CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority under 35 U.S.C. § 1 19 of U.S.

Provisional Application Serial No. 62/571,017 filed on October 1 1 , 2017, the content of which is relied upon and incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] The disclosure generally relates to bendable display modules and articles, particularly bendable display modules including a glass-containing cover.

BACKGROUND

[0003] Flexible versions of products and components that are traditionally rigid in nature are being conceptualized for new applications. For example, flexible electronic devices can provide thin, lightweight and flexible properties that offer opportunities for new applications including curved displays and wearable devices. Many of these flexible electronic devices incorporate flexible substrates for holding and mounting the electronic components of these devices. Metal foils have some advantages including thermal stability and chemical resistance, but suffer from high cost and a lack of optical transparency. Polymeric foils have some advantages including low cost and impact resistance, but suffer from marginal optical transparency, lack of thermal stability, limited hermeticity and cyclic fatigue performance.

[0004] Some of these electronic devices also can make use of flexible displays. Optical transparency and thermal stability are often desirable properties for flexible display applications. In addition, flexible displays should have high fatigue and puncture resistance, including resistance to failure at small bend radii, particularly for flexible displays that have touch screen functionality and/or can be folded. Further, flexible displays should be easy to bend and fold by the consumer, depending on the intended application for the display.

[0005] Some flexible glass and glass-containing materials offer many desirable properties for flexible and foldable substrate and display applications. However, efforts to harness glass materials for these applications have been difficult to date. Generally, glass substrates can be manufactured to very low thickness levels (< 25 μηι) to achieve smaller and smaller bend radii. These "thin" glass substrates suffer from limited puncture resistance. At the same time, thicker glass substrates (> 150 μηι) can be fabricated with better puncture resistance, but these substrates lack suitable fatigue resistance and mechanical reliability upon bending.

[0006] Further, as these flexible glass materials are employed as cover elements in modules that also contain electronic components (e.g., thin film transistors ("TFTs"), touch sensors, etc.), additional layers (e.g., polymeric electronic device panels) and adhesives (e.g., epoxies, optically clear adhesives ("OCAs")), interactions between these various components and elements can lead to increasingly complex stress states that exist during use of the module within an end product, e.g., an electronic display device. These complex stress states can lead to increased stress levels and/or stress concentration factors experienced by the cover elements. As such, these cover elements can be susceptible to cohesive and/or delamination failure modes within the module. Further, these complex interactions can lead to increased bending forces to bend and fold the cover element by the consumer.

[0007] Thus, there is a need for flexible, glass-containing materials and module designs that employ these materials for use in various electronic device applications, particularly for flexible electronic display device applications, and more particularly for foldable display device applications.

SUMMARY

[0008] According to a first aspect of the disclosure, a display module is provided that includes: a cover element having a thickness from about 25 μηι to about 200 μηι and a cover element elastic modulus from about 20 GPa to about 140 GPa, the cover element further comprising a component having a glass composition, a first primary surface, and a second primary surface; and a stack comprising: (a) a substrate comprising a component having a glass composition and a thickness from about 100 μηι to 1500 μηι, and (b) a first adhesive joining the stack to the second primary surface of the cover element, the first adhesive comprising an elastic modulus from about 0.001 GPa to about 10 GPa and a thickness from about 5 μηι to about 50 μηι. Further, the display module comprises an impact resistance characterized by a tensile stress of less than about 4700 MPa at the second primary surface of the cover element upon an impact to the cover element in a Quasi-Static Indentation Test. [0009] According to a second aspect of the disclosure, a display module is provided that includes: a cover element having a thickness from about 25 μηι to about 200 μηι and a cover element elastic modulus from about 20 GPa to about 140 GPa, the cover element further comprising a component having a glass composition, a first primary surface, and a second primary surface; and a stack comprising: (a) a substrate comprising a component having a glass composition and a thickness from about 100 μηι to 1500 μηι, and (b) a first adhesive joining the stack to the second primary surface of the cover element, the first adhesive comprising an elastic modulus from about 0.001 GPa to about 10 GPa and a thickness from about 5 μηι to about 50 μηι. Further, the display module comprises an impact resistance characterized by a tensile stress of less than about 4000 MPa at the first primary surface of the cover element and a tensile stress of less than about 12000 MPa at the second primary surface of the cover element upon an impact to the cover element in a Pen-Drop Test.

[0010] According to a third aspect of the disclosure, a display module is provided that includes: a cover element having a thickness from about 25 μηι to about 200 μηι and a cover element elastic modulus from about 20 GPa to about 140 GPa, the cover element further comprising a component having a glass composition, a first primary surface, and a second primary surface; and a stack comprising: (a) a substrate comprising a component having a glass composition and a thickness from about 100 μηι to 1500 μηι, and (b) a first adhesive joining the stack to the second primary surface of the cover element, the first adhesive comprising an elastic modulus from about 0.001 GPa to about 10 GPa and a thickness from about 5 μηι to about 50 μηι. The display module comprises an impact resistance

characterized by a tensile stress of less than about 4700 MPa at the second primary surface of the cover element upon an impact to the cover element in a Quasi-Static Indentation Test. Further, the display module comprises a stiffness of about 750 N/mm or more, as measured during the Quasi-Static Indentation Test.

[0011] Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings. For example, the various features may be combined according to the following embodiments.

[0012] Embodiment 1. A display module, comprising: a cover element having a thickness from about 25 μηι to about 200 μηι and a cover element elastic modulus from about 20 GPa to about 140 GPa, the cover element further comprising a component having a glass composition, a first primary surface, and a second primary surface; and

a stack comprising:

(a) a substrate comprising a component having a glass composition and a thickness from about 100 μηι to 1500 μηι, and

(b) a first adhesive joining the stack to the second primary surface of the cover element, the first adhesive comprising an elastic modulus from about 0.001 GPa to about 10 GPa and a thickness from about 5 μηι to 50 μηι,

wherein the display module comprises an impact resistance characterized by a tensile stress of less than about 4700 MPa at the second primary surface of the cover element upon an impact to the cover element in a Quasi-Static Indentation Test.

[0013] Embodiment 2. The display module according to Embodiment 1 , wherein the display module comprises an impact resistance characterized by a tensile stress of less than about 3200 MPa at the second primary surface of the cover element upon an impact to the cover element in a Quasi-Static Indentation Test.

[0014] Embodiment 3. The display module according to Embodiment 2 or Embodiment 3, wherein the first adhesive further comprises a thickness from about 5 μηι to about 25 μηι, and the cover element further comprises a thickness from about 50 μηι to about 150 μηι.

[0015] Embodiment 4.The display module according to any one of Embodiments 1-3, wherein the first adhesive comprises one or more of an epoxy, a urethane, an acrylate, an acrylic, a styrene copolymer, a polyisobutylene, a polyvinyl butyral, an ethylene vinyl acetate, sodium silicate, an optically clear adhesive (OCA), a pressure sensitive adhesive (PSA), polymeric foam, a natural resin, or a synthetic resin.

[0016] Embodiment 5. The display module according to any one of Embodiments 1-4, wherein the stack further comprises:

(c) an interlayer having a thickness from about 25 μηι to about 200 μηι and an interlayer elastic modulus from about 20 GPa to about 140 GPa, the interlayer further comprising a component having a glass composition; and (d) a second adhesive joining the interlayer to the substrate, the second adhesive comprising an elastic modulus from about 0.001 GPa to about 10 GPa and a thickness from about 5 μηι to about 50 μηι.

[0017] Embodiment 6. The display module according to Embodiment 5, wherein the display module comprises an impact resistance characterized by a tensile stress of less than about 4200 MPa at the second primary surface of the cover element upon an impact to the cover element in a Quasi-Static Indentation Test.

[0018] Embodiment 7. The display module according to Embodiment 6, wherein each of the first and second adhesives further comprises a thickness from about 5 μηι to about 25 μηι, and each of the cover element and the interlayer further comprises a thickness from about 75 μηι to about 150 μηι.

[0019] Embodiment 8. The display module according to any one of Embodiments 5-7, wherein each of the first and second adhesives comprises one or more of an epoxy, a urethane, an acrylate, an acrylic, a styrene copolymer, a polyisobutylene, a polyvinyl butyral, an ethylene vinyl acetate, sodium silicate, an optically clear adhesive (OCA), a pressure sensitive adhesive (PSA), polymeric foam, a natural resin, or a synthetic resin.

[0020] Embodiment 9. A display module, comprising:

a cover element having a thickness from about 25 μηι to about 200 μηι and a cover element elastic modulus from about 20 GPa to about 140 GPa, the cover element further comprising a component having a glass composition, a first primary surface, and a second primary surface; and

a stack comprising:

(a) a substrate comprising a component having a glass composition and a thickness from about 100 μηι to 1500 μηι, and

(b) a first adhesive joining the stack to the second primary surface of the cover element, the first adhesive comprising an elastic modulus from about 0.001 GPa to about 10 GPa and a thickness from about 5 μηι to about 50 μηι, wherein the display module comprises an impact resistance characterized by a tensile stress of less than about 4000 MPa at the first primary surface of the cover element and a tensile stress of less than about 12000 MPa at the second primary surface of the cover element upon an impact to the cover element in a Pen Drop Test. [0021] Embodiment lO.The display module according to Embodiment 9, wherein the display module comprises an impact resistance characterized by a tensile stress of less than about 4000 MPa at the first primary surface of the cover element and a tensile stress of less than about 9000 MPa at the second primary surface of the cover element upon an impact to the cover element in a Pen Drop Test.

[0022] Embodiment 1 l .The display module according to Embodiment 10, wherein the first adhesive further comprises a thickness from about 5 μηι to about 25 μηι, and the cover element further comprises a thickness from about 50 μηι to about 150 μηι.

[0023] Embodiment 12. The display module according to any one of Embodiments 9-11 , wherein the first adhesive comprises one or more of an epoxy, a urethane, an acrylate, an acrylic, a styrene copolymer, a polyisobutylene, a polyvinyl butyral, an ethylene vinyl acetate, sodium silicate, an optically clear adhesive (OCA), a pressure sensitive adhesive (PSA), polymeric foam, a natural resin, or a synthetic resin.

[0024] Embodiment 13. The display module according to any one of Embodiments 9-12, wherein the stack further comprises:

(c) an interlayer having a thickness from about 25 μηι to about 200 μηι and an interlayer elastic modulus from about 20 GPa to about 140 GPa, the interlayer further comprising a component having a glass composition; and

(d) a second adhesive joining the interlayer to the substrate, the second adhesive comprising an elastic modulus from about 0.001 GPa to about 10 GPa and a thickness from about 5 μηι to about 50 μηι.

[0025] Embodiment 14.The display module according to Embodiment 13 , wherein the display module comprises an impact resistance characterized by a tensile stress of less than about 4000 MPa at the first primary surface of the cover element and a tensile stress of less than about 1 1000 MPa at the second primary surface of the cover element upon an impact to the cover element in a Pen Drop Test.

[0026] Embodiment 15. The display module according to Embodiment 14, wherein each of the first and second adhesives further comprises a thickness from about 5 μηι to about 25 μηι, and each of the cover element and the interlayer further comprises a thickness from about 50 μηι to about 150 μηι. [0027] Embodiment 16.The display module according to any one of Embodiments 13-15, wherein each of the first and second adhesives comprises one or more of an epoxy, a urethane, an acrylate, an acrylic, a styrene copolymer, a polyisobutylene, a polyvinyl butyral, an ethylene vinyl acetate, sodium silicate, an optically clear adhesive (OCA), a pressure sensitive adhesive (PSA), polymeric foam, a natural resin, and a synthetic resin.

[0028] Embodiment 17. A display module, comprising:

a cover element having a thickness from about 25 μηι to about 200 μηι and a cover element elastic modulus from about 20 GPa to about 140 GPa, the cover element further comprising a component having a glass composition, a first primary surface, and a second primary surface; and

a stack comprising:

(a) a substrate comprising a component having a glass composition and a thickness from about 100 μηι to about 1500 μηι, and

(b) a first adhesive joining the stack to the second primary surface of the cover element, the first adhesive comprising an elastic modulus from about 0.001 GPa to about 10 GPa and a thickness from about 5 μηι to about 50 μηι, wherein the display module comprises an impact resistance characterized by a tensile stress of less than about 4700 MPa at the second primary surface of the cover element upon an impact to the cover element in a Quasi-Static Indentation Test, and

further wherein the display module comprises a stiffness of about 750 N/mm or more, as measured during the Quasi-Static Indentation Test.

[0029] Embodiment 18.The display module according to Embodiment 17, wherein the display module comprises an impact resistance characterized by a tensile stress of less than about 3200 MPa at the second primary surface of the cover element upon an impact to the cover element in a Quasi-Static Indentation Test, and further wherein the display module comprises a stiffness of about 1000 N/mm or more, as measured during the Quasi-Static Indentation Test.

[0030] Embodiment 19.The display module according to Embodiment 18, wherein the first adhesive further comprises a thickness from about 5 μηι to about 25 μηι, and the cover element further comprises a thickness from about 50 μηι to about 150 μηι.

[0031] Embodiment 20.The display module according to Embodiment 19, wherein the first adhesive comprises one or more of an epoxy, a urethane, an acrylate, an acrylic, a styrene copolymer, a polyisobutylene, a polyvinyl butyral, an ethylene vinyl acetate, sodium silicate, an optically clear adhesive (OCA), a pressure sensitive adhesive (PSA), polymeric foam, a natural resin, or a synthetic resin.

[0032] Embodiment 21. A display module, comprising:

a cover element having a thickness from about 25 μηι to about 200 μηι and a cover element elastic modulus from about 20 GPa to about 140 GPa, the cover element further comprising a component having a glass composition, a first primary surface, and a second primary surface; and

a stack comprising:

(a) a substrate comprising a thickness from about 100 μηι to 1500 μηι, and

(b) a first adhesive joining the stack to the second primary surface of the cover element, the first adhesive comprising an elastic modulus from about 0.001 GPa to about 10 GPa and a thickness from about 5 μηι to 50 μηι, and further wherein the display module comprises at least one of:

an impact resistance characterized by a tensile stress of less than about 4700 MPa at the second primary surface of the cover element upon an impact to the cover element in a Quasi- Static Indentation Test;

an impact resistance characterized by a tensile stress of less than about 4000 MPa at the first primary surface of the cover element and a tensile stress of less than about 12000 MPa at the second primary surface of the cover element upon an impact to the cover element in a Pen Drop Test; and

a stiffness of about 750 N/mm or more, as measured during the Quasi-Static

Indentation Test.

[0033] It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understanding the nature and character of the claims. The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiments, and together with the description serve to explain principles and operation of the various embodiments. Directional terms as used herein— for example, up, down, right, left, front, back, top, bottom— are made only with reference to the figures as drawn and are not intended to imply absolute orientation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1A is a cross-sectional view of a three-layer display module according to some aspects of the disclosure.

[0035] FIG. IB is a cross-sectional view of a five-layer display module according to some aspects of the disclosure.

[0036] FIG. 2 depicts a display module within a Pen Drop Test apparatus for measuring quasi-static and dynamic impact resistance, according to some aspects of the disclosure.

[0037] FIG. 3 A is a plot of the maximum principal stress at the second primary surface of the cover element of a display module vs. load subjected to the module in a modeled Quasi- Static Indentation Test up to a peak load of 60 N, according to some aspects of the disclosure.

[0038] FIG. 3B is a plot of load vs. deformation for a display module subjected to a modeled Quasi-Static Indentation Test up to a peak load of 60 N, according to some aspects of the disclosure.

[0039] FIG. 4 is a plot of peak failure load for a portion of the modules schematically depicted in FIG. 3A and tested in a Quasi-Static Indentation Test.

[0040] FIG. 5 A is a plot of the maximum principal stress at the second primary surface of the cover element of a display module vs. distance from the impact location, as modeled in a Pen Drop Test with a pen drop height of 25 cm, according to some aspects of the disclosure.

[0041] FIG. 5B is a plot of the maximum principal stress at the first primary surface of the cover element of a display module vs. distance from the impact location, as modeled in a Pen Drop Test with a pen drop height of 25 cm, according to some aspects of the disclosure.

[0042] FIGS. 6A & 6B are plots of the maximum principal stress and deformation, respectively, at the second primary surface of the cover element of a display module vs. time from impact, as modeled in a Pen Drop Test with a pen drop height of 25 cm, according to some aspects of the disclosure.

[0043] FIG. 7 is a bar chart of the maximum principal stress at the second primary surface of the cover element of the display modules depicted in FIGS. 3A-6B, along with the percentage increase of each of these stress values over the lowest maximum principal stress observed in the samples. DETAILED DESCRIPTION

[0044] Reference will now be made in detail to embodiments according to the claims, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. Ranges can be expressed herein as from "about" one particular value, and/or to "about" another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another embodiment. Whether or not a numerical value or end-point of a range in the specification recites "about," the numerical value or end- point of a range is intended to include two embodiments: one modified by "about," and one not modified by "about." It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[0045] The terms "substantial," "substantially," and variations thereof as used herein are intended to note that a described feature is equal or approximately equal to a value or description. For example, a "substantially planar" surface is intended to denote a surface that is planar or approximately planar. Moreover, "substantially" is intended to denote that two values are equal or approximately equal. In some embodiments, "substantially" may denote values within about 10% of each other, such as within about 5% of each other, or within about 2% of each other.

[0046] Among other features and benefits, the display modules and articles of the disclosure offer unexpectedly high quasi-static and dynamic impact resistance. These modules attain these impact resistance levels through design of the thickness of the adhesives and cover element, along with the number of layers within the module. Further, the enhancement to the impact resistance attributes associated with these modules can also contribute to mechanical reliability and puncture resistance. With regard to mechanical reliability, the display modules of the disclosure are configured to avoid failures in their glass-containing cover elements upon flexing, bending or other deformations to the module. For example, the display module may be used as one or more of: a cover on the user-facing portion of a foldable electronic display device, a location in which puncture resistance is particularly desirable; a substrate module, disposed internally within the device itself, on which electronic components are disposed; or elsewhere in a display device. Alternatively, the display modules of the disclosure may be used in a device not having a display, but one in which a glass or glass-containing layer is used for its beneficial properties and is folded or otherwise bent, in a similar manner as in a foldable display, to a tight bend radius. The puncture resistance is particularly beneficial when the display module is used on the exterior of the device, at a location in which a user will interact with it.

[0047] More specifically, the display modules and articles in the disclosure can obtain some or all of the foregoing advantages through control of the material properties and thicknesses the cover element, adhesives and interlayers employed within the modules. For example, these display modules can exhibit enhanced impact resistance, as characterized by reduced tensile stresses at the primary surfaces of the cover element that are measured in a modeled or actual Quasi-Static Indentation or dynamic Pen Drop Test, through increased thickness of the interlayer, increased elastic modulus of the interlayer and/or increased elastic modulus of the first adhesive. These lower tensile stresses associated with quasi-static and dynamic loading can lead to improved module reliability, particularly in terms of failure resistance of the cover element as the module is subjected to application-driven impact evolutions. Moreover, the embodiments and concepts in the disclosure provide a framework for those with ordinary skill to design display modules to reduce tensile stresses at the primary surfaces of the cover element, which can contribute to the reliability,

manufacturability and suitability of these modules for use in various applications including differing degrees and quantities of bending and folding evolutions.

[0048] Referring to FIG. 1A, a display module 100a is depicted in exemplary form as a three-layer module, according to some aspects of the disclosure. The module 100a includes a cover element 50, first adhesive 10a, and substrate 60. Further, a stack 90a is referenced that includes the adhesive 10a and the substrate 60. Further, cover element 50 has a thickness 52, a first primary surface 54 and a second primary surface 56. Thickness 52 can range from about 25 μηι to about 200 μηι, for example from about 25 μηι to about 175 μηι, from about 25 μηι to about 150 μηι, from about 25 μηι to about 125 μηι, from about 25 μηι to about 100 μηι, from about 25 μηι to about 75 μηι, from about 25 μηι to about 50 μηι, from about 50 μηι to about 175 μηι, from about 50 μηι to about 150 μηι, from about 50 μηι to about 125 μηι, from about 50 μηι to about 100 μηι, from about 50 μηι to about 75 μηι, from about 75 μηι to about 175 μηι, from about 75 μηι to about 150 μηι, from about 75 μηι to about 125 μηι, from about 75 μηι to about 100 μηι, from about 100 μηι to about 175 μηι, from about 100 μηι to about 150 μηι, from about 100 μηι to about 125 μηι, from about 125 μηι to about 175 μηι, from about 125 μηι to about 150 μηι, and from about 150 μηι to about 175 μηι. In other aspects, thickness 52 can range from about 25 μηι to 150 μηι, from about 50 μηι to 100 μηι, or from about 60 μηι to 80 μηι. The thickness 52 of the cover element 50 can also be set at other thicknesses or thickness ranges between the foregoing ranges. Some aspects of the display modules 100a incorporate a cover element 50 with a relatively lower thickness, e.g., from about 75 μηι to about 125 μηι, compared to the thicknesses of other glass cover elements employed in such electronic device applications. The use of such cover elements 50 with relatively lower thickness values unexpectedly provides an enhanced degree of resistance to quasi-static and dynamic impacts, as manifested in a reduced tensile stresses observed at the first and second primary surfaces 54, 56 of the cover element 50 upon an impact in a Quasi-Static Indentation or a Pen Drop Test.

[0049] The display module 100a depicted in FIG. 1A includes a cover element 50 with a cover element elastic modulus from about 20 GPa to 140 GPa, for example from about 20 GPa to about 120 GPa, from about 20 GPa to about 100 GPa, from about 20 GPa to about 80 GPa, from about 20 GPa to about 60 GPa, from about 20 GPa to about 40 GPa, from about 40 GPa to about 120 GPa, from about 40 GPa to about 100 GPa, from about 40 GPa to about 80 GPa, from about 40 GPa to about 60 GPa, from about 60 GPa to about 120 GPa, from about 60 GPa to about 100 GPa, from about 60 GPa to about 80 GPa, from about 80 GPa to about 120 GPa, from about 80 GPa to about 100 GPa, and from about 100 GPa to about 120 GPa. The cover element 50 may be a component having a glass composition or include at least one component having a glass composition. In the latter case, the cover element 50 can include one or more layers that include glass-containing materials, e.g., element 50 can be a polymer/glass composite configured with second phase glass particles in a polymeric matrix. In some aspects, the cover element 50 is a glass element characterized by an elastic modulus from about 50 GPa to about 100 GPa, or any elastic modulus value or range of values between these limits. In other aspects, the cover element elastic modulus is about 20 GPa, 30 GPa, 40 GPa, 50 GPa, 60 GPa, 70 GPa, 80 GPa, 90 GPa, 100 GPa, 110 GPa, 120 GPa, 130 GPa, 140 GPa, or any elastic modulus value or range of values between these values.

[0050] In certain aspects of the display module 100a depicted in FIG. 1A, the cover element 50 can include a glass layer. In other aspects, the cover element 50 can include two or more glass layers. As such, the thickness 52 reflects the sum of the thicknesses of the individual glass layers making up the cover element 50. In those aspects in which the cover element 50 includes two or more individual glass layers, the thickness of each of the individual glass layers is 1 μηι or more. For example, the cover element 50 employed in the module 100a can include three glass layers, each having a thickness of about 8 μηι, such that the thickness 52 of the cover element 50 is about 24 μηι. It should also be understood, however, that the cover element 50 could include other non-glass layers (e.g., compliant polymer layers) sandwiched between multiple glass layers. In other implementations of the module 100a, the cover element 50 can include one or more layers that include glass- containing materials, e.g., element 50 can be a polymer/glass composite configured with second phase glass particles in a polymeric matrix.

[0051] In FIG. 1A, a display module 100a including a cover element 50 comprising a glass material can be fabricated from alkali-free aluminosilicate, borosilicate, boroaluminosilicate, and silicate glass compositions. The cover element 50 can also be fabricated from alkali- containing aluminosilicate, borosilicate, boroaluminosilicate, and silicate glass compositions. In certain aspects, alkaline earth modifiers can be added to any of the foregoing compositions for the cover element 50. In some aspects, glass compositions according to the following are suitable for a cover element 50 having one or more glass layers: S1O2 at 50 to 75% (by mol%); AI2O3 at 5 to 20%; B2O3 at 8 to 23%; MgO at 0.5 to 9%; CaO at 1 to 9%; SrO at 0 to 5%; BaO at 0 to 5%; Sn0 ₂ at 0.1 to 0.4%; Zr0 ₂ at O to 0.1%; and Na ₂ 0 at 0 to 10%, K ₂ 0 at 0 to 5%, and L12O at 0 to 10%. In some aspects, glass compositions according to the following are suitable for a cover element 50 having one or more glass layers: S1O2 at 64 to 69% (by mol%); AI2O3 at 5 to 12%; B2O3 at 8 to 23%; MgO at 0.5 to 2.5%; CaO at 1 to 9%; SrO at 0 to 5%; BaO at 0 to 5%; Sn0 ₂ at 0.1 to 0.4%; Zr0 ₂ at 0 to 0.1%; and Na ₂ 0 at 0 to 1 %. In other aspects, the following composition is suitable for the cover element 50: S1O2 at -67.4% (by mol%); AI2O3 at -12.7%; B2O3 at -3.7%; MgO at -2.4%; CaO at 0%; SrO at 0%; Sn0 ₂ at -0.1 %; and Na20 at -13.7%. In further aspects, the following composition is also suitable for a glass layer employed in the cover element 50: S1O2 at 68.9% (by mol%); AI2O3 at 10.3%; Na ₂ 0 at 15.2%; MgO at 5.4 %; and Sn0 ₂ at 0.2%. In other aspects, the cover element 50 can employ the following glass composition ("Glass 1"): S1O2 at -65% (by mol%); B2O3 at -5%; AI2O3 at -14%; Na ₂ 0 at -14%; and MgO at -2 mol%. In further aspects, the following composition is also suitable for a glass layer employed in the cover element 50: S1O2 at 68.9% (by mol%); AI2O3 at 10.3%; Na ₂ 0 at 15.2%; MgO at 5.4 %; and Sn0 ₂ at 0.2%. Various criteria can be used to select the composition for a cover element 50 comprising a glass material, including but not limited to ease of manufacturing to low thickness levels while minimizing the incorporation of flaws; ease of development of a compressive stress region to offset tensile stresses generated during bending, optical transparency; and corrosion resistance.

[0052] The cover element 50 employed in the foldable module 100a can adopt a variety of physical forms and shapes. From a cross-sectional perspective, the element 50, as a single layer or multiple layers, can be flat or planar. In some aspects, the element 50 can be fabricated in non-rectilinear, sheet-like forms depending on the final application. As an example, a mobile display device having an elliptical display and bezel could employ a cover element 50 having a generally elliptical, sheet-like form.

[0053] Again referring to FIG. 1A, the display module 100a further includes: a stack 90a having a thickness 92a from about 100 μηι to 1600 μηι; and a first adhesive 10a configured to join the stack 90a to the second primary surface 56 of the cover element 50, the first adhesive 10a characterized by a thickness 12a and an elastic modulus from about 0.001 GPa to about 10 GPa, for example, from about 0.001 GPa to about 8 GPa, from about 0.001 GPa to about 6 GPa, from about 0.001 GPa to about 4 GPa, from about 0.001 GPa to about 2 GPa, from about 0.001 GPa to about 1 GPa, from about 0.01 GPa to about 8 GPa, from about 0.01 GPa to about 6 GPa, from about 0.01 GPa to about 4 GPa, from about 0.01 GPa to about 2 GPa, from about 0.1 GPa to about 8 GPa, from about 0.1 GPa to about 6 GPa, from about 0.1 GPa to about 4 GPa, from about 0.2 GPa to about 8 GPa, from about 0.2 GPa to about 6 GPa, and from about 0.5 GPa to about 8 GPa. According to some implementations of the first aspect of the display module 100a, the first adhesive 10a is characterized by an elastic modulus of about 0.001 GPa, 0.002 GPa, 0.003 GPa, 0.004 GPa, 0.005 GPa, 0.006 GPa, 0.007 GPa, 0.008 GPa, 0.009 GPa, 0.01 GPa, 0.02 GPa, 0.03 GPa, 0.04 GPa, 0.05 GPa, 0.1 GPa, 0.2 GPa, 0.3 GPa, 0.4 GPa, 0.5 GPa, 0.6 GPa, 0.7 GPa, 0.8 GPa, 0.9 GPa, 1 GPa, 2 GPa, 3 GPa, 4 GPa, 5 GPa, 6 GPa, 7 GPa, 8 GPa, 9 GPa, 10 GPa, or any amount or range of amounts between these elastic modulus values.

[0054] Referring again to the display module 100a depicted in FIG. 1A, the first adhesive 10a is characterized by a thickness 12a from about 5 μηι to about 60 μηι, for example, from about 5 μηι to about 50 μηι, from about 5 μηι to about 40 μηι, from about 5 μηι to about 30 μηι, from about 5 μηι to about 20 μηι, from about 5 μηι to about 15 μηι, from about 5 μηι to about 10 μηι, from about 10 μηι to about 60 μηι, from about 15 μηι to about 60 μηι, from about 20 μηι to about 60 μηι, from about 30 μηι to about 60 μηι, from about 40 μηι to about 60 μηι, from about 50 μηι to about 60 μηι, from about 55 μηι to about 60 μηι, from about 10 μηι to about 50 μηι, from about 10 μηι to about 40 μηι, from about 10 μηι to about 30 μηι, from about 10 μηι to about 20 μηι, from about 10 μηι to about 15 μηι, from about 20 μηι to about 50 μηι, from about 30 μηι to about 50 μηι, from about 40 μηι to about 50 μηι, from about 20 μηι to about 40 μηι, and from about 20 μηι to about 30 μηι. Other embodiments have a first adhesive 10a characterized by a thickness 12a of about 5 μηι, 10 μηι, 15 μηι, 20 μηι, 25 μηι, 30 μηι, 35 μηι, 40 μηι, 45 μηι, 50 μm, 55 μηι, 60 μm, or any thickness or range of thicknesses between these thickness values. In some aspects, the thickness 12a of the first adhesive 10a is from about 5 μηι to 50 μηι. Some aspects of the display modules 100a incorporate an adhesive 10a with a relatively lower thickness, e.g., from about 5 μηι to about 25 μηι, compared to the thicknesses of conventional adhesives employed in such electronic device applications. The use of such adhesives 10a with relatively lower thickness values unexpectedly provides an enhanced degree of resistance to quasi-static and dynamic impacts, as manifested in a reduced tensile stresses observed at the first and second primary surfaces 54, 56 of the cover element 50 upon an impact in a Quasi-Static Indentation or a Pen Drop Test.

[0055] In some embodiments of the display module 100a depicted in FIG. 1A, the first adhesive 10a is further characterized by a Poisson's ratio from about 0.1 to about 0.5, for example, from about 0.1 to about 0.45, from about 0.1 to about 0.4, from about 0.1 to about 0.35, from about 0.1 to about 0.3, from about 0.1 to about 0.25, from about 0.1 to about 0.2, from about 0.1 to about 0.15, from about 0.2 to about 0.45, from about 0.2 to about 0.4, from about 0.2 to about 0.35, from about 0.2 to about 0.3, from about 0.2 to about 0.25, from about 0.25 to about 0.45, from about 0.25 to about 0.4, from about 0.25 to about 0.35, from about 0.25 to about 0.3, from about 0.3 to about 0.45, from about 0.3 to about 0.4, from about 0.3 to about 0.35, from about 0.35 to about 0.45, from about 0.35 to about 0.4, and from about 0.4 to about 0.45. Other embodiments include a first adhesive 10a characterized by a Poisson's ratio of about 0.1 , 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or any Poisson's ratio or range of ratios between these values. In some aspects, the Poisson's ratio of the first adhesive 10a is from about 0.1 to about 0.25.

[0056] As outlined above, the display module 100a depicted in FIG. 1A includes an adhesive 10a with certain material properties (e.g., an elastic modulus from about 0.001 GPa to 10 GPa). Example adhesives that can be employed as the adhesive 10a in the module 100a include optically clear adhesives ("OCAs") (e.g., Henkel Corporation LOCTITE ^® liquid OCAs), epoxies, and other joining materials as understood by those with ordinary skill in the field that are suitable to join the stack 90a (e.g., the substrate 60) to the second primary surface 56 of the cover element 50. Other example adhesives that can be employed as adhesive 10a in the module 100a include one or more of an epoxy, a urethane, an acrylate, an acrylic, a styrene copolymer, a polyisobutylene, a polyvinyl butyral, an ethylene vinyl acetate, sodium silicate, an optically clear adhesive (OCA), a pressure sensitive adhesive (PSA), polymeric foam, a natural resin, and a synthetic resin.

[0057] Referring again to FIG. 1 A, the stack 90 a of the foldable module 100a further includes a substrate 60 comprising a component having a glass composition, first and second primary surfaces 64, 66, and a thickness 62. Owing to comprising a component having a glass composition, the substrate 60 can, in some embodiments, have an elastic modulus from about 20 GPa to 140 GPa, for example from about 20 GPa to about 120 GPa, from about 20 GPa to about 100 GPa, from about 20 GPa to about 80 GPa, from about 20 GPa to about 60 GPa, from about 20 GPa to about 40 GPa, from about 40 GPa to about 120 GPa, from about 40 GPa to about 100 GPa, from about 40 GPa to about 80 GPa, from about 40 GPa to about 60 GPa, from about 60 GPa to about 120 GPa, from about 60 GPa to about 100 GPa, from about 60 GPa to about 80 GPa, from about 80 GPa to about 120 GPa, from about 80 GPa to about 100 GPa, and from about 100 GPa to about 120 GPa. The substrate 60 may be a component having a glass composition or include at least one component having a glass composition. In the latter case, the substrate 60 can include one or more layers that include glass-containing materials, e.g., substrate 60 can be a polymer/glass composite configured with second phase glass particles in a polymeric matrix. In some aspects, the substrate is a glass element characterized by an elastic modulus from about 50 GPa to about 100 GPa, or any elastic modulus value or range of values between these limits. In other aspects, the elastic modulus of the substrate 60 is about 20 GPa, 30 GPa, 40 GPa, 50 GPa, 60 GPa, 70 GPa, 80 GPa, 90 GPa, 100 GPa, 110 GPa, 120 GPa, 130 GPa, 140 GPa, or any elastic modulus value or range of values between these values. Further, in some embodiments, the substrate 60 is substantially similar to or the same as the cover element 50 in terms of glass composition.

[0058] In embodiments of the display module 100a depicted in FIG. 1A, the substrate 60 has a thickness 62 from about 100 μηι to about 1500 μηι, for example, from about 100 μηι to about 1250 μηι, from about 100 μηι to about 1000 μηι, from about 100 μηι to about 750 μηι, from about 100 μηι to about 500 μηι, from about 100 μηι to about 400 μηι, from about 100 μηι to about 300 μηι, from about 100 μηι to about 200 μηι, 500 μηι to about 1500 μηι, for example, from about 500 μηι to about 1250 μηι, from about 500 μηι to about 1000 μηι, from about 500 μηι to about 750 μηι, from about 750 μηι to about 1500 μηι, from about 750 μηι to about 1250 μηι, from about 750 μηι to about 1000 μηι, from about 1000 μηι ίο about 1500 μηι, from about 1000 μηι to about 1250 μηι, or any thickness or range of thicknesses between these thickness values. Further, given the thickness 62 of the substrate 60, the display module 100a can be bent, flexed or otherwise mechanically deformed to a certain degree in certain embodiments, e.g., to a bend radii of about 10 mm or greater, or 5 mm or greater.

[0059] In some implementations, suitable materials that can be employed as the substrate 60 in the module 100a include various thermoset and thermoplastic materials, e.g., polyimides, suitable for mounting electronic devices 102 and possessing high mechanical integrity and flexibility when subjected to the bending associated with the foldable electronic device module 100a. For example, substrate 60 may be an organic light emitting diode ("OLED") display panel. The material selected for the substrate 60 may also exhibit a high thermal stability to resist material property changes and/or degradation associated with the application environment for the module 100a and/or its processing conditions.

[0060] The stack 90a of the display module 100a shown in FIG. 1A can also include one or more electronic devices (not shown) coupled to the substrate 60. These electronic devices can be conventional electronic devices employed in conventional OLED-containing display devices. For example, the substrate 60 of the stack 90a can include one or more electronic devices in the form and structure of a touch sensor, polarizer, etc. , and other electronic devices, along with adhesives or other compounds for joining these devices to the substrate 60. Further, the electronic devices can be located within the substrate 60 and/or on one or more of its primary surfaces 64, 66.

[0061] As also depicted in FIG. IB, a display module 100b is shown in exemplary form as a five-layer module with a stack 90a that further includes (i.e., in addition to the first adhesive 10a and the substrate 60) an interlayer 70 having a thickness 72 from about 25 μηι to about 200 μηι and an interlayer elastic modulus from about 20 GPa to about 140 GPa, the interlayer 70 further comprising a component having a glass composition; and (d) a second adhesive 10b joining the interlayer 70 to the substrate 60, the second adhesive 10b comprising an elastic modulus from about 0.001 GPa to about 10 GPa and a thickness 12b from about 5 μηι to about 50 μηι. Unless otherwise noted, the interlayer 70 can be configured with the same or similar composition, thickness and elastic modulus as the cover element 50. Further, unless otherwise noted, the second adhesive 10b can be configured with the same or similar composition, thickness and elastic modulus as that of the first adhesive 10a. More generally, the configuration of the display modules 100a, 100b demonstrates that display modules having any number of layers can be employed according to the principles of this disclosure.

[0062] Referring now to FIG. 2, a pen drop test apparatus 200 is depicted. As used herein, a "Pen Drop Test" was conducted with a pen drop apparatus 200 to assess the impact resistance of the display modules 100a, 100b (see FIGS. 1A & IB), as characterized by the stress state observed at the primary surfaces 54, 56 of the cover element. As described and referred to herein, a Pen Drop Test is a dynamic test that is conducted such that the display modules 100a, 100b samples are tested with the load (i.e., from a pen dropping at a fixed height of 25 cm) imparted to the exposed surface of the cover element 50, i.e., primary surface 54. The opposite side of the display module 100a, 100b, e.g., at primary surface 66 (see FIGS. 1 A & IB), is supported by an aluminum plate (6063 aluminum alloy, as polished to a surface roughness with 400 grit paper). One tube is used according to the Pen Drop Test to guide the pen to the sample, and the tube is placed in contact with the top surface of the sample so that the longitudinal axis of the tube is substantially perpendicular to the top surface of the sample. Each tube has an outside diameter of 2.54 cm (1 inch), an inside diameter of 1.4 cm (nine sixteenths of an inch) and a length of 90 cm. An acrylonitrile butadiene ("ABS") shim is employed to hold the pen at the desired height (of the ball above the surface of the substrate) of 25 cm for each test. After each drop, the tube is relocated relative to the sample to guide the pen to a different impact location on the sample. The pen employed in the Pen Drop Test has a ball point tip 212 of 0.35 mm diameter, and a weight of 5.7 grams as including the cap. According to the Pen Drop Test depicted in FIG. 2, the pen is dropped with the cap attached to the top end (i.e., the end opposite the tip) so that the ball point 212 can interact with the test sample, i.e., a display module 100a, 100b.

[0063] Advantageously, the Pen Drop Test, as conducted with the pen drop test apparatus depicted in FIG. 2, was modeled using FEA techniques to estimate tensile stresses generated at the primary surfaces 54, 56 of the cover element 50 based on a fixed pen drop height of 25 cm. Certain assumptions were made in conducting this modeling, as further understood by those with ordinary skill in the field of the disclosure, i particular, the cover element 50 and substrate 60 were assumed to have an elastic modulus of 71 GPa and a Poisson's ratio of 0.22. Further, a typical optical adhesive was assumed for the first and second adhesives, as exhibiting an elastic modulus of 0.3 GPa and a Poisson's ratio of 0.49. With further regard to the Pen Drop Test modeling, the following additional assumptions were made: the pen tip 212 was modeled as a rigid body with no pen tip deformation; a quarter symmetry slice of a module 100a was employed; all interfaces in the module 100a were assumed to be perfectly bonded during the analysis, with no delamination; the aluminum support plate referenced in connection with the pen drop test apparatus 200 was modeled as a rigid body aluminum plate; firictionless contact was assumed between the module 100a and the aluminum support plate; it was assumed that the pen tip 212 did not penetrate the cover element 50 of the module 100a; the use of linear-elastic or hyper-elastic material properties for the elements of the module 100a; the use of a large deformation approach; and that the module 100a was at room temperature during the simulated testing.

[0064] In certain implementations of the display module 100a, 100b (see FIGS. 1A & IB), the module can exhibit an impact resistance characterized by a tensile stress of less than about 4000 MPa at the first primary surface 54 of the cover element 50 and a tensile stress of less than about 12000 MPa at the second primary surface 56 of the cover element 50 upon an impact to the cover element in a Pen Drop Test, as modeled with a pen drop height of 25 cm (see FIG. 2). Unexpectedly, as understood through such modeling of the Pen Drop Test, the thickness 12a, 12b of the adhesives 10a, 10b and the thickness 52 of the cover element 50 can be adjusted to further enhance the impact resistance of the module 100a such that a tensile stress of less than about 4000 MPa at the first primary surface 54 of the cover element 50 and a tensile stress of less than about 9000 MPa at the second primary surface 56 of the cover element 50 upon an impact to the cover element in a Pen Drop Test. Aspects of the display modules 100a can also incorporate a first adhesive 10a with a relatively lower thickness 12a, e.g., from about 5 μηι to about 25 μηι, as compared to the thickness of conventional adhesives employed in such electronic device applications. Similarly, the display modules 100a can also incorporate a cover element 50 with a relatively lower thickness 52, e.g., from about 75 μηι to about 150 μηι, or from about 50 μηι to about 150 μηι, as compared to the thickness of other glass-containing cover elements employed in such electronic device applications. With such modeling and design of the first adhesive 10a and the cover element 50, the tensile stresses at the first primary surface 54 of the cover element 50 can be reduced to less than about 4000 MPa, 3900 MPa, 3800 MPa, 3700 MPa, 3600 MPa, 3500 MPa, 3400 MPa, 3300 MPa, 3200 MPa, 3100 MPa, 3000 MPa, and lower. Similarly, the tensile stresses at the second primary surface 56 of the cover element 50 can be reduced to less than about 12000 MPa, 11000 MPa, 10000 MPa, 9000 MPa, 8000 MPa, 7500 MPa, 7000 MPa, 6500 MPa, 6000 MPa, 5500 MPa, 5000 MPa, 4500 MPa, 4000 MPa, 3500 MPa, 3000 MPa, and lower.

[0065] Referring again to FIG. 2, a pen drop test apparatus 200 is depicted. As used herein, a "Quasi-Static Indentation Test" was conducted with a pen drop apparatus 200 to assess the impact resistance of the display modules 100a, 100b (see FIGS. 1A & IB), as characterized by the stress state observed at the primary surfaces 54, 56 of the cover element. As described and referred to herein, a Quasi-Static Indentation Test is a quasi-static test that is conducted such that the display modules 100a, 100b samples are tested with a constant load of 60N imparted to the exposed surface of the cover element 50, i.e., primary surface 54. The opposite side of the display module 100a, 100b, e.g., at primary surface 66 (see FIGS. 1A & IB), is supported by an aluminum plate (6063 aluminum alloy, as polished to a surface roughness with 400 grit paper). The pen employed in the Quasi-Static Indentation Test has a ball point tip 212 of 0.5 mm diameter, and a weight of 5.7 grams as including the cap.

According to the Quasi-Static Indentation Test depicted in FIG. 2, the pen is applied directly to the exposed surface of the cover element 50 with a constant load of 60 N or with successively higher loads, starting from 5 N, until failure. [0066] Advantageously, the Quasi-Static Indentation Test, as conducted with the pen drop test apparatus depicted in FIG. 2, was modeled using FEA techniques to estimate tensile stresses generated at the primary surfaces 54, 56 of the cover element 50 based on an applied load of 60 N. Certain assumptions were made in conducting this modeling, as further understood by those with ordinary skill in the field of the disclosure. In particular, the cover element 50 and substrate 60 were assumed to have an elastic modulus of 71 GPa and a Poisson's ratio of 0.22. Further, a typical optical adhesive was assumed for the first and second adhesives, as exhibiting an elastic modulus of 0.3 GPa and a Poisson's ratio of 0.49. With further regard to the Quasi-Static Test modeling, the following additional assumptions were made: the pen tip 212 was modeled as a rigid body with no pen tip deformation; a quarter symmetry slice of a module 100a, 100b was employed; all interfaces in the module 100a, 100b were assumed to be perfectly bonded during the analysis, with no delamination; the aluminum support plate referenced in connection with the pen drop test apparatus 200 was modeled as a rigid body aluminum plate; frictionless contact was assumed between the module 100a, 100b and the aluminum support plate; it was assumed that the pen tip 212 did not penetrate the cover element 50 of the module 100a, 100b; the use of linear-elastic or hyper-elastic material properties for the elements of the module 100a, 100b; the use of a large deformation approach; and that the module 100a, 100b was at room temperature during the simulated testing.

[0067] In certain implementations of the display module 100a, 100b (see FIGS. 1A & IB), the module can exhibit an impact resistance characterized by a tensile stress of less than about 4700 MPa at the second primary surface 56 of the cover element 50 upon an impact to the cover element in a Quasi-Static Indentation Test, as modeled with a fixed load of 60 N (see FIG. 2). Unexpectedly, as understood through such modeling of the Quasi-Static Indentation Test, the thickness 12a, 12b of the adhesives 10a, 10b and the thickness 52 of the cover element 50 can be adjusted to further enhance the impact resistance of the module 100a, 100b such that a tensile stress of less than about 3200 MPa at the second primary surface 56 of the cover element 50 upon an impact to the cover element in a Quasi-Static Indentation Test. Aspects of the display modules 100a can also incorporate a first adhesive 10a with a relatively lower thickness 12a, e.g., from about 5 μηι to about 25 μηι, as compared to the thickness of conventional adhesives employed in such electronic device applications. Similarly, the display modules 100a can also incorporate a cover element 50 with a relatively lower thickness 52, e.g., from about 75 μηι to about 150 μηι, or from about 50 μηι to about 150 μηι, as compared to the thickness of other glass-containing cover elements employed in such electronic device applications. With such modeling and design of the first adhesive 10a and the cover element 50, the tensile stresses at the second primary surface 56 of the cover element 50 can be reduced to less than about 4700 MPa, 4600 MPa, 4500 MPa, 4400 MPa, 4300 MPa, 4200 MPa, 4100 MPa, 4000 MPa, 3900 MPa, 3800 MPa, 3700 MPa, 3600 MPa, 3500 MPa, 3400 MPa, 3300 MPa, 3200 MPa, 3100 MPa, 3000 MPa, and lower.

[0068] Still referring to FIGS. 1A & IB, the cover element 50 of the display module 100a, 100b can, in certain aspects of the disclosure, comprise a glass layer or component with one or more compressive stress regions (not shown) that extend from the first and/or second primary surfaces 54, 56 to a selected depth in the cover element 50. Further, in certain aspects of the module 100a, 100b, edge compressive stress regions (not shown) that extend from edges of the element 50 (e.g., as normal or substantially normal to primary surfaces 54, 56) to a selected depth can also be developed. For example, the compressive stress region or regions (and/or edge compressive stress regions) contained in a glass cover element 50 can be formed with an ion-exchange ("IOX") process. As another example, a glass cover element 50 can comprise various tailored glass layers and/or regions that can be employed to develop one or more such compressive stress regions through a mismatch in coefficients of thermal expansion ("CTE") associated with the layers and/or regions.

[0069] In those aspects of the display module 100a, 100b with a cover element 50 having one or more compressive stress regions formed with an IOX process, the compressive stress region(s) can include a plurality of ion-exchangeable metal ions and a plurality of ion- exchanged metal ions, the ion-exchanged metal ions selected so as to produce compressive stress in the compressive stress region(s). In some aspects of the module 100a containing compressive stress region(s), the ion-exchanged metal ions have an atomic radius larger than the atomic radius of the ion-exchangeable metal ions. The ion-exchangeable ions (e.g., Na ⁺ ions) are present in the glass cover element 50 before being subjected to the ion exchange process. Ion-exchanging ions (e.g., K ⁺ ions) can be incorporated into the glass cover element 50, replacing some of the ion-exchangeable ions within region(s) within the element 50 that ultimately become the compressive stress region(s). The incorporation of ion-exchanging ions, for example, K ⁺ ions, into the cover element 50 can be effected by submersing the element 50 (e.g., prior to formation of the complete module 100a) in a molten salt bath containing ion- exchanging ions (e.g., molten KNO3 salt). In this example, the K ⁺ ions have a larger atomic radius than the Na ⁺ ions and tend to generate local compressive stress in the glass cover element 50 wherever present, e.g., in the compressive stress region(s).

[0070] Depending on the ion-exchanging process conditions employed for the cover element 50 employed in the display module 100a, 100b depicted in FIGS. 1A & IB, the ion- exchanging ions can be imparted from the first primary surface 54 of the cover element 50 down to a first ion exchange depth (not shown, "DOL"), establishing an ion exchange depth- of-compression ("DOC"). As used herein, DOC means the depth at which the stress in the chemically strengthened alkali aluminosilicate glass article described herein changes from compressive to tensile. DOC may be measured by surface stress meter (FSM - using commercially available instruments such as the FSM-6000, manufactured by Orihara Industrial Co., Ltd. (Japan)) or a scattered light polariscope (SCALP) depending on the ion exchange treatment. Where the stress in the glass article is generated by exchanging potassium ions into the glass article, FSM is used to measure DOC. Where the stress is generated by exchanging sodium ions into the glass article, SCALP is used to measure DOC. Where the stress in the glass article is generated by exchanging both potassium and sodium ions into the glass, the DOC is measured by SCALP, since it is believed the exchange depth of sodium indicates the DOC and the exchange depth of potassium ions indicates a change in the magnitude of the compressive stress (but not the change in stress from compressive to tensile); the exchange depth of potassium ions in such glass articles is measured by FSM. Compressive stress (including surface CS) is measured by FSM. Surface stress

measurements rely upon the accurate measurement of the stress optical coefficient (SOC), which is related to the birefringence of the glass. SOC in turn is measured according to Procedure C (Glass Disc Method) described in ASTM standard C770-16, entitled "Standard Test Method for Measurement of Glass Stress-Optical Coefficient," the contents of which are incorporated herein by reference in their entirety. Similarly, a second compressive stress region can be developed in the element 50 from the second primary surface 56 down to a second ion exchange depth. Compressive stress levels within the DOL that far exceed 100 MPa can be achieved with such IOX processes, up to as high as 2000 MPa. The compressive stress levels in the compressive stress region(s) within the cover element 50 can serve to offset tensile stresses generated in the cover element 50 upon bending of the foldable electronic device module 100a.

[0071] Referring again to FIGS. 1A & IB, the display module 100a, 100b can, in some implementations, include one or more edge compressive stress regions in the cover element 50 at edges that are normal to the first and second primary surfaces 54, 56, each defined by a compressive stress of 100 MPa or more. It should be understood that such edge compressive stress regions can be developed in the cover element 50 at any of its edges or surfaces distinct from its primary surfaces, depending on the shape or form of element 50. For example, in some implementations of display module 100a, 100b having an elliptical-shaped cover element 50, edge compressive stress regions can be developed inward from the outer edge of the element that is normal (or substantially normal) from the primary surfaces of the element. IOX processes that are similar in nature to those employed to generate the compressive stress region(s) in proximity to the primary surfaces 54, 56 can be deployed to produce these edge compressive stress regions. More specifically, any such edge compressive stress regions in the cover element 50 can be used to offset tensile stresses generated at the edges of the element through, for example, quasi-static or dynamic impact to the cover element 50 (and module 100a, 100b) across any of its edges and/or non-uniform bending of the cover element 50 at its primary surfaces 54, 46. Alternatively, or as an addition thereto, without being bound by theory, any such edge compressive stress regions employed in the cover element 50 may offset adverse effects from an impact or abrasion event at or to the edges of the element 50 within the module 100a, 100b.

[0072] Referring again to FIGS. 1A & IB, in those aspects of the display module 100a, 100b with a cover element 50 having one or more compressive stress regions formed through a mismatch in CTE of regions or layers within the element 50, these compressive stress regions are developed by tailoring of the structure of the element 50. For example, CTE differences within the element 50 can produce one or more compressive stress regions within the element. In one example, the cover element 50 can comprise a core region or layer that is sandwiched by clad regions or layers, each substantially parallel to the primary surfaces 54, 56 of the element. Further, the core layer is tailored to a CTE that is greater than the CTE of the clad regions or layers (e.g., by compositional control of the core and clad layers or regions). After the cover element 50 is cooled from its fabrication processes, the CTE differences between the core region or layer and the clad regions or layers cause uneven volumetric contraction upon cooling, leading to the development of residual stress in the cover element 50 manifested in the development of compressive stress regions below the primary surfaces 54, 56 within the clad region or layers. Put another way, the core region or layer and the clad regions or layers are brought into intimate contact with one another at high temperatures; and these layers or regions are then cooled to a low temperature such that the greater volume change of the high CTE core region (or layer) relative to the low CTE clad regions (or layers) creates the compressive stress regions in the clad regions or layers within the cover element 50.

[0073] Still referring to the cover element 50 in the module 100a, 100b that is depicted in FIGS. 1A & IB with CTE-developed compressive stress regions, the CTE-related compressive stress regions reach from the first primary surface 54 down to a first CTE region depth and the second primary surface 56 to a second CTE region depth, respectively, thus establishing CTE-related DOLs for each of the compressive stress regions associated with the respective primary surfaces 54, 56 and within the clad layer or regions. In some aspects, the compressive stress levels in these compressive stress regions can exceed 150 MPa.

Maximizing the difference in CTE values between the core region (or layer) and the clad regions (or layers) can increase the magnitude of the compressive stress developed in the compressive stress regions upon cooling of the element 50 after fabrication. In certain implementations of the display module 100a, 100b with a cover element 50 having such CTE-related compressive stress regions, the cover element 50 employs a core region and clad regions with a thickness ratio of greater than or equal to 3 for the core region thickness divided by the sum of the clad region thicknesses. As such, maximizing the size of the core region and/or its CTE relative to the size and/or CTE of the clad regions can serve to increase the magnitude of the compressive stress levels observed in the compressive stress regions of the display module 100a, 100b.

[0074] Among other advantages, the compressive stress regions (e.g., as developed through the IOX- or CTE-related approaches outlined in the foregoing paragraphs) can be employed within the cover element 50 to offset tensile stresses generated in the element upon quasi-static or dynamic impacts to the display module 100a, 100b (see FIGS. 1A & IB), particularly tensile stresses that reach a maximum on one of the primary surfaces 54, 56, depending on the nature of the impact. In certain aspects, the compressive stress region can include a compressive stress of about 100 MPa or more at the primary surfaces 54, 56 of the cover element 50. In some aspects, the compressive stress at the primary surfaces is from about 600 MPa to about 1000 MPa. In other aspects, the compressive stress can exceed 1000 MPa at the primary surfaces, up to 2000 MPa, depending on the process employed to produce the compressive stress in the cover element 50. The compressive stress can also range from about 100 MPa to about 600 MPa at the primary surfaces of the element 50 in other aspects of this disclosure. In additional aspects, the compressive stress region (or regions) within the cover element 50 of the module 100a, 100b can exhibit a compressive stress from about 100 MPa to about 2000 MPa, for example, from about 100 MPa to about 1500 MPa, from about 100 MPa to about 1000 MPa, from about 100 MPa to about 800 MPa, from about 100 MPa to about 600 MPa, from about 100 MPa to about 400 MPa, from about 100 MPa to about 200 MPa, from about 200 MPa to about 1500 MPa, from about 200 MPa to about 1000 MPa, from about 200 MPa to about 800 MPa, from about 200 MPa to about 600 MPa, from about 200 MPa to about 400 MPa, from about 400 MPa to about 1500 MPa, from about 400 MPa to about 1000 MPa, from about 400 MPa to about 800 MPa, from about 400 MPa to about 600 MPa, from about 600 MPa to about 1500 MPa, from about 600 MPa to about 1000 MPa, from about 600 MPa to about 800 MPa, from about 800 MPa to about 1500 MPa, from about 800 MPa to about 1000 MPa, and from about 1000 MPa to about 1500 MPa.

[0075] Within such a compressive stress region employed in the cover element 50 of a display module 100a, 100b (see FIGS. 1A & IB) the compressive stress can stay constant, decrease or increase as a function of depth from the primary surfaces down to one or more selected depths. As such, various compressive stress profiles can be employed in the compressive stress region. Further, the depth of each of the compressive stress regions can be set at approximately 15 μηι or less from the primary surfaces 54, 56 of the cover element 50. In other aspects, the depth of the compressive stress region(s) can be set such that they are approximately 1/3 of the thickness 52 of the cover element 50 or less, or 20% of the thickness 52 of the cover element 50 or less, from the first and/or second primary surfaces 54, 56.

[0076] Referring again to FIGS. 1A & IB, the display module 100a, 100b can include a cover element 50 comprising a glass material having one or more compressive stress regions with a maximum flaw size of 5 μηι or less at the first and/or second primary surfaces 54, 56. The maximum flaw size can also be held to about 2.5 μηι or less, 2 μηι or less, 1.5 μηι or less, 0.5 μηι or less, 0.4 μηι or less, or even smaller flaw size ranges. Reducing the flaw size in the compressive stress region of a glass cover element 50 can further reduce the propensity of the element 50 to fail by crack propagation upon the application of tensile stresses by virtue of impact-related forces to the display module 100a, 100b (see FIGS. 1A, IB and 2). In addition, some aspects of the module 100a, 100b can include a surface region with a controlled flaw size distribution (e.g., flaw sizes of 0.5 μηι or less at the first and/or second primary surfaces 54, 56) without employing one or more compressive stress regions.

[0077] Again referring to FIGS. 1A & IB, other implementations of the display module 100a, 100b can include a cover element 50 comprising a glass material subjected to various etching processes that are tailored to reduce the flaw sizes and/or improve the flaw distribution within the element 50. These etching processes can be employed to control the flaw distributions within the cover element 50 in close proximity to its primary surfaces 54, 56, and/or along its edges (not shown). For example, an etching solution containing about 15 vol% HF and 15 vol% HCl can be employed to lightly etch the surfaces of a cover element 50 having a glass composition. The time and temperature of the light etching can be set, as understood by those with ordinary skill, according to the composition of the element 50 and the desired level of material removal from the surfaces of the cover element 50. It should also be understood that some surfaces of the element 50 can be left in an un-etched state by employing masking layers or the like to such surfaces during the etching procedure. More particularly, this light etching can beneficially improve the strength of the cover element 50. In particular, cutting or singulating processes employed to section the glass structure that is ultimately employed as the cover element 50 can leave flaws and other defects within the surfaces of the element 50. These flaws and defects can propagate and cause glass breakage during the application of stresses to the module 100a, 100b containing the element 50 from the application environment and usage. The selective etching process, by virtue of lightly etching one or more edges of the element 50, can remove at least some of the flaws and defects, thereby increasing the strength and/or fracture resistance of the lightly-etched surfaces. Additionally, or alternatively, a light etching step may be performed after chemical tempering (e.g., ion exchange) of the cover element 50. Such light etching after chemical tempering may reduce any flaws introduced by the chemical tempering process itself and thus may increase the strength and/or fracture resistance of the cover element. [0078] It should also be understood that the cover element 50 employed in the display module 100a, 100b depicted in FIGS. 1A & IB can include any one or more of the foregoing strength-enhancing features: (a) IOX-related compressive stress regions; (b) CTE-related compressive stress regions; and (c) etched surfaces with smaller defect sizes. These strength- enhancing features can be used to offset or partially offset tensile stresses generated at the surfaces of the cover element 50 associated with the application environment, usage and processing of the display module 100a, 100b.

[0079] In some implementations, the display module 100a, 100b depicted in FIGS. 1A & IB can be employed in a display, printed circuit board, housing or other features associated with an end product electronic device. For example, the display module 100a, 100b can be employed in an electronic display device containing numerous thin film transistors ("TFTs") or in an LCD or OLED device containing a low-temperature polysilicon ("LTPS") backplane. When the display module 100a, 100b is employed in a display, for example, the module 100a, 100b can be substantially transparent. Further, the module 100a, 100b can have desirable impact resistance, with regard to quasi-static and dynamic impacts, as described in the foregoing paragraphs. In some implementations, the display module 100a, 100b is employed in a wearable electronic device, for example, a watch, wallet or bracelet. As defined herein, "foldable" includes complete folding, partial folding, bending, flexing, discrete bends, and multiple-fold capabilities; further the device can be folded so that the display is either on the outside of the device when folded, or the inside of the device when folded.

[0080] EXAMPLES

[0081] In this example, comparative display modules (Comp. Ex. 1) and display modules consistent with aspects of the disclosure (e.g., Exs. 1 -1 to 1-4, 2-1 and 2-2) were modeled as subjected to simulated quasi-static and dynamic impacts according to the respective Quasi- Static Indentation Test and the Pen Drop Test. In addition, actual Quasi-Static Indentation Tests were performed on some of the samples to obtain peak load to failure values, recognizing that actual indentation loads were varied until failure. The results of these modeling and experimental measurements are depicted in FIGS. 3A-7. Further, the legends in these charts describe the configurations of the display modules modeled and/or tested. For example, Comp. Ex. 1 is configured with a glass cover element having a thickness of 100 μηι, a first adhesive comprising PSA material with a thickness of 100 μηι and a substrate containing the Glass 1 composition having a thickness of 1.1 mm. Although the substrate was modeled at a thickness of 1.1 mm, such was done to show the effects of the adhesive layer on the stack. The substrate need not have a thickness of 1.1 mm; instead, as noted elsewhere, the substrate may have a thickness of less than 1.1 mm, for example thicknesses as described above in connection with substrate 62, and the trends will still be similar to those observed with the 1.1 mm thick glass substrate.

[0082] Referring to FIG. 3 A, a plot is provided of the maximum principal stress at the second primary surface of the cover element of a display module vs. load subjected to the module in a modeled Quasi-Static Indentation Test up to a peak load of 60 N, according to some aspects of the disclosure. As is evident from the figure, three-layer display modules with first adhesives having a smaller thickness from about 15 μηι to about 50 μηι (Exs. 1-1 to 1-4), as compared to the module with the largest first adhesive thickness of about 100 μηι (Comp. Ex. 1), demonstrate the lowest maximum principal stress levels at the second primary surface of the cover element. Further, the three-layer display modules (Exs. 1-1 to 1 -4) demonstrate lower maximum principal stress levels at the second primary surface of the cover element compared to the five-layer display modules (Ex. 2-1 & 2-2). i addition, display modules with slightly thicker cover elements (Ex. 1-4, cover element thickness = 130 μηι) demonstrate lower maximum principal stress levels at the second primary surface of the cover element compared to a comparably configured display module with a slightly thinner cover element (Ex. 1 -2, cover element thickness = 100 μηι).

[0083] Without being bound by theory, and in view of the results shown in FIG. 3 A, the relatively softer first adhesive material comprising a pressure sensitive adhesive (PSA) material facilitates localized bending of the display glass underneath the puncture tip of the testing apparatus. The small radius of the tip (see FIG. 2, radius = 0.5 mm) tends to result in highly localized bending that creates high tensile stresses on the primary surfaces of the cover element. As bending stresses are related to the overall stiffness of the module, it is further believed that increasing the stiffness of the module can lead to improved impact performance.

[0084] Referring now to FIG. 3B, a plot is provided of load vs. deformation for display modules subjected to a modeled Quasi-Static Indentation Test up to a peak load of 60 N, previously employed to generate the results in FIG. 3 A. Further, the slope of the load vs. deformation curves in FIG. 3B is a measure of the stiff of the display module. Given the results shown earlier in FIG. 3A, it is evident that the modules with higher stiffness values, as shown in FIG. 3B, tended to perform better in terms of reduced maximum principal stresses at the second primary surface of the cover element. Put another way, the maximum tensile stress at the second primary surface of the cover element observed from the Quasi-Static Indentation Test is inversely proportional to the stiffness of the module.

[0085] Referring now to FIG. 4, a plot is provided of experimentally-determined peak failure loads for a portion of the modules schematically depicted in FIGS. 3 A and 3B and modeled with the Quasi-Static Indentation Test. In particular, two three-layer modules (Ex. 1 -2 and 1 - 3) and two five-layer modules (Ex. 2-1 and 2-2) were subjected to actual Quasi-Static Indentation Test with increasing applied loads (not a constant load of 60 N) to generate and average load to failure. Fractography analyses conducted on these samples revealed that all experienced a biaxial failure mechanism. Further, it is evident from the results shown in FIG. 4 that the three-layer display modules exhibited significantly higher peak loads to failure as compared to the five-layer display modules. It is believed that this result is due to the fact that the three-layer display modules are stiffer than their five-layer counterparts given the relatively lower amounts of adhesives present in these designs (i.e., one adhesive for the 3- layer modules and two adhesive layers for the 5 -layer modules).

[0086] Referring now to FIGS. 5A and 5B, plots are provided of the maximum principal stress at the second primary surface and first primary surface of the cover element, respectively, of the same group of display modules depicted in FIGS. 3 A and 3B vs. distance from the impact location, as modeled in a Pen Drop Test with a pen drop height of 25 cm. As is generally evident from FIGS. 5A and 5B, the tensile stresses at the second primary surface of the cover element are significantly higher in magnitude relative to the tensile stresses observed at the first primary surface for the same pen drop height of 25 cm. Without being bound by theory, it is believed that the higher tensile stresses observed at the second primary surface of the cover element are due to localized bi-axial bending of the cover element and the somewhat lower tensile stresses at the first primary surface are associated with Hertzian contact with the pen tip from the Pen Drop Test (see FIG. 2).

[0087] Referring again to FIGS. 5A and 5B, the spatial variation of tensile stresses at the second and first primary surfaces of the cover element are depicted, as resulting from the simulated Pen Drop Test with a 25 cm pen drop height. In particular, the display modules with thinner first adhesive thickness levels (e.g., Exs. 1-1 to 1-3, thicknesses from about 15 to 50 μηι) experienced lower tensile stresses at both primary surfaces compared to the display module with a larger first adhesive thickness (i.e., Comp. Ex. 1, thickness = 100 μηι).

Further, the three-layer display modules (Exs. 1 -1 to 1 -4) demonstrate lower maximum principal stress levels at both primary surfaces of the cover element compared to the five- layer display modules (Ex. 2-1 & 2-2), as resulting from the Pen Drop Test. In addition, display modules with slightly thicker cover elements (Ex. 1-4, cover element thickness = 130 μηι) demonstrate lower maximum principal stress levels at both of the primary surfaces of the cover element compared to a comparably configured display module with a slightly thinner cover element (Ex. 1 -2, cover element thickness = 100 μηι).

[0088] Referring now to FIGS. 6A & 6B, plots are provided of the maximum principal stress and deformation, respectively, at the second primary surface of the cover element for the same group of display modules depicted in FIGS. 3 A and 3B vs. time from impact, as modeled in a Pen Drop Test with a pen drop height of 25 cm. In particular, FIGS. 6A and 6B show that the maximum tensile stress observed at the second primary surface occurs when the display module experiences its largest deformation associated with the pen drop at 25 cm. Accordingly, the maximum tensile stress observed at the second primary surface of the cover element is a function of the overall stiffness of the display module.

[0089] Referring now to FIG. 7, a bar chart is provided of the maximum principal stress at the second primary surface of the cover element of the same group of display modules depicted in FIGS. 3A-3B, along with the percentage increase of each of these stress values over the lowest maximum principal stress observed in the samples. That is, the display module with the best performance (i.e., the lowest observed maximum principal stress at the second primary surface of the cover element, -7700 MPa), Ex. 1-1 , serves as the baseline for this chart. In particular, the display module with an adhesive comprising PSA and a thickness of 15 μηι exhibited the best performance. The chart in FIG. 7 further demonstrates that increasing the thickness of the adhesive (e.g., Comp. Ex. 1 , thickness -100 μηι), results in an increase in tensile stress of about 59% over the baseline condition. The chart in FIG. 7 also further demonstrates that the three-layer display modules (Exs. 1 -1 to 1-4) exhibit lower maximum principal stress levels at the second primary surface of the cover element relative to the five-layer display modules (Exs. 2-1 and 2-2). [0090] It will be apparent to those skilled in the art that various modifications and variations can be made to the foldable electronic device modules of the disclosure without departing from the spirit or scope of the claims.