Foldable display device

The present applicationis a Reissue of U.S. Pat. No. 9,983,424 B2 issued on May 29, 2018 (U.S. patent application Ser. No. 15/175,702 filed on Jun. 7, 2016), whichclaims the benefit of Korean Patent Application No. 10-2015-0080871 filed in Korea on Jun. 8, 2015, and Korean Patent Application No. 10-2016-0064898 filed in Korea on May 26, 2016, all of which are hereby incorporated by reference for all purposes as if fully set forth herein.

Field of the Invention

The present invention relates to a foldable display device and a method of manufacturing the same. More particularly, the present invention relates to a foldable display device with improved reliability.

Discussion of the Related Art

As information technology and mobile communication technology have been developed, a display device being capable of displaying a visual image has also been developed. Flat panel display devices, such as a liquid crystal display (LCD) device and an organic light emitting display (OLED) device, are developed and used.

In general, an LCD device includes a liquid crystal panel, which includes upper and lower substrates and a liquid crystal layer therebetween. The liquid crystal layer is driven by an electric field induced between a pixel electrode and a common electrode to display images.

An OLED device includes an organic emitting diode which includes an anode, a cathode and an organic emitting layer therebetween. In the organic emitting diode, holes and electrodes respectively from the anode and the cathode are combined such that light is emitted from the organic emitting layer to display images.

Recently, a foldable display device, which is fabricated by using a flexible substrate, is in demand. The foldable display device is folded to be portable and is unfolded to display images. Namely, with the foldable display device, a large-sized image display can be provided, and portability of the display device is improved.

1 FIG. is a schematic cross-sectional view of a foldable display device according to the related art.

1 FIG. 10 20 30 40 As shown in, the foldable display deviceincludes a display panel, a backplateand a cover window.

20 22 24 22 22 The display panelincludes a flexible substrate, a display parton the flexible substrate. For example, the flexible substratemay be a polyimide substrate.

20 24 When the display panelis an organic emitting diode panel, the display partmay include an organic emitting diode and a thin film transistor (TFT) for driving the organic emitting diode. The organic emitting diode may include an anode, which is connected to the TFT, an organic emitting layer on the anode, and a cathode on the organic emitting layer. In addition, an encapsulation film for preventing moisture penetration may cover the organic emitting diode.

20 24 22 22 22 22 20 On the other hand, when the display panelis a liquid crystal panel, the display partmay include a thin film transistor (TFT) on the flexible substrate, a pixel electrode, which is connected to the TFT, a counter substrate, which faces the flexible substrate, a common electrode, which is on the flexible substrateor the counter substrate, and a liquid crystal layer between the flexible substrateand the counter substrate. The display panelmay further include a backlight unit.

22 22 20 With a carrier substrate (not shown) attached to a lower surface of the flexible substrate, elements such as the TFT are formed on the flexible substrate, and the carrier substrate is released to obtain the flexible display panel.

20 22 30 20 22 30 20 32 In the flexible display panel, since the flexible substrateis thin, the backplatefor supporting the display panelis disposed under the flexible substrate. For example, the backplatemay be formed of polyethylene terephthalate (PET) and may be attached to the display panelby an adhesive layer.

40 20 20 40 40 20 The cover windowis attached to an upper side of the display panel. The damage on the display panelfrom outer impacts is prevented by the cover window. Although not shown, the cover windowmay be attached to the display panelby an adhesive layer.

30 10 30 In the related art foldable display device, the PET film having about 100 micrometers is used for the backplate. When the folding and unfolding operation is repeated in the foldable display device, plastic deformation occurs in the backplatesuch that the restoration of the folded display device to its original configuration may become difficult.

2 2 FIGS.A andB 1 FIG. 2 FIG.A 2 FIG.B 30 10 10 30 30 Namely, as shown in, since there is a plastic deformation problem in the backplate(of) of the PET film, there may be limitations in the folding and unfolding operation of the foldable display device. Namely, the folding and unfolding characteristics of the foldable display devicedeteriorate.illustrates that the backplateis deformed and does not revert to its original shape when external force is removed. Inshows a result of plastic deformation of the backplateafter a repeated folding and unfolding where a center portion is plastic deformed downward and two wing portions are plastic deformed upward.

30 30 30 By reducing a thickness of the backplate, the plastic deformation problem in the backplatemay be decreased. However, the elastic restoring energy of the backplatehaving such a reduced thickness may be decreased and the time for restoring the folded display device to its original state may also be increased.

Accordingly, the present invention is directed to a foldable display device and a method of manufacturing the same that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, a foldable display device may include, for example, a display panel; and a backplate on a surface of the display panel, the backplate including a folding region and unfolding regions at both sides of the folding region, the backplate including at least two opening patterns in the folding region that are different from each other.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

3 FIG. is a schematic cross-sectional view of a foldable display device according to an embodiment of the present invention.

3 FIG. 100 110 180 110 182 190 110 180 As illustrated in, a foldable display deviceaccording to an embodiment of the present invention includes a display panel, a backplate, which is disposed under the display paneland includes at least two opening patternsin a folding region FR, and a cover windowdisposed on the display panel. Namely, the backplateincludes two or more holes in the folding region FR.

110 112 114 112 112 The display panelincludes a flexible substrateand a display parton the flexible substrate. For example, the flexible substratemay be a polyimide substrate.

114 112 114 112 110 A process of forming the display partis performed on the flexible substrateattached to a carrier substrate (not shown) such as a glass substrate. After the process of forming the display part, the carrier substrate and the flexible substrateare separated or released to obtain the display panel.

4 4 FIGS.A andB are schematic cross-sectional views of display panels for a foldable display device according to embodiments of the present invention.

4 FIG.A 110 As illustrated in, the display panelmay be an organic emitting diode panel.

120 112 120 120 A buffer layeris formed on the flexible substrate, and a thin film transistor (TFT) Tr is formed on the buffer layer. The buffer layermay be omitted.

122 120 122 A semiconductor layeris formed on the buffer layer. The semiconductor layermay include an oxide semiconductor material or polycrystalline silicon.

122 122 122 122 122 122 When the semiconductor layerincludes the oxide semiconductor material, a light-shielding pattern (not shown) may be formed under the semiconductor layer. The light to the semiconductor layeris shielded or blocked by the light-shielding pattern such that thermal degradation of the semiconductor layercan be reduced or prevented. On the other hand, when the semiconductor layerincludes polycrystalline silicon, impurities may be doped into both sides of the semiconductor layer.

124 122 124 A gate insulating layeris formed on the semiconductor layer. The gate insulating layermay be formed of an inorganic insulating material such as silicon oxide or silicon nitride.

130 124 122 A gate electrode, which is formed of a conductive material, e.g., metal, is formed on the gate insulating layerto correspond to a center of the semiconductor layer.

4 FIG.A 124 112 124 130 In, the gate insulating layeris formed on the entire surface of the flexible substrate. Alternatively, the gate insulating layermay be patterned to have the same shape as the gate electrode.

132 112 130 132 An interlayer insulating layer, which is formed of an insulating material, is formed on an entire surface of the flexible substrateincluding the gate electrode. The interlayer insulating layermay be formed of an inorganic insulating material, e.g., silicon oxide or silicon nitride, or an organic insulating material, e.g., benzocyclobutene or photo-acryl.

132 134 136 122 134 136 130 130 The interlayer insulating layerincludes first and second contact holesandexposing both sides of the semiconductor layer. The first and second contact holesandare positioned at both sides of the gate electrodeto be spaced apart from the gate electrode.

4 FIG.A 134 136 124 124 130 134 136 124 In, the first and second contact holesandextend into the gate insulating layer. Alternatively, when the gate insulating layeris patterned to have the same shape as the gate electrode, there may be no first and second contact holesandin the gate insulating layer.

140 142 132 140 142 130 122 134 136 A source electrodeand a drain electrode, which are formed of a conductive material, e.g., metal, are formed on the interlayer insulating layer. The source electrodeand the drain electrodeare spaced apart from each other with respect to the gate electrodeand respectively contact both sides of the semiconductor layerthrough the first and second contact holesand.

122 130 140 142 The semiconductor layer, the gate electrode, the source electrodeand the drain electrodeconstitute the TFT Tr, and the TFT Tr serves as a driving element.

4 FIG.A 130 140 142 122 In, the gate electrode, the source electrodeand the drain electrodeare positioned over the semiconductor layer. Namely, the TFT Tr has a coplanar structure.

Alternatively, in the TFT Tr, the gate electrode may be positioned under the semiconductor layer, and the source and drain electrodes may be positioned over the semiconductor layer such that the TFT Tr may have an inverted staggered structure. In this instance, the semiconductor layer may include amorphous silicon.

112 112 Although not shown, a gate line and a data line are disposed on or over the flexible substrateand cross each other to define a pixel region. In addition, a switching element, which is electrically connected to the gate line and the data line, may be disposed on the flexible substrate. The switching element is electrically connected to the TFT Tr as the driving element.

112 130 112 In addition, a power line, which is parallel to and spaced apart from the gate line or the data line, may be formed on or over the flexible substrate. Moreover, a storage capacitor for maintaining a voltage of the gate electrodeof the TFT Tr during one frame, may be further formed on the flexible substrate.

150 152 142 A passivation layer, which includes a drain contact holeexposing the drain electrodeof the TFT Tr, is formed to cover the TFT Tr.

160 142 152 160 160 A first electrode, which is connected to the drain electrodeof the TFT Tr through the drain contact hole, is separately formed in each pixel region. The first electrodemay be an anode and may be formed of a conductive material having a relatively high work function. For example, the first electrodemay be formed of a transparent conductive material such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO).

110 160 When the display panelis operated in a top-emission type, a reflection electrode or a reflection layer may be formed under the first electrode. For example, the reflection electrode or the reflection layer may be formed of aluminum-paladium-copper (APC) alloy.

166 160 150 160 166 A bank layer, which covers edges of the first electrode, is formed on the passivation layer. A center of the first electrodein the pixel region is exposed through an opening of the bank layer.

162 160 162 162 160 An organic emitting layeris formed on the first electrode. The organic emitting layermay have a single-layered structure of an emitting material layer formed of an emitting material. Alternatively, to improve emitting efficiency, the organic emitting layermay have a multi-layered structure including a hole injection layer, a hole transporting layer, the emitting material layer, an electron transporting layer and an electron injection layer sequentially stacked on the first electrode.

164 112 162 164 164 164 A second electrodeis formed over the flexible substrateincluding the organic emitting layer. The second electrodeis positioned at an entire surface of the display area. The second electrodemay be a cathode and may be formed of a conductive material having a relatively low work function. For example, the second electrodemay be formed of aluminum (Al), magnesium (Mg) or Al—Mg alloy.

160 162 164 The first electrode, the organic emitting layerand the second electrodeconstitute the organic emitting diode D.

170 An encapsulation filmis formed on the organic emitting diode D to prevent penetration of moisture into the organic emitting diode D.

170 172 174 176 The encapsulation filmmay have has a triple-layered structure of a first inorganic layer, an organic layerand a second inorganic layer. However, it is not limited thereto.

170 A polarization plate (not shown) may be disposed on the encapsulation filmto reduce an ambient light reflection. The polarization plate may be a circular polarization film.

4 FIG.B 210 110 On the other hand, as illustrated in, a liquid crystal panelmay be used for the display panel.

210 212 250 260 262 The liquid crystal panelincludes first and second flexible substratesand, which face each other, and a liquid crystal layer, which includes liquid crystal molecules, therebetween.

220 212 212 220 A first buffer layeris formed on the first flexible substrate, and a TFT Tr is formed on the first buffer layer. The first buffer layermay be omitted.

222 220 224 222 222 220 A gate electrodeis formed on the first buffer layer, and a gate insulating layeris formed on the gate electrode. In addition, a gate line (not shown), which is connected to the gate electrode, is formed on the first buffer layer.

226 222 224 226 A semiconductor layer, which corresponds to the gate electrode, is formed on the gate insulating layer. The semiconductor layermay include an oxide semiconductor material. Alternatively, the semiconductor layer may include an active layer of intrinsic amorphous silicon and an ohmic contact layer of impurity-doped amorphous silicon.

230 232 226 230 A source electrodeand a drain electrode, which are spaced apart from each other, are formed on the semiconductor layer. In addition, a data line (not shown), which is electrically connected to the source electrodeand crosses the gate line to define a pixel region, is formed.

222 226 230 232 The gate electrode, the semiconductor layer, the source electrodeand the drain electrodeconstitute the TFT Tr.

234 236 232 A passivation layer, which includes a drain contact holeexposing the drain electrode, is formed on the TFT Tr.

240 232 236 242 240 234 A pixel electrode, which is connected to the drain electrodethrough the drain contact hole, and a common electrode, which is alternately arranged with the pixel electrode, are formed on the passivation layer.

252 250 254 252 256 252 252 254 A second buffer layeris formed on the second flexible substrate, and a black matrix, which shields a non-display region such as the TFT Tr, the gate line and the data line, is formed on the second buffer layer. In addition, a color filter layer, which corresponds to the pixel region, is formed on the second buffer layer. The second buffer layerand the black matrixmay be omitted.

212 250 260 262 260 240 242 The first and second flexible substratesandare attached with the liquid crystal layertherebetween. The liquid crystal moleculesof the liquid crystal layeris driven by an electric field between the pixel and common electrodeand.

212 250 260 212 250 212 Although not shown, first and second alignment layers may be formed over the first and second flexible substratesandto be adjacent to the liquid crystal layer. In addition, first and second polarization plates, which have perpendicular transmission axes, may be attached to an outer side of each of the first and second flexible substratesand. Moreover, a flexible backlight unit may be disposed under the first flexible substrateto provide light.

3 FIG. 180 110 110 180 180 112 Referring again to, the backplateis disposed under the display panelsuch that the display panelis supported by the backplate. For example, the backplatemay be attached to the flexible substrateusing an adhesive layer (not shown).

180 112 180 112 The backplatehas a high stiffness than the flexible substrate. Namely, the backplatehas a Young's modulus value (i.e., elastic modulus value) larger than the flexible substrate.

180 For example, the backplatemay be formed of a metal (e.g., stainless-steel (SUS)) or a polymer (e.g., polymethylmetacrylate (PMMA), polycarbonate (PC), polyacrylate (PA), polyvinylalcohol (PVA), acrylonitrile-butadiene-styrene (ABS), polyethylene terephthalate (PET)).

180 180 180 180 110 180 180 When the backplateis formed of a high stiffness material, e.g., SUS, the backplatehas a high restoring force. Accordingly, a thickness of the backplatecan be reduced. In addition, since the backplateof the high stiffness material has a desired stiffness with a relatively low thickness, the display panelis sufficiently supported by the backplate. Moreover, there is no the plastic deformation problem in the backplateby reducing the thickness.

180 However, when the backplateis formed of a high stiffness material, an elastic deformation region becomes narrow such that that the restoration of the folded display device to its original configuration becomes difficult. Namely, the foldable display device maintains the folding configuration even if the foldable display device is unfolded. In other words, a time from the folding configuration to its original configuration is increased.

100 180 182 180 182 180 180 In the foldable display deviceaccording to an embodiment of the present invention, since the backplateincludes at least two opening patterns (or holes)at the folding region FR, the elastic deformation region of the backplateis enlarged or expanded. The opening patternsat the folding region FR serves as a spring such that the restoration characteristic of the backplateis improved. Accordingly, the problem in the time from the folding configuration to its original configuration by reducing the thickness of the backplate.

180 180 182 180 180 100 In other words, since the backplateis formed of a high stiffness material, the restoration characteristic of the backplateis increased. In addition, due to the opening patterns, the elastic deformation region of the backplateis expanded. Accordingly, the backplatehas a relatively small thickness (e.g., about 2 mm), and the folding property (or characteristic) of the foldable display deviceis improved.

182 180 182 186 188 180 186 180 188 180 180 110 186 188 110 180 186 188 180 On the other hand, an image defect may occur by the opening patternsof the backplate. To prevent the image defect problem and protect the opening patterns, first and second step compensation layersandmay be formed on opposite sides of the backplate, respectively. Namely, the first step compensation layeris formed on a rear surface of the backplate, and the second step compensation layeris formed on a front surface of the backplate. As a result, the backplateis positioned between the display paneland the first step compensation layer, and the second step compensation layeris positioned between the display paneland the backplate. In addition, the first and second step compensation layersandmay have stress compensation function for the backplate.

186 188 180 186 188 Each of the first and second step compensation layersandis formed of a material having a low stiffness than the backplate. For example, each of the first and second step compensation layersandmay be formed of one of polyurethane (PU), thermoplastic polyurethane (TPU), polyacrylate, rubber and silicon (Si).

186 188 182 182 186 188 182 The first and second step compensation layersandcover and protect the opening patterns, and the step by the opening patternsis removed by the first and second step compensation layersand. Accordingly, the image defect resulted from the step of the opening patternsis prevented.

186 188 186 188 180 186 188 186 188 182 3 FIG. One or both of the first and second step compensation layersandmay be omitted.illustrates the first and second step compensation layersandcovering an entire surface of the backplate. Alternatively, each of the first and second step compensation layersandmay be formed in the folding region FR except the unfolding region. In addition, one of the first and second step compensation layersandmay be formed to fill a space of the opening patterns.

190 110 110 190 The cover windowprotects the display panelfrom outer impacts and prevents damages (e.g., scratches) on the display panel. The cover windowmay be omitted.

110 190 Although not shown,Further,a touch panel102may be disposed between the display paneland the cover window.

100 180 180 182 180 100 As explained above, in the foldable display deviceincluding a high stiffness backplate, the backplatehas reduced thickness. In addition, since the opening patternsserving as the spring is formed in the folding region FR, the restoration force of the high stiffness backplate is increased. Namely, the backplatehaving a relatively small thickness and a high restoration force is provided. Accordingly, the foldable display devicehaving excellent folding/unfolding properties and a thin profile can be provided.

5 5 FIGS.A toD are schematic plane views of backplates for a foldable display device according to an embodiment of the present invention.

5 FIG.A 180 180 182 182 As illustrated in, in the folding region FR of the backplate, the opening patternincluding a first patterna arranged in a (2n−1)th row (e.g., an odd row) and a second patternb arranged in a (2n)th row (e.g., an even row) is formed. (n is a positive integer)

5 FIG.A 180 In, the folding region FR is positioned at a center of the backplate. However, a position of the folding region FR is not limited. In addition, at least two folding regions FR may be defined.

182 182 182 182 Each of the first and second patternsa andb has a rectangular shape. A space between adjacent two second patternsb in the (2n)th row may correspond to the first patterna in the (2n−1)th row.

182 182 180 Both ends of the first patterna may be positioned in the folding region FR, while an end of the second patternb may be positioned at an edge of the backplatein the folding region FR.

180 180 182 182 182 Namely, a side of the backplatemay be discontinuous in the (2n)th row (or (2n−1)th row). In the folding region FR, the side of the backplateis connected by a portion between the first and second patternsa andb and a portion between adjacent two second patternsb in one row such that the folding region FR has the spring-like function.

5 FIG.A 182 182 182 182 182 182 In, one first patterna is formed in each odd row, and two second patternsb are formed in each even row. However, there is no limitation to the number of the first and second patternsa andb. For example, at least two first patternsa may be formed in each odd row, and at least three second patternsb may be formed in each even row.

182 182 182 182 Each of the first and second patternsa andb is formed to extend along the row direction. Namely, each of the first and second patternsa andb has a major axis along the row direction.

182 1 1 1 1 1 1 In addition, adjacent two of the second patternsb are separated by a first distance Dalong the row direction has a first length (i.e., the major axis) L. The first distance Dis equal to or smaller than the first length L. It is preferred that the first distance Dis smaller than the first length L.

180 182 180 100 Accordingly, the backplatein folding region FR, where the opening patternis formed, has a spring-like function in the unfolding operation such that an elastic restoration energy of the backplatecan be increased. Accordingly, the unfolding speed of the foldable display devicecan be increased and/or the unfolding time can be decreased.

5 FIG.B 280 280 282 282 Referring to, in the folding region FR of the backplate, the opening pattern282including a first patterna arranged in a (2n−1)th row (e.g., an odd row) and a second patternb arranged in a (2n)th row (e.g., an even row) is formed. (n is a positive integer)

5 FIG.B 280 In, the folding region FR is positioned at a center of the backplate. However, a position of the folding region FR is not limited. In addition, at least two folding regions FR may be defined.

282 282 282 282 282 282 282 282 282 282 Each of the first and second patternsa andb has a diamond shape. The first patterna in the (2n−1)th row may correspond to the second patternb in the (2n)th row. The first and second patternsa andb are arranged to be spaced apart from each other. For example, the first patternsa in the (2n−1)th row are spaced apart from each other, and the second patternsb in the (2n)th row are spaced apart from each other. In addition, the first patterna in the (2n−1)th row and the second patternb in the (2n)th row are spaced apart from each other.

282 282 2 2 2 2 2 2 Each of the first and second patternsa andb is separated by a second distance Dalong the row direction has a second length L. The second distance Dis equal to or smaller than the second length L. It is preferred that the second distance Dis smaller than the second length L.

280 282 280 100 Accordingly, the backplatein folding region FR, where the opening patternis formed, has the spring-like function in the unfolding operation such that an elastic restoration energy of the backplateis increased. Accordingly, the unfolding speed of the foldable display deviceis increased.

5 FIG.C 380 380 382 382 Referring to, in the folding region FR of the backplate, the opening pattern382including a first patterna arranged in a (2n−1)th row (e.g., an odd row) and a second patternb arranged in a (2n)th row (e.g., an even row) is formed. (n is a positive integer)

5 FIG.C 380 In, the folding region FR is positioned at a center of the backplate. However, a position of the folding region FR is not limited. In addition, at least two folding regions FR may be defined.

382 382 382 382 382 382 382 382 Each of the first and second patternsa andb has a diamond shape. The first patterna in the (2n−1)th row may correspond to a space between adjacent two second patternsb in the (2n)th row. For example, a center of the first patterna may correspond to the space between adjacent two second patternsb, and a center of the second patternb may correspond to a space between adjacent two first patternsa.

382 382 3 3 3 3 3 3 Each of the first and second patternsa andb is separated by a third distance Dalong the row direction has a third length L. The third distance Dis equal to or smaller than the third length L. It is preferred that the third distance Dis smaller than the third length L.

380 382 380 100 Accordingly, the backplatein folding region FR, where the opening patternis formed, has the spring-like function in the unfolding operation such that an elastic restoration energy of the backplateis increased. Accordingly, the unfolding speed of the foldable display deviceis increased.

5 FIG.D 480 480 482 482 Referring to, in the folding region FR of the backplate, the opening pattern482including a first patterna arranged in a (2n−1)th row (e.g., an odd row) and a second patternb arranged in a (2n)th row (e.g., an even row) is formed. (n is a positive integer)

5 FIG.D 480 In, the folding region FR is positioned at a center of the backplate. However, a position of the folding region FR is not limited. In addition, at least two folding regions FR may be defined.

482 482 482 482 Each of the first and second patternsa andb has an oval-like shape having a constant minor axis length. Namely, each of the first and second patternsa andb has a shape where a semi-circle is combined to both ends of a rectangular center.

482 482 482 482 482 482 In addition, The first patterna in the (2n−1)th row may correspond to a space between adjacent two second patternsb in the (2n)th row. For example, a center of the first patterna may correspond to the space between adjacent two second patternsb, and a center of the second patternb may correspond to a space between adjacent two first patternsa.

482 482 482 482 482 482 4 4 4 4 4 4 482 482 Each of the first and second patternsa andb is formed to extend along the row direction. Namely, each of the first and second patternsa andb has a major axis along the row direction. Each of the first and second patternsa andb is separated by a fourth distance Dalong the row direction has a fourth length L. The fourth distance Dis equal to or smaller than the fourth length L. It is preferred that the fourth distance Dis smaller than the fourth length L. In addition, the semi-circle in the end of each of the first and second patternsa andb has a pre-determined radius of curvature (RC).

480 482 480 100 Accordingly, the backplatein folding region FR, where the opening patternis formed, has the spring-like function in the unfolding operation such that an elastic restoration energy of the backplateis increased. Accordingly, the unfolding speed of the foldable display deviceis increased.

5 5 FIGS.A toD In, the opening pattern has a rectangular shape, a diamond shape or an oval-like shape, but it is not limited thereto. For example, the opening pattern may have a circle shape, an oval shape, a square shape or a trapezoid shape.

6 FIG. is a schematic cross-sectional view of a foldable display device according to an embodiment of the present invention.

6 FIG. 500 510 580 510 582 590 510 580 As illustrated in, a foldable display deviceaccording to an embodiment of the present invention includes a display panel, a backplate, which is disposed under the display paneland includes at least two opening patternsin a folding region FR, and a cover windowdisposed on the display panel. Namely, the backplateincludes two or more holes in the folding region FR.

510 Although not shown, the display panelincludes a flexible substrate and a display part on the flexible substrate. For example, the flexible substrate may be a polyimide substrate, and the display part may be an organic emitting diode.

580 510 510 580 580 510 The backplateis disposed under the display panelsuch that the display panelis supported by the backplate. For example, the backplatemay be attached to the display panelusing an adhesive layer (not shown).

580 510 580 The backplatehas a high stiffness than the flexible substrate of the display panel. Namely, the backplatehas a Young's modulus value (i.e., elastic modulus value) larger than the flexible substrate.

500 580 1 2 1 584 580 In the foldable display device, the backplatehas a first thickness tin the folding region FR and a second thickness t, which is greater than the first thickness t, in the unfolding region UFR at both sides of the folding region FR. Namely, a concave portionis formed in backplatein the folding region FR.

580 1 510 580 For example, when the backplatehas the first thickness tin both the folding region FR and the unfolding region UFR, the folding property in the folding region FR can be satisfied but there is a problem in the support of the display panelin the unfolding region UFR because the stiffness of the backplateis reduced.

580 2 On the other hand, when the backplatehas the second thickness tin both the folding region FR and the unfolding region UFR, there is a problem in the folding property in the folding region FR.

500 580 2 1 580 However, in the foldable display deviceaccording to an embodiment of the present invention, since the backplatehas a relatively large thickness (e.g., the second thickness t) in the unfolding region UFR and a relatively small thickness (e.g., the first thickness t) in the folding region FR, both the stiffness and the folding property of the backplatecan be satisfied.

500 580 582 580 582 584 580 582 580 In addition, in the foldable display deviceaccording to an embodiment of the present invention, since the backplateincludes at least two opening patterns (or holes)at the folding region FR, the elastic deformation region of the backplateis enlarged or expanded. The opening patternis positioned in the concave portionof the backplate. The opening patternsat the folding region FR serves as a spring such that the restoration characteristic of the backplatecan be improved.

582 5 5 FIGS.A toD The shape or the arrangement of the opening patterncan be variously modified as shown in.

482 482 482 482 1 580 1 1 1 580 5 FIG.D For example, when the first and second patternsa andb have an oval-like shape having a constant minor axis length as shown in, the diameter of the semi-circle in the end of the first and second patternsa andb is equal to the first thickness tof the backplatein the folding region FR or is smaller than one and half times the first thickness t, (t≤2RC≤1.5*t). As a result, with sufficient stiffness, the folding property of the backplatecan be improved.

584 582 584 580 582 An etching process is performed to form the concave portionand the opening pattern. Namely, a first etching process is performed to the concave portionto reduce a thickness of the backplatein the folding region FR, and a second etching process is performed to the opening pattern.

6 FIG. 500 590 500 580 584 580 In, the foldable display deviceis folded toward the side of the cover window. Namely, when the foldable display deviceis folded, the backplateis disposed at an outer side and the concave portionis disposed at an outer surface of the backplate.

500 580 584 580 584 510 Alternatively, the foldable display devicemay be folded toward the side of the backplate. In this instance, the concave portionmay be formed at an inner surface of the backplate. Namely, the concave portionmay be formed at a surface facing the display panel.

7 7 FIGS.A toC are schematic cross-sectional views of backplates for a foldable display device according to an embodiment of the present invention.

7 FIG.A 586 580 586 580 584 Referring to, a first step compensation layermay be formed at a side of the backplate. The first step compensation layeris disposed at a surface of the backplateincluding the concave portion.

586 3 4 3 Accordingly, the first step compensation layerhas a third thickness tin the folding region FR and a fourth thickness t, which is smaller than the third thickness t, in the unfolding region UFR.

7 FIG.B 586 584 586 580 Referring to, a first step compensation layermay be formed only in the concave portion. Namely, the first step compensation layerforms a flat top surface with the backplate.

7 FIG.C 586 588 580 586 580 584 588 580 588 5 5 588 3 4 580 500 Referring to, first and second step compensation layersandmay be formed at opposite sides of the backplate, respectively. The first step compensation layeris formed at a surface of the backplate, where the concave portionis formed, and the second step compensation layeris formed at an opposite surface of the backplate. In this instance, the second step compensation layerhas an uniform fifth thickness t. The fifth thickness tof the second step compensation layermay be smaller than the third thickness tand larger than the fourth thickness tsuch that the backplatehas a compressive state in the folding state. Accordingly, the folding/unfolding property of the foldable display devicecan be further improved.

586 588 580 580 586 588 586 588 580 Each of the first and second step compensation layersandis formed of a material having a low stiffness than the backplatesuch that the stress applied to the backplateby the folding operation is compensated or relaxed. For example, each of the first and second step compensation layersandmay be formed of one of polyurethane (PU), thermoplastic polyurethane (TPU), polyacrylate, rubber and silicon (Si). Namely, each of the first and second step compensation layersandhas a Young's modulus value (i.e., elastic modulus value)largersmallerthan the backplate.

586 588 582 582 586 588 582 The first and second step compensation layersandcover and protect the opening patterns, and the step by the opening patternsis removed by the first and second step compensation layersand. Accordingly, an image defect resulted from the step of the opening patternscan be reduced or prevented.

586 580 586 580 584 586 580 On the other hand, since the first step compensation layerand the backplateare formed of different materials, a boundary between the first step compensation layerand the backplatein an end of the concave portionmay be observed by the viewer. Namely, the image quality of the foldable display device may be degraded by a difference in refractive index of the different materials of first step compensation layerand the backplate.

584 586 580 584 166 254 4 FIG.A 4 FIG.B To address this problem, the end (e.g., an edge) of the concave portion(e.g., a boundary between first step compensation layerand the backplate) corresponds to a boundary of adjacent pixel regions in the display panel. For example, the end of the concave portionmay correspond to the bank(of) or the black matrix(of).

8 8 FIGS.A toC are schematic views illustrating backplates for a foldable display device according to an embodiment of the present invention.

8 FIG.A 680 682 682 680 As illustrated in, a folding region FR and an unfolding region UFR are defined in the backplate, and the folding region FR includes a center portion CN and an edge portion ED. An opening pattern, which is formed in the folding region FR, has the same size and has a difference in a distance. Namely, a pitch variable opening patternsare formed in the folding region FR of the backplate.

682 1 682 2 1 With respect to a folding direction, the opening patternsin the edge portion ED are arranged with a first distance d, and the opening patternsin the center portion CN are arranged with a second distance dbeing smaller than the first distance d.

8 FIG.B 8 FIG.A 680 682 680 Referring to, which illustrates the backplatein a folding state, with a distance variable opening patterns, the backplatehas a first curvature radius in the edge portion ED of the folding region FR (of) and a second curvature radius, which is smaller than the first curvature radius, in the center portion CN of the folding region FR.

8 FIG.C 1 2 2 682 1 682 682 2 Referring to, the folding region FR may include a center portion CN, a first edge portion EDand a second edge portion EDbetween the center portion CN and the first edge portion ED. In this instance, with respect to the folding direction, the opening patternsin the first edge portion EDare arranged with a first distance, the opening patternsin the center portion CN are arranged with a second distance, and the opening patternsin the second edge portion EDare arranged with a third distance being larger than the second distance and smaller than the first distance.

682 With respect to the folding direction, the distance between adjacent opening patternsmay be gradually decreased from the edge to the center.

1 682 680 The stress is concentrated in a curvature-starting point (i.e., the edge portion ED or the first edge portion ED) such that the display panel may be damaged in the curvature-starting point. In the foldable display device according to an embodiment of the present invention, the distance between adjacent opening patternsformed in the folding region FR of the backplateis controlled such that the curvature radius in the curvature-starting point (or a folding-starting point) is increased. As a result, the stress on the display device in the curvature-starting point can be decreased or relaxed such that damages on the display panel can be reduced or prevented.

9 9 FIGS.A toC are schematic views illustrating backplates for a foldable display device according to an embodiment of the present invention.

9 FIG.A 780 782 782 780 As illustrated in, a folding region FR and an unfolding region UFR are defined in the backplate, and the folding region FR includes a center portion CN and an edge portion ED. An opening pattern, which is formed in the folding region FR, are arranged with a constant distance and has a difference in size. Namely, a size variable opening patternsare formed in the folding region FR of the backplate.

782 1 782 2 1 With respect to a folding direction, the opening patternin the edge portion ED has a first width w, and the opening patternin the center portion CN has a second width wbeing larger than the first width w.

9 FIG.B 9 FIG.A 780 782 780 Referring to, which shows the backplatein a folding state, with a size variable opening patterns, the backplatehas a first curvature radius in the edge portion ED of the folding region FR (of) and a second curvature radius, which is smaller than the first curvature radius, in the center portion CN of the folding region FR.

9 FIG.C 1 2 2 782 1 782 782 2 Referring to, the folding region FR may includes a center portion CN, a first edge portion EDand a second edge portion EDbetween the center portion CN and the first edge portion ED. In this instance, with respect to the folding direction, the opening patternin the first edge portion EDhas a first width, the opening patternin the center portion CN has a second width, and the opening patternin the second edge portion EDhas a third width being larger than the first width and smaller than the third width.

782 With respect to the folding direction, the size of the opening patternmay be gradually increased from the edge to the center.

682 780 In the foldable display device according to an embodiment of the present invention, the size of the opening patternformed in the folding region FR of the backplateis controlled such that the curvature radius in the curvature-starting point (or a folding-starting point) is increased. As a result, the stress on the display device in the curvature-starting point is decreased or relaxed such that damages on the display panel can be reduced or prevented.

8 8 9 9 FIGS.A toC andA toC 7 FIG.A 584 In, the distance between adjacent opening patterns or the size of the opening pattern is controlled in the backplate including the concave portion(of). Alternatively, the backplate may have an uniform thickness without the concave portion.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.