Patent Publication Number: US-11662774-B2

Title: Electronic device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. application Ser. No. 17/131,675, filed on Dec. 22, 2020, which is a continuation application of U.S. application Ser. No. 15/698,744, filed on Sep. 8, 2017, which claims the benefit of U.S. Provisional Application No. 62/500,539, filed on May 3, 2017, and claims the benefit of U.S. Provisional Application No. 62/512,733, filed on May 31, 2017. The contents of these applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     1. Field of the Disclosure 
     The present invention is generally related to flexible electronics (electronic devices), and in particular, flexible touch display devices. 
     2. Description of the Prior Art 
     Flexible electronics is an emerging technology that fabricates thin electronic components and devices on a foldable (or similarly, bendable, stretchable, or flexible) substrate. Flexible electronics offers many benefits over rigid electronics, including a small form factor, cost effectiveness, lightweight, durability, flexibility, and portability. The technology is gaining popularity because of its potential use in many electronics applications, including flexible displays, flexible touch panels, wearable electronic devices, among others. 
     Extensive studies have been made on the research and development of flexible displays and foldable touch panels. Flexible displays with a foldable touch panel, also referred to as a flexible touch display panel (TDP), shows promise in becoming the mainstream of next-generation portable applications and display systems. However, improvements in durability are still desired. For instance, and referring to  FIGS.  1 A- 1 B  shown are schematic diagrams that illustrate stresses imposed on a cover window layer of flexible touch display devices, such as flexible touch display device  10 .  FIG.  1 A  shows the flexible touch display device  10  comprising a cover window layer  12  disposed over a touch display panel  14 .  FIG.  1 A  depicts the flexible touch display device  10  without any bending stress imposed on the cover window layer  12 .  FIG.  1 B  shows the flexible touch display device  10  under a bending stress, as represented by a stress symbol depicted as centrally located and proximal to the top surface of the cover window layer  12 . In particular, the bending stress is primarily if not entirely imposed at the cover window layer  12 . 
     SUMMARY OF THE DISCLOSURE 
     In one embodiment, an electronic device includes a substrate, a touch layer and a cover window layer. The touch layer includes a plurality of touch units on the substrate. The cover window layer is disposed on the touch layer, wherein the cover window layer includes a plurality of structures disposed on the substrate. At least one of the touch units partially overlaps with at least two of the structures of the cover window layer, and at least one of the structures is directly touchable from outside. 
     In one embodiment, an electronic device includes a substrate, a touch layer and a cover window layer. The touch layer includes a plurality of touch units on the substrate. The cover window layer is disposed on the touch layer, wherein the cover window layer includes a plurality of structures disposed on the substrate. An area of at least one of the touch units is greater than an area of at least one of the structures in a top view, and at least one of the structures is directly touchable from outside. 
     These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the invention can be better understood with reference to the following drawings, which are diagrammatic. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG.  1 A  to  FIG.  1 B  are schematic diagrams that illustrate stresses imposed on a conventional cover window layer of a flexible touch display device. 
         FIG.  2    is a schematic diagram that illustrates an embodiment of an example flexible touch display panel. 
         FIG.  3 A  to  FIG.  3 D  are schematic diagrams that illustrate features of an embodiment of an example flexible touch display panel. 
         FIG.  4    is a schematic diagram that illustrates features of an embodiment of an example flexible touch display device including two folding types. 
         FIG.  5 A  to  FIG.  5 B  are schematic diagrams that illustrate, in top plan view, example patterned, cover window layers for an embodiment of a flexible touch display device. 
         FIG.  6 A  to  FIG.  6 B  are schematic diagrams that illustrate some example alternative unit configurations for a patterned window cover layer for an embodiment of a flexible touch display device. 
         FIG.  7 A  to  FIG.  7 B  are schematic diagrams that illustrate, in cross-sectional view, an embodiment of a flexible touch display device with a fully-etched cover window layer. 
         FIG.  8 A  to  FIG.  8 B  are schematic diagrams that illustrate, in cross-sectional view, an embodiment of a flexible touch display device with a partially-etched cover window layer. 
         FIG.  9 A  to  FIG.  9 B  are schematic diagrams that illustrate an embodiment of a type 1 flexible touch display device. 
         FIG.  10 A  to  FIG.  10 B  are schematic diagrams that illustrate an embodiment of a type 2 flexible touch display device. 
         FIG.  11 A  to  FIG.  11 B  are schematic diagrams that illustrate an embodiment of a type 3 flexible touch display device. 
         FIG.  12 A  to  FIG.  12 C  are schematic diagrams that illustrate, in cross-sectional view, example cover window layer patterns of units of different shapes and differences in cracking risk. 
         FIG.  13    and  FIG.  14    are schematic diagrams that illustrate an experimental arrangement and a graph of probability of cracks found from the experimental arrangement for the example cover window layer patterns of  FIG.  12 A  to  FIG.  12 C . 
         FIG.  15 A  to  FIG.  15 C  are schematic diagrams that illustrate example size differences between regions of an embodiment of a flexible touch display device. 
         FIG.  16 A  to  FIG.  16 B  are schematic diagrams that illustrate touch electrode and touch mesh type touch regions in a foldable region for an embodiment of a flexible touch display device. 
         FIG.  17 A  to  FIG.  17 B  are schematic diagrams that illustrate example structures for touch electrode type units and cover window layer units in a foldable region for selection for an embodiment of a flexible touch display device. 
         FIG.  18 A  to  FIG.  18 B  are schematic diagrams that illustrate example structures for a touch mesh type units and cover window layer units in a foldable region for selection for an embodiment of a flexible touch display device. 
         FIG.  19 A  to  FIG.  19 B  are schematic diagrams that illustrate an example reliability experimental arrangement for evaluating probability of damage for the example structures of  FIG.  17 A  to  FIG.  18 B . 
         FIG.  20    is a schematic diagram that illustrates the probability of damage for the example structures of  FIG.  17 A  to  FIG.  18 B . 
         FIG.  21 A  to  FIG.  21 C  are schematic diagrams that illustrate, example relative dimensions for parameters of interest for example cover window layer units for an embodiment of a flexible touch display device. 
         FIG.  22 A  to  FIG.  22 B  are schematic diagrams that illustrate example relative dimensions for parameters of interest for example cover window layer units and touch electrode type touch units for an embodiment of a flexible touch display device. 
         FIG.  23 A  to  FIG.  23 D  are schematic diagrams that illustrate example relative dimensions for parameters of interest for example cover window layer units and touch mesh type touch units for an embodiment of a flexible touch display device. 
         FIG.  24 A ,  FIG.  24 B ,  FIG.  25 A ,  FIG.  25 B ,  FIG.  26 A  and  FIG.  26 B  are schematic diagrams that illustrate example area combinations for a foldable region for an embodiment of a flexible touch display device. 
         FIG.  27 A  to  FIG.  27 B  are schematic diagrams that illustrate, in cross-sectional view, an embodiment of a flexible touch display device comprising a base layer. 
         FIG.  28 A  to  FIG.  28 C  are schematic diagrams that illustrate, in cross-sectional view, formation of a cover window layer, touch layer, and polarizer layer for an embodiment of a flexible touch display device. 
         FIG.  29 A  to  FIG.  29 E  are schematic diagrams that illustrate example cover window layers with recessed patterns of units for an embodiment of a flexible touch display device. 
         FIG.  30 A  to  FIG.  30 C  are schematic diagrams that illustrate example cover window layer units configured as protrusions and example relative dimensions for an embodiment of a flexible touch display device. 
         FIG.  31    is a schematic diagram that illustrates example cover window layer units configured as protrusions among different regions of a cover window layer for an embodiment of a flexible touch display device. 
         FIG.  32    is a schematic diagram that illustrates example cover window layer units configured as recesses and disposed in a select region of a cover window layer for an embodiment of a flexible touch display device. 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed herein are certain embodiments of a flexible touch display device that uses select parameters for unit configurations in a foldable region and the arrangement of the units in both a cover window layer and a touch layer of the device. Through fine tuning of these parameters, a flexible touch display device may realize improvements in resistance to cracking upon contact at the cover window layer and generally improve the resistance to damage from bending the device. In one embodiment, a touch display device is disclosed, comprising: a substrate including a first region, wherein the first region is foldable. A display layer is disposed on the substrate. The touch display device also comprises a touch layer, including a plurality of touch units on the first region of the substrate. The touch display device further comprises a cover window layer disposed on the touch layer, wherein the cover window layer includes a plurality of first patterns on the first region of the substrate, wherein an area of at least one of the plurality of touch units is greater than an area of at least one of the plurality of first patterns. 
     In another embodiment, an apparatus is disclosed, the apparatus comprising a substrate that comprises at least a first region and a second region. The first region is more flexible than the second region. The apparatus further comprises first and second layers. The first layer is disposed over the first region, and comprises plural first units. The second layer is disposed over the first layer. The second layer comprises plural second units, wherein an area of at least one unit of the plural first units is greater than an area of at least one unit of the plural second units. 
     Having summarized certain features of a flexible touch display device of the present disclosure, reference will now be made in detail to the description of a flexible touch display device as illustrated in the drawings. While a flexible touch display device will be described in connection with these drawings, there is no intent to limit the flexible touch display device to the embodiment or embodiments disclosed herein. Further, although the description identifies or describes specifics of one or more embodiments, such specifics are not necessarily part of every embodiment, nor are all various stated advantages necessarily associated with a single embodiment or all embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents consistent with the disclosure as defined by the appended claims. Further, it should be appreciated in the context of the present disclosure that the claims are not necessarily limited to the particular embodiments set out in the description. 
     Both embodiments use patterned cover window layers with a fine-tuning of parameters among the cover window layer and touch layer to provide a robust flexible touch display device that mitigates the risk of cracking and/or damage from bending. 
     Attention is directed to  FIGS.  2 - 4   , which illustrate the bendability or foldability of certain embodiments of a flexible touch display device. Referring first to  FIG.  2   , shown is a schematic diagram that illustrates an example flexible touch display device  16 . The flexible touch display device  16  comprises a flexible substrate providing flexible characteristics that enable the flexible touch display device  16  to be configured in a curved, bendable, foldable, rollable, or stretchable configuration. In the example depicted in  FIG.  2   , the flexible touch display device  16  comprises a folding axis  18  disposed approximately midway along the length of the flexible touch display device  16 , and another folding axis  20  proximal to one end of the flexible touch display device  16 , separating control circuitry (e.g., an integrated circuit) adjacent an end of the flexible touch display device  16  from the foldable region. 
     Referring now to  FIGS.  3 A- 4   , shown are schematic diagrams that illustrate features of an embodiment of an example flexible touch display device  16  (e.g.,  16 A and  16 B). In  FIG.  3 A , the flexible touch display device  16 A comprises a cover window layer  22  mounted on a touch display panel  24 . Note that the cover window layer  22  is depicted  FIGS.  3 A- 4    as a contiguous layer for simplicity in illustration, and is actually a patterned layer with plural units (protrusions or recesses), as explained below. The cover window layer  22  may contain silsequioxane resin, acrylate-based polymer, aluminum oxide, aluminum nitride, aluminum oxynitride, oxidized silicon, nitride silicone, urethane, urethane acrylates, or binder (polyesteracrylate, epoxyacrylate, urethaneacrylate and siloxane modified acrylate) cured by UV radiation. In the depicted example, the flexible touch display device  16 A comprises a foldable region  26  and two adjacent flat regions  28  and  30 , the foldable region  26  disposed between the flat regions  28  and  30 . Note that reference to “flat” does not necessarily mean that the regions have a flat surface, particularly in the presence of protrusions when viewed on the microscopic level. Rather, flat refers to unbending, as opposed to foldable, characteristics or features of those regions. The foldable region  26  comprises a foldable angle θ, that comprises a foldable range between −180 degrees to +180 degrees. Referring to  FIGS.  3 B and  3 C , the cover window layer  22  is folded inwardly, such that the cover window layer  22  in the flat regions  28  and  30  is face to face, and the foldable angle θ is referred to positive degrees. In  FIG.  3 B , the cover window layer  22  in the flat regions  28  and  30  is parallel, and the foldable angle θ is +180 degrees. Referring to  FIG.  3 D , the cover window layer  22  is folded outwardly to form a foldable region  32 , such that the cover window layer  22  in the flat regions  28  and  30  is away from each other, and the foldable angle θ is referred to negative. Referring to  FIG.  4   , the flexible touch display device  16 B includes two types of folding, inwardly folding and outwardly folding. That is, the cover window layer  22  is folded inwardly to form a foldable region  26 , and is folded outwardly to form a foldable region  32 . 
     Having generally described the bendable or foldable nature of certain embodiments of a flexible touch display device  16  (and  16 A and  16 B), attention is now directed to  FIGS.  5 A- 8 B , which illustrate patterned, cover window layers for certain embodiments of flexible touch display devices. Referring  FIGS.  5 A- 5 B , shown (in top plan view) are example cover window layers  22 A and  22 B, respectively, with units of different configurations. In  FIG.  5 A , a cover window layer  22 A is shown, including a matrix or array of units  36 A (also, referred to herein as patterns) configured in the depicted embodiment as protrusions with an oblong (e.g., rounded-edge, rectangular) shape. In other words, the units  36 A collectively comprise a cover window layer pattern depicted as aligned rows and columns of the units  36 A. Each of the units  36 A is shown having an oblong shape, though other shapes may be used as described below. Referring to  FIG.  5 B , shown is a cover window layer  22 B comprising a matrix or array of units  36 B configured in the depicted embodiment as protrusions in a six-sided (hexagonal) geometric shape or configuration. Though the units  36 B in  FIG.  5 B  are aligned along the depicted columns, alignment along each row is evident when viewed for every other unit  36 B. Variations of the arrangement or patterns of units  36 A,  36 B are contemplated to be within the scope of the disclosure. For instance, and referring to  FIGS.  6 A- 6 B , shown are schematic diagrams that illustrate some alternative example unit shapes/configurations, including a rectangular or square-shaped unit  36 C ( FIG.  6 A ) or a frustum-shaped unit  36 D ( FIG.  6 B ), to name a few examples. 
       FIGS.  7 A- 8 B  show certain embodiments of flexible touch display devices  16 C ( FIGS.  7 A- 7 B ) and  16 D ( FIGS.  8 A- 8 B ), in cross-sectional view, having a patterned cover window layer  22  (e.g., similar to those shown in  FIGS.  5 A- 5 B ) disposed on a touch display panel  24 . In particular,  FIGS.  7 A- 7 B  illustrate a patterned cover window layer  22 C with units  36 C formed through complete etching (e.g., exposing from above gapped surfaces of the touch display panel  24 ), with  FIG.  7 A  illustrating no bending stresses and  FIG.  7 B  illustrating bending stresses (as represented by the stress symbol on one of the units  36 C of the cover window layer  22 C). The patterned cover window layer  22 C can release at least some of the cover window layer film stress when compared to a contiguous cover window layer (the latter as illustrated in  FIG.  1 B ), reducing the probability of cracking of the cover window layer  22 C.  FIGS.  8 A- 8 B  show a flexible touch display device  16 D in an unstressed and stressed (bended) configuration, respectively. In this example, the cover window layer  22 D is disposed on the touch display panel  24 , and the cover window layer  22 D is partially etched (e.g., leaving no surfaces, between the units  36 C, of the flexible touch display device  10  exposed from the top). Like the patterned cover window layer  22 C in  FIGS.  7 A- 7 B , the patterned cover window layer  22 D serves to reduce the bending stresses commonly observed with conventional cover window layers (e.g., in  FIG.  1 B ). 
     Having described certain features of the cover window layer for certain embodiments of a flexible touch display device, attention is now directed to  FIGS.  9 A- 11 B , which provide additional detail of certain embodiments of flexible touch display devices, and in particular, the touch display panel  24 .  FIGS.  9 A- 11 B  illustrate various types of touch display panels  24  for certain embodiments of flexible touch display devices  16  (e.g.,  16 E- 16 G). For all of the flexible touch display devices  16  in  FIGS.  9 A- 11 B , there is a top patterned (though depicted as contiguous for simplicity of illustration) cover window layer  22 , but three different touch display panel structure types. Referring to  FIGS.  9 A- 9 B , shown is a flexible touch display device  16 E comprising a type 1 flexible touch display panel  24 A having a structure that comprises, from bottom layer to top layer, a substrate  38 , a circuit layer  40 , a display layer  42 , and a touch layer  44 A. Note that the touch layer  44 A is depicted in  FIGS.  9 A and  9 B  as a contiguous layer for simplicity in illustration, and is actually a patterned layer with plural touch units, as explained below. In addition, the touch layer  44 A can be a single layer, can include two layers or multiple layers. The panel structure of  FIGS.  9 A- 9 B  is also referred to as a touch on display (TOD) and out-cell touch type configuration. Referring in particular to  FIG.  9 B , the substrate  38  is depicted with a supporting film and a flexible substrate disposed over (or on) the supporting film. Other components of the substrate  38  may include supporting film glue. The circuit layer  40  is depicted with a thin film semiconductor layer with sources and gates sandwiched between two buffer layers. For instance, the circuit layer  40  includes a thin film transistor, signal trace, buffer layer, etc. The display layer  42  can comprise cathode  42 C and anode  42 A structures and an encapsulation layer  420  disposed over the structures. The touch layer  44 A is disposed over the display layer  42  (e.g., over the encapsulation layer  420 ). In other words, the type 1 flexible touch display panel  24 A comprises a touch layer  44 A on the display layer  42 , including directly on (touch on display) and indirectly on (out-cell touch, adhesive layer between the touch layer  44 A and the display layer  42 ). 
     Referring now to  FIGS.  10 A- 10 B , shown is a flexible touch display device  16 F comprising a type 2 flexible touch display panel  24 B. The panel  24 B comprises a structure that comprises, from bottom layer to top layer, the substrate  38 , the circuit layer  40 , a display layer  42  (including a first touch layer  44 B 1 ), and a second touch layer  44 B 2 . Note that the first touch layer  44 B 1  and the second touch layer  44 B 2  are depicted in  FIGS.  10 A and  10 B  as a contiguous layer for simplicity in illustration, and are actually a patterned layer with plural touch units, as explained below. Referring in particular to  FIG.  10 B , the substrate  38  is depicted with a supporting film and a flexible substrate disposed over (or on) the supporting film. The circuit layer  40  is depicted with a thin film semiconductor layer with sources and gates sandwiched between two buffer layers. The display layer  42  comprises cathode and anode structures and an encapsulation layer disposed over the structures. The first touch layer  44 B 1  can be in the display layer. For example, the first touch layer  44 B 1  can be formed by the same process and by the same layer with the anode  42 A or the cathode  42 C of the display layer  42 .  FIG.  10 B  shows that the first touch layer  44 B 1  is formed by the same process and by the same layer with the cathode  42 C. The second touch layer  44 B 2  is disposed between the display layer  42  and the cover window layer  22 . In other words, the touch layer is partially in the display layer  42 , partially on the display layer  42 . Thus, the panel structure of  FIGS.  10 A- 10 B  is also referred to as a hybrid touch type configuration. 
       FIGS.  11 A- 11 B  are schematic diagrams that illustrate a flexible touch display device  16 G comprising a type 3 flexible touch display panel  24 C. The panel  24 C comprises a structure that comprises, from bottom layer to top layer, the substrate  38 , the circuit layer  40 , a touch layer  44 C, and the display layer  42 . Note that the touch layer  44 C is depicted in  FIGS.  11 A and  11 B  as a contiguous layer for simplicity in illustration, and are actually a patterned layer with plural touch units, as explained below. The panel structure of  FIGS.  11 A- 11 B  is also referred to as a touch in display (TID) type configuration. Referring in particular to  FIG.  11 B , the substrate  38  is depicted with a supporting film and a flexible substrate disposed over (or on) the supporting film. The circuit layer  40  is depicted with a thin film semiconductor layer with sources and gates sandwiched between two buffer layers. The touch layer  44 C is disposed between the circuit layer  40  and the display layer  42 . The display layer  42  comprises cathode and anode structures and an encapsulation layer disposed over the structures, and the display layer  42  is disposed on the touch layer  44 C. Thus, unlike the other panel types 1 and 2, the type 3 flexible touch display panel  24 C comprises the touch layer  44 C underneath the display layer  42 , between the display layer  42  and the circuit layer  40 . 
     According to some embodiments, the display layer in touch display device can include a liquid crystal layer, an organic light emitting diode layer, a quantum dot light emitting diode (QLED), or a micro-LED layer. Therefore, the flexible touch display device can be a LCD display device, an OLED display device, a QLED display device, or a micro-LED display device. For example, the touch display devices in  FIG.  9 A to  11 B  can be shown as OLED display devices or QLED display devices, but this invention is not limited to such devices. 
       FIGS.  12 A- 23 B  are schematic diagrams that are used to illustrate some fine-tuning of the structure of certain embodiments of a flexible touch display device to improve resistance to cracking and robustness during bending stresses. For instance,  FIGS.  12 A- 14    help to illustrate some considerations for the design of a suitable unit shape for a cover window layer to improve resistance to cracking. Referring in particular to  FIG.  12 A , shown, in cross-sectional view, is a flexible touch display device  16 H comprising an example cover window layer  22 C disposed over a touch display panel  24 . The cover window layer  22 C comprises a completely etched pattern of rectangular-shaped units  36 C. Each unit  36 C comprises an interior angle formed by the top surface and side surface of θ 1 , where θ 1 =90 degrees±5 degrees. A representation  50  of a touch object (e.g., pencil head) is depicted making contact with an edge of one of the units  36 C. The entirety of the structure in  FIG.  12 A  of the flexible touch display device  16 H is also referred to as structure A. 
     In  FIG.  12 B , a similar arrangement fora flexible touch display device  16 I having a completely etched, patterned cover window layer  22 E is shown, also disposed over a touch display panel  24 . The units  36 D comprising the cover window layer  22 E are frustum-shaped. Each unit  36 D comprises an interior angle formed by the top surface and side surface of θ 2 , where θ 2 =120 degrees±5 degrees. A representation  50  of a touch object (e.g., pencil head) is depicted making contact with an edge of one of the units  36 D. The entirety of the structure in  FIG.  12 B  of the flexible touch display device  16 I is also referred to as structure B. 
     In  FIG.  12 C , shown is a similar arrangement of a flexible touch display device  16 J having a completely etched, patterned cover window layer  22 A disposed over a touch display panel  24 . The units  36 A comprising the cover window layer  22 A are curved (e.g., oblong shaped), with a somewhat flat top surface that curves downwards to the surface of the touch display panel  24 . Each unit  36 A comprises an interior angle formed by the top surface and side surface of θ 3 , where θ 3 =120 degrees±5 degrees. A representation  50  of a touch object (e.g., pencil head) is depicted making contact with a curved edge of one of the units  36 A. The entirety of the structure in  FIG.  12 C  of the flexible touch display device  16 J is also referred to as structure C. 
     The structures A-C each comprise cover window layers  22  with units  36  configured as protrusions of the same material and size, with the structures A and B having unit configurations that are of an angular shape and structure C having a unit configuration that is of a curved shape. With continued reference to  FIGS.  12 A- 12 C , attention is directed to  FIGS.  13  and  14   , where an experimental arrangement is depicted ( FIG.  13   ) and the results of the experiment involving structures A-C are graphed ( FIG.  14   ). With regard to  FIG.  13   , shown is a flexible touch display device  16  comprising a cover window layer  22  (e.g., patterned and completely etched) disposed over the touch display panel  24 , and the object  50  (pencil) depicted as moving linearly to the left and the right to rub the cover window layer  22  one thousand times (1000×) for each of the structures A-C. The rubbing can be performed at a rate of 3 mm/sec under a load of 1.0 kg according to JISK5400, and the rubbing distance can be 50 mm long. 
     The result is depicted in  FIG.  14   , which comprises a bar graph  52  having on the vertical axis  54  the probability of cracks, and on the horizontal axis  56 , the structures A, B, and C. The results indicate that the probability of cracks based on the experiment shown in  FIG.  13    are 35%, 23%, and 8% for structure A, structure B, and structure C, respectively. In other words, structures B and C, with a θ 2  and θ 3 =120 degrees±5 degrees, perform better than structure A, with a θ 1 =90 degrees±5 degrees. Even further, structure C, with its curved shape and θ 3 =120 degrees±5 degrees, performs better than the angled-unit, cover window layers for structures A and B. In other words, the cover window layer  22 A of structure C, with its curved unit configuration ( 36 A) and θ 3 =120 degrees±5 degrees, reduces the cracking risk when compared to the other structures A and B having the cover window layers  22 C and  22 E. 
     Referring now to  FIGS.  15 A- 15 C , shown are yet other parameters to fine tune to reduce stresses on the cover window layer. In particular,  FIGS.  15 A- 15 C  illustrate example size differences between regions of an embodiment of a flexible touch display device. In  FIG.  15 A , shown is an embodiment of a flexible touch display device  16  comprising a touch display panel  24  having a patterned (though depicted as contiguous for simplicity of illustration) cover window layer  22  disposed over the panel  24 . The flexible touch display device  16  is shown in  FIG.  15 A  folded over (e.g., +180 degrees), revealing a foldable region  26  and a flat region  28  (and flat region  30 ). With continued reference to  FIG.  15 A , and focusing now on  FIG.  15 B , shown is one embodiment of a cover window layer  22 F in top plan view, with the foldable region  26  adjacent the flat region  28 . The foldable region  26  comprises plural units  36 A arranged in an array or matrix, each unit  36 A having an area equal to A 1 . The flat region  28  comprises a single unit  36 A- 1  with an area of A 2 . In one embodiment, A 1 &lt;A 2 . Referring to  FIG.  15 C , shown is an embodiment of a cover window layer  22 G with the foldable region  26  and the adjacent flat region  28 A. In this depicted embodiment, the cover window layer  22 G comprises an array or matrix of the units  36 A (in the foldable region  26 ), each unit  36 A having an area, A 1 . The cover window layer  22 G comprises an array or matrix of the units  36 A- 2  in the adjacent flat region  28 A (on either side of the foldable region, but focusing on the left hand side of the foldable region), with each unit  36 A- 2  having an area A 2 . In one embodiment, A 2 &gt;A 1 . By configuring the foldable region  26  to have units  36 A, each of a smaller area (A 1 ) than the area of the unit  36 A- 1  or  36 A- 2  of the flat region  28  (or  28 A), the folding stresses on the cover window layer  22  (e.g., 22 F,  22 G) are reduced. In one embodiment, each unit  36 A in the foldable region  26  has an area that is greater than 10 μm 2  but less than 800 μm 2 . Variations in the size range may be used in some embodiments. 
     As evident from the description above, various parameters of the cover window layer in the foldable region may be adjusted to control stress during bending or folding. However, the touch layer of the foldable region also has parameters that may be adjusted to reduce stress during bending and folding. In some embodiments, adjustments to parameters of both the cover window layer and the touch layer are adjusted to improve stress reduction performance. As mentioned above, the touch layers  44  shown in  FIGS.  9 A- 11 B  are patterned. For example, the touch layer  44  can be a touch electrode type structure  58  as shown in  FIG.  16 A . Alternatively, the touch layer  44  can be a touch mesh type structure  60  as shown in  FIG.  16 B . 
     In some embodiments, referring to  FIG.  16 A , the touch electrode type structure  58  can include plurality of touch units  62  to form a plurality of driving electrodes Tx and a plurality of sensing electrodes Rx. The touch units  62  shown in  FIG.  16 A  is in rhombic shape, for example only. The touch units  62  can be in other shape, and the shape is not limited. The driving electrodes Tx can be arranged along a column direction, and the sensing electrodes Rx can be arranged along a row direction. Each column of driving electrode Tx include a plurality of touch units  62  labeled as TP 1 , and two adjacent touch units TP 1  can be connected by a connecting part  602 . Each row of sensing electrode Rx include a plurality of touch units  62  labeled as TP 2 , and two adjacent touch units TP 2  can be connected by a connecting part  604  (shown by a dashed line). The connecting part  602  and the connecting part  604  are insulated by an insulating part  62 N. In one example operation, the first touch unit (electrode) TP 1  and the second touch unit (electrode) TP 2  may perform a mutual capacitive touch sensing function. The material for the touch unit  62  can be transparent conductive material. For example, one common material for the touch unit  62  is ITO (indium tin oxide), though other material may be used as is known. An area of the touch unit  62  is shown encompassed by the thick line around the perimeter of the unit  62 X. 
     In  FIG.  16 B , the touch mesh type structure  60  uses a conceptually similar operation to that described above for the touch electrode type structure  58 , but is configured with an array or matrix of touch units  64  each formed as a metal mesh electrode. Referring  FIGS.  16 B,  23 C, and  23 D  together, the touch mesh type structure  60  is formed by the mesh material  60 M and plural openings are formed in the mesh material  60 M. In  FIG.  23 C , two adjacent touch units  64 - 1  and  64 - 2  are labeled, and two openings  641  and  645  are formed in the touch units  64 - 1  and  64 - 2  respectively. Referring to  FIG.  23 D , the touch unit  64 - 1  is defined by the dashed line L running centrally between the outer and interior boundary of the mesh material. In other words, referring to  FIGS.  23 C and  23 D , the boundary between two adjacent touch units  64 - 1  and  64 - 2  is in the middle of the mesh material between the two touch units  64 - 1  and  64 - 2 . 
     Specifically, the dashed line L is defined as the boundary of one touch unit  64 - 1 . The mesh material within the boundary L in the touch unit  64 - 1  is defined as the touch enclosing part  642  (depicted in shadow area). The touch unit  64 - 1  includes the opening  641  and the touch enclosing part  642  enclosing the opening  641 , and the touch unit  64 - 2  includes the opening  645  and the touch enclosing part  646  enclosing the opening  645 . In some portion, the enclosing part  642  of the touch unit  64 - 1  and the enclosing part  646  of the touch unit  64 - 2  are continuously connected. The area of the touch unit  64 - 1  is sum of the area of the opening  641  and the area of the touch enclosing part  642 . The width of the touch enclosing part  642  is labeled as W 3 . 
     The material for the touch unit  64  can be metal. Common material for the touch unit  64  includes Ti, Al, Ti/Al/Ti among other materials as is known. In general, the touch units  62  and  64  sense touch activity of a user, and may perform a mutual-capacitive touch sensing function, a self-capacitive touch sensing function, or similar. 
     The touch unit size and the cover window layer size may be adjusted to achieve an optimal relative size between the two layers. To further illustrate this point, attention is first directed to  FIGS.  17 A- 17 B , which illustrate example structures for touch electrode type units and cover window layer units in a foldable region for selection for an embodiment of a flexible touch display panel. Referring to  FIG.  17 A , shown is a patterned cover window layer  22 A- 1  (similar to pattern cover window layer  22 A,  FIG.  5 A ) disposed over a touch layer  58 , the cover window layer  22 A- 1  comprising an array or matrix of units  36 A in the foldable region and the touch layer  58  comprising an array or matrix of touch (touch electrode type) units  62  in the foldable region. As depicted in  FIG.  17 A , the touch unit area is greater than the cover window layer unit area. The structure in  FIG.  17 A  is denoted, structure D. Referring to  FIG.  17 B , shown is a patterned cover window layer  22 A- 2  (similar to  22 A- 1  except larger units  36 A- 3 ) disposed over a touch layer  58 , the cover window layer  22 A- 2  comprising an array or matrix of units  36 A- 3  in the foldable region and the touch layer  58  comprising an array or matrix of touch (touch electrode type) units  62  in the foldable region. As depicted in  FIG.  17 B , the touch unit area is less than the cover window layer unit area. The structure in  FIG.  17 B  is denoted, structure E. 
     Turning now to  FIGS.  18 A- 18 B , shown are schematic diagrams that illustrate example structures for touch mesh type units and cover window layer units in a foldable region for selection for an embodiment of a flexible touch display panel. Referring to  FIG.  18 A , shown is a patterned cover window layer  22 A- 1  disposed over a touch layer  60 , the cover window layer  22 A- 1  comprising an array or matrix of units  36 A in the foldable region and the touch layer  60  comprising an array or matrix of touch (touch mesh type) units  64  in the foldable region. As depicted in  FIG.  18 A , the touch unit area is greater than the cover window layer unit area. The structure in  FIG.  18 A  is denoted, structure F. Referring to  FIG.  18 B , shown is a patterned cover window layer  22 A- 2  disposed over a touch layer  60 , the cover window layer  22 A- 2  comprising an array or matrix of units  36 A- 3  in the foldable region and the touch layer  60  comprising an array or matrix of touch (touch mesh type) units  64  in the foldable region. As depicted in  FIG.  18 B , the touch unit area is less than the cover window layer unit area. The structure in  FIG.  18 B  is denoted, structure G. 
     To determine the reliability of structures D, E, F, and G for evaluating probability of damage, two types of tests are used, as illustrated in  FIGS.  19 A- 19 B . In  FIG.  19 A , shown is a rubbing test  66  wherein a touch object  50  (e.g., pencil) is rubbed back along the patterned (though depicted as contiguous for simplicity in illustration) cover window layer  22  of the structures D-G one thousand times (1000×). The rubbing test is similar to that mentioned in  FIG.  13   . In  FIG.  19 B , shown is a folding test  68  wherein the structures D-G are folded one thousand times (1000×). After the rubbing test and folding test are performed, observations of the structures D-G were made with a microscope to facilitate a calculation on the probability of damage. The results are shown in  FIG.  20   , which illustrates the probability of damage for the example structures D-G. In particular,  FIG.  20    shows a bar graph  70  that comprises a vertical axis  72  of probability of damage (in percentage) and a horizontal axis  74  with the different structures D-G. Two columns of data are shown, including a touch electrode type column  76  for corresponding type structures D and E, and a touch mesh type column  78  for corresponding type structures F and G. As shown, the probability of damage is approximately 18% for structure D, 29% for structure E, 12% for structure F, and 21% for structure G. In other words, in terms of having a lower probability of damage, structure D is better than structure E and structure F is better than structure G, leading to the conclusion that for structures (e.g., structures D and F) with the area for each of the cover window layer units less than the area for each of the touch units, the reliability is better. Also, since structures F and G performed better than structures D and E, respectively, the conclusion is that the touch mesh type touch units are better than the touch electrode type units in terms of reliability (for similar relative unit areas). 
     Referring now to  FIGS.  21 A- 23 D , shown are some parameters that illustrate the fine tuning of unit spacing and dimensions for certain embodiments of a flexible touch display device. As described further below, one or more parameters of the cover window layer are adjusted to further control the bending stresses, including the parameters of unit width, unit height, and unit spacing distance. A touch unit size (described below) is also controlled and has an important effect on the stress when certain embodiments of a flexible touch display device undergoes bending or folding, as described further below. Adjustments are made to the parameters of the cover window layer and/or the touch layer of certain embodiments of a flexible touch display device to reduce the probability of damage from bending stresses and/or reduce the probability of cracking. In  FIG.  21 A , shown in top view is an example cover window layer  22 A showing curved units  36 A arranged in an array or matrix. The units  36 A are also referred to as main protected portions, and all other space in the cover window layer  22 A is referred to as release stress portions. In one embodiment, the main protected portion areas&gt;release stress portion areas. Referring to  FIG.  21 B , shown is the cover window layer  22 A (completely etched and patterned) in cross sectional view, the cover window layer  22 A disposed on a touch display panel  24 . The touch object  50  is depicted in  FIG.  21 B  disposed between two of the units  36 A of the cover window layer  22 A, touching the curved edges of the two units  36 A. Several parameters of interest are illustrated. Within the touch object  50 , a circular graphic  80  is shown superimposed on the curved end of the touch object  50 , the circular graphic  80  comprising a center  82  and a radius (R) extending to the curved edge of the unit  36 A. Similarly, depicted in the centrally-located unit  36 A of  FIG.  21 B  and adjacent one of the curved edges of the unit  36 A is a circular graphic  84  having a center  86  and a radius (r′) to the curved edge of the unit  36 A. At the unit  36 A on the left hand side in  FIG.  21 B , shown is a height or thickness (H) parameter corresponding to the distance between the top surface of the touch display panel  24  and the top surface of the unit  36 A. Also shown in between the left hand and central units  36 A is a unit (or pattern) spacing distance, D 1 , between the points of the units  36 A adjacent the touch display panel top surface. Stated otherwise, a curvature radius of a tip of the touch object  50  (e.g., touch pen, finger, etc.) for touching a surface of the cover window layer  22 A may be R, a thickness of each of the units  36 A may be H, and a maximum gap between adjacent ones of the units  36 A may be D 1 , satisfying the following equation: 
     
       
         
           
             
               
                 
                   
                     
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     If Rmin approaches 0, the unit spacing distance, D 1   max  approaches  2 H. Upon collisions and friction being imposed between the touch object  50  and the units  36 A of the cover window layer  22 A, the curved shape type units  36 A reduce the cracking risk of the cover window layer  22 A. 
       FIG.  21 C  shows a variation of the cover window layer  22 A, denoted in  FIG.  21 C  as  22 A- 1 , where the curved units  36 A are separated by the cover window layer areas remaining from a partial etch. Shown are similar parameters of unit thickness (H) between the top surface of the unit  36 A and the top surface of the touch display panel  24 , a spacing distance or gap D 1  between adjacent units  36 A, and a unit width, W 1 , the dimensions D 1  and W referenced from the top surface of the remaining cover window layer material disposed directly on the touch display panel  24 . It is noted that the units  36 A are also referred to as main protected portions, and the space (remaining from the partial etch) between the units  36 A referred to as release stress portions. Also, D 1 &lt;W 1  (for both structures shown in  FIGS.  21 B and  21 C ). 
     Applying the above-described parameter constraints to particular flexible touch display device structures, reference is made to  FIGS.  22 A- 22 B  (for structure D described in association with  FIG.  17 A ) and  FIGS.  23 A- 23 D  (for structure F described in association with  FIG.  18 A ). For instance, and referring to  FIGS.  22 A- 22 B , shown are the parameter constraints (described in association with  FIGS.  21 A- 21 C ) for a flexible touch display device  16   k  corresponding to structure D. Referring to  FIG.  22 A , shown is a flexible touch display device  16   k  comprising a patterned (partially etched) cover window layer  22 A- 1  disposed over a touch layer  58 , which in turn is disposed over a display panel  124 . The display panel  124  can include the substrate  38 , the circuit layer  40  and the display layer  42 , as described and depicted in  FIGS.  9 A to  11 B . The cover window layer  22 A- 1  comprises plural cover window layer units  36 A. The touch layer  58  comprises plural touch electrode type touch units  62 . Parameters of interest include the width (W 1 ) of each of the cover window layer units  36 A, the spacing (D 1 ) or gap between the base of adjacent cover window layer units  36 A, and the width (W 2 ) of each of the touch electrode type touch units  62 . In one embodiment, D 1 &lt;W 1 &lt;W 2 . Referring to  FIG.  22 B , shown is a flexible touch display device  16   l  comprising a patterned (fully etched) cover window layer  22 A disposed over a touch layer  58 , which in turn is disposed over a display panel  124 , that in  FIG.  22 B  is shown expanded with the structures similar to that shown in the type 1 display panel of  FIG.  9 B . The cover window layer  22 A comprises plural cover window layer units  36 A. The touch layer  58  comprises plural touch electrode type touch units  62 . Parameters of interest include the width (W 1 ) of each of the cover window layer units  36 A, the spacing (D 1 ) or gap between the base of adjacent cover window layer units  36 A, and the width (W 2 ) of each of the touch electrode type touch units  62 . In one embodiment, D 1 &lt;W 1 &lt;W 2 . 
       FIGS.  23 A- 23 D  are schematic diagrams that illustrate example relative dimensions for parameters of interest for example cover window layer units and touch mesh type touch units for an embodiment of a flexible touch display device. For instance, and referring to  FIGS.  23 A- 23 D , shown are the parameter constraints (described in association with  FIGS.  21 A- 21 C ) for a flexible touch display device  16   m  corresponding to structure F. In particular,  FIGS.  23 A- 23 D  illustrate some relative dimensions for parameters of interest for structure F illustrated in  FIG.  18 A . Referring to  FIG.  23 A , shown is a flexible touch display device  16   m  comprising a patterned (partially etched) cover window layer  22 A- 1  disposed over a touch layer  60 , which in turn is disposed over a display panel  124 . The cover window layer  22 A- 1  comprises plural cover window layer units  36 A. The touch layer  60  comprises plural touch mesh type touch units  64 . Parameters of interest include the width (W 1 ) of each of the cover window layer units  36 A, the spacing (D 1 ) or gap between the base of adjacent cover window layer units  36 A, the width (W 2 ) between the centers of the touch mesh type touch units  64 , and a touch enclosing part width (W 3 ), explained below.  FIG.  23 B  illustrates a flexible touch display device  16   m  corresponding to structure F, yet with the display panel  24  expanded, the flexible touch display device  16   m  of  FIG.  23 B  comprising the same parameters of interest expressed above for  FIG.  23 A  and omitted here for brevity. In  FIG.  23 C , shown a top view of plural touch mesh type touch units  64  of the touch layer  60 , upon which is disposed the cover window layer  22 A- 1  with the plural cover window layer units  36 A. Of particular relevance, and referring also to  FIG.  23 D , the touch mesh type touch unit  64 - 1  is characterized with an opening  641  and a touch enclosing part  642  bounded by the dashed line L. The touch enclosing part width (W 3 ) is shown as the dimension between an interior of one of the units  64  and the dashed line L. In one embodiment, D 1 &lt;W 3 &lt;W 1 . 
       FIG.  24 A  to  FIG.  26 B  are schematic diagrams that illustrate example area combinations for a foldable region for an embodiment of a flexible touch display device. Referring to  FIG.  24 A , shown is a flexible touch display device  16   n  comprising a foldable region  26  disposed between two flat regions  28 ,  30 . The flexible touch display device  16   n  comprises a cover window layer  22  disposed over a touch display panel  24 . The flat region  30  is shown folded over the flat region  28 , the folding enabled by the foldable region  26 . In  FIG.  24 B , shown is a top plan view of the foldable region  26 A, which illustrates the patterned cover window layer  22 A- 3  having an array or matrix of cover window layer units  36 A- 4 ,  36 A- 5 . In the depicted embodiment, the area of each of the units  36 A- 5  is greater than each of the units  36 A- 4 , the units  36 A- 4  localized more centrally to the foldable region  26 A. 
       FIG.  25 A  and  FIG.  25 B  illustrate foldable regions  26 B and  26 B- 1  for a touch layer  58 A of the touch display panel  24 , respectively. The touch layer  58 A comprises an array or matrix of touch electrode type touch units  62 A and  62 B. The touch units  62 A, located more centrally to the foldable region  26 B, include the designation A 3  representing their respective touch units areas, and the touch units  62 B include the designation A 4  representing their respective touch unit areas. In one embodiment, the areas A 3  and A 4  are different within the foldable region  26 B, wherein A 4  is less than A 3 .  FIG.  25 B  illustrates the foldable region  26 B- 1  with the cover window layer  22 A- 3  disposed over the touch layer  58 A of  FIG.  25 A , where the minimum touch unit area (A 4 ) is greater than the maximum cover window unit area (e.g.,  36 A- 5  of  FIG.  24 B ). Note that there is overlap between the cover window layer units  36 A- 4  and the touch units  62 A (A 3 ). 
     Referring to  FIG.  26 A , shown is the foldable region  26 C with a touch layer  60 A comprising an array or matrix of touch mesh type touch units  64 A and  64 B, wherein the area of the touch units  64 A have a respective area with designation A 5 , and wherein the area of the touch units  64 B have a respective area with designation A 6 , and where A 6  is less than A 5 . In  FIG.  26 B , the foldable region  26 C- 1  is shown with the cover window layer  22 A- 3  disposed over the touch layer  60 A. Note that there is overlap between the cover window layer units  36 A- 4  and the touch units  64 A. The minimum touch unit area (A 6 ) is greater than the maximum cover window unit area (units  36 A- 5 ). 
     Having described some example relative dimensions for particular parameters that influence the reliability of certain embodiments of a flexible touch display device, attention is directed to  FIGS.  27 A- 27 B , which illustrate an embodiment of a flexible touch display device. Referring to  FIGS.  27 A- 27 B , shown is a flexible touch display device  16   o  comprising a patterned cover window layer  22 A having plural cover window layer units  36 A disposed over a base layer  88 , the base layer  88  disposed over a touch display panel  24 . In some embodiments, the base layer  88  may be a separate layer from the cover window layer  22 A. The cover window layer units  36 A may be comprised of a material having a hardness that is higher than that of the material of the base layer  88 . In one embodiment, the pencil hardness of the cover window layer units  158  may be  5 H or more. The material of the base layer  88  may be comprised of a polyester resin, among other material. Referring more specifically to  FIG.  27 B , the base layer  88  is disposed between a touch layer  58  (e.g., touch layer  58  of  FIG.  16 A , though mesh type touch layers, similar to that shown in  FIG.  16 B , may be used) and the cover window layer  22 A. In one embodiment, the base layer  88  is a polarizer (e.g., to affect the optical properties of the flexible touch display device  16   o ). 
     Referring to  FIG.  28 A  to  FIG.  28 C , shown is one method embodiment for forming a cover window layer, touch layer, and base (polarizer) layer for an embodiment of a flexible touch display device. Referring to  FIG.  28 A , shown is an optical film  90  comprising a polarizer substrate. A cover window layer (glass)  92  is deposited and patterned over the optical film  90 . Referring to  FIG.  28 B , the touch electrodes of the touch layer  94  are formed on the backside of the optical film  90 . In  FIG.  28 C , an adhesive layer  96  is formed on the touch layer  94 , and a display panel  124  is formed on the adhesive layer  96 . 
     Referring now to  FIGS.  29 A- 29 E , shown are example cover window layers with recessed patterns for a foldable region of an embodiment of a flexible touch display device. Referring to  FIG.  29 A , shown is a top view of a cover window layer  22 H with an array or matrix of cover window layer units  98  configured as recesses (not protrusions). The cover window layer units  98  are also referred to herein as recessed units  98 . Dimensions for parameters of interest include a recessed spacing distance (D 2 ), which indicates a distance between adjacent recessed units  98  (e.g., along a row). Also depicted is a recessed unit width (W 12 ). Referring to  FIGS.  29 B- 29 E , shown are cross-sectional views of flexible touch display devices  16   p ,  16   q ,  16   r , and  16   s  respectively, that illustrate relative dimensions for parameters of interest, and also the different configurations or shapes of the recessed units  98 . In  FIG.  29 B , a flexible touch display device  16   p  is shown, with a cover window layer  22 H- 1  comprising plural recessed units  98 A configured as square or rectangular type recesses. The spacing distance (D 2 ) between recessed units  98 A is greater than the recessed unit width (W 12 ). The cover window layer  22 H- 1  is disposed over a touch display panel  24 . Referring to  FIG.  29 C , a flexible touch display device  16   q  is shown, with a cover window layer  22 H- 2  comprising plural recessed units  98 B configured as round or curved recesses. The spacing distance (D 2 ) between recessed units  98 B is greater than the recessed unit width (W 12 ). The cover window layer  22 H- 2  is disposed over a touch display panel  24 . In  FIG.  29 D , a flexible touch display device  16   r  is shown, with a cover window layer  22 H- 3  comprising plural recessed units  98 C configured as angled recesses. The spacing distance (D 2 ) between recessed units  98 C is greater than the recessed unit width (W 12 ). The cover window layer  22 H- 3  is disposed over a touch display panel  24 . In  FIG.  29 E , a flexible touch display device  16   s  is shown, with a cover window layer  22 H- 4  comprising plural recessed units  98 D. The recessed units  98 D is configured as narrower to wider from base to top. The spacing distance (D 2 ) between recessed units  98 D is greater than the recessed unit width (W 12 ). The cover window layer  22 H- 4  is disposed over a touch display panel  24 . 
       FIGS.  30 A- 30 C  are schematic diagrams that illustrate example cover window layer units configured as protrusions and example relative dimensions for an embodiment of a flexible touch display device. Referring to  FIG.  30 A , shown is a cover window layer  22 A comprising an array or matrix of cover window layer units  36 A configured as respective protrusions. Referring to  FIG.  30 B , a cover window layer unit  36 A is shown with rounded edges, though other configurations for a protrusion may be used. Referring to  FIG.  30 C , the spacing distance (D 1 ) between the units  36 A is less than the unit width (W 1 ). 
     Referring to  FIG.  31   , shown is a schematic diagram that illustrates example cover window layer units among different regions of a cover window layer for an embodiment of a flexible touch display device. For instance, a cover window layer  22 F (similar to  FIG.  15 B ) is shown in top plan view, including a foldable region  26  and two flat regions  28 ,  30 . In the foldable region  26 , shown is an array or matrix of cover window layer units  36 A configured as protrusions. In the flat regions  28  and  30 , shown are respective (single) cover window layer units  36 A- 1 ,  36 A- 6  configured as protrusions. 
       FIG.  32    is a schematic diagram that illustrates example cover window layer units disposed in a select region of a cover window layer for an embodiment of a flexible touch display device. For instance, a cover window layer  100  is shown in top plan view, including a foldable region  102  and two flat regions  104 ,  106 . In the foldable region  102 , shown is an array or matrix of cover window layer units  98  configured as recesses. The flat regions  104 ,  106  comprise no units. 
     Note that various combinations of the disclosed embodiments may be used, and hence reference to an embodiment or one embodiment is not meant to exclude features from that embodiment from use with features from other embodiments. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. Further, note that reference to a structure (e.g., first structure) that is disposed on (or over) a substrate includes the presence of one or more intermediate structures between the first structure and the substrate. In addition, the meaning that the second structure is disposed on (or over) the first structure can refer to that the second structure is directly disposed on the first structure (with no intermediate structure between the first and second structures), or can refer to that the second structure is indirectly disposed on the first structure (in the presence of one or more intermediate structures between the first and second structures). Also, pattern and unit is used interchangeably herein. Further, variations (e.g., in size, geometry) of a given structure or component (e.g., units, layers, etc.) that is similar in principle are provided herein with a suffix of a reference numeral, or a combination of a suffix and appended numeral to the reference numeral. For instance, a unit in a cover window layer may be referenced using reference numeral  36 , yet different geometries of a cover window layer unit are distinguished by using a suffix (e.g.,  36 A for rounded edges,  36 B for hexagonal geometries), or different areas or other differences denoted using the suffix and a hyphened numeral (e.g.,  36 A- 1  for a rounded cover window layer unit of one size, and  36 A- 6  for a rounded unit of a different size) for a component or structure that is similar in principle. Note that certain examples are depicted using a particular geometry and/or area dimension (or complete etch versus partial etch), with the understanding that, to the extent that performance is similar, various geometries, areas, and/or type of etch may be interchangeable in some embodiments. Though described using different embodiments, features from some embodiments may be interchangeable with, combined, or replaced with features from other embodiments. Reference to the terms first and second or the like are used as a method of distinction in the claims, and not necessarily limited to use of that term in the specification. Also, cover window layers are to be construed as patterned (e.g., with plural protrusions or recesses) in all figures except  FIGS.  1 A- 1 B .