Patent Publication Number: US-11043549-B2

Title: Flexible display device and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional application of U.S. patent application Ser. No. 15/979,747 filed May 15, 2018, which claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2017-0060264, filed on May 16, 2017, in the Korean Intellectual Property Office (KIPO), the disclosures of which are incorporated by reference herein in their entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present disclosure relate to a flexible display device and to a method of manufacturing the flexible display device. 
     DISCUSSION OF RELATED ART 
     Display devices display images using light emitting elements. In recent times, flat panel display (“FPD”) devices have been widely used as display devices. The FPD display devices may be classified into liquid crystal display (“LCD”) devices, organic light emitting diode (“OLED”) display devices, plasma display panel (“PDP”) devices, electrophoretic display devices, and the like based on a light emitting scheme thereof. 
     Flexible display panels that can be bent have been developed recently. Such a flexible display panel may be used in various fields because it may be used in a folded or curved form. Since organic light emitting elements may be manufactured in a stack structure of a thin film type, they have excellent flexibility and are thus attracting attention as display elements of the flexible display panel. 
     However, when a stress is concentrated on a metal thin film formed on a flexible substrate, cracks may be generated and a metal thin film may be detached off from the flexible substrate. 
     It is to be understood that this background is intended to provide useful background for understanding the subject matter of the present disclosure, and as such disclosed herein, the background may include ideas, concepts, or recognitions that are not a part of what is known or appreciated by those skilled in the pertinent art prior to a corresponding effective filing date of the present disclosure. 
     SUMMARY 
     Embodiments of the present disclosure may be directed to a flexible display device and a method of manufacturing the flexible display device that may substantially prevent detachment of a metal thin film formed on a flexible substrate. 
     According to an exemplary embodiment, a flexible display device includes: a flexible substrate; a photo-curable adhesive layer disposed on the flexible substrate; and a metal wiring disposed on the photo-curable adhesive layer. The metal wiring defines a plurality of holes. 
     Each of the plurality of holes may have an area in a range from about 0.1 μm 2  to about 0.2 μm 2  on a plane. 
     Each of the plurality of holes may have at least one of a circular shape and a polygonal shape. 
     The plurality of holes may include a first hole, a second hole, and a third hole that are adjacent to each other, and a first imaginary straight line passing through a center of the first hole and a center of the second hole and a second imaginary straight line passing through the center of the first hole and a center of the third hole may substantially form a right angle. 
     The plurality of holes may include a first hole, a second hole, and a third hole that are adjacent to each other, and a first imaginary straight line passing through a center of the first hole and a center of the second hole and a second imaginary straight line passing through the center of the first hole and a center of the third hole may substantially form 60 degrees. 
     The holes may be spaced apart from each other at a substantially equal spatial interval. 
     The holes may be spaced apart from each other by a spatial interval of about 300 nm or more. 
     The metal wiring may be in the form of a matrix. 
     The metal wiring may include at least one of aluminum (Al), silver (Ag), copper (Cu), gold (Au), platinum (Pt), iron (Fe), nickel (Ni), and/or titanium (Ti). 
     According to an exemplary embodiment, a method of manufacturing a flexible display device includes: depositing a metal thin film on a mold substrate defined with a plurality of grooves; forming a photo-curable adhesive layer on a flexible substrate; transferring the metal thin film on the photo-curable adhesive layer to form a metal wiring that defines a plurality of holes corresponding to the plurality of grooves; and curing the photo-curable adhesive layer. 
     Each of the plurality of grooves and the plurality of holes may have an area in a range from about 0.1 μm 2  to about 0.2 μm 2  on a plane. 
     Each of the plurality of grooves and the plurality of holes may have at least one of a circular shape and a polygonal shape on a plane. 
     The plurality of holes may include a first hole, a second hole, and a third hole that are adjacent to each other, and a first imaginary straight line passing through a center of the first hole and a center of the second hole and a second imaginary straight line passing through the center of the first hole and a center of the third hole may substantially form a right angle. 
     The plurality of holes may include a first hole, a second hole, and a third hole that are adjacent to each other, and a first imaginary straight line passing through a center of the first hole and a center of the second hole and a second imaginary straight line passing through the center of the first hole and a center of the third hole may substantially form 60 degrees. 
     The grooves and the holes may be spaced apart from each other at a substantially equal spatial interval. 
     The grooves and the holes may be spaced apart from each other by a spatial interval of about 300 nm or more. 
     The metal wiring may be in the form of a matrix. 
     The method may further include pre-curing the photo-curable adhesive layer before transferring the metal thin film on the photo-curable adhesive layer to form the metal wiring that defines the plurality of holes. 
     The metal wiring may include at least one of Al, Ag, Cu, Au, Pt, Fe, Ni, and/or Ti. 
     The foregoing is illustrative only, and is not intended to be in any way limiting. In addition to the illustrative aspects, exemplary embodiments, and features described above, further aspects, exemplary embodiments, and features will become apparent to those of ordinary skill in the art by reference to the drawings, and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the present disclosure will become more apparent by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, wherein: 
         FIG. 1  is a cross-sectional view illustrating a flexible display device according to an exemplary embodiment; 
         FIGS. 2A, 2B, and 2C  are plan views illustrating metal wirings according to first, second, and third exemplary embodiments; 
         FIGS. 3A, 3B, and 3C  are plan views illustrating metal wirings according to fourth, fifth, and sixth exemplary embodiments; 
         FIG. 4  is a flowchart illustrating a process of manufacturing a flexible display device according to a first exemplary embodiment; 
         FIGS. 5A, 5B, 5C, and 5D  are views illustrating a process of manufacturing the flexible display device according to the first exemplary embodiment; 
         FIG. 6A  is a plan view illustrating a part A of  FIG. 5D ; 
         FIG. 6B  is a plan view illustrating a part B of  FIG. 5D ; 
         FIGS. 7A and 7B  are views illustrating mechanical characteristics of a metal wiring according to an exemplary embodiment; 
         FIG. 8  is a plan view illustrating a flexible display device according to an exemplary embodiment; and 
         FIG. 9  is a cross-sectional view taken along the line I-I′ of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings. Although the present disclosure may be modified in various manners and have several exemplary embodiments, the exemplary embodiments are illustrated in the accompanying drawings and will be mainly described in the present disclosure. However, the scope of the present disclosure is not limited to the exemplary embodiments and should be construed as including changes, equivalents, and substitutions without deviating from the spirit and scope of the present disclosure. 
     In the drawings, thicknesses of layers and areas are illustrated in an enlarged manner for clarity and ease of description thereof. When a layer, area, or plate is referred to as being “on” another layer, area, or plate, it may be directly on the other layer, area, or plate, or one or more intervening layers, areas, or plates may be present therebetween. Conversely, when a layer, area, or plate is referred to as being “directly on” another layer, area, or plate, intervening layers, areas, or plates may be absent therebetween. Further when a layer, area, or plate is referred to as being “below” another layer, area, or plate, it may be directly below the other layer, area, or plate, or one or more intervening layers, areas, or plates may be present therebetween. Conversely, when a layer, area, or plate is referred to as being “directly below” another layer, area, or plate, intervening layers, areas, or plates may be absent therebetween. 
     The spatially relative terms “below”, “beneath”, “lower”, “above”, “upper,” and the like, may be used herein for ease of description to describe the spatial 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 located “below” or “beneath” another device may be placed “above” or “on” another device. Accordingly, the illustrative term “below” or “beneath” may include both the lower and upper positions. The device may also be oriented in the other direction, and the spatially relative terms may be interpreted differently depending on the orientations. 
     Throughout the present disclosure, when an element is referred to as being “connected” to another element, the element is “directly connected” to the other element, or “electrically connected” to the other element with one or more intervening elements interposed therebetween. It will be further understood that the terms “comprises,” “including,” “includes,” and/or “including,” when used in the present disclosure, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     It will be understood that, although the terms “first,” “second,” “third,” and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. Thus, “a first element” discussed below could be termed “a second element” or “a third element,” and “a second element” and “a third element” may be termed likewise without departing from the teachings herein. 
     “About” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for a particular value or a range or values as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular value(s) (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(s). 
     Unless otherwise defined, terms used herein (including technical and scientific terms) have the same meaning as commonly understood by those skilled in the art to which the present disclosure pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an ideal or excessively formal sense unless clearly defined in the present disclosure. 
     Some of the parts that are not associated with the description may not be provided to specifically describe embodiments of the present disclosure, and like reference numerals refer to like elements throughout the present disclosure. 
     Hereinafter, an exemplary embodiment will be described in detail with reference to  FIGS. 1 to 9 . 
       FIG. 1  is a cross-sectional view illustrating a flexible display device according to an exemplary embodiment. 
     Referring to  FIG. 1 , a flexible display device includes a flexible substrate  110 , a photo-curable adhesive layer  310 , and a metal wiring  320 . 
     The flexible substrate  110  may include a flexible material. The flexible material may include a plastic material. For example, the flexible substrate  110  may include one selected from a group consisting of: kapton, polyethersulphone (PES), polycarbonate (PC), polyimide (PI), polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), polyacrylate (PAR), fiber reinforced plastic (FRP), and/or the like. 
     The flexible substrate  110  may have a thickness in a range from about 5 μm to about 200 μm. When the flexible substrate  110  has a thickness less than about 5 μm, it is difficult for the flexible substrate  110  to stably support an organic light emitting element thereon. On the other hand, when the flexible substrate  110  has a thickness of about 200 μm or more, the flexible characteristics of the flexible substrate  110  may be degraded. 
     The photo-curable adhesive layer  310  is disposed on the flexible substrate  110 . For example, the photo-curable adhesive layer  310  is disposed between the flexible substrate  110  and the metal wiring  320  to be described below. 
     The photo-curable adhesive layer  310  may be a resin such as a photo-curable resin including a monomer, an oligomer, and a small amount of photo-initiator. When the photo-initiator included in the resin is irradiated to light, e.g., ultraviolet (UV) light, photopolymerization reaction is initiated such that the monomer and the oligomer may instantaneously form a polymer to be cured. 
     The metal wiring  320  is disposed on the photo-curable adhesive layer  310 . For example, the metal wiring  320  directly contacts the photo-curable adhesive layer  310  when disposed on the photo-curable adhesive layer  310 . 
     The metal wiring  320  may define a plurality of holes  330 . The plurality of holes  330  will be described in detail below with reference to  FIGS. 2A, 2B, 2C, 3A, 3B, and 3C . 
     The metal wiring  320  may include at least one of aluminum (Al), silver (Ag), copper (Cu), gold (Au), platinum (Pt), iron (Fe), nickel (Ni), and titanium (Ti). 
       FIGS. 2A, 2B, and 2C  are plan views illustrating metal wirings according to first, second, and third exemplary embodiments. 
     Referring to  FIGS. 2A, 2B, and 2C , metal wirings  321 ,  322 , and  323  define a plurality of holes  331   a ,  331   b , and  331   c . Each of the plurality of holes  331   a ,  331   b , and  331   c  may have a circular shape on a plane. Accordingly, the metal wirings according to an exemplary embodiment may improve mechanical durability regardless of a direction of an applied stress, thereby substantially preventing detachment of the metal wirings from the flexible substrate  110 . 
     Each of the plurality of holes  331   a ,  331   b , and  331   c  may have a diameter R of about 200 nm or more and about 500 nm or less on the plane. Accordingly, each of the plurality of holes  331   a ,  331   b , and  331   c  may have an area in a range from about 0.1 μm 2  to about 0.2 μm 2  on the plane. 
     Referring to  FIG. 2A , the plurality of holes  331   a ,  331   b , and  331   c  include a first hole  331   a , a second hole  331   b , and a third hole  331   c  that are adjacent to each other. For example, when a center of the first hole  331   a  is defined as a first center C 1 , a center of the second hole  331   b  is defined as a second center C 2 , and a center of the third hole  331   c  is defined as a third center C 3 , the first center C 1  may be spaced equally from the second center C 2  and the third center C 3  (W 1 =W 2 ). In such an exemplary embodiment, the first center C 1  may be spaced apart from each of the second center C 2  and the third center C 3  by a spatial interval of about 300 nm or more and about 700 nm or less. 
     When an imaginary straight line passing through the first center C 1  and the second center C 2  is defined as a first straight line L 1 , and another imaginary straight line passing through the first center C 1  and the third center C 3  is defined as a second straight line L 2 , the first straight line L 1  and the second straight line L 2  may substantially form a first angle (e.g., θ1=90 degree). 
     Referring to  FIG. 2B , the plurality of holes  331   a ,  331   b , and  331   c  include a first hole  331   a , a second hole  331   b , and a third hole  331   c  that are adjacent to each other. The first, second, and third holes  331   a ,  331   b , and  331   c  may be spaced apart from each other at substantially equal spatial intervals. For example, when a center of the first hole  331   a  is defined as a first center C 1 , a center of the second hole  331   b  is defined as a second center C 2 , and a center of the third hole  331   c  is defined as a third center C 3 , the first center C 1  may be spaced equally from the second center C 2  and the third center C 3  (W 1 =W 2 ). In such an exemplary embodiment, the first, second, and third holes  331   a ,  331   b , and  331   c  may be spaced apart from each other by a spatial interval of about 300 nm or more and about 700 nm or less. That is, the first center C 1  may be spaced apart from each of the second center C 2  and the third center C 3  by a spatial interval of about 300 nm or more and about 700 nm or less. 
     In addition, when an imaginary straight line passing through the first center C 1  and the second center C 2  is defined as a first straight line L 1 , and another imaginary straight line passing through the first center C 1  and the third center C 3  is defined as a second straight line L 2 , the first straight line L 1  and the second straight line L 2  may substantially form a second angle (e.g., θ2=60 degree). 
     Referring to  FIG. 2C , the plurality of holes  331   a ,  331   b , and  331   c  include a first hole  331   a , a second hole  331   b , and a third hole  331   c  that are adjacent to each other. The first, second, and third holes  331   a ,  331   b , and  331   c  may be spaced from each other at different spatial intervals. For example, when a center of the first hole  331   a  is defined as a first center C 1 , a center of the second hole  331   b  is defined as a second center C 2 , and a center of the third hole  331   c  is defined as a third center C 3 , the first center C 1  may be spaced apart from the second center C 2  and the third center C 3  by different spatial intervals. In such an exemplary embodiment, the first, second, and third holes  331   a ,  331   b , and  331   c  may be spaced apart from each other by different spatial intervals of about 300 nm or more and about 700 nm or less. That is, the first center C 1  may be spaced apart from the second center C 2  and the third center C 3  by different spatial intervals, respectively, of about 300 nm or more and about 700 nm or less. 
       FIGS. 3A, 3B, and 3C  are plan views illustrating metal wirings according to fourth, fifth, and sixth exemplary embodiments. 
     Referring to  FIGS. 3A, 3B, and 3C , metal wirings  324 ,  325 , and  326  define a plurality of holes  332   a ,  332   b , and  332   c . The plurality of holes  332   a ,  332   b , and  332   c  may have a quadrangular shape on a plane. However, exemplary embodiments are not limited thereto, and the plurality of holes  332   a ,  332   b , and  332   c  may have a polygonal shape on a plane. Accordingly, mechanical durability of the metal wirings may be improved in a predetermined direction depending on the shape of the plurality of holes  332   a ,  332   b , and  332   c , and the detachment of the metal wiring from the flexible substrate  110  may be substantially prevented. 
     Each of the plurality of holes  332   a ,  332   b , and  332   c  may have a diagonal line R of about 200 nm or more and about 500 nm or less on the plane. Accordingly, the plurality of holes  332   a ,  332   b , and  332   c  may have an area in a range from about 0.1 μm 2  to about 0.2 μm 2  on the plane. 
     Referring to  FIG. 3A , the plurality of holes  332   a ,  332   b , and  332   c  include a first hole  332   a , a second hole  332   b , and a third hole  332   c  that are adjacent to each other. The first, second, and third holes  332   a ,  332   b , and  332   c  may be spaced apart from each other at substantially equal spatial intervals. For example, when a center of the first hole  332   a  is defined as a first center C 1 , a center of the second hole  332   b  is defined as a second center C 2 , and a center of the third hole  332   c  is defined as a third center C 3 , the first center C 1  may be spaced equally from the second center C 2  and the third center C 3  (W 1 =W 2 ). In such an exemplary embodiment, the first center C 1  may be spaced apart from each of the second center C 2  and the third center C 3  by a spatial interval of about 300 nm or more and about 700 nm or less. 
     In addition, when an imaginary straight line passing through the first center C 1  and the second center C 2  is defined as a first straight line L 1 , and another imaginary straight line passing through the first center C 1  and the third center C 3  is defined as a second straight line L 2 , the first straight line L 1  and the second straight line L 2  may substantially form a first angle (e.g., θ1=90 degree). 
     Referring to  FIG. 3B , the plurality of holes  332   a ,  332   b , and  332   c  include a first hole  332   a , a second hole  332   b , and a third hole  332   c  that are adjacent to each other. The first, second, and third holes  332   a ,  332   b , and  332   c  may be spaced apart from each other at substantially equal spatial intervals. For example, when a center of the first hole  332   a  is defined as a first center C 1 , a center of the second hole  332   b  is defined as a second center C 2 , and a center of the third hole  332   c  is defined as a third center C 3 , the first center C 1  may be spaced equally from the second center C 2  and the third center C 3  (W 1 =W 2 ). In such an exemplary embodiment, the first, second, and third holes  332   a ,  332   b , and  332   c  may be spaced apart from each other by a spatial interval of about 300 nm or more and about 700 nm or less. That is, the first center C 1  may be spaced apart from each of the second center C 2  and the third center C 3  by a spatial interval of about 300 nm or more and about 700 nm or less. 
     In addition, when an imaginary straight line passing through the first center C 1  and the second center C 2  is defined as a first straight line L 1 , and another imaginary straight line passing through the first center C 1  and the third center C 3  is defined as a second straight line L 2 , the first straight line L 1  and the second straight line L 2  may substantially form a second angle (e.g., θ2=60 degree). 
     Referring to  FIG. 3C , the plurality of holes  332   a ,  332   b , and  332   c  include a first hole  332   a , a second hole  332   b , and a third hole  332   c  that are adjacent to each other. The first, second, and third holes  332   a ,  332   b , and  332   c  may be spaced from each other at different spatial intervals. For example, when a center of the first hole  332   a  is defined as a first center C 1 , a center of the second hole  332   b  is defined as a second center C 2 , and a center of the third hole  332   c  is defined as a third center C 3 , the first center C 1  may be spaced apart from each of the second center C 2  and the third center C 3  by different spatial intervals. In such an exemplary embodiment, the first, second, and third holes  332   a ,  332   b , and  332   c  may be spaced apart from each other by different spatial intervals of about 300 nm or more. That is, the first center C 1  may be spaced apart from the second center C 2  and the third center C 3  by different spatial intervals, respectively, of about 300 nm or more. 
     In an exemplary embodiment, the metal wirings  321 ,  322 ,  323 ,  324 ,  325 , and  326  respectively defining the plurality of holes  331   a ,  331   b ,  331   c  or the plurality of holes  332   a ,  332   b , and  332   c  are connected in the form of a matrix. Accordingly, electric conductivity of the metal wirings  321 ,  322 ,  323 ,  324 ,  325 , and  326  may not be reduced, and the mechanical durability of the metal wirings is improved. Accordingly, detachment of the metal wirings  321 ,  322 ,  323 ,  324 ,  325 , and  326  from the flexible substrate  110  may be substantially prevented. 
       FIG. 4  is a flowchart illustrating a process of manufacturing a flexible display device according to a first exemplary embodiment.  FIGS. 5A, 5B, 5C, and 5D  are views illustrating a process of manufacturing the flexible display device according to the first exemplary embodiment.  FIG. 6A  is a plan view illustrating a part A of  FIG. 5D , and  FIG. 6B  is a plan view illustrating a part B of  FIG. 5D . 
     Hereinafter, a process of manufacturing a flexible display device according to the first exemplary embodiment will be described in detail with reference to  FIGS. 4, 5A, 5B, 5C, 5D, 6A , and  6 B. 
     First, as illustrated in  FIGS. 4 and 5A , a metal thin film  320 ′ is deposited on a mold substrate  500  defined with a plurality of grooves  510  (S 01 ). 
     The mold substrate  500  may include a polymer having elasticity. For example, the mold substrate  500  may include polydimethylsiloxane (PDMS), polyurethane acrylate (PUA), or the like. 
     The metal thin film  320 ′ may be deposited on the mold substrate  500  by one of a sputtering method, an E-beam evaporation method, a thermal evaporation method, a laser molecular beam epitaxy (L-MBE) method, and a pulsed and laser deposition (PLD) method. 
     When the metal thin film  320 ′ is deposited on the mold substrate  500 , as the linearity of a metal material forming the metal thin film  320 ′ increases, the metal thin film  320 ′ may be substantially prevented from being deposited on a side surface of the plurality of grooves  510  of the mold substrate  500 , such that the plurality of holes  331   a ,  331   b , and  331   c  of the metal wiring  320  to be described below may be more accurately defined. 
     Subsequently, as illustrated in  FIG. 5B , the photo-curable adhesive layer  310  is formed on the flexible substrate  110  (S 02 ). For example, the photo-curable adhesive layer  310  may be formed by a spin coating method and may be formed on the flexible substrate  110  to have a uniform thickness. 
     Although not illustrated, pre-curing of the photo-curable adhesive layer  310  on the flexible substrate  110  may be further performed. For example, to transfer the metal thin film  320 ′ to the photo-curable adhesive layer  310  in a step to be described below, adhesiveness of the photo-curable adhesive layer  310  may be maintained by controlling a pre-curing time. 
     Next, the metal thin film  320 ′ is transferred onto the photo-curable adhesive layer  310  to form the metal wiring  320  that defines the plurality of holes  331   a ,  331   b , and  331   c  (S 03 ). For example, the metal thin film  320 ′ is brought into contact with the photo-curable adhesive layer  310 , and a pressing force is applied to the mold substrate  500  and the flexible substrate  110  to transfer the metal thin film  320 ′ disposed on the mold substrate  500  to the photo-curable adhesive layer  310 . In such an exemplary embodiment, the pressing force applied to the mold substrate  500  and the flexible substrate  110  may be controlled so that the metal thin film  320 ′ deposited inside the plurality of grooves  510  is not transferred to the photo-curable adhesive layer  310 . 
     Finally, the photo-curable adhesive layer  310  is completely cured (S 04 ). Accordingly, the metal thin film  320 ′ is completely transferred to the photo-curable adhesive layer  310 . 
     The mold substrate  500  and the flexible substrate  110  are detached from each other, and the metal wiring  320  formed of the metal thin film  320 ′ is separated from the mold substrate  500 , as illustrated in  FIG. 5D . 
     The metal thin film  320 ′ except for a portion deposited inside the plurality of grooves  510  is transferred to the photo-curable adhesive layer  310 . That is, the portion of the metal thin film  320 ′ located on the photo-curable adhesive layer  310  corresponding to the plurality of grooves  510  of the mold substrate  500  is not transferred. Accordingly, the plurality of holes  331   a ,  331   b , and  331   c  are defined at positions corresponding to the plurality of grooves  510  by the metal wiring  320  that is formed of the metal thin film  320 ′. 
     As illustrated in  FIG. 6A , the plurality of holes  331   a ,  331   b , and  331   c  may include a first hole  331   a , a second hole  331   b , and a third hole  331   c  that are adjacent to each other. The first, second, and third holes  331   a ,  331   b , and  331   c  may be spaced apart from each other at substantially equal spatial intervals. For example, when a center of the first hole  331   a  is defined as a first center C 1 , a center of the second hole  331   b  is defined as a second center C 2 , and a center of the third hole  331   c  is defined as a third center C 3 , the first center C 1  may be spaced equally from the second center C 2  and the third center C 3  (W 1 =W 2 ). In such an exemplary embodiment, the first center C 1  may be spaced apart from each of the second center C 2  and the third center C 3  by a spatial interval of about 300 nm or more and about 700 nm or less. In addition, when an imaginary straight line passing through the first center C 1  and the second center C 2  is defined as a first straight line L 1 , and another imaginary straight line passing through the first center C 1  and the third center C 3  is defined as a second straight line L 2 , the first straight line L 1  and the second straight line L 2  may substantially form a first angle (e.g., θ1=90 degree). However, exemplary embodiments are not limited thereto, and as in the second exemplary embodiment, the first straight line L 1  and the second straight line L 2  may substantially form a second angle θ2 that is different from the first angle θ1 (θ2=60 degree). 
     Each of the plurality of holes  331   a ,  331   b , and  331   c  may have a diameter R of about 200 nm or more and about 500 nm or less on a plane. Accordingly, each of the plurality of holes  331   a ,  331   b , and  331   c  may have an area in a range from about 0.1 μm 2  to about 0.2 μm 2  on the plane. 
     The plurality of grooves  510  of the mold substrate  500  may include a first groove  511 , a second groove  512 , and a third groove  513  that are adjacent to each other. The first, second, and third grooves  511 ,  512  and  513  may be spaced from each other at substantially equal spatial intervals. For example, when a center of the first groove  511  is defined as a fourth center C 4 , a center of the second groove  512  is defined as a fifth center C 5 , and a center of the third groove  513  is defined as a sixth groove C 6 , the fourth center C 4  may be spaced equally from the fifth center C 5  and the sixth center C 6  (W 1 ′=W 2 ′). In such an exemplary embodiment, the first center C 1  may be spaced apart from each of the second center C 2  and the third center C 3  by a spatial interval of about 300 nm or more and about 700 nm or less. In addition, when an imaginary straight line passing through the fourth center C 4  and the fifth center C 5  is defined as a third straight line L 3 , and another imaginary straight line passing through the fourth center C 4  and the sixth center C 6  is defined as a fourth straight line L 4 , the third straight line L 3  and the fourth straight line L 4  may substantially form a first angle (θ1′=90 degree). However, exemplary embodiments are not limited thereto, and as in the second exemplary embodiment, the third straight line L 3  and the fourth straight line L 4  may substantially form a second angle θ2′ that is different from the first angle θ1′ (e.g., θ2′=60 degree). 
     Each of the plurality of grooves  511 ,  512 , and  513  may have a diameter R′ of about 200 nm or more and about 500 nm or less on a plane. Accordingly, each of the plurality of grooves  511 ,  512 , and  513  may have an area in a range from about 0.1 μm 2  to about 0.2 μm 2  on a plane. 
     According to the first exemplary embodiment, while the metal thin film  320 ′ is transferred to the photo-curable adhesive layer  310 , the plurality of holes  331   a ,  331   b , and  331   c  overlap the plurality of grooves  511 ,  512 , and  513 . For example, as illustrated in  FIGS. 6A and 6B , the first, second, and third centers C 1 , C 2 , and C 3  substantially overlap the fourth, fifth, and sixth centers C 4 , C 5 , and C 6 , respectively, and the first and second straight lines L 1  and L 2  substantially overlap the third and fourth straight lines L 3  and L 4 , respectively. 
     The plurality of holes  331   a ,  331   b , and  331   c  have substantially equal sizes and substantially identical shapes as those of the plurality of grooves  511 ,  512 , and  513 , respectively. For example, each of the plurality of holes  331   a ,  331   b , and  331   c  and the plurality of grooves  511 ,  512 , and  513  may have a circular shape having the substantially equal diameter R. However, exemplary embodiments are not limited thereto, and each of the plurality of holes  331   a ,  331   b , and  331   c  and the plurality of grooves  511 ,  512 , and  513  may have a polygonal shape having a substantially equal diagonal line. 
     The first angle θ1 between the first straight line L 1  and the second straight line L 2  may be substantially equal to the first angle θ1′ between the third straight line L 3  and the fourth straight line L 4 . 
       FIGS. 7A and 7B  are views illustrating mechanical characteristics of a metal wiring according to an exemplary embodiment. 
     A relative change in the mechanical durability and electric conductivity of the metal wiring according to an exemplary embodiment will be described in detail with reference to  FIGS. 7A and 7B . 
       FIG. 7A  is a graph showing a relative change in electric conductivity of a silver (Ag) film as represented by ΔR/R 0  (here R 0  represents a baseline resistance when the bending radius is 20 mm, and ΔR represents a change of the resistance compared to the baseline resistance R 0  as the bending radius changes) depending on a bending radius of a flexible substrate. In the case of a conventional Ag film not defined with holes, it may be appreciated that the relative change of electric conductivity increases as the bending radius decreases. On the other hand, in the case of Ag films according to the first exemplary embodiment having the Ag film with a square hole pattern and the second exemplary embodiment having the Ag film with a hexagonal hole pattern, it may be appreciated that the relative change of electric conductivity is relatively less than that of the conventional Ag film with no holes. In particular, it may be appreciated that the relative change of electric conductivity of the Ag film according to the second exemplary embodiment with a hexagonal hole pattern is smaller than that according to the first exemplary embodiment with a square hole pattern. 
       FIG. 7B  is a graph showing a relative change ΔR/R 0  of electric conductivity of an Ag film depending on a bending cycle of a flexible substrate. In the case of a conventional Ag film not defined with holes, it may be appreciated that the relative change ΔR/R 0  of electric conductivity increases as the bending cycle increases. On the other hand, it may be appreciated that, in the case of the Ag films according to the first exemplary embodiment and the second exemplary embodiment, as compared to the conventional Ag film, the relative change ΔR/R 0  of electric conductivity depending on bending cycle is relatively small, and the relative change ΔR/R 0  of electric conductivity does not greatly increases although the bending cycle increases. In particular, in the case of the Ag film according to the second exemplary embodiment with a hexagonal hole pattern, it may be appreciated that the relative change ΔR/R 0  of electric conductivity depending on bending cycle is smaller than the first exemplary embodiment with a square hole pattern, and substantially no relative change ΔR/R 0  is observed although the bending cycles up to 10000 cycles. 
       FIG. 8  is a plan view illustrating a flexible display device according to an exemplary embodiment, and  FIG. 9  is a cross-sectional view taken along the line I-I′ of  FIG. 8 . 
     The flexible display device is assumed to be an organic light emitting diode (“OLED”) display device. However, the scope of exemplary embodiments is not limited to the OLED display device. For example, exemplary embodiments may be applied to a liquid crystal display (“LCD”) device. 
     Referring to  FIGS. 8 and 9 , the flexible display device includes a flexible substrate  110 , a wiring portion  130 , and an OLED  210 . 
     A buffer layer  120  is disposed on the flexible substrate  110 . The buffer layer  120  may include one or more layers selected from various inorganic layers and organic layers. The buffer layer  120  may serve to substantially prevent infiltration of undesirable elements, such as impurities and moisture, into the wiring portion  130  and the OLED  210 , and to planarize a surface below the buffer layer  120 . However, the buffer layer  120  is not invariably necessary and may be omitted. 
     The wiring portion  130  is disposed on the buffer layer  120 . The wiring portion  130  includes a switching thin film transistor (“TFT”)  10 , a driving TFT  20 , and a capacitor  80  that drives the OLED  210 . The OLED  210  emits light according to a driving signal received from the wiring portion  130  to display images. 
       FIGS. 8 and 9  illustrate an active matrix-type organic light emitting diode (AMOLED) display device having a 2Tr-1Cap structure. For example, the 2Tr-1Cap structure may include two TFTs, e.g., the switching TFT  10  and the driving TFT  20 , and one capacitor  80  in each pixel, but exemplary embodiments are not limited thereto. For example, the OLED display device may include three or more TFTs and two or more capacitors in each pixel and may further include additional wirings. Herein, the term “pixel” refers to a unit for displaying an image, and the OLED display device displays images using a plurality of pixels. 
     Each pixel includes the switching TFT  10 , the driving TFT  20 , the capacitor  80 , and the OLED  210 . In addition, a gate line  151  extending along one direction, and a data line  171  and a common power line  172  insulated from and intersecting the gate line  151  are also provided in the wiring portion  130 . Each pixel may be defined by the gate line  151 , the data line  171 , and the common power line  172  as a boundary, but exemplary embodiments are not limited thereto. The pixels may be defined by a pixel defining layer  190 . 
     The capacitor  80  includes a pair of capacitor plates  158  and  178 , having an insulating interlayer  145  interposed therebetween. In such an exemplary embodiment, the insulating interlayer  145  may be a dielectric element. A capacitance of the capacitor  80  is determined by electric charges accumulated in the capacitor  80  and a voltage across the pair of capacitor plates  158  and  178 . 
     The switching TFT  10  includes a switching semiconductor layer  131 , a switching gate electrode  152 , a switching source electrode  173 , and a switching drain electrode  174 . The driving TFT  20  includes a driving semiconductor layer  132 , a driving gate electrode  155 , a driving source electrode  176 , and a driving drain electrode  177 . A gate insulating layer  140  is further provided to insulate the semiconductor layers  131  and  132  and the gate electrodes  152  and  155 . 
     The switching TFT  10  may function as a switching element that selects a pixel to perform light emission. The switching gate electrode  152  is connected to the gate line  151 , and the switching source electrode  173  is connected to the data line  171 . Spaced apart from the switching source electrode  173 , the switching drain electrode  174  is connected to one of the capacitor plates of the capacitor  80 , e.g., the capacitor plate  158 . 
     The driving TFT  20  applies a driving power that allows an organic light emitting layer  212  of an OLED  210  in a selected pixel to emit light to a first electrode  211  that is a pixel electrode PE. The driving gate electrode  155  is connected to said one capacitor plate  158  that is connected to the switching drain electrode  174 . Each of the driving source electrode  176  and the other capacitor plate of the capacitor  80 , e.g., the capacitor plate  178 , is connected to the common power line  172 . The driving drain electrode  177  is connected to the first electrode  211  of the OLED  210  through a contact hole. 
     The switching TFT  10  is driven based on a gate voltage applied to the gate line  151  and serves to transmit a data voltage applied to the data line  171  to the driving TFT  20 . A voltage equivalent to a difference between a common voltage applied to the driving TFT  20  from the common power line  172  and the data voltage transmitted by (or from) the switching TFT  10  is stored in the capacitor  80 , and a current corresponding to the voltage stored in the capacitor  80  flows to the OLED  210  through the driving TFT  20  such that the OLED  210  may emit light. 
     According to an exemplary embodiment, the gate line  151 , the data line  171 , and the common power line  172  may include the photo-curable adhesive layer  310  and the metal wiring  320  described above. That is, according to an exemplary embodiment, each of the gate line  151 , the data line  171 , and the common power line  172  may define a plurality of holes, and the gate line  151 , the data line  171 , and the common power line  172  may be improved in terms of mechanical durability such that detachment of the metal wiring  320 , such as the gate line  151 , the data line  171 , and the common power line  172 , may be substantially prevented. 
     A planarization layer  146  is disposed on the insulating interlayer  145 . The planarization layer  146  includes an insulating material and protects the wiring portion  130 . 
     The OLED  210  is disposed on the planarization layer  146 . The OLED  210  includes a first electrode  211 , an organic light emitting layer  212  disposed on the first electrode  211 , and a second electrode  312  disposed on the organic light emitting layer  212 . Holes and electrons are injected into the organic light emitting layer  212  from the first electrode  211  and the second electrode  312 , respectively, and are combined therein to form an exciton. When the exciton falls from an excited state to a ground state, light emission occurs. 
     The first electrode  211  is an anode for injecting holes, and the second electrode  213  is a cathode for injecting electrons. However, exemplary embodiments are not limited thereto, and the first electrode  211  may be a cathode, and the second electrode  213  may be an anode. 
     The first electrode  211  may include a reflective layer, and the second electrode  213  may include a semi-transmissive layer. Accordingly, a light generated in the organic light emitting layer  212  is emitted through the second electrode  213 , and thus the structure of a top emission type may be achieved. However, exemplary embodiments are not limited thereto. 
     The reflective electrode and the semi-transmissive electrode may include one or more metals of magnesium (Mg), silver (Ag), gold (Au), calcium (Ca), lithium (Li), chromium (Cr), copper (Cu), and aluminum (Al), or an alloy thereof. In such an exemplary embodiment, the reflective electrode or the semi-transmissive electrode may be determined according to the thickness. In general, the semi-transmissive electrode may have a thickness of about 200 nm or less. 
     For example, the first electrode  211  may include a reflective layer including one or more metals of magnesium (Mg), silver (Ag), gold (Au), calcium (Ca), lithium (Li), chromium (Cr), copper (Cu), and aluminum (Al) and a transparent conductive layer disposed on the reflective layer. In such an exemplary embodiment, the transparent conductive layer may include transparent conductive oxide (TCO). Examples of the TCO may include: indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), aluminum zinc oxide (AZO), and/or indium oxide (In 2 O 3 ). Since such a transparent conductive layer including TCO has a high work function, hole injection through the first electrode  211  may become smooth. 
     In addition, the first electrode  211  may have a triple-layer structure in which a transparent conductive layer, a reflective layer, and a transparent conductive layer are sequentially stacked. 
     The second electrode  213  may include a semi-transmissive layer including one or more metals selected from the group consisting of magnesium (Mg), silver (Ag), gold (Au), calcium (Ca), lithium (Li), chromium (Cr), copper (Cu), and aluminum (Al). 
     Although not illustrated, at least one of a hole injection layer HIL and a hole transport layer HTL may further be disposed between the first electrode  211  and the organic light emitting layer  212 . In addition, at least one of an electron transport layer ETL and an electron injection layer EIL may further be disposed between the organic light emitting layer  212  and the second electrode  213 . 
     The pixel defining layer  190  has an opening. The opening of the pixel defining layer  190  exposes a portion of the first electrode  211 . The first electrode  211 , the organic light emitting layer  212 , and the second electrode  213  are sequentially stacked at the opening of the pixel defining layer  190 . As such, the pixel defining layer  190  may define a light emission area. 
     In an exemplary embodiment, the second electrode  213  may be disposed on the pixel defining layer  190  as well as on the organic light emitting layer  212 . 
     As set forth hereinabove, according to one or more exemplary embodiments, the flexible display device may provide the following effects. 
     Metal wirings of a metal thin film disposed on a flexible substrate are connected in the form of a matrix such that detachment of metal wirings may be substantially prevented while electric conductivity is not reduced. 
     While the present disclosure has been illustrated and described with reference to the exemplary embodiments thereof, it will be apparent to those of ordinary skill in the art that various changes in form, and detail may be formed thereto without departing from the spirit, and scope of the present disclosure.