WO2020142363A1

WO2020142363A1 - Cover window for a foldable display

Info

Publication number: WO2020142363A1
Application number: PCT/US2019/068703
Authority: WO
Inventors: Vincent Chien; Mike Liu; Davis OU; Chun Tseng
Original assignee: Google Llc
Priority date: 2018-12-30
Filing date: 2019-12-27
Publication date: 2020-07-09

Abstract

A foldable display includes an OLED display layer and a composite transparent cover window layer covering an outer surface of the OLED display layer, the cover window layer including a glass layer and a low-modulus non-glass transparent layer, where the cover window layer is disposed between the OLED display layer and the low-modulus non-glass transparent layer, and where the foldable display is configured to be folded around a bend having a radius of less than 6 mm.

Description

COVER WINDOW FOR A FOLDABLE DISPLAY

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Provisional Application No. 62/786,537, filed on December 30, 2018, entitled“COVER WINDOW FOR A FOLDABLE DISPLAY”, the disclosure of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

[0002] The present disclosure relates to a display for a mobile computing device and more specifically, to a cover window for a foldable display, where the cover window includes multiple layers with a protective material around a perimeter of a glass layer.

BACKGROUND

[0003] Modem computing devices often attempt to achieve a balance between portability and functionality. A tension can exist between having a display that provides for a rich display of information on a single surface, which suggests a relatively large form factor of the device to accommodate a relatively large display, and a device that is small enough to be easily carried and accessed by a user, which suggests a relatively small form factor of the device.

[0004] A potential solution to address this dilemma is to use a foldable flexible display in the computing device, so that in the display’s folded configuration, the computing device has a relatively small form factor, and in the display’s unfolded configuration, the computing device can have a relatively large display. To keep the form factor of the computing device small and slim, it is desirable to have relatively thin displays. However, folding a relatively thin display can result in small radius bends at the fold in the display, which may be detrimental to sensitive components of the display, for example, thin film transistors (TFTs), organic light-emitting diodes (OLEDs), thin-film encapsulation (TFE) and the like. In addition, thin displays can be relatively fragile and in need of protection against breakage from impacts to the front surface of the device, for example, due to“pen drop” impacts that concentrate an impact force on a small area of the display. [0005] It can be difficult to create foldable top-emitting plastic OLED displays that have a small folding radius, especially when the display is folded in both directions (i.e., having two surfaces of the display fold both towards each other and away from each other) and that can survive many fold-unfold cycles. For example, creating sturdy, durable Z-fold displays (i.e., displays with both inward and outward folds) is greatly complicated by the fragility of the thin-film layers in the display stack.

[0006] In addition, the outer surface of a plastic OLED display can be relatively susceptible to scratches, when degrade the quality of the display.

[0007] Furthermore, flexible displays can be susceptible to warpage at locations where they are repeatedly bent, which also degrades the appearance of the display for a user.

SUMMARY

[0008] In a general aspect, a foldable display of a computing device includes a back stiffening layer, a transparent frontplate layer, a composite transparent cover window layer including a glass layer and a low-modulus non-glass transparent layer, and an OLED display layer disposed between the back stiffening layer and the transparent frontplate layer. The OLED display layer is characterized by a Young’s modulus that is lower than the Young’s modulus of the transparent frontplate layer and that is lower than the Young’s modulus of the back stiffening layer. A neutral plane of the foldable display is located within the OLED display layer, and the foldable display is configured to be folded around a bend having a radius of less than 6 mm.

[0009] Implementations can include one or more of the following features, alone or in any combination.

[0010] For example, the low-modulus, non-glass transparent layer can include silicone rubber.

[0011 ] The low-modulus, non-glass transparent layer can include

fluoroelastomer material.

[0012] A thickness of the glass layer of the cover window layer can be less than 125 microns.

[0013] The frontplate layer can include glass.

[0014] The foldable display can include a touch layer disposed between the back stiffening layer and the transparent frontplate layer.

[0015] A neutral plane of the foldable display can be located within a middle 20% of the OLED display layer.

[0016] The foldable display can be configured to be folded at a first location in a first direction and can be configured to be folded at a second location in a second direction that is opposite to the first direction.

[0017] In another general aspect, a foldable display includes an OLED display layer and a composite transparent cover window layer covering an outer surface of the OLED display layer, the cover window layer including a glass layer and a low-modulus non-glass transparent layer, where the cover window layer is disposed between the OLED display layer and the low- modulus non-glass transparent layer, and where the foldable display is configured to be folded around a bend having a radius of less than 6 mm.

[0018] Implementations can include one or more of the following features, alone or in any combination.

[0019] For example, a neutral plane of the foldable display can be located within the OLED display layer.

[0020] A neutral plane of the foldable display can be located within a middle 20% of the OLED display layer.

[0021 ] A surface of the low-modulus, non-glass transparent can be treated with an oleophobic coating.

[0022] The low-modulus, non-glass transparent layer can include silicone rubber.

[0023] The low-modulus, non-glass transparent layer can include a fluoroelastomer material.

[0024] A surface of the low-modulus, non-glass transparent layer can be fluorinated.

[0025] A transparency of the low-modulus, non-glass transparent layer can be greater than 90%, greater than 92.5%, and greater than 95%.

[0026] A thickness of the glass layer of the cover window layer can be less than 125 microns.

[0027] The foldable display can be configured to be folded at a first location in a first direction and can be configured to be folded at a second location in a second direction that is opposite to the first direction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 is a perspective view of a computing device that includes a foldable display with a single inward fold and the foldable display in a partially folded configuration.

[0029] FIG. 2 is a perspective view of the computing device with a single inward fold, with the display in a folded configuration.

[0030] FIG. 3 is a schematic diagram of a flexible display device having a plurality of bendable sections that are bendable in different directions. .

[0031] FIG. 4 is a schematic diagram of a flexible display device having a stack of a number of different layers.

[0032] FIG. 5 is a schematic diagram of a foldable display having a bendable section that is bent around a minimum radius, Rmin.

[0033] FIG. 6 is a graph showing an example stiffness curve for a foldable display in which the limit radius is reached when the foldable display is folded.

[0034] FIG. 7 is a schematic diagram of a foldable display having a bendable section that is bent around a minimum radius, Rmin.

[0035] The components in the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding parts throughout the several views.

DETAILED DESCRIPTION

[0036] As described herein, a cover window can be added to a foldable display, where the cover window includes a thin glass layer and an outer transparent layer over the thin glass layer, where the outer transparent layer includes a thin layer of low-modulus transparent rubber material. The cover window that includes both glass and transparent rubber can protect the foldable display from mechanical damage while also permitting the display to fold easily and while imparting relatively low stress to the foldable device. The cover window that includes glass can be relatively scratch-resistant and the glass layer can decrease warpage of the device. The thin layer of low-modulus transparent rubber material can help protect the cover window glass and the underlying display layers from mechanical damage, for example, damage due to mechanical impacts. [0037] In addition, to control the location of the neutral plane in the final display device, after fabrication of the display -touch layer, a thin back stiffening layer and a thin transparent frontplate layer, both having high modulus, can be laminated with thin bondhnes or deposited on either side of a display -touch layer of the foldable device. By sandwiching the delicate display -touch layers between two stiff outer layers, the location of the neutral plane can be stabilized, and subsequent layers that are added on either side can have less influence on the neutral axis location, thus improving in-system reliability. In implementations, the back stiffening layer can be combined with the backplate layer to create a surface-stiffened backplate layer.

[0038] FIG. 1 is a perspective view of a computing device 100 that includes a foldable display with a single inward fold, with the foldable display 102 in a partially folded configuration. The device 100 has the foldable display 102 mounted so that it folds with the viewable face inward. It is also possible to mount the foldable display 102 on the opposite side of device 100 so that the display folds with its viewable surface facing outward (not shown).

[0039] FIG. 2 is a perspective view of the computing device 100, with the display 102 in a folded configuration. The foldable display 102 may be, for example, a TFT (Thin-Film-Transistor) OLED (Organic Light Emitting Diode) display, or other appropriate display technology. The foldable display 102 may include appropriate circuitry for driving the display to present graphical and other information to a user.

[0040] As shown in FIG. 1 and FIG. 2, the foldable display 102 can include a first relatively flat, rigid, or-semi-rigid, section 112, a second relatively flat, rigid, or- semi-rigid, section 114, and a third bendable section 116. In some implementations, the foldable display 102 can include more than two flat rigid sections 112, 114 and more than one bendable section 116. In some implementations, the foldable display 102 can include zero, or only one, flat rigid section 112, 114. For example, when a foldable display 102 includes zero flat rigid sections, the display 102 can be continuously bendable, and can be rolled up, as in a scroll. The foldable display 102 shown in FIG. 1 and FIG. 2 has a bendable section 116 that allows the foldable display to bend about an axis. In other implementations, the foldable display 102 can include bendable sections that allow the display to bend about more than one axis.

[0041] The bendable section 116 of the foldable display 102 allows the display 102 to bend in an arc that has a radius, and the bendable section can be made to become rigid when the radius of the bendable section reaches a specified minimum radius. This minimum radius may be selected to prevent the display from bending in a radius so small that fragile components of the display would be damages. In some implementations, the minimum radius is greater than or equal to 2.5 millimeters, or greater than or equal to 3.0 millimeters, or greater than or equal to 5 millimeters.

Thus, the bendable section can be flexible when bent in a radius greater than the minimum radius and then become rigid when the bend radius is equal to or smaller than the minimum radius.

[0042] FIG. 3 is a schematic diagram of a flexible display device 300 having a plurality of bendable sections 304, 306 that are bendable in different directions. The flexible display device 300 can have a display surface 302a, 302b, 302c that can take on a“Z” shape when the device is folded in its folded, compact configuration, with a portion of the display surface 302a, 302b folded inward with the surfaces 302a, 302b facing each other, and a portion of the display 302c folded outward. To assume the “Z” shaped configuration, the display device 300 can be have a bendable section 304 that is bendable in a clockwise direction, as shown in FIG. 3, and a bendable section 306 that is bendable in a counter-clockwise direction, as shown in FIG. 3.

[0043] FIG. 4 is a schematic diagram of a flexible display device 400 having a stack of a number of different layers. For example, in some implementations, a flexible light-emitting layer 410 can be sandwiched between a back stiffening layer 414 and a transparent frontplate layer 406. The light-emitting layer can include a layer of organic light-emitting diodes and can be referred to in this disclosure, as an OLED layer 410, for convenience. The OLED layer 410 can include, at least, OLED functionality to generate the visual information displayed by the display device 400.

In some implementations, the OLED layer 410 can also include touch-sensitive elements to detect a user’s touch at particular locations on the display device 400 and to generate electrical signals in response to the detected touch. In some

implementations, a layer (not shown in FIG. 4) separate from the OLED layer 410 can include the touch-sensitive elements Furthermore, in some implementations, the OLED layer 410 can include other functional elements of the display device 400, such as, for example, TFTs, an encapsulation layer, and anti-reflection optical elements to reduce glare from the display, but in some implementations these functional elements can be included in separate layers from the OLED layer 410. [0044] In some implementations, the OLED layer 410 can be coupled to a frontplate layer 406 by an optically clear adhesive (OCA) layer 408. An optically clear adhesive layer 404 can be applied to a front surface of the frontplate layer 406 to couple the frontplate layer 406 to a cover window layer 402 that serves to protect the device on the front side. In some implementations, the frontplate layer 406 and the OCA layer 408 can be omitted, and the cover window layer 402 can be coupled to the OLED layer 408 without an intermediate frontplate layer 406.

[0045] In some implementations, a polarization layer can included in the cover window layer 402, or can be included in the OLED layer 410. The polarization layer can provide anti-reflection properties to the cover window layer 402. In some implementations, a polarization layer may not be included in either the OLED layer 410 or the cover window layer 410, but can be added to the stack of the device 400 as a separate layer between the OLED layer 410 and the frontplate layer 406 or between the frontplate layer 406 and the cover window layer 402. In some implementations, as described in more detail below, the cover window layer 402 can include a plurality of different layers 403, 405 that include different materials. In general, different adjacent discrete layers of the device 400 can be joined by an adhesive material between the adjacent materials. Adhesive material used in the optical path between the OLED emitters of the OLED layer 410 and user’s eye are OCA.

[0046] In some implementations, the OLED layer 410 can be coupled to the back stiffening layer 414 by an adhesive layer 412. In some implementations, the OLED layer 410 can be directly deposited on the back stiffening layer 414. In some implementations, the back stiffening layer 414 can be coupled to a backplate layer 418, for example, by an adhesive layer 416, or can be directly bonded to the backplate layer 418. In some implementations, the back stiffening layer 414 can be combined with the backplate layer 418 to form an integrated surface-stiffened backplate layer. As explained in more detail below, the mechanical properties of the back stiffening layer 414 and the frontplate layer 406 can be controlled to manage the location of the neutral axis of a finished product that incorporates the display device 400. For example, in some implementations, materials used for the frontplate layer 406 and the backplate stiffening layer 414 can include glass to provide adequate stiffness to manage the location of the neutral axis within the stack and to allow light to pass through the frontplate layer 406. [0047] Because the thickness of each layer of the stack is important to the overall thickness of the device 400, it is desirable to have a relatively thin thickness for the layers. For example, in some non-limiting examples, the thickness of the flexible OLED layer 410 can be less than 100 pm; the thickness of frontplate layer 406 and the back stiffening layer 414 can be less than 75 pm; the thickness of the optically clear adhesive layers 404, 408, 412 can be less than 25 pm; the thickness of the cover window layer 402 can be less than 150 pm or less than 100 pm; and the thickness of the backplate layer can be less than 75 pm. Thus, an overall thickness of the device 400 can be on the order of a millimeter or less and the device can have layers with individual thicknesses that are fractions of a millimeter. In some implementations, the overall thickness of the display device 400 can be less than one millimeter.

[0048] The cover window layer can include a composite cover window 402 that can be used in a foldable display. For example, the cover window 402 can include a thin glass layer 403 for strength and superior optical transparency and a transparent low-modulus protective layer 405 for resilience and protection against scratches and damage, e.g., due to“pen drops” impacts and the like. In some implementations, the transparent low-modulus layer can include silicone rubber or fluoroelastomer material (including, for example, FKM (by ASTM D1418 standard, equivalent to FPM by ISO/DIN 1629 standard); perfluoro-elastomers (FFKM); and tetrafluoro ethylene/propylene rubbers (FEPM)). Although silicone rubber and fluoroelastomer materials generally may not be considered to be transparent, when fabricated in a sufficiently thin layer, the layer can be sufficiently transparent to use in a cover window 402 of a foldable display. For example, in some implementations, the optical loss of light passing though the layer 405 can be less than 10% (i.e., greater than 90% transparency). In some implementations, the optical loss of light passing though the layer 405 can be less than 7.5% (i.e., greater than 92.5% transparency). In some implementations, the optical loss of light passing though the layer 405 can be less than 5% (i.e., greater than 95% transparency).

[0049] In some implementations, the thin glass layer can include a bendable glass material, such as, for example, borosilicate glass. In some implementations, the glass layer can include an akalai free borosilicate glass. In some implementations, the thin glass layer 403 can have a thickness of less than 150 pm. In some implementations, the thin glass layer 403 can have a thickness of less than 100 pm. In some implementations, the thin glass layer 403 can have a thickness of less than 75 pm. In some implementations, the thin glass layer can have a width less than or equal to the width of the OLED layer. In some implementations, the thin glass layer can have a width less than or equal to the width of the OLED layer.

[0050] As explained above, in some implementations, the transparent low- modulus layer 405 can include silicone rubber and/or fluoroelastomer materials. The transparent low-modulus layer 405 can cover the thin glass layer 403, such that that thin glass layer 403 is disposed between the OLED layer 410 and the transparent low- modulus layer 405 in the display 400. In some implementations, the transparent low- modulus layer 405 can have a maximum thickness of less than 100 pm. In some implementations, the transparent low-modulus layer 405 can have a thickness of less than 75 pm. In some implementations, the transparent low-modulus layer 405 can have a thickness of less than 50 pm. In some implementations, the transparent low- modulus layer 405 can have a width less than or equal to the width of the thin glass layer 403. In some implementations, the transparent low-modulus layer 405 can have a width greater than the width of the thin glass layer 403, and the transparent low- modulus layer 405 can surround edges 407 of the thin glass layer 403 to provide protection to the edges of the thin glass layer. Thus, in some implementations, the transparent low-modulus layer 405 can surround the thin glass layer 403 on three sides of the thin glass layer.

[0051] In some implementations, the composite cover window layer 402 can be formed in a molding process in which the transparent low-modulus layer 405 is molded around the thin glass layer 403. For example, the thin glass layer 403 can be placed in a mold, and then transparent low-modulus material 405 can be injected into the mold and heated to a high temperature to all the material 405 to flow easily over the surface of the glass layer 403 to form the desired shape of material 405 on, and in some implementations, around, the thin glass layer 403. In this manner, a predetermined shape of the material 405 can be defined in relation to the thin glass layer 403 to achieve a desired configuration of the cover window layer 402. After the composite cover window layer 402 has been molded and cools it can be removed from the mold and bonded to other layers of the display with an OCA layer 404.

[0052] In some implementations, an outer surface of the low-modulus layer 405 can be fluorinated (e.g. by bathing the surface in a fluorine gas) to make the surface smoother and to reduce a coefficient of friction of the surface. In some implementations, an outer surface of the low-modulus layer 405 can be treated with an oleophobic coating to reduce the effect of fingerprints on the surface of the layer. The combination of the thin glass layer 403 having a thickness of, for example, less than 150 microns, less than 100 microns, or less than 75 microns and the low-modulus layer 405 having a thickness of less than 100 microns, less than 75 microns, or less than 50 microns can achieve the goal for a cover window layer having a transparency of greater than 90% or greater than 92.5%, because the thickness of the low-modulus layer is thin enough. The cover window formed of the specified thin layers of such material also can bend around a radius of less than 6 mm, because the thickness of the glass layer 403 is thin enough to bend in such a radius without breaking. The cover window formed of the specified thin layers of such material also can provide reasonable mechanical protection, for example, against ball and pen drops, to sensitive and fragile components of the device 400 and to the glass layer 403 of the cover window.

[0053] The components of the stack of the device 400 have different as- fabricated properties, including stresses and strains that exist in the components when the layer is fabricated. Additional stresses and strains can be induced in the layers of the stack when the display is bent into a configuration that is different from the configuration in which the layer was fabricated. For example, if the layer was flat when it was fabricated, then additional strain can be induced by stretching or bending the layer, and if the layer was fabricated in a curved configuration, then additional strain can be induced by flattening the layer. If the bend-induced strain exceeds a threshold value characteristic of a component of the stack, the component can be damaged by the strain due to cracking, buckling, delamination, etc. This characteristic damage threshold strain may be different depending on temperature, humidity, required cycle life, and other use and environmental factors. Brittle inorganic layers of the stack can typically withstand less strain than inorganic layers before they are damaged by the strain, and they may be particularly susceptible to tensile strain. Nevertheless, organic materials in the stack also can be damaged by excessive strain that is induced by bending.

[0054] FIG. 5 is a schematic diagram of a foldable display 500 having a bendable section 501 (the curved portion shown in FIG. 5) that is bent around a minimum radius, Rmin. The foldable display 500 can include an OLED layer 502 that includes components that generate images on the display (emitted from the side of the display that faces toward the inside of the bend), a high- modulus back stiffening layer 504, a high-modulus frontplate layer 512, and a cover window layer 514. The frontplate layer can be coupled to the OLED layer 502 and to the cover window layer 514 with OCA. The back stiffening layer 504 can be coupled to the OLED layer with an adhesive, which does not need to be OCA. The modulus of the layers 502, 504,

512 can be parameterized by the Young’s modulus of the layer. The modulus of the back stiffening layer 504 and the frontplane layer 512 can be greater than then modulus of the OLED layer 502. The display 500 can also include a bend limit layer 520 that limits the radius at which the foldable display 400 can bend to greater than or equal to the minimum radius, Rmin.

[0055] The cover window layer 514 can be similar to the cover window layer 402 describe with respect to FIG. 4, and can include a thin, flexible glass layer and a protective transparent rubber layer.

[0056] When the OLED layer 502 is fabricated in a flat configuration, then bending the OLED layer 502 in the absence of the bend limit layer 520 may cause the bendable section to assume a radius less than the minimum radius, Rmin, which may induce excessive strain within the OLED layer 502. The OLED layer 502 can be characterized by a plane 506 at which no strain is induced when the OLED layer 502 is bent. This plane is referred to herein as the“neutral plane” 506. When the OLED layer 502 is bent and the neutral plane is in the middle of the OLED layer 502, compressive strain may be induced along the inner radius of the bend, Rimer, and tensile strain will be induced along the outer radius of the bend, Router.

[0057] If the stack of materials and material thicknesses within the device 500 is symmetrical about a midplane of the OLED layer 502, then the neutral plane 506 corresponds to the midplane of the layer 502. However, different material properties (e.g., thickness, Young’s modulus, etc.) of different layers within the device 500 can cause the neutral plane 506 to be displaced above or below the midplane of the OLED layer 502. For example, having a thick, high-modulus layer on only one side of the OLED layer 502 will move the neutral plane toward the high-modulus layer. The location of the neutral plane within the device 500, along with the maximum tolerable strain values of the materials within the layers of the device 500, determines the minimum bend radius that can be tolerated without causing damage to components within the device 500, especially fragile components in the OLED layer 502.

[0058] The bend limit layer 520 can be attached to the OLED layer 502 to provide support for the OLED layer 502 and also can prevent the OLED layer 502 from being bent around a radius that is smaller than its minimum tolerable bend radius. In some implementations, the functionality of the bend limit layer 520 can be combined in a single layer with the functionality of the back stiffening layer 504. The bend limit layer 520 can be relatively flexible when it bent in radii such that the radius of the inner portion of the OLED layer 502 is greater than Rmin and then can become stiff and inflexible when the radius of the bend approaches, or matches, Rmin. Stiffness can be parameterized by the change in bend radius per unit of applied force that causes the foldable display 500 to bend. For example, in FIG. 6, when the display is folded in half around a 180 degree bend, twice the radius of the bend is shown by the parameter, x, when a force, F, is applied to bend the foldable display. The stiffness of the foldable display 500 then can be parameterized by the derivative, k = dF/dx. The strength of the foldable display can be characterized as the maximum force, F, that the foldable display 500 can withstand before failure of the display occurs.

[0059] When the foldable display 500 is laid flat in its folded configuration, it can be maintained in its folded configuration by the force of gravity on the upper folded portion of the display, such that zero additional force is needed to be applied to the upper folded portion to maintain the foldable display in its flat folded

configuration, or, in other implementations, additional force can be applied by external means such as latches, magnets, etc. to maintain the display in its folded configuration. In this configuration the radius of the bend can be defined as the limit radius, Riimit, i.e., the radius at which the back stiffening layer 504 limits the further bending of the foldable display unless additional external force is applied. To bend the foldable display further from this configuration requires additional external force to overcome the stiffness of the bend limit layer 520. Thus, an example stiffness curve for a foldable display in which the limit radius is reached with the foldable display is folded 180 degrees, showing stiffness as a function of x is shown in FIG. 5.

[0060] It can be advantageous to have a foldable display with a stiffness curve that exhibits a relatively sharp increase in stiffness once the limit radius is reached, such that the foldable display can be easily folded into its folded configuration in which Riimit is close to Rmin, and then the foldable display will become quite stiff, such that it remains in this configuration despite forces pressing it toward a radius smaller than Riimit.

[0061] The bend limit layer 520 is shown on the outside of the bend in FIG. 5, with the OLED-display layer 502 being disposed in the stack toward the inside of the bend. However, the bend limit layer 520 also can be on the inside of the bend 501, for example, as shown in FIG. 7, in which case OLED layer 502 is on the outside of the bend and the content displayed by the display is on the outside of the bend 501.

[0062] The mechanical properties of the back stiffening layer 504, and the frontplate layer 512 can be controlled, so as to maintain the neutral plane 506 at, or close to the mid-plane of the fragile OLED layer 502, so that the OLED layer 502 can tolerate relatively small bend radii. Because other layers of the stack (e.g., the bend limit layer 520, the cover window layer 514, etc.) can affect the location of the neutral plane 506 within the device 500, the mechanical properties (e.g., the thicknesses, densities, material composition, etc.) of the back stiffening layer 504 and the frontplate layer 512 must be selected in relation to those of other layers in the stack to maintain the neutral plane at or near the midplane of the OLED layer 506. In some implementations, the mechanical properties of the back stiffening layer 504, and the frontplate layer 512 can be controlled, so as to maintain the neutral plane 506 within the OLED layer. In some implementations, the mechanical properties of the back stiffening layer 504, and the frontplate layer 512 can be controlled, so as to maintain the neutral plane 506 within the middle 50% of the OLED layer. In some implementations, the mechanical properties of the back stiffening layer 504, and the frontplate layer 512 can be controlled, so as to maintain the neutral plane 506 within the middle 20% of the OLED layer.

[0063] Referring again to FIG. 4, in some implementations, the back stiffening layer 414 or the surface-stiffened backplate layer that includes the properties of the back stiffening layer 414 can be transparent, and can include glass material. For example, if a camera or optical sensor is located behind the display, the back stiffening layer 414 can be transparent to allow light to pass from the front of the display, through the back stiffening layer 414, to the camera or sensor. In some implementations, the back stiffening layer 414 or the surface-stiffened backplate layer that includes the properties of the back stiffening layer 414 can be opaque since light from the OLED layer 410 does not need to be transmitted through it. Therefore, the back stiffening layer 414 can be made using a large variety of materials and processes. However, the frontplate layer 406 must be transparent, because light from the OLED layer 410 must be transmitted through it. Ordinary plastic films are ill- suited as materials for the frontplate layer 406, because their modulus is relatively low, and transparent oxide thin films can be too fragile. However, the frontplate layer 406 can be made from high-modulus, transparent materials, including glass and glass composites, such as, for example, glass-fiber and polymer materials. Other high- modulus, transparent materials also can be used, such as, for example, a thin glass layer (e g., about 30 miti-50 pm thick), which may include high quality soda-lime or which may include ion-exchange strengthened alumino-silicate.

[0064] Because the frontplate layer 406 can be covered and protected by the cover window layer 402, delicate materials of the transparent frontplate layer 406 that rely on being clean and defect-free to achieve the desired mechanical properties of the frontplate layer 406 can be protected during system assembly and end use. To additionally reduce surface damage and breakage during frontplate layer lamination, the glass can be supplied in roll format with a thm, adhesion-enhancing and protective polymer layer already applied on each side.

[0065] Referring again to FIG. 5 and FIG. 7, in some implementations (particularly when the CW layer 514 and the frontplate layer 512 are on the outside of the bend 501, as shown in FIG. 7), glass used in one or more of the layers 502, 512, 514 can be fabricated to avoid the glass forming sharp shards when the glass is broken. For example, in one implementation, the glass used in one or more of the layers 502, 512, 514 can be treated with patterned ion-implantation (e g , a grid pattern), so that when the glass breaks it is more likely to break along, or between, the pattern, thus avoiding sharp shards of glass.

[0066] The devices and apparatuses described herein can be included as part of a computing device, that includes, for example, a processor for executing instructions and a memory for storing the executable instructions. Specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. Example embodiments, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein.

[0067] It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term and/or includes any and all combinations of one or more of the associated listed items.

[0068] It will be understood that when an element is referred to as being connected or coupled to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being directly connected or directly coupled to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., between versus directly between, adjacent versus directly adjacent, etc.).

[0069] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms a, an and the are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms comprises, comprising, includes and/or including, when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.

[0070] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.

[0071] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0072] It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise, or as is apparent from the discussion, terms such as processing or computing or calculating or determining of displaying or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical, electronic quantities within the computer system’s registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.

[0073] Lastly, it should also be noted that whilst the accompanying claims set out particular combinations of features described herein, the scope of the present disclosure is not limited to the particular combinations hereafter claimed, but instead extends to encompass any combination of features or embodiments herein disclosed irrespective of whether or not that particular combination has been specifically enumerated in the accompanying claims at this time.

Claims

WHAT IS CLAIMED IS:

1. A foldable display of a computing device, the foldable display comprising: a back stiffening layer;

a transparent frontplate layer;

a composite transparent cover window layer including a glass layer and a low- modulus non-glass transparent layer; and

an OLED display layer disposed between the back stiffening layer and the transparent frontplate layer, the OLED display layer characterized by a Young’s modulus that is lower than the Young’s modulus of the transparent frontplate layer and that is lower than the Young’s modulus of the back stiffening layer,

wherein a neutral plane of the foldable display is located within the OLED display layer,

wherein the foldable display is configured to be folded around a bend having a radius of less than 6 mm.

2. The foldable display of claim 1 , wherein the low-modulus, non-glass transparent layer includes silicone rubber.

3. The foldable display of any of the preceding claims, wherein the low-modulus, non-glass transparent layer includes fluoroelastomer material.

4. The foldable display of any of the preceding claims, wherein a thickness of the glass layer of the cover window layer is less than 125 microns.

5. The foldable display of any of the preceding claims, wherein the frontplate layer includes glass.

6. The foldable display of any of the preceding claims, further comprising a touch layer disposed between the back stiffening layer and the transparent frontplate layer.

7. The foldable display of any of the preceding claims, wherein a neutral plane of the foldable display is located within a middle 20% of the OLED display layer.

8. The foldable display of any of the preceding claims, wherein the

foldable display is configured to be folded at a first location in a first direction and is configured to be folded at a second location in a second direction that is opposite to the first direction.

9. A foldable display comprising:

an OLED display layer; and

a composite transparent cover window layer covering an outer surface of the OLED display layer, the cover window layer including a glass layer and a low- modulus non-glass transparent layer, wherein the cover window layer is disposed between the OLED display layer and the low-modulus non-glass transparent layer, wherein the foldable display is configured to be folded around a bend having a radius of less than 6 mm.

10. The foldable display of claim 9, wherein a neutral plane of the foldable display is located within the OLED display layer.

11. The foldable display of any of claims 9 - 10, wherein a neutral plane of the foldable display is located within a middle 20% of the OLED display

layer.

12. The foldable display of any of claims 9 - 11, wherein a surface of the low- modulus, non-glass transparent is treated with an oleophobic coating.

13. The foldable display of any of claims 9 - 13, wherein the low-modulus, non glass transparent layer includes silicone rubber.

14. The foldable display of any of claims 9 - 13, wherein the low-modulus, non glass transparent layer includes a fluoroelastomer material.

15. The foldable display of claim 14, wherein a surface of the low-modulus, non glass transparent layer is fluonnated.

16. The foldable display of any of claims 9 - 15, wherein a transparency of the low-modulus, non-glass transparent layer is greater than 90%.

17. The foldable display of any of claims 9 - 16, wherein a transparency of the low-modulus, non-glass transparent layer is greater than 92.5%.

18. The foldable display of of any of claims 9 - 17, wherein a transparency of the low-modulus, non-glass transparent layer is greater than 95%.

19. The foldable display of any of claims 9 - 18, wherein a thickness of the glass layer of the cover window layer is less than 125 microns.

20. The foldable display of any of claims 9 - 19, wherein the foldable display is configured to be folded at a first location in a first direction and is configured to be folded at a second location in a second direction that is opposite to the first direction.