Abstract:
Provided is a method for fabricating a flexible display device. The method includes attaching a shape memory alloy film memorizing a shape thereof as a curved shape at a shape memory temperature or lower to a flexible substrate at a temperature higher than the shape memory temperature, forming a display device on the flexible substrate, and returning the shape memory alloy to the curved shape to remove the shape memory alloy film from the flexible substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. non-provisional patent application claims priority under 35 U.S.C. §119 of Korean Patent Application No. 10-2013-0154746 filed on Dec. 12, 2013, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention disclosed herein relates to a method for fabricating a flexible display, and more particularly, to a method for fabricating a flexible display by using a shape memory alloy. 
     For easiness of processes, a flexible display is fabricated by using a method in which processes are performed on a rigid carrier, such as a glass or silicon carrier, and then the carrier is removed. In order to remove the carrier, since a complicated process which includes forming a sacrificial layer and applying of a solvent or irradiating of infrared rays, the removing of the carrier influences the flexibility of the plastic substrate. In another method, an etching stop layer is formed on a glass carrier and then the glass carrier is removed by using an enchant, such as a hydrofluoric acid or the like. However, this method has also limitations, such as process complexity, high costs, etc. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method for fabricating a flexible display that removes a carrier by using the restoring force of a shape memory alloy. 
     Embodiments of the present invention provide methods for fabricating a flexible display including attaching a shape memory alloy film memorizing a curved shape at a shape memory temperature to a flexible substrate at a temperature higher than the shape memory temperature, forming a display device on the flexible substrate, and returning the shape memory alloy film to the curved shape to remove the shape memory alloy film from the flexible substrate. 
     In some embodiments, the shape memory alloy film may include a Ti—Ni alloy, a Ti—Ni—Fe alloy, a Cu—Al—Ni alloy, an Ag—Cd alloy, and any combinations thereof. 
     In other embodiments, the shape memory temperature may have a range from about −50° C. to about 0° C. 
     In still other embodiments, the attaching of the shape memory alloy film to the flexible memory may include fixing the shape memory alloy film aligned on the flexible substrate to the flexible substrate by pressing the shape memory alloy film with a roller. 
     In even other embodiments, the forming of the display device may include forming a thin film transistor array and a pixel array electrically connected to the thin film transistor array on the flexible substrate supported by the shape memory alloy film. 
     In yet other embodiments, the thin film transistor array may include a gate electrode, a gate insulting film, a source/drain electrode, and an oxide semiconductor thin film, and the pixel array may include a pixel electrode, an organic light emitting diode film, and an upper electrode. 
     In further other embodiments, the thin film transistor may be a bottom gate thin film transistor, which includes a gate buried in a gate insulating film disposed on the flexible substrate, an oxide semiconductor film embedded in the gate insulating film and disposed on the gate, and a source/drain electrode disposed on the gate insulting film. 
     In still further embodiments, the removing of the shape memory film may include cooling the shape memory alloy film to the shape memory temperature. 
     In even further embodiments, the above method may further include forming an encapsulation member on the display device after forming the display device on the flexible substrate. 
     In yet further embodiments, the encapsulation member may include a glass substrate or a metal cap. 
     In much further embodiments, the forming of the encapsulation member may include applying a sealant to an edge portion of the flexible substrate and curing the sealant to attach the flexible substrate and the encapsulation member to each other. 
     In still much further embodiments, the flexible substrate may be a plastic substrate. 
     In other embodiments of the present invention, methods for fabricating a flexible display include memorizing a curved shape in a shape memory alloy at a shape memory temperature, flattening the shape memory alloy film at a temperature higher than the shape memory temperature, attaching the shape memory alloy film to a plastic substrate, and returning the shape memory alloy film to the memorized curved shape by cooling the shape memory alloy film to a temperature not higher than the shape memory temperature to remove the shape memory alloy film from the plastic substrate. 
     In some embodiments, the above method may further include forming a polymer film in the plastic substrate such that upper portions of the polymer film are exposed spaced a predetermined distance before or after attaching the shape memory alloy film to the plastic substrate. 
     In other embodiments, the memorizing of the curved in the shape memory alloy film may include fixing the shape memory alloy film in the curved shape in a space between an inner cylinder with a small diameter and an outer cylinder with a large diameter surrounding the inner cylinder; and memorizing the curved shape in the shape memory alloy film by maintaining the shape memory alloy film fixed in the curved shape at the space between the inner cylinder and the outer cylinder at the shape memory temperature. 
     In still other embodiments, the forming of the display element on the plastic substrate may include forming a thin film transistor array on the plastic substrate, and forming a pixel array electrically connected to the thin film transistor array on the plastic substrate. 
     In even other embodiments, the plastic substrate may include an organic film. 
     In yet other embodiments, the organic film may include a polydimethylsiloxane. 
     In further other embodiments, the polymer film may include a polyimide. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the present invention, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present invention and, together with the description, serve to explain principles of the present invention. In the drawings: 
         FIGS. 1 to 6  are cross-sectional views showing a method for fabricating a flexible display device according to an embodiment of the present invention; and 
         FIGS. 7 and 8  are cross-sectional views showing a method for fabricating a flexible display device according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Such benefits and advantages of the present invention will be apparent through detailed description described with reference to the accompanying drawings, and claims. Particularly, the present invention is well specified and apparently claimed in claims. However, the present invention will be more fully understood by referring to the following detailed description in conjunction with the accompanying drawings. In figures, like reference numerals refer to like elements. 
     Hereinafter, methods for fabricating a flexible display according to embodiments of the present invention will be described with reference to the accompanying drawings. 
       FIGS. 1 to 6  are cross-sectional views showing a method for fabricating a flexible display according to an embodiment of the present invention. 
     Referring to  FIG. 1 , a shape memory alloy film  10  may be prepared. A shape memory temperature of the shape memory alloy film  10  may have a range from about −50° C. to about 0° C. The shape memory alloy film  10  may include a Ti—Ni alloy (for example, Ti-51Ni), a Ti—Ni—Fe alloy (for example, Ti-47Ni-3Fe), a Cu—Al—Ni alloy (for example, Cu-14.5Al-4.4Ni), an Ag—Cd alloy (for example, Ag-45Cd), and any combination thereof. To memorize a curved shape, the shape memory alloy film  10  may be fixed in the curved shape between two cylinders  12  and  14  having different diameters. For example, the shape memory alloy film  10  is disposed at a space between the inner cylinder  12  with a small diameter and an outer cylinder  14  with a large diameter surrounding the inner cylinder  12 , and may be maintained at a shape memory temperature for a predetermined time. Therefore, the curved shape may be memorized in the shape memory alloy film  10 . 
     Referring to  FIG. 2 , the shape memory alloy film  10  may be flattened at a temperature (for example, room temperature of from about 20° C. to about 25° C.) higher than the shape memory temperature. The shape memory alloy film  10  may be used as a carrier in a fabrication process of a flexible display. 
     Referring to  FIG. 3 , the shape memory alloy film  10  may be attached to a plastic substrate  20 , for example, by using glue (not shown). The plastic substrate  20  may have the same or a similar shape or size as the shape memory alloy film  10 . 
     Referring to  FIG. 4 , a thin film transistor (TFT) array  1  and a pixel array  2  electrically connected to the TFT array  1  may be formed on the plastic substrate  20 . The TFT array  1  may include a gate electrode  30 , a gate insulating film  40  covering the gate electrode  30 , an oxide semiconductor film  50  provided on the gate insulating film  40  on the gate electrode  30 , and source/drain electrodes  60  disposed on the gate insulating film  40  and facing each other at both sides of the oxide semiconductor film  50 . A protective film  70  may be formed on the plastic substrate  20  including the source/drain electrodes  60 . While  FIG. 4  shows a bottom gate thin film transistor structure, the TFT array  1  is not limited to this structure and may have a variety of structures. 
     The pixel array  2  may include a pixel electrode  80  electrically connected to the source/drain electrodes  60 , an organic light emitting diode (OLED) film  90  formed in the protective film  70  and disposed in an opening  72  exposing the pixel electrode  80 , and an upper electrode  100  disposed on the OLED film  90  and the protective film  70 . An insulating film  75  filling the opening  72  in which the upper electrode  100  is formed may be formed. 
     Referring  FIG. 5 , an encapsulation member  110  may be formed on the plastic substrate  20 . The encapsulation member  110  is disposed on the upper electrode  100  and the insulting film  75  to encapsulate a display device including the TFT array  1  and the pixel array  2 . To encapsulate the encapsulation member  110 , a sealant may be applied along an edge portion of the plastic substrate  20 . After the sealant is applied, the sealant may be cured by using UV (ultra violet) curing or thermal curing to bond the plastic substrate  20  and the encapsulation member  110 . 
     The encapsulation member  110  may be formed to a glass substrate or metal cap. The encapsulation member  110  can prevent moisture or oxygen from permeating into the TFT array  1  and the pixel array  2 . 
     Referring  FIG. 6 , the shape memory alloy film  10  may be separated from the plastic substrate  20 . By cooling the shape memory alloy film  10  to a shape memory recovery temperature (for example, a temperature of from about −50° C. to about 0° C.) to change the shape of the plastic substrate  20  to the curved shape, the shape memory alloy film  10  may be separated from the plastic substrate  20 . According to this embodiment, the shape memory alloy film  10  may be separated from the plastic substrate  20  only by cooling. Therefore, the method in accordance with this embodiment does not needs a sacrificial film, such as an etching stop layer for separating the carrier, and does not affect the characteristics of the plastic substrate  20 . 
       FIGS. 7 and 8  are cross-sectional views showing a method for fabricating a flexible display according to another embodiment of the present invention. The method according to the another embodiment is the same as or similar to the method according to the previous embodiment. Therefore, description of the another embodiment will be made centered on differences from the previous embodiment. 
     Referring to  FIG. 7 , a shape memory alloy film  310  memorizing a curved shape may be attached to a plastic substrate  320 . The plastic substrate  320  may include an organic film and a plurality of polymer films  330  aligned spaced a predetermined distance in the organic film. Upper portions of the polymer films  330  may be exposed. The polymer films  330  may be formed before or after the shape memory alloy film  310  is attached to the plastic substrate  320 . The plastic substrate  320  may include, for example, a polydimethylsiloxane (PDMS), and the polymer films  330  may include, for example, a polyimide. A TFT array  1  having the same or similar structure to that shown in  FIG. 4  may be formed on the polymer films  330 . A pixel array  2  having the same or similar structure to that shown in  FIG. 4  may be formed on the plastic substrate  320 . By disposing the rigid polymer films  330  on the plastic substrate  320  formed of a flexible organic film, a stretchable display device may be implemented in a curved shape. 
     Referring to  FIG. 8 , the shape memory alloy film  310  may be separated from the plastic substrate  320 . By cooling the shape memory alloy film  310  to a shape memory recovery temperature to change the shape of the plastic substrate  320  to a curved shape, the shape memory alloy film  310  may be separated from the plastic substrate  320 . Since the shape memory alloy film  310  may be separated from the plastic substrate  320  only by cooling, the method in accordance with this embodiment does not need a sacrificial film for removing the carrier and does not affect the characteristics of the plastic substrate  320 . 
     In the method for fabricating a flexible display device according to the embodiment, the method has low cost and good flexible characteristic because that has simple process by using a shape memory alloy film and does not affect the flexibility of the plastic substrate. Also, since the shape memory alloy film is used as carrier can be used repeatedly, the flexible display device may be realized inexpensively. 
     The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the present invention. Thus, to the maximum extent allowed by law, the scope of the present invention 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.