Abstract:
The cell forming apparatus includes at least a pressurized device and a pressure distribution device, wherein the pressurized device is utilized to assemble a first substrate and a second substrate, and the pressure distribution device is used to distribute the pressure imposed on the panel in an attempt to create a regular cell gap. The aforesaid pressure distribution device can be a mask having a number of dents corresponding to the display areas of the panel and connecting to each other with trenches.

Description:
[0001]    This application incorporates by reference Taiwanese application Serial No. 90114213, Filed Jun., 12, 2001.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to a device for manufacturing a liquid crystal display (LCD) panel and a fabrication method therefor, particularly to a method capable of forming a uniform cell gap.  
           [0004]    2. Description of the Related Art  
           [0005]    Compared to a conventional display panel, liquid crystal display (LCD) panel has the potential of lightweight, low power consumption and high resolution for which are gradually beloved by the consuming public. Also, the other portable products, such as personal digital assistant (PDA) and cellular phone, enjoy a rapid growth in the market. With the increasing demand, the image display of those portable products is expected to have the same resolution as that of a personal computer. For example, the liquid crystal on silicon (LCOS), which generally applies to a small display panel, is a panel composed of a silicon substrate and a glass substrate with liquid crystal injected between. As such LCOS panel differs from the common liquid crystal panel that utilizes two substrates both made of glass, it can be smaller and lighter and can provide a high-resolution display quality. The resolution of a LCOS panel is shown by the number of pixels similar to a liquid crystal display panel; that is, the more pixels it possesses the higher resolution it displays. Furthermore, the semiconductor process, like the CMOS technology, finds application in the production of the driving circuit of pixels in a LCOS panel. By this method, the silicon wafer as the substrate can be manufactured in employing the 0.35 μm semiconductor process. Thus, there is no need to throw in extra investment in production equipment and the display resolution of a LCOS panel is greater than that of a glass-substrate liquid crystal panel.  
           [0006]    Generally, LCOS panel has two basic types: transmissive and reflective. Nevertheless, the most research and development work is centered on the reflective LCOS panel. Referring to FIG. 1, it is a sectional view of a pixel of a reflective LCOS panel. The LCOS panel comprises a first plate  100  and a second plate  101 , wherein said second plate  101  made of a silicon substrate  102  consists of a thin film transistor (TFT)  106  for controlling pixel movement, a light shielding film  107  for blocking light irradiation on the TFT, a capacitor  108  for sustaining pixel brightness, a metal layer  111  in connecting the TFT  106  with the capacitor  108 , an insulating layer  109  capping the metal layer  111 , a pixel electrode  110 , and a reflector  112 , and wherein said second plate  100  made of a glass substrate  120  includes a transparent electrode (ITO)  118 . The first substrate  100  and the second substrate  101  are assembled and inserted with a liquid crystal molecule  115  to form a liquid crystal layer  114  in between said two substrates. In addition, an orientation film  113  and  116  are formed above the reflector  112  and beneath the ITO  118 , respectively.  
           [0007]    With reference to FIG. 1, the incoming light passing through the liquid crystal layer  114  (as shown in Arrow I) directly emerges from the glass substrate  120  via the reflector  112  (as shown in Arrow O). With the variance of voltage charged on the pixel electrode  110 , the liquid crystal molecule  115  changes its alignment, so as to control the polarization of light passing through the liquid crystal layer  114 . Therefore, the emerging light will, through the application of the polarizer (not shown in FIG. 1) disposed above the substrate  120 , be visible.  
           [0008]    Referring to FIG. 2 which is a schematic diagram of FIG. 1, the LCOS panel consists of the glass substrate  120  and the silicon substrate  102 , both of which possess a plurality of corresponding pixel electrodes, such as pixel electrode  204   a  and  204   b , and the cell gap H, the distance between the corresponding pixel electrodes, is inserted with the liquid crystal (other elements are omitted in FIG. 2). The optical effect of the liquid crystal will vary with the width of the cell gap. An uneven cell gap between the substrates resulting in the interfering ring visible to the naked eyes is called “Newton ring” that may cause injury to the display effect of the LCOS pixel.  
           [0009]    Moreover, unlike the large size LCD panel, the LCOS application is aimed at small size panel, such as projector or LC panel used in project TV. The LCOS panel with general pixel size of 0.7 inch, 0.9 inch or 1.3 inch needs to amplify its image to 60 to 100 inch if applied in project TV. Under such a high amplification rate, the imperfection shown in the applied product will even more conspicuous once the display effect of the panel itself is not so satisfactory. Therefore, an important goal for research efforts is retaining a uniform cell gap H that is to control the space between the glass substrate  120  and the silicon substrate  102 .  
           [0010]    Typically, the solution to the problem of an uneven cell gap is to apply spacers randomly between the liquid crystal layers. With reference to FIG. 3, it depicts the sectional view of a traditional LCOS panel. The LCOS panel consists of a glass substrate  320  and a silicon substrate  302  with a liquid crystal layer  306  inserted in between. A plurality of corresponding pixel electrodes, like  304   a  and  304   b , is arranged between the substrates, wherein the cell gap H between  304   a  and  304   b  is upheld by virtue of disposing spacer. When the glass substrate  320  and the silicon substrate  302  are uneven or suffer external pressure, said disposing spacer could avoid a direct contact of the two substrates. Meanwhile, this method incurs many shortcomings that in addition to strictly controlling the particle size of each spacer, these randomly disposing spacers incline to gather in particular place during liquid crystal injection, thereby failing to produce a uniform cell gap H. Moreover, in its application in project TV, the disposing spacers that incidentally fall above the pixel will result in tiny black spots in the display. Thus, the shadow caused by applying spacers randomly will decrease the display performance of the LCOS panel.  
           [0011]    Another conventional method of controlling the cell gap is to form slender protrusions between the pixels. FIG. 4 shows the sectional view of another conventional LCOS panel, wherein all pixels  402  are spaced apart from each other by a spacing  404 . The pixel  402  corresponds to the display area of the LCOS panel, whereas the spacing  404  corresponds to the non-display area. The protrusion is made of curable material after UV and heating treatments, e.g. silicon dioxide or silicon nitride, and is formed in the spacing  404  a shape with a width approximately 0.35-0.5 micron and a height approximately 3-5 micron. The protrusion is also called a photo spacer  406 , which is perpendicular to the pixel  402 . The photo spacer  406  formed in the spacing  404  is able to uphold the space between the glass substrate and the silicon substrate so as to uniformize the cell gap. Even so, such method has several disadvantages; for example, the slim structure of said photo spacer  406  causes process difficulty and said photo spacer is vulnerable for its lack of sustentation. Furthermore, the bottom part of said photo spacer is likely to have deformation when affected by the heat in the process. If the bottom deformation is too severe, it may cover up the pixel  402  partially, as shown in the dotted line  406  of FIG. 4, thereby hampering the aperture ratio of the pixel  402 ; on the other hand, the liquid crystal is susceptible to contamination during the process.  
           [0012]    For the above, a solution is desirous as to how to maintain a uniform cell gap width H in order to prevent a Newton ring and display an excellent picture quality.  
         SUMMARY OF THE INVENTION  
         [0013]    The present invention is intended to provide a device for manufacturing a liquid crystal display panel with uniform cell gap and its fabrication method. By virtue of a device capable of pressure distribution, the objective of cell gap control in avoidance of a Newton ring is attained.  
           [0014]    The other objective of this invention is to provide a cell forming apparatus and a cell forming process aimed at producing a liquid crystal display panel with high aperture ratio.  
           [0015]    The cell forming apparatus includes at least a pressurized device and a pressure distribution device, wherein the pressurized device is utilized to assemble a first substrate and a second substrate, and the pressure distribution device is used to distribute the pressure imposed on the panel in an attempt to create a regular cell gap. The aforesaid pressure distribution device can be a mask having a number of dents corresponding to the display areas of the panel and connecting to each other with trenches.  
           [0016]    According to the present invention, the cell forming process refers to exerting evenly distributed pressure on a first substrate and a second substrate, sealing the first substrate and the second substrate thereafter with sealant so as to enhance the uniformity of a cell gap. Meanwhile, the aforesaid pressure exertion area does not include a display area of the substrate.  
           [0017]    According to the invention, manufacture of a liquid crystal display panel comprises a step of providing a cell forming apparatus at least including a pressurized device and a pressure distribution device. A first substrate and a second substrate on said cell forming apparatus are provided. Pressure on at least one of the first substrate and the second substrate by said pressurized device of the cell forming apparatus is imposed to assemble a liquid crystal display panel. The pressure distribution device is provided between the pressurized device, and one of the first substrate and the second substrate for distributing pressure when the pressurized device imposes pressure on at least one of the first substrate and the second substrate, thereby forming a uniform cell gap.  
           [0018]    For the objects of the present invention, it addresses a method for manufacturing a liquid crystal display panel. The panel comprises a plurality of display areas and a plurality of non-display areas, and is assembled into by a first substrate and a second substrate with sealant. The cell forming process is fulfilled by utilizing a manufacturing device. The manufacturing device includes, a first hot plate, a second hot plate, a first cushion, a second cushion and a mask, wherein the first cushion is disposed in the inner side of the first hot plate, the second cushion is disposed in the inner side of the second hot plate, and the mask is sandwiched between the first cushion and the second cushion. The first cushion and the second cushion are used to equally distribute the heat energy passed on by the first hot plate and the second hot plate. The mask includes a plurality of dents and a plurality of trenches connecting to each other, and a plurality of outlets are formed on the edge of the mask in communication with the external air.  
           [0019]    The cell forming process includes the steps of: heating the first hot plate and the second hot plate; placing a panel between the second cushion and the mask wherein the dents of the mask correspond to the display areas of the panel and the other portions correspond to the non-display areas of the panel; then, exerting pressure on the first hot plate so as to press down the first hot plate along with the first cushion and the mask in completing the cell forming process after the sealant curing; and finally, removing the first hot plate, the first cushion and the mask above the panel to retrieve the panel.  
           [0020]    According to the present invention, it offers a method for manufacturing a liquid crystal display panel. The liquid crystal display panel includes a plurality of display areas and a plurality of non-display areas, and is constructed by a first substrate and a second substrate with sealant. The cell forming process is accomplished by utilizing a manufacturing device. The manufacturing device comprises a hot plate, a heat-conducting plate, a mask, and a silicone membrane, wherein a vacuity hole is placed above the hot plate and the heat-conducting plate is deposited on the hot plate to distribute the heat energy coming from the hot plate evenly and the mask is situated above the heat-conducting plate and the silicone membrane is located above the mask. The mask is patterned with a plurality of dents and a plurality of trenches in which the dents connect to the trenches. A plurality of outlets is formed on the edge of the mask so as to communicate with the external air. The cell forming process comprises the steps of: heating the hot plate; then, depositing the panel between the heat-conducting plate and the mask, wherein the dents of the mask correspond to the display areas of the panel and the other portions correspond to the non-display areas of the panel; thereafter, covering the mask with the silicon membrane so as to form a sealed space; then, vacuuming the sealed space through the vacuity hole to exert pressure on the sealed space; and finally, opening the vacuity hole to restore the pressure within the sealed space, and removing the silicone membrane and the mask to retrieve the panel.  
           [0021]    By employing the manufacturing device and the method of the present invention, the liquid crystal display panel is able to generate a uniform cell gap so that the image quality can be enhanced to avoid the occurrence of a Newton ring. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    The above objects and other advantages of the present invention will become more apparently by describing in detail the preferred embodiment of the present invention with reference to the attached drawings in which:  
         [0023]    [0023]FIG. 1 (prior art) is a schematic sectional view showing of a pixel of a reflective LCOS panel;  
         [0024]    [0024]FIG. 2 (prior art) is a schematic diagram of FIG. 1;  
         [0025]    [0025]FIG. 3 (prior art) is a schematic sectional diagram showing of a conventional LCOS panel;  
         [0026]    [0026]FIG. 4 (prior art) is a schematic sectional diagram depicting a conventional LCOS panel;  
         [0027]    [0027]FIG. 5A is a top view of a LCOS panel;  
         [0028]    [0028]FIG. 5B is a top view of one embodiment of this invention;  
         [0029]    [0029]FIG. 5C is a stereographic view of FIG. 5B;  
         [0030]    [0030]FIG. 6 schematically shows a diagram of another embodiment of this invention;  
         [0031]    [0031]FIG. 7 is a schematic diagram of the cell forming process of the LCOS panel in utilization of the mask according to the present invention;  
         [0032]    [0032]FIG. 8 is a partially enlarged diagram of FIG. 7 in performing the cell process; and  
         [0033]    [0033]FIG. 9 is a schematic diagram of the cell forming process in utilization of the mask according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0034]    The present invention lies in forming a regular cell gap by utilizing a mask in which the dents correspond to the display areas of the panel and the other portions correspond to the non-display areas to carry out the cell forming process. The process of the present invention is simple as compared to that of a conventional method since it does not require applying any spacer in the liquid crystal layer. Moreover, the manufacturing cost will not increase as the cell forming process. The following is the detailed description of the preferred embodiments of the present invention. Nevertheless, the manufacturing device designed in accordance with the present invention can be applicable in the cell forming process of the conventional liquid crystal panel.  
         [0035]    As shown in FIG. 5A depicting nine pixels for illustration, pixel  502  is spaced apart from each other by spacing  504 .  
         [0036]    As shown in FIG. 5B, a mask  510 , e.g. made of acrylic material, possesses of the dent  512  corresponding to pixel  502  wherein the dents  512  connect to each other via a trench  516 , having an outlet on the edge of the mask  510 . With reference to FIG. 5C showing the stereographic view of FIG. 5B, an important aspect is that the dent  512  formed on the mask  510  is running from top  520  through bottom  522  and that the trench  516  in connection with the dent  512  is formed either on the top  520  or through the bottom with one end extending outside the mask  510 .  
         [0037]    As shown in FIG. 6, a sealant  606  is applied along the edge of (not shown in FIG. 6) a substrate  604  and UV gel is further applied to cause curing of the sealant  606 . Thereafter, the cell forming process by utilizing the said mask is performed on the LCOS panel in order to generate a uniform cell gap, approximately 15-20 micron. The manufacturing device employed in the cell process is hot press apparatus and vacuum press apparatus, for example. An explanation with respect to the aforesaid two apparatus is given below.  
         [0038]    As shown in FIG. 7, the hot press apparatus includes a hot plate  702 ,  704  and a cushion  706 ,  708 , which are placed below the plate  702  and above the plate  704 , respectively. A mask  510  is deposited below the cushion  706 , and a LCOS panel  604  is placed on a conveyor belt  712 . The cushion  706  and  708  which are made of soft material works to evenly distribute the heat energy passed on by the hot plate  702  and  704  in avoiding the occurrence of partial overheating during the cell forming process as well as absorbing partial overstress. At the beginning, the hot plate  702 , the cushion  706  and the mask  510  exert pressure P on the LCOS panel simultaneously, and the heat energy generating from the heat plate  702 ,  704  pass through the cushion  706 ,  708  to make the sealant  606  curing. The dent  512  of the mask  510  is corresponding to the pixel  502  (display area), while the other portion is corresponding to the space  504  (non-display area). The trench  516  of the mask  510  is either facing the cushion  706  or the substrate  602 .  
         [0039]    As shown in FIG. 8, when the LCOS panel undergoes the cell forming process, only the space  504 , not the pixel, is subject to a local pressure. As the sealant  606  inserted between the substrates  602 ,  604  is made of some fiber material, it can sustain stress and prevent contact between the substrate  602  and the substrate  604 . Furthermore, when the cushion  706  and the mask  510  press closely on the substrate  602 , the non-dent portion will have direct contact with the substrate  602  and a chamber  802  will be formed between the cushion  706  and the dents of the mask  510 . In the hot press process, the heat energy will conduct to the cushion  706  and indirectly increase the temperature inside the chamber  802 . While the temperature within the chamber  802  is getting higher, the pressure is increasing; therefore, it is a likelihood of transformation on the substrate  602 . To circumvent this problem, the mask  510  has the trench structure  516  (as shown in FIG. 5C) for releasing the air circulating within the chamber  802  outside the mask.  
         [0040]    As above, the trench  516 , acting as an outlet, is designed for the purpose of keeping a balance between the air pressure inside the chamber  802  and the outside atmosphere. Without limitation to the methods provided in FIG. 5B- 5 C, the trench connection can be vertical, crosswise, or any other methods. A uniform cell gap can be achieved by connecting dents with trenches and having an outlet for air expelling.  
         [0041]    As described above, the object of forming a uniform cell gap on the LCOS panel can be achieved by utilizing a mask in the cell forming process. The said mask has dents and trenches, and such trenches connect with the external atmosphere. In performing the cell process, the dent is aimed at the pixel (display area) while the non-dent portion is concentrated on the non-display area. A local pressure, aimed at the non-display area portion, is exerted on the LCOS panel and the connecting trench functions as an outlet to let go the air above the substrate to the outside, thereby generating a regular cell gap.  
         [0042]    In addition to the above-disclosed hot press apparatus, the vacuum press apparatus is also frequently seen in the cell forming process. As shown in FIG. 9, the vacuum press apparatus has a heat plate  902  with vacuity holes on both the right and left side. A heat-conducting plate  906  is disposed above the hot plate  902 , acting as the cushion  706  in the hot press, in order to secure even heat distribution. A LCOS panel and a mask are accordingly stacked on the heat-conducting plate  906 . Thereafter, a silicon membrane  910  covers the heat plate  902 , the heat-conducting plate  906  and the LCOS panel to form a sealed space. In the cell forming process, the air below the silicon membrane  910  will be evacuated via the vacuity hole  908  thereby generating a downward pressure on the LCOS panel. The substrates  602 ,  604  are thus assembled.  
         [0043]    Although the aforesaid embodiments are illustrated with reference to the hot press apparatus and vacuum press apparatus, under the spirit of this invention, the mask contemplated according to this invention can find application in any press machine without limitation to the above-mentioned. For example, the press machine with UV-irradiation can achieve an equal cell gap in utilization of the mask according to this invention.  
         [0044]    Still further, the mask contemplated according to this invention can also apply to the traditional manufacturing process for liquid crystal panel. The usual methods for solving the uneven cell gap problem is dispersing spacer or forming photo spacer between pixels. Such conventional processes can utilize said mask to obtain an even cell gap. Moreover, the above explanation of the embodiments is focused the production process of the LCOS panel, but the mask contemplated according to this invention and the aforesaid cell process are capable of finding application in all manufacturing process of liquid crystal display panel.  
         [0045]    The advantage of this invention disclosed in the above embodiments is to manufacture a panel with a regular cell gap so as to enhance the image quality and prevent a Newton ring. Furthermore, a uniform cell gap can be obtained by utilizing the conventional manufacturing device, e.g. hot press and vacuum press, together with the mask contemplated according to this invention without increasing manufacturing cost.  
         [0046]    Once given the above disclosure, many other features, modifications, and improvements will become apparent to the skilled artisan. Such other features, modifications, and improvements are, therefore, considered to be a part of this invention, the scope of which is to be determined by the following claims.