Abstract:
The present invention discloses a liquid crystal display device, comprising: a first upper substrate including: a) a switching element on the first upper substrate; b) a passivation film formed over the whole surface of the first upper substrate while covering the switching element; c) a pixel electrode on the passivation film; d) a black matrix formed on the passivation film and over the switching element; e) a color filter formed over the pixel electrode; and f) a first orientation film formed on the black matrix and the color filter and above the pixel electrode; a lower second substrate having a common electrode and a second orientation film, the orientation film formed on the common electrode; sealing the first and second substrates with a sealant and a liquid crystal layer interposed between the first upper and second lower substrates.

Description:
CROSS REFERENCE 
     This application claims the benefit of Korean Patent Application No. 1999-32448, filed on Aug. 7, 1999, under 35 U.S.C. § 119, the entirety of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display (LCD) device and a method of manufacturing the same. 
     2. Description of Related Art 
     Recently, a liquid crystal display device adopts a structure wherein a color filter and a black matrix are formed over a thin film transistor array substrate to obtain a higher aperture ratio. The liquid crystal display device having such a structure (hereinafter, referred to simply as “the C/F and BM on array structure”) includes a top substrate, a bottom substrate, and a liquid crystal layer interposed between the two opposite substrates. The bottom substrate has an array of thin film transistors formed over the top surface of the bottom substrate, and both a black matrix and a color filter are formed over the thin film transistor array. 
     As described above, the liquid crystal display device having the C/F and BM on array structure has the advantage of a high aperture ratio. However, most of the liquid crystal display devices having the C/F and BM on array structure have an additional black matrix formed over the bottom surface of the top substrate in order to prevent a diffused reflection, or a reflection or dispersion of light. 
       FIG. 1  is a plan view illustrating arrangement of the thin film transistors and the pixels of the conventional liquid crystal display device having the C/F and BM on array substrate. 
     Referring to the  FIG. 1 , on a first substrate  10  of the liquid crystal display device, a plurality of gate lines  32  are arranged in a transverse direction and spaced apart from each other, and a plurality of data lines  36  are arranged in a longitudinal direction perpendicular to the gate lines  32  and spaced apart from each other. Pixel electrodes A 1  to A 9  are respectively formed over an area defined by the two adjacent gate lines  32  and two adjacent data lines  36 , and thin film transistors  20  are respectively formed near cross points of the gate lines  32  and the data lines  36 . 
     Each of the thin film transistors  20  has a gate, a source, and a drain electrode. The gate electrode, the source electrode and the drain electrode are electrically connected with the gate line  32 , the data line  36 , and the pixel electrode, respectively. 
       FIG. 2  is a cross sectional view showing the typical transmissive liquid crystal display device having the C/F and BM on array structure. Referring to  FIG. 2 , in the conventional liquid crystal display device, a second substrate  50  (as an upper substrate) is aligned with the first substrate  10  (as a lower substrate), a liquid crystal layer  60  is interposed between the two opposite substrates  10  and  50 , and a back light device  80  is positioned under the first substrate  10 . 
     On the first substrate  10 , a gate electrode  22  of the thin film transistor  20  is formed, and a gate insulating layer  42  is formed on the exposed surface of the substrate  10  while covering the gate electrode  22 . 
     On the gate insulating layer  42 , a semiconductor island  24  of the thin film transistor  20  is formed over the gate electrode  22 , and an ohmic contact layer  26  of the thin film transistor  20  is formed on the semiconductor island  24 . 
     Further, the source and the drain electrodes  28   a  and  29   b  (spaced apart from each other) are formed covering the ohmic contact layer  26  over the semiconductor island  24 , and a passivation film  48  is formed covering the thin film transistors  20 , and has a contact hole  30  on a predetermined portion of the drain electrode  28   b . The pixel electrode  102  is formed on the passivation film  48  and is electrically connected with the corresponding drain electrode  28   b  through the corresponding contact hole  30 . A first black matrix  46  is formed on a portion of the passivation film  48  over the TFT. 
     Color filter  104  of red (R), green (G) and blue (B) are formed on the corresponding pixel electrode  102 , respectively.  FIG. 2  shows only the color filter layers G and R. 
     On the color filter  104  and the black matrix  46 , a first orientation film  44  is formed and faced with liquid crystal layer  60 . 
     On the bottom surface of the second substrate  50 , a second black matrix  56  is formed. The second black matrix  56  has the almost same shape as the black matrix  46  of the first substrate  10 . A common electrode  52  is formed to cover the second black matrix  56 . 
     On the bottom surface of the common electrode  52 , a second orientation film  54  is formed and faced with the liquid crystal  60 . 
     At this point, the first black matrix  46  of the first substrate  10  serves to prevent light from passing through the gap between the gate line  32  and the pixel electrode  102  and the data line  36  and the pixel electrode  102 , and shield the thin film transistors  20  from incident light. In other words, the first black matrix and the color filter are usually formed at the substrate having the thin film transistors in order to improve the aperture ratio by minimizing an alignment margin which is employed when the first and second substrates  10  and  50  are aligned with and fixed to each other. 
     However, the second black matrix  56  of the second substrate  50  is adopted to prevent a degradation of a contrast ratio, or a variation of the colors. The variation of colors may occur when elements of dispersed light passing through the respective color filter layers are mixed in a region of the adjacent color filter layer. It is preferred that the width of the second black matrix  56  is narrower than that of the first black matrix  46  in order not to affect the alignment margin. 
     Though the width of the second black matrix  56  is narrower than that of the first black matrix  46 , since both the first and the second substrates have the first and second black matrices, respectively, the substrate-aligning process is complicated, leading to increase in alignment error. That is to say, the addition of the second black matrix results in an addition of an inferiority factor to the substrate-aligning process. 
     Further, the number of processes for forming the second black matrix  56  at the second substrate is increased due to the addition of the additional black matrices  56 . 
     For the foregoing reason, there is a need for a liquid crystal display device that is free from the effect of the dispersion reflection, and has a high aperture ratio and a simplified substrate-aligning process. 
     SUMMARY OF THE INVENTION 
     It is an objective of the present invention to provide a liquid crystal display device having a high image quality of contrast, high aperture ratio and a simplified substrate-aligning process. 
     The present invention discloses a liquid crystal display device, comprising: 
     an upper substrate including: a) a switching element on the upper substrate; b) a passivation film formed over the whole surface of the upper substrate while covering the switching element; c) a pixel electrode on the passivation film; d) a black matrix formed over the switching element; e) a color filter formed over the pixel electrode; and f) a first orientation film formed on the black matrix and the pixel electrode; a lower substrate having a common electrode and a second orientation film, the orientation film formed on the common electrode; and a liquid crystal layer interposed between the upper and lower substrates. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which like reference numerals denote like parts, and in which: 
         FIG. 1  is a plan view illustrating arrangement of the thin film transistors and the pixels of the conventional liquid crystal display device; 
         FIG. 2  is a partial cross-sectional view illustrating the conventional liquid crystal display device; 
         FIG. 3  is a simplified cross-sectional view illustrating a configuration of the liquid crystal display device according to a preferred embodiment of the present invention; 
         FIG. 4  is a partial cross-sectional view illustrating a liquid crystal display device according to a preferred embodiment of the present invention; 
         FIG. 5  is a partial cross-sectional view illustrating a modification of the liquid crystal display device according to a preferred embodiment of the present invention; and 
         FIG. 6  is a partial cross-sectional view illustrating another modification of the liquid crystal display device according to a preferred embodiment of the present invention. 
         FIG. 7  is a simplified cross-sectional view illustrating a configuration of the liquid crystal display device according to a preferred embodiment of the present invention; 
         FIG. 8  is a partial cross-sectional view illustrating a liquid crystal display device according to another preferred embodiment of the present invention; 
         FIG. 9  is a partial cross-sectional view illustrating a modification of the liquid crystal display device according to another preferred embodiment of the present invention; and 
         FIG. 10  is a partial cross-sectional view illustrating another modification of the liquid crystal display device according to another preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference will now be made in detail to a preferred embodiment of the present invention, examples of which are illustrated in the accompanying drawings. 
       FIG. 3  is a schematic view illustrating a transmissive liquid crystal display device according to a preferred embodiment of the present invention. As shown in FIG.  3 , the transmissive liquid crystal display device according to the preferred embodiment of the present invention includes a back light device  80  and a liquid crystal panel  90 . The liquid crystal display panel  90  has a first substrate  10  and a second substrate  50  with a liquid crystal layer (not shown) interposed there-between. The liquid crystal display panel  90  is located over the back light device  80  so that a bottom surface of the second substrate  50  is adjacent to the back light device  80 . 
     As the upper substrate, the first substrate  10  has pixel electrodes, thin film transistors as a switching element, color filters, and a black matrix disposed between boundaries of the color filters. As the lower substrate, the second substrate  50  has a common electrode. 
       FIG. 4  is a cross sectional view illustrating the transmissive liquid crystal display device according to the preferred embodiment of the present invention. As shown in  FIG. 4 , an upper substrate  10  has a thin film transistor, a black matrix  46 , a pixel electrode  102  and a color filter  104 . The upper substrate  10  is the one in which the thin film transistor array substrate is turned upside down. The thin film transistor  20  has a gate electrode  22 , a semiconductor layer  24 , an ohmic contact layer  26 , a source electrode  28   a  and a drain electrode  28   b . To manufacture the upper substrate  10 , first the gate electrode  22  is formed on the upper substrate  10 , and then a gate insulating layer  42  is formed on the exposed bottom surface of the upper substrate  10  while covering the gate electrode  22 . The gate electrode  22  extends from the gate line (not shown) and made of Al or Cr, and the gate insulating layer is made of an inorganic or organic material. The semiconductor layer  24  in the form of an island is formed over the gate electrode  22 , and the ohmic contact layer  26  is formed on the semiconductor layer  24  by ion-doping. The source and drain electrodes  28   a  and  28   b  are formed to overlap the ohmic contact layer  26 , respectively. The source and drain electrode  28   a  and  28   b  are made of Al or Cr. The source electrode  28   a  extends from the data line (not shown). Then, a passivation film  48  is formed over the whole surface of the upper substrate  10  while covering the source and drain electrodes  28   a  and  28   b . The passivation film  48  is made of an inorganic or organic material. The passivation film  48  has a contact hole  30  on a predetermined portion of the drain electrode  28   b . The pixel electrode  102  is formed on the passivation film  28  and is electrically connected with the drain electrode  28   b  through the contact hole  30 . The pixel electrode  102  is made of indium tin oxide (ITO). The black matrix  46  is formed over the TFT and the gate and data lines, and the color filter  104  is formed over the pixel electrode  102 . Finally, a first orientation film  44  is formed covering the black matrix  46  and color filter  104 . After manufacturing, the thin film transistor array substrate  10  is turned upside down to align with the lower substrate  50 . 
     The black matrix  46  prevent light of the back light device  80  from passing through the gaps between the gate line and the pixel electrode and the data line and the pixel electrodes. Also, the black matrix  46  shields the thin film transistors from incident light and prevents the mixing of dispersed portions of light passing through the respective color filter layers. The mixing of the light passing through the respective color filters results in degradation of a contrast ratio or variation of the colors. To maximize an aperture ratio, the pixel electrodes may overlap the gate and data lines so that the black matrix is formed only over the thin film transistor. Since the gaps are excluded, the black matrices have a smaller size, serving only to shield the thin film transistors from the light of the back light device  80 , and thus the aperture ratio becomes maximized. In that case, the gate and data lines prevent the above-mentioned light leakage and the mixing of the disposed portion of light passing through the respective color filter layers. 
     Further, the first orientation film  44  is preferably made of a polyimide film. 
     The lower substrate  50  has a common electrode  52  and a second orientation film  54  formed on the common electrode  52 . The common electrode  52  is preferably made of a transparent conductive material like indium tin oxide (ITO), and the second orientation film  54  is preferably made of a polyimide film. 
     When the upper and lower substrates  10  and  50  are aligned with each other and sealed by a sealant, the liquid crystal is injected into a gap between the upper and lower substrates  10  and  50  so that the liquid crystal layer  60  is interposed between the first and second orientation film  44  and  54 . 
     As described above, by using the thin film transistor array substrate  10  turned upside down as the upper substrate, the degradation of the contrast resulting from the mixing of the dispersed light can be prevented. 
     Further, since the second substrate has only the common electrode  52  and the second orientation film  44  without additional black matrices, a process of aligning the two substrates becomes simplified. That is to say, when aligning the upper substrate having the black matrices with the lower substrate having no black matrices, an alignment margin of the aligning process is not affected by the black matrices of the lower substrate. 
     On the contrary, when aligning the upper substrate having the black matrices with the lower substrate having another black matrices, an alignment margin of the aligning process is affected by a relative position between the black matrices of the upper substrates and the black matrices of the lower substrate. 
       FIG. 5  shows a modification of the liquid crystal display device according to a preferred embodiment of the present invention. 
     As shown in  FIG. 5 , in order to prevent a reflection of incident light from the gate electrode, the source electrode, the drain electrode, and the gate and data lines, a gate light absorbing film  34 , a source light absorbing film  38   a , and a drain light absorbing film  38   b  are formed under the gate electrode  22 , the source electrode  28   a , and the drain electrode  28   b , respectively. Further, the source light absorbing film  38   a  shields the data line (not shown) from incident light, and the gate light absorbing film  34  shields the gate line (not shown) from incident light. The light absorbing films  34 ,  38   a  and  38   b  are made of a low reflectance material such as an oxidation film, or a nitride film, and a black resin. 
     In other words, after a first light absorbing film for the gate light-absorbing pattern  24  is deposited on the first substrate  10 , a first metal layer for the gate electrodes  18  and the gate lines such as aluminum or chromium is deposited on the light absorbing film. Then, the light absorbing film and the first metal layer are patterned at the same time so as to form the gate light-absorbing layer  34 , the gate electrodes  22  and the gate lines (not shown). 
     Further, before a second metal layer for the source and the drain electrodes  28   a  and  28   b  and the data lines are deposited, a second light absorbing film is deposited over an gate insulating layer  42  so as to cover an ohmic contact layer  26 . Then, the second metal layer is deposited on the second light absorbing film, and the second metal layer and the second light absorbing film are patterned at the same time so as to form the source and drain light-absorbing films  38   a  and  38   b , the data lines, and the source and the drain electrodes  28   a  and  28   b.    
     Natural light incident to a top surface of the first substrate  10  is not reflected by metal patterns of the first substrate  10  such as the gate electrodes  22 , the gate lines, the data lines, and the source and the drain electrodes  28   a  and  28   b  because the gate light absorbing film  34  and the source and drain light-absorbing films  38   a  and  38   b  absorb the natural incident light. Thus, a dazzling problem that the reflected light dazzles the eyes of an observer is greatly reduced. 
       FIG. 6  shows another modification of the liquid crystal display device according to the preferred embodiment of the present invention. 
     As shown in  FIG. 6 , the data light-absorbing pattern  38  is formed between a gate insulating layer  42  and a semiconductor layer  24 . That is to say, before a semiconductor layer  24  is deposited, the second light absorbing film is deposited on the gate insulating layer  42  and patterned so as to form the data light-absorbing pattern  38 . 
     Hereinbefore, the preferred embodiment of the present invention is explained centering on the transmissive liquid crystal display device, but the preferred embodiment of the present invention can be also directed to the reflective liquid crystal display device.  FIGS. 7 to 10  shows the reflective liquid crystal display device according to the preferred embodiment of the present invention. The reflective liquid crystal display device according to this preferred embodiment of the present invention has the same configuration as the transmissive liquid crystal display device, except that the back light device  80  is not present, and the common electrode  52  is made of an opaque conductive material. Therefore, the detailed explanation for the reflective liquid crystal display device according to the preferred embodiment of the present invention is omitted for the sake of the simplicity. 
     As described herein before, according to the preferred embodiment invention, the liquid crystal display device can have a high aperture ratio, a high display quality and a high contrast ratio. Further, the liquid crystal display device can be manufactured by a simplified process. Besides, the dazzling of the screen due to the reflection of incident light can be prevented. 
     The present invention is not intended to be limited to the specific form set forth herein, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents, as can be reasonably included within the spirit and scope of the invention.