Patent Publication Number: US-2022238049-A1

Title: Display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to and the benefit of Korean Patent Application No. 10-2021-0009404 filed in the Korean Intellectual Property Office on Jan. 22, 2021, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Aspects of some embodiments of the present disclosure relate to a display device. 
     2. Description of the Related Art 
     Various electronic devices, such as mobile phones, tablets, multimedia players, or televisions, to which a liquid crystal display (LCD) or an organic light emitting diode (OLED) is applied as a display device, have been used. 
     Recently, various types of display devices have been developed. For example, flexible display devices that may be bent in a curved way, folded, or wrapped thereby allowing a wide control range of shapes and sizes are being developed. A flexible substrate used in a flexible display devices may be very thin, so a back plate for supporting the flexible substrate may be positioned at the bottom of the flexible substrate. However, when the display device is repeatedly folded and unfolded, plastic deformation of the back plate and/or the flexible substrate so that the display device may not be restored to the proper or intended shape, and a high amount of stress may be applied to the back plate. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background and therefore the information discussed in this Background section does not necessarily constitute prior art. 
     SUMMARY 
     Aspects of some embodiments of the present invention may include a display device that may be relatively easily folded or unfolded in at least two directions. 
     According to some embodiments of the present invention, a display device includes: a display panel; and a back plate including a first folding area positioned on the display panel and folded in a first direction and a second folding area crossing the first folding area and folded in a second direction. 
     According to some embodiments, the first folding area may include a plurality of first holes of which a length in the first direction is less than a length in the second direction in a plan view. 
     According to some embodiments, the first holes may be arranged with a first length in the first direction and may be arranged with a second length in the second direction, and the first length may be less than the second length. 
     According to some embodiments, the second folding area may include a plurality of second holes of which a length in the first direction is greater than a length in the second direction in a plan view. 
     According to some embodiments, the second holes may be arranged with a third length in the first direction and may be arranged with a fourth length in the second direction, and the third length may be greater than the fourth length. 
     According to some embodiments, the display panel may include a flexible substrate, and a modulus of the back plate may be greater than that of the flexible substrate. 
     According to some embodiments, the first holes may have at least one shape of a rectangle of which a long side is parallel with the second direction, a rhombus of which a long side is parallel with the second direction, an oval of which a long axis is parallel with the second direction, and a square. 
     According to some embodiments, the second holes may have at least one shape of a rectangle of which a long side is parallel with the first direction, a rhombus of which a long side is parallel with the first direction, an oval of which a long axis is parallel with the first direction, and a square. 
     According to some embodiments, the back plate may further include a third folding area, and the third folding area may include a region in which the first folding area overlaps the second folding area. 
     According to some embodiments, a length of the third folding area in the first direction may be greater than the first length, and a length thereof in the second direction may be greater than the fourth length in a plan view. 
     According to some embodiments, the third folding area may include a plurality of third holes of which a length in the first direction is greater than the length in the second direction in a plan view, and the third holes may be arranged with a first length in the first direction and may be arranged with a fourth length in the second direction. 
     According to some embodiments, the third folding area may include a plurality of third holes of which a length in a first direction is less than a length in a second direction in a plan view, and the third holes may be arranged with a first length in the first direction and may be arranged with a fourth length in the second direction. 
     According to some embodiments, the third folding area may include a plurality of third holes of which a length in a first direction is the same as a length in a second direction in a plan view, and the third holes may be arranged with a first length in the first direction and may be arranged with a fourth length in the second direction. 
     According to some embodiments, the third folding area may be made of at least one of polyurethane (PU), thermoplastic polyurethane (TPU), polyacrylate, or rubber. 
     According to some embodiments, the third folding area may be manufactured by at least one method of injection molding, extrusion molding, vacuum molding, and casting molding. 
     According to some embodiments, the back plate may further include a step compensating member for filling the third holes. 
     According to some embodiments, the step compensating member may be made of at least one of polyurethane (PU), thermoplastic polyurethane (TPU), polyacrylate, and rubber. 
     According to some embodiments, the third holes may penetrate the back plate in a thickness direction of the back plate. 
     According to some embodiments, the third holes may be positioned on at least one of an upper side or a lower side of the back plate, and a depth of the third hole may be less than a depth of the back plate. 
     According to some embodiments of the present invention, a back plate includes: a first folding area folded in a first direction; a second folding area crossing the first folding area and folded in a second direction; and a third folding area in which the first folding area overlaps the second folding area, wherein the first folding area may include a plurality of first holes of which a length in the first direction is less than a length in the second direction in a plan view, the first holes are arranged with a first length in the first direction and may be arranged with a second length in the second direction, the first length may be less than the second length, the second folding area may include a plurality of second holes of which a length in the first direction is greater than a length in the second direction in a plan view, the second holes may be arranged with a third length in the first direction and may be arranged with a fourth length in the second direction, the third length may be greater than the fourth length, the third folding area may include a plurality of third holes of which a length in a first direction is the same as a length in a second direction in a plan view, and the third holes may be arranged with a first length in the first direction, and may be arranged with a fourth length in the second direction. 
     According to some embodiments of the present disclosure, the display device may be relatively easily folded and unfolded. 
     According to some embodiments of the present disclosure, durability of a display device may be relatively improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective view of a display device according to some embodiments of the present disclosure. 
         FIG. 2  shows a cross-sectional view of a display device with respect to a line I-I′ of  FIG. 1 . 
         FIG. 3  shows a cross-sectional view of a display device with respect to a line II-II′ of  FIG. 1 . 
         FIG. 4  shows a top plan view of a back plate of a display device according to some embodiments of the present disclosure and an enlarged portion of a region. 
         FIG. 5A  to  FIG. 5D  show top plan views of an example of a pattern positioned in an overlapping region of a back plate of  FIG. 4 . 
         FIG. 6A  to  FIG. 6D  show separated cross-sectional views of an overlapping area in a display device in which a hole positioned in a back plate is arranged with a pattern according to  FIG. 5A . 
         FIG. 7  shows a top plan view of a back plate of a display device according to some embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Aspects of some embodiments of the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which aspects of some embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of embodiments according to the present invention. 
     Descriptions of some components or parts that may not be necessary to enable a person having ordinary skill in the art to make, use, and understand aspects of embodiments according to the present invention may be omitted, and the same elements in different embodiments may be designated by the same reference numerals throughout the specification. 
     The size and thickness of each configuration shown in the drawings are arbitrarily shown for better understanding and ease of description, but the present invention is not limited thereto. In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. The thicknesses of some layers and areas are exaggerated for convenience of explanation. 
     It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. The word “on” or “above” means positioned on or below the object portion, and does not necessarily mean positioned on the upper side of the object portion based on a gravitational direction. 
     Unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. 
     Terms “x”, “y”, and “z” are used, and here, “x” is a first direction, “y” is a second direction that is perpendicular to the first direction, and “z” is a third direction that is 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 display device. 
     The phrase “in a plan view” means viewing an object portion from the top, and the phrase “in a cross-sectional view” means viewing a cross-section of which the object portion is vertically cut from the side. 
       FIG. 1  shows a perspective view of a display device according to some embodiments of the present disclosure. 
     The display device  10  may include a display panel  110  for receiving data signals and displaying images. 
     While the display device  10  is unfolded, the display panel  110  may include a display area  1100   a  for displaying images, and a non-display area  1100   b  positioned at an edge of the display area  1100   a  (e.g., around a periphery or outside a footprint of the display area  1100   a ) at which images are not displayed. That is, the non-display area  1100   b  may operate as a bezel area. The display area  1100   a  may face toward a front of the display device  10  and may display images. Certain signal wires or driving circuits for applying signals to the display area  1100   a  may be located in the non-display area  1100   b.    
     Referring to  FIG. 1 , the display area  1100   a  is illustrated as having a rectangular shape, but according to various embodiments, the display area  1100   a  may have a rectangular shape with round corners, and/or the display area  1100   a  may have various other shapes such as squares, polygons, circles, or ovals. 
     The display panel  110  of the display device  10  according to some embodiments may include a plurality of folding areas. The display panel  110  may be folded along folding lines FL 1  and FL 2 . When the display panel  110  is folded, it may not be folded so as to have a specific angle in a folding line (e.g., a set or predetermined folding line), but it may be folded with a curvature (e.g., a set or predetermined curvature), so that the folding area is positioned at a set or predetermined section or location of the display panel  110 . That is, when the display panel  110  is folded with respect to the folding line FL 1 , the folding area FA 1  may be bent with a curvature (e.g., a set or predetermined curvature) at the respective positions. When the display panel  110  is folded with respect to the folding line FL 2 , the folding area FA 2  may be bent with a curvature (e.g., a set or predetermined curvature) at the respective positions. 
     A plurality of folding areas may include a first folding area FA 1  and a second folding area FA 2 . The first folding area FA 1  may be folded along the first folding line FL 1 , and the second folding area FA 2  may be folded along the second folding line FL 2 . Referring to  FIG. 1 , the first folding area FA 1  and the second folding area FA 2  are shown to be positioned in a center of the display panel  110 , but the positions of the folding areas (FA 1  and FA 2 ) are not limited thereto. Further, at least two of the folding areas (FA) may be defined. According to some embodiments, the display panel  110  may include more than two folding areas. 
     As shown in  FIG. 1 , the display panel  110  may include a first folding area FA 1 , a second folding area FA 2 , and a first region  1100   a,  a second region  1100   b,  a third region  1100   c,  and a fourth region  1100   d  partitioned by the first folding area FA 1  and the second folding area FA 2 . 
     The first folding area FA 1  and the second folding area FA 2  may extend in different directions. For example, the first folding area FA 1  may extend in a first direction, and the second folding area FA 2  may extend in a second direction crossing the first direction. The first direction may, for example, be perpendicular to the second direction. 
     An overlapping area (OA)  300  may be a region in which the first folding area FA 1  overlaps the second folding area FA 2 . That is, the first folding area FA 1  and the second folding area FA 2  may extend from the overlapping area  300 . 
     The first folding area FA 1  of the display panel  110  according to some embodiments may be inner-folded so that a displaying side of the first region  1100   a  and the third region  1100   c  may face a displaying side of the second region  1100   b  and the fourth region  1100   d  along the first folding line FL 1 . The first folding area FA 1  may also be outer-folded so that the displaying side of the first region  1100   a  and the third region  1100   c  and the displaying side of the second region  1100   b  and the fourth region  1100   d  may face outside along the first folding line FL 1 . 
     The second folding area FA 2  of the display panel  110  according to some embodiments may be inner-folded so that the displaying side of the first region  1100   a  and the second region  1100   b  may face the displaying side of the third region  1100   c  and the fourth region  1100   d  along the second folding line FL 2 . The second folding area FA 2  may be outer-folded so that the displaying side of the first region  1100   a  and the second region  1100   b  and the displaying side of the third region  1100   c  and the fourth region  1100   d  may face outside along the second folding line FL 2 . 
       FIG. 2  shows a cross-sectional view of a display device with respect to a line I-I′ of  FIG. 1 , illustrating a stacking structure of a display device. 
     As shown, the display device  10  includes a cover member  210 , a display panel  240 , and a back plate  270 . Referring to  FIG. 2 , the cross-sections of respective layers are marked with hatching, which distinguishes the respective layers and does not show patterns formed on the layers. 
     The cover member  210  may be positioned on an upper side of the display panel  240  so as to protect the display panel  240  from external impacts. According to some embodiments, the cover member  210  may be attached to the display panel  240  by an adhesive layer. 
     The cover member  210  may, for example, be a member with various functions such as a touch panel, a polarizer, or a window, or a combination thereof. 
     When the cover member  210  corresponds to the window, the cover member  210  may have a light-permeable material so as to recognize an image generated by the display panel through the cover member  210  from the outside. For example, the cover member  210  may include a glass material, or may include a plastic material such as poly(methyl methacrylate) (PMMA) resin or polycarbonate (PC) resin. The cover member  210  may be made in a relatively thin film shape so that it may have a flexible characteristic, that is, it is easily bent or folded together with the display panel. 
     The display panel  240  may include a substrate  250  and a displaying element  230  formed on the substrate  250 . The display panel  240  may receive data signals and may display images. 
     When the display panel  240  is a flexible display panel, the display panel  240  may be realized with an organic light emitting diode (OLED), an electrophoretic display, an electrochromic display (ECD), an electro-wetting display panel, or a quantum dot display panel. 
     When the display panel  240  is a flat display panel, the display panel  240  may be realized with a liquid crystal display (LCD) or a plasma display device (PDP). 
     For example, when the display panel  240  is a light emitting diode (LED) panel, the displaying element  230  may include a light emitting diode (LED) and a thin film transistor for driving the light emitting diode (LED). In this instance, the light emitting diode (LED) may include an anode connected to the thin film transistor, an organic emission layer positioned on the anode, and a cathode positioned on the organic emission layer. A barrier film for preventing or reducing permeation of external moisture or other contaminants may be further formed on the light emitting diode (LED). 
     The substrate  250  may be a flexible substrate including a flexible polymer material such as a polyimide. 
     The back plate  270  may support the display panel  240 . The back plate  270  may include a first support area  270   a  corresponding to a position of a first region  1100   a,  a second support area  270   b  corresponding to a position of a second region  1100   b,  and a region  275  corresponding to a position of the first folding area FA 1 . 
     The back plate  270  may overlap the substrate  250  in a thickness direction, and may be arranged at a bottom of the substrate  250 . The back plate  270  may be made of a metal material such as stainless steel (SUS) or aluminum, or a polymer such as poly(methyl methacrylate) (PMMA), polycarbonate (PC), polyvinyl alcohol (PVA), acrylonitrile-butadiene-styrene (ABS), or polyethylene terephthalate (PET). 
     The back plate  270  may have greater rigidity than that of the substrate  250 . That is, the back plate  270  may have a greater modulus than that of the substrate  250 . Therefore, when an external force for bending the display device  10  is applied, a force that is in an opposite direction to the external force is generated to the back plate  270 , and the back plate  270  may maintain the display device  10  in a relatively flat state. Accordingly, it may not be easy to bend the display device  10 . In addition, the back plate  270 , once it is bent, may not be easily restored to the original flat state. That is, when the display device  10  is repeatedly folded and unfolded, a plastic deformation may be generated to the back plate  270  to disable restoration of the display device  10 , and many stresses may be applied to the back plate  270 . 
     To solve this problem, the thickness of the back plate  270  may be reduced, but when the thickness of the back plate  270  is reduced, elastic restoring energy may also be reduced and the restoration may require a relatively long period of time. 
     According to some embodiments of the present disclosure, holes with various patterns may be formed in the region  275  corresponding to the first folding area FA 1  by performing an etching process to the back plate  270 . Here, the region  275  may be formed with a same width as the first folding area FA 1 . The region  275  may be formed to have a width that is greater than that of the first folding area FA 1 . The hole may be at least one of an opening, a through hole, or a recess portion (a groove or a hollow), and it includes a shape that may be formed in the back plate  270  by the etching process, but embodiments according to the present disclosure are not limited thereto. 
     A hole may be arranged in the region  275  along the first folding line FL 1  of the first folding area FA 1 . In the region  275 , respective holes may be arranged at equal intervals, and the shapes, sizes, widths, gaps of the holes, and the positions among the respective holes are modifiable. For example, the hole may have various shapes such as a rectangle, a rhombus, an oval shape with a constant shortened length, a circle, a square, or a trapezoid shape, and the shapes are not limited. The region  275  will be described in more detail in the latter portion of the present specification with reference to  FIG. 4 . 
     According to some embodiments, the hole positioned in the back plate  270  may be filled with a step compensating member with a same height as the back plate  270 . The step compensating member may be made of a material with less rigidity than the back plate  270 . That is, the step compensating member may have a lesser modulus than the back plate  270 . 
     For example, the step compensating member may be made of a resin such as polyurethane (PU), thermoplastic polyurethane (TPU), polyacrylate, or rubber, and without being limited thereto, it may be made of any materials that may allow buffering. For example, the step compensating member may be manufactured by various forming methods such as injection molding, extrusion molding, vacuum molding, or casting molding, and for example, it may have a film shape, but is not limited thereto. 
     The step compensating member may ease the stress applied to the back plate  270  by a folding operation. The step compensating member may prevent the holes arranged on upper/lower portions from being damaged in a process of folding the display device  10 , and a force of restoration may be additionally provided to the pattern that is changed for the folding process. 
       FIG. 3  shows a cross-sectional view of a display device with respect to a line II-II′ of  FIG. 1 . 
     As described above, the display device  10  according to some embodiments of the present disclosure includes a cover member  210 , a displaying element  230 , a substrate  250 , and a back plate  280 . 
     The cover member  210 , the displaying element  230 , and the substrate  250  are as described above. 
     The back plate  280  may include a third support area  280   a  and a fourth support area  280   b  corresponding to the position of the second folding area FA 2 , and a region  285  corresponding to the position of the overlapping area  300 . 
     By performing an etching process to the back plate  280 , the holes may be formed with various patterns in the third support area  280   a  and the fourth support area  280   b  corresponding to the second folding area FA 2 . 
     In the third support area  280   a  and the fourth support area  280   b,  the holes may be arranged along the folding line FL 2 . The respective holes may be arranged at equal intervals, and the shapes, sizes, widths, gaps of the holes, and the positions among the respective holes are modifiable. For example, the hole may have various shapes such as a rectangle, a rhombus, an oval shape with a constant shortened length, a circle, a square, or a trapezoid shape, and the shapes are not limited. 
     The region  285  is positioned on the back plate  280  corresponding to the position of the overlapping area  300  in which the first folding area FA 1  overlaps the second folding area FA 2 . The region  285  may have the same area as the overlapping area  300 , or it may include the overlapping area  300  and may have a greater area than the overlapping area  300 . 
     In the region  285 , the holes may be arranged with a pattern that is symmetric with respect to the first folding line FL 1  and is symmetric with respect to the second folding line FL 2 . The holes in the region  285  may have shapes such as circles, squares, or crosses, and may have arbitrary shapes in a direction parallel with the first folding line FL 1  and in a direction parallel with the second folding line FL 2 . A third pattern region will be described with reference to  FIG. 5A  to  FIG. 5D . 
       FIG. 4  shows a top plan view of a back plate of a display device according to some embodiments of the present disclosure and an enlarged portion of regions of the back plate. 
     Referring to  FIG. 4 , the back plate may include a first folding area FA 1 , a second folding area FA 2 , and a first region  4100   a,  a second region  4100   b,  a third region  4100   c,  and a fourth region  4100   d  partitioned by a plurality of folding areas. 
     A plurality of holes may be arranged in the first folding area FA 1  along the folding line FL 1 . A region  4001  shows an enlarged portion of the first folding area FA 1 . As shown in the region  4001 , a plurality of holes positioned in the first folding area FA 1  may be arranged so that respective long axes may be positioned to be parallel with the first folding line FL 1  and short axes may be positioned to be parallel with the folding direction. A plurality of holes may be formed with a same width as the first folding area FA 1 , and may be formed with a width that is greater than the width of the first folding area FA 1 . 
     The first folding area FA 1  may include a plurality of holes formed with a first pattern  4001   a  positioned in the (2n−1)-th column and a second pattern  4001   b  positioned in the 2n-th column, where n is a positive integer (e.g., greater than 0). The first pattern  4001   a  and the second pattern  4001   b  are configured to respectively extend in the column direction. That is, the respective long axes of the first pattern  4001   a  and the second pattern  4001   b  may be parallel with the first folding line FL 1 . 
     A first distance D 1  between the first pattern  4001   a  and the second pattern  4001   b  may be equal to respective first lengths L 1  of the first pattern  4001   a  and the second pattern  4001   b  or may be less than the first lengths L 1 . 
     The holes arranged in the (2n−1)-th column as a first pattern  4001   a  may be positioned among the holes arranged in the 2n-th column as a second pattern  4001   b.  For example, the center of the hole arranged as the first pattern  4001   a  may correspond to a space among the holes arranged with the second pattern  4001   b,  and the center of the hole arranged as the second pattern  4001   b  may correspond to a space among the holes arranged with the first pattern  4001   a.  The holes formed with the first pattern  4001   a  in the (2n−1)-th column may be arranged to correspond to the holes formed with the second pattern  4001   b  in the 2n-th column. 
     The holes may have symmetric shapes with respect to the direction of the first folding line FL 1 , and the shapes are not limited thereto. For example, the hole may have a shape such as a rectangle of which a long side is parallel with the first folding line FL 1  direction in a plan view, or a rhombus, and may have a shape of which a long axis is parallel with the first folding line FL 1  direction, or an oval, a circle, or a square. 
     When the display device is folded in the first folding line FL 1 , a repulsive force generated to the folding according to a gap (T 1 ) between the holes may be changed. A curvature radius of the display device may be changed when the display device is folded by adjusting an arrangement of holes in the pattern formed in the back plate. Hence, the stress applied to the display panel may be eased to minimize the damage to the display panel. 
     A plurality of holes may be arranged in the second folding area FA 2  along the folding line FL 2 . A region  4002  shows an enlarged portion of the second folding area FA 2 . As shown in the region  4002 , a plurality of holes positioned in the second folding area FA 2  may be arranged so that respective long axes may be positioned to be parallel with the second folding line FL 2  and short axes may be positioned to be parallel with the folding direction. A plurality of holes may be arranged with a same width as the second folding area FA 2 , and may be arranged with a width that is greater than the width of the second folding area FA 2 . 
     The second folding area FA 2  may include a plurality of holes formed with a first pattern  4002   a  positioned in the (2n−1)-th row and a second pattern  4002   b  positioned in the 2n-th row, where n is a positive integer (e.g., greater than 0). The first pattern  4002   a  and the second pattern  4002   b  are configured to respectively extend in the row direction. That is, the respective long axes of the first pattern  4002   a  and the second pattern  4002   b  may be parallel with the second folding line FL 2 . 
     A first distance D 1  between the first pattern  4001   a  and the second pattern  4001   b  may be equal to respective first lengths L 1  of the first pattern  4001   a  and the second pattern  4001   b  or may be less than the first lengths L 1 . 
     The holes arranged in the (2n−1)-th row as a first pattern  4002   a  may be positioned among the holes arranged in the 2n-th row as a second pattern  4002   b.  For example, the center of the hole arranged as the first pattern  4002   a  may correspond to a space among the holes arranged with the second pattern  4002   b,  and the center of the hole arranged as the second pattern  4002   b  may correspond to a space among the holes arranged with the first pattern  4002   a.  The holes arranged with the first pattern  4002   a  in the (2n−1)-th row may be arranged to correspond to the holes arranged with the second pattern  4002   b  in the 2n-th row. 
     The holes may have symmetric shapes with respect to the direction of the second folding line FL 2 , and the shapes are not limited thereto. For example, the hole may have a shape such as a rectangle of which a long side is parallel with the second folding line FL 2  direction in a plan view, or a rhombus, and may have a shape of which a long axis is parallel with the second folding line FL 2  direction, or an oval, a circle, or a square. 
     When the display device is folded in the second folding line FL 2 , a repulsive force generated to the folding according to a gap (T 2 ) between the holes may be changed. A curvature radius of the display device may be changed when the display device is folded by adjusting an arrangement of holes in the pattern formed in the back plate. Hence, the stress applied to the display panel may be eased to minimize or reduce the damage to the display panel. 
     A plurality of holes arranged with a third pattern may be formed in the overlapping area  301  in which the first folding area FA 1  overlaps the second folding area FA 2 . The holes in the overlapping area  301  may have a symmetric shape with respect to the direction of the first folding line FL 1  and also with respect to the direction of the second folding line FL 2 . The holes in the overlapping area  301  will be described in a latter portion of the present specification with reference to  FIG. 5A  to  FIG. 5D . 
     As described above, various patterns may be formed in the overlapping area  301  by performing an etching process on the back plate. After various patterns are formed in the overlapping area  301 , the holes positioned in the overlapping area  301  may be filled with a step compensating member. 
     According to some embodiments, a portion that corresponds to the overlapping area  301  in the back plate may be made of a resin such as polyurethane (PU), thermoplastic polyurethane (TPU), polyacrylate, or rubber, and without being limited thereto, and it may be made of any materials for allowing buffering. In addition, the above-described various patterns may be formed thereon.  FIG. 5A  to  FIG. 5D  show top plan views of an example of a pattern in which a plurality of holes are arranged in an overlapping area  301  of a back plate of  FIG. 4 . For ease of description, the holes located in the overlapping area  301  are shown in  FIG. 5A  to  FIG. 5D  to be formed or arranged to be symmetric with the first folding line FL 1  and the second folding line FL 2 , and a plurality of holes may be arranged to be symmetric with respect to an arbitrary line in parallel with the first folding line FL 1  and an arbitrary line in parallel with the second folding line FL 2 . Further, for ease of description, part of the patterns for forming holes in the overlapping area  301  is illustrated, and is not limited thereto. 
       FIG. 5A  illustrates a pattern formed in the overlapping area  301  of the back plate. As shown in  FIG. 5A , a plurality of holes in a circular shape in a plan view may be repeatedly arranged in the overlapping area  301 . For example, the overlapping area  301  may have a pattern in which a first hole  501   a,  a second hole  501   b,  a third hole  501   c,  and a fourth hole  501   d  are arranged. The first hole  501   a,  the second hole  501   b,  the third hole  501   c,  and the fourth hole  501   d  may have circular shapes in a plan view. A case in which the overlapping area  301  in which a plurality of holes in a circular shape are arranged is incised with respect to a line III-III′ in a plan view will be described in more detail below with reference to  FIG. 6A  to  FIG. 6D . 
       FIG. 5B  shows another example of a pattern formed in an overlapping area  301  of a back plate. As shown in  FIG. 5B , a hole in a shape in which circles  502   a,    502   c,    502   d,  and  502   e  are arranged among two perpendicular rectangles  502   b  to respective ends of which semicircles are combined and four corners may be repeatedly arranged in the overlapping area  301  in a plan view. The first length L 11  may be substantially equal to the second length L 12 . 
       FIG. 5C  shows another example of a pattern formed in an overlapping area  301  of a back plate. As shown in  FIG. 5C , a plurality of holes in a square shape may be repeatedly arranged in the overlapping area  301  in a plan view. For example, the overlapping area  301  may have a pattern in which a first hole  503   a,  a second hole  503   b,  a third hole  503   c,  and a fourth hole  503   d  are arranged. The first hole  503   a,  the second hole  503   b,  the third hole  503   c,  and the fourth hole  503   d  may have a square shape in a plan view. 
       FIG. 5D  shows another example of a pattern formed in an overlapping area  301  of a back plate. As shown in  FIG. 5D , a hole in a shape in which squares  504   a,    504   c,    504   d,  and  504   e  are arranged among two perpendicular rectangles  504   b  and four corners may be repeatedly arranged in the overlapping area  301 . The first length L 21  may be substantially equal to the second length L 22 . 
     That is, the shape of a plurality of holes positioned in the overlapping area  301  is modifiable in many ways as shown in  FIG. 5A  to  FIG. 5D , and holes may be formed with an arbitrary (or any suitable) pattern that is symmetric with respect to the direction of the first folding line FL 1  and is also symmetric with respect to the direction of the second folding line FL 2 . For example, the shapes of the plurality of holes located in the overlapping area  301  may be the same (or substantially the same) as the shapes of the plurality of holes in the first and second folding areas FA 1  and FA 2  in  FIG. 4 . 
       FIG. 6A  to  FIG. 6D  show separated cross-sectional views of an overlapping area when a hole positioned in a back plate is arranged with a pattern according to  FIG. 5A . 
     The display device  10  shown in  FIG. 6A  to  FIG. 6D  may include a cover member  210 , a displaying element  230 , a substrate  250 , and a back plate  670 . The cover member  210 , the displaying element  230 , and the substrate  250  correspond to the above-provided descriptions. Referring to  FIG. 6A  to  FIG. 6D , the back plate  670  has a thickness T 6 . 
     The back plate  670  may have the above-noted first hole  501   a,  the second hole  501   b,  the third hole  501   c,  and the fourth hole  501   d.    
       FIG. 6A  shows a display device  10  including a hole positioned in a back plate  670 . The holes positioned in the overlapping area  301  may penetrate the back plate  670  in a thickness direction of the back plate  270 . 
       FIG. 6B  shows a display device  10  including a hole positioned in an upper side and a lower side of the back plate  670  with a thickness (e.g., a set or predetermined thickness). The hole positioned on the lower side of the back plate  270  may be positioned corresponding to the respective positions of the holes positioned in the upper side of the back plate  670 . The hole positioned in the upper side of the back plate  670  may have a first thickness T 61 , and the hole positioned in the lower side may have a second thickness T 62 . The first thickness T 61  and the second thickness T 62  may be substantially the same or may be different from each other. In this instance, a sum of the first thickness T 61  and the second thickness T 62  is less than the thickness T 6 . 
       FIG. 6C  shows a display device  10  in which a hole has an overlapping area  300  formed with a thickness (e.g., a set or predetermined thickness) on a lower side of the back plate  670 . The hole positioned in the lower side of the back plate  670  may have a third thickness T 63 . The third thickness T 63  is less than the thickness T 6 . 
       FIG. 6D  shows a display device  10  in which a hole has an overlapping area  300  formed with a thickness (e.g., a set or predetermined thickness) on an upper side of the back plate  670 . The hole positioned in the upper side of the back plate  670  may have a fourth thickness T 64 . The fourth thickness T 64  is less than the thickness T 6 . 
     As shown in  FIG. 6A  to  FIG. 6D , the hole may be formed in the back plate  670  by a method that is appropriate for the display device  10 . For example, when the display device  10  is inner-folded, the hole may be formed in the back plate  670  as shown in  FIG. 6A  or  FIG. 6C . 
     As described above, the holes shown in  FIG. 6A  to  FIG. 6D  may be filled with a step compensating member. 
       FIG. 7  shows a top plan view of a back plate of a display device according to some embodiments of the present disclosure. 
     Referring to  FIG. 7 , the back plate may include a first folding area FA 1 , a second folding area FA 2 , and a first region  7100   a,  a second region  7100   b,  a third region  7100   c,  and a fourth region  7100   d  partitioned by the first folding area FA 1  and the second folding area FA 2 . 
     The first region  7100   a,  the second region  7100   b,  the third region  7100   c,  and the fourth region  7100   d  are similar to the above-described first region  4100   a,  second region  4100   b,  third region  4100   c,  and fourth region  4100   d,  so some repetitive descriptions thereof may be omitted. 
     A plurality of holes may be arranged along the first folding line FL 1  in the first folding area FA 1 . Regarding a plurality of holes positioned in the first folding area FA 1 , respective long axes may be positioned in parallel with the first folding line FL 1 , and short axes may be arranged in parallel with the folding direction. A plurality of holes may be formed with the same width as the first folding area FA 1 , and they may be formed with the width that is greater than the width of the first folding area FA 1 . The holes may have a shape that is symmetric with respect to the direction of the first folding line FL 1 , and the shape is not limited. 
     A plurality of holes may be arranged along the folding line FL 2  in the second folding area FA 2 . Regarding a plurality of holes positioned in the second folding area FA 2 , respective long axes may be positioned in parallel with the second folding line FL 2 , and short axes may be arranged in parallel with the folding direction. A plurality of holes may be formed with the same width as the second folding area FA 2 , and they may be formed with the width that is greater than the width of the second folding area FA 2 . The holes may have a shape that is symmetric with respect to the direction of the second folding line FL 2 , and the shape is not limited. 
     A flexible portion  701  may include an overlapping area of the first folding area FA 1  and the second folding area FA 2 . The flexible portion  701  may have a width in the direction of the first folding line FL 1  that is greater than the width of the second folding area FA 2  in the direction of the first folding line FL 1 , and may have a width in the direction of the second folding line FL 2  that is greater than the width of the first folding area FA 1  in the direction of the second folding line FL 2 . Referring to  FIG. 7 , the flexible portion  701  is illustrated to be a quadrangle, and it may have an arbitrary shape including the overlapping area. 
     The flexible portion  701  may be made of resin such as polyurethane (PU), thermoplastic polyurethane (TPU), polyacrylate, rubber, silicon (Si), or a combination thereof, and without being limited thereto, and it may be made of any materials for allowing buffering, and a combination thereof. For example, the flexible portion  701  may be configured with what is manufactured by various forming methods such as injection molding, extrusion molding, vacuum molding, or casting molding. 
     No holes may be positioned in the flexible portion  701 . The case in which a plurality of holes are positioned in the flexible portion  701  may be referred to as what is described with reference to  FIG. 4 . 
     The use of all examples or illustrative terms (for example, etc.) in the present invention is merely for describing the present invention in detail, and the scope of the present invention is not limited by examples or illustrative terms unless limited by the claims. In addition, a person skilled in the art may recognize that various modifications, combinations, and changes may be configured according to design conditions and factors within the scope of the appended claims or their equivalents. 
     While this invention has been described in connection with what is presently considered to be practical embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and their equivalents.