Abstract:
A method of stacking a flexible substrate is provided. The method includes the steps of: preparing a carrier substrate; stacking an adhesive layer on the carrier substrate; and stacking a flexible substrate having at least one image display device on the adhesive layer using a laminating or pressing method. Thus, the flexible substrate is easily fabricated without modification of conventional mass-production equipment for fabricating a display, and thereby a lightweight, thin, and compact flexible display can be realized.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 2006-0082746, filed Aug. 30, 2006, the disclosure of which is incorporated herein by reference in its entirety. 
       BACKGROUND 
       [0002]    1. Field of the Present Invention 
         [0003]    The present invention relates to a method of stacking a flexible substrate, and more particularly, to a method of fabricating a flexible substrate capable of preventing bending of the flexible substrate without modification of production lines of conventional semiconductor and display devices. 
         [0004]    2. Discussion of Related Art 
         [0005]    As modern society is becoming increasingly information-oriented, the importance of the display unit, which enables visualization of Various types of information output from various devices, is increasing. Moreover, this trend is expected to continue for some time. As the information revolution progresses, the demand for information increases proportionately. In the field of displays, which are man-machine interfaces for information delivery, research aimed at enabling viewing without constraints and expressing true colors and the full intricacy of nature is actively progressing. 
         [0006]    In general, displays have been widely adapted in TVs, monitors and mobile phones. However, as technology develops, there is increasing demand for displays that are small, lightweight, have wide views, superior resolution, and fast response times. In reaction to such demand, efforts have been stepped up to enlarge displays and reduce the density and thickness of their glass substrate. 
         [0007]    However, such efforts cause problems in ensuring processability and reliability, and thus technological limits are confronted. An additional problem is that downsizing of display devices for portability clashes with consumers&#39; desire for widescreen displays. Thus, in order to simultaneously obtain superior flexibility, light weight, and portability, a need has arisen for a flexible display substrate in which interconnections and elements of the display are formed on a flexible substrate. 
         [0008]    However, when using a flexible substrate to form an image display device, a difference in coefficient of thermal expansion between the flexible substrate and a carrier substrate may result in the application of stress to an adhesive layer joining the two substrates in a high temperature process (150-250° C.). An additional problem is that, because it lacks rigidity, the flexible substrate cannot be processed by conventional semiconductor manufacturing equipment or by display manufacturing equipment for liquid crystal displays and e-paper. So, it is necessary to either develop special equipment or drastically modify the conventional manufacturing equipment. Existing display set providers such as Sharp and Phillips have invented a chuck for a flexible display and applied it to a conventional manufacturing process. However, this method leads to difficulties in mass-production and processing and, consequently, higher production costs. 
       SUMMARY OF THE PRESENT INVENTION 
       [0009]    The present invention is directed to providing a method of stacking a flexible substrate capable of preventing bending of the flexible substrate using conventional display manufacturing equipment applied in flexible display fabrication. 
         [0010]    One aspect of the present invention provides a method of stacking a flexible substrate comprises the steps of: preparing a carrier substrate; stacking an adhesive layer on the carrier substrate; and stacking a flexible substrate having at least one image display device on the adhesive layer using a laminating or pressing method. 
         [0011]    To stack the adhesive layer, the laminating or pressing method may be used. The laminating method may use a laminator having an upper roller rolling over the adhesive layer or the flexible substrate, and a lower roller rolling under the carrier substrate. Also, the laminating method may use a laminator having an upper roller rolling over the adhesive layer or the flexible substrate, and a lower Support formed under the carrier substrate. 
         [0012]    The pressing method may use a presser having an upper presser formed over the adhesive layer or the flexible substrate and movable vertically, and a fixed presser formed under the carrier substrate or a lower presser movable vertically. 
         [0013]    The laminator and the presser may further comprise a protective body formed in a region with which the carrier substrate, the adhesive layer or the flexible substrate contacts in order to prevent damage to the carrier substrate, the adhesive layer or the flexible substrate. The protective body made of rubber or fabric may be coated or stacked. 
         [0014]    The laminator and the presser may be controlled within a temperature range from 0 to 160° C. The laminator and the presser may be controlled mechanically or by air pressure. The laminator may be controlled within an air pressure range from 0.1 to 10 kg/cm 2 . The presser may be controlled within an air pressure range from 0.1 to 100 kg/cm 2 . The step of stacking the adhesive layer and the flexible substrate may be performed under atmospheric pressure, inert atmosphere or vacuum. The carrier substrate may be formed of glass or silicon. 
         [0015]    The adhesive layer may comprise a support, and adhesive agent layers formed on and under the support. The support may be formed of one of polyethylene terephthalate, polybutylenes terephthalate, polyimide, polyester, and polyolefine. The flexible substrate may be formed of one of a metal thin film, plastic and ultra thin glass. 
         [0016]    After forming the image display device on the flexible substrate, the present invention may further comprise the step of removing the carrier substrate therefrom. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
           [0018]      FIGS. 1A to 1D  are cross-sectional views schematically illustrating a method of stacking a flexible substrate according to an exemplary embodiment of the present invention; 
           [0019]      FIGS. 2A to 2C  are cross-sectional views schematically illustrating a method of stacking a flexible substrate according to another exemplary embodiment of the present invention; and 
           [0020]      FIGS. 3A to 3C  are cross-sectional views schematically illustrating a method of fabricating a display having a flexible substrate using a method of stacking the flexible substrate according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0021]    A method of stacking a flexible substrate and a method of fabricating a flexible display according to the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the present invention are shown. 
         [0022]      FIGS. 1A to 1D  are cross-sectional views illustrating a method of stacking a flexible substrate according to an exemplary embodiment of the present invention. 
         [0023]    Referring to  FIG. 1A , a carrier substrate  110  is prepared. The carrier substrate  110  may be formed of various kinds of materials, for example, glass, silicon, etc. Referring to  FIG. 1B , an adhesive layer  120  is stacked on the carrier substrate  110 . The adhesive layer  120  is composed of a support  121  and bonding materials  122  and  123  respectively formed on and under the support  121 . The support  121  may be formed of polyethylene terephthalate, polybutylenes terephthalate, polyimide, polyester, or polyolefine. 
         [0024]    As illustrated in  FIG. 1B , the adhesive layer  120  is disposed by a laminator method using rollers  140   a  and  140   b . Rollers rolling in the same direction are prepared under the carrier substrate  110  and over the adhesive layer  120 , and upper and lower rollers  140   a  and  140   b  formed over and under the carrier substrate  110  roll over and under the carrier substrate  110  so as to dispose the adhesive layer  120  thereon. 
         [0025]    In the next step, as illustrated in  FIG. 1C , a flexible substrate  130  on which an image display device will be formed is stacked on the adhesive layer  120  using the roller  140   a . The flexible substrate  130  may be a metal thin film (stainless foil and aluminum thin film), a thin glass substrate (e.g., thinner than 0.3 mm) or a plastic substrate. To stack the flexible substrate  130 , the upper roller  140   a  is prepared on the flexible substrate  130 , and the lower support  150  is prepared under the carrier substrate  110 . By such a structure, the lower support  150  fixes and supports the carrier substrate  110 , and the upper roller  140   a  rolls on the flexible substrate  130  so as to stack the flexible substrate  130 . 
         [0026]    Meanwhile, the rollers  140   a  and  140   b  illustrated in  FIGS. 1B and 1C  are composed of a roller main body  142  and a protective body  141  surrounding the roller main body  142  and formed of rubber or soft fabric. To minimize damage to the stacked structures (e.g., the adhesive layer, the flexible substrate, the carrier substrate, etc.), the protective body  141  surrounds or coats the roller main body  142 . The lower support  150  formed under the carrier substrate  110  is composed of a support main body  152  and a support protective body  151 . Like the protective body  141 , the support protective body  151  is also formed of rubber or soft fabric. 
         [0027]    Referring to  FIGS. 1B and 1C , in  FIG. 1B , the rollers  140   a  and  140   b  are disposed on and under the adhesive layer  120  and a different number of rollers are disposed thereon, respectively. In  FIG. 1C , the upper roller  140   a  is disposed over the flexible substrate  130 , and the lower support  150  is disposed under the carrier substrate  110 . That is, to stack the adhesive layer  120  and the flexible substrate  130 , without regard to the number of the rollers  140   a  and  140   b , a support supporting the carrier substrate may be used instead of the roller. When using the rollers, one to five rollers may be used over and under the carrier substrate, respectively. A gap between the rollers may be controlled to ensure close adhesion between the carrier substrate  110  and the adhesive layer  120 , and between the adhesive layer  120  and the flexible substrate  130 . Here, the gap between the rollers  140   a  and  140   b  may be controlled mechanically and by air pressure. When the gap between the rollers is controlled by air pressure, the air pressure may depend on the size and use of the adhesive layer  120  or the flexible substrate  130 , but preferably be 0.1 to 10 kg/cm 2 . Also, a preferable temperature of the rollers  140   a  and  140   b  is in the range of 0 to 160° C. to enhance the close adhesion between the carrier substrate  110  and the adhesive layer  120 . 
         [0028]    In the embodiments described above, the adhesive layer  120  utilizes the upper and lower rollers  140   a  and  140   b , and the flexible substrate  130  utilizes the upper roller  140   a  and the lower support  150 , but these may be freely changed. 
         [0029]      FIG. 1D  illustrates a stacking structure of a flexible substrate fabricated by the stacking method of the flexible substrate shown in  FIGS. 1A to 1C . As illustrated in  FIG. 1D , the stacking structure of the flexible substrate is composed of the carrier substrate  110 , the adhesive layer  120  and the flexible substrate  130 . 
         [0030]      FIGS. 2A to 2C  are cross-sectional views schematically illustrating a method of stacking a flexible substrate according to another exemplary embodiment of the present invention. 
         [0031]    Referring to  FIGS. 2A to 2C , a carrier substrate  110  is prepared, and an adhesive layer  120  is stacked on the carrier substrate  110 . The adhesive layer  120  is stacked using a presser P, and the presser P is composed of an upper presser  240  disposed over the adhesive layer  120 , and a lower presser  250  or a fixed presser  260 . The upper and lower pressers  240  and  250  and the fixed presser  260  are composed of presser main bodies  242 ,  252  and  262 , and protective bodies  241 ,  251  and  261  corresponding to the adhesive layer  120  formed under the presser main bodies  242 ,  252  and  262  and protecting structures which will be stacked later. The protective bodies  241 ,  251  and  261  are made of rubber or soft fabric, and coated or stacked on the Dresser main bodies  242 ,  252  and  262 , respectively. Referring to  FIG. 2B , the upper and lower pressers  240  and  250  move vertically and press the structures. And, referring to  FIG. 2C , the upper presser  240  which can move vertically and the fixed presser  260  press the structures. The presser P may operate at a temperature ranging from 0 to 160° C., and be controlled mechanically or by air pressure for close adhesion to the adhesive layer  120  or the flexible substrate  130 . When the presser P is controlled by air pressure, the air pressure may be in a range of 0.1 to 100 kg/cm 2 . When the presser is controlled mechanically, pressure may be controlled by a screw, etc. Also, the presser P may ensure the close adhesion of the adhesive layer  120  by operating under atmospheric pressure, inert atmosphere or vacuum. Then, a flexible substrate  130  is stacked on the adhesive layer  120  using the presser P as described above. 
         [0032]    In the above-described embodiment, the adhesive layer  120  utilizes the upper and lower pressers  240  and  250  which can move vertically, and the flexible substrate  130  utilizes the upper presser  240  which can move vertically, and the fixed presser  260  disposed under the substrate. However, the present invention may not be limited to the embodiment, and freely make other choices. 
         [0033]      FIGS. 3A to 3C  are cross-sectional views schematically illustrating a method of fabricating a display having a flexible substrate using a method of stacking the flexible substrate according to the present invention. 
         [0034]    In the exemplary embodiment, first, a carrier substrate  110 , an adhesive layer  120 , and a flexible substrate  130  are sequentially stacked. When the flexible substrate  130  is stacked on the carrier substrate  110 , an image display device including a light-emitting device  330  and a transistor  310 , i.e. a driving device is formed on the flexible substrate  130 . To form the light-emitting device  330  and the transistor  310 , a buffer layer  301  and a semiconductor layer  315  are sequentially formed on the flexible substrate  130 , and a gate insulating layer  302 , a gate electrode  311 , an interlayer insulating layer  303 , source and drain electrodes  312  and a passivation layer  304  are formed on the semiconductor layer  315 . Then, the light-emitting device  330  electrically connected to the transistor  310  through a contact hole (not illustrated) formed in the passivation layer is formed on the transistor  310  including the gate electrode  311  and the source and drain electrodes  312 . The light-emitting device  330  includes an anode  331 , an emission layer  333  and a cathode  335 . A pixel defining layer  305  is formed on the anode  331  of the light-emitting device  330  and the passivation layer  304 . 
         [0035]    As described above, when a display having the image display device including the light-emitting device  330  and the transistor  310  is formed on the flexible substrate  130 , the carrier substrate  110  disposed under the flexible substrate  130  is removed. Here, the adhesive layer  120  may be removed with the carrier substrate  110 . In this case, the carrier substrate  110  may be removed by heat or pressure. 
         [0036]    Consequently, an adhesive layer for a flexible display can offset stress generated by a difference in coefficients of thermal expansion between a flexible substrate and a carrier substrate in a process of forming an image display device on a flexible substrate such as a plastic substrate, thereby effectively reducing bending of the flexible substrate. 
         [0037]    Also, a method of stacking a flexible substrate using a laminator or presser with rollers enables mass-production of flexible displays using flexible substrates without an additional investment in manufacturing equipment, because a conventional manufacturing line for semiconductors and displays can be applied to the present invention without equipment modification. 
         [0038]    While the present invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.