Patent Abstract:
A liquid crystal display device includes a driving circuit provided with a switching device on a liquid crystal display panel, the switching device including a plurality of thin film transistors connected in parallel and commonly interconnected using a gate electrode.

Full Description:
This application is a Divisional of application Ser. No. 10/876,619 filed Jun. 28, 2004, now U.S. Pat. No. 7,550,764 now allowed; which claims priority to Korean Patent Application No. 10-2003-57518, filed Aug. 20, 2003 all of which are hereby incorporated by reference for all purposes as if fully set forth herein. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a display device and a method of fabricating a display device, and more particularly, to a liquid crystal display device and a method of fabricating a liquid crystal display device. 
   2. Description of the Related Art 
   In general, a liquid crystal display (LCD) device controls light transmittance of a liquid crystal material using an electric field to display images. 
     FIG. 1  is a schematic plan view of an LCD device according to the related art. In  FIG. 1 , an LCD device includes an LCD panel  5  having liquid crystal cells arranged in a matrix configuration, and a driving circuit  7  for driving the LCD panel  5 . 
   Although not shown, gate lines and data lines are arranged to cross each other within the LCD panel  5 . Each of the liquid crystal cells is positioned at each area where the gate lines cross the data lines. In addition, the LCD panel  5  is provided with a pixel electrode and a common electrode for applying an electric field to each of the liquid crystal cells. Each pixel electrode is connected, via source and drain electrodes of a thin film transistor (TFT), which functions as a switching device, to any one of the data lines. Similarly, the gate electrodes of the TFT are connected to any one of the gate lines, thereby allowing a pixel voltage signal to be supplied to the pixel electrodes for each of the data lines. 
   The TFT allows the pixel voltage signal to be charged in a corresponding pixel electrode in response to a gate high voltage Vgh transmitted along the gate lines. Accordingly, the liquid crystal cells charge the corresponding pixel voltage signals from the data lines when the TFT is turned ON due to the gate high voltage Vgh that is sequentially supplied along the gate lines, and any remaining charge is retained when the TFT is turned ON again. The pixel voltage signal is to be charged in the liquid crystal cell of a certain n th -numbered gate line remaining due to a storage capacitor Cst (not shown) formed by an overlap of the pixel electrode and the gate line of a previous stage gate line. 
   In general, the gate high voltage Vgh is supplied to each of the gate lines for every frame only during a period of time that the gate line is driven, i.e., only during one horizontal period 1 H allowing the pixel voltage signal charged in the pixel electrode, and a gate low voltage Vgl is supplied during a rest period. The storage capacitor Cst remains charged with a voltage charged to the pixel electrode of a present stage gate line by the gate low voltage Vgl supplied to the gate line of the previous stage gate line. 
   In  FIG. 1 , the driving circuit  17  includes a gate driver  27  for driving the gate lines, a data driver  17  for driving the data lines, a timing controller  11  for controlling the gate driver  27  and the data driver  17 , and a power supply (not shown) for supplying various driving voltages used in the LCD panel  5 . The timing controller  11  controls driving timing of the gate driver  27  and the data driver  17 , and supplies a pixel data signal to the data driver  17 . The power supply generates driving voltages, such as the gate high voltage Vgh and the gate low voltage Vgl. The gate driver  27  sequentially supplies scanning signals to the gate lines to sequentially drive the liquid crystal cells on the LCD panel  5  on a one gate line-by-one gate line basis. The data driver  17  supplies data voltage signals to each of the data lines whenever the gate signal is supplied to any one of the gate lines. Accordingly, the LCD controls light transmittance by an electric field supplied between the pixel electrode and the common electrode in accordance with the pixel voltage signal for each liquid crystal cell, and thereby displays images. 
   The data driver  17  and the gate driver  27  are directly connected to the LCD panel  5 , and are both integrated into a plurality of integrated circuits (IC&#39;s). In addition, each of the data drive ICs  15  and the gate drive ICs  25  are mounted in a tape carrier package (TCP) to be connected to the LCD panel  5  using a tape automated bonding (TAB) system, or mounted onto the LCD panel  5  by a chip on glass (COG) system. 
   In  FIG. 1 , the drive IC&#39;s  15  and  25  are connected, via the TCPs  13  and  23 , to the LCD panel  5  by the TAB system, and are connected to each other and receive control signals and direct current voltage signals input from an exterior over signal lines mounted onto a printed circuit board (PCB)  31  and  33  connected to the TCPs  13  and  23 . For example, the data drive IC&#39;s  25  are connected in series via signal lines mounted on a data PCB, and commonly receive control signals and pixel data signals from the timing controller  11  and driving voltages from the power supply. The gate drive IC&#39;s  25  are connected in series via signal lines mounted on the gate PCB  33 , and commonly receive control signals from the timing controller and driving voltages from the power supply. 
     FIG. 2  is a schematic plan view of an LCD device having a gate driving circuit according to the related art. In  FIG. 2 , a gate driving circuit is mounted onto an LCD panel for manufacturing a thinner type LCD device, thereby reducing manufacturing costs. 
     FIG. 3  is a schematic plan view of an LCD device having a gate driving circuit and a data driving circuit according to the related art. In  FIG. 3 , an LCD panel includes a gate driving circuit, as well as a portion of a data driving circuit, formed on the LCD panel. 
   Switching devices have been proposed in the U.S. Pat. No. 6,522,768, which is hereby incorporated by reference in its entirety, that may be used in a driving circuit of an LCD device. Accordingly, although the switching devices, i.e., TFTs, have rapid response speeds, the TFTs are formed of amorphous silicon fabricated using simple processes and have relatively good uniformity rather than formed of polycrystalline silicon fabricated using more difficult processes, such as crystallizing a silicon layer using a laser beam. 
     FIG. 4  is a schematic plan view of a switching device for a driving circuit according to the related art. In  FIG. 4 , a switching device may be composed of a TFT that includes a gate electrode  56  connected to a gate line  52  formed on a lower substrate, a source electrode  60  connected to a source line  64 , a drain electrode  72  connected to a drain line  73  arranging in opposition to the source electrode  60 , and a semiconductor layer  68  forming a channel between the source electrode  60  and the drain electrode  72 , and an insulating film (not shown). In addition, the semiconductor layer  68  has a stacked active layer configuration including the source electrode  60 , the drain electrode  72 , and an ohmic contact layer for providing ohmic contact between the source and drain electrodes  60  and  72  and the semiconductor layer  68 . 
   In  FIG. 4 , the switching device has a relatively wide channel width W 1  for switching relatively high voltages. For example, the switching device has the relatively wide channel width W 1  contrary to a configuration in which a TFT is provided within a pixel region and configured to include a plurality of TFTs provided within a pixel region, which has been proposed in the Japanese Laid-Open Patent No. H5-341316. For instance, the channel width W 1  of the TFT formed within the pixel region is within a range of several to several tens of micrometers, and the channel width of the driving circuit is within a range of several thousand to several tens of thousand of micrometers. 
     FIG. 5  is a graph demonstrating a relation between channel width and current variation according to the related art, and  FIG. 6  is a graph demonstrating a relation between channel width and electric charge mobility according to the related art. In  FIGS. 5 and 6 , a current variation flowing within a channel of a switching device decreases, and an electric charge mobility also decreases depending on an increase of a channel width of the switching device. 
   For example, although the switching device has a relatively wide channel width for switching relatively high voltages, the decrease of the variation of the current flowing within the channel of the switching device is dependent upon the increase of the channel width of the switching device. Moreover, a current efficiency is decreased depending on the increase of the channel width, as shown in  FIG. 5 . Furthermore, since the current efficiency decreases depending on the increase of the channel width, the electric charge mobility decreases, thereby reducing response speed of the switching device. 
   In addition, when the switching device becomes damaged due to sparks created during fabrication processes or as a result of overcurrents, switching characteristic of the switching device deteriorates, thereby providing abnormal driving characteristics. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is directed to an LCD device and method of fabricating an LCD device 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 LCD device including a driving circuit having an enhanced response speed. 
   Another object of the present invention is to provide a method of fabricating an LCD device including a driving circuit having an enhanced response speed. 
   Another object of the present invention is to provide an LCD device including a driving circuit having enhanced stability. 
   Another object of the present invention is to provide a method of fabricating an LCD device including a driving circuit having enhanced stability. 
   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. 
   To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a liquid crystal display device includes a driving circuit provided with a switching device on a liquid crystal display panel, the switching device including a plurality of thin film transistors connected in parallel and commonly interconnected using a gate electrode. 
   In another aspect, a method of fabricating a liquid crystal display includes forming a switching device on a liquid crystal display panel, the switching device having a plurality of amorphous thin film transistors connected in parallel, wherein the forming the switching device includes forming a gate electrode on a substrate, forming a plurality of source electrodes and a plurality of drain electrodes arranged to oppose each other with the gate electrode therebetween, and forming a semiconductor pattern including a plurality of channels between the source electrodes and the drain electrodes. 
   It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 

   
     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. In the drawings: 
       FIG. 1  is a schematic plan view of an LCD device according to the related art; 
       FIG. 2  is a schematic plan view of an LCD device having a gate driving circuit according to the related art; 
       FIG. 3  is a schematic plan view of an LCD device having a gate driving circuit and a data driving circuit according to the related art; 
       FIG. 4  is a schematic plan view of a switching device for a driving circuit according to the related art; 
       FIG. 5  is a graph demonstrating a relation between channel width and current variation according to the related art; 
       FIG. 6  is a graph demonstrating a relation between channel width and electric charge mobility according to the related art; 
       FIG. 7  is a schematic plan view of an exemplary driving circuit of an LCD device according to the present invention; 
       FIG. 8  is a schematic plan view of an exemplary switching of a driving circuit of an LCD device according to the present invention; 
       FIG. 9  is a cross sectional view along I-I′ of  FIG. 8  according to the present invention; 
       FIGS. 10A to 10D  are cross sectional views of an exemplary method of fabricating the switching device of  FIG. 9  according to the present invention; 
       FIG. 11  is a schematic plan view of another exemplary switching device of a driving circuit of an LCD device according to the present invention; 
       FIG. 12  is a schematic plan view of another exemplary switching device of a driving circuit of an LCD device according to the present invention; 
       FIG. 13  is a schematic plan view of another exemplary switching device of a driving circuit of an LCD device according to the present invention; 
       FIG. 14  is a block diagram of an exemplary data driving circuit according to the present invention; and 
       FIG. 15  is a schematic circuit diagram of an exemplary multiplexer of  FIG. 14  according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     FIG. 7  is a schematic plan view of an exemplary driving circuit of an LCD device according to the present invention,  FIG. 8  is a schematic plan view of an exemplary switching of a driving circuit of an LCD device according to the present invention, and  FIG. 9  is a cross sectional view along I-I′ of  FIG. 8  according to the present invention. In  FIG. 7 , a driving circuit may include a gate line  152 , a first drain line  153 , and a source line  140  formed with the gate line  152  in a side-by-side configuration, and switching devices  185  having a plurality of TFTs may be connected in parallel. 
   In  FIGS. 8 and 9 , a switching device  185  may include a gate electrode  156  connected to the gate line  152  formed on a lower substrate  102 , a plurality of source electrodes  160  commonly connected to a second source line  164  extending from a first source line  140 , a plurality of drain electrodes  172  that face the source electrodes  160  and may be commonly connected to the second drain electrode  173  that extends from the first drain line  153 , and a semiconductor layer  168  formed to overlap with the gate electrodes  156  with a gate insulating film disposed therebetween. Accordingly, the semiconductor layer  168  may include a plurality of channels formed between the source electrode  160  and the drain electrode  172 . In addition, the semiconductor layer  168  may include an active layer  114  and an ohmic contact layer  148 . 
   Accordingly, although one of the switching devices  185  may be damaged due to overcurrents flowing through any one of the TFTs and/or sparks created during fabrication processes, remaining ones of the switching device  185  may be normally driven. Thus, the switching device  185  formed in the driving circuit may have a configuration in which a plurality of TFTs may be electrically independent and mutually connected in parallel, thereby increasing stability of the switching devices  185 . 
     FIGS. 10A to 10D  are cross sectional views of an exemplary method of fabricating the switching device of  FIG. 9  according to the present invention. In  FIG. 10A , a gate metal layer may be deposited onto a lower substrate  102  by a sputtering method. Then, the gate metal layer may be patterned by photolithographic processes using an etching process including an etch mask, thereby forming a gate electrode  156  on the lower substrate  102 . The gate metal may include chrome Cr, molybdenum Mo, or aluminum-based metals formed as a single layer or formed as a double layer configuration. 
   In  FIG. 10B , a gate insulating film  144  may be formed along an entire surface of the lower substrate  102  having the gate electrode  156 . The gate insulating film  144  may include an inorganic insulating material, such as silicon oxide SiOx or silicon nitride SiNx. 
   Then, an amorphous silicon layer and a N +  amorphous silicon layer may be sequentially formed on the lower substrate  102  having the gate insulating film  144  using a depositing method, such as PECVD and sputtering. Next, the amorphous silicon layer and the N +  amorphous silicon layer may be patterned by photolithographic processes and an etching process using a mask. Then, a semiconductor pattern  168  may be formed to have a number of narrow channel widths, wherein the semiconductor pattern  168  may have a double layer configuration comprising an active layer  114  and an ohmic contact layer  148 . 
   In  FIG. 10C , a source/drain metal layer may be formed along the entire surface of the lower substrate  102  having the semiconductor pattern  168  by a depositing method, such as PECVD and sputtering. Next, a photoresist pattern may be formed on the source/drain metal layer by photolithographic processes using a mask. Then, the source/drain metal layer may be patterned by a wet etching process using the photoresist pattern. Accordingly, the source/drain patterns may be formed to include a plurality of source electrodes  160  and a plurality of drain electrodes  172  connected to a data line. 
   In  FIG. 10C , the ohmic contact layer  148  corresponding to channel region may be removed by etching using the source electrode  160  and the drain electrode  172  as masks to expose the channel region of the active layer  114 . A metal for forming the source/drain electrodes may include Mo, Ti, Ta, and Mo alloys. 
   In  FIG. 10D , a passivation layer  150  may be formed along the entire surface of the lower substrate  102  having the source/drain patterns using an etching method, such as PECVD. 
     FIG. 11  is a schematic plan view of another exemplary switching device of a driving circuit of an LCD device according to the present invention. Since the components shown in  FIGS. 8 and 9  may be similar to the components shown in  FIG. 11 , explanation of the similar components has been omitted for the sake of brevity. However, similar components shown in  FIG. 11  may have the same referenced number. 
   In  FIG. 11 , each of the semiconductor patterns of the switching device may be formed to have a channel between any one of a plurality of the source electrodes  160  and the drain electrode  172  arranged in opposition to the source electrode  160 . For example, the semiconductor patterns may be formed such that the summation of the channel widths W 2  of the respective semiconductor patterns  168  may be equal to a single channel width of a TFT. Accordingly, a TFT device may be formed having multiple channels having the channel width W 2  formed in parallel with each other. Thus, benefits of a wide channel width TFT device may be achieved by a combination of each of the channel widths W 2 . Furthermore, since each of the channels  195  may be electrically separated from each other, each of the TFTs may not affect each other during operation. Since the deterioration of current efficiency reduced by widening of the channel widths W 2 , electric charge mobility may be increased, thereby enhancing response speed of the TFT device. 
     FIG. 12  is a schematic plan view of another exemplary switching device of a driving circuit of an LCD device according to the present invention. The switching device of  FIG. 12  may have similar components as those shown in  FIG. 8 , except for configurations of the source/drain electrodes. Accordingly, components similar to those shown in  FIG. 8  may be given the same reference numerals, wherein detailed description therefore have been omitted. 
   In  FIG. 12 , a plurality of holes  190  may be formed within a semiconductor pattern  168 , and a channel  195  may be formed at an area provided between the holes  190 . In addition, the area between a second source line  164  and a drain line  173  may be formed to be relatively narrow, wherein the source electrodes  164  and  164  may be formed to have a concave-convex configuration and may both be commonly connected to the second source line  164 . Similarly, the drain electrodes  172  and  172  may be formed to have a concave-convex configuration and may both be commonly connected to the second drain line  173 . For example, the channels  195  may be formed between a convex portion of the source electrode  164  formed on the second source line  164  and a concave portion of the drain electrode  172  formed on the second drain line  173 , and between a concave portion of the source electrode  16 A formed on the second source line  164  and a convex portion of the drain electrode  172 , respectively. 
   An effective channel width of the semiconductor pattern  168  may be formed as a summation of each of the channel width W 2  of the plurality of narrow channels  195  formed on the semiconductor pattern  168 . Accordingly, each of the switching devices in a driving circuit of an LCD panel may be electrically separated and connected in parallel. Thus, effects of a wide channel width may be obtained by adding each of the narrow channel widths W 2 . Furthermore, since each of the channels  195  may be electrically separated from each other, each of the TFTs may not affect each other during operation. Since deterioration of current efficiency may be reduced by widening of the channel widths, electric charge mobility may increase, thereby enhancing response speed. In addition, since each of the switching devices may be formed to be electrically independent from each other, damaged ones of the TFTs may not affect normal driving of an LCD panel. Moreover, since the space between the second source line  164  and the second drain line  173  is formed relatively narrow, an overall size of the switching device may be reduced, thereby reducing fabrication costs. 
     FIG. 13  is a schematic plan view of another exemplary switching device of a driving circuit of an LCD device according to the present invention. In  FIG. 13 , a channel region may be formed between the source electrode  164  and the drain electrode  172 , although the source and drain metal layers of the switching device may not be properly formed due to processing variations. In other words, since the channel may be formed between the source electrode and the drain electrode, although the source and drain electrodes may not be properly formed, the switching device may still be driven normally. 
     FIG. 14  is a block diagram of an exemplary data driving circuit according to the present invention. In  FIG. 14 , a data driving circuit may include a data driving IC  300  including a shift register  271  for sampling a dot clock of a data control signal, first and second latches  272  and  273 , which may be responsive to a clock signal from the shift register, for storing data on a line-by-line basis and simultaneously outputting the stored data on a line-by-line basis, a level shifter  274  for level-shifting a digital data voltage from the second latch  273 , and a digital/analog converter  275  for selecting a positive/negative gamma voltage corresponding to the digital data. The data driving circuit also may include a multiplexer  280  for selecting a data line  255  to which an analogue data converted by the positive/negative gamma voltage is supplied, and an output buffer  276  connected between the multiplexer  208  and the data line  255 . 
     FIG. 15  is a schematic circuit diagram of an exemplary multiplexer of  FIG. 14  according to the present invention. In  FIG. 15 , each of the multiplexers  280  (in  FIG. 14 ) may be connected to a plurality of data lines DLk 1  to DLk 3 . Accordingly, each of the multiplexers  280  may sequentially supply video signals from the data driving IC  300  to the three data lines DLk 1  to DLk 3 . Thus, each of the multiplexers  280  may include three switching devices SW 1  to SW 3  connected between the data driving IC  300  and the three data lines DLk 1  to DLk 3 . In addition, switching devices included in each of the multiplexers  280  may be applicable to a configuration in which a plurality of TFTs, which may be electrically separated from each other, may be connected in parallel. For example, the exemplary switching devices shown in  FIGS. 7-13  may be used as the switching devices SW 1 , SW 2 , and SW 3  in  FIG. 15 . Alternatively, combinations of the exemplary switching devices shown in  FIGS. 7-13  may be used as the switching devices SW 1 , SW 2 , and SW 3  in  FIG. 15 . Furthermore, the exemplary switching devices shown in  FIGS. 7-13  may be used as the switching devices of a gate driving part including shift registers. 
   It will be apparent to those skilled in the art that various modifications and variations can be made in the LCD device and method of fabricating an LCD device 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 Classification (CPC): 6