18). Based on this result, it is expected that adding about 5 wt% to about 12 wt% (e.g., from about 8 wt% to about 12 wt%) K2CO3 to the molten salt bath will also exhibit an unexpected increase in compressive stress (when chemically strengthening substrates with a thickness greater than 50 μm (e.g., from about 50 μm to about 100 μm or from about 50 μm to about 90 μm) at 380 °C). Figure 20 There is also shown a difference 2017 between the compressive stress of Comparative Example GG (line 2005) and that of Example 18 (line 2005) of about 50 MPa or greater (e.g., about 60 MPa or greater, 59 MPa), which corresponds to an increase in compressive stress of about 5% or greater (i.e., 5.5%) from Comparative Example GG to Example 18.

[0243] As shown in Table 4 (but not plotted in Figure 20 ), Example 20 corresponds to Example 18 without silica, and Example 20 still exhibits an increase in compressive stress (relative to Comparative Examples GG - HH, but not relative to Example 18). This implies that thinner substrates (Table 3) are more sensitive to the silica content, while thicker substrates (Table 4) are less sensitive.

[0244] Examples 1 - 20 and Comparative Examples AA - HH were cooled relatively rapidly in air (e.g., quenched) before washing in deionized water; however, it is not always possible to cool the substrates in an industrial environment, especially when the molten salt bath contains several tons and exhibits significant thermal mass. Although not shown, residual molten salt deposits and / or optical deformations were observed on substrates cooled in air under industrial conditions (where it is believed the cooling rate is slower). Therefore, controlled cooling conditions are described in Tables 5 - 6.

[0245] Table 5-6 presents the processing conditions and properties of Examples 21-28. In addition to the chemical strengthening detailed in Table 5-6, Examples 21-28 were also processed as follows: The substrate was removed from the molten salt solution (380 °C or 420 °C) and transferred to a cooling chamber (which was initially physically located above the molten salt solution for 5 minutes to allow the residual molten salt bath to drip back into the molten salt bath from the substrate when the substrate was transferred to the cooling chamber), and held at 285 °C for 5 minutes, after which it was cooled from an initial temperature of approximately 270 °C to a final temperature of approximately 70 °C (an approximately linear cooling profile at a cooling rate of approximately 4 °C / minute), and then washed in a deionized water bath and cooled to ambient temperature.

[0246] Table 5 presents the results for Composition 1 with a thickness of 75 μm (and having undergone the cooling treatment described in the previous paragraph). As shown, the molten salt solutions with 5 wt% K2CO3 (both with and without silicic acid, Examples 22-24) exhibit an increase in compressive stress of approximately 5% or higher (e.g., 4.8% or higher for Examples 22-24), and chemical strengthening with 380 °C K2CO3 confirmed an increase in compressive stress of approximately 7% or more (Examples 22 and 24) relative to Example 21.

[0247] Table 5: Processing Conditions and Properties of Examples 21-24 (75-μm-thick Composition 1) with Cooling Treatment

[0248]

[0249]

[0250] Table 6: Processing Conditions and Properties of Examples 25-28 (75-μm-thick Composition 2) with Cooling Treatment

[0251]

[0252] Table 6 presents the results for Composition 2 with a thickness of 75 μm (and with the cooling treatment described above). As shown, molten salt solutions with 5 wt% K2CO3 (both with and without silicic acid, Examples 26 - 28) exhibit an increase in compressive stress, with a chemical strengthening of K2CO3 at 380 °C confirming an increase in compressive stress of about 3.5% or more (Examples 26 and 28), and Example 28 showing an increase in compressive stress of about 5% or more (i.e., 6.5%) relative to Example 25. Additionally, although not shown, visual inspection of Examples 21 - 28 with the naked eye did not detect any residue or optical deformation from the molten salt solutions. Examples 21 - 28 (Tables 5 - 6) confirm that the controlled cooling conditions did not result in optical deformation (for substrate thicknesses of 50 μm or greater), and the addition of K2CO3 (e.g., about 2 wt% to about 12 wt%, about 2 wt% to about 5 wt%, or about 2.5 wt% to about 5.0 wt%) still produced an increase in compressive stress (especially at temperatures less than 400 °C).

[0253] Table 7 presents the processing conditions and properties for Examples 29 - 39, which explored the cooling treatment (in combination with a second potassium salt) for thinner (30 μm thickness) composition substrates. Comprising Figures 26A - 26C to convey the level of deformation recorded in the "Visual Inspection" column of Table 7. In Figures 26A - 26C , the outline of the fluorescent tube light reflected from the substrate is schematically shown. Figure 26A Substrate 2601 with "slight deformation" is shown, where the profiles 2603 and 2605 are relatively smooth, with little to no local deviation of the profile relative to the general shape of the profile, which is the target condition. Figure 26B Substrate 2611 with "moderate deformation" is shown, where the profiles 2613, 2615, and 1617 show undulations (e.g., undulation 2614), which are significant local deformations in the general shape of the profile (e.g., compared to the smoothness of the profiles 2603 and 2605 in Figure 26A ), and other profiles (e.g., profile 219) may be relatively unaffected. Figure 26C Substrate 2621 with "high deformation" is shown, where the profiles 2623, 2625, 2627, and 2629 exhibit extreme waviness, e.g., the profiles appear discontinuous (or nearly discontinuous) and / or the local shape of the profile has little to no similarity to the shape of less deformed substrates (e.g., compared to Figures 26A - 26B ). Although Figure 26A the angle of observation of the substrate in Figures 26B - 26C is different from the angle of observation of

[0254] In Table 7, the compressive stress differences are relative to the properties of Example 29. In Table 7, Examples 32, 34 - 36, and 38 exhibit high deformation. Additionally, Examples 32, 34 - 36, and 38 exhibit waviness in the surface, which is observed when the surface is viewed at an oblique angle. It is noted that Examples 34 and 36 with high deformation are cooled in ambient air, which is relatively slow (e.g., much less than 4 °C per minute) under the industrial conditions used (for Examples 29 - 39). Similarly, Example 35 with high deformation is cooled at a rate of less than 4 °C / min (e.g., less than 3 °C / min). The high deformation combined with waviness observed in Example 32 implies that the chemical strengthening was too rapid (e.g., reaching a high temperature (400 °C for 8 minutes) in too short a time for a thickness of less than 50 μm) to achieve a uniform compressive stress layer. Examples 30 and 39 exhibit medium deformation. Examples 29, 31, 33, 37, and 39 exhibit slight deformation. It should be noted that Examples 29 - 31, 33, and 37 with medium or slight deformation have a cooling rate of 4 °C / min or greater. Examples 31, 33, and 37 imply that a cooling treatment that rapidly decreases the temperature by about 100 °C or more (e.g., about 120 °C or more) relative to the temperature of the molten salt solution is associated with reduced deformation. Comparing Examples 21 - 28 with a thickness of 75 μm in Tables 5 - 6, Examples 29 - 39 in Table 7 confirm that thinner substrates (e.g., thicknesses of about 50 μm or less, about 10 μm to about 50 μm, or about 10 μm to about 30 μm) are much more sensitive to the conditions of the cooling treatment. As discussed above, it is believed that small differences (e.g., non - uniformities) in the compressive stress established in thinner substrates can lead to optical deformation. Thus, in addition to decreasing the temperature of the cooling chamber at about 4 °C / min or greater (e.g., about 4 °C / min to about 20 °C / min), rapidly reducing the temperature (e.g., reducing by about 100 °C or more or about 120 °C or more) when removing the substrate from the molten salt solution can reduce residual chemical strengthening.

[0255] Table 7: Processing Conditions and Properties of Examples 29 - 39 (Composition 1, 30 μm thick) with Cooling Treatments

[0256]

[0257]

[0258]

[0259]

[0260] Figures 21 - 22Table 8-9 presents the performance (survival rate % - % of samples withstood) of Examples 40 - 47 and Comparative Examples II - LL for various parallel plate spacings. For Examples 40 - 47 and Comparative Examples II - LL, a sample size of 30 pieces was used for testing. In Figures 21 - 22 , the vertical axis 2103 or 2203 (e.g., the y-axis) corresponds to the % of samples that withstood the parallel plate spacing (i.e., % survival rate), and the horizontal axis 2101 or 2202 (e.g., the x-axis) corresponds to the parallel plate spacing at which the test was conducted (in mm). Note that the horizontal axis 2101 or 2202 is not linear; rather, the axis markings correspond to different spacings at which the samples were measured, which are roughly logarithmically spaced (but not exactly).

[0261] Table 8 presents the processing conditions and properties of Examples 40 - 43 and Comparative Examples II - JJ with Composition 1 and a substrate thickness of 70 μm (for non-industrial conditions, rapid cooling in air). Table 8 presents the % survival rate (i.e., % of samples that withstood) at parallel plate spacings of 5 mm and 3 mm, highlighting the trend shown in Figure 21 with additional points (e.g., a total of approximately a dozen different parallel plate spacings). In Figure 21 curves 2105 and 2107 correspond to Comparative Examples II - JJ, respectively; while curves 2109, 2111, 2113, and 2115 correspond to Examples 40 - 43, respectively. Unless otherwise stated, the etching of the examples involves a 2 wt% HF (non-buffered) solution. As shown, curve 2107 (Comparative Example JJ, with 0% of CS etched away) has 0% of the samples withstanding even a 5 mm parallel plate spacing. Curve 2105 (Comparative Example II, with 18% of CS etched away) has 100% of the samples withstanding a 5 mm parallel plate spacing, but 3% of the samples withstanding a 3 mm parallel plate spacing. Examples 40 - 43, which were chemically strengthened with 5 wt% K2CO3 and had different amounts of compressive stress (CS) removed by etching, had 90% or more (e.g., 95% or more, about 97% or more) of the samples withstanding a 5 mm parallel plate spacing. Specifically, Examples 42 - 43 (where the amount of compressive stress removed in Example 42 was approximately equal to that of Comparative Example II) had 10% or more (e.g., about 20% or more) of the samples withstanding a 3 mm parallel plate spacing, which is much higher than that observed for Comparative Example II. Thus, adding 5 wt% K2CO3 can improve the foldability of the substrate, as confirmed by the parallel plate performance (e.g., for the case of 3 mm with a substrate thickness of 70 μm (about 50 μm to about 100 μm or about 50 μm to about 90 μm)).

[0262] Table 8: Processing Conditions and Properties of Examples 40 - 43 and Comparative Examples II - JJ (Composition 1 with a Thickness of 70 μm)

[0263]

[0264]

[0265] Table 9: Processing Conditions and Properties of Examples 44 - 47 and Comparative Examples KK - LL (Composition 2 with 70 - μm Thickness)

[0266]

[0267]

[0268] Table 9 presents the processing conditions and properties of Examples 40 - 43 and Comparative Examples II - JJ with Composition 2 and a substrate thickness of 70 μm (for non - industrial conditions, rapid cooling in air). Table 9 presents the survival rate % (i.e., % of samples that withstood) at parallel - plate spacings of 5 mm and 3 mm, highlighting the trends shown with additional points (e.g., a total of approximately a dozen different parallel - plate spacings). Figure 22 as shown in Figure 22 where curves 2205 and 2207 correspond to Comparative Examples KK - LL, respectively; and curves 2209, 2211, 2213, and 2215 correspond to Examples 44 - 47, respectively. As shown, curve 2207 (Comparative Example LL, with 0% of CS etched away) has 0% of samples withstanding even a 5 - mm parallel - plate spacing. Curve 2105 (Comparative Example LL, with 18% of CS etched away) has 97% of samples withstanding a 5 - mm parallel - plate spacing and 60% of samples withstanding a 3 - mm parallel - plate spacing. Examples 44 - 47, which are chemically strengthened with 5 wt% K2CO3 and have different amounts of compressive stress (CS) etched away, have 90% or more (e.g., 95% or more, about 97% or more, or about 100% for Examples 45 and 47) of samples withstanding a 5 - mm parallel - plate spacing. Examples 46 - 47 have 10% or more (e.g., about 20% or more, about 30% or more, or about 40% or more) of samples withstanding a 3 - mm parallel - plate spacing. Example 47 has 63% of samples withstanding a 3 - mm parallel - plate spacing, which is much higher than that observed for Comparative Example KK. Thus, adding 5 wt% K2CO3 can maintain or improve the foldability of the substrate, as confirmed by the parallel - plate performance (e.g., for the case of 3 mm with a substrate thickness of 70 μm (about 50 μm to about 100 μm or about 50 μm to about 90 μm)).

[0269] Figures 23 - 24Table 10-11 presents the performance (survival rate %, % of samples withstood) of Examples 47-52 and Comparative Example MM-PP for various parallel plate spacings. For Examples 48-53 and Comparative Example MM-PP, a sample size of 30 pieces was used for testing. In Figures 23 - 24 , the vertical axis 2303 or 2403 (e.g., the y-axis) corresponds to the % of samples that withstood the parallel plate spacing (i.e., % survival rate), and the horizontal axis 2301 or 2402 (e.g., the x-axis) corresponds to the parallel plate spacing tested (in mm). Note that the horizontal axis 2301 or 2402 is linear (corresponding to measurements for every 0.2 mm decrease in parallel plate spacing, which is different from the Figures 21 - 22 scale used).

[0270] Table 10 presents the processing conditions and properties of Examples 48-50 and Comparative Example MM-NN with Composition 1 and a substrate thickness of 30 μm (for non-industrial conditions, rapid cooling in air). Table 10 presents the % survival rate (i.e., % of samples that withstood) at parallel plate spacings of 2 mm and 1 mm, highlighting the trend shown in Figure 23 with additional points (e.g., a total of about seven different parallel plate spacings). In Figure 23 , curves 2305 and 2307 correspond to Comparative Example MM-NN, respectively; while curves 2309, 2311, 2313, and 2315 correspond to Examples 48-50, respectively. As shown, curve 2307 (Comparative Example NN, 0% of CS etched away) has 30% of the samples withstood a parallel plate spacing of 2 mm and 0% of the samples withstood a parallel plate spacing of 1 mm. Curve 2305 (Comparative Example MM, 18% of CS etched away) has 100% of the samples withstood a parallel plate spacing of 2 mm, but 10% of the samples withstood a parallel plate spacing of 1 mm. Examples 47-49, which were chemically strengthened with 5 wt% K2CO3 and had different amounts of compressive stress (CS) etched away, had 90% or more of the samples withstood a parallel plate spacing of 2 mm. Specifically, Example 50 had 95% or more (e.g., about 100%) of the samples withstood a parallel plate spacing of 2 mm and more than 10% (e.g., 15% or more or about 20% or more) of the samples withstood a parallel plate spacing of 1 mm, which is much higher than that observed for Comparative Example MM. Therefore, adding 5 wt% K2CO3 can improve or maintain the foldability of the substrate, as confirmed by the parallel plate performance (e.g., for the case of 1 mm with a substrate thickness of 30 μm (about 10 μm to about 50 μm or about 10 μm to about 30 μm)).

[0271] Table 10: Processing Conditions and Properties of Examples 48-50 and Comparative Example MM-NN (Composition 1 with a Thickness of 30 μm)

[0272]

[0273]

[0274] Table 11: Processing Conditions and Properties of Examples 51 - 53 and Comparative Examples OO - PP (Composition 2 with 30 μm Thickness)

[0275]

[0276] Table 11 presents the processing conditions and properties of Examples 51 - 53 and Comparative Examples OO - PP with Composition 2 and a substrate thickness of 30 μm (for non - industrial conditions, rapid cooling in air). Table 11 presents the survival rate % (i.e., % of samples that withstood) at parallel - plate spacings of 2 mm and 1 mm, highlighting the trends shown with additional points (e.g., a total of about seven different parallel - plate spacings). Figure 24 as shown in Figure 24 In, curves 2405 and 2407 correspond to Comparative Examples OO - PP, respectively; while curves 2409, 2411, 2413, and 2415 correspond to Examples 51 - 53, respectively. As shown, curve 2407 (Comparative Example PP, with 0% of CS etched away) has 60% of the samples withstanding a parallel - plate spacing of 2 mm and 0% of the samples withstanding a parallel - plate spacing of 1 mm. Curve 2405 (Comparative Example OO, with 18% of CS etched away) has 95% of the samples withstanding a parallel - plate spacing of 2 mm and 25% of the samples withstanding a parallel - plate spacing of 1 mm. Examples 51 - 53, which were chemically strengthened with 5 wt% K2CO3 and had different amounts of compressive stress (CS) etched away, have 90% or more of the samples withstanding a parallel - plate spacing of 2 mm. Specifically, Examples 52 - 53 have 95% or more (e.g., about 100%) of the samples withstanding a parallel - plate spacing of 2 mm. For Example 53, the lower survival rate % at a 1 - mm parallel - plate spacing is believed to be attributed to handling problems. Based on the results in Table 10 and the survival rate at 2 mm in Table 11, adding 5 wt% K2CO3 can improve or maintain the foldability of the substrate, as confirmed by the parallel - plate performance (e.g., for a substrate thickness of 30 μm (about 10 μm to about 50 μm or about 10 μm to about 30 μm)).

[0277] Table 12 presents the threshold pen-down heights of Example 3 with a substrate of Composition 1 and 80 μm thickness, and Comparative Examples AA and MM. In Table 12, the samples were not etched to isolate the effect of the molten salt solution on the impact resistance, which was evaluated by the pen-down test. As shown, Example 3 has a threshold pen-down height of 16.6 cm, which is 3.1 cm higher than Comparative Example MM (a 23% increase relatively) and 2 cm higher than Comparative Example AA (a 14% increase relatively). Thus, adding 5 wt% K2CO3 can increase the impact resistance of the substrate, as measured by the pen-down threshold height.

[0278] Table 12: Threshold Pen-down Heights of Example 3 and Comparative Examples AA and MM (Composition 1 and 80 μm Thickness)

[0279]

[0280] Table 13: Pen-down Heights of Example 6 and Comparative Examples CC and NN (Composition 2 and 80 μm Thickness)

[0281]

[0282] Table 13 presents the threshold pen-down heights of Example 6 with a substrate of Composition 2 and 80 μm thickness, and Comparative Examples CC and NN. In Table 13, the samples were not etched to isolate the effect of the molten salt solution on the impact resistance, which was evaluated by the pen-down test. As shown, Example 6 has a threshold pen-down height of 21.1 cm, which is 12.8 cm higher than Comparative Example NN (a 152% increase relatively) and 4.9 cm higher than Comparative Example CC (a 30% increase relatively). Thus, adding 5 wt% K2CO3 can increase the impact resistance of the substrate, as measured by the pen-down threshold height. Specifically, Example 6 can withstand a pen-down height of 20 cm or greater.

[0283] For the remaining examples, unless otherwise stated, the examples (and comparative examples) were chemically strengthened in 100 wt% KNO3 maintained at 400 °C for 12 minutes. Additionally, unless otherwise stated, the etching treatment was carried out at 22 °C.

[0284] Table 14 presents the etchant compositions and conditions for Examples 54 - 56 and Comparative Example SS. Comparative Example SS is an unbuffered HF solution, while Examples 54 - 56 are buffered HF solutions due to the addition of NH4F. As shown, the buffered HF solutions (Examples 54 - 56) have a higher pH compared to Comparative Example SS. However, as shown in the "Visual Inspection" column, these samples have various problems. Examples 54 and Comparative Example SS have a blue color, which disappears when the HF concentration in Examples 55 - 56 drops to less than 2 wt% HF. Example 55 exhibits perceptible warping. Example 56 is cloudy, which is attributed to the formation of precipitates during patterned etching, likely due to its higher NH4F concentration.

[0285] Table 14: Etching Conditions and Properties of Examples 54 - 56 and Comparative Example SS (Composition 2 with 30 - μm Thickness)

[0286]

[0287]

[0288] Therefore, a study of the variation of etching conditions was conducted on Examples 57 - 61 shown in Table 15 (again presenting Example 56 and the Comparative Example for comparison). For Examples 57 - 58, the substrate was cleaned midway during etching (after 50 seconds), then etched for the remaining time (another 50 seconds), and then cleaned again; while Examples 56 and 59 - 61 were only cleaned after the entire etching time. In Example 57, deionized water (DI) was used for the midway cleaning, which reduced the haze but also made the surface have slightly wrinkled. Example 58 used HNO3 instead of DI for the midway cleaning during etching, but Example 58 also exhibited low haze and low wrinkling. It is believed that the following situations exist: (1) multiple substrate transfers between the etchant and the cleaning solution cause the residual etchant on some parts of the surface to continue etching while other parts do not; (2) some precipitates still accumulate on the surface effectively masking the progress of etching; or (3) both of these situations. In addition, although the total etching time is the same (50 seconds multiplied by 2 cycles = 100 seconds), Examples 57 - 58 removed more compressive stress compared to Example 56. Conversely, Examples 59 - 61 used a shorter overall etching time to reduce the ability of the precipitates formed on the surface to mask the etching process. In Example 59, the substrate was cleaned with DI; in Example 60, the substrate was cleaned with oxalic acid; and in Example 61, the substrate was cleaned with nitric acid. In addition, Examples 59 - 61 exhibited perceptible wrinkling on the surface.

[0289] Table 15: Etching Conditions and Properties of Examples 56 - 61 and Comparative Example SS (Composition 2 with 30 - μm Thickness)

[0290]

[0291]

[0292] Table 16 further explores modifications to the etching conditions and to the buffered HF compositions of Examples 62 - 66 (repeating Example 56 for comparison). In Examples 62 - 63, the etching temperature was increased, which decreased the haze, but there was still perceivable haze and some surface wrinkling (Example 63 was additionally warped). Examples 64 - 66 decreased the etchant concentration (i.e., halved relative to Example 56 concentration), which had no perceivable defects to the naked eye. The same was true for etching times of 100 seconds to 200 seconds (studied) and temperatures of 22 °C to 30 °C (studied). Additionally, as noted in Table 16, Examples 64 - 66 had an etching rate of about 1.0 μm / minute or less, while Examples 56 and 62 - 63 had higher etching rates. Thus, an etching rate of about 1.0 μm / minute or less unexpectedly provided an etched substrate that did not have visually visible defects. It was noted that this was only an issue for thinner substrates (e.g., about 50 μm or less, about 10 μm to about 50 μm, or about 10 μm to about 30 μm) and certain compositions (e.g., Composition 2, but not necessarily Composition 1).

[0293] Table 16: Etching Conditions and Properties for Examples 56 and 62 - 66 (Composition 2 at 30 μm Thickness)

[0294]

[0295] Table 17 implements the etching compositions and cleaning conditions for Examples 65 and 67 - 68 and Comparative Example TT (all of which have a substrate thickness of 30 μm). Comparative Example TT has Composition 1 and it is confirmed that the blue color seen in Composition 2 (Comparative Example SS) is not seen for Composition 1. For Example 67, the substrate is cleaned twice (evenly spaced) during the etching process and again at the end (effectively three etching - cleaning cycles). Despite having a lower etchant concentration (Example 67 compared to Example 62), Example 67 has perceivable haze and surface wrinkles. This implies that some non - uniform etching occurs when the substrate is transferred from the etching solution to the DI rinse. Example 68 is the same as Example 67, but the rinse solution is 5 wt% nitric acid instead of DI, but Example 68 also has perceivable wrinkles on the surface. Despite the wrinkles seen in Examples 67 - 68, both Examples 67 - 68 have higher survival rates (68% and 23% respectively) compared to Comparative Example TT for a 1 - mm parallel - plate spacing. However, Example 65 (discussed above) can have more than 20% (e.g., about 30% or more, about 40% or more) of the samples withstand a 1 - mm parallel - plate spacing without any visually visible defects.

[0296] Table 17: Processing Conditions and Properties of Examples 65 and 67 - 68 and Comparative Example TT (30 - μm Thickness)

[0297]

[0298] Table 18: Processing Conditions and Properties of Examples 70 - 73 and Comparative Examples AA and SS (Composition 2 with 30 - μm Thickness)

[0299]

[0300] Table 18 and Figure 25 presents the properties of Examples 69 - 72 and Comparative Examples AA and SS. As noted above, Examples 69 - 72 and Comparative Examples AA and SS were chemically strengthened in 100 wt% KNO3 maintained at 400 °C for 12 minutes before rapid cooling (instead of the industrial setting). Table 18 presents the composition of the etching solution and the time the etching solution was in contact with the substrate. In Figure 25 , the vertical axis 2503 (e.g., the y - axis) presents the survival rate (i.e., the percentage of samples that withstand a specific parallel - plate spacing), while the horizontal axis 2501 (e.g., the x - axis) presents the parallel - plate spacing (in mm) at which the tests were conducted on a linear scale. In Figure 25 , the curves 2505 and 2515 correspond to Comparative Examples AA and SS respectively. The curves 2507, 2509, 2511, and 2513 correspond to Examples 69 - 72 respectively. As Figure 18 andFigure 25 As shown, in Comparative Example AA, 35% of the samples withstood a parallel plate spacing of 2 mm, but 0% withstood a parallel plate spacing of 1 mm. Comparative Example SS performed better, with 93% of the samples withstanding a parallel plate spacing of 2 mm and 15% of the samples withstanding a parallel plate spacing of 1 mm.

[0301] Examples 69 - 72 used the lower concentration buffered HF solution of Examples 64 - 65 with different treatment times, increasing from 50 seconds to 175 seconds from Example 69 to Example 72. As shown, all of Examples 69 - 72 had over 90% (e.g., about 95% or more) of the samples withstand a parallel plate spacing of 2 mm. Examples 70 - 72 had over 20% of the samples withstand a parallel plate spacing of 1 mm, which was better than Comparative Examples AA and SS. Additionally, Examples 71 - 72 had about 30% or more (e.g., about 40% or more or about 50% or more) of the samples withstand a parallel plate spacing of 1 mm, which was more than twice the proportion of Comparative Example SS. This confirmed that the lower concentration buffered HF etch solution (e.g., treatment time less than 3.5 minutes and etch rate about 1.0 μm / min or lower) provided an unexpected improvement in foldability and reliability, as evidenced by the increased survival rate at a 1 mm parallel plate spacing.

[0302] The above observations can be combined to provide a chemically strengthened substrate (e.g., a foldable substrate) and a method for chemically strengthening a substrate (e.g., for manufacturing it). Providing a glass - based substrate and / or a ceramic - based substrate can provide good dimensional stability, can reduce the incidence of mechanical instability, and / or can provide good impact resistance and puncture resistance. The methods of aspects of the present disclosure can increase the drop height that a foldable device and / or a foldable substrate can withstand, can increase the survival rate of the substrate folded to parallel plate spacings of 5 mm, 3 mm, 2 mm, and / or 1 mm, and / or can increase the foldability of the substrate.

[0303] In an aspect, a substrate can be chemically strengthened with a molten salt solution that includes two anions associated with at least a first potassium salt and a second potassium salt. Providing multiple (i.e., two or more) potassium atoms per anion for the first potassium salt can increase the effective concentration and / or activity of potassium in the molten salt solution, which can contribute to an increase in the maximum compressive stress in the resulting chemically strengthened foldable substrate. Providing a pKa of about 9 or greater and / or a molten salt solution pH of about 9 to 12 for the first potassium salt in the molten salt solution can improve the strength and / or foldability of the resulting chemically strengthened foldable substrate, for example, by selectively etching inherent flaws in the foldable substrate (which might otherwise be amplified due to the chemical strengthening process). As discussed herein with reference to the examples, potassium carbonate (K2CO3) has a more pronounced and unexpected increase in compressive stress compared to other components in the molten salt solution. Further, without being bound by theory, it is believed that the carbonate anion can contribute to the precipitation of other cations (e.g., lithium, sodium) exchanged from the foldable substrate, which can increase the lifetime of the molten salt solution (e.g., by removing components from the solution phase that would otherwise "poison" the molten salt solution). As confirmed by the examples discussed herein, providing a first temperature of the molten salt solution below 400 °C can increase the maximum compressive stress established for a predetermined layer depth and / or compressive depth. Further, for some of the molten salt solutions discussed herein, a temperature of 350 °C or higher can be used to ensure salt melting.

[0304] It has been observed that a foldable substrate having a thickness of about 50 μm or less (e.g., about 10 μm to about 50 μm or about 10 μm to about 30 μm) is unexpectedly sensitive to events that occur after the foldable substrate is removed from a molten salt solution. For these thin foldable substrates, even relatively small differences in compressive stress on their surfaces can cause rippling and / or warping, which can produce optical deformations that are visually visible to the user of a consumer electronic product that may incorporate the foldable substrate. Thus, a controlled temperature in the cooling chamber can contribute to relatively uniform compressive stress on the surface of the foldable substrate. Additionally, providing an initial temperature in the cooling chamber of 180 °C or higher (e.g., 200 °C or higher or 220 °C or higher) can facilitate removal of the remaining portion of the molten salt solution before it solidifies. Without wishing to be bound by theory, the first potassium salt can have a higher melting temperature compared to the second potassium salt, which means that incorporating the first potassium salt in the molten salt solution can increase the viscosity of the molten salt solution and / or can cause the molten salt solution to solidify at a higher temperature compared to a molten salt solution without the first potassium salt. Thus, when the molten salt solution contains the first potassium salt, it can be particularly useful to allow the remaining portion of the molten salt solution on the foldable substrate after the foldable substrate is removed from the molten salt solution. Reducing the temperature of the cooling chamber to a final temperature of about 100 °C or lower (e.g., about 25 °C to about 100 °C or about 60 °C to about 90 °C) can enable subsequent treatment of the foldable substrate with an aqueous solution (e.g., relatively quickly or immediately) (e.g., rinsing with water or an alkaline detergent solution, contacting with an aqueous acidic solution). Providing a cooling rate of about 4 °C / minute to about 20 °C / minute can cause the temperature of the cooling chamber (and the foldable substrate) to drop rapidly while maintaining a relatively consistent temperature throughout the cooling chamber (and / or the foldable substrate), e.g., thereby producing relatively uniform compressive stress on the surface of the foldable substrate.

[0305] Providing an etching rate of about 1 μm / minute or less (e.g., about 1.0 μm / minute or less) can facilitate substantially uniform material removal from the surface(s) of the foldable substrate. As discussed above, a foldable substrate having a thickness of about 50 μm or less (e.g., about 10 μm to about 50 μm or about 10 μm to about 30 μm) is quite sensitive to differences in compressive stress and thickness variations on its surface. Thus, providing an etching rate of about 1 μm / minute can remove a relatively uniform thickness and compressive stress portion from the surface(s), thereby reducing the likelihood of rippling and / or warping that can produce optical deformations that are visually visible to the user of a consumer electronic product that may incorporate the foldable substrate. Without wishing to be bound by theory, providing an acidic solution at a lower temperature (e.g., about 20 °C to about 40 °C or about 20 °C to about 25 °C) can reduce the concentration of the SiF6 - anion, since H2SiF6 dissociates into 2H + + and SiF6- The reaction is endothermic. Reducing the concentration of the SiF6 - anion is associated with a decrease in the deposition (e.g., redeposition) of silica or silica-like materials on the surface, which otherwise would result in a change in the thickness and / or compressive stress on the surface of the foldable substrate. Providing a higher pH (e.g., from about 3.5 to about 4.5, from about 3.6 to about 4.3, or from about 3.7 to about 4.0) decreases the etch rate, which can help produce relatively uniform compressive stress and thickness on the foldable substrate. Providing a total concentration of HF and NH4F of about 4.0 wt% or less, about 3.5 wt% or less, about 3.0 wt% or less, about 2.5 wt% or less, or about 2.0 wt% or less (e.g., from about 1.25 wt% to about 4.0 wt%, from about 1.3 wt% to about 3.5 wt%, from about 1.35 wt% to about 3.0 wt%, from about 1.4 wt% to about 2.5 wt%, from about 1.5 wt% to about 2.0 wt%) can provide relatively controlled and uniform etching of the foldable substrate and / or can reduce the deposition of materials (e.g., silica, silica-like materials, ammonium fluoride crystals) on the foldable substrate that would degrade the optical properties of the foldable substrate.

[0306] In an aspect, the substrate thickness of the substrate can be about 50 μm or thicker (e.g., about 50 μm to about 100 μm, about 50 μm to about 90 μm, or any corresponding sub-range therebetween as discussed above) and combined with one or more of the following properties: (1) the compression depth is about 10% to about 30%, about 16% to about 26%, or any corresponding sub-range therebetween as discussed above, based on the percentage of the substrate thickness; (2) the layer depth of potassium (e.g., the first layer depth and / or the second layer depth) ranges from about 3 μm to about 20 μm, about 10 μm to about 15 μm, or any corresponding sub-range as discussed above; and / or (3) the maximum compression stress (e.g., the first maximum compression stress and / or the second maximum compression stress) ranges can be about 650 MPa to about 1200 MPa, about 800 MPa to about 1100 MPa, about 850 MPa to about 1200 MPa, or any corresponding sub-range as discussed above. In an aspect, the substrate thickness can be about 50 μm or thinner (e.g., about 10 μm to about 50 μm, about 10 μm to about 30 μm, or any corresponding sub-range therebetween as discussed above) and combined with one or more of the following properties: (1) the compression depth is about 10% to about 30%, about 12% to about 19%, or any corresponding sub-range therebetween as discussed above, based on the percentage of the substrate thickness; (2) the layer depth of potassium ranges from about 3 μm to about 20 μm, about 5 μm to about 9 μm, or any corresponding sub-range as discussed above; and / or (3) the maximum compression stress (e.g., the first maximum compression stress and / or the second maximum compression stress) ranges can be about 650 MPa to about 1200 MPa, about 750 MPa to about 1100 MPa, about 750 MPa to about 1,000 MPa, or any corresponding sub-range as discussed above.

[0307] The directional terms used herein, such as up, down, left, right, front, back, top, bottom, are only with reference to the drawn figures and are not used to represent an absolute orientation.

[0308] It will be understood that the various aspects disclosed may relate to specific features, elements, or steps described in connection with a particular aspect. It will also be understood that, although specific features, elements, or steps are described in connection with one aspect, different aspects may be interchanged or combined with each other in various combinations or permutations not shown.

[0309] It should also be understood that the terms "the", "a", or "an" as used herein mean "at least one (a)", and should not be limited to "only one (a)" unless explicitly stated to the contrary. Thus, for example, reference to "a" component includes aspects having two or more such components unless otherwise explicitly stated in the text. Similarly, "plural" is intended to mean "more than one".

[0310] As used herein, the term "about" means that a quantity, size, formulation, parameter, and other variables and characteristics are not and need not be exact, but can be approximate and / or larger or smaller as needed, reflecting tolerances, conversion factors, rounding, measurement errors, and other factors known to those skilled in the art. In this document, a range can be expressed as starting from "about" another specific value and / or ending at "about" another specific value. When expressing such a range, an aspect includes starting from a specific value and / or ending at another specific value. Similarly, when using the antecedent "about" to indicate that a numerical value is approximate, it should be understood that the specific numerical value constitutes another aspect. Whether or not the numerical values or endpoints of the ranges in this specification state "about", the endpoints of the numerical values or ranges are intended to include two aspects: one modified by "about" and one not modified by "about". It should also be understood that each endpoint value of a range is meaningful both in relation to and independent of another endpoint value.

[0311] As used herein, the terms "substantially", "essentially" and their variations are intended to mean that the described feature is equivalent or approximately the same as the numerical value or description. For example, a "substantially flat" surface is intended to mean a flat or approximately flat surface. In addition, as defined above, "substantially similar" is intended to mean that two values are equal or approximately equal. In an aspect, "substantially similar" can mean that the numerical values differ from each other by within about 10%, for example, within about 5%, or within about 2%.

[0312] Unless otherwise stated, none of the methods described herein are intended to be understood as requiring their steps to be performed in a specific order. Thus, when method claims do not actually recite that their steps follow a certain order or when they are not otherwise specifically indicated in the claims or the specification to be limited to a specific order, no particular order is intended to be implied.

[0313] Although the transitional phrase "comprising" will be used to disclose the various features, elements or steps of a particular aspect, it should be understood that this implies alternative aspects that can be described by the transitional phrases "consisting of", "consisting essentially of". Thus, for example, the implicit alternative aspects of a device comprising A + B + C include the aspect where the device consists of A + B + C and the aspect where the device consists essentially of A + B + C. As used herein, unless otherwise specified, the terms "comprising" and "including" and their variations should be understood as synonyms and are open-ended.

[0314] The above aspects and the features of those aspects are exemplary and can be provided alone or in any combination with any one or more features of other aspects provided herein without departing from the scope of the present disclosure.

[0315] It will be apparent to those skilled in the art that various modifications and variations can be made to the present disclosure without departing from the scope and spirit of the present disclosure. Accordingly, the present disclosure covers modifications and variations of aspects herein, provided they fall within the scope of the appended claims and their equivalents.

Claims

1. A method for chemically strengthening a substrate, the substrate comprising a thickness of 10 micrometers to 100 micrometers defined between an existing first major surface and an existing second major surface opposite to the existing first major surface, the method comprising: The existing first major surface of the substrate is contacted with a molten salt solution maintained at a first temperature for a first time period, the molten salt solution comprising at least two anions associated with at least a first potassium salt and a second potassium salt, the concentration of the first potassium salt and the concentration of the second potassium salt being 2% by weight or greater of the molten salt solution, the first temperature being in the range of about 350° C. to about 400° C., and the first time period being in the range of about 10 minutes to about 90 minutes.

2. The method of claim 1, wherein: The first potassium salt includes two or more potassium atoms per anion, and the pKa of the potassium salt is 9 or greater, and the concentration of the first potassium salt ranges from about 2 wt % to about 12 wt % of the molten salt solution.

3. The method according to any one of claims 1 to 2, wherein: The first potassium salt is potassium carbonate K2CO3, and the concentration of the first potassium salt ranges from about 2 wt% to about 12 wt% of the molten salt solution.

4. The method according to any one of claims 1 to 3, wherein: The concentration of the first potassium salt ranges from about 2.5 wt % to about 5.0 wt %.

5. The method according to any one of claims 1 to 3, wherein: The concentration of the first potassium salt ranges from about 5 wt % to about 12 wt %.

6. The method according to any one of claims 2 to 5, wherein: The molten salt solution also includes 0 wt % to 5 wt % of a third potassium salt associated with a third anion, the third anion being different from anions associated with the first potassium salt and the second potassium salt, and the third potassium salt includes two or more potassium atoms per anion.

7. The method of claim 6, wherein: The third potassium salt includes potassium sulfate, K2SO4, and the concentration of the third potassium salt is about 0.5 wt% to about 5 wt%.

8. The method according to any one of claims 1 to 7, wherein: The second potassium salt is potassium nitrate KNO3, and the concentration of the second potassium salt ranges from about 50 wt% to about 98 wt% of the molten salt solution.

9. The method according to any one of claims 1 to 7, wherein: The pH range of the molten salt solution at the first temperature is about 9-12.

10. The method according to any one of claims 1 to 9, wherein: The presence of the first potassium salt increases the compressive stress imparted by the existing first major surface in contact with the molten salt solution by about 5% or more relative to immersing the substrate in a comparative molten salt solution having the same composition as the molten salt solution without the first potassium salt.

11. The method according to any one of claims 1 to 10, wherein: The thickness of the substrate ranges from about 15 μm to about 50 μm.

12. The method according to any one of claims 1 to 11, further comprising, after the first main surface has been contacted with the molten salt solution: The substrate is transferred from the molten salt solution to a cooling chamber, and the temperature of the cooling chamber is reduced from an initial temperature to a final temperature at a cooling rate of about 4°C / min to about 20°C / min, the initial temperature ranges from about 180°C to about 300°C, and the final temperature ranges from about 25°C to about 100°C.

13. The method of claim 12, wherein: The initial temperature ranges from about 180°C to about 220°C.

14. The method according to any one of claims 12 to 13, further comprising: After the cooling chamber reaches the final temperature, the substrate is rinsed with water, an alkaline detergent solution, or a combination thereof.

15. The method according to any one of claims 1 to 14, wherein: After the first major surface has been contacted with the molten salt solution, the substrate has an initial maximum compressive stress of about 800 megapascals to about 1500 megapascals.

16. The method of any one of claims 1 to 15, further comprising: contacting the existing first major surface with an acidic solution for a second period of time to remove the outer layer from the existing first major surface to form a new first major surface, the acidic solution having a pH in the range of 3.5 to 4.5, and the second period of time being about 10 seconds to about 3.5 minutes; and then The new first major surface is cleaned with water.

17. A method of chemically strengthening a substrate, the substrate comprising a thickness defined between an existing first major surface and an existing second major surface opposite the existing first major surface, the method comprising: chemically strengthening the substrate in a molten salt solution maintained at a first temperature for a first time period, the first temperature being in a range of about 350° C. to about 400° C., and the first time period being in a range of about 10 minutes to about 90 minutes; contacting the existing first major surface with an acidic solution for a second period of time to remove the outer layer from the existing first major surface to form a new first major surface, the acidic solution having a pH in the range of 3.5 to 4.5, and the second period of time being about 10 seconds to about 3.5 minutes; and then The new first major surface is cleaned with water.

18. The method according to any one of claims 16 to 17, wherein: The second temperature ranges from about 20°C to about 25°C.

19. The method according to any one of claims 16 to 18, wherein: In terms of weight % of the acidic solution, the acidic solution comprises: from about 0.5 wt % to about 1.5 wt % HF; and About 0.75 wt % to about 2.5 wt % NH4F.

20. The method of any one of claims 16 to 19, wherein: The acidic solution removes the outer layer at a rate of about 1.0 micron / minute or less.

21. The method of any one of claims 16 to 20, wherein: The substrate comprises an initial maximum compressive stress prior to contacting the acidic solution, the substrate comprises a final maximum compressive stress after contacting the acidic solution, and the final maximum compressive stress is about 10% to about 25% less than the initial maximum compressive stress as a percentage of the initial maximum compressive stress.

22. The method of any one of claims 16 to 21, wherein: The ultimate maximum compressive stress ranges from about 700 MPa to about 1200 MPa.

23. The method of any one of claims 16 to 22, wherein: The substrate exhibits a pen drop threshold height of 20 cm or more in the pen drop height.

24. The method of any one of claims 16 to 23, wherein: When the thickness ranges from about 50 microns to about 100 microns, about 30% or more of the substrate samples can withstand a parallel plate spacing of 3 millimeters.

25. The method of any one of claims 16 to 23, wherein: The thickness was 10 microns to 50 microns, and 90% or more of the substrate samples were able to withstand a parallel plate spacing of 2 mm.

26. A chemically strengthened substrate comprising: defining a thickness between a first major surface and a second major surface opposite the first major surface, the thickness being from about 10 microns to about 100 microns; as well as a first compressive stress region extending from the first major surface to a first compressive depth, the first layer depth of potassium being about 5 microns or greater, and a maximum first compressive stress being about 650 megapascals to about 1200 megapascals, Wherein the chemically strengthened substrate comprises a glass-based material, 95% or more of the samples of the chemically strengthened substrate are able to withstand a parallel plate spacing of 5 mm, and the substrate exhibits a pen drop threshold height of 10 cm or greater in a pen drop test.

27. The chemically strengthened substrate according to claim 24, wherein The composition of the chemically strengthened substrate is, in terms of mole % of the chemically strengthened substrate: about 60 mol % to about 70 mol % SiO2; about 8 mol % to about 16 mol % Al2O3; about 12 mol % to about 18 mol % Na2O; about 2 mol % to about 6 mol % MgO; and About 0.1 mol % to about 2.0 mol % CaO.

28. The chemically strengthened substrate according to any one of claims 26 to 27, wherein 90% or more of the substrate samples were able to withstand a parallel plate spacing of 5 mm.

29. The chemically strengthened substrate according to any one of claims 26 to 28, wherein The thickness was about 10 microns to about 50 microns, and 90% or more of the substrate samples were able to withstand a parallel plate spacing of 2 millimeters.

30. The chemically strengthened substrate according to any one of claims 26 to 29, wherein About 30% or more of the chemically strengthened substrate samples were able to survive a parallel plate spacing of 3 mm.

Images