Patent Publication Number: US-10334737-B2

Title: Flexible display device and manufacturing method thereof

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 USC § 119 from, and the benefit of, Korean Patent Application No. 10-2016-0072571, filed in the Korean Intellectual Property Office on Jun. 10, 2016, the contents of which are herein incorporated by reference in their entirety. 
     BACKGROUND 
     1. Technical Field 
     Embodiments of the present disclosure are generally directed to a flexible display device. More particularly, embodiments of the present disclosure are generally directed to a method for manufacturing a flexible display device that includes a process for incising a substrate by use of laser beams, and a flexible display device manufactured using the same method. 
     2. Discussion of the Related Art 
     A flexible display device typically includes a flexible substrate, and a display unit and a pad portion disposed on the flexible substrate. The display unit includes a plurality of signal lines and a plurality of pixels, and displays an image by combining light emitted by the pixels. The pad portion includes a plurality of pad electrodes that transmit electrical signals to signal lines of the display unit. 
     A method for manufacturing a flexible display device may include forming a plurality of cell areas on a flexible substrate in a raw state, forming a display unit and a pad portion in a plurality of cell areas, irradiating laser beams on edges of the cell areas, and cutting the flexible substrate accordingly. By the above-noted stages, a plurality of flexible display devices can be simultaneously manufactured. 
     SUMMARY 
     Embodiments of the present disclosure can provide a method for manufacturing a flexible display device for controlling generation of defects by foreign particles by removing the foreign particles from an cutting portion of a flexible substrate, and a flexible display device manufactured by the same method. 
     An exemplary embodiment provides a flexible display device that includes a flexible substrate; a display unit disposed in a first region of a first side of the flexible substrate and that includes a plurality of pixels; and a pad portion disposed in a second region of the first side and that includes a plurality of pad electrodes. The flexible substrate includes a stepwise recess portion disposed along an edge of the first side on which end portions of the pad electrodes are provided. 
     The stepwise recess portion may include a bottom side, and a first lateral side that connects the one side and the bottom side. The bottom side may have protrusions and depressions associated with a plurality of concave grooves. The concave grooves may be adjacent to each other in a direction parallel to the pad electrodes and may extend linearly in a second direction perpendicular to the first direction. The bottom side may be flat. The first lateral side may have a slanted side. 
     The flexible substrate may include a main substrate that has a first side and a second side that are opposite each other; and a passivation film attached to the second side by an adhesion layer. The display unit and the pad portion may be provided on the first side. The stepwise recess portion may be provided in the main substrate, may be provided in the main substrate and the adhesion layer, or may be provided in the main substrate, the adhesion layer, and the passivation film. 
     Another embodiment provides a method for manufacturing a flexible display device, including: forming a plurality of cell areas on a first side of a main substrate, and forming a display unit that includes a plurality of pixels and a pad portion that includes a plurality of pad electrodes in each of the cell areas; attaching a passivation film to a second side of the main substrate, that is opposite the first side using an adhesion layer; cutting the main substrate and the passivation film by irradiating a first laser beam on an edge of the cell areas; and removing foreign particles generated by the first laser beam by irradiating a second laser beam on an edge of the first side on which end portions of the pad electrodes are provided. The second laser beam has a shorter wavelength than the first laser beam. 
     Adjacent cell areas may be separated by a single border line. 
     The second laser beam may be a short pulse laser beam, and an irradiation width of the second laser beam may be equal to or greater than a width of a region in which the foreign particles are generated. The second laser beam may be focused to one of the main substrate, the adhesion layer, and the passivation film. 
     The second laser beam may have a Gaussian shape, and may be scanned at least twice while changing an irradiation position in a direction that is parallel to the pad electrodes. 
     The second laser beam may include a flat front end and may be scanned at least once. The second laser beam may be scanned at least twice while changing an irradiation position in a direction that is parallel to the pad electrodes. 
     Another embodiment provides a flexible display device that includes a flexible substrate that includes a main substrate with a first side and a second side that are opposite each other; and a passivation film attached to the second side by an adhesion layer. The flexible substrate includes a stepwise recess portion disposed along an end portion thereof, and the stepwise recess portion is provided in the main substrate, is provided in the main substrate and the adhesion layer, or is provided in the main substrate, the adhesion layer, and the passivation film. 
     The flexible display device may further include a display unit disposed in a first region of the first side of the flexible substrate and that includes a plurality of pixels, and pad portion disposed in a second region of the first side and that includes a plurality of pad electrodes. The stepwise recess portion is disposed along an edge of the first side on which end portions of the pad electrodes are provided. 
     The stepwise recess portion may include a bottom side and a first lateral side that connects the first side and the bottom side. The bottom side may have protrusions and depressions associated with a plurality of concave grooves that are adjacent to each other in a first direction parallel to the pad electrodes and extend linearly in a second direction perpendicular to the first direction. The bottom side may be flat. The first lateral side may be slanted. 
     According to exemplary embodiments, the conductive carbonized material does not remain on the flexible substrate when the flexible substrate is cut, so the plurality of pad electrodes can remain insulators. Hence, a flexible display device is substantially free of driving defects caused by electrical connections among the plurality of pad electrodes. Further, there is no dummy area among a plurality of cell areas, which increases the usable area of the flexible substrate and improves productivity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flowchart of a method for manufacturing a flexible display device according to an exemplary embodiment. 
         FIG. 2  is a top plan view of a main substrate in a first step shown in  FIG. 1 . 
         FIG. 3  is a cross-sectional view with respect to line III-III′ of  FIG. 2 . 
         FIG. 4  is an enlarged view of a main substrate shown in  FIG. 3 . 
         FIG. 5  and  FIG. 6  are partial cross-sectional views of a main substrate and a passivation film in a second step shown in  FIG. 1 . 
         FIG. 7  and  FIG. 8  are perspective views of a flexible substrate in a third step shown in  FIG. 1 . 
         FIG. 9  and  FIG. 10  are cross-sectional views of a flexible substrate that shows an enlarged region A of  FIG. 8 . 
         FIG. 11  is a top plan view of a region A of  FIG. 8 . 
         FIG. 12  is a perspective view of a flexible substrate in a fourth step shown in  FIG. 1 . 
         FIG. 13  is a cross-sectional view of a flexible substrate that shows an enlarged region B of  FIG. 12 . 
         FIG. 14  is a perspective view of a flexible substrate that shows an enlarged region B of  FIG. 12 . 
         FIG. 15  is a cross-sectional view of a flexible substrate that shows a first exemplary variation of a stepwise recess portion shown in  FIG. 13 . 
         FIG. 16  is a cross-sectional view of a flexible substrate that shows a second exemplary variation of a stepwise recess portion shown in  FIG. 13 . 
         FIG. 17  and  FIG. 18  are cross-sectional views of a flexible substrate that show a third exemplary variation of a stepwise recess portion shown in  FIG. 13 . 
         FIG. 19  is a cross-sectional view of a flexible substrate that shows a fourth exemplary variation of a stepwise recess portion shown in  FIG. 13 . 
         FIG. 20  is a cross-sectional view of a flexible substrate that shows a fifth exemplary variation of a stepwise recess portion shown in  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the disclosure are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present disclosure. 
     When it is said that any part, such as a layer, film, region, or plate, is positioned on another part, it means the part is directly on the other part or above the other part with at least one intermediate part. 
     The size and thickness of each component shown in the drawings may be arbitrarily shown for better understanding and ease of description, but embodiments of the present disclosure are not limited thereto. 
       FIG. 1  is a flowchart of a method for manufacturing a flexible display device according to an exemplary embodiment. 
     Referring to  FIG. 1 , a method for manufacturing a flexible display device includes: forming a display unit and a pad portion of a plurality of respective cell areas formed on a first side of a main substrate (S 10 ); attaching a passivation film to a second side of the main substrate using an adhesion layer (S 20 ); irradiating first laser beams to edges of the plurality of cell areas to cut the flexible substrate (S 30 ); and irradiating second laser beams along an edge of the first side on which an end portion of a plurality of pad electrodes are provided (S 40 ). 
     According to an embodiment, the first laser beam is a laser beam in the infrared wavelength band. The second laser beam has a shorter wavelength than the first laser beam, and it may be a short pulse laser beam. The second laser beam removes foreign particles generated in step S 30  to control generation of defects caused by foreign particles in the flexible display device. 
     A method for manufacturing a flexible display device will now be described in detail with reference to  FIG. 2  to  FIG. 20 .  FIG. 2  to  FIG. 20  show major constituent elements relating to a manufacturing method of a flexible display device. 
       FIG. 2  is a top plan view of a main substrate in a first step shown in  FIG. 1 ,  FIG. 3  is a cross-sectional view with respect to line III-III′ of  FIG. 2 , and  FIG. 4  shows an enlarged view of a main substrate shown in  FIG. 3 . 
     Referring to  FIG. 2  to  FIG. 4 , in step S 10 , a main substrate  11  is in a raw state and has a size sufficient to simultaneously manufacture a plurality of flexible display devices. The main substrate  11  is a flexible substrate that can be easy bent, and a hard carrier substrate  90  supports the main substrate  11 . 
     According to an embodiment, the main substrate  11  has a multi-layered structure. For example, the main substrate  11  can have a stacked structure of a first plastic layer  111 , a first barrier layer  112 , a second plastic layer  113 , and a second barrier layer  114 . The first plastic layer  111  and the second plastic layer  113  may include a polyimide. The first barrier layer  112  and the second barrier layer  114  may include a silicon nitride film and a silicon oxide film. However, embodiments of the main substrate  11  are not limited to the above-described example. 
     According to an embodiment, the main substrate  11  includes a first side  11   a  and a second side  11   b  that oppose each other. A plurality of cell areas (CA) are provided on the first side  11   a  of the main substrate  11 , and a display unit  20  and a pad portion  30  are formed in each of the plurality of respective cell areas (CA).  FIG. 2  shows eight cell areas (CA) for convenience of description, but embodiments are not limited thereto, and in other embodiments, more cell areas (CA) are provided on the main substrate  11 . The pad portion  30  is provided on one side of the display unit  20 , and one cell area (CA) corresponds to one flexible display device. 
     According to an embodiment, the display unit  20  includes a plurality of signal lines  21  and a plurality of pixels  22 , and the pad portion  30  includes a plurality of pad electrodes  31 . The pad electrodes  31  are electrically connected to the signal lines  21 , and, after step S 40 , are electrically connected to a chip on film (COF). The pad electrodes  31  can transmit an electrical signal received from the COF to the signal lines  21 . 
     A flexible display device according to a present exemplary embodiment is an organic light emitting device, in which each pixel  22  includes at least two thin film transistors, at least one capacitor, and an organic light emitting diode. According to an embodiment, the display unit  20  is covered by an encapsulator  40 , and an upper passivation film  50  is disposed on the encapsulator  40 . The encapsulator  40  is a stacked structure of an inorganic film, an organic film, and an inorganic film. 
     According to an embodiment, in step S 10 , a plurality of cell areas (CA) are arranged so that their edges meet each other in an X direction and a Y direction, where the X direction is perpendicular to the Y direction. That is, no dummy areas are provided between the plurality of cell areas (CA), and two adjacent cell areas (CA are separated by a single border line. 
       FIG. 5  and  FIG. 6  are partial cross-sectional views of a main substrate and a passivation film in a second step shown in  FIG. 1 . 
     According to an embodiment, referring to  FIG. 5  and  FIG. 6 , in step S 20 , the carrier substrate  90  is separated from the main substrate  11 , and a lower passivation film  13  is attached to the second side  11   b  of the main substrate  11  by an adhesion layer  12 . The passivation film  13  is thicker than the main substrate  11 , and it may include, for example, polyethylene terephthalate. The main substrate  11 , the adhesion layer  12 , and the passivation film  13  make up a flexible substrate  10 . 
       FIG. 7  and  FIG. 8  are perspective views of a flexible substrate in a third step shown in  FIG. 1 . 
     According to an embodiment, referring to  FIG. 7  and  FIG. 8 , in step S 30 , the flexible substrate  10  is mounted on a first stage  61 , and a first laser oscillator  62  is provided over the flexible substrate  10 . A first transfer unit is combined with one of the first stage  61  and the first laser oscillator  62 . 
     In detail, the first laser oscillator  62  is disposed over one border line parallel to the Y direction between adjacent cell areas (CA), and irradiates a first laser beam LB 1  to the border line. Simultaneously, either the first laser oscillator  62  is moved in the negative (−) Y direction by the first transfer unit, or the first stage  61  moves in the positive (+) Y direction. 
     According to an embodiment, the first laser beam LB 1  is irradiated along the border line parallel to the Y direction to cut the flexible substrate  10 . This incision is sequentially performed for all border lines that are parallel to the Y direction. 
     In addition, the first laser oscillator  62  is also provided over one border line parallel to the X direction, and irradiates the first laser beam LB 1  to the border line. Simultaneously, either the first laser oscillator  62  is moved in the (+) X direction by the first transfer unit, or the first stage  61  moves in the (−) X direction. 
     According to an embodiment, the first laser beam LB 1  is irradiated along the border line t parallel to the X direction to cut the flexible substrate  10 . This incision is sequentially performed for all border lines that are parallel to the X direction. 
     For convenience of description,  FIG. 7  shows that one X direction border line and three Y direction border lines are provided in the flexible substrate  10 , but embodiments are not limited thereto, and in other embodiments the number of border lines on the flexible substrate  10  may be greater. By the incisions of step S 30 , the flexible substrate  10  is divided into the number of cell areas (CAs). 
       FIG. 9  and  FIG. 10  are cross-sectional views of a flexible substrate that show an enlarged region A of  FIG. 8 , and  FIG. 11  shows a top plan view of a region A of  FIG. 8 . 
     According to an embodiment, referring to  FIG. 9  to  FIG. 11 , the first laser beam LB 1  is an infrared wavelength laser beam, and, for example, may be a carbonate gas (CO 2 ) laser beam. A carbonate gas laser is a gas laser that uses a transition between vibrational levels of CO 2  molecules, and emits a substantially 9 μm to 10 μm wavelength laser beam. 
     According to an embodiment, the first laser beam LB 1  irradiated onto the border lines between adjacent cell areas (CAs) may have a Gaussian or triangular cross-section, and the first laser beam LB 1  is focused on or below a lower side  102  of the flexible substrate  10 . A cutting surface  14  in the flexible substrate  10  is a slanted side corresponding to the shape of the first laser beam LB 1 . The slanted side may be straight or curved. 
     In step S 30 , the flexible substrate  10  may be damaged by heat from the first laser beam LB 1 , and as a result, foreign particles may be generated in or around the cutting surface  14 . That is, the foreign particles may be generated in at least part of the cutting surface  14  and an edge portion of an upper side  101  of the flexible substrate  10  that is close to the cutting surface  14 . Here, the upper side  101  of the flexible substrate  10  is a side where the display unit  20  and the pad portion  30  are disposed, and the lower side  102  of the flexible substrate  10  is the opposite side. 
     The foreign particle may be a conductive carbonized material  70  formed from the carbon of the plastic of the flexible substrate  10 , and, for example, may be graphite. The conductive carbonized material  70  is primarily generated around the main substrate  11 . 
     According to an embodiment, the pad electrodes  31  disposed on the pad portion  30  are substantially parallel to the Y direction, and end portions of the pad electrodes  31  are provided on one edge of the upper side  101  of the flexible substrate  10  that is parallel to the X direction. The conductive carbonized material  70  is generated among the plurality of pad electrodes  31  and can electrically connect the pad electrodes  31 . In this case, the pad electrodes  31  can lose their original function of transmitting electrical signals, and generate driving defects. 
       FIG. 12  is a perspective view of a flexible substrate in a fourth step shown in  FIG. 1 . 
     According to an embodiment, referring to  FIG. 12 , in step S 40 , the flexible substrate  10  is mounted on a second stage  63 , and a second laser oscillator  64  is provided over the flexible substrate  10 . A second transfer unit is combined with one of the second stage  63  and the second laser oscillator  64 . 
     The second laser oscillator  64  irradiates a second laser beam LB 2  onto an end portion of the flexible substrate  10  that is parallel to the X direction and that touches the end portions of the pad electrodes  31 . Simultaneously, the second laser oscillator  64  is either moved in the (+) X direction by the second transfer unit, or the second stage  63  moves in the (−) X direction. The second laser beam LB 2  is then irradiated along the end portion of the flexible substrate  10  parallel to the X direction to remove the conductive carbonized material  70 . 
     In step S 40 , the second laser beam LB 2  has a shorter wavelength than the first laser beam LB 1 , and it may be a short pulse (ultrashort pulse) laser beam with a pulse duration of femtoseconds or picoseconds. 
     According to an embodiment, a short pulse laser beam can minimize energy transfer because of the short pulse width and a high peak output, and does not generate physical or chemical deformation by heat diffusion or deteriorate the precision during a process. Further, unlike the first laser beam LB 1 , particles or by-products such as craters are rarely generated. Step S 40  is respectively performed for a flexible display device  200 . 
     In step S 40 , an irradiation width of the second laser beam LB 2  is equal to or greater than a width W 1  of the region of the conductive carbonized material  70 , to remove the conductive carbonized material  70 . For example, in step S 20 , the conductive carbonized material  70  may be generated over a region that is about 50 μm wide, and in step S 40 , the irradiation width of the second laser beam LB 2  may be greater than about 50 μm. 
     According to an embodiment, the second laser beam LB 2  may be a Gaussian or flat-top shaped beam. When a front end portion width of the second laser beam LB 2  is greater than the width of the region of the conductive carbonized material  70 , the conductive carbonized material  70  can be removed through a single scan, and when a front end portion width of the second laser beam LB 2  is less than the width of the region of the conductive carbonized material  70 , the conductive carbonized material  70  can be removed through at least two scans. 
       FIG. 13  and  FIG. 14  are a cross-sectional view and a perspective view of a flexible substrate that shows an enlarged region B of  FIG. 12 . 
     According to an embodiment, referring to  FIG. 12  to  FIG. 14 , the second laser beam LB 2  is a Gaussian shaped beam, and the front end portion width of the second laser beam LB 2  is less than the width W 1  of the region of the conductive carbonized material  70 . 
     According to an embodiment, step S 40  includes: a first scanning process of focusing the second laser beam LB 2  to a first position P 1  in the flexible substrate  10  and moving the second laser beam LB 2  in the X direction; and a second scanning process of focusing the second laser beam LB 2  to a second position P 2  that is separated in the Y direction from the first position P 1  and moving the second laser beam LB 2  in the X direction ( ). 
     According to an embodiment, to move the second laser beam LB 2  to the second position P 2  from the first position P 1 , the second laser oscillator  64  either moves in the (−) Y direction or the second stage  63  moves in the (+) Y direction. During a second scanning process, the second laser beam LB 2  scans a region that overlaps a region scanned by the second laser beam LB 2  in a first scanning process. 
       FIG. 13  shows, for example, a case in which the second laser beam LB 2  has scanned the flexible substrate  10  six times, from the first position P 1  to the sixth position P 6 , but the number of scans of the second laser beam LB 2  are not limited thereto, and may differ in other embodiments. In this embodiment, distances between two adjacent positions (P 1 -P 2 , P 2 -P 3 , P 3 -P 4 , P 4 -P 5 , and P 5 -P 6 ) from the first position P 1  to the sixth position P 6  is the same. 
     According to an embodiment, the second laser beam LB 2  is focused into the flexible substrate  10 , unlike the first laser beam LB 1 .  FIG. 13  and  FIG. 14  illustrate examples of a case in which the second laser beam LB 2  is focused into the passivation film  13 . A stepwise recess portion  80  is formed in the flexible substrate  10  by the second laser beam LB 2  in step S 40 . 
     According to an embodiment, a depth (D) of the stepwise recess portion  80  is less than a thickness (T) of the flexible substrate  10 , and a width W 2  of the stepwise recess portion  80  corresponds to the irradiation width of the second laser beam LB 2 . 
     According to an embodiment, the stepwise recess portion  80  includes a bottom side  81  disposed in the passivation film  13 , and a first lateral side  82  that connects the upper side  101  of the flexible substrate  10  and the bottom side  81  of the stepwise recess portion  80 . The bottom side  81  is connected to the lower side  102  of the flexible substrate  10  by a second lateral side  83 . The second lateral side  83  is a remaining portion of the cutting surface  14  generated in step S 30 . 
     According to an embodiment, the first lateral side  82  is slanted, corresponding to the shape of the second laser beam LB 2 . The slanted side may be straight or curved. A plurality of concave grooves  84  arranged in the Y direction are formed on the bottom side  81 . a number of concave grooves  84  corresponds to a number of scans of the second laser beam LB 2 . The concave grooves  84  extend parallel to the X direction and are adjacent to each other in the Y direction. 
       FIG. 15  is a cross-sectional view of a flexible substrate that shows a first exemplary variation of a stepwise recess portion shown in  FIG. 13 . 
     According to an embodiment, referring to  FIG. 15 , in step S 40 , the second laser beam LB 2  is focused into the adhesion layer  12  or into a region of the adhesion layer  12  that borders the passivation film  13 . In this case, the stepwise recess portion  80   a  includes a bottom side  81  disposed on the adhesion layer  12 , and a first lateral side  82  that connects the upper side  101  of the flexible substrate  10  and the bottom side  81  of the stepwise recess portion  80   a . A plurality of concaves grooves  84  adjacent to each other in the Y direction are formed in the bottom side  81 . 
       FIG. 16  is a cross-sectional view of a flexible substrate that shows a second exemplary variation of a stepwise recess portion shown in  FIG. 13 . 
     According to an embodiment, referring to  FIG. 16 , in step  840 , the second laser beam LB 2  is focused into the main substrate  11  or into a region of the main substrate  11  that borders the adhesion layer  12 . In this case, a stepwise recess portion  80   b  includes a bottom side  81  disposed on the main substrate  11 , and a first lateral side  82  that connecting the upper side  101  of the flexible substrate  10  and the bottom side  81  of the stepwise recess portion  80   b . A plurality of concave grooves  84  adjacent to each other in the Y direction are formed in the bottom side  81 . 
       FIG. 17  and  FIG. 18  are cross-sectional views of a flexible substrate that show a third exemplary variation of a stepwise recess portion shown in  FIG. 13 . 
     According to an embodiment, referring to  FIG. 17  and  FIG. 18 , in step S 40 , the second laser beam LB 2  has a flat front end, and the second laser beam LB 2  is focused into the passivation film  13 . 
     According to an embodiment, regarding  FIG. 17 , a width of a front end of the second laser beam LB 2  is equal to or greater than the width W 1  of the generation region of the conductive carbonized material  70 . In this case, in step S 40 , the second laser beam LB 2  is scanned once. 
     According to an embodiment, regarding  FIG. 18 , the width of the second laser beam LB 2  is less than the width W 1  of the generation region of the conductive carbonized material  70 . In this case, in step  840 , the second laser beam LB 2  is scanned at least twice. Here, in the respective scanning operations, the irradiation positions of the second laser beam LB 2  differ in the Y direction. 
     According to an embodiment, referring to  FIG. 17  and  FIG. 18 , a stepwise recess portion  80   c  includes a bottom side  81  formed in the passivation film  13 , and a first lateral side  82  that connects the upper side  101  of the flexible substrate  10  and the bottom side  81  of the stepwise recess portion  80   c . The bottom side  81  is flat with few protrusions and depressions, and the first lateral side  82  is slanted. 
       FIG. 19  is a cross-sectional view of a flexible substrate that shows a fourth exemplary variation of a stepwise recess portion shown in  FIG. 13 . 
     According to an embodiment, referring to  FIG. 19 , in step S 40 , the second laser beam LB 2  has a flat front end, and the second laser beam LB 2  is focused on region of the adhesion layer  12  that borders the passivation film  13 . In this case, a stepwise recess portion  80   d  includes a bottom side  81  that corresponds to the upper side of the passivation film  13 , and a first lateral side  82  that connects the upper side  101  of the flexible substrate  10  and the bottom side  81  of the stepwise recess portion  80   d . The bottom side  81  is flat with few protrusions and depressions, and the first lateral side  82  is slanted. 
       FIG. 20  is a cross-sectional view of a flexible substrate that shows a fifth exemplary variation of a stepwise recess portion shown in  FIG. 13 . 
     According to an embodiment, referring to  FIG. 20 , in step S 40 , the second laser beam LB 2  has a flat front end, and the second laser beam is focused on a region of the main substrate  11  that borders the adhesion layer  12 . In this case, a stepwise recess portion  80   e  includes a bottom side  81  that corresponds to the upper side of the adhesion layer  12 , and a first lateral side  82  that connects the upper side  101  of the flexible substrate  10  and the bottom side  81  of the stepwise recess portion  80   e . The bottom side  81  is flat with few protrusions and depressions, and the first lateral side  82  is slanted. 
     According to an embodiment, referring again to  FIG. 1 , substantially no conductive carbonized material  70  remain on the flexible substrate  10  after step S 40 , so that a plurality of pad electrodes  31  can remain insulators. Therefore, the flexible display device  200  manufactured according to above-described methods according to embodiments can prevent driving defects caused by electrical connections among the plurality of pad electrodes  31 . 
     Table 1 shows test results of electrical connections of sample groups 1, 2, 3, and 4 according to a comparative example. The sample groups 1 to 4 according to a comparative example are samples of a flexible display device manufactured according to steps S 10  and S 20  of  FIG. 1 . Sample groups 1 to 4 according to a comparative example respectively include 90 samples. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Sample 
                   
                   
               
               
                 groups 
                 Current values (A) 
                 Results 
               
               
                   
               
             
            
               
                 1 
                 Equal to or greater than 10 −15  and less than 
                 58.89% of 
               
               
                   
                 10 −12 : 17 samples 
                 electrical 
               
               
                   
                 Equal to or greater than 10 −12  and less than 
                 connection 
               
               
                   
                 10 −9 : 20 samples 
               
               
                   
                 Equal to or greater than 10 −9 : 53 samples 
               
               
                 2 
                 Equal to or greater than 10 −15  and less than 
                 42.22% of 
               
               
                   
                 10 −12 : 30 samples 
                 electrical 
               
               
                   
                 Equal to or greater than 10 −12  and less than 
                 connection 
               
               
                   
                 10 −9 : 22 samples 
               
               
                   
                 Equal to or greater than 10 −9 : 38 samples 
               
               
                 3 
                 Equal to or greater than 10 −15  and less than 
                 71.11% of 
               
               
                   
                 10 −12 : 4 samples 
                 electrical 
               
               
                   
                 Equal to or greater than 10 −12  and less than 
                 connection 
               
               
                   
                 10 −9 : 22 samples 
               
               
                   
                 Equal to or greater than 10 −9 : 64 samples 
               
               
                 4 
                 Equal to or greater than 10 −15  and less than 
                 85.56% of 
               
               
                   
                 10 −12 : 2 samples 
                 electrical 
               
               
                   
                 Equal to or greater than 10 −12  and less than 
                 connection 
               
               
                   
                 10 −9 : 12 samples 
               
               
                   
                 Equal to or greater than 10 −9 : 77 samples 
               
               
                   
               
            
           
         
       
     
     During the electrical connections test, two nanoprobes are provided to contact two points of the end portion of the pad portion, an electrical signal is applied to one nanoprobe, and a current value detected from the other nanoprobe is set to be a reference value. When the measured current value is equal to or greater than 10 −9  A, it is classified as electrically connected. As expressed in Table 1, the sample groups show high electrical connection rates in order of 4, 3, 1, and 2. 
     Table 2 expresses test results of electrical connection of sample groups 5, 6, 7, and 8 according to an exemplary embodiment. The sample groups 5 to 8 according to an exemplary embodiment are samples of a flexible display device manufactured according to steps S 10 , S 20 , step S 30  of  FIG. 1 . Sample groups 5 to 8 according to an exemplary embodiment respectively include 90 samples. 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Sample 
                   
                   
               
               
                 groups 
                 Current values (A) 
                 Results 
               
               
                   
               
             
            
               
                 5 
                 Equal to or greater than 10 −15  and less than 10 −12 : 
                 No 
               
               
                   
                 90 samples 
                 electrical 
               
               
                   
                 Equal to or greater than 10 −12  and less than 10 −9 : 0 
                 connection 
               
               
                   
                 samples 
               
               
                   
                 Equal to or greater than 10 −9 : 0 samples 
               
               
                 6 
                 Equal to or greater than 10 −15  and less than 10 −12 : 
                 No 
               
               
                   
                 90 samples 
                 electrical 
               
               
                   
                 Equal to or greater than 10 −12  and less than 10 −9 : 0 
                 connection 
               
               
                   
                 samples 
               
               
                   
                 Equal to or greater than 10 −9 : 0 samples 
               
               
                 7 
                 Equal to or greater than 10 −15  and less than 10 −12 : 
                 No 
               
               
                   
                 89 samples 
                 electrical 
               
               
                   
                 Equal to or greater than 10 −12  and less than 10 −9 : 1 
                 connection 
               
               
                   
                 samples 
               
               
                   
                 Equal to or greater than 10 −9 : 0 samples 
               
               
                 8 
                 Equal to or greater than 10 −15  and less than 10 −12 : 
                 No 
               
               
                   
                 90 samples 
                 electrical 
               
               
                   
                 Equal to or greater than 10 −12  and less than 10 −9 : 0 
                 connection 
               
               
                   
                 samples 
               
               
                   
                 Equal to or greater than 10 −9 : 0 samples 
               
               
                   
               
            
           
         
       
     
     The electrical connections test is performed in a manner similar to that of sample groups 1 to 4 according to a comparative example. As expressed in Table 2, it can be seen that the sample groups 5 to 8 according to an exemplary embodiment do not generate electrical connections. 
     According to embodiments, the second laser beam LB 2  removes part of the flexible substrate  10  in a thickness direction of the flexible substrate  10  to leave the stepwise recess portion  80 . Therefore, the cutting surface  14  of the flexible substrate  10  formed in step S 30  maintains its shape during step S 40 . This indicates that when a plurality of cell areas (CAs) are formed in the main substrate  11  in step S 10 , there is no need to provide a dummy area between the cell areas (CAs) in the Y direction. 
     Assuming that part of the flexible substrate that corresponds to the region where conductive carbonized material is generated is removed, the final cutting surface of the flexible substrate is inward from from the cutting surface generated in step S 30 . In this case, when a plurality of cell areas are formed on the main substrate in step S 10 , dummy areas must be provided by the removed region among a plurality of cell areas arranged in the Y direction. 
     According to the present exemplary embodiment, there is no dummy area among the cell areas (CA) arranged in the Y direction, which increases the usable area of the flexible substrate  10  and improves productivity. 
     While this disclosure has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.