Foldable display device

Abstract

A foldable display device is provided. The foldable display device includes: a display panel; a cover window disposed on the display panel; and a base film attached below the display panel, wherein the base film includes a first metal sheet and a second metal sheet bonded to the first metal sheet, and the first metal sheet includes a first flat portion, a second flat portion, and an inclined portion bent from the first flat portion and the second flat portion.

Description

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2019-0008157, filed on January 22, 2019, which is hereby incorporated by reference for all purposes as if fully set forth herein. Technical Field

[0002] Exemplary embodiments of the invention relate to a foldable display device. Background Art

[0003] Display devices such as organic light-emitting display devices and liquid crystal display devices include display panels manufactured by forming multiple layers and elements on a substrate. Glass is used as a substrate for the display panel. However, the glass substrate is heavy and fragile. In addition, the glass substrate is rigid, so it is difficult to deform the display panel. Recently, a flexible display panel using a flexible substrate that is light, resistant to external impact and easy to deform and a flexible display device including the flexible display panel have been developed.

[0004] Flexible display devices can be classified into bendable display devices, foldable display devices, rollable display devices, and stretchable display devices according to usage or type. Among them, the foldable display device can be folded or unfolded like a book.

[0005] The foldable display device can be folded to be compact and portable, and in the case of using the foldable display device, the foldable display device can be unfolded to display a wide screen. When the foldable display device is repeatedly folded and unfolded, the bending area (hereinafter referred to as the bending area) of the display panel may be deformed, and the bending area may be damaged. In addition, the bending area and other areas may be deformed (such as buckled or cracked), thereby being damaged.

[0006] The above information disclosed in this Background section is only for understanding the background of the inventive concept and therefore it may contain information that does not constitute the prior art. Summary of the invention

[0007] Exemplary embodiments of the invention provide a foldable display device for reducing deformation and damage.

[0008] Additional features of the inventive concepts 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 inventive concepts.

[0009] An exemplary embodiment of the invention provides a foldable display device, the foldable display device comprising: a display panel; a cover window disposed on the display panel; and a base film attached below the display panel. The base film comprises a first metal sheet and a second metal sheet bonded to the first metal sheet, and the first metal sheet comprises a first flat portion, a second flat portion, and an inclined portion bent from the first flat portion and the second flat portion.

[0010] When the foldable display device is folded, the bent portions at the sides of the inclined portion may unfold, and the first metal sheet may be deformed.

[0011] The first metal sheet may include a first portion and a second portion that are separated from each other.

[0012] The first portion may include a first flat portion, a second flat portion, and an inclined portion bent from the first flat portion and the second flat portion. The second portion may include a first flat portion, a second flat portion, and an inclined portion bent from the first flat portion and the second flat portion.

[0013] The second planar portion of the first part may face the second planar portion of the second part, and the second metal sheet may overlap the second planar portion of the first part and the second planar portion of the second part.

[0014] An upper surface of the first flat portion of the first part, an upper surface of the first flat portion of the second part, and an upper surface of the second metal sheet may be disposed at the same level.

[0015] A lower surface of the first flat portion of the first part, a lower surface of the first flat portion of the second part, and a lower surface of the second metal sheet may be disposed at the same level.

[0016] The base film may further include a step compensation layer disposed on the first metal sheet and the second metal sheet.

[0017] The base film may further include a step compensation layer disposed on the first metal sheet and not disposed on the second metal sheet.

[0018] A gap between the inclined portion and the second metal sheet may be filled with a filler.

[0019] The first metal sheet may further include a third flat portion and an inclined portion bent from the second flat portion and the third flat portion.

[0020] When the curvature radius of the base film that is bent when the foldable display device is folded is set to r mm, the distance between the first flat portion and the third flat portion may be within (πr+10) mm.

[0021] A plurality of holes may be defined in the inclined portion, and the second metal sheet may include a plurality of protrusions inserted into the plurality of holes.

[0022] Another exemplary embodiment of the invention provides a foldable display device, the foldable display device comprising: a display panel; a cover window disposed on the display panel; and a base film attached below the display panel. The base film may include a first metal sheet and a second metal sheet stacked with the first metal sheet, and the first metal sheet may include a first portion and a second portion separated, and the second metal sheet may be coupled to the first portion and the second portion.

[0023] The first portion may include a first flat portion, a second flat portion, and an inclined portion bent from the first flat portion and the second flat portion. The second portion may include a first flat portion, a second flat portion, and an inclined portion bent from the first flat portion and the second flat portion.

[0024] The second flat portion of the first part may face the second flat portion of the second part, and the second metal sheet may be bonded to the second flat portion of the first part and the second flat portion of the second part.

[0025] The inclined portion of the first portion may be bent at an acute angle from the first flat portion of the first portion, and the inclined portion of the second portion may be bent at an acute angle from the first flat portion of the second portion.

[0026] When the foldable display device is folded, the bent portions at the sides of the inclined portion may unfold, and the length of the first metal sheet may increase.

[0027] The base film may further include a step compensation layer disposed on the first metal sheet and the second metal sheet, and the base film may be attached to the display panel through an adhesive layer.

[0028] The base film may further include a step compensation layer disposed on the first metal sheet and not disposed on the second metal sheet, and the base film may be attached to the display panel through an adhesive layer.

[0029] Another exemplary embodiment of the invention provides a foldable display device, the foldable display device comprising: a display panel; a cover window disposed on the display panel; and a base film attached below the display panel. The base film may include a metal sheet, and the metal sheet may include a first flat portion, a second flat portion, a third flat portion, a first inclined portion disposed between the first flat portion and the second flat portion, and a second inclined portion disposed between the second flat portion and the third flat portion, the first inclined portion may be bent at an obtuse angle from the first flat portion and the second flat portion, and the second inclined portion may be bent at an obtuse angle from the second flat portion and the third flat portion.

[0030] 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the inventive concept.

[0032] Figure 1 A perspective view illustrating an unfolded state of a foldable display device according to an exemplary embodiment.

[0033] Figure 2 Shows Figure 1 A perspective view of a first folded state of a foldable display device shown in FIG.

[0034] Figure 3 Shows Figure 1 A perspective view of a second folded state of the foldable display device shown in FIG.

[0035] Figure 4 Shown along Figure 1 0 is a cross-sectional view of a foldable display device according to an exemplary embodiment taken along line IV-IV′ in FIG.

[0036] Figure 5 Shown along Figure 1 2 is a cross-sectional view of a base film according to an exemplary embodiment taken along line VV′ in FIG.

[0037] Figure 6 Shown along Figure 1 2 is a cross-sectional view of a base film according to an exemplary embodiment taken along line VV′ in FIG.

[0038] Figure 7 Shown along Figure 1 2 is a cross-sectional view of a base film according to an exemplary embodiment taken along line VV′ in FIG.

[0039] Figure 8 A perspective view illustrating a base film in a foldable display device according to an exemplary embodiment.

[0040] Fig. 9 Shown along Figure 8 A cross-sectional view taken along line IX-IX'.

[0041] Fig.10 Shows Figure 8 0 is a cross-sectional view of a state of the base film shown in the first folded state.

[0042] Fig.11 Shows Figure 80 is a cross-sectional view of the state of the base film shown in the second folded state.

[0043] Fig.12 Shown along Figure 1 2 is a cross-sectional view of a foldable display device according to an embodiment taken along line IV-IV′ in FIG.

[0044] Fig.13 A perspective view illustrating a base film in a foldable display device according to an exemplary embodiment.

[0045] Fig.14 Shown along Fig.13 A cross-sectional view taken along line XIV-XIV'.

[0046] Fig.15 A cross-sectional view of a display panel according to an exemplary embodiment is shown. DETAILED DESCRIPTION

[0047] In the following description, for the purpose of explanation, many specific details are set forth to provide a thorough understanding of the various exemplary embodiments of the invention. As used herein, an "embodiment" is a non-limiting example of a device or method using one or more inventive concepts disclosed herein. However, it is apparent that various exemplary embodiments may be practiced without these specific details or with one or more equivalent arrangements. In other cases, in order to avoid making the various exemplary embodiments unnecessarily obscure, known structures and devices are shown in block diagram form. In addition, various exemplary embodiments may be different, but need not be exclusive. For example, without departing from the inventive concept, the specific shape, construction and characteristics of the exemplary embodiment may be used or implemented in another exemplary embodiment.

[0048] Unless otherwise specified, the exemplary embodiments shown will be understood as providing exemplary features of details of variations in which some of the inventive concepts can be actually implemented. Therefore, unless otherwise specified, the features, components, modules, layers, films, panels, regions and / or aspects, etc. (hereinafter individually or collectively referred to as "elements") of the various embodiments may be further combined, separated, interchanged and / or rearranged without departing from the inventive concept.

[0049] The use of cross hatching and / or shadows is usually provided in the drawings to make the boundaries between adjacent elements clear. In this way, unless otherwise specified, the presence or absence of cross hatching or shadows does not express or represent any preference or requirement for the specific material, material properties, size, ratio, commonality between the elements shown and / or any other characteristics, attributes, properties, etc. of the elements. In addition, in the drawings, the size and relative size of the elements can be exaggerated for clarity and / or descriptive purposes. When the exemplary embodiment can be implemented differently, the specific process sequence can be performed differently from the described order. For example, two processes described in succession can be performed substantially simultaneously or in an order opposite to the described order. In addition, the same reference numerals represent the same elements.

[0050] When an element or layer is referred to as being "on" another element or layer, "connected to" or "bonded to" another element or layer, the element or layer may be directly on, directly connected to or directly bonded to the other element or layer, or there may be an intermediate element or intermediate layer. However, when an element or layer is referred to as being "directly on" another element or layer, "directly connected to" or "directly bonded to" another element or layer, there is no intermediate element or intermediate layer. For this reason, the term "connection" may refer to a physical connection, an electrical connection and / or a fluid connection with or without an intermediate element. In addition, the D1 axis, the D2 axis and the D3 axis are not limited to three axes such as the x-axis, the y-axis and the z-axis of a rectangular coordinate system, and may be interpreted in a broader sense. For example, the D1 axis, the D2 axis and the D3 axis may be perpendicular to each other, or may represent different directions that are not perpendicular to each other. For the purpose of this disclosure, "at least one of X, Y, and Z" and "at least one selected from the group consisting of X, Y, and Z" may be interpreted as any combination of only X, only Y, only Z, or two or more of X, Y, and Z, such as XYZ, XYY, YZ, and ZZ. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0051] Although the terms "first", "second", etc. may be used herein to describe various types of elements, these elements should not be limited by these terms. These terms are used to distinguish one element from another element. Therefore, without departing from the disclosed teachings, the first element discussed below may be named as the second element.

[0052] For descriptive purposes, spatially relative terms such as "under," "below," "under," "down," "above," "upper," "above," "higher," "side" (e.g., as in "sidewall"), etc., may be used herein to describe the relationship of one element to another (other) element as shown in the accompanying drawings. In addition to the orientation depicted in the accompanying drawings, the spatially relative terms are intended to include different orientations of the device in use, operation, and / or manufacture. For example, if the device in the accompanying drawings is turned over, an element described as "under" or "beneath" other elements or features will subsequently be positioned "above" the other elements or features. Thus, the exemplary term "under" can include both above and below orientations. In addition, the device can be positioned otherwise (e.g., rotated 90 degrees or at other orientations), and as such, the spatially relative descriptors used herein are interpreted accordingly.

[0053] The terms used here are for the purpose of describing specific embodiments, and are not intended to be limited. As used here, unless the context clearly indicates otherwise, the singular "one", "one (kind / person)" and "described (the)" are also intended to include plural forms. In addition, when the terms "include", "comprise" and / or their variations are used in this specification, it is explained that there are stated features, integral bodies, steps, operations, elements, components and / or their groups, but one or more other features, integral bodies, steps, operations, elements, components and / or their groups are not excluded from existence or addition. It should also be noted that, as used here, the terms "substantially", "approximately (about)" and other similar terms are used as approximate terms and are not used as degree terms, so that they are used to explain the inherent deviations of measured values, calculated values ​​and / or provided values ​​that will be recognized by those of ordinary skill in the art.

[0054] Various exemplary embodiments are described herein with reference to cross-sectional views and / or exploded views as schematic diagrams of idealized exemplary embodiments and / or intermediate structures. As such, variations in the illustrated shapes due to, for example, manufacturing techniques and / or tolerances are anticipated. Therefore, the exemplary embodiments disclosed herein need not necessarily be construed as being limited to the shapes of the specifically illustrated regions, but will include shape deviations due to, for example, manufacturing. In this manner, the regions shown in the accompanying drawings may be schematic in nature, and the shapes of these regions may not reflect the actual shapes of the regions of the device, and as such, no limitation is necessarily intended.

[0055] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this disclosure is a part. Terms (such as those defined in general dictionaries) should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and should not be interpreted in an idealized or overly formal sense unless explicitly so defined herein.

[0056] The phrase "in a plan view" refers to viewing a target portion from the top, and the phrase "in a cross-sectional view" refers to a cross section obtained by viewing a vertically cut target portion from the side.

[0057] A foldable display device according to exemplary embodiments will now be described with reference to the accompanying drawings.

[0058] In the drawings, the symbol x used to indicate a direction indicates a first direction, the symbol y indicates a second direction perpendicular to the first direction, and the symbol z indicates a third direction perpendicular to the first direction and the second direction. The first direction x, the second direction y, and the third direction z may correspond to a horizontal direction, a vertical direction, and a thickness direction of the foldable display device, respectively.

[0059] Now refer to Figures 1 to 3 A foldable display device is described.

[0060] Figure 1 A perspective view showing an unfolded state of a foldable display device 1 according to an exemplary embodiment, Figure 2 Shows Figure 1 A perspective view of a first folded state of the foldable display device 1 shown in FIG. Figure 3 Shows Figure 1 A perspective view of a second folded state of the foldable display device 1 shown in FIG.

[0061] The foldable display device 1 (hereinafter also referred to as a display device) can be Figure 1 is unfolded flat as shown in , and can be Figure 2 and Figure 3 The display device 1 may include a bending area BA and first and second flat areas FA1 and FA2 disposed on respective sides of the bending area BA. The bending area BA is an area that bends when the display device 1 is folded, and the first and second flat areas FA1 and FA2 are substantially not bent.

[0062] One curved area BA is shown, and the display device 1 may include a plurality of curved areas BA that are separated from each other or curved with different radii of curvature. For example, the display device 1 may include at least two curved areas and at least three flat areas.

[0063] The display device 1 may include a display area DA for displaying an image and a non-display area NA for surrounding the display area DA. The display area DA may correspond to a screen in which pixels PX are arranged, and the non-display area NA may correspond to a bezel.

[0064] like Figure 2 As shown in , the display device 1 can be folded to expose the screen to the outside (hereinafter, referred to as the outer fold or the first fold). Figure 3 As shown in , the display device 1 can be folded so that the screens face each other, that is, the screen of the first flat area FA1 can face the screen of the second flat area FA2 (hereinafter, referred to as the inner fold or the second fold). In the outer folded state, the screen of the curved area BA can be exposed so that the user can watch it, and in the inner folded state, the screen of the curved area BA can be covered. The display device 1 can be designed to allow one of outer folding and inner folding. When the display device 1 includes a plurality of curved areas BA, one of the plurality of curved areas BA may be a curved area that allows outer folding, and the other curved areas BA may be curved areas that allow inner folding.

[0065] The display device 1 may further include a housing and various components for constructing the display device 1 , for example, a display panel, a driving device, a processor, a memory, a printed circuit board (PCB), a battery, a communication module, a speaker, or various sensors may be accommodated in the housing.

[0066] Figure 4 Shown along Figure 1 2 is a cross-sectional view of the foldable display device 1 according to an exemplary embodiment taken along line IV-IV′ in FIG.

[0067] Reference Figure 4 , the display device 1 has a configuration in which various structures are stacked. The display device 1 includes a display panel DP and a cover window CW for protecting the display panel DP. At least one of the functional layers FL1 and FL2 may be disposed between the display panel DP and the cover window CW. The base film BF may be disposed under the display panel DP. The buffer layer CL may be disposed under the base film BF. The display panel DP, the cover window CW, the functional layers FL1 and FL2, the base film BF, and the buffer layer CL may be attached by adhesive layers AL1 to AL5.

[0068] The display panel DP is a panel in which pixels for displaying an image are formed on a substrate. The display panel DP may include light emitting diodes (LEDs) corresponding to the pixels. The display panel DP is a flexible panel, at least a portion of which can be bent. For example, an area of ​​the display panel DP corresponding to at least the bending area BA of the display device 1 may be flexible and may be bent, and it may be substantially flexible.

[0069] The cover window CW is an optically transparent layer, and a surface thereof is exposed to the outside of the display device 1. The cover window CW may protect components disposed therebelow, particularly, the display panel DP.

[0070] The cover window CW is a flexible window, at least a portion of which is bendable. For example, the area of ​​the cover window CW corresponding to at least the bending area BA of the display device 1 may be flexible and may be bent, and it may be completely flexible. The cover window CW may be a polymer film made of a polymer such as polyimide (PI) or polyethylene terephthalate (PET) to achieve flexible properties. The cover window CW may be a glass film formed as a thin film (e.g., a thickness of less than 100 microns), or may be a glass film produced by locally thinly forming an area corresponding to the bending area BA of the display device 1. When protecting the display panel DP from external impacts, the flexible cover window CW may be weaker than a rigid cover window CW (e.g., a glass plate about 100 microns thick).

[0071] The first functional layer FL1 and the second functional layer FL2 may be disposed between the display panel DP and the cover window CW. In this specification, the functional layer refers to a layer for performing a specific function other than the adhesion function. For example, one of the first functional layer FL1 and the second functional layer FL2 may be a touch panel, and the other of the first functional layer FL1 and the second functional layer FL2 may be an anti-reflection layer.

[0072] Regarding the touch panel, a touch sensor layer may be formed exemplarily on a polymer film such as polyimide. The touch sensor layer may sense contact touch and / or contactless touch of a user. The touch sensor layer may include a touch electrode formed of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO) or a metal mesh, and the touch electrode may be formed as a single layer or multiple layers. The touch sensor layer may not be provided in the form of a touch panel, and it may be formed on the surface of the display panel DP.

[0073] The anti-reflection layer is a layer for reducing reflection of external light, and the anti-reflection layer may include a polarizing layer and / or a phase retardation layer, and the polarizing layer and / or the phase retardation layer may have a film form. The anti-reflection layer may be formed on the display panel DP, for example, the anti-reflection layer may be coated on the display panel DP.

[0074] The base film BF disposed under the display panel DP may have a relatively high modulus (or elastic modulus), for example, the base film BF may have a modulus of about 10 GPa to about 100 GPa, or the base film BF may have a modulus equal to or greater than 100 GPa. The base film BF improves the deformation of the bending area BA and allows the bending area BA to bend with a constant curvature. The base film BF can reduce the buckling of the components disposed under the display panel DP and the deformation caused by the separation or buckling of the layers. The base film BF may be a metal sheet made of a metal or a metal alloy such as Invar or stainless steel (or SUS). The metal sheet may have a thickness based on microns, for example, the metal sheet may be about 15 microns to about 50 microns thick. The base film BF may be made of a polymer such as polyimide (PI) or polyethylene terephthalate (PET). When the base film BF is a polymer film, the base film BF may have a modulus of about 1 GPa to about 10 GPa.

[0075] The buffer layer CL disposed under the base film BF can protect the components disposed thereon, in particular, the display panel DP. The buffer layer CL can absorb impact to protect the display panel DP, and the buffer layer CL can attach the display panel DP to other components such as a frame, a bracket or a housing without damage. The buffer layer CL can be illustratively a porous layer such as a foam resin. In addition to the buffer layer CL, a functional sheet such as a shading sheet, a heating sheet or a waterproof tape can also be disposed under the base film BF.

[0076] In the exemplary embodiment shown, adhesive layers AL1 to AL5 are respectively disposed between the cover window CW and the first functional layer FL1, between the first functional layer FL1 and the second functional layer FL2, between the second functional layer FL2 and the display panel DP, between the display panel DP and the base film BF, and between the base film BF and the buffer layer CL. The adhesive layers AL1 to AL5 may include a pressure sensitive adhesive (PSA) or an optically clear adhesive (OCA).

[0077] When the base film BF is a metal sheet, the base film BF has a significantly higher modulus than the display panel DP, the functional layers FL1 and FL2, and / or the cover window CW of the display device 1, so the base film BF applies stress to the display panel DP, the functional layers FL1 and FL2, and / or the cover window CW, thereby causing rupture. In addition, metal has a short deformation section due to its characteristics, so when the stress increases to above the yield stress, the metal reaches the limit stress and ruptures, resulting in very small deformation. There are flexible metals that are easily deformed, but it is difficult to use them as the base film BF of the foldable display device 1.

[0078] When the foldable display device 1 in which a plurality of components are stacked is repeatedly folded and unfolded, fatigue stress of the display panel DP, the functional layers FL1 and FL2, and / or the cover window CW is accumulated and deformed (e.g., stretched). However, when the foldable display device 1 is repeatedly folded and unfolded, the base film BF of the metal sheet is rarely deformed, so the display panel DP, the functional layers FL1 and FL2, and / or the cover window CW are buckled, and separation or rupture of the layers may occur due to the buckling.

[0079] Now refer to Figures 5 to 14 The base film BF made of a metal sheet and deformable in accordance with the deformation of other layers in the foldable display device 1 is described. Even if not specifically mentioned, reference will be made to Figures 1 to 4 To describe the relationship with other components of the foldable display device 1.

[0080] Figure 5 , Figure 6 and Figure 7 Each of the Figure 1 2 is a cross-sectional view of a base film BF according to an exemplary embodiment taken along line VV′.

[0081] Reference Figure 5 The base film BF includes a first metal sheet 10 , a second metal sheet 20 and a step compensation layer 30 .

[0082] The first metal sheet 10 includes a first portion 11 and a second portion 12 separated from each other. The first portion 11 may be disposed in the first flat area FA1 and the curved area BA of the display device 1, and the second portion 12 may be disposed in the second flat area FA2 and the curved area BA of the display device 1. The first portion 11 and the second portion 12 are bent in the first direction x. Therefore, the first portion 11 includes a first flat portion 111, a second flat portion 112, and an inclined portion 115 disposed between the first flat portion 111 and the second flat portion 112. The second portion 12 includes a first flat portion 121, a second flat portion 122, and an inclined portion 125 disposed between the first flat portion 121 and the second flat portion 122.

[0083] The inclined portions 115 and 125 are bent at an acute angle from the first flat portions 111 and 121, and are bent at an acute angle from the second flat portions 112 and 122. The second flat portions 112 and 122 are disposed below the first flat portions 111 and 121 through the inclined portions 115 and 125, that is, the second flat portions 112 and 122 are farther from the display panel DP than the first flat portions 111 and 121. Due to the inclined portions 115 and 125, there is a step between the first flat portions 111 and 121 and the second flat portions 112 and 122, and thus the inclined portions 115 and 125 may be referred to as "step portions".

[0084] The first flat portion 111 of the first portion 11 may be equal to or substantially at the same level as the first flat portion 121 of the second portion 12, and the second flat portion 112 of the first portion 11 may be equal to or substantially at the same level as the second flat portion 122 of the second portion 12. The second flat portion 112 of the first portion 11 and the second flat portion 122 of the second portion 12 face each other and are separated from each other with a predetermined interval therebetween.

[0085] Regarding the display device 1, the first flat portion 111 may be provided in the first flat area FA1, the first flat portion 121 may be provided in the second flat area FA2, and the second flat portions 112 and 122 may be provided in the curved area BA. The inclined portion 115 may be provided in the first flat area FA1, may be provided in the curved area BA, or may be provided in the first flat area FA1 and the curved area BA; the inclined portion 125 may be provided in the second flat area FA2, may be provided in the curved area BA, or may be provided in the second flat area FA2 and the curved area BA.

[0086] When the bending area BA is small, for example, when the base film BF is designed to be bent with a curvature radius of about 1.0 mm when the display device 1 is folded, the width of the bending area BA is several millimeters. Therefore, when the first metal sheet 10 is formed integrally, it may be difficult to form the inclined portions 115 and 125 by a stamping process using a mold. However, when the first metal sheet 10 is divided into two parts 11 and 12, the inclined portions 115 and 125 are formed by applying a stamping process to the parts 11 and 12, and thus it becomes easy to form the inclined portions 115 and 125.

[0087] The second metal sheet 20 is arranged on the second flat portions 112 and 122 along the bending area BA in the second direction y, and overlaps with the second flat portions 112 and 122. The second metal sheet 20 and the first metal sheet 10 are combined with each other by welding, brazing or pressing. The second metal sheet 20 can be combined with the second flat portions 112 and 122 in the first metal sheet 10. The upper surface of the second metal sheet 20 can be equal to or at substantially the same level as the upper surface of the first flat portions 111 and 121 of the first metal sheet 10. That is, the upper surface of the second metal sheet 20 can be coplanar with the upper surface of the first flat portions 111 and 121 of the first metal sheet 10. The first metal sheet 10 and the second metal sheet 20 combined with each other are metal sheets that substantially constitute the base film BF. The first metal sheet 10 and the second metal sheet 20 can have a thickness of about 15 microns to about 50 microns, respectively.

[0088] The step compensation layer 30 is disposed on the first metal sheet 10 and the second metal sheet 20. The step compensation layer 30 flattens the upper surface of the base film BF by compensating for a step that may be generated between the first metal sheet 10 and the second metal sheet 20. The step compensation layer 30 may be formed of a pad or resin having high elasticity. The step compensation layer 30 may be attached to the surfaces of the first metal sheet 10 and the second metal sheet 20 in the form of a buffer tape, for example. Figure 4 , the display panel DP may be disposed on the step compensation layer 30, and may be attached to the step compensation layer 30 of the base film BF through the adhesive layer AL4. The step compensation layer 30 may be omitted. In this case, the display panel DP may be attached to the first metal sheet 10 and the second metal sheet 20 of the base film BF through the adhesive layer AL4.

[0089] When the first metal sheet 10 is bonded to the second metal sheet 20 and the first metal sheet 10 includes the inclined portions 115 and 125 as described above, and when the bending area BA is bent due to the folding of the display device 1, the bent portions on the sides of the inclined portions 115 and 125 are unfolded, and the length of the first metal sheet 10 can be increased. The bent portions on the sides of the inclined portions 115 and 125 act as springs. Therefore, when the display panel DP, the functional layers FL1 and FL2, and / or the cover window CW are deformed, the base film BF can be deformed according to the deformation, and thus the display panel DP, the functional layers FL1 and FL2, and / or the cover window CW can be prevented from being buckled or broken.

[0090] Reference Figure 6 , with reference to Figure 5 In a similar manner to the exemplary embodiment described above, the base film BF includes a first metal sheet 10, a second metal sheet 20, and a step compensation layer 30. However, the first metal sheet 10 and the second metal sheet 20 are formed as if Figure 5 The first metal sheet 10 and the second metal sheet 20 shown in FIG. are turned over. Figure 6 The exemplary embodiments shown will focus on Figure 5 Differences of the exemplary embodiments shown.

[0091] The first metal sheet 10 includes a first portion 11 and a second portion 12 separated from each other. The first portion 11 includes a first flat portion 111, a second flat portion 112, and an inclined portion 115 disposed between the first flat portion 111 and the second flat portion 112, and the second portion 12 includes a first flat portion 121, a second flat portion 122, and an inclined portion 125 disposed between the first flat portion 121 and the second flat portion 122. The inclined portions 115 and 125 are bent at an acute angle from the first flat portions 111 and 121, respectively, and are bent at an acute angle from the second flat portions 112 and 122, respectively. The second flat portions 112 and 122 are disposed above the first flat portions 111 and 121 through the inclined portions 115 and 125, that is, the second flat portions 112 and 122 are disposed close to the display panel DP, and the upper surfaces of the second flat portions 112 and 122 are disposed above the upper surfaces of the first flat portions 111 and 121.

[0092] The second metal sheet 20 is disposed below the second flat portions 112 and 122 along the bending area BA in the second direction y, and is bonded to the first metal sheet 10. The lower surface of the second metal sheet 20 may be identical to or substantially at the same level as the lower surfaces of the first flat portions 111 and 121 of the first metal sheet 10, that is, the lower surface of the second metal sheet 20 may be substantially coplanar with the lower surfaces of the first flat portions 111 and 121 of the first metal sheet 10. The first metal sheet 10 and the second metal sheet 20 bonded to each other are metal sheets that substantially constitute the base film BF.

[0093] The step compensation layer 30 is disposed on the first metal sheet 10. In more detail, the step compensation layer 30 may be disposed on the first flat portions 111 and 121 of the first metal sheet 10, and the step compensation layer 30 may not be disposed on the second metal sheet 20. The step compensation layer 30 may be attached to the upper surfaces of the first flat portions 111 and 121 in the form of a buffer tape, for example. The upper surface of the step compensation layer 30 and the upper surface of the second flat portions 112 and 122 of the first metal sheet 10 may be substantially coplanar. Therefore, the step compensation layer 30 may planarize the upper surface of the base film BF by compensating for steps that may be generated between the first flat portions 111 and 121 and the second flat portions 112 and 122 of the first metal sheet 10. Referring to Figure 4 , the display panel DP may be disposed on the step compensation layer 30, and the display panel DP may be attached to the step compensation layer 30 of the base film BF and the second flat portions 112 and 122 of the first metal sheet 10 through the adhesive layer AL4. The step compensation layer 30 may be omitted. In this case, the display panel DP may be attached to the first metal sheet 10 of the base film BF through the adhesive layer AL4.

[0094] When the first metal sheet 10 and the second metal sheet 20 are combined as described above and the first metal sheet 10 includes the inclined portions 115 and 125, when the bending area BA is bent according to the folding of the display device 1, the bending portions on the sides of the inclined portions 115 and 125 are unfolded, and the length of the first metal sheet 10 can be increased. Therefore, when the display panel DP, the functional layers FL1 and FL2, and / or the cover window CW are deformed, the base film BF can be deformed, and thus the deformation such as buckling on the display panel DP, the functional layers FL1 and FL2, and / or the cover window CW or the generation of damage such as cracks can be controlled.

[0095] Reference Figure 7 The base film BF includes a metal sheet 10 and a step compensation layer 30. Figure 5 and Figure 6 Unlike the described exemplary embodiment including two metal sheets 10 and 20 , the base film BF according to the present exemplary embodiment includes one metal sheet 10 , and the metal sheet 10 is not divided into two parts but is formed integrally.

[0096] The metal sheet 10 includes a first flat portion 111, a second flat portion 112, a third flat portion 113, a first inclined portion 115 disposed between the first flat portion 111 and the second flat portion 112, and a second inclined portion 117 disposed between the second flat portion 112 and the third flat portion 113. The first inclined portion 115 is bent at an obtuse angle from the first flat portion 111 and the second flat portion 112, and the second inclined portion 117 is bent at an obtuse angle from the second flat portion 112 and the third flat portion 113. Therefore, like the letter "Z", the metal sheet 10 includes a folded portion (the first inclined portion 115 and the second inclined portion 117 and the bent portions on each side), so that when the display device 1 is folded, the metal sheet 10 can become thinner than the first flat portion 111 and the second flat portion 112. Figure 5 and Figure 6 The metal sheet 10 shown in FIG. 1 is long. Therefore, a margin of the base film BF to be deformed may be increased corresponding to the deformation of the display panel DP, the functional layers FL1 and FL2, and / or the cover window CW.

[0097] The upper surface of the first flat portion 111 and the upper surface of the third flat portion 113 may be substantially coplanar. The metal sheet 10 is bent so that the second flat portion 112 may be disposed above the first flat portion 111 and the third flat portion 113. Unlike the illustration, the metal sheet 10 may be bent so that the first flat portion 111 and the third flat portion 113 may be disposed above the second flat portion 112, in which case the display panel DP may be attached to the first flat portion 111 and the third flat portion 113 of the metal sheet 10 of the base film BF through the adhesive layer AL4.

[0098] The step compensation layer 30 is disposed on the metal sheet 10. In more detail, the step compensation layer 30 may be disposed on the first flat portion 111 and the third flat portion 113 of the metal sheet 10. The upper surface of the step compensation layer 30 and the upper surface of the second flat portion 112 of the metal sheet 10 may be substantially coplanar. Therefore, the step compensation layer 30 may planarize the upper surface of the base film BF by compensating for the steps that may be generated between the first flat portion 111 and the third flat portion 113 of the metal sheet 10 and the second flat portion 112. The step compensation layer 30 may be omitted.

[0099] Figure 8 1 is a perspective view showing a base film BF in a foldable display device 1 according to an exemplary embodiment, Fig. 9 Shown along Figure 8 A cross-sectional view taken along line IX-IX'. Fig.10 Shows Figure 8 A cross-sectional view of a state of the base film BF shown in the first folded state, Fig.11 Shows Figure 8 0 is a cross-sectional view of a state of the base film BF shown in the second folded state.

[0100] Reference Figures 8 to 11 The base film BF described is similar to that of reference Figure 5 The base film BF is described, and in order to make the structure of the metal sheet clear, the base film BF will be shown without the step compensation layer 30. Therefore, the description of the above structure will be omitted, and the deformation of the metal sheet when the base film BF is folded will be mainly described.

[0101] Reference Figure 8 , Fig. 9 and Fig.10 , when the display device 1 is folded outward, the second metal sheet 20 and the second flat portions 112 and 122 of the first metal sheet 10 may be bent at a predetermined radius of curvature. The second metal sheet 20 may be bent to be disposed further outward than the second flat portions 112 and 122. In this case, the bent portions B11, B12, B21, and B22 on each side of the inclined portions 115 and 125 of the first metal sheet 10 are unfolded, and the length of the first metal sheet 10 may be increased. Specifically, referring to Fig.10 , when the length of the inclined portion 115 of the first portion 11 is set to α, and the angle (eg, acute angle) at which the inclined portion 115 is bent from the first flat portion 111 is set to θ 1 When the bent portions B11 and B12 of the first portion 11 of the first metal sheet 10 are fully unfolded as shown by the dotted line, the increment δ of the length of the first portion 11 is 1 Basically as follows.

[0102] δ1 =α(1-cosθ 1 )

[0103] Similarly, when the length of the inclined portion 125 of the second portion 12 is set to β, and the angle (eg, acute angle) at which the inclined portion 125 is bent from the first flat portion 121 is set to θ 2 When the bent portions B21 and B22 of the second portion 12 of the first metal sheet 10 are fully unfolded as shown by the dotted line, the increment δ of the length of the second portion 12 is 2 Basically as follows.

[0104] δ 2 =β(1-cosθ 2 )

[0105] Therefore, by controlling the lengths α and β of the inclined portions 115 and 125 and the bending angle θ 1 and θ 2 To determine the deformation (i.e., the length increment δ 1 and δ 2 ). The increment δ of the length of the first metal sheet 10 1 and δ 2 The length of the inclined portions 115 and 125 and the bending angle θ can be set accordingly. 1 and θ 2 , so that the length of the first metal sheet 10 can be increased corresponding to the deformation of the display panel DP, the functional layers FL1 and FL2 and / or the cover window CW, to reduce or prevent the occurrence of buckling, layer separation or cracking caused by the characteristic differences between the layers of the display device 1.

[0106] When the display device 1 is bent, the bent portions B11, B12, B21, and B22 of the first metal sheet 10 may not be fully unfolded but may be partially unfolded, so the increment (δ 1 +δ 2 ) can represent the maximum length increment allowed. In addition, α and β can be equal to or different from each other, θ 1 and θ 2 Can be equal to or different from each other.

[0107] The first metal sheet 10 is bonded to the display panel DP, the functional layers FL1 and FL2, and the cover window CW through adhesive layers AL1 to AL4, so when the display panel DP, the functional layers FL1 and FL2 and / or the cover window CW are deformed, the bent portions B11, B12, B21, and B22 of the first metal sheet 10 may be unfolded like a spring, or may be bent and deformed.

[0108] Reference Figure 8 , Fig. 9 and Fig.11 , when the display device 1 is folded, the second metal sheet 20 and the second flat portions 112 and 122 of the first metal sheet 10 may be bent. The second metal sheet 20 may be bent to be located further inside than the second flat portions 112 and 122. In this case, the bent portions B11, B12, B21, and B22 at the sides of the inclined portions 115 and 125 of the first metal sheet 10 are unfolded, and the length of the first metal sheet 10 may be increased. Specifically, referring to Fig.11 , when the bent portions B11 and B12 of the first portion 11 of the first metal sheet 10 are fully unfolded as shown by the dotted line, the increment λ of the length of the first portion 11 1 The increment λ of the length of the second portion 12 when the bent portions B21 and B22 of the second portion 12 of the first metal sheet 10 are fully unfolded as shown by the dotted line 2 Basically as follows.

[0109] λ 1 =α(1-cosθ 1 ),as well as

[0110] λ 2 =β(1-cosθ 2 )

[0111] Therefore, the maximum increase in length (λ) of the first metal sheet 10 in the case of inward folding 1 +λ 2 ) can be compared with the maximum increment (δ) of the length of the first metal sheet 10 in the case of external folding. 1 +δ 2 )equal.

[0112] Fig.12 Shown along Figure 1 2 is a cross-sectional view of the foldable display device 1 according to an exemplary embodiment taken along line IV-IV′ in FIG.

[0113] Reference Fig.12 and Figure 5 , the substrate film BF and Figure 5Similar to the base film BF shown in , the first metal sheet 10 is not divided but formed integrally. In detail, the metal sheet 10 includes a first flat portion 111, a second flat portion 112, and a third flat portion 113, and includes a first inclined portion 115 between the first flat portion 111 and the second flat portion 112 and a second inclined portion 117 between the second flat portion 112 and the third flat portion 113. The first inclined portion 115 is bent at an acute angle from the first flat portion 111 and the second flat portion 112, and the second inclined portion 117 is bent at an acute angle from the second flat portion 112 and the third flat portion 113. When the bending area BA is not very narrow, when the metal sheet 10 is formed integrally, the inclined portions 115 and 117 can be easily formed according to a stamping process. In addition, Figure 5 and Figure 6 The first metal sheet 10 shown in FIG. 1 may be Fig.12 As shown in FIG.

[0114] When the radius of curvature of the base film BF that is bent when the display device 1 is folded is r millimeters, the distance d between the first flat portion 111 and the third flat portion 113 can be within (πr+10) millimeters (here, π is pi). The purpose of doing this is to set the first inclined portion 115 and the second inclined portion 117 within a range in which shear deformation of the adhesive layers AL4 and AL5 is basically generated (an area in which deformation or buckling of the layers can be easily generated). When the first inclined portion 115 and the second inclined portion 117 are set within such a range, deformation of the first metal sheet 10 (i.e., unfolding of the bent portions on each side of the first inclined portion 115 and the second inclined portion 117) can be quick and easy. For the same reason, in an exemplary embodiment in which the first metal sheet 10 is divided into two parts 11 and 12 (for example, refer to Figure 5 and Figure 6 ), the distance between the first flat portion 111 of the first portion 11 and the first flat portion 121 of the second portion 12 may be within (πr+10) mm.

[0115] In another exemplary embodiment, a gap may exist between the inclined portions 115 and 117 of the first metal sheet 10 and the second metal sheet 20. In order to prevent the gap from being visible, the gap may be filled with a filler F such as a resin.

[0116] Fig.13 1 is a perspective view showing a base film BF in a foldable display device 1 according to an exemplary embodiment, Fig.14 Shown along Fig.13 In order to make the structure of the metal sheet clear, Fig.13 The base film BF excluding the step compensation layer 30 is shown.

[0117] Reference Fig.13 and Fig.14 , although similar to the reference Figures 8 to 11 The base film BF of the described exemplary embodiment, but the holes H are formed in the inclined portions 115 and 125 of the first metal sheet 10 at a predetermined pitch in the second direction y. In addition, protrusions P corresponding to the holes H of the inclined portions 115 and 125 are formed on respective edges on the second metal sheet 20 along the second direction y. The protrusions P of the second metal sheet 20 are inserted into the holes H of the inclined portions 115 and 125. The upper surface of the protrusions P of the second metal sheet 20 may be at substantially the same level as the upper surface of the first flat portions 111 and 121 of the first metal sheet 10. When the first metal sheet 10 and the second metal sheet 20 of the base film BF are formed and combined as described above, the gap between the inclined portions 115 and 125 and the second metal sheet 20 may be reduced, the visibility of the gap may be suppressed, or the flatness of the base film BF may be improved.

[0118] Fig.13 and Fig.14 1 shows a configuration in which the first metal sheet 10 is divided into a first portion 11 and a second portion 12, and the first metal sheet 10 can be Fig.12 The embodiments described above are formed integrally in a similar manner. Fig.13 and Fig.14 In the display device 1, the second metal sheet 20 may be disposed between the first metal sheet 10 and the display panel DP. Alternatively, the base film BF may be disposed such that the first metal sheet 10 may be disposed between the second metal sheet 20 and the display panel DP in the display device 1. In this case, the base film BF may be disposed such that the first metal sheet 10 may be disposed between the second metal sheet 20 and the display panel DP in the display device 1. Figure 6 As shown in FIG. 8 , a step compensation layer 30 is provided.

[0119] Finally, we will now refer to Fig.15 A configuration of a display panel DP included in the foldable display device 1 according to an exemplary embodiment is described.

[0120] Fig.15 A cross-sectional view of a display panel DP according to an exemplary embodiment is shown. Fig.15 A cross-sectional view illustrating an example of a stacked configuration of a display panel DP according to an exemplary embodiment. Fig.15 The cross section shown in may correspond to substantially one pixel area.

[0121] The display panel DP includes a substrate SUB, a transistor TR formed on the substrate SUB, and an organic light emitting diode OLED connected to the transistor TR.

[0122] The substrate SUB may be a flexible substrate made of a polymer such as polyimide (PI), polyamide (PA) or polyethylene terephthalate (PET). The substrate SUB may be a barrier layer for preventing moisture or oxygen from penetrating from the outside. For example, the substrate SUB may include at least one polymer layer and at least one barrier layer, and the polymer layer and the barrier layer may be alternately stacked.

[0123] The first insulating layer IN1 is disposed on the substrate SUB. The first insulating layer IN1 may be referred to as a buffer layer, and the first insulating layer IN1 may prevent impurities that may diffuse from the substrate SUB to the semiconductor layer A and reduce stress applied to the substrate SUB during a process for forming the semiconductor layer A. The barrier layer and the first insulating layer IN1 may include an inorganic insulating material such as silicon oxide or silicon nitride.

[0124] The semiconductor layer A of the transistor TR is disposed on the first insulating layer IN1, and the second insulating layer IN2 is disposed on the semiconductor layer A. The semiconductor layer A includes a source region, a drain region, and a channel region disposed between the source region and the drain region. The semiconductor layer A may include a semiconductor material such as polycrystalline silicon, an oxide semiconductor, or amorphous silicon. The second insulating layer IN2 may be referred to as a gate insulating layer, and the second insulating layer IN2 may include an inorganic insulating material.

[0125] A gate conductor including a gate electrode G of the transistor TR is disposed on the second insulating layer IN2. The gate conductor may include a metal such as molybdenum (Mo), copper (Cu), aluminum (Al), silver (Ag), chromium (Cr), tantalum (Ta), titanium (Ti), or a metal alloy thereof.

[0126] The third insulating layer IN3 is disposed on the gate conductor. The third insulating layer IN3 may be referred to as an interlayer insulating layer, and may include an inorganic insulating material.

[0127] A data conductor including a source electrode S and a drain electrode D of the transistor TR is disposed on the third insulating layer IN3. The source electrode S and the drain electrode D are connected to a source region and a drain region of the semiconductor layer A through contact holes formed in the third insulating layer IN3 and the second insulating layer IN2. The data conductor may include a metal such as aluminum (Al), copper (Cu), silver (Ag), molybdenum (Mo), chromium (Cr), gold (Au), platinum (Pt), palladium (Pd), tantalum (Ta), tungsten (W), titanium (Ti), or nickel (Ni), or a metal alloy thereof.

[0128] The fourth insulating layer IN4 is disposed on the data conductor. The fourth insulating layer IN4 may be referred to as a planarization layer, and may include an organic insulating material.

[0129] The first electrode E1 is disposed on the fourth insulating layer IN4. The first electrode E1 may be referred to as a pixel electrode. The first electrode E1 may be connected to the drain electrode D through a contact hole formed in the fourth insulating layer IN4, and may receive a data signal for controlling the brightness of the organic light emitting diode OLED.

[0130] The fifth insulating layer IN5 is disposed on the fourth insulating layer IN4. The fifth insulating layer IN5 may be referred to as a pixel defining layer, and includes an opening overlapping the first electrode E1. The light emitting layer EL is disposed on the first electrode E1 in the opening of the fifth insulating layer IN5, and the second electrode E2 is disposed on the light emitting layer EL. The second electrode E2 may be referred to as a common electrode.

[0131] The first electrode E1, the light emitting layer EL and the second electrode E2 constitute an organic light emitting diode OLED. The first electrode E1 may be an anode of the organic light emitting diode OLED, and the second electrode E2 may be a cathode of the organic light emitting diode OLED.

[0132] The encapsulation layer EC is disposed on the second electrode E2. The encapsulation layer EC may encapsulate the organic light emitting diode OLED to prevent moisture or oxygen from penetrating from the outside. The encapsulation layer EC may include at least one inorganic material layer and at least one organic material layer, and the inorganic material layer and the organic material layer may be alternately stacked.

[0133] A passivation film PF for protecting the display panel DP may be disposed under the substrate SUB.

[0134] Return to reference Figure 4 The cover window CW, the first functional layer FL1 and / or the second functional layer FL2 may be attached to the encapsulation layer EC of the display panel DP through adhesive layers AL1, AL2 and AL3. The base film BF and the buffer layer CL may be attached under the passivation film PF of the display panel DP through adhesive layers AL4 and AL5.

[0135] The case where the display panel DP is the organic light emitting panel has been exemplified, and for example, the display panel DP may be various display panels such as a display panel including light emitting diodes (LEDs) or a display panel including a liquid crystal layer.

[0136] According to the inventive concept, deformation and damage can be reduced while maintaining the folding property of the foldable display device.

[0137] Although certain exemplary embodiments have been described herein, other embodiments and modifications will be apparent from this description. Therefore, as will be apparent to one of ordinary skill in the art, the inventive concept is not limited to such embodiments, but to the broader scope of the claims and various obvious modifications and equivalent arrangements.

Claims

1. A foldable display device, comprising: Display panel; A cover window, disposed on the display panel; as well as A base film is attached below the display panel. in: The base film includes a first metal sheet and a second metal sheet bonded to the first metal sheet; The first metal sheet includes a first flat portion at a first height, a second flat portion at a second height different from the first height, and an inclined portion bent from the first flat portion and the second flat portion and extending obliquely from the first flat portion to the second flat portion, and the second metal sheet overlaps the second flat portion, and When the foldable display device is folded, the bent portions at the sides of the inclined portion are unfolded, and the first metal sheet is deformed.

2. The foldable display device according to claim 1, wherein: The first metal sheet includes a first portion and a second portion that are separated from each other.

3. The foldable display device according to claim 2, wherein: The first portion includes the first flat portion, the second flat portion, and the inclined portion bent from the first flat portion and the second flat portion; and The second portion includes the first flat portion, the second flat portion, and the inclined portion bent from the first flat portion and the second flat portion.

4. The foldable display device according to claim 3, wherein: the second flat portion of the first portion faces the second flat portion of the second portion; and The second metal sheet overlaps the second flat portion of the first portion and the second flat portion of the second portion.

5. The foldable display device according to claim 4, wherein: An upper surface of the first flat portion of the first part, an upper surface of the first flat portion of the second part, and an upper surface of the second metal sheet are disposed at the same height.

6. The foldable display device according to claim 4, wherein: A lower surface of the first flat portion of the first part, a lower surface of the first flat portion of the second part, and a lower surface of the second metal sheet are disposed at the same height.

7. The foldable display device according to claim 1, wherein: The base film further includes a step compensation layer disposed on the first metal sheet and the second metal sheet.

8. The foldable display device according to claim 1, wherein: The base film further includes a step compensation layer disposed on the first metal sheet and not disposed on the second metal sheet.

9. The foldable display device according to claim 1, wherein: A gap between the inclined portion and the second metal sheet is filled with a filler.

10. The foldable display device according to claim 1, wherein: The first metal sheet further includes a third flat portion and an inclined portion bent from the second flat portion and the third flat portion.

11. The foldable display device according to claim 10, wherein: When a curvature radius of the base film that is bent when the foldable display device is folded is set to r millimeters, a distance between the first flat portion and the third flat portion is within (πr+10) millimeters.

12. The foldable display device according to claim 1, wherein: A plurality of holes are defined in the inclined portion, and the second metal sheet includes a plurality of protrusions inserted into the plurality of holes.

13. A foldable display device, comprising: Display panel; A cover window, disposed on the display panel; as well as A base film is attached below the display panel. in: The base film includes a metal sheet; The metal sheet includes a first flat portion located at a first height, a second flat portion located at a second height different from the first height, a third flat portion located at the first height, a first inclined portion provided between the first flat portion and the second flat portion, and a second inclined portion provided between the second flat portion and the third flat portion, the first inclined portion being bent at an obtuse angle from the first flat portion and the second flat portion and extending obliquely from the first flat portion to the second flat portion, and the second inclined portion being bent at an obtuse angle from the second flat portion and the third flat portion and extending obliquely from the second flat portion to the third flat portion, and When the foldable display device is folded, the bent portions at the sides of the inclined portion are unfolded, and the length of the metal sheet increases.

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