WO2024065155A1

WO2024065155A1 - Carrier for an electronic display

Info

Publication number: WO2024065155A1
Application number: PCT/CN2022/121598
Authority: WO
Inventors: Wei Xiao; Feng He
Original assignee: Schott Glass Technologies (Suzhou) Co. Ltd.
Priority date: 2022-09-27
Filing date: 2022-09-27
Publication date: 2024-04-04

Abstract

A carrier (1) for an electronic display (3), wherein the carrier (1) comprises a flat glass element (5) with two opposing side faces (50, 51), wherein the glass of the glass element (5) has a composition with an alkali oxide content of at least 1 weight percent, and wherein the glass element (5) has a varying bending stiffness along a line (40) across the glass element (5), with the bending stiffness being reduced at a position (42) along the line (40) with respect to the bending stiffness of two other positions (44, 46), wherein the position (42) with reduced bending stiffness is located along the line (40) between the two other positions (44, 46), so that the glass element (5) is bendable at the position with reduced bending stiffness about a bending axis (24) perpendicular to the line (40) across the glass element (5), and wherein both side faces (50, 51) are covered by a polymer layer (12, 14) bonded or fixed to the respective side face (50, 51) of the glass element (5).

Description

Carrier for an electronic display

Description Field of the invention

The invention generally concerns a support or carrier for an electronic display such as a display for a mobile electronic device. In particular, the invention concerns a support or carrier for a flexible electronic display.

Background

Flexible and in particular foldable electronic displays have been subject to intense research and development. Providing a display, which is both flexible and durable, has been proven to be challenging.

According to typical foldable display stack designs, a back-plate is provided between the bottom layer of the OLED display and rigid copper plates in the non-foldable sections. Currently, a structured metal plate is used as back-plate to flexibly support the display and reduce the folding resistance by providing a tuned folding force through local structuring. Typically, stainless steel or titanium with a thickness of about 0.15 mm is used for this back-plate.

US 2022/0103672 A1 discloses a flexible display with a glass layer including a plurality of openings filled with a filling material. Different shapes of the opening are shown. Because the glass layer is on top of the display layer and facing the user, the refractive index of the filling material is required to match the glass. For mechanical support, a metal sheet plate, preferably from stainless steel and reinforcing plates in the non-folding areas of the display are proposed, both of which are disposed below the display layer. The metal sheet plate can include a folding area.

Similarly, US 2021/0337686 A1 discloses a metal hinge element used as a back-plate for flexible displays. The publication also describes that the metal plate may include at least one layer disposed between the display module and the metal plate or on the rear surface of the metal plate, e.g., for adhesion, impact absorption, heat dissipation or sensing inputs from external devices.

However, there are certain disadvantages of typical designs employing a metal back-plate:

1) Metal is not transparent. Therefore, a cut-out in the metal plate is required for an in-display optical fingerprint sensor.

2) Metal may also attenuate ultrasonic waves. Therefore, for in-display ultrasonic fingerprint sensors, cut-outs in the metal plates are required.

3) The density of metal is comparably high, and therefore such a plate adds a decent amount of weight to the mobile device.

4) Metal is prone to fatigue (strength degradation after load cycles) and creep (continuous deformation occurs at stresses below the yield strength) and thus lacks of long term mechanical reliability.

KR20180036904A describes a typical back panel for a foldable display. A rigid panel with a structured foldable mid-section is provided. The flexibility of the panel is gained by a plurality of openings in the folding. The back panel is supposed to support the back surface of a flexible display panel and reinforce rigidity of the display panel. The shown back panel may comprise a lightweight and high-strength material. For example it may be formed of one of glass fiber reinforced plastics (GFRP) , carbon fiber reinforced plastics (CFRP) , aluminum, or plastic. However, similarly to metals in general, these materials may suffer from fatigue in the long term.

WO 2020/228893 A1 discloses a method for producing a flexible display on a glass carrier substrate. In a first step, modifications are introduced, by means of laser radiation into the carrier substrate along a continuous or linear contour. A layer structure consisting of a plurality of layers is then applied to the substrate surface at least in the region having the modifications. A side of the carrier substrate facing away from the layer is subsequently etched, as a result of which material of the carrier substrate is removed along the contour of the laser modified regions such that recesses extend between the layer and an outer surface. However, the etching process may affect the layer structure of the OLED display.

It is therefore an object of the invention to provide a flexible carrier for a foldable or flexible display, which overcomes the aforementioned problems.

Summary of the invention

The invention provides a carrier for an electronic display, wherein the carrier comprises a flat or, respectively, plate shaped glass element with two opposing side faces, wherein the glass of the glass element has a composition with an alkali oxide content of at least 1 weight percent. The glass element has a varying bending stiffness along a line across the glass element, with the bending stiffness being reduced at a position along the line with respect to the bending stiffness of two other positions, wherein the position with reduced bending stiffness being located along the line between the two other positions, so that the glass element is bendable at the position with reduced bending stiffness about a bending axis perpendicular to the line across the glass element. Both side faces are covered by a polymer layer bonded or fixed to the respective side face of the glass element.

A locally reduced bending stiffness, as defined above with three points along a line may be achieved in various ways. It is, however, particularly preferred that the glass element has at least one section extending between two edges of the glass element, wherein the section has a reduced stiffness, in particular with respect to at least one other part or section of the glass element, so that the glass element is bendable at the section. In the following, the term “stiffness” specifically refers to the bending stiffness.

In a preferred refinement, the glass of the glass element has a content of Na ₂O of more than 5 wt-%, preferably of more than 10 wt%. Generally, alkali oxides are advantageous for the mechanical properties of the glass to ensure a high break strength. As the glass element is encapsulated by the polymer layers, migration of alkali ions into electronic functional layers of the display is blocked.

The feature of a bendable glass element according to this disclosure is understood as a glass element which may be bent by at least 90°, preferably by at least 160° without breaking.

This design has various advantages compared to prior art carriers for electronic displays. Using glass as a material for the carrier avoids the above mentioned fatigue and creep phenomena as they are inherent for metal carriers. On the other hand, even though it is not likely, structured glass has the risk of breakage and damaging of other components during impact. In this regard, the polymer layers provide additional protection since they can efficiently absorb impact energy and bond glass fragments in case of breakage. Particularly, since the glass element is embedded between two polymer layers, glass chips are retained and bound within the carrier and cannot damage other components. Further, the polymer layers can be adapted to adjust the bending force of the structured glass without sacrificing the bending strength. The adaptation may be achieved, e.g., by changing the modulus and thickness of the polymer coating.

In another alternative or additional embodiment solving the above discussed problems, a carrier for an electronic display is provided, wherein the carrier comprises a flat or, respectively, plate shaped glass element with two opposing side faces. As in the embodiment described above, the glass element has a varying bending stiffness along a line across the glass element, with the bending stiffness being reduced at a position along the line with respect to the bending stiffness of two other positions, wherein the position with reduced bending stiffness being located along the line between the two other positions, so that the glass element is bendable at the position with reduced bending stiffness about a bending axis perpendicular to the line across the glass element. Both side faces are covered by a polymer layer and bonded or fixed to the respective side face of the glass element. Further, at least one side surface of the carrier is electrically conductive. This embodiment may also be realised using a glass having a content of alkali oxides of less than 1 weight percent or being free of alkali oxides. Generally, for both embodiments, the bendability of the section may be achieved by a stiffness reducing structuring. Further, generally, bonding of the polymer layer may be achieved by a suitable adhesive.

The conductivity of the carrier has the main purpose to provide a ground pad or grounded base. This way, any unwanted/excess electricity, such as static electricity may be discharged. According to one embodiment, an electrically conductive side surface of the carrier may be achieved with at least one of the polymer layers comprising an electrically conductive component, or an electrically conductive filler, respectively. Generally, it is preferred that the conductivity of the carrier surface is at least 10 ^-2 S/m, preferably, at least 1 S/m. To discharge excess electricity or to provide a defined ground potential, the electrically conductive surface may be electrically connected to a part of an electronic device being equipped with a display on the basis of a carrier as described herein. The part to be connected to may be a frame or a conductor, e.g., a ground conductor.

According to a further additional or alternative embodiment, at least one side of the carrier may comprise an electrically conductive coating. Preferably, the coating is deposited onto or embedded within at least one of the polymer layers. Yet a further embodiment which may be employed alternatively or in addition to the other embodiments using a coating or an electrically conductive filler embedded in the polymer layer is an arrangement of electrically conductive wires provided on at least one side of the carrier. It is preferred to use metal wires for good deformability and good conductivity.

Using the carrier according to this disclosure, a bendable or foldable electronic display, e.g., a display for a smart phone may be produced. Specifically, an electronic display is provided comprising a carrier as described herein, wherein the display comprises functional structured layers for converting electrical signals into optical signals. These layers are arranged on one of the polymer layers. The display is bendable or foldable by bending the carrier about the section having the stiffness reducing structuring.

Brief description of the drawings

Fig. 1 shows a schematic cross section of a carrier with a glass element.

Fig. 2 shows the carrier in folded state.

Fig. 3 shows top view of a glass element.

Fig. 4 shows a top view of a variant of the glass element shown in Fig. 3.

Fig. 5 is a cross-sectional view of a refinement of the example shown in Fig. 1.

Fig. 6 shows a further refinement, wherein a filling of openings is provided by the polymer of the polymer layers.

Fig. 7 shows a variant of the examples of Figs. 3, 4, having three stripe shaped bendable sections.

Fig. 8 shows the glass element of Fig. 7 in folded state.

Fig. 9 shows a variant of the embodiment of Fig. 1 comprising recesses as stiffness reducing elements.

Fig. 10 schematically shows an electronic display with a carrier.

Figs. 11 to 15 show further embodiments of glass elements, which may be folded once.

Fig. 16 shows a glass element, which may be folded twice.

Fig. 17 shows a glass element having stiffness reducing openings with a narrowed waist.

Fig. 18 shows a setup for testing material fatigue of a glass element.

Fig. 19, 20, 21 show chemically toughened glass elements.

Detailed description

Fig. 1 shows a carrier 1 with a glass element 5 and two encapsulating polymer layers 12, 14, each on one

side

50, 51 of the glass element 5. The

edges

90, 91 may be exposed, or, as shown in the example, covered with a polymer layer as well. The latter embodiment can provide a full encapsulation of the glass element.

The glass element 5 comprises a section 7 with a stiffness reducing structuring or patterning 70. Due to this design, the bending stiffness varies along the glass element 5. In the example as shown, the bending stiffness varies along the glass element 5 in a direction or along a line beween the

edges

90, 91, having a minimum in section 7. According to a preferred embodiment, which is also realised in the example of Fig. 1, the glass element 5 comprises two

second sections

6, 8 adjoining the section 7 having the stiffness reducing structuring 70. These two

seconds sections

6, 8 have a higher stiffness compared to the section 7 having the stiffness reducing structuring 70. This way, the carrier 1 may be folded about the section 7 without substantially bending the adjoining second sections 5. Thus, if folded, the carrier 1 may have the shape of a closed book cover with the section 7 forming the spine of the book cover. Fig. 2 shows the carrier 1 in this folded state. In this folded state, the surfaces of the

second sections

6, 8 of one side face of the carrier face each other. The surfaces of the other side face forming opposite sides of the booklet shaped carrier 1. As the side faces facing each other are parallel in folded state, the glass element 5 as shown is bendable in a way that it can be bent by 180° without breaking.

In a preferred embodiment and without restriction to the specific example of Fig. 1, the stiffness reducing structuring 70 comprises a pattern of openings 18. These openings may extend from one side face 50 of the glass element 5 to the opposite side face 51, thereby forming through holes. Due to the openings 19, there is less glass present in the section 7 compared to a massive section of the glass element 5 having the same thickness. However, if an average thickness is assigned, this average thickness which also considers the areas of the openings 19 having zero glass thickness, this average glass thickness is lower in the structured section 7 compared to a massive section of the element 1. Accordingly, the section 7 with the stiffness reducing structuring has a reduced average glass thickness compared to the thickness of the glass element 5, whereby the thickness d of the glass element 5 is defined by the distance of its opposing side faces 50, 51. For the same reason, the section 7 has a lower average surface density compared to the surface density of a massive glass element having the same thickness. These two features are not restricted to an embodiment with openings 19 forming the stiffness reducing patterning but also to other kinds of structurings 70.

The thickness d of the glass element 5 is preferably within a range of from 0.7 mm to 1.5 mm to provide both sufficient stability and flexibility.

As a polymer for at least one of the polymer layers 12, 14, polyurethane is suited. In particular, TPU (thermoplastic polyurethane) may be used and is a preferred component of the polymer layers. Besides or in combination with TPU, polycarbonate, polyimide, poly (methyl methacrylate) or polyethylene terephthalate may be used. Generally, without restriction to the aforementioned polymers, it is preferred that the polymer layer comprises a thermoplastic polymer. This way, the polymer layer can be easily applied, e.g., by molding or laminating a polymer foil onto the glass element 5. Generally, according to a further embodiment, at least one of the polymer layers 12, 14 comprises an elastomer, or an elastomeric polymer, respectively. This may reduce additional stiffness of the carrier 1 induced by the outer polymer layers 12, 14. Specifically, a thermoplastic elastomer is particularly suited since such a polymer can be as easily applied as other thermoplastic polymers. According to one embodiment, at least one, preferably both polymer layers contain a TPU that is a thermoplastic elastomer.

The glass of the glass element 5 has a content of one or more alkali oxides of at least 1 weight percent. In particular, the glass may comprise Na ₂O in an amount of more than 5 wt-%, preferably of more than 10 wt%.

According to a further embodiment, one or both of the polymer layers 12, 14 may comprise an electrically conductive filler so that the

polymer layer

12, 14 and hence the

respective side surface

100, 101 of the carrier 1 is electrically conductive, serving, e.g., as a ground surface for the display and/or to avoid damage due to electrostatic discharge.

Fig. 3 shows a top view onto one of the side faces 50 of the glass element 5. Due to the structuring, the glass element 5 has a varying bending stiffness along a line 40 across the glass element 5, whereby the bending stiffness is lower at a position 40 along the line 40 with respect to the bending stiffness of two

other positions

44, 46 on that line, wherein the position 42 with reduced bending stiffness is located along the line 40 between the two

other positions

44, 46. The position 42 with reduced stiffness is located within section 7, whereas the

other positions

44, 46 can be selected to be whithin the adjacent

stiffer sections

6, 8. It is obvious that the line 40 is imaginary. Further, typically,

various positions

42, 44, 46 may be selected, fulfilling the above described condition that the glass element 5 has a reduced bending stiffness at the intermediate position 42.

To provide a high flexibility of the bendable section 7, it is advantageous and preferred that the openings 18 are arranged in rows 23. The section 7 extends between two edges, in particular, two

opposite edges

9, 10 of the glass element 5. Further, it is preferred that these rows extend along, or parallel, respectively, to the bending axis 24 of the glass element 5. Without restriction to the specific embodiment as shown, it is advantageous for a high flexibility, if the rows 23 of openings 18 are staggered in the direction along the bending axis 24. This means that the centers of the openings 18 of adjacent rows 23 are staggered in a direction along the side surface 51 and vertically to the direction of the bending axis 24. Generally, a staggering, which amounts to one half of the period length of the arrangement of openings 18 within a row 23, is preferred. In this embodiment, which is also realized in the shown example, the positions of the openings in direction along the bending axis coincide for every second row 23. Further, according to yet a further embodiment, which is realized in the example of Fig. 3 as well, it is advantageous for the flexibility if the openings 18 are elongated or oblong, particularly, if the openings 18 are elongated in the direction along the bending axis 24. Generally, the pattern of the openings 18 in the section 7 may be optimized based on the folding force requirement to reach a balance between bending force, minimum bending radius and convenience of manufacturing. In yet further embodiments as described below, the carrier 1 can contain more than one bendable section 7. It is possible to have at least two bendable sections 7 and three second sections, respectively, to realize multi-foldable electronic displays, for instance S-fold type displays. The two bendable sections 7 can have similar orientations of the bending axes 24. In particular, the bending axes can be oriented parallel.

Using a flexible glass element as a base for the carrier 1 has many advantages compared to state of the art metallic back plates. Using a structured glass encapsulated by polymer coating to replace the currently used metal back-plates is helpful to reduce the weight of portable devices. This is since glass typically has a smaller density compared to metal. Further, glass shows no fatigue upon continuous folding and no creep when stored for a longer time in folded state. On the other hand, metals generally have a higher thermal conductivity compared to glasses. If thermal conductivity is an issue to dissipate heat from the display, a suitable structuring of the glass may be helpful. Specifically, according to a further embodiment, at least one of the

second sections

6, 8 comprises an arrangement of through holes 21. These through holes may be used to transport heat through the glass element 5. The arrangement may be regular or irregular, depending on where the heat is generated. If the heat is generated uniformly across the display, a regular arrangement of through holes 21 is suitable. However, there may also be localized heat sources on the display. In this case, through holes may be provided which are placed underneath or at least in the vicinity of the one or more heat sources.

Fig. 4 shows a variant of the example of Fig. 3, wherein through holes 21 are provided in the

second sections

6, 8. As can be seen, the through holes 21 are arranged in a regular pattern. Additionally or alternatively, through holes 21 arranged in an irregular or non-periodic pattern may be present. In the shown example, one L-shaped through hole is present in second section 8 which does not coincide with the regular, periodic pattern of the other through holes. This L-shaped through hole 21 may be placed, e.g, , to dissipate heat of a chip or antenna or other heat generating element which is mounted on top of this through hole 21. Further, a through hole 21 may be provided for a fingerprint sensor. This sensor may be arranged below the display. Besides of an improvement in heat dissipation, the through holes 21 in the more rigid

second sections

6, 8 may also serve to further reduce the weight and halt cracks if there are any. According to one embodiment, the through holes 21 may have a maximum lateral dimension in the range of from 0.5 mm to 2.5 mm. In case of round through holes, this maximum lateral dimension is the hole diameter. In case of the quadratic through holes as in the shown example, the maximum lateral dimension is the diagonal length of the holes. For example, the through holes 21 may have a maximum lateral dimension of about 1 mm. Although the through holes 21 may reduce the rigidity of the

second sections

6, 8, these through holes 21 are arranged and sized so that the two

second sections

6, 8 adjoining the section 7 having the stiffness reducing structuring 70, still have a higher stiffness compared to the section 7 with the stiffness reducing structuring 70.

Fig. 5 is a cross-sectional view of a refinement of the example shown in Fig. 1. In this refinement, a glass element 5 similarly to the embodiment of Fig. 4 is used. Accordingly, the glass element 5 has openings 18 in the bendable section 7 and additional through holes 21 within the adjoining

second sections

6, 8. According to an advantageous refinement, which is not restricted to the specific example as depicted in Fig. 5, at least one of the through holes 21 is filled with a filling 26. According to a refinement of this embodiment, the filling 26 has a higher thermal conductivity than the glass of the glass element 5. A high thermal conductivity may be achieved using a polymer as a binder together with suitable fillers such as metal particles. Generally, without restriction to specific embodiments depicted in the figures, the polymer layers 12, 14 and/or optional fillings 26 in through holes 21 and/or openings 18 may have a thermal conductivity of at least 1.3 W/m·K, preferably at least 1.5 W/m·K.

This is a simple and effective measure to improve heat dissipation through the carrier. The openings 18 of the stiffness reducing structuring may be filled as well, in particular, the openings 18 may be filled with the same filling 26 as it is present in the through holes 21. However, as in the depicted example, the openings 18 may as well be void. This can be easily achieved by applying lamination foils as polymer layers 12, 14. The lamination foils then span over the openings 18. An embodiment with void openings 18 can be advantageous to provide a very high flexibility of the bendable section 7.

According to a further alternative or additional refinement, the filling 26 can be electrically conductive. This way, inter alia, the filling 26 may serve as a through contact, e.g. to assure the same electrical potential on both sides of the carrier 1. Generally, it is preferred that the conductivity of the filling is at least 10 ^-2 S/m, preferably, at least 1 S/m.

As a further alternative or additional refinement, an elastic or elastomeric polymer may be chosen as the filling or a component thereof. This may advantageously reduce the bending force compared to a non-elaastomeric filling.

Fig. 6 shows a further refinement, wherein a filling of openings is provided by the polymer of the polymer layers 12, 14. In this embodiment, both the openings 18, which reduce the stiffness of bendable section 7 and the through holes 21 of the adjoining

second sections

6, 8, are filled with a filling 26. Generally, without restriction to the embodiment as shown, at least one opening 18 of the stiffness reducing structuring 70 is filled with a filling 26. This embodiment is independent from the presence of through holes 21 in the

adjacent sections

6, 8. In particular, similarly to the embodiment of Fig. 5, the filling 26 within the opening 18 can advantageously have a higher thermal conductivity than the glass of the glass element 5 to promote heat dissipation.

Generally, as in the embodiment of Fig. 6, the polymer layer material which forms the polymer layers 12, 14 may also form the fillings 26. In this regard, it is advantageous, if the polymer layers 12, 14 have a higher thermal conductivity than the glass element 5. Of course, the through holes 21 are optional. Thus, according to a further embodiment, only the openings 18 are present and are filled with the material of the polymer layers 12 and/or 14, or filled with another filler, e.g. a heat conductive filler similarly to that within the trough holes 21 of Fig. 5.

To provide an electrically conductive surface 100 and/or 101 of the carrier 1, an electrically conductive coating 16 may be provided on the respective side surface. According to a preferred refinement of this embodiment, an electrically conductive oxide forms the electrically conductive coating 16. In particular, the electrically conductive coating 16 may comprise indium tin oxide and/or aluminum zinc oxide. The coating 16 may be embedded within the

polymer layer

12, 14, or, as shown, deposited onto the

polymer layer

12, 14.

According to another preferred embodiment, the

polymer layer

12, 14 comprises an electrically conductive filler such as conductive powder, particularly metal powder or metal nanowires. In this case, the whole polymer layer becomes electrically conductive. Of course, the embodiments using an electrically conductive filler and a coating 16 may also be combined.

Further, one or both of the polymer layers 12, 4 may comprise conductive wires, and/or an electrically conductive mesh. Again, these embodiments may be combined with the other possibilities mentioned herein to provide an electrically

conductive side surface

100, 101 of the carrier.

Fig. 7 shows a further variant of a glass element 5. This variant is particularly suited to support a water droplet like fold, or, in other words, a fold, which is bulging outwards. This is advantageous to increase the bending radius and thereby to reduce bending stress. This is achieved by a glass element 5 comprising three stripe shaped sections 7 having a stiffness reducing structuring 70 and intermediate

second sections

6, 8 having a higher stiffness compared to the three sections 7 having the stiffness reducing structuring 70. Two further rigid

second sections

66, 88 are arranged adjacent to the outer stripe shaped bendable sections 7. These

second sections

66, 88 form the flat support for the main part of the display, similarly to

sections

6, 8 of the examples of Figs. 3, 4.

Fig. 8 shows the glass element of Fig. 7 in folded state. As can be seen, the sequence of flexible elements 7 and rigid

second sections

66, 6, 8, 88 supports the bulging out of the fold without the need of a continuous stiffness reducing patterning 70.

In the embodiments described so far, the stiffness reducing structuring 70 included openings 18 forming through holes through the glass element 5. However, the stiffness may also be reduced by thinning the glass element 5. Thus, according to a further embodiment, the flexible section 7 has a pattern of recesses which reduce the stiffness, or increase the flexibility of the section 7, respectively. A reduced glass thickness at the recess, however, has the disadvantage that a crack may propagate through the recess. In contrast thereto, an opening 18 effectively stops crack propagation. On the other hand, a recess provides a closed surface and may therefore be preferred. Of course, it is also possible to combine both embodiments, i.e. recesses and openings as stiffness reducing elements. Fig. 9 shows such an embodiment, wherein the stiffness reducing patterning includes both recesses 19 and openings 18.

Fig. 10 shows an electronic display 3. Generally, the electronic display 3 comprises a carrier 1 according to this disclosure. Further, the display 3 comprises functional

structured layers

31, 32, 33 for converting electrical signals into optical signals, wherein the

layers

31, 32, 33 are arranged on one of the polymer layers 12, 14. Due to the bendable design of the carrier 1, the display 3 is bendable or foldable as well by bending the carrier 1 about its section 7 having the stiffness reducing structuring 70. According to a further embodiment, the section 7 is not only bendable but also stretchable and/or compressable in length. This may be advantageous to avoid damage of the display layers upon bending. A stretchable or compressable section 7 may in particular be achieved by providing openings 18 as stiffness reducing features.

The

side surface

100, 101 of the carrier 1 that is electrically conductive preferably forms a ground layer for the electronic display. It is particularly preferred that the

functional layers

31, 32, 33 form an OLED display which is particularly suited for a bendable device. Typically, a transparent glass or plastics cover 34 is provided which covers and encapsulates the functional layers 31 –33 of the display 3.

On the back side of the carrier 1, i.e. on the side opposite to the side carrying the functional layers 31-33, further elements or layers may be attached. In particular, these elements may be separated at the bendable section 7, so that these elements or layers are not stretched upon bending. This way, even rigid layers can be attached. According to a refinement, as shown in Fig. 10, a metal plate 28 may be attached to the carrier 1 on the side opposite to the side on which the functional layers of the display are arranged, the metal plate 28 comprising two separate parts, with the separation extending along the section 7 with reduced bending stiffness. The metal plate 28 may, e.g., be a copper plate to improve heat dissipation.

A suitable glass for the glass element 5 is an alumino silicate glass. These glasses typically have a high strength.

Usually, alkali oxide containing glasses are avoided for optoelectronic devices since alkali ions may migrate into the functional layers of the device and deteriorate its functionality. However, as the glass element 5 is encapsulated with the polymer layers 12, 14, this is no longer an issue. It is therefore according to another embodiment even preferred to use an alkali oxide containing glass due to its high strength. Further, the glass element 5 may be chemically strengthened to improve its stability. Again, alkali oxide containing glasses are particularly suited for chemical strengthening. For example, a lithium-aluminosilicate glass may be used for the glass element 5. Other types of glasses include alkali oxide containing borosilicate glasses. According to a first embodiment, the glass of the glass element has a composition comprising the following constituents:

According to a second embodiment, the glass of the glass element has a composition comprising the following constituents:

According to a third embodiment, the glass of the glass element 5 has a composition comprising the following constituents:

According to a fourth embodiment, the glass of the glass element 5 has a composition comprising the following constituents:

The glasses having compositions with the above listed constituents may additionally contain coloring oxides like Nd ₂O ₃, Fe ₂O ₃, CoO, NiO, V ₂O ₅, MnO ₂, TiO ₂, CuO, CeO ₂, Cr ₂O ₃, in an amount of 0 -2 wt. -%. Furher, the glass may contain one or more of the constituents As ₂O ₃, Sb ₂O ₃, SnO ₂, SO ₃, Cl, F, CeO ₂ as fining agent.

According to a fifth embodiment, the glass of the glass element 5 has a composition comprising the following constituents:

A suitable method to produce a glass element 5 having a section 7 with a stiffness reducing structuring 70 comprising openings 18 or recesses 19 is described in EP 3 936 485 A1. Regarding the glass element 5 and its manufacturing, the content of this document is included by reference in its entirety. This document describes an element of an inorganic brittle material corresponding to the glass element 5 according to this disclosure. The element has two opposed sides and a circumferential edge and comprises at least three sections, the at least three sections including a first section and two second sections, the second sections adjoining the first section so that the first section is arranged between the second sections, wherein the first section comprises an arrangement of openings forming passages from one side to the opposed side of the element so that the first section has a higher flexibility than the second sections. The first section corresponds to the flexible section 7 of the glass element according to this disclosure and the second sections correspond to

sections

6, 8 of glass element 5. The openings corresponding to openings 18, as well as optional through holes 21 of the glass element 5 are produced by focusing intense laser light within the glass and thereby producing filament shaped flaws along the contour lines of the openings to be produced. Then, the glass element is subjected to an etching medium, which widens the flaws to form channels which eventually combine so that the glass part inside the contour is unhitched. Accordingly, using this procedure, a carrier 1 according to this disclosure may be produced with a method comprising the steps of

-providing a plate shaped glass element, the glass of the glass element 5 preferably having an alkali oxide content of at least 1 weight percent,

-directing and focusing the laser beam of an ultrashort pulsed laser onto the element, the laser beam having a wavelength at which the glass of the element 5 is transparent so that the laser beam can penetrate into the element,

-the laser beam being focused to produce a preferably elongated focus within the element, the intensity of the laser beam being sufficient to produce a filament shaped damage zone within the element along the focus, and

-the laser beam being moved relative to the element to insert a plurality of filament shaped damage zones side by side along a multitude of ring shaped paths,

-etching by exposing the element to an etchant, the etchant intruding into the filament shaped damage zones, so that the filament shaped damage zones are widened to form channels which combine due to the widening, so that the part of the element encompassed by the ring shaped paths detaches and openings 18 are produced so that a section 7 with the stiffness reducing structuring 70 is formed, Preferably, the glass element is structured so that two

second sections

6, 8, adjoin the section 7 so that the section 7 is arranged between the second sections, with the

second sections

6, 8 having a higher bending stiffness than the section 7 with the stiffness reducing structuring 70. The method further comprises the steps of covering each

side face

50, 51 of the glass element 5 with a

polymer layer

12, 14, so that the openings 18 in the section 7 are closed by the respective polymer layers 12, 14. The polymer layer may be adapted so that at least one surface of the carrier thereby produced, or of the covering is electrically conductive. Alternatively or additionally, an electrically conductive coating may be deposited onto one or both of the polymer layers 12, 14.

Before covering the side faces 50, 51 of the glass element with the polymer layers, the glass element 5 structured using the above specified method may be chemically toughened. Embodiments of chemical toughening are described below with respect to Figs. 19 to 21.

Figs. 11 to 17 show further embodiments of glass elements 5. In each of Figs. 11 to 15, chart (a) shows a top view and chart (b) a side view cross section ot the glass element 5.

Fig. 11 shows a variant of the embodiment of Fig. 7. Similarly to Fig. 7, the glass element 5 has three elongated or stripe shaped sections 7 with a reduced bending stiffness compared to the

second sections

66, 6, 8, 88. Similarly to Fig. 7, the center section 7 with reduced bending stiffness has an arrangement of openings 18. However, the outer sections 7 with reduced stiffness have recesses 19 to to increase the flexibility. Generally and without restriction to the specific embodiment as shown, the stiffness reducing patterning 70 may comprise at least one recess 19 having the shape of a groove 190. Advantageously, the groove 190 may extend from one edge 9 to the other, opposite edge 10. Generally, also, the longitudinal direction of the groove defines the orientation of the bending axis of the respective section 7.

Further, as in the exemplary embodiment of Fig. 11, the stiffness reducing patterning 70 may comprise an arrangement of parallel oriented grooves 190.

The embodiment of Fig. 12 is another variant of the examples of Figs. 7 and 11. In this variant, the stiffness reducing structuring 70 of the outer sections 7 is formed from a single groove 190 extending from one edge 9 to the opposite edge 10. Both embodiments of Fig. 11 and Fig. 12 may be folded to a booklet or droplet like shape as shown in Fig. 8.

Fig. 13 shows an embodiment similarly to Fig. 9. The glass element 5 as shown in Fig. 13 has a single section 7 with a stiffness reducing patterning 70. The patterning 70 generally comprises different stiffness reducing elements, namely a stripe shaped part with an arrangement of openings 18 framed by adjacent recesses 19 in the form of grooves 190. This embodiment is also similar to Fig. 12, if the intermediate

second sections

6, 8 are omitted.

Fig. 14 is an embodiment with a simple stiffness reducing patterning 70 having the shape of a single broad groove 190. This patterning may also be regarded as a slimmed region 191 forming section 7. As in the other embodiments, the slimmed region has a reduced average glass thickness compared to the thickness of the glass element 5. Similarly, the slimmed section 7 has a lower average surface density compared to the surface density of a massive glass element having the same thickness.

Fig. 15 shows a further embodiment where the stiffness is reduced by slimming. In this embodiment, however, there is no stepwise reduction of the stiffness, or, respectively, no

second sections

6, 8 with substantially constant bending stiffness. Rather, the glass element has a gradually varying thickness, with a slimming increasing from the

edges

90, 91 towards the center of the glass element 5. In other words, the glass element 5 has a concave cross section, as is evident from chart (b) of Fig. 15. Thus, the center forms a slimmed region 191 as well. This way, a varying bending stiffness along an imaginary line 40 across the glass element 5 is achieved, with the bending stiffness being reduced at a position 42 along the line 40 with respect to the bending stiffness of two

other positions

44, 46, wherein the position 42 with reduced bending stiffness is located along the line 40 between the two

other positions

44, 46, The other positions are located closer to the

edges

90, 90.

The example of Fig. 16 is based on an embodiment of a glass element 5 having two

sections

7, 700 with reduced bending stiffness adjacent to a second section 8, wherein two further

second sections

6, 88 adjoin the

sections

7, 700, wherein the two

sections

7, 700 with reduced bending stiffness have a different width. In the depicted example, the section 700 has a larger width than the other section 7 with reduced bending stiffness. This way, the glass element 5, or the carrier 1, respectively, can be folded twice. Specifically, in a first step, the outer second section 6 can be folded over the centered second section 8. In a second step, the other outer second section 88 can be folded over the second second section 6. The larger width of 700 is useful for the larger bending radius at this section.

The stiffness reducing openings 18 preferably and as shown so far have an elongated shape. This is useful to impart an anisotropic bending stiffness so that the pattern 70 has a lower bending stiffness for bending about the intended bending axis, compared to a bending about an axis vertically thereto. The bending force may be further reduced with openings 18 as schematically shown in Fig. 17. The openings 18 are elongated as well, however, with expanded ends 180 and a narrowed waist 181.

Other shapes and arrangements of openings for bendable sections of glass elements are known from EP 3 936 485 A1 and EP 22 187 862.2. The content of these documents regarding the design of flexible sections of glass elements is herein incorporated by reference.

Fig. 18 shows a setup for testing material fatigue of a glass element 5. The testing apparatus 60 has a base plate 61 onto which the glass element 5 is fixed at a second section 8. The other second section 6 is supported by a movable plate 64 which is guided by bearings 65 that are movable along channels 63 following a circular path. This way, the intermediate section 7 is bent. Bending angle may be up to, e.g. 180° so that the glass element 5 is folded similarly as shown in Fig. 2 or Fig. 8. The test may as well be carried out with the carrier 1 comprising the glass element 5 and the encapsulating polymer layers 12, 14. According to an embodiment, the glass element 5, or, respectively, the carrier 1 is folded until a target angle or a target bending radius is reached. After moving the plate 64 back, the bending is repeated. According to one embodiment, the glass element 5 or carrier 1, or, respectively, the section 7 with reduced bending stiffness is bendable to a bending radius of 1 mm for 200.000 times without developing cracks. Similarly, according to an additional or alternative embodiment, the glass element 5 or carrier 1 can be bent to a bending angle of 180° for 200.000 times without developing cracks. This fatigue resistance is in particular achievable using a chemically strengthened glass element 5.

Generally, chemical toughening provides a particularly durable glass element 5, or carrier 1, respectively. However, the strengthening of the glass element 5 may also lead to a slight volume expansion of the carrier 1. The volume expansion is determined by the amount of ion exchanged and the thickness, and therefore the expansion of different areas of the carrier 1 may not be matched because of different amount of ion exchanged or different thicknesses. Further, the unbalanced expansion between the area with higher stiffness of the glass and the area of the stiffness reducing structuring 70 may cause some deformations, which occurs typically especially between the area of the stiffness reducing structuring 70 and the adjacent

second sections

6, 8 have a higher bending stiffness. These effects may be overcome or at least reduced by balancing the volume expansion between the areas with different bending stiffness. Thus, according to an embodiment of the glass element 5, the glass element 5 is chemically toughened, and has a section 7 with reduced bending stiffness extending between two

edges

9, 10 of the glass element 1, wherein the section 7 has a stiffness reducing structuring 70, and wherein adjacent

second sections

6, 8 have a higher bending stiffness compared to the at least one section 7 with the stiffness reducing structuring 70. To achieve that, the section 7 with the stiffness reducing structuring 70 has a similar expansion compared to the expansion of the adjacent

second sections

6, 8, a glass element 5 or a carrier 1 with a glass element 5 is provided, wherein the ion exchange layers 52 at the side faces 50, 51 of the glass element 5 have a different chemical structuring in terms of compressive stress (CS) and/or depth of layer (DOL) compared to the compressive stress at the adjacent

second sections

6, 8. This embodiment can generally also be used for other applications than forming the basis for a carrier 1 with encapsulating polymer layers 12, 14.

The balancing of the expansion may be achieved in various ways. Fig. 19 shows a first embodiment. According to this embodiment, some glass is locally removed at the side faces 50, 51 within section 7, resulting in a reduced thickness.

Typically, the structuring 70 is introduced before chemical toughening. Thus, the ion exchange layer 52 would also extend along the stiffness reducing features like the holes 18 of the depicted embodiment. The ion exchange layer along the walls of the openings 18, however, is omitted in the figure for the sake of simplicity.

According to a further embodiment, the time for chemical toughening is shortened at the section 7, resulting in a lower depth of the ion exchange layer 52. For example, the chemical toughening may be performed in two steps, wherein in one step the whole glass element 5 is exposed to the ion exchange medium, typically a bath of molten salt like KNO ₃. In another step, the section 7 with the stiffness reducing structuring 70 is masked to impede ion exchange, whereas the ion exchange proceeds in the adjacent parts of the glass element 5. The sequence of these steps is arbitrary. In this embodiment, the ion exchange layer 52 has a reduced depth within section 7. Fig. 20 shows such an embodiment of a glass element (5) . Of course, a reduced depth of the ion exchange layer is also present in the embodiment of Fig. 19. However, in the embodiment of Fig. 20, the glass thickness is not altered.

A third possibility is a local reverse ion exchange layer 53 within section 7 as shown in Fig. 21. In this reverse ion exchange layer 53, larger alkali ions are at least partially exchanged by smaller alkali ions. For example, K ⁺-ions introduced by the chemical toughening are exchanged back into Na ⁺-ions. This reduces the volume expansion. Thus, to produce a glass element 5 according to this embodiment, a two-step ion exchange may be performed, wherein in one step the ion exchange layer 52 is produced, and wherein in another step the glass element 5 is masked, covering the

second sections

6, 8 and exposing the side faces 50, 51 at section 7. Then, a second ion exchange is performed in a different salt bath comprising smaller alkali ions such as Na ⁺ or Li ⁺-ions so that the higher volume expansion at section 7 is partially relieved to match the initially lower expansion at the adjacent

second sections

6, 8.

List of reference signs

1	Carrier
3	electronic display
5	glass element
6, 8, 66, 88	second section of element 5
7, 700	bendable section of 5
9, 10, 90, 91	edge of glass element 5
12, 14	polymer layer
16	coating
18	opening
19	recess
21	through hole in 6, 8
23	row of openings 18
24	bending axis
26	filling

28	metal plate
31, 32, 33	functional layers of display 3
34	cover
40	line across the glass element
42	position with reduced bending stiffness
44, 46	positions with higher bending stiffness
50.51	side face of glass element 5
52	ion exchange layer
53	reverse ion exchange layer
60	test apparatus
61	base plate
62	bearing
63	channel
64	movable plate
70	stiffness reducing structuring
100, 101	side surface of carrier 1
180	expanded end of opening 18
181	narrowed waist of opening 18
190	groove
191	slimmed region

Claims

A carrier (1) for an electronic display (3) , wherein the carrier (1) comprises a flat glass element (5) with two opposing side faces (50, 51) , wherein the glass of the glass element (5) has a composition with an alkali oxide content of at least 1 weight percent, and wherein the glass element (5) has a varying bending stiffness along a line (40) across the glass element (5) , with the bending stiffness being reduced at a position (42) along the line (40) with respect to the bending stiffness of two other positions (44, 46) , wherein the position (42) with reduced bending stiffness is located along the line (40) between the two other positions (44, 46) , so that the glass element (5) is bendable at the position with reduced bending stiffness about a bending axis (24) perpendicular to the line (40) across the glass element (5) , and wherein both side faces (50, 51) are covered by a polymer layer (12, 14) bonded or fixed to the respective side face (50, 51) of the glass element (5) .
A carrier (1) for an electronic display (3) , in particular according to one of the preceding claims, wherein the carrier (1) comprises a flat glass element (5) with two opposing side faces (50, 51) , wherein the glass element (5) has a varying bending stiffness along a line (40) across the glass element (5) , with the bending stiffness being reduced at a position (42) along the line (40) with respect to the bending stiffness of two other positions (44, 46) , wherein the position (42) with reduced bending stiffness is located along the line (40) between the two other positions (44, 46) , so that the glass element (5) is bendable at the position with reduced bending stiffness about a bending axis (24) perpendicular to the line (40) across the glass element (5) , and wherein both side faces (50, 51) are covered by a polymer layer (12, 14) bonded or fixed to the respective side face (50, 51) of the glass element (5) , and wherein at least one side surface (100, 101) of the carrier (1) is electrically conductive.
The carrier (1) according to claim 2, having at least one of the following features to provide an electrically conductive side surface (100, 101) of the carrier (1) :

- at least one of the polymer layers (12, 14) comprises an electrically conductive filler,

- at least one side of the carrier (1) comprises an electrically conductive coating (16) , preferably, wherein the coating (16) is deposited onto or embedded within at least one of the polymer layers (12, 14) .
The carrier (1) according to the preceding claim, wherein the electrically conductive coating (16) is formed by an electrically conductive oxide, in particular, wherein the electrically conductive coating (16) comprises indium tin oxide or aluminum zinc oxide.
The carrier (1) according to one of the preceding claims, wherein at least one of the polymer layers (12, 14) contains at least one of the following electrically conductive components: conductive wires, conductive powder, an electrically conductive mesh.
The carrier (1) according to one of the preceding claims, wherein at least one of the polymer layers (12, 14) comprises at least one of the following features:

- the polymer layer (12, 14) comprises a thermoplastic polymer,

- the polymer layer (12, 14) comprises a thermoplastic elastomeric polymer,

- the polymer layer (12, 14) comprises polyurethane,

- the polymer layer (12, 14) has a thermal conductivity of at least 1.3 W/m·K.
The carrier according to one of the preceding claims, wherein the glass element (5) has at least one section (7) extending between two edges (9, 10) of the glass element (1) , and wherein the section (7) has a reduced bending stiffness with respect to at least one other part or section of the glass element (1) , so that the glass element (1) is bendable at the section (7) .
The carrier (1) according to the preceding claims, characterized in that the section (7) comprises an arrangement of openings (18) forming through holes.
The carrier according to one of the two preceding claims, characterized in that the section (7) comprises at least one of

- at least one recess (19) , preferably having the shape of a groove (190) extending from one edge (9) of the glass element (5) to another, opposite edge (10) ,

- a slimmed region (191) .
The carrier (1) according to one of the preceding claims, characterized in that the glass element (5) comprises at least two second sections (6, 8) adjoining the at least one section (7) having a reduced bending stiffness, wherein the at least two seconds sections (6, 8) have a higher stiffness compared to the at least one section (7) having the stiffness reducing structuring (70) .
The carrier (1) according to the preceding claim, characterized in that at least one of the second sections (6, 8) comprises an arrangement of through holes (21) .
The carrier (1) according to the preceding claims 7 to 11, characterized in that at least one of the through holes (21) or at least one opening (18) of the stiffness reducing structuring is filled with a filling (26) , .
The carrier (1) according to the preceding claim, characterized by at least one of the following features of the filling (26) :

- the filling (26) having a higher thermal conductivity than the glass of the glass element (5)

- the filling (26) is electrically conductive

- the filling (26) comprises an elastomeric polymer.
The carrier (1) according to one of claims 5 to 7, comprising three stripe shaped sections (7) having a stiffness reducing structuring (70) and intermediate second sections (6, 8) having a higher stiffness compared to the three sections (7) having the stiffness reducing structuring (70) .
The carrier (1) according to one of the preceding claims, characterized by at least one of the following features:

- the section (7) with the stiffness reducing structuring has a reduced average glass thickness compared to the thickness of the glass element (5) , the thickness of the glass element (5) being defined by the distance of its opposing side faces (50, 51) ,

- the section (7) has a lower average surface density compared to the surface density of a massive glass element having the same thickness,

- the section (7) has a pattern of openings (18) or recesses (19) which reduce the stiffness, or increase the flexibility of the section (7) , respectively.
The carrier (1) according to one of the preceding claims, characterized by at least one of the following features:

- the glass element (5) is chemically strengthened,

- the glass element (5) or carrier (1) is bendable to a bending radius of 1 mm for 200.000 times without developing cracks,

- the glass element (5) or carrier (1) is bendable to a bending angle of 180° for 200.000 times without developing cracks.
The carrier (1) according to one of the preceding claims, characterized in that the glass element (5) is chemically toughened and having a section (7) with reduced bending stiffness extending between two edges (9, 10) of the glass element (5) wherein the section (7) has a stiffness reducing structuring (70) , and wherein adjacent second sections (6, 8) have a higher bending stiffness compared to the at least one section (7) with the stiffness reducing structuring (70) .
The carrier (1) according to the preceding claim wherein the ion exchange layers (52) at the side faces (50, 51) of the glass element have a different chemical structuring in terms of CS and/or DOL compared to the compressive stress at the adjacent second sections (6, 8) .
The carrier (1) according to the preceding claim, characterized by at least one of the following features:

- at the side faces (50, 51) within section (7) , glass being locally removed, so that the thickness of the glass element (5) is reduced,

- the ion exchange layer (52) has a reduced depth within section (7) .
An electronic display (3) comprising a carrier (1) according to one of the preceding claims, the display (3) comprising functional structured layers (31, 32, 33) for converting electrical signals into optical signals, wherein the layers (31, 32, 33) are arranged on one of the polymer layers (12, 14) , and wherein the display (3) is bendable or foldable by bending the carrier (1) about its section (7) having the stiffness reducing structuring (70) .
The electronic display (3) according to the preceding claim, wherein the side surface (100, 101) of the carrier (1) that is electrically conductive forms a ground layer for the electronic display.
A method for producing a carrier 1 according to one of claims 1 to 15, comprising the steps of

- providing a plate shaped glass element (5) , the glass of the glass element (5) having an alkali oxide content of at least 1 weight percent,

- directing and focusing the laser beam of an ultrashort pulsed laser onto the element, the laser beam having a wavelength at which the glass of the element (5) is transparent so that the laser beam can penetrate into the element (5)

- the laser beam being focused to produce a preferably elongated focus within the glass element (5) , the intensity of the laser beam being sufficient to produce a filament shaped damage zone within the element along the focus, and

- the laser beam being moved relative to the glass element (5) to insert a plurality of filament shaped damage zones side by side along a multitude of ring shaped paths

, - etching by exposing the element to an etchant, the etchant intruding into the filament shaped damage zones, so that the filament shaped damage zones are widened to form channels which combine due to the widening, so that the part of the element (5) encompassed by the ring shaped paths detaches and openings (18) are produced so that a section (7) with a stiffness reducing structuring (70) is formed, and whereby the glass element (5) is structured so that two second sections (6, 8) , adjoin the section (7) so that the section (7) is arranged between the second sections (6, 8) , whereby the second sections (6, 8) have a higher bending stiffness than the section (7) having the stiffness reducing structuring (70) , and

- covering each side face (50, 51) of the glass element (5) with a polymer layer (12, 14) so that the openings (18) in the section (7) are closed by the respective polymer layers (12, 14) .
The method according to the preceding claim, wherein the glass element (5) is chemically toughened prior to covering the side faces (50, 51) with the polymer layers (12, 14) .