Patent Publication Number: US-2007096208-A1

Title: Manufacturing method for flat panel display

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims priority from Korean Patent Application No. 2005-0099486, filed on Oct. 21, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
     FIELD OF THE INVENTION  
      The present invention relates to a dummy glass substrate and a method for manufacturing a display apparatus using the same, and more particularly, to a dummy glass substrate having a stress relaxation portion formed with a groove and a display apparatus manufacturing method using the dummy glass substrate.  
     DESCRIPTION OF THE RELATED ART  
      Flat panel displays, such as the liquid crystal display (LCD) and the organic light emitting diode (OLED) display are replacing cathode ray tube displays. The LCD includes a first substrate having thin film transistors, a second substrate arranged facing the first substrate, and an LCD panel having a liquid crystal layer interposed between the first and second substrates. The LCD panel may include a backlight unit since the LCD is a non-light emitting element. The amount of light emitted from the backlight unit is determined by the orientation of the crystals in the liquid crystal layer.  
      The LCD includes a driving circuit for applying driving signals to gate lines and data lines arranged in the first substrate. The driving circuit includes a gate driving chip, a data driving chip, and a printed circuit board (PCB) provided with a timing controller and a driving voltage generator. An organic light emitting diode (OLED) includes a light emitting layer that emits light by combining holes and electrons implanted from a pixel electrode and a common electrode, respectively. The OLED provides a superior viewing angle and has the advantage that a backlight unit is not required.  
      Recently, a plastic insulation substrate has been widely used, replacing the conventional glass insulation substrate so that flat panel displays can be made thinner and lighter in weight. The thin plastic insulation substrate has the problem of being easily deformable, especially by heat, and thus needs to be backed by a supporting member such as a dummy glass substrate, a special use stainless steel (SUS) substrate, or a plastic substrate. However, it is difficult to apply a spin process to the SUS substrate since the SUS substrate is relatively heavy even though made as thin as possible. The plastic substrate needs to be quite thick to be used as the supporting member and is also likely to be deformed by high temperatures.  
      The dummy glass substrate is flat and is resistive to heat and chemicals. If a plastic insulation substrate is attached to a dummy glass substrate, the manufacturing process requires a high temperature process and a low temperature process. However, deformation of the plastic insulation substrate may occur due to different coefficients of thermal expansion (CTE) of the glass and the plastic, i.e., a so-called bimetal effect occurs between the plastic insulation substrate and the dummy glass substrate.  
     SUMMARY OF THE INVENTION  
      The present invention overcomes certain of the above problems by providing a dummy glass substrate supporting a plastic insulation substrate wherein the dummy glass substrate includes a stress relaxation portion having plurality of grooves. Each grove has a depth which corresponds to 0.1% to 25% of the thickness of the dummy glass substrate. In an illustrative embodiment, the width of each groove ranges from 5 μm to 50 μm and the groove is formed in a dotted groove pattern wherein the size of each dotted groove ranges from 0.1 mm×0.1 mm to 10 mm×10 mm and may be of rectangular or hexagonal shape and may have a rectangular or V-shaped cross sections.  
      In one embodiment, the dummy glass substrate will include a plurality of such grooves formed in parallel. In another embodiment the dummy glass substrate will include two sets of mutually parallel grooves formed perpendicular to each other across one surface of the substrate.  
      The display apparatus of the invention may be manufactured by the following steps: preparing a dummy glass substrate having a stress relaxation portion in which a groove is formed; adhering one side of a plastic insulation substrate to the stress relaxation portion of the dummy glass substrate; forming a display element on the other side of the plastic insulation substrate; and detaching the dummy glass substrate from the plastic insulation substrate. According to an aspect of the present invention, the adhesive has the characteristic of being detachable at a low temperature. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
      The above and/or other aspects and advantages of the prevent invention will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompany drawings, in which:  
       FIG. 1  is a perspective view of a dummy glass substrate according to a first exemplary embodiment of the present invention;  
       FIG. 2A  to  FIG. 2C  are sectional views showing a method for manufacturing a display apparatus using the dummy glass substrate according to the first exemplary embodiment of the present invention;  
       FIG. 3  shows deformation of a plastic substrate of a display apparatus during a manufacturing process.  
       FIG. 4  is a perspective view of a dummy glass substrate according to a second exemplary embodiment of the present invention;  
       FIG. 5  to  FIG. 7  are top plane views showing dummy glass substrates according to third, fourth, and fifth exemplary embodiments of the present invention, respectively. 
    
    
     DESCRIPTION  
      Referring to  FIG. 1 , a perspective view of a dummy glass substrate according to the first exemplary embodiment of the present invention is shown. Dummy glass substrate  10  may be formed in a square plate shape, with a thickness d 1  of 0.7 to 1.1 mm. One side of the dummy glass substrate  10  is formed with a stress relaxation surface  20 . A plurality of grooves such as groove  21 , are formed in the stress relaxation surface  20 . Grooves such as groove  21  extend longitudinally and transversely over the entire surface of the stress relaxation surface  20  and divides the stress relaxation surface  20  into a plurality of squares as shown in isometric view in  FIG. 1 . Each groove  21  has a rectangular shaped cross section, and the depth d 2  of the groove  12  may be about 0.1% to 25% of the height d 1  of the dummy glass substrate  10 .  
      It has been found that the stress relaxation effect becomes insignificant and the manufacturing process becomes complicated when the depth d 2  ( FIG. 1 ) of groove  21  is less than 0.1% of the thickness d 1  of dummy glass substrate  10 . When the depth d 2  of groove  21  is greater than 25% of the height d 1  of the dummy glass substrate  10 , the strength of the dummy glass substrate  10  may be adversely affected. The interval d 4  between the respective adjacent grooves  21  arranged in parallel may be about 0.1 mm to 10 mm. The width d 3  of groove  21  may be about 5 μm to 50 μm. When the width d 3  of groove  21  is less than 5 μm, the stress relaxation effect becomes insignificant. When the width d 3  of groove  21  is greater than 50 μm, processing fluids such as cleansing water or etching water may reduce the adhesion between the plastic insulation substrate  21  and the dummy glass substrate  10 . Groove  21  may be formed by performing a photolithographic process or a laser process on the dummy glass substrate  10 .  
      A method for manufacturing the dummy glass substrate according to the first exemplary embodiment of the present invention will now be described with reference to  FIG. 2A  to  FIG. 2C , and  FIG. 3 . Amorphous silicon (a-Si) thin film transistor, a poly silicon thin film transistor, an organic semiconductor thin film transistor, and a color filter, etc., may be formed on the plastic insulation layer to be formed on the stress relaxation surface  20  of dummy glass substrate  10 . A plastic insulation substrate  120  is adhered on the stress relaxation surface  20  of the dummy glass substrate  10  using an adhesive  110  as shown in  FIG. 2A . The dummy glass substrate  10  and the plastic insulation substrate  120  are adhered to each other by coating one surface of the plastic insulation substrate  120  with the adhesive  110  and then attaching the surface of substrate  120  coated with the adhesive  110  to the dummy glass substrate  10 . Plastic insulation substrate  120  may be made of polycarbon, polyimide, polyethersulfone (PES), polyacrylate (PAR), polyethylenenaphthalate (PEN), and polyethylene terephthalate (PET), etc.  
      The thickness of the plastic insulation substrate  120  may range from about 0.05 mm to 0.2 mm. When using the plastic insulation substrate  120 , the processing temperature should be within an allowable thermal range of 150 to 200° C., as lower temperatures may adversely affect adhesion. When the dummy glass substrate  10  and the plastic insulation substrate  120  are adhered to one another, there is no adhesion where grooves  21  are present.  
      As shown in  FIG. 2B , gate line  131 , gate insulation layer  132 , semiconductor layer  133 , and a resistance contact layer  134  are formed on the plastic insulation layer  120 . The gate insulation layer  132 , the semiconductor layer  133 , and the resistance contact layer  134  are formed consecutively using chemical vapor deposition (CVD). The three consecutive layers are formed at a relatively high temperature, and accordingly, the plastic insulation substrate  120  may be deformed due to the different thermal expansion coefficients of the substrate  120  and the dummy glass substrate  10 . Such a deformation of the plastic insulation substrate  120  would ordinarily affect a display element (e.g. a thin film transistor), and furthermore, the deformation might cause the thin films found on substrate  120  to lift away from the plastic insulation substrate  120 . However, this condition is avoided by the present embodiment.  
      Referring to  FIG. 3 , when heat is applied, the dummy glass substrate  10  and the plastic insulation substrate  120  both expand. Since the thermal expansion coefficient of the plastic insulation substrate  120  is greater than that of the dummy glass substrate  10 , a center portion of the plastic insulation substrate  120  is bent upward. The thermal expansion coefficient of the plastic insulation substrate  120  may be more than 10 to 30 times that of the dummy glass substrate  10 . Such an expansion may cause a problem when the process temperature exceeds 130° C.  
      On the other hand, the dummy glass substrate  10  and the plastic insulation substrate  120  both shrink at cold temperatures. During the cooling process, moisture or air may penetrate into the plastic insulation substrate  120 , thereby accelerating the shrinkage of the plastic insulation substrate  120 . Accordingly, the center portion of the plastic insulation substrate  120  is bent downward. The amount of bending at the center portion of the insulation substrate  120  may be defined as the difference in height n of the center portion with respect to an edge portion of the plastic insulation substrate  120 . Accurate deposition of the display elements becomes difficult when the plastic insulation substrate  120  is deformed, and the thin film formed on the plastic insulation substrate  120  may lift away due to the expansion and shrinkage. The deformation of the plastic insulation substrate  120  is caused by the “bimetal effect” occurring between the dummy glass substrate  10  and the plastic insulation substrate  120 .  
      According to the embodiment of the present invention, the plastic insulation substrate  120  and the dummy glass substrate  10  are partially separated due to the presence of grooves such as groove  21 . Grooves  21  significantly reduce deformation of the dummy grass substrate  120  by relaxing stress applied to the dummy glass substrate during the expansion and shrinkage. As the dummy glass substrate  10  is less deformed, the plastic insulation substrate  120  adhered to the stress relaxation surface  20  is deformed less. Subsequently, the semiconductor layer  133  and the resistance contact layer  134  are patterned and a source electrode  135  and a drain electrode  135  are formed, to thereby complete the thin film transistor  130  ( FIG. 2C .  
      An organic light emitting apparatus may be manufactured by forming a pixel electrode, an organic light emission layer, and a common electrode on the thin film transistor  130 , or a liquid crystal display apparatus may be manufactured by forming a pixel electrode on the thin film transistor  130  and then coupling the thin film transistor  130  with another substrate.  
      After the thin film transistor  130  is formed, grooves  21  will relax the stress applied to the dummy glass substrate  10 , thereby reducing deformation of the plastic insulation substrate  120 .  
      Table 1 shows a measurement result of a deformation amount of the plastic insulation substrate  120  using the dummy glass substrate  10 . The dummy glass substrate  120  used for this measurement has a thickness d 1  of 1.1 mm and was of 300 mm*400 mm. Grooves  21  are arranged at the interval d 4  of 5 mm, and each has a depth d 2  of 10 μm and a width d 3  of 10 μm. The measuring of the deformation amount h of the plastic insulation substrate was performed after heating the dummy glass substrate  10  and the plastic insulation substrate  120  at 150° C. for about 10 minutes and cooling the substrates at the normal temperature.  
                               TABLE 1                                   Embodiment   Sample 1   Sample 2                                                    Condition   Adhesion to   No groove   Adhesion to opposite           stress relax-       surface of stress           ation surface       relaxation surface       Deformation(mm)   1.69   2.58   2.46                  
 
      As shown in Table 1, the deformation amount of the plastic insulation substrate is 2.58 mm (Sample 1) when using a dummy glass substrate having no groove formed therein. When the plastic insulation substrate is adhered to an opposite surface to the stress relaxation surface of the dummy glass substrate (Sample 2), the deformation amount of the plastic insulation substrate becomes 2.46 mm. The two comparison results are not greatly different from each other. However, when the plastic insulation substrate is adhered to the stress relaxation substrate where the grooves are formed (the “Embodiment”), the deformation amount becomes 1.69 mm, which is 35% less than the above results.  
      The shape of each groove of the first exemplary embodiment may vary depending on the size of the dummy glass substrate, the adhesive force between the plastic insulation substrate and the dummy glass substrate, and the deformation amount of the plastic insulation substrate.  
      The following second to fifth exemplary embodiments of the present inventions show variation of the shape of the groove.  
       FIG. 4  is a perspective view of a dummy glass substrate according to the second exemplary embodiment of the present invention. Grooves  22  are arranged in parallel on a dummy glass substrate  11  according to the second exemplary embodiment of the present invention, and each groove  22  has a “V” shaped cross-section. The respective grooves  22  may be manufactured by a photo-lithographic etching process or by a mechanical process.  
       FIG. 5  to  FIG. 7  are top plan views of dummy glass substrates according to the third to fifth exemplary embodiments of the present invention, respectively. Grooves  23 , each in a square shape, are regularly arranged on a dummy glass substrate  12  according to the third exemplary embodiment of the present invention as shown in  FIG. 5 . Each side of the respective groove  23  is about 0.1 mm to 10 mm. Grooves  24 , each having a regular hexagon shape, are regularly arranged on a dummy glass substrate  13  according to the fourth exemplary embodiment of the present invention as shown in  FIG. 6 . The size d 6 ×d 7  of each groove  24  is about 0.1 mm to 10 mm. Grooves  25 , each in a hexagonal shape, are arranged in a honeycomb shape on a dummy glass substrate  14  according to the fifth exemplary embodiment of the present invention as shown in  FIG. 7 .  
      As described above, the present invention provides a dummy glass substrate for reducing deformation of a plastic insulation substrate during a display apparatus manufacturing process. In addition, the present invention provides a method for manufacturing a display apparatus for reducing deformation of a plastic insulation substrate.  
      Although a few exemplary embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without, however, departing from the spirit and scope of the invention.