Abstract:
A liquid crystal panel includes a first substrate having thereon a display active region; an inner spacer wall disposed on the first substrate along periphery of the display active region; an outer spacer wall disposed adjacent to the inner spacer wall on the first substrate; a groove formed between the inner spacer wall and the outer spacer wall; a seal spread in the groove; a second substrate being supported by the inner spacer wall and the outer spacer wall and being glued to the first substrate via the seal, wherein the first substrate, the second substrate and the inner spacer wall define a chamber; and a liquid crystal layer filling the chamber by using one-drop-fill process.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application is a continuation application of and claims priority to U.S. patent application Ser. No. 11/306,587, filed on Jan. 3, 2006, and entitled “LIQUID CRYSTAL PANEL HAVING MULTIPLE SPACER WALLS AND METHOD OF MAKING THE SAME” the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a liquid crystal panel, and more particularly, to a liquid crystal-on-silicon (LCOS) panel utilizing one or multiple spacer walls and one-drop-fill technology. 
         [0004]    2. Description of the Prior Art 
         [0005]    Liquid crystal-on-silicon (LCOS) micro-display panel is arguably the heart of the reflective LCOS projectors and rear-projection televisions. The LCOS micro-display devices are tiny, less expensive, and have high resolution. As known in the art, the difference between a LCOS micro-display and a conventional thin film transistor-liquid crystal display (TFT-LCD) is materials used for forming substrates. Both of a cover and a backplane are made of glass in a TFT-LCD, nevertheless, the cover in a LCOS display is made of glass, but the backplane in a LCOS display is a semiconductor silicon substrate. Therefore, a LCOS process combines LCD techniques and complementary metal-oxide semiconductor (CMOS) processes. 
         [0006]    Please refer to  FIG. 1  and  FIG. 2 , wherein  FIG. 1  is a schematic top view of a LCOS panel  10  according to the prior art and  FIG. 2  is a schematic cross-sectional view of the LCOS panel  10  taken along line I-I of  FIG. 1 . The prior art LCOS panel  10  comprises a silicon substrate  12  used as a backplane and a glass substrate  16  being composed of, for example, indium tin oxide (ITO) glass. The silicon substrate  12  further comprises a plurality of pixel arrays (not explicitly shown) formed on its display active region  14 . A liquid crystal layer  18  is sealed between the silicon substrate  12  and the glass substrate  16 . Spherical spacers  22  of approximately equal size are disposed between the silicon substrate  12  and the glass substrate  16 . In addition, a plurality of bonding pads  122  are formed on the longer side of the silicon substrate  12  used for soldering up the backplane and the cover in subsequent processes. 
         [0007]    In LCD devices, the thickness of the liquid crystal layer  18 , or the cell gap (i.e., the space between a transparent conducting substrate and a semiconductor substrate) has to be precisely controlled to a specific value so as to ensure the display performance. In order to maintain the cell gap, plastic beads, glass beads or glass fibers are normally interposed between two liquid crystal display substrates and used as spacers. Thus, this cell gap is defined by the spacer height. In a conventional LCD process, the spacers are positioned by spraying, so the positions between the two liquid crystal display substrates cannot be controlled accurately. Consequently, the display performance of the liquid crystal display device is affected due to light scattering by the spacers that are present in the light transmitting regions. Furthermore, the spacers tend to be mal-distributed so that the display performance in portions of the LCD with spacers bunched is impaired, and the uniformity of the cell gap cannot be precisely maintained. 
         [0008]    According to the prior art, seal glue  20  is applied to the periphery of the display active area  14  of the silicon substrate  10 . The seal glue  20  has a slit or break in it for liquid crystal injection in the subsequent processes. The prior art LCOS panel  10  has a drawback in that the design width of the seal glue  20  is about 2000 micrometers and the design width is about 500 micrometers, which occupy a large chip surface area. Further, in the traditional LC injection method, the cell will be vacuum filled by capillary attraction after the glass substrate  16  and the silicon substrate  12  are assembled. Such injection method has the drawbacks of wasting time and liquid crystal material. 
       SUMMARY OF THE INVENTION 
       [0009]    Accordingly, it is the primary object of the present invention to provide an improved LCOS panel and method of making in order to solve the above-mentioned problems. 
         [0010]    According to the claimed invention, a liquid crystal panel includes a first substrate having thereon a display active region; an inner spacer wall disposed on the first substrate along periphery of the display active region; an outer spacer wall disposed adjacent to the inner spacer wall on the first substrate, wherein the inner spacer wall and the outer spacer wall are of approximately equal height; a groove formed between the inner spacer wall and the outer spacer wall; a seal spread in the groove; a second substrate being supported by the inner spacer wall and the outer spacer wall and being glued to the first substrate via the seal, wherein the first substrate, the second substrate and the inner spacer wall define a chamber; and a liquid crystal layer filling the chamber by using one-drop-fill process. 
         [0011]    According to another preferred embodiment, a method of fabricating a liquid crystal panel is disclosed. The method comprises the following steps: 
         [0012]    (a) providing a first substrate comprising thereon a display active region; 
         [0013]    (b) depositing a dielectric layer over the first substrate by using various deposition methods; 
         [0014]    (c) etching a portion of the dielectric layer to expose the display active area and to form an inner spacer wall and an outer spacer wall enclosing the display active region, and a groove between the inner spacer wall and the outer spacer wall, wherein the inner spacer wall and the outer spacer wall are of approximately equal height; 
         [0015]    (d) spreading seal in the groove; 
         [0016]    (e) performing an one-drop-fill process to dispose drops of liquid crystal on the display active region within the inner spacer wall; 
         [0017]    (f) placing a second substrate on the first substrate, wherein the second substrate is supported by the inner and outer spacer walls and is glued to the first substrate via the seal; and 
         [0018]    (g) curing the seal. 
         [0019]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
           [0021]      FIG. 1  is a schematic top view of a liquid crystal-on-silicon (LCOS) panel according to the prior art; 
           [0022]      FIG. 2  is a schematic cross-sectional view of the LCOS panel taken along line I-I of  FIG. 1 ; 
           [0023]      FIG. 3  is a schematic top view of a LCOS panel according to one preferred embodiment of the present invention; 
           [0024]      FIG. 4  is a schematic cross-sectional view of the LCOS panel taken along line II-II of  FIG. 3 ; and 
           [0025]      FIG. 5  to  FIG. 9  are schematic, cross-sectional diagrams showing the method of fabricating a LCOS panel with dual spacer walls in accordance with one preferred embodiment of this invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Please refer to  FIG. 3  and  FIG. 4 , wherein  FIG. 3  is a schematic top view of a LCOS panel  50  according to one preferred embodiment of the present invention and  FIG. 4  is a schematic cross-sectional view of the LCOS panel  50  taken along line II-II of  FIG. 3 . The LCOS panel  50  comprises a silicon substrate  52  used as a backplane, and a glass substrate  56  being composed of, for example, indium tin oxide (ITO) glass. The silicon substrate  52  further comprises a plurality of pixel arrays (not explicitly shown) formed on its display active region  54 . A liquid crystal layer  58  is sealed between the silicon substrate  52  and the glass substrate  56 . 
         [0027]    It is one salient feature of the invention that the display active region  54  of the silicon substrate  52  is surrounded by dual spacer walls including an inner spacer wall  62  and an outer spacer wall  64 . According to the preferred embodiment of this invention, the inner spacer wall  62  and the outer spacer wall  64  are two parallel walls of approximately equal height. A groove  66  is provided in between the inner spacer wall  62  and the outer spacer wall  64  for accommodating seal  70 . The groove  70  also increases the effective contact area between the seal  70  and the silicon substrate  52  such that the adhesion is improved. The inner spacer wall  62  and the outer spacer wall  64  have a flat top surface  62   a  and a flat top surface  64   a , respectively. In addition, the plural bonding pads  522  are disposed on the shorter side of the silicon substrate  52 . 
         [0028]    According to this invention, the inner spacer wall  62  and the outer spacer wall  64  are fabricated at the last stage of the fabrication processes for making the silicon substrate  52 . The inner spacer wall  62  and the outer spacer wall  64  are fabricated and defined along the periphery of the display active region  54  by using standard semiconductor processes such as chemical vapor deposition (CVD) methods, chemical mechanical polish (CMP), lithography and etching. According to the preferred embodiment, the inner spacer wall  62  and the outer spacer wall  64  are made of dielectric materials such as silicon dioxide, but not limited thereto. 
         [0029]    In typical LCD devices, as mentioned above, spherical spacers such as plastic beads or glass beads are dispersed randomly on the entire silicon substrate, even in the display active region or viewing areas, or mixed with the glue seal. However, spacers in the viewing area of a display frequently lead to the reduced contrast of the display. In the present invention, the plastic beads or glass beads are not used and are replaced with the dual spacer walls, i.e., the inner spacer wall  62  and the outer spacer wall  64 . By doing this, the cell gap is effectively controlled so as to assure the proper operation of the LCD devices. Since the conventional spherical spacers such as plastic beads or glass beads are omitted, the cost of the panel product can be reduced. 
         [0030]    As shown in  FIG. 4 , it is another salient feature of the invention that by using the dual spacer walls, the design width of the seal  70  shrinks from 2000 micrometers to about 500 micrometers. By shrinking the design width of the seal  70 , the surface area of each panel can be reduced and the number of the panels of each wafer is increased. 
         [0031]    Please refer to  FIG. 5  to  FIG. 9 .  FIG. 5  to  FIG. 9  are schematic, cross-sectional diagrams showing the method of fabricating a LCOS panel with dual spacer walls in accordance with one preferred embodiment of this invention. As shown in  FIG. 5 , a wafer or silicon substrate  152  having thereon a display active region  154  is provided. The display active region  154  has therein an integrated control circuit, electrodes connected to the integrated control circuit, and metal mirror plates for reflecting light (not explicitly shown). It is understood that the integrated control circuit may comprises an array of transistors such as MOS transistors. A chemical vapor deposition process is carried out to deposit a silicon dioxide layer  112  over the silicon substrate  152 . The thickness of the silicon dioxide layer  112  is approximately equal to the cell gap of the LCOS panel. Thereafter, a photoresist pattern  114 , which defines the position and pattern of the dual spacer walls to be etched into the underlying silicon dioxide layer  112 , is formed over the silicon dioxide layer  112 . According to another embodiment, prior to the deposition of the silicon dioxide layer  112 , a protective film or an alignment film may be deposited over the silicon substrate  152 . 
         [0032]    As shown in  FIG. 6 , using the photoresist pattern  114  as an etching hard mask, an anisotropic dry etching process is carried out to remove the silicon dioxide layer  112  that is not covered by the photoresist pattern  114  until the silicon substrate  152  is exposed, whereby forming the dual spacer walls  160  enclosing the display active region  154 . The dual spacer walls  160  include an inner spacer wall  162  and an outer spacer wall  164 . The photoresist pattern  114  is then stripped. According to this invention, the inner spacer wall  162  and the outer spacer wall  164  are both continuous walls and have no break or slit. The inner spacer wall  162  minimizes the contact between the seal and the liquid crystal, thereby preventing potential pollution of the liquid crystal. 
         [0033]    Since the inner spacer wall  162  and the outer spacer wall  164  are fabricated by standard semiconductor processes, the deviation of the height of the spacer walls is very small. The cell gap between the silicon substrate  152  and glass substrate is effectively controlled so as to assure the proper operation of the LCD devices. A groove  166  is formed between the inner spacer wall  162  and the outer spacer wall  164 . As previously described, the groove  166  is used to accommodate seal and to increase the contact between the silicon substrate  152  and the seal. 
         [0034]    As shown in  FIG. 7 , after the formation of the dual spacer walls  160 , one-drop-fill (ODF) process is carried out to form liquid crystal drops on the silicon substrate  152 . The ODF process is to drop the liquid crystal  158  directly on display active region  154  within the inner spacer wall  162 . The ODF Process is a technology currently developed in the LCD field. With the utilization of this state-of-the-art technology, it increases the efficiency in the manufacturing of large sized panel. The ODF Process can save a great deal of time and liquid crystal material that has a competitive edge particularly for large size panel. For example, it requires about 5 days to fill the liquid crystal for a 30 inches panel according to the traditional vacuum suction method, but it only needs 5 minutes by adoption of the ODF method. Thereby the consumption of liquid crystal material can be reduced to approximately 40% as compared to the traditional method. 
         [0035]    As shown in  FIG. 8 , seal  170  is provided in the groove  166  between the inner spacer wall  162  and the outer spacer wall  164  under vacuum environment or reduced pressure. It is noteworthy that the volume of the seal  170  spread in the groove  166  is slightly greater than the space of the groove  166 . According to the preferred embodiment of this invention, the seal  170  may be photo hardening seal, ultraviolet-type seal or thermal hardening seal. 
         [0036]    Finally, as shown in  FIG. 9 , a glass substrate  156  is glued together with the silicon substrate  152  via seal  170  to form panel assembly. The glass substrate  156  is in parallel with the silicon substrate  152 . The panel assembly is then subjected to ultraviolet to cure the seal  170 . In another case, the panel assembly is treated with thermal process to harden the seal  170 . The panel assembly is then cut into panel die by using conventional methods. 
         [0037]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.