Patent Document

This is a division of application No. 09/235,205 filed Jan. 21, 1999 now U.S. Pat. No. 6,445,435. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a liquid crystal display device, and more particularly, an in-plane switching mode liquid crystal display device having a high aperture ratio. 
     2. Discussion of Related Art 
     Twisted nematic liquid crystal display devices (hereinafter TN LCDs) having high image quality and low power consumption are widely applied to flat panel display devices. The TN LCDs, however, have a narrow viewing angle due to refractive anisotropy of liquid crystal molecules. 
     To solve this problem, a multi-domain LCD such as a two-domain TN LCD(TDTN LCD) and a domain divided TN LCD(DDTN LCD), and a TN LCD including an optical compensation film have been introduced. In such LCDs, however, a contrast ratio is decreased and a color shift is generated depending on a viewing angle. 
     Further, for the purpose of a wide viewing angle, an in-plane switching mode LCD is also proposed. The in-plane switching mode liquid crystal display device, which is suggested to materialize wide viewing angle, is disclosed in the JAPAN DISPLAY 92 P547, Japanese Patent Unexamined Publication No. 7-36058, Japanese Patent Unexamined Publication No. 7-225388 and ASIA DISPLAY 95 P707, and etc. 
     FIG. 1A is a plan view of a unit pixel of a conventional in-plane switching mode active matrix LCD. FIG. 1B is a sectional view according to line I-I′ of FIG.  1 A. As shown in the drawings, the apparatus comprises a gate bus line  1  and a data bus line  2  in which the lines  1 ,  2  are perpendicularly arranged in a matrix form on a transparent first substrate  10  thereby defining an unit pixel region, a common line  3  arranged parallel to the gate bus line  1  in the pixel region, thin film transistor (TFT) formed adjacent a cross point of the gate bus line  1  and the data bus line  2 , and a data electrode  8  and a common electrode  9  formed in the pixel region. 
     The TFT includes a gate electrode  5  electrically coupled with the gate bus line  1 , a gate insulator  12  on the gate electrode  5 , a semiconductor layer  15  on the gate insulator  12 , a channel layer on the semiconductor layer  15 , and source/drain electrodes  6 ,  7  which are electrically coupled the data bus line  2  and the data electrode  8  respectively. 
     The common electrode  9  is formed concurrently with the gate electrode  5  and electrically coupled to the common line  3 . Further, a passivation layer  20  and a first alignment layer  23   a  are deposited on the inner surface of the first substrate  10 . 
     On a transparent second substrate  11 , a black matrix  28  is formed to prevent a light leakage generating around the TFT, the gate bus line  1 , and the data bus line  2 . A color filter layer  29 , an over-coat layer (not illustrated), and a second alignment layer  23   b  are formed on the black matrix  28  in sequence. Finally, a liquid crystal layer  30  is formed between the first and second alignment layers  23   a,    23   b.    
     In general, a storage capacitor in a liquid crystal display device is applied to prevent the apparatus from a gray inversion, a flicker, and an afterimage. Methods of forming this storage capacitor are divided into a storage on gate (SOG) mode and a storage on common (SOC) mode. In the SOG mode, some part of the (n−1) th  gate bus line is applied as a storage capacitor in the n th  pixel region. Further, in the SOC mode, a separated electrode for storage capacitor is electrically coupled to the common electrode. 
     For the use of the above storage capacitor, the aperture ratio is decreased, and the metal lines may cause a short state, thereby decreasing a yield. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to an in-plane switching mode LCD that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide an in-plane switching mode LCD having the high aperture ratio and the high yield by using the SOG mode storage capacitor only, or both SOG mode storage capacitor and SOC mode storage capacitor. 
     Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     In order to achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an in-plane switching mode liquid crystal display device comprises first and second substrates; a data bus line and a gate bus line arranged in a matrix on said first substrate and defining a unit pixel region; a thin film transistor (TFT) formed adjacent a cross point of the gate bus line and the data bus line, and a data electrode which partially covers adjacent the gate bus line; a passivation layer on the TFT and the data electrode; a common electrode substantially parallel to the data electrode and covering the gate bus lines of n th  and (n+1) th , or n th  and (n−1) th ; a common line covering the gate bus lines of n th  and (n+1) th , or n th  and (n−1) th ; a first alignment layer on the common electrode; a black matrix for preventing a light leakage which is generated around the TFT, the gate bus line, and the data bus line; a color filter layer and a second alignment layer on the black matrix in sequence; and a liquid crystal layer between said first and second substrates. 
     A storage capacitor is formed by the gate bus line, the data electrode, and the common electrode or the common line. 
     In another embodiment according to the present invention, certain part of the data electrode covers the n th  gate bus line. In addition, a part of the common electrode covers adjacent the data electrode and another part of the common electrode does not cover the opposite data electrode and the gate bus line. In this case, the storage capacitor is formed by the gate bus line, the data electrode, and the common electrode or the common line. 
     According to another embodiment of the present invention, a liquid crystal display device has a substrate, first and second gate lines arranged substantially in parallel above the substrate, a bus line arranged to intersect the first and second gate lines to define a pixel, a transistor having a source and a drain formed near an intersection part of the bus line and the first gate line, the source being connected to the bus line, and at least one data electrode connected to the drain of the transistor. A passivation layer is generally formed above the transistors and the at least one data electrode. Moreover, at least one common electrode is arranged above the passivation layer in parallel with the second gate line, the common electrode and the data electrode. In this configuration, the portions of at least two of the second gate line, the data electrode and the common electrode are overlapping with each other. 
     According to one feature of the present invention, the portions of the second gate line, the data electrode and the common electrode all overlap with each other. Alternatively, the second gate line has no overlapping portions with the data electrode and the common electrode. 
     According to another feature of the present invention, the data electrode has no overlapping portions with the common electrode. Alternatively, the second gate line has no overlapping portions with the common electrode. 
    
    
     These and other aspects, features and advantages of the present invention will be better understood by studying the detailed description in conjunction with the drawings and the accompanying claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
     FIG. 1A is a plan view of a unit pixel of a conventional in-plane switching mode LCD; 
     FIG. 1B is a sectional view according to line I-I′ of FIG. 1A; 
     FIG. 2A is a plan view of a unit pixel according to a first embodiment of the present invention; 
     FIG. 2B is a sectional view according to line II-II′ of FIG. 2A; 
     FIG. 3A is a plan view of a unit pixel according to a second embodiment of the present invention; 
     FIG. 3B is a sectional view according to line III-III′ of FIG. 3A; 
     FIG. 3C is a sectional view of a third embodiment of the present invention; and 
     FIG. 3D is a sectional view of a fourth embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiment of the present invention, example of which is illustrated in the accompanying drawings. FIG. 2A is a plan view of a unit pixel according to a first embodiment of the present invention. FIG. 2B is a sectional view according to line II-II′ of FIG.  2 A. 
     As shown in the drawings, in a unit pixel region of LCD according to the first embodiment of the present invention, two gate bus lines  101 ,  101 ′ and two data bus line  102 ,  102 ′ are perpendicularly arranged in a matrix form on a transparent first substrate  110  thereby defining the unit pixel region. Actually, LCDs have a plurality of pixel regions(n×m) including a large number of gate bus line(n) and data bus line(m). A gate insulator  112  is formed on the gate bus lines  101 ,  101 ′. The gate insulator  112  made of any suitable non-conductive materials, such as SiNx and SiOx, is formed on the gate electrode preferably by chemical vapor deposition(CVD) method. 
     A semiconductor layer  115  as channel layer is formed on the gate insulator  112  by depositing and etching an a-Si. An ohmic contact layer  116  made of a n +  a-Si is formed on the semiconductor layer  115 . The data bus lines  102 ,  102 ′, a source electrode  106 , and a data electrode  108  are formed above the ohmic contact layer  116  and the gate insulator  112 . Then the data electrode  108  is formed by etching a metal thin film preferably made of Al, Cr, Ti, or Al alloy after they are deposited on the gate insulator  112  by a sputtering method. 
     Alternatively, after depositing and patterning the gate bus line made of Al, the gate electrode made of Cr is patterned. After that, on the substrate which the gate bus line is patterned, the gate insulator, the semiconductor layer and the ohmic contact layer are formed in sequence. The data electrode and the source/drain electrode are formed by depositing and patterning Cr after pad opening. 
     The passivation layer  120  is formed on the TFT, the data bus lines  102 ,  102 ′, the data electrode  108 , and the gate insulator  112  by depositing an inorganic material, such as SiNx or SiOx, or an organic material such as benzocyclobutene(BCB). 
     Further, after pad opening, a common electrode  109  and common bus line  103  are formed by etching a thin metal film preferably made of Al, Mo, Ta, Cr, Al, or indium tin oxide(ITO) alloy after they are deposited on the substrate  110  by a sputtering method, then a first alignment layer  123   a  is formed thereon. The common electrode  109  which is substantially parallel to the data electrode  108  is formed on the gate bus lines  101 ,  101 ′. 
     A circular mark  125  represents a group of electrodes which are overlapped to form a storage capacitor. In the present invention, the storage capacitor is formed by the common electrode  109  which is substantially parallel to the data electrode  108  and covers the gate bus lines of n th  and (n+1) th , or n th  and (n−1) th  and the common line which is on a same plane of the common electrode and covers the gate bus lines of n th  and (n+1) th , or n th  and (n−1) th . 
     On a second substrate  111 , a black matrix  128  is formed to, prevent a light leakage generating around the TFT, the gate bus lines  101 ,  101 ′ and the data bus lines  102 ,  102 ′ by etching a thin layer made of Cr, CrOx, or black resin which are deposited by sputtering method. A color filter layer  129 , an over-coat layer (not shown), and a second alignment layer  123   b  are formed on the black matrix  128  in sequence, as shown in FIG.  2 B. Finally, a liquid crystal layer  130  is formed between the first and second alignment layers  123   a ,  123   b.    
     Preferably, each of alignment directions of the first and second alignment layers  123   a ,  123   b  is determined by a rubbing method using polyamide, polyimide, SiO 2 , polyvinylalcohol(PVA) or polyamic acid, or by photo-alignment method using photosensitive material such as polyvinylcinnamate(PVCN), polysiloxanecinnamate(PSCN) or cellulosecinnamate(CelCN). 
     FIG. 3A is a plan view of a unit pixel according to a second embodiment of the present invention. FIG. 3B is a sectional view according to line III-III′ of FIG.  3 A. Regarding FIG.  3 A and FIG. 3B, the common electrode  119  and the common line  103  cover some part of the data electrode  108  but do not cover the gate bus lines  101 ,  101 ′. 
     FIG. 3C is a sectional view of a third embodiment of the present invention. In FIG.  3 C and similar to FIG. 3B, the common electrode  119  overlaps the data electrode  108 . However, the common electrode  119  and the data electrode  108  do not overlap any portion of the gate bus line  101 . The overlapping of the common electrode  119  and the data electrode  108  in effect creates a capacitor between the two layers. 
     FIG. 3D is a sectional view of a fourth embodiment of the present invention. As illustrated, the common electrode  119  does not overlap the data electrode  108 , but overlaps the gate bus line  101 . In addition, certain portions of the data electrode  108  overlaps the gate bus line  101 . The above conductive lines and electrodes in effect creates a capacitor between two overlapping conductive layers. Moreover, certain capacitance is formed even between non-overlapping conductive layers which are in near vicinity of each other. 
     In accordance with the present invention, it is possible to achieve the high aperture ratio by using SOG mode storage capacitor only, or both SOG mode storage capacitor and SOC mode storage capacitor. 
     Further, it is possible to prevent the apparatus from a short which may be generated between the gate bus line, the electrode, and the common electrode in the prior art. 
     It will be apparent to those skilled in the art that various modifications and variation can be made in the in-plane switching mode LCD of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Technology Category: g