Abstract:
A liquid crystal display device is disclosed that is capable of preventing poor alignment caused by a column spacer to improve the contrast ratio. The liquid crystal display device includes a color filter and column spacers located between a first substrate and a second substrate. The column spacers maintain the cell gap between the first and second substrates. The color filter contains pixels having multiple sub-pixels of different colors. The column spacers in regions of sub-pixels of the same color are randomly formed within the regions.

Description:
This application claims the benefit of Korean Patent Application No. P2003-78853 filed in Korea on Nov. 8, 2003, which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device capable of preventing poor alignment caused by a column spacer to improve a contrast ratio. 
     2. Description of the Related Art 
     In general, a liquid crystal display (LCD) device controls the light transmittance of liquid crystal cells in response to video signals to thereby display pictures corresponding to the video signals on a liquid crystal display panel. To this end, the LCD device includes a liquid crystal display panel having liquid crystal cells arranged in an active matrix form, and driving circuits for driving the liquid crystal display panel. 
     Depending on a direction of an electric field driving a liquid crystal material, the LCD device is generally classified into two modes—a twisted nematic (TN) mode using a vertical electric field and an in-plane switching (IPS) mode using a horizontal electric field. 
     The TN mode LCD device drives the liquid crystal material using a vertical electric field formed between a common electrode and an opposing pixel electrode. The TN mode LCD device has high aperture ratios, but narrow viewing angles. The IPS mode LCD device drives the liquid crystal material using a horizontal electric field formed between the pixel electrode and the common electrode located in parallel on one substrate. The IPS mode LCD device has wide viewing angles, but low aperture ratios. 
       FIG. 1  is a plan view illustrating a related art IPS mode liquid crystal display panel. 
     Referring to  FIG. 1 , the IPS mode liquid crystal display panel includes: a color filter array substrate having a black matrix, a color filter, a planarization layer, a column spacer  13 , and an upper alignment layer, which are sequentially formed on an upper substrate whose rear surface is covered with materials (not shown) for a transparent electrode for preventing static electricity; a thin film transistor array substrate having a thin film transistor (TFT), a common electrode, a pixel electrode, and a lower alignment layer, all of which are formed on a lower substrate; and a liquid crystal material (not shown) injected in the inner space between the color array substrate and the thin film transistor array substrate. 
     The column spacer  13  is regularly formed at a defined location on a red sub-pixel R region within one pixel having red, green and blue sub-pixels to serve to maintain a cell gap between the color filter array substrate and the thin film transistor array substrate. Also, the column spacer  13  may be regularly formed at a defined location on a green sub-pixel G region within one pixel and may be regularly formed at a defined location on a blue sub-pixel B region within one pixel. 
     Meanwhile, a rubbing process is performed on the upper and the lower alignment films in order to control initial alignment of the liquid crystal disposed therebetween. In the rubbing process, a rubbing roller rolls up a rubbing material. The surface of the alignment film is rubbed using the rubbing roller with the rubbing material in a direction defined from upward to downward such as in a direction parallel to an alignment direction A of the column spacer  13  as shown in  FIG. 2 . 
     However, if the rubbing process is performed, then the rubbing material passes by the column spacer  13  regularly formed on the defined location, to thereby cause sectional damage at a particular portion of the rubbing material. 
     In other words, a rubbing scratch S, representing uneven alignment concentrated along the column spacer  13  arranged in a line as shown in  FIG. 2 , occurs, to thereby generate light leakage. As a result, a black brightness is increased, to thereby deteriorate the contrast ratio. 
     Meanwhile, in order to prevent the sectional damage in the rubbing material, as shown in  FIG. 3 , there has been proposed a structure, in which the column spacer  13  is formed within the other sub-pixels in one pixel. However, the red, green and blue color filters have different thicknesses due to process deviations. Accordingly, the cell gap is uneven. 
     SUMMARY 
     By way of introduction only, a liquid crystal display device according to an embodiment includes column spacers located between a first substrate and a second substrate to maintain a cell gap. The column spacers are randomly formed in sub-pixels of the same color. 
     The display device has pixels of multiple sub-pixels including red, green, and blue sub-pixels. A column spacer is located in each pixel. 
     The first substrate includes a black matrix, a color filter formed on the black matrix, and a common electrode formed on the color filter. 
     The first substrate includes a black matrix, a color filter formed on the black matrix, and a planarization layer formed to cover the color filter. 
     A method of fabricating a liquid crystal display device includes forming first and second substrates and forming column spacers maintaining a cell gap between the first and the second substrate. The column spacers in regions of sub-pixels of the same color are randomly formed within the sub-pixel regions. 
     Each pixel includes red, green, and blue sub-pixels and has a column spacer located therein. 
     Forming the first substrate includes: forming a black matrix; forming a color filter on the black matrix; and forming a common electrode on the color filter. 
     Forming the first substrate includes: forming a black matrix; forming a color filter on the black matrix; and forming a planarization layer to cover the color filter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description of the embodiments of the present invention reference the accompanying drawings, in which: 
         FIG. 1  is a plan view illustrating a related art IPS mode liquid crystal display panel; 
         FIG. 2  is a diagram representing a scratch made during a rubbing process of the related liquid crystal display panel; 
         FIG. 3  is a plan view illustrating the liquid crystal display panel having a structure in which a related art column spacer is formed within the other sub-pixels in one pixel; 
         FIG. 4  is a plan view illustrating a liquid crystal display panel according to one embodiment of the present invention; 
         FIG. 5  is a sectional view showing a portion of the liquid crystal display panel shown in  FIG. 4 ; 
         FIG. 6  shows randomly formed column spacers on the sub-pixel in the pixel shown in  FIG. 3 ; and 
         FIGS. 7A to 7F  are sectional views sequentially illustrating a method of fabricating a color filter array substrate of the liquid crystal display panel of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to  FIGS. 4 to 7 . 
       FIG. 4  is a plan view illustrating an IPS mode liquid crystal display panel according to an embodiment of the present invention, and  FIG. 5  is a sectional view showing a portion of the liquid crystal display panel shown in  FIG. 4 . 
     Referring to  FIGS. 4 and 5 , the IPS mode liquid crystal display panel includes: a color filter array  100  substrate having a black matrix  104 , a color filter  106 , a planarization layer  108 , a column spacer  113 , and an upper alignment layer  110 , all of which are sequentially formed on an upper substrate  102  whose rear surface is covered with materials (not shown) for a transparent electrode to prevent static electricity; a thin film transistor array substrate  120  having a thin film transistor (TFT)  130 , a common electrode  124 , a pixel electrode  134 , and a lower alignment layer  142 , all of which are formed on a lower substrate  122 ; and liquid crystal material (not shown) injected in the inner space between the color filter array substrate  100  and the thin film transistor array substrate  120 . 
     In the color filter array substrate  100 , the black matrix  104  is formed so as to overlap the area of the TFT  130  on the lower substrate  122  and with the area (not shown) of gate and data lines, and partitions the cell regions at which the color filter  106  is to be formed. The black matrix  104  serves to prevent light leakage and absorb external light, to thereby improve the contrast ratio. The color filter  106  is formed at the cell region partitioned by the black matrix  104 . The color filter  106  is formed by separate red (R), green (G), and blue (B) filters and represents red, green, and blue colors. The planarization layer  108  is formed to cover the color filter  106  and planarizes the upper substrate  102 . The column spacer  113  maintains the cell gap between the upper substrate  102  and the lower substrate  122 . 
     The column spacer  113  is formed on a red sub-pixel R region in one pixel including red, green, blue color filter  106 . Each column spacer  113  is randomly formed on each red sub-pixel R region irrespective of a defined regulation. Accordingly, when a rubbing process for aligning a liquid crystal material is performed, sectional damage of the rubbing material is prevented. 
     In the thin film transistor array substrate  120 , the TFT  130  includes: a gate electrode  132  along with a gate line  135  formed on the lower substrate  122 ; a semiconductor layer  140  formed to overlap the gate electrode  132  with a gate insulating layer  126  positioned therebetween; and source/drain electrodes  168  and  170  formed along with a data line  164  with the semiconductor layer  140  positioned therebetween. 
     The TFT supplies pixel signals from the data line to the pixel electrode  134  in response to scan signals from the gate line  135 . 
     The pixel electrode  134  is made of a transparent conductive material with a high light transmittance, and contacts a drain electrode  170  of the TFT  130  with a passivation film  144  positioned therebetween. The common electrode  124  is formed in a stripe form so as to alternate with the pixel electrode  134 . A common voltage to drive the liquid crystal material is applied to the common electrode  124 . 
     A horizontal electric field formed by the common voltage and a pixel voltage supplied to the pixel electrode  134  makes the liquid crystal material rotate in a horizontal direction. 
     As set forth above, according to the embodiment of the liquid crystal display panel, the column spacer  113  is randomly formed on the red sub-pixel R region in one pixel region without having a defined regulation. Accordingly, when a rubbing process is performed, sectional damage caused by the column spacer  113  is prevented and the alignment becomes uniform. Thus, the contrast ratio is improved. 
     More specifically, a rubbing process is performed on the upper and the lower alignment films  110  and  142  in order to control the initial alignment of the liquid crystal material. In the rubbing process, a rubbing roller rolls up a rubbing material. The surface of the alignment film is rubbed by using the rubbing roller with the rubbing material in a direction defined from upward to downward. When the rubbing process is performed, as shown in  FIG. 6 , the column spacer  113  is randomly formed on the sub-pixel providing equal color in each pixel irrespective of the particular regulation. Thus, the sectional damage of the rubbing material is prevented. 
     Accordingly, it is possible to prevent unevenness of the alignment occurring when the related art column spacer is regularly arranged. As a result, the light leakage is remarkably reduced. Hereby, the black brightness is decreased and thus, the contrast ratio is improved. 
       FIGS. 7A to 7F  are sectional views sequentially illustrating a method of fabricating the color filter array substrate of the IPS mode liquid crystal display panel according to an embodiment of the present invention. 
     First of all, an opaque material such as a nontransparent metal or a nontransparent resin is deposited on the upper substrate  102 . Then, the nontransparent material is patterned by photolithography using a mask and etching. Consequently, the black matrix  104  is formed as shown in  FIG. 7A . 
     A red resin is deposited on the upper substrate  102  having the black matrix formed thereon. Then, the red resin is patterned by photolithography using a mask and etching. Consequently, a red color filter R is formed as shown in  FIG. 7B . 
     A green resin is deposited on the upper substrate  102  having the red color filter R formed thereon. Then, the green resin is patterned by photolithography using a third mask and etching. Consequently, a green color filter G is formed as shown in  FIG. 7C . 
     A blue resin is deposited on the upper substrate  102  having the green color filter G formed thereon. Then, the blue resin is patterned by photolithography using a mask and etching. Consequently, a blue color filter B is formed as shown in  FIG. 7D . 
     A planarization material is deposited on the entire surface of the upper substrate  102  having the red, green, and blue color filters  106  formed thereon. Consequently, the planarization layer  108  is formed as shown in  FIG. 7E . 
     A spacer material is deposited on the upper substrate  102  having the planarization layer  108  formed thereon. Then, the spacer material is patterned by photolithography using a mask and etching. Consequently, the column spacer  113  is formed as shown in  FIG. 7F . The column spacer  113  is randomly formed on the sub-pixel R region providing a red color in each pixel having the red, green and blue filters  106  without having a particular regulation. 
     Meanwhile, the column spacer  113  may be formed on the thin film transistor array substrate to overlap the TFT, the gate line and the data line formed on the thin film transistor array substrate. 
     As set forth above, the upper alignment film  110  is applied on the upper substrate  102  in which the column spacer  113  is randomly formed. The lower alignment film  142  is applied on the lower substrate  122  in which the pixel electrode  134  is formed. Thereafter, the rubbing process for aligning the liquid crystal material is performed. 
     A method randomly forming a column spacer without having a particular regulation in a sub-pixel representing an equal color is easily applicable to not only a liquid crystal display panel of an in-plane-switching IPS mode but also a liquid crystal display of a twisted nematic TN mode and a vertical alignment VA mode. 
     As described above, according to the liquid crystal display device and the method of fabricating the liquid crystal display device herein, the column spacer is randomly formed without having a particular regulation in the sub-pixel providing the equal color. As a result, when the rubbing process is performed, sectional damage of the rubbing material and the light leakage caused by the scratch by the uneven alignment of the alignment film are prevented. Accordingly, the black brightness is decreased, to thereby improve the contrast ratio. 
     Although the present invention has been explained by the embodiments shown in the drawings described above, it should be understood to the ordinary skilled person in the art that the invention is not limited to the embodiments, but rather that various changes or modifications thereof are possible without departing from the spirit of the invention. Accordingly, the scope of the invention shall be determined only by the appended claims and their equivalents.