Patent Publication Number: US-11653520-B2

Title: Display device

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority to and benefits of Korean Patent Application No. 10-2020-0078744 under 35 U.S.C. § 119, filed on Jun. 26, 2020 in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     (a) Technical Field 
     The disclosure herein relates to a display device. 
     (b) Description of the Related Art 
     An electronic device for providing an image to a user, for example, a smartphone, a digital camera, a laptop computer, a navigation unit, and a smart television, may include a display device for displaying an image. The display device generates an image to provide the generated image to the user through a display screen. 
     In recent years, as technologies of the display device are developed, various types of display devices have been developed. For example, various flexible display devices that are deformable, foldable, and rollable into a curved shape have been developed. The flexible display devices that are deformable into various shapes may be portable and thus increase user convenience. 
     A folding display device among the flexible display devices may include a display module folded with respect to a folding axis extending in one direction. The display module may be folded or unfolded with respect to the folding axis. The display module may include a folding area that may be bent during a folding operation. As the folding area is repeatedly folded or unfolded, the folding area may be deformed. Thus, a technology capable of reducing deformation of the folding area is currently in demand. 
     It is to be understood that this background of the technology section is, in part, intended to provide useful background for understanding the technology. However, this background of the technology section may also include ideas, concepts, or recognitions that were not part of what was known or appreciated by those skilled in the pertinent art prior to a corresponding effective filing date of the subject matter disclosed herein. 
     SUMMARY 
     The disclosure provides a display device capable of reducing deformation of a folding area. 
     An embodiment provides a display device that may include a display module including a first non-folding area, a second non-folding area, and a folding area disposed between the first non-folding area and the second non-folding area, the first non-folding area, the second non-folding area, and the folding area being arranged in a first direction; a first support disposed below the first non-folding area; a second support disposed below the second non-folding area; and a hinge including a biaxial rotation shaft disposed between the first support and the second support, the biaxial rotation shaft extending in a second direction intersecting the first direction. The folding area may have a curvature radius in a range of about 1.5 mm to about 5.0 mm when the display module is folded by a rotation of the first support and the second support with respect to the biaxial rotation shaft. 
     In an embodiment, the folding area may have a length in a range of about 35 mm to about 45 mm in the first direction when the display module is unfolded. 
     In an embodiment, the folding area may include a curved part bent to have the curvature radius when the display module is folded; a first extension part bent from the first non-folding area to extend to the curved part; and a second extension part bent from the second non-folding area to extend to the curved part, wherein a distance between the first non-folding area and the second non-folding area may be less than the curvature radius of the curved part of the folding area when the display module is folded. 
     In an embodiment, the first extension part and the second extension part may be symmetric when the display module is folded, and the first extension part may form an acute angle with a first reference line extending from the first non-folding area to the curved part in a same direction as an extension direction of the first non-folding area when the display module is folded. 
     In an embodiment, the acute angle may be in a range of about 6.5° to about 12.5°. 
     In an embodiment, the display device may further include a first support plate disposed between the first support and the first non-folding area; and a second support plate disposed between the second support and the second non-folding area, wherein the first support plate may extend below the first extension part and the curved part, the second support plate may extend below the second extension part and the curved part, and the first support plate may be spaced apart from the second support plate below the curved part. 
     In an embodiment, the first support plate and the second support plate may be attached to the first non-folding area, the second non-folding area, the first extension part, and the second extension part, and the first support plate and the second support plate may not be attached to the curved part. 
     In an embodiment, the first support plate may be bent at a boundary between the first non-folding area and the first extension part when the display module is folded, and the second support plate may be bent at a boundary between the second non-folding area and the second extension part when the display module is folded. 
     In an embodiment, each of the first support plate and the second support plate may have a thickness in a range of about 80 μm to about 150 μm in a third direction perpendicular to a plane defined by the first and second directions when the display module is unfolded. 
     In an embodiment, the display device may further include a black coating layer coated on each of a top surface of the first support plate and a top surface of the second support plate; a first cushion layer disposed below the first support plate; and a second cushion layer disposed below the second support plate. 
     In an embodiment, the first support may extend below the first extension part, the second support may extend below the second extension part, a top surface of the first support facing the first extension part may have a first inclined surface in a plan view, and a top surface of the second support facing the second extension part may have a second inclined surface in the plan view. 
     In an embodiment, the display device may further include a first wing plate disposed between the first extension part and the first inclined surface of the top surface of the first support and rotatably connected to a portion of the first support, wherein the portion of the first support may overlap a boundary between the first non-folding area and the first extension part in a plan view; and a second wing plate disposed between the second extension part and the second inclined surface of the top surface of the second support and rotatably connected to a portion of the second support, wherein the portion of the second support may overlap a boundary between the second non-folding area and the second extension part in a plan view, wherein the first wing plate and the second wing plate may rotate with respect to a first rotation shaft and a second rotation shaft extending in the second direction. 
     In an embodiment, the second wing plate may be symmetric to the first wing plate, the second inclined surface of the top surface of the second support may be symmetric to the first inclined surface of the top surface of the first support, a distance between the first wing plate and the first inclined surface of the top surface of the first support may increase in a direction toward the curved part when the display module is unfolded, and the first inclined surface of the top surface of the first support may form an angle in a range of about 6.5° to about 12.5° with the first wing plate when the display module is unfolded. 
     In an embodiment, the first wing plate may contact the first inclined surface of the top surface of the first support, and the second wing plate may contact the second inclined surface of the top surface of the second support upon a stress of the folding area when the display module is folded. 
     In an embodiment, the hinge may include a cover part disposed between the first support and the second support and below the first wing plate and the second wing plate; a first rotation unit and a second rotation unit connected to opposite ends of the cover part in the second direction; and a plurality of hinge parts connected to opposite sides of the first support and the second support in the second direction, and the first rotation unit and the second rotation unit, wherein the cover part may include a groove facing the curved part and extending in the second direction, and the biaxial rotation shaft may overlap the curved part and the groove in a plan view. 
     In an embodiment, a side of the first wing plate and a side of the second wing plate facing each other, and a central portion of the curved part may be disposed in the groove when the display module is folded. 
     In an embodiment, the first non-folding area may face the second non-folding area when the display module is in-folded. 
     In an embodiment, a display device may include a display panel including a first non-folding area, a second non-folding area, and a folding area disposed between the first non-folding area and the second non-folding area, the first non-folding area, the second non-folding area, and the folding area being arranged in a first direction; a reflection preventing layer disposed on the display panel; a window disposed on the reflection preventing layer; a window protection layer disposed on the window; a panel protection layer disposed below the display panel; a first support plate disposed below the first non-folding area; and a second support plate disposed below the second non-folding area. The folding area may include a curved part having a predetermined curvature radius when the display panel is folded; a first extension part bent from the first non-folding area extending to the curved part; and a second extension part bent from the second non-folding area extending to the curved part. A distance between the first non-folding area and the second non-folding area may be less than the predetermined curvature radius of the curved part when the display panel is folded. 
     In an embodiment, the window may have a thickness greater than about 30 μm and equal to or less than about 80 μm, the window protection layer may have a thickness in a range of about 55 μm to about 100 μm, and each of the first support plate and the second support plate may have a thickness in a range of about 80 μm to about 150 μm in a third direction perpendicular to a plane defined by the first direction and the second direction. 
     In an embodiment, the display device may further include a black coating layer coated on each of a top surface of the first support plate and a top surface of the second support plate; a first adhesive layer disposed between the window protection layer and the window; a second adhesive layer disposed between the window and the reflection preventing layer; a third adhesive layer disposed between the display panel and the panel protection layer; and a fourth adhesive layer disposed between the panel protection layer and the black coating layer. 
     In an embodiment, a display device may include a display module including a first non-folding area, a second non-folding area, and a folding area disposed between the first non-folding area and the second non-folding area, the first non-folding area, the second non-folding area, and the folding area being arranged in a first direction; a first support disposed below the first non-folding area; and a second support disposed below the second non-folding area. The display module may be folded by rotation of the first support and the second support that rotate with respect to biaxial rotation shafts disposed below the folding area. The folding area may include a curved part bent to have a predetermined curvature radius when the display panel is folded; a first extension part disposed between the first non-folding area and the curved part; and a second extension part disposed between the second non-folding area and the curved part. The folding area may have a length in a range of about 35 mm to about 45 mm in the first direction when the display panel is unfolded, and the first extension part may form an angle in a range of about 6.5° to about 12.5° with a first reference line extending from the first non-folding area to the curved part in a same direction as an extension direction of the non-folding area when the display module is folded. 
     In an embodiment, the curved part of the folding area may be bent to have a predetermined curvature radius in a range of about 1.5 mm to about 5.0 mm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and, together with the description, serve to explain principles of the disclosure. In the drawings: 
         FIG.  1    is a perspective view illustrating a display device according to an embodiment; 
         FIG.  2    is a view illustrating a folded state of the display device in  FIG.  1   ; 
         FIG.  3    is a perspective view illustrating a display device according to an embodiment; 
         FIG.  4    is a view illustrating a folded state of the display device in  FIG.  3   ; 
         FIG.  5    is a plan view illustrating the display device in  FIG.  1   ; 
         FIG.  6    is a schematic cross-sectional view taken along line I-I′ of  FIG.  1   ; 
         FIG.  7    is a schematic cross-sectional view exemplarily illustrating a display panel in  FIG.  6   ; 
         FIGS.  8  to  10    are views illustrating various bent states of the display module and support plates; 
         FIGS.  11  and  12    are exploded perspective views illustrating a support on which the display module and the support plate in  FIG.  6    are disposed; 
         FIG.  13    is a plan view illustrating the support obtained by coupling first and second supports, first and second wing plates, and a hinge in  FIGS.  11  and  12   ; 
         FIG.  14    is a perspective view illustrating the support in  FIG.  13   ; 
         FIG.  15    is a view illustrating a folded state of the support in  FIG.  14   ; 
         FIG.  16    is a schematic cross-sectional view taken along line II-II′ of  FIG.  14   ; 
         FIG.  17    is a view illustrating a folded state of the display device in  FIG.  16   ; 
         FIG.  18    is an enlarged photograph illustrating a folding area of a comparative display module; 
         FIG.  19    is a graph showing a deformed state of the folding area in  FIG.  18   ; 
         FIG.  20    is an enlarged photograph showing the folding area of the display module according to an embodiment; 
         FIG.  21    is a graph showing a deformed state of the folding area in  FIG.  20   ; 
         FIG.  22    is an enlarged photograph showing a surface of the comparative display module; and 
         FIG.  23    is an enlarged photograph showing a surface of the display module in  FIG.  6   . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In this specification, it will also be understood that when one component (or region, layer, portion) is referred to as being ‘on’, ‘connected to’, or ‘coupled to’ another component, it can be directly disposed/connected/coupled on/to the one component, or an intervening third component may also be present. 
     Like reference numerals refer to like elements throughout. Also, in the figures, the thickness, ratio, and dimensions of components are exaggerated for clarity of illustration. 
     The term “and/or” includes any and all combinations of one or more of the associated listed items. 
     The terms “and” and “or” may be used in the conjunctive or disjunctive sense and may be understood to be equivalent to “and/or.” In the specification and the claims, the phrase “at least one of” is intended to include the meaning of “at least one selected from the group of” for the purpose of its meaning and interpretation. For example, “at least one of A and B” may be understood to mean “A, B, or A and B. 
     As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     It will be understood that although the terms such as ‘first’ and ‘second’ are used herein to describe various elements, these elements should not be limited by these terms. The terms are only used to distinguish one component from other components. For example, a first element referred to as a first element in one embodiment can be referred to as a second element in another embodiment without departing from the scope of the appended claims. The terms of a singular form may include plural forms unless referred to the contrary. 
     The spatially relative terms “below”, “beneath”, “lower”, “above”, “upper”, or the like, may be used herein for ease of description to describe the relations between one element or component and another element or component as illustrated in the drawings. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation, in addition to the orientation depicted in the drawings. For example, in the case where a device illustrated in the drawing is turned over, the device positioned “below” or “beneath” another device may be placed “above” another device. Accordingly, the illustrative term “below” may include both the lower and upper positions. The device may also be oriented in other directions and thus the spatially relative terms may be interpreted differently depending on the orientations. 
     Additionally, the terms “overlap” or “overlapped” mean that a first object may be above or below or to a side of a second object, and vice versa. Additionally, the term “overlap” may include layer, stack, face or facing, extending over, covering or partly covering or any other suitable term as would be appreciated and understood by those of ordinary skill in the art. The terms “face” and “facing” mean that a first element may directly or indirectly oppose a second element. In a case in which a third element intervenes between the first and second element, the first and second element may be understood as being indirectly opposed to one another, although still facing each other. When an element is described as ‘not overlapping’ or ‘to not overlap’ another element, this may include that the elements are spaced apart from each other, offset from each other, or set aside from each other or any other suitable term as would be appreciated and understood by those of ordinary skill in the art. 
     The phrase “in a plan view” means viewing the object from the top, and the phrase “in a schematic cross-sectional view” means viewing a cross-section of which the object is vertically cut from the side. 
     “About” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “about” may mean within one or more standard deviations, or within +30%, 20%, 10%, 5% of the stated value. 
     As used herein, the term “unit” and/or “module” denotes a structure or element as illustrated in the drawings and as described in the specification. However, the disclosure is not limited thereto. The term “unit” and/or “module” is not to be limited to that which is illustrated in the drawings. 
     Also, ““under”, “below”, “above”, “upper”, and the like are used for explaining relation association of components illustrated in the drawings. The terms may be a relative concept and described based on directions expressed in the drawings but are not limited thereto. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as generally understood by those skilled in the art. Terms as defined in a commonly used dictionary should be construed as having the same meaning as in an associated technical context, and unless defined apparently in the description, the terms are not ideally or excessively construed as having a formal meaning. 
     The meaning of ‘include’, ‘includes’, ‘including’ or ‘comprise’, ‘comprises’, or ‘comprising’ or ‘has’, ‘have’ or ‘having’ and their variations specify a property, a fixed number, a step, an operation, an element, a component or a combination thereof, but does not exclude other properties, fixed numbers, steps, operations, elements, components or combinations thereof. 
     Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. 
       FIG.  1    is a perspective view illustrating a display device according to an embodiment.  FIG.  2    is a view illustrating a folded state of the display device in  FIG.  1   . 
     Referring to  FIG.  1   , a display device DD according to an embodiment may have a substantially rectangular shape having long sides in a first direction DR 1  and short sides in a second direction DR 2  intersecting the first direction DR 1 . However, the embodiment is not limited thereto. For example, the display device DD may have various shapes such as a substantially circular shape and a substantially polygonal shape. The display device DD may be a flexible display device. 
     Hereinafter, a direction that intersects a plane defined by the first and second directions DR 1  and DR 2  in a substantially perpendicular manner is defined as a third direction DR 3 . In the specification, an expression “viewed on a plane” may be defined as a state when viewed in the third direction DR 3 . 
     The display device DD may include a folding area FA and non-folding areas NFA 1  and NFA 2 . The non-folding areas NFA 1  and NFA 2  may include a first non-folding area NFA 1  and a second non-folding area NFA 2 . The folding area FA may be disposed between the first non-folding area NFA 1  and the second non-folding area NFA 2 . The folding area FA, the first non-folding area NFA 1 , and the second non-folding area NFA 2  may be arranged in the first direction DR 1 . 
     Although a folding area FA and two non-folding areas NFA 1  and NFA 2  are illustrated, the embodiment is not limited to the number of each of the folding area FA and the non-folding areas NFA 1  and NFA 2 . For example, the display device DD may include two or more non-folding areas and folding areas disposed therebetween. 
     A top surface of the display device DD may be defined as a display surface DS and have a plane defined by the first direction DR 1  and the second direction DR 2 . Images IM generated in the display device DD may be provided to a user through the display surface DS. 
     The display surface DS may include a display area DA and a non-display area NDA around the display area DA. The display area DA may display an image, and the non-display area NDA may display no image. The non-display area NDA may define an edge of the display device DD, which may surround or may be adjacent to the display area DA and may be printed in a predetermined color. 
     Referring to  FIG.  2   , the display device DD may be a folding-type (foldable) display device that may be folded or unfolded. For example, the display device DD may be folded such that the folding area FA is bent with respect to a folding axis FX parallel to the second direction DR 2 . The folding axis FX may be defined as a minor axis parallel to the short side of the display device DD. 
     In a case that the display device DD is folded, the first non-folding area NFA 1  and the second non-folding area NFA 2  may face each other, and the display device DD may be in-folded so that the display surface DS is not exposed to the outside. 
       FIG.  3    is a perspective view illustrating a display device according to an embodiment.  FIG.  4    is a view illustrating a folded state of the display device in  FIG.  3   . 
     A display device DD_ 1  in  FIG.  3    may have substantially the same configuration as the display device DD in  FIG.  1    except for a folding operation. Thus, hereinafter, the folding operation of the display device DD_ 1  will be mainly described. 
     Referring to  FIGS.  3  and  4   , the display device DD_ 1  may include a folding area FA′ and non-folding areas NFA 1 ′ and NFA 2 ′. The non-folding areas NFA 1 ′ and NFA 2 ′ may include a first non-folding area NFA 1 ′ and a second non-folding area NFA 2 ′. The folding area FA′ may be disposed between the first non-folding area NFA 1 ′ and the second non-folding area NFA 2 ′. The folding area FA′, the first non-folding area NFA 1 ′, and the second non-folding area NFA 2 ′ may be arranged in the second direction DR 2 . 
     The display device DD_ 1  may be folded such that the folding area FA′ is bent with respect to a folding axis FX′ parallel to the first direction DR 1 . The folding axis FX′ may be defined as a major axis parallel to a long side of the display device DD_ 1 . The display device DD in  FIG.  1    may be folded with respect to the minor axis, and, in contrast, the display device DD_ 1  in  FIG.  3    may be folded with respect to the major axis. The display device DD_ 1  may be in-folded so that the display surface DS is not exposed to the outside. 
     Hereinafter, the display device DD that is in-folded with respect to the folding axis FX parallel to the minor axis will be described. 
       FIG.  5    is a plan view illustrating the display device DD in  FIG.  1   . 
     Referring to  FIG.  5   , the display device DD may include a display panel DP, a scan driver SDV, a data driver DDV, an emission driver EDV, and pads PD. 
     The display panel DP may have a substantially rectangular shape having long sides extending in the first direction DR 1  and short sides extending in the second direction DR 2 . However, the embodiment is not limited to the shape of the display panel DP. The display panel DP may include a display area DA and a non-display area NDA surrounding or adjacent to the display area DA. 
     The display panel DP may include pixels PX, scan lines SL 1  to SLm, data lines DL 1  to DLn, emission lines EL 1  to ELm, first and second control lines CSL 1  and CSL 2 , first and second power lines PL 1  and PL 2 , and connection lines CNL. 
     Here, m and n are integers. 
     The pixels PX may be disposed on the display area DA. The scan driver SDV and the emission driver EDV may be disposed on the non-display areas NDA adjacent to the long sides of the display panel DP, respectively. The data driver DDV may be disposed on the non-display area NDA adjacent to one of the short sides of the display panel DP. When viewed in a plan view, the data driver DDV may be disposed adjacent to a lower end of the display panel DP. 
     The scan lines SL 1  to SLm may each extend in the second direction DR 2  and may be electrically connected to the pixels PX and the scan driver SDV. The data lines DL 1  to DLn may each extend in the first direction DR 1  and may be electrically connected to the pixels PX and the data driver DDV. The emission lines EL 1  to ELm may each extend in the second direction DR 2  and may be electrically connected to the pixels PX and the emission driver EDV. 
     The first power line PL 1  may extend in the first direction DR 1  and may be disposed on the non-display area NDA. Although the first power line PL 1  may be disposed between the display area DA and the emission driver EDV, the embodiment is not limited thereto. For example, the first power line PL 1  may be disposed between the display area DA and the scan driver SDV. 
     The connection lines CNL may each extend in the second direction DR 2  and may be arranged in the first direction DR 1 . The connection lines CNL may be electrically connected to the first power line PL 1  and the pixels PX. A first voltage may be applied to the pixels PX through the first power line PL 1  and the connection lines CNL electrically connected to each other. 
     The second power line PL 2  may be disposed on the non-display area NDA. The second power line PL 2  may extend along the long sides of the display panel DP, and the other of the short sides of the display panel DP at which the data driver DDV is not disposed. The second power line PL 2  may be disposed further than the scan driver SDV and the emission driver EDV. 
     Although not shown, the second power line PL 2  may extend toward the display area DA and may be electrically connected to the pixels PX. A second voltage having a level lower than the first voltage may be applied to the pixels PX through the second power line PL 2 . 
     The first control line CSL 1  may be electrically connected to the scan driver SDV and may extend toward the lower end of the display panel DP when viewed on the plane. The first control line CSL 1  may be electrically connected to the scan driver SDV and may extend toward the lower end of the display panel DP when viewed on the plane. The data driver DDV may be disposed between the first control line CSL 1  and the second control line CSL 2 . 
     The pads PD may be disposed on the display panel DP. The pads PD may be disposed closer to the lower end of the display panel DP than to the data driver DDV. The data driver DDV, the first power line PL 1 , the second power line PL 2 , the first control line CSL 1 , and the second control line CSL 2  may be electrically connected to the pads PD. The data lines DL 1  to DLn may be electrically connected to the data driver DDV, and the data driver DDV may be electrically connected to the pads PD corresponding to the data lines DL 1  to DLn. 
     Although not shown, the display device DD may include a timing controller for controlling an operation of each of the scan driver SDV, the data driver DDV, and the emission driver EDV and a voltage generator for generating the first and second voltages. The timing controller and the voltage generator may be electrically connected to corresponding pads PD through a printed circuit board. 
     The scan driver SDV may generate scan signals, and the scan signals may be applied to the pixels PX through the scan lines SL 1  to SLm. The data driver DDV may generate data voltages, and the data voltages may be applied to the pixels PX through the data lines DL 1  to DLn. The emission driver EDV may generate emission signals, and the emission signals may be applied to the pixels PX through the emission lines EL 1  to ELm. 
     The pixels PX may receive the data voltages in response to the scan signals. The pixels PX may emit light having luminance corresponding to the data voltages in response to the emission signals to thus display an image. The pixels PX may have an emission time that may be controlled by the emission signals. 
       FIG.  6    is a schematic cross-sectional view taken along line I-I′ of  FIG.  1   . 
     Referring to  FIG.  6   , the display device DD may include a display module DM, a support plate SPT, a cushion layer CUL, an insulating tape ITP, an impact absorbing layer ISL, and a black coating layer BCT. The display module DM may include the first non-folding area NFA 1 , the folding area FA, and the second non-folding area NFA 2 , which are arranged in the first direction DR 1 , like the display device DD. 
     The folding area FA may include a curved part CSP, a first extension part EX 1  disposed between the curved part CSP and the first non-folding area NFA 1 , and a second extension part EX 2  disposed between the curved part CSP and the second non-folding area NFA 2 . Further detailed shapes of the curved part CSP, the first non-folding area NFA 1 , and the second non-folding area NFA 2  will be described below. 
     The support plate SPT may be disposed below the display module DM. The support plate SPT may include a metal material such as stainless steel. Although the support plate SPT may include STS 316  as an example, the embodiment is not limited thereto. For example, the support plate SPT may include various metal materials. The support plate SPT may support the display module DM. In addition, the support plate SPT may increase the heat dissipation performance of the display device DD. 
     The support plate SPT may include a first support plate SPT 1  disposed below the first non-folding area NFA 1  and a second support plate SPT 2  disposed below the second non-folding area NFA 2 . The first support plate SPT 1  and the second support plate SPT 2  may each extend below the folding area FA and may be spaced apart from each other. 
     The first support plate SPT 1  may extend below the first extension part EX 1  and the curved part CSP. The second support plate SPT 2  may extend below the second extension part EX 2  and the curved part CSP. The first support plate SPT 1  and the second support plate SPT 2  may be spaced apart from each other below the curved part CSP. 
     The cushion layer CUL may be disposed below the support plate SPT. The cushion layer CUL may absorb an external impact applied to a lower portion of the display module DM to protect the display module DM. The cushion layer CUL may include a foam sheet having a predetermined elastic force. The cushion layer CUL may include foam, sponge, polyurethane, or thermoplastic polyurethane. 
     The cushion layer CUL may include a first cushion layer CUL 1  disposed below the first support plate SPT 1  and a second cushion layer CUL 2  disposed below the second support plate SPT 2 . The first cushion layer CUL 1  and the second cushion layer CUL 2  may each extend below the folding area FA and may be spaced apart from each other. 
     The insulating tape ITP may be disposed below the cushion layer CUL. The insulating tape ITP may include an insulating material. The insulating tape ITP may include a first insulating tape ITP 1  disposed below the first cushion layer CUL 1  and a second insulating tape ITP 2  disposed below the second cushion layer CUL 2 . The first insulating tape ITP 1  and the second insulating tape ITP 2  may each extend below the folding area FA and may be spaced apart from each other. 
     The impact absorbing layer ISL may be disposed below the cushion layer CUL. The impact absorbing layer ISL may be disposed adjacent to an edge of the cushion layer CUL. The impact absorbing layer ISL may be disposed further than the insulating tape ITP. The impact absorbing layer ISL may absorb an external impact applied to the edge of the display device DD. The impact absorbing layer ISL may include a pressure sensitive adhesive (PSA). 
     The impact absorbing layer ISL may include a first impact absorbing layer ISL 1  disposed below the first cushion layer CUL 1  and a second impact absorbing layer ISL 2  disposed below the second cushion layer CUL 2 . The first impact absorbing layer ISL 1  may be disposed further than the first insulating tape ITP 1 . The second impact absorbing layer ISL 2  may be disposed further than the second insulating tape ITP 2 . Thus, the first and second insulating tapes ITP 1  and ITP 2  may be disposed between the first impact absorbing layer ISL 1  and the second impact absorbing layer ISL 2 . 
     The black coating layer BCT may be disposed between the display module DM and the support plate SPT. The black coating layer BCT may be coated on each of a top surface of the first support plate SPT 1  and a top surface of the second support plate SPT 2 . The black coating layer BCT may include a black material. The black coating layer BCT may prevent structures disposed therebelow from being seen from above. 
     The display module DM may include the display panel DP, a reflection preventing layer RPL, a window WIN, a window protection layer WP, a panel protection layer PPL, and a printed layer PIT. The display panel DP according to an embodiment may be a light emitting display panel. For example, the display panel DP may be an organic light emitting display panel or a quantum dot light emitting display panel. The organic light emitting display panel may include a light emitting layer containing an organic light emitting material. The quantum dot light emitting display panel may include a light emitting layer containing a quantum dot or a quantum rod. Hereinafter, the display panel DP will be described as the organic light emitting display panel. 
     The display panel DP may be a flexible display panel. The display panel DP may include a first non-folding area NFA 1 , a folding area FA, and a second non-folding area NFA 2 , which are arranged in the first direction DR 1 , like the display module DM. Also, the folding area FA of the display panel DP may include a curved part CSP, a first extension part EX 1 , and a second extension part EX 2  like the display module DM. The display panel DP may include pixels for displaying an image. The pixels may include organic light emitting elements. 
     The reflection preventing layer RPL may be disposed on the display panel DP. The reflection preventing layer RPL may be disposed directly on the display panel DP. However, the embodiment is not limited thereto. For example, the reflection preventing layer RPL may be manufactured as a separate panel and attached to the display panel DP by using an adhesive. 
     The reflection preventing layer RPL may be defined as an external light reflection preventing film. The reflection preventing layer RPL may reduce a reflectance of external light incident to the display panel DP from above the display device DD. 
     In a case that the external light incident to the display panel DP is reflected by the display panel DP and redirected to an external user, the user may recognize the external light. To prevent the above-described phenomenon, the reflection preventing layer RPL may include color filters displaying the same color as the pixels. 
     The color filters may filter out external light to display the same color as the pixels. The external light may not be recognized by the user. However, the embodiment is not limited thereto. For example, the reflection preventing layer RPL may include a phase retarder and/or a polarizer. 
     The window WIN may be disposed on the reflection preventing layer RPL. The window WIN may protect the display panel DP and the reflection preventing layer RPL from external scratches. The window WIN may be optically transparent. The window WM may include glass. The window WIN may be defined as an ultra-thin glass (UTG). However, the embodiment is not limited thereto. For example, the window WIN may include a synthetic resin film. 
     The window protection layer WP may be disposed on the window WIN. The window protection layer WP may protect the window WIN. The window protection layer WP may include a flexible plastic material such as polyimide (PI) or polyethylene terephthalate (PET). Although not shown, a hard coating layer may be provided on the window protection layer WP. In addition, an anti-fingerprint layer or an anti-scattering layer, which is defined as a functional layer, may be provided on the window protection layer WP. 
     The panel protection layer PPL may be disposed below the display panel DP. The panel protection layer PPL may protect a lower portion of the display panel DP. The panel protection layer PPL may include a flexible plastic material. For example, the panel protection layer PPL may include polyethylene terephthalate (PET). 
     The display device DD may include first to fourth adhesive layers AL 1  to AL 4 . The first adhesive layer AL 1  may be disposed between the window protection layer WP and the window WIN. The second adhesive layer AL 2  may be disposed between the window WIN and the reflection preventing layer RPL. The third adhesive layer AL 3  may be disposed between the display panel DP and the panel protection layer PPL. 
     The fourth adhesive layer AL 4  may be disposed between the panel protection layer PPL and the support plate SPT. In detail, the fourth adhesive layer AL 4  may be disposed between the panel protection layer PPL and the black coating layer BCT. 
     Each of the first to fourth adhesive layers AL 1  to AL 4  may include a transparent adhesive such as a pressure sensitive adhesive (PSA) or an optically clear adhesive (OCA). 
     The window protection layer WP and the window WIN may be attached to each other by the first adhesive layer AL 1 . The window WIN and the reflection preventing layer RPL may be attached to each other by the second adhesive layer AL 2 . The display panel DP and the panel protection layer PPL may be attached to each other by the third adhesive layer AL 3 . 
     The panel protection layer PPL and the support plate SPT may be attached to each other by the fourth adhesive layer AL 4 . In detail, the panel protection layer PPL may be attached to the black coating layer BCT by the fourth adhesive layer AL 4 . 
     The printed layer PIT may be disposed on a bottom surface of the window protection layer WP. The printed layer PIT may overlap the non-display area NDA when viewed on the plane. The first adhesive layer AL 1  may be disposed below the window protection layer WP to cover or overlap the printed layer PIT. Although the printed layer PIT may have a black color as an example, the embodiment is not limited thereto. For example, the printed layer PIT may have various colors. 
     When viewed on the plane, the fourth adhesive layer AL 4  may overlap the first and second non-folding areas NFA 1  and NFA 2 . In addition, when viewed on the plane, the fourth adhesive layer AL 4  may overlap the first and second extension parts EX 1  and EX 2  and may not overlap the curved part CSP. Thus, the first and second support plates SPT 1  and SPT 2  may be attached to the first and second non-folding areas NFA 1  and NFA 2  and the first and second extension parts EX 1  and EX 2  and may not be attached to the curved part CSP. 
     In the third direction DR 3 , the reflection preventing layer RPL may have a thickness less than that of the display panel DP, the window WIN may have a thickness greater than that of the display panel DP, and the window protection layer WP may have a thickness greater than that of the window WIN. In the third direction DR 3 , the first adhesive layer AL 1  may have the same thickness as that of the second adhesive layer AL 2 . In addition, each of the first adhesive layer AL 1  and the second adhesive layer AL 2  may have a thickness greater than that of the window WIN and less than that of the window protection layer WP. 
     In the third direction DR 3 , the panel protection layer PPL may have the same thickness as that of the window WIN, and the third adhesive layer AL 3  may have a thickness less than that of the display panel DP and greater than that of the reflection preventing layer RPL. In the third direction DR 3 , the fourth adhesive layer AL 4  may have a thickness less than that of the third adhesive layer AL 3  and greater than that of the reflection preventing layer RPL. 
     In the third direction DR 3 , the window WIN may have a thickness greater than about 30 μm and less than about or equal to 80 μm, and the window protection layer WP may have a thickness in a range from about 55 μm to about 100 μm. In the third direction DR 3 , the support plate SPT may have a thickness in a range from about 80 μm to about 150 μm 
     In the third direction DR 3 , the support plate SPT may have a thickness greater than that of the window WIN. In the third direction DR 3 , the cushion layer CUL may have a thickness equal to or greater than that of the support plate SPT. In the third direction DR 3 , each of the insulating tape ITP and the impact absorbing layer ISL may have the same thickness as that of the panel protection layer PPL. 
     In the first direction DR 1  and the second direction DR 2 , the window protection layer WP may have a width greater than that of the window WIN. In the first direction DR 1  and the second direction DR 2 , each of the display panel DP, the reflection preventing layer RPL, and the panel protection layer PPL may have a width greater than that of the window protection layer WP. 
     In the first direction DR 1  and the second direction DR 2 , the display panel DP, the reflection preventing layer RPL, and the panel protection layer PPL may have the same width as each other. In the first direction DR 1  and the second direction DR 2 , the first adhesive layer AL 1  may have the same width as that of the window protection layer WP, and the second adhesive layer AL 2  may have a width less than that of the window WIN. 
     Since the window WIN and the second adhesive layer AL 2  between the window protection layer WP and the display panel DP have different widths, the difference in width therebetween may form a stepped structure therebetween. The window protection layer WP may have a thickness sufficient to prevent the stepped structure from being recognized from the outside. For example, in a case that the window protection layer WP has a thickness in a range from about 55 μm to about 100 μm, the stepped structure may not be recognized from the outside. 
     When viewed on the plane, each of the first and second support plates SPT 1  and SPT 2 , the first and second cushion layers CUL 1  and CUL 2 , the first and second insulating tapes ITP 1  and ITP 2 , and the first and second impact absorbing layers ISL 1  and ISL 2  may be disposed at an inner side more than the edge of the display panel DP. 
       FIG.  7    is a schematic cross-sectional view illustrating the display panel DP in  FIG.  6   . 
     Referring to  FIG.  7   , the display panel DP may include a substrate SUB, a circuit element layer DP-CL disposed on the substrate SUB, a display element layer DP-OLED disposed on the circuit element layer DP-CL, a thin-film encapsulation layer TFE disposed on the display element layer DP-OLED, and an input sensing part ISP disposed on the thin-film encapsulation layer TFE. 
     The substrate SUB may include a display area DA and a non-display area NDA around the display area DA. The substrate SUB may include a flexible plastic material. For example, the substrate SUB may include polyimide (PI). The display element layer DP-OLED may be disposed on the display area DA. 
     The circuit element layer DP-CL may include an insulation layer, a semiconductor pattern, a conductive pattern, and a signal line. Each of the insulation layer, the semiconductor layer, and the conductive layer may be provided on the substrate SUB through coating, deposition, and the like within the spirit and the scope of the disclosure. Thereafter, the insulation layer, the semiconductor layer, and the conductive layer may be selectively patterned through photolithography processes to provide the semiconductor pattern, the conductive pattern, and the signal line. 
     The circuit element layer DP-CL may include transistors constituted by the semiconductor pattern, the conductive pattern, and the signal line. The display element layer DP-OLED may include light emitting elements electrically connected to the transistors. The pixels PX may include the transistors and the light emitting elements. 
     The thin-film encapsulation layer TFE may be disposed on the circuit element layer DP-CL to cover or overlap the display element layer DP-OLED. The thin-film encapsulation layer TFE may include an inorganic layer, an organic layer, and an inorganic layer, which are sequentially laminated with each other. The inorganic layers may contain an inorganic material and protect the pixels PX from moisture or oxygen. The organic layer may contain an organic material and protect the pixels PX from foreign substances such as dust particles. 
     The input sensing part ISP may include sensors (not shown) for sensing an external input. The sensors may sense the external input by a capacitive method. The external input may include various types of inputs using a portion of a user&#39;s body, light, heat, a pen, or pressure. 
     The input sensing part ISP may be manufactured on the thin-film encapsulation layer TFE in a case that the display panel DP is manufactured. However, the embodiment is not limited thereto. For example, the input sensing part ISP may be manufactured on a panel distinct from the display panel DP and then attached to the display panel DP by an adhesive layer. 
       FIGS.  8  to  10    are views illustrating various bent states of the display module and the support plates. 
       FIGS.  8  to  10    show results obtained by performing tests for the curved part CSP of the display module DM to have a specific or predetermined curvature. 
     For example, the display module DM and support plates SPT_ 1  to SPT_ 3  for supporting the display module DM are illustrated in  FIGS.  8  to  10   . The support plates SPT_ 1  to SPT_ 3  may have the same configuration as the support plate SPT in  FIG.  6   . However, the support plates SPT_ 1  to SPT_ 3  may have different thicknesses. 
     The cushion layer CUL, the insulating tape ITP, and the impact absorbing layer ISL, which are disposed below the support plates SPT_ 1  to SPT_ 3 , are omitted for convenience of description. In addition, the black coating layer BCT disposed on the support plates SPT_ 1  to SPT_ 3  is omitted. 
     Referring to  FIGS.  8  to  10   , jigs JIG 1  and JIG 2  may be used to fold the display module DM. Each of the support plates SPT_ 1  to SPT_ 3  may have a thickness in a range from about 80 μm to about 150 μm like the support plate SPT. The support plates SPT_ 1  to SPT_ 3  may have different thicknesses. 
     The support plate SPT_ 1  in  FIG.  8    may have a first thickness TH 1  greater than a second thickness TH 2  of the support plate SPT_ 2  in  FIG.  9   . The second thickness TH 2  of the support plate SPT_ 2  in  FIG.  9    may be greater than a third thickness TH 3  of the support plate SPT_ 3  in  FIG.  10   . 
     Each of a length of the folding area FA and lengths of the first and second non-folding areas NFA 1  and NFA 2  may be varied according to positions of the jigs JIG 1  and JIG 2  contacting the display module DM. 
     Hereinafter, a virtual line extending toward the curved part CSP from the first non-folding area NFA 1  in the same direction (e.g. third direction DR 3 ) as an extension direction of the first non-folding area NFA 1  when the display module DM may be folded may be defined as a first reference line RFL 1 . In addition, a virtual line extending toward the curved part CSP from the second non-folding area NFA 2  in the same direction (e.g. third direction DR 3 ) as an extension direction of the second non-folding area NFA 2  when the display module DM may be folded may be defined as a second reference line RFL 2 . 
     Hereinafter, bent points between the first extension part EX 1  and the first non-folding area NFA 1  may be defined as first points P 1 _ 1 , P 1 _ 2 , and P 1 _ 3 . In addition, bent points between the second extension part EX 2  and the second non-folding area NFA 2  may be defined as second points P 21 , P 2 _ 2 , and P 2 _ 3 . 
     Referring to  FIG.  8   , as the display module DM is folded by using the jigs JIG 1  and JIG 2 , the folding area FA may be bent. The jigs JIG 1  and JIG 2  may include a first jig JIG 1  and a second jig JIG 2 . The first jig JIG 1  may be disposed at a boundary between the folding area FA and the first non-folding area NFA 1 , and the second jig JIG 2  may be disposed at a boundary between the folding area FA and the second non-folding area NFA 2 . 
     As the first and second jigs JIG 1  and JIG 2  move to be adjacent to each other, the first non-folding area NFA 1  and the second non-folding area NFA 2  may be adjacent to each other. In a case that the display module DM is folded, the first and second non-folding area NFA 1  and NFA 2  may each extend in the third direction DR 3 . 
     In a case that the display module DM is folded, the folding area FA may include the bent curved part CSP, the first extension part EX 1  disposed between the curved part CSP and the first non-folding area NFA 1 , and the second extension part EX 2  disposed between the curved part CSP and the second non-folding area NFA 2 . 
     The curved part CSP may be bent to have a predetermined curvature. In detail, in a case that the display module DM is folded, the curved part CSP may be bent to have a predetermined radius Rc of curvature (hereinafter, referred to as a predetermined curvature radius Rc). 
     The first extension part EX 1  may be bent from the first non-folding area NFA 1  by the first jig JIG 1  and may extend to the curved part CSP. The second extension part EX 2  may be bent from the second non-folding area NFA 2  by the second jig JIG 2  and may extend to the curved part CSP. 
     A distance DT between the first non-folding area NFA 1  and the second non-folding area NFA 2  may be less than the curvature radius Rc. By the above-described structure, the display module DM may be folded into a substantially dumbbell shape. 
     The support plate SPT_ 1  may include a first support plate SPT 1 _ 1  disposed on the first extension part EX 1  and a second support plate SPT 2 _ 1  disposed on the second extension part EX 2 . 
     In a case that the display module DM is folded, the first support plate SPT 1 _ 1  may be bent at the first point P 1 _ 1  by the first jig JIG 1 . The first support plate SPT 1 _ 1  may be bent at a boundary between the folding area FA and the first non-folding area NFA 1  by the first jig JIG 1 . 
     In a case that the display module DM is folded, the second support plate SPT 2 _ 1  may be bent at the second point P 2 _ 1  by the second jig JIG 2 . The second support plate SPT 2 _ 1  may be bent at a boundary between the folding area FA and the second non-folding area NFA 2  by the second jig JIG 2 . 
     Since the first support plate SPT 1 _ 1  is attached to the first extension part EX 1  by the fourth adhesive layer AL 4  in  FIG.  6   , the first extension part EX 1  may maintain a flat state by the first support plate SPT 1 _ 1 . Since the second support plate SPT 2 _ 1  is attached to the second extension part EX 2  by the fourth adhesive layer AL 4  in  FIG.  6   , the second extension part EX 2  may maintain a flat state by the second support plate SPT 2 _ 1 . 
     As previously described in  FIG.  6   , the curved part CSP may not be attached to the first and second support plates SPT 1 _ 1  and SPT 2 _ 1 . Thus, the curved part CSP may be bent in a case that the display module DM is folded. 
     The first extension part EX 1  may make a first angle θ 1 _ 1  with the first reference line RFL 1 . The second extension part EX 2  may make a second angle θ 2 _ 1  with the second reference line RFL 2 . Each of the first angle θ 11  and the second angle θ 2 _ 1  may be an acute angle. In a case that the display module DM is folded, the first extension part EX 1  and the second extension part EX 2  may extend to be symmetric to each other. Thus, the first angle θ 1 _ 1  may be equal to the second angle θ 2 _ 1 . However, an embodiment is not limited thereto. For example, the first angle θ 1 _ 1  may be different from the second angle θ 2 _ 1 . 
     The curved part CSP may be bent to have a desired or predetermined curvature radius RC according to a bent angle of the support plate SPT_ 1 . The bent angle of the support plate SPT_ 1  may be the first angle θ 1 _ 1  and the second angle θ 21  and may be varied according to the thickness TH 1  of the support plate SPT_ 1 . 
     In a case that the display module DM is folded, a stress generated in the folding area FA may push the support plate SPT_ 1  to the outside. However, the support plate SPT_ 1  having a greater thickness may have a high resistance against the stress generated in the folding area FA. 
     A bent point of the support plate SPT_ 1  may be transferred from the first and second points P 1 _ 1  and P 2 _ 1  to first and second points P 1 ′ and P 2 ′, which may be closer to the curved part CSP, in  FIG.  8   . The curved part CSP may be bent to have a large or great curvature as illustrated by a dotted line by the resistance according to the thickness TH 1  of the support plate SPT_ 1  illustrated by a dash-dotted line, thereby having a curvature radius less than the curvature radius Rc. The curved part CSP may not be bent at the desired or predetermined curvature. 
     A distance between the first point P 1 _ 1  and the second point P 2 _ 1  may be defined as that from the first point P 1 _ 1  to the second point P 2 _ 1  along the display module DM. The distance between the first point P 1 _ 1  and the second point P 2 _ 1  may be defined as a length of the folding area FA in a case that the folding area FA is unfolded. A distance between the first point P 1 ′ and the second point P 2 ′ may be defined as a distance from the first point P 1 ′ to the second point P 2 ′ along the display module DM. 
     The distance between the first point P 1 _ 1  and the second point P 2 _ 1  may be less than that between the first point P 1 ′ and the second point P 2 ′. The curvature radius Rc of the curved part CSP may be varied according to distances between the bent points P 1 _ 1 , P 2 _ 1 , P 1 ′, and P 2 ′ of the support plate SPT_ 1 . 
     In summary, the curvature radius Rc of the curved part CSP may be varied according to the bent angle θ 1 _ 1  and θ 2 _ 1  of the support plate SPT_ 1 , the thickness TH 1  of the support plate SPT_ 1 , and the distance between the bent points P 1 _ 1  and P 2 _ 1  of the support plate SPT_ 1 . 
     Hereinafter, in  FIGS.  9  and  10   , different components from those in  FIG.  8    and a structure of each of the support plates SPT_ 2  and SPT_ 3  having the curvature radius Rc will be mainly described. 
     Referring to  FIG.  9   , the support plate SPT_ 2  may include a first support plate SPT 1 _ 2  and a second support plate SPT 2 _ 2 . The support plate SPT_ 2  may have a second thickness TH 2  less than the first thickness TH 1 . Since the support plate SPT_ 2  may have a smaller thickness, the support plate SPT_ 2  may have a resistance less than that of the support plate SPT_ 1  in  FIG.  8    against the stress generated in the folding area FA. 
     The first support plate SPT 1 _ 2  and the second support plate SPT 2 _ 2  may be bent at the first point P 1 _ 2  and the second point P 2 _ 2 , respectively, which may be closer to the curved part CSP than to the first point P 1 _ 1  and the second point P 2 _ 1  in  FIG.  8    so that the curved part CSP has the curvature radius Rc. 
     A distance between the first point P 1 _ 2  and the second point P 2 _ 2  may be defined as that from the first point P 1 _ 2  to the second point P 2 _ 2  along the display module DM. The distance between the first point P 1 _ 2  and the second point P 2 _ 2  may be less than that between the first point P 1 _ 1  and the second point P 2 _ 1 . Thus, a first angle θ 1 _ 2  and a second angle θ 2 _ 2  may be greater than the first angle θ 1 _ 1  and the second angle θ 2 _ 1  in  FIG.  8   , respectively. 
     Referring to  FIG.  10   , the support plate SPT_ 3  may include a first support plate SPT 1 _ 3  and a second support plate SPT 2 _ 3 . The support plate SPT_ 3  may have a third thickness TH 3  less than the second thickness TH 2 . Since the support plate SPT_ 3  may have a smaller thickness, the support plate SPT_ 3  may have a resistance less than that of the support plate SPT_ 2  in  FIG.  9    against the stress generated in the folding area FA. 
     The first support plate SPT 1 _ 3  and the second support plate SPT 2 _ 3  may be bent at the first point P 1 _ 3  and the second point P 2 _ 3 , respectively, which may be closer to the curved part CSP than to the first point P 1 _ 2  and the second point P 2 _ 2  in  FIG.  9    so that the curved part CSP has the curvature radius Rc. 
     A distance between the first point P 1 _ 3  and the second point P 2 _ 3  may be defined as that from the first point P 1 _ 3  to the second point P 2 _ 3  along the display module DM. The distance between the first point P 1 _ 3  and the second point P 2 _ 3  may be less than that between the first point P 1 _ 2  and the second point P 2 _ 2 . Thus, a first angle θ 1 _ 3  and a second angle θ 2 _ 3  may be greater than the first angle θ 1 _ 2  and the second angle θ 22  in  FIG.  9   , respectively. 
     Referring to  FIGS.  8 ,  9 , and  10   , the curvature radius Rc of the curved part CSP may be set to a range of about 1.5 mm to about 5.0 mm, as an example, about 2.5 mm. The distance between the first points P 1 _ 1 , P 1 _ 2 , and P 1 _ 3  and the second points P 21 , P 2 _ 2 , and P 2 _ 3  may be set to a range of about 35 mm to about 45 mm, as an example about 40 mm. The distance between the first points P 1 _ 1 , P 1 _ 2 , and P 1 _ 3  and the second points P 21 , P 2 _ 2  and P 2 _ 3  may be substantially defined as the length of the folding area FA. 
     The first angles θ 1 _ 1 , θ 1 _ 2 , and θ 1 _ 3  may be set toa range of about 6.5° to about 12.5°, as an example about 9.5°, so that the curved part CSP has the curvature radius Rc. The second angles θ 2 _ 1 , θ 2 _ 2 , and θ 2 _ 3  may be about equal to the first angles θ 1 _ 1 , θ 1 _ 2 , and θ 1 _ 3 , respectively. The thicknesses TH 1 , TH 2 , and TH 3  of the support plates SPT_ 1 , SPT_ 2 , and SPT_ 3  may be set to a range of about 80 μm to about 150 μm, as an example about 80 μm, so that the curved part CSP has the curvature radius Rc. Effects caused by the above numerical values will be described in detail below. 
       FIGS.  11  and  12    are exploded perspective views illustrating a support on which the display module DM and the support plate SPT in  FIG.  6    are disposed.  FIG.  13    is a plan view illustrating the support obtained by coupling first and second supports, first and second wing plates, and a hinge in  FIGS.  11  and  12   . 
       FIG.  11    is an upper exploded perspective view illustrating a support SUP when viewed from above the support SUP, and  FIG.  12    is a lower exploded perspective view illustrating the support SUP when viewed from below the support SUP. 
     Referring to  FIGS.  11 ,  12 , and  13   , the display device DD may include the support SUP, and the support SUP may include a first support SUP 1 , a second support SUP 2 , a first wing plate WPT 1 , a second wing plate WPT 2 , and a hinge HIG. The first support SUP 1  and the second support SUP 2  may be arranged in the first direction DR 1 . The first support SUP 1  and the second support SUP 2  may have a plane defined by the first and second directions DR 1  and DR 2 . 
     A recessed portion RES may be defined in a top surface of the first support SUP 1 . Although not shown, various components may be disposed in the recessed portion RES. For example, a battery for supplying power to the display module DM or a system board for providing a driving signal to the display module DM may be disposed in the recessed portion RES. An opening OP disposed adjacent to the recessed portion RES may be defined in the first support SUP 1 . A sensor or a camera may be disposed in the opening OP. 
     The top surface of the first support SUP 1  may be adjacent to a side OS 1  of the first support SUP 1 , facing the second support SUP 2  and may have a first inclined surface SLP 1 . The first inclined surface SLP 1  may have a height that gradually decreases in a direction toward the side OS 1  of the first support SUP 1 . The recessed portion RES may be adjacent to the first inclined surface SLP 1 . 
     A top surface of the second support SUP 2  may be adjacent to a side OS 2  of the second support SUP 2 , facing the first support SUP 1  and may have a second inclined surface SLP 2 . The second inclined surface SLP 2  may have a height that gradually decreases in a direction toward the side OS 2  of the second support SUP 2 . 
     The first wing plate WPT 1  may be disposed on the first support SUP 1  and connected to the first support SUP 1 . The first wing plate WPT 1  may be disposed on the first inclined surface SLP 1  and rotatably coupled to an upper side of the first inclined surface SLP 1 , which is the most away from the side OS 1  of the first support SUP 1 . 
     A first connection pin PIN 1  extending in the second direction DR 2  and connected to the first support SUP 1  may be disposed at a side of the first wing plate WPT 1 . The side of the first wing plate WPT 1  may overlap the upper side of the first inclined surface SLP 1 . The first connection pin PIN 1  may have a substantially cylindrical shape extending in the second direction DR 2 . 
     The second wing plate WPT 2  may be disposed on the second support SUP 2  and connected to the second support SUP 2 . The second wing plate WPT 2  may be disposed on the second inclined surface SLP 2  and rotatably coupled to an upper side of the second inclined surface SLP 2 , which is the most away from the side OS 2  of the second support SUP 2 . 
     A second connection pin PIN 2  extending in the second direction DR 2  and connected to the second support SUP 2  may be disposed at a side of the second wing plate WPT 2 . The side of the second wing plate WPT 2  may overlap the upper side of the second inclined surface SLP 2 . The second connection pin PIN 2  may have a substantially cylindrical shape extending in the second direction DR 2 . 
     The hinge HIG may be connected to the first support SUP 1  and the second support SUP 2 . The hinge HIG may include a biaxial rotation shaft RX 1  and RX 2  between the first support SUP 1  and the second support SUP 2 . The biaxial rotation shaft RX 1  and RX 2  may include a first rotation shaft RX 1  and a second rotation shaft RX 2 , which may be spaced apart from each other in the first direction DR 1  and may extend in parallel to each other in the second direction DR 2 . 
     The hinge HIG may include hinge parts HGP, a cover part CVP, and first and second rotation units RU 1  and RU 2 . The hinge parts HGP may be connected to sides of the first support SUP 1 , which may be opposite to each other, and sides of the second support SUP 2 , which may be opposite to each other. 
     For example, coupling grooves CGV may be defined in the sides of the first support SUP 1  and the sides of the second support SUP 2 , and the hinge parts HGP may be disposed in the coupling grooves CGV. The coupling grooves CGV may be defined from the side OS 1  of the first support SUP 1  and the side OS 2  of the second support SUP 2 . Although not shown, connection pins for coupling the hinge parts HGP to the coupling grooves CGV may be provided on the hinge parts HGP. 
     The cover part CVP may extend in the second direction DR 2  and may be disposed between the first support SUP 1  and the second support SUP 2 . A groove GOV extending in the second direction DR 2  may be defined in the cover part CVP. 
     A pair of the first and second rotation units RU 1  and RU 2  may be connected to ends of the cover part CVP, respectively, which are opposite to each other in the second direction DR 2 . Each of the ends of the cover part CVP, which are opposite to each other in the second direction DR 2 , may have a substantially sidewall shape. The pair of the first and second rotation units RU 1  and RU 2  may be spaced apart from each other in the first direction DR 1  and may each extend in the second direction DR 2 . 
     The first rotation shaft RX 1  may be defined by the first rotation unit RU 1 , and the second rotation shaft RX 2  may be defined by the second rotation unit RU 2 . The first rotation unit RU 1  may rotate around the first rotation shaft RX 1 , and the second rotation unit RU 2  may rotate around the second rotation shaft RX 2 . 
     The hinge part HGP may be connected to the first and second rotation units RU 1  and RU 2 . In detail, sides of the hinge parts HGP facing each other in the first direction DR 1  may be connected to the first rotation unit RU 1  and the second rotation unit RU 2 . Thus, the hinge parts HGP may rotate around the first and second rotation shafts RX 1  and RX 2  by the first and second rotation units RU 1  and RU 2 . 
     For example, two hinge parts HGP arranged in the first direction DR 1  may be connected to the pair of first and second rotation units RU 1  and RU 2 . In addition, other two hinge parts HGP arranged in the first direction DR 1  may be connected to the other pair of first and second rotation units RU 1  and RU 2 . 
       FIG.  14    is a perspective view illustrating the support in  FIG.  13   .  FIG.  15    is a view illustrating a folded state of the support in  FIG.  14   . 
     Referring to  FIGS.  14  and  15   , the hinge parts HGP connected to the first and second rotation units RU 1  and RU 2  may rotate around the first and second rotation shafts RX 1  and RX 2  so that the support part SUP is folded. The first and second supports SUP 1  and SUP 2  connected to the hinge parts HGP may move while rotating around the first and second rotation shafts RX 1  and RX 2  as the hinge parts HGP rotate. 
     The first support SUP 1  and the second support SUP 2  may move by rotating in opposite directions. The first support SUP 1  may move by rotating in a clockwise direction around the first rotation shaft RX 1 . The second support SUP 2  may move by rotating in a counterclockwise direction around the second rotation shaft RX 2 . Thus, as the support SUP is folded, the top surface of the first support SUP 1  and the top surface of the first support SUP 1  may face each other. 
       FIG.  16    is a schematic cross-sectional view taken along line II-II′ of  FIG.  14   .  FIG.  17    is a view illustrating a folded state of the display device in  FIG.  16   . 
     As an example, the display module DM and the support plate SPT are illustrated in conjunction with the support SUP in  FIGS.  16  and  17   . In addition, the cushion layer CUL, the insulating tape ITP, the impact absorbing layer ISL, which are disposed below the support plate SPT, and the black coating layer BCT disposed on the support plate SPT are omitted. 
     Referring to  FIG.  16   , the display module DM and the support plate SPT may be disposed on the support SUP. The display module DM and the support plate SPT may be in an unfolded state that is defined as a flat state. The first and second rotation shafts RX 1  and RX 2  may be defined below the curved part CSP of the folding area FA. 
     In a case that the display module DM is in the unfolded state, the folding area FA may have a length of about 35 mm to about 45 mm in the first direction DR 1 . The distance between the first points P 1 _ 1 , P 1 _ 2 , and P 1 _ 3  and the second points P 21 , P 2 _ 2 , and P 2 _ 3  may be substantially defined as the length of the folding area FA. 
     In a case that the display module DM is in the unfolded state, each of the first and second support plates SPT 1  and SPT 2  may have a thickness of about 80 μm to about 150 μm in the third direction DR 3 . The respective thicknesses of the first and second support plates SPT 1  and SPT 2  may be the above-described first, second, and third thicknesses TH 1 , TH 2 , and TH 3 . 
     The first support SUP 1  may be disposed below the first non-folding area NFA 1 . The second support SUP 2  may be disposed below the second non-folding area NFA 2 . The first support plate SPT 1  may be disposed between the first support SUP 1  and the first non-folding area NFA 1 . The second support plate SPT 2  may be disposed between the second support SUP 2  and the second non-folding area NFA 2 . 
     The first support plate SPT 1  may extend below the first extension part EX 1 , and the second support plate SPT 2  may extend below the second extension part EX 2 . When viewed on the plane while facing the first extension part EX 1 , the top surface of the first support SUP 1  overlapping the first extension part EX 1  may be defined as the first inclined surface SLP 1 . When viewed on the plane while facing the second extension part EX 2 , the top surface of the second support SUP 2  overlapping the second extension part EX 2  may be defined as the second inclined surface SLP 2 . 
     The first wing plate WPT 1  may be disposed between the first extension part EX 1  and the first inclined surface SLP 1 . The first wing plate WPT 1  may be rotatably coupled to a portion of the first support SUP 1  overlapping a boundary between the first non-folding area NFA 1  and the first extension part EX 1  when viewed on the plane. 
     The first wing plate WPT 1  may rotate around a third rotation shaft RX 3  extending in the second direction DR 2 . The third rotation shaft RX 3  may be defined by the first connection pin PIN 1 . The portion of the first support SUP 1 , which overlaps the boundary between the first non-folding area NFA 1  and the first extension part EX 1 , may be defined as the upper side of the first inclined surface SLP 1 . 
     The second wing plate WPT 2  may be disposed between the second extension part EX 2  and the second inclined surface SLP 2 . The second wing plate WPT 2  may be rotatably coupled to a portion of the second support SUP 2  overlapping a boundary between the second non-folding area NFA 2  and the second extension part EX 2  when viewed on the plane. 
     The second wing plate WPT 2  may rotate around a fourth rotation shaft RX 4  extending in the second direction DR 2 . The fourth rotation shaft RX 4  may be defined by the second connection pin PIN 2 . The portion of the second support SUP 2 , which overlaps the boundary between the second non-folding area NFA 2  and the second extension part EX 2 , may be defined as the upper side of the second inclined surface SLP 2 . 
     The first wing plate WPT 1  and the second wing plate WPT 2  may be symmetric to each other. The first inclined surface SLP 1  and the second inclined surface SLP 2  may be symmetric to each other. A distance between the first wing plate WPT 1  and the first inclined surface SLP 1  may increase in a direction toward the curved part CSP while the display module DM and the support SUP are unfolded. In addition, a distance between the second wing plate WPT 2  and the second inclined surface SLP 2  may increase in a direction toward the curved part CSP while the display module DM and the support SUP are unfolded. 
     The first wing plate WPT 1  and the first inclined surface SLP 1  may make a first angle θ 1  while the display module DM and the support SUP are unfolded. The first angle θ 1  may be in a range from about 6.5° to about 12.5°. The first angle θ 1  may be equal to the above-described first angles θ 1 _ 1 , θ 1 _ 2 , or θ 1 _ 3 . A second angle θ 2  between the second wing plate WPT 2  and the second inclined surface SLP 2  may be equal to the first angle θ 1 . 
     A structure of the support SUP may be determined depending on the test results described in  FIGS.  8  to  10   . For example, the first and second wing plates WPT 1  and WPT 2  may overlap the folding area FA having a length of about 35 mm to about 45 mm. In addition, the first angle θ 1  between the first inclined surface SLP 1  and the first wing plate WPT 1  may be determined as the above-described first angles θ 1 _ 1 , θ 1 _ 2 , or θ 1 _ 3 . The first angles θ 1 _ 1 , θ 1 _ 2 , and θ 1 _ 3  may be numerical values determined in consideration of the thicknesses TH 1 , TH 2 , and TH 3  of the support plates SPT_ 1 , SPT_ 2 , and SPT_ 3 . 
     The cover part CVP may be disposed between the first support SUP 1  and the second support SUP 2 . The cover part CVP may be disposed below the first and second wing plates WPT 1  and WPT 2 . A portion of the first wing plate WPT 1  and a portion of the second wing plate WPT 2  may be disposed on the cover part CVP. The groove GOV defined in the cover part CVP may face the curved part CSP. 
     The first rotation shaft RX 1  and the second rotation shaft RX 2  may overlap the curved part CSP and the groove GOV when viewed on the plane. In addition, the first rotation shaft RX 1  and the second rotation shaft RX 2  may overlap the groove GOV when viewed in the second direction DR 2 . 
     Referring to  FIG.  17   , as the first and second supports SUP 1  and SUP 2  rotate around the first and second rotation shafts RX 1  and RX 2 , respectively, the display module DM may be folded. The folding area FA may be bent to have a curvature radius Rc in a range of about 1.5 mm to about 5.0 mm. The display module DM may be in-folded so that the first non-folding area NFA 1  and the second non-folding area NFA 2  face each other. The distance DT between the first non-folding area NFA 1  and the second non-folding area NFA 2  may be less than the curvature radius Rc. 
     In a case that the display module DM is folded, the first wing plate WPT 1  may rotate around the third rotation shaft RX 3  to contact the first inclined surface SLP 1  according to the stress of the folding area FA. In a case that the display module DM is folded, the second wing plate WPT 2  may rotate around the fourth rotation shaft RX 4  to contact the second inclined surface SLP 2  according to the stress of the folding area FA. 
     In a case that the display module DM is folded, the first support plate SPT 1  may be bent at the boundary between the first non-folding area NFA 1  and the first extension part EX 1  by the first wing plate WPT 1 . In a case that the display module DM is folded, the second support plate SPT 2  may be bent at the boundary between the second non-folding area NFA 2  and the second extension part EX 2  by the second wing plate WPT 2 . 
     In a case that the display module DM is folded, a central portion of the curved part CSP may be disposed in the groove GOV. In addition, in a case that the display module DM is folded, the side of the first wing plate WPT 1  and the side of the second wing plate WPT 2 , which face each other, may be disposed in the groove GOV. 
     As described in  FIGS.  8  to  10   , in a case that the support plates SPT_ 1 , SPT_ 2 , and SPT_ 3  are bent at the first angles θ 1 _ 1 , θ 1 _ 2 , and θ 1 _ 3 , respectively, according to the thicknesses TH 1 , TH 2 , and TH 3  of the support plates SPT_ 1 , SPT_ 2 , and SPT_ 3 , the curved part CSP may have a predetermined curvature radius Rc. 
     As the first wing plate WPT 1  and the first inclined surface SLP 1  have the first angle θ 1  therebetween in a case that the display module DM is unfolded, and the first wing plate WPT 1  and the first inclined surface SLP 1  contact each other in a case that the display module DM is folded, the first extension part EX 1  may form the first angle θ 1  with the first reference line RFL 1 . 
     Likewise, as the second wing plate WPT 2  contacts the second inclined surface SLP 2 , the second extension part EX 2  may form the second angle θ 1  with the second reference line RFL 2 . Thus, in a case that the display module DM is folded, the curved part CSP of the folding area FA may be bent to have a curvature radius Re in a range of about 1.5 mm to about 5.0 mm. 
       FIG.  18    is an enlarged photograph showing a folding area of a comparative display module.  FIG.  19    is a graph showing a deformed state of the folding area in  FIG.  18   .  FIG.  20    is an enlarged photograph showing the folding area of the display module according to an embodiment.  FIG.  21    is a graph showing a deformed state of the folding area in  FIG.  20   . 
     A comparative display module DM′ in  FIG.  18    may be folded instead of having a dumbbell structure and may have a curvature radius different from the curvature radius Rc. 
     Horizontal axes in  FIGS.  19  and  21    represent distances from central portions of curved parts CSP′ and CSP in the first direction DR 1 . Vertical axes in  FIGS.  19  and  21    represent deformation of the curved parts CSP′ and CSP in the third direction DR 3 . 
       FIGS.  18  and  20    are photographs obtained by photographing the curved parts CSP′ and CSP in a state in which the comparative display module DM′ and the display module DM are folded, the folded state thereof is maintained for a predetermined time, the comparative display module DM′ and the display module DM are unfolded, and a predetermined time has elapsed. 
     Referring to  FIGS.  18  and  19   , a crease CRS&#39; may be generated in the curved part CSP′ of the comparative display module DM′. A difference between a maximum height and a minimum height of the crease CRS&#39; may be defined as a first deformation STR 1 . 
     Referring to  FIGS.  20  and  21   , a crease CRS may be generated in the curved part CSP of the display module DM. A difference between a maximum height and a minimum height of the crease CRS may be defined as a second deformation STR 2 . 
     Referring to  FIGS.  18  to  21   , the first deformation STR 1  of the curved part CSP′ may be greater than the second deformation STR 2  of the curved part CSP. Thus, the crease CRS&#39; generated in the curved part CSP′ may be more clearly recognized. In addition, the crease CRS generated in the curved part CSP may not be recognized. 
     In an embodiment, as the folding area FA is bent into the substantially dumbbell shape, and the curved part CSP may be bent to have a curvature radius Rc of about 1.5 mm to about 5.0 mm, and thus deformation of the folding area FA may be reduced. 
       FIG.  22    is an enlarged photograph showing a surface of the comparative display module.  FIG.  23    is an enlarged photograph showing a surface of the display module in  FIG.  6   . 
     A surface of the display module DM may be defined as the top surface of the display module DM. A surface of a comparative display module DM″ may be defined as a top surface of the comparative display module DM″. 
       FIGS.  22  and  23    are photographs obtained by capturing surfaces by using Optimap PSD, which is a coating surface measurement analyzer, of Rhopoint instruments. 
     Referring to  FIGS.  22  and  23   , a window of the comparative display module DM″ may have a thickness of about 30 μm. As described above, the window WIN of the display module DM may have a thickness greater than about 30 μm and equal to or less than about 80 μm. For example, the window WIN of the display module DM in  FIG.  23    may have a thickness of about 50 m. 
     The window WIN of the display module DM may have a greater thickness. The comparative display module DM″ including the window having a smaller thickness had a surface quality index of about 0.46 Kc. The display module DM including the window WIN having a greater thickness had a surface quality index of about 0.34 Kc. 
     As the surface quality index (Kc) decreases, an object to be measured may have a smoother surface. Thus, the display module DM may have a surface quality index greater than that of the display module DM′. The display module DM may have a top surface smoother than that of the display module DM′. 
     According to the embodiment, the deformation of the folding area may be reduced as the folding area is folded to have the curvature radius capable of minimizing the deformation of the folding area. 
     Although embodiments have been described, it is understood that the disclosure should not be limited to these embodiments but rather various changes and modifications can be made by one of ordinary skill in the art within the spirit and scope of the disclosure as hereinafter claimed. Thus, the scope of the disclosure is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.