Abstract:
An array substrate for a liquid crystal display device and a fabrication method thereof, and a liquid crystal display device having the same are disclosed. The array substrate for a liquid crystal display device and a fabrication method thereof, and a liquid crystal display device having the same according to the present disclosure eliminate optical loss by use of a shielding film that can decrease the optic leakage current to minimize the optic leakage loss, thus it is possible to improve the picture quality.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority under 35 U.S.C. 119 to Korean Patent Application No. 10-2008-0099401, filed on Oct. 10, 2008, which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    1. Field of the Disclosure 
         [0003]    This disclosure relates to a liquid crystal display device, and more particularly to an array substrate for a liquid crystal display device and a manufacturing method thereof, which is adaptive for improve the picture quality by minimizing photo leakage current, and a liquid crystal display device having the same. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, a liquid crystal display device controls the light transmittance of liquid crystal by use of electric field, thereby displaying a picture. To this end, the liquid crystal display device includes a liquid crystal display panel where pixel areas are arranged in a matrix shape, a drive circuit for driving the liquid crystal display panel, and a backlight unit for supplying a designated amount of light to the liquid crystal display panel. 
         [0006]    In the liquid crystal display panel, a plurality of gate lines and a plurality of date lines are arranged to cross, and a pixel area is located in an area which is defined by the perpendicular intersection of the gate lines and the date lines. A common electrode and pixel electrodes for applying electric field to each of the pixel areas are formed in the liquid crystal display panel. Each of the pixel electrodes is connected to the data line through a source terminal and a drain terminal of a thin film transistor that is a switching device. The thin film transistor is turned on by a scan pulse applied to the gate line to make a data signal of the data line charged in the pixel electrode. 
         [0007]    The liquid crystal display panel includes two substrates (upper and lower substrates) and a liquid crystal layer formed between the two substrates. A color filter and a black matrix are formed in the upper substrate of the two substrates, and a thin film transistor (TFT) is formed in the lower substrate to correspond to the black matrix. 
         [0008]    The light exited from the light source of the backlight unit is reflected by the liquid crystal cells forming a liquid crystal layer, the black matrix and the color filter of the upper substrate of the liquid crystal display panel, thereby affecting a channel layer of the thin film transistors. Hereby, a pixel voltage charged in the pixel electrode is affected to generate a difference between the pixel electrode charged in the pixel electrode and the actual data signal supplied to the data line, thereby generating a picture quality deterioration problem, e.g., a picture which is not wanted is displayed. 
         [0009]    The channel layer of the thin film transistor is affected by light, thus a leakage current is generated in the channel layer if the light reflected by the liquid crystal cell, the black matrix and the color filter of the upper substrate enters into the channel layer of the thin film transistor. Because of this, the pixel voltage charged in the pixel electrode is affected, thereby generating a picture quality deterioration, e.g., patterns which are not wanted are generated. 
       BRIEF SUMMARY 
       [0010]    Accordingly, the present embodiments are directed to a liquid crystal display device that substantially obviates one or more of problems due to the limitations and disadvantages of the related art. 
         [0011]    An object of the embodiment of the present disclosure is to provide an array substrate for a liquid crystal display device and a manufacturing method thereof, which is adaptive for minimizing a picture quality deterioration caused by a leakage current of a channel layer of a thin film transistor by way of forming a shielding film on a passivation layer, which corresponds to the channel layer of the thin film transistor, in order to intercept the light reflected by the liquid crystal cell, a black matrix and a color filter, and a liquid crystal display device having the same. 
         [0012]    Another object of the embodiment of the present disclosure is to provide an array substrate for a liquid crystal display device and a manufacturing method thereof, which is adaptive for improving picture quality, and a liquid crystal display device having the same. 
         [0013]    Additional features and advantages of the embodiments 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 embodiments. The advantages of the embodiments will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
         [0014]    In one general aspect of the present embodiment, an array substrate for a liquid crystal display device includes a substrate; a gate electrode formed on the substrate; a gate insulating film formed on the substrate where the gate electrode is formed; a semiconductor layer formed on the substrate where the gate insulating film is formed so as to correspond to the gate electrode; source and drain electrodes which are separated from each other on the substrate where the semiconductor layer is formed; a passivation layer formed in the entire surface of the substrate where the source and drain electrodes are formed; a shielding film located on the passivation layer to correspond to the gate electrode; and a pixel electrode which is formed on the passivation layer to be separated from the shielding film and is electrically connected to the drain electrode through the contact hole. 
         [0015]    In another aspect of the present embodiment, a fabricating method of an array substrate for a liquid crystal display device includes a step of preparing a substrate: a first mask process step of forming a gate electrode on the substrate; a step of forming a gate insulating film on the substrate where the gate electrode is formed; a second mask process step of forming, on the substrate where the gate insulating film is formed, an active layer to correspond to the gate electrode, source and drain electrodes on the active layer to be separated from each other, and an ohmic contact layer between the source and drain electrodes and the active layer; a step of forming a passivation layer on the substrate where the source and drain electrodes and the ohmic contact layer is formed; a third mask process step of forming a contact hole on the passivation layer to make a part of the drain electrode exposed; and a fourth mask process step of forming a pixel electrode that is connected to the drain electrode through the contact hole on the passivation layer, and a shielding film which is formed at the same time as the pixel electrode and is located to correspond to the gate electrode. 
         [0016]    In another aspect of the present embodiment, a liquid crystal display device includes a liquid crystal display panel; and a light source that illuminates light to the liquid crystal display panel, and wherein the liquid crystal display panel includes a first substrate having a thin film transistor that includes a gate electrode, a gate insulating film formed on the gate electrode, a semiconductor layer formed on the gate insulating film to correspond to the gate electrode, source and drain electrodes separated from each other on the semiconductor layer, a passivation layer formed on the source and drain electrodes, a pixel electrode electrically connected through a contact hole to the drain electrode on the passivation layer, and a shielding film that is formed at the same time as the pixel electrode and is located to correspond to the gate electrode on the passivation layer; a second substrate that faces the first substrate and includes a color filter and a black matrix; and an active layer formed on the first and second substrates, and wherein the shielding film intercepts the light exiting from the light source so that the light is prevented from entering into a channel part of the semiconductor layer by being reflected in the liquid crystal layer and the black matrix and the color filter of the second substrate. 
         [0017]    Other systems, methods, features and advantages will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the disclosure, and be protected by the following claims. Nothing in this section should be taken as a limitation on those claims. Further aspects and advantages are discussed below in conjunction with the embodiments. It is to be understood that both the foregoing general description and the following detailed description of the present disclosure are exemplary and explanatory and are intended to provide further explanation of the disclosure as claimed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The accompanying drawings, which are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the disclosure and together with the description serve to explain the disclosure. In the drawings: 
           [0019]      FIG. 1  is a diagram illustrating part of an array substrate for a liquid crystal display device according to an embodiment of the present disclosure; 
           [0020]      FIG. 2  is a sectional view of thin film transistors (TFT) of  FIG. 1 , taken along the line I-I′; 
           [0021]      FIGS. 3 to 8  are diagrams sequentially illustrating a fabrication process of the thin film transistor of  FIG. 1 ; and 
           [0022]      FIG. 9  is a graph comparing the leakage current of a related art thin film transistor with that of the thin film transistor according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. These embodiments introduced hereinafter are provided as examples in order to convey their spirits to the ordinary skilled person in the art. Therefore, these embodiments might be embodied in a different shape, so are not limited to these embodiments described here. Also, the size and thickness of the device might be expressed to be exaggerated for the sake of convenience in the drawings. Wherever possible, the same reference numbers will be used throughout this disclosure including the drawings to refer to the same or like parts. 
         [0024]      FIG. 1  is a diagram illustrating part of an array substrate for a liquid crystal display device according to an embodiment of the present disclosure. 
         [0025]    As shown in  FIG. 1 , an array substrate for a liquid crystal display device according to an embodiment of the present disclosure includes a gate line GL which has a gate pad  214  at an end and a data line DL which crosses the gate line GL to define a pixel area P and which has a data pad  218  at one end, on a glass substrate  201 . 
         [0026]    A gate pad electrode  216  and a data pad electrode  220  are each located at and in contact with the upper parts of the gate pad  214  and the data pad  218 . 
         [0027]    A thin film transistor TFT including a gate electrode  202 , a semiconductor layer  204  inclusive of an ohmic contact layer, a source electrode  206 , a drain electrode  208  and a shielding pattern  212  is formed at an intersection area of the gate line GL and the data line DL. 
         [0028]    A pixel electrode  210  electrically connected to the drain electrode  208  of the thin film transistor TFT is formed in the pixel area P. 
         [0029]    The gate electrode  202  of the thin film transistor TFT is formed at the same time as the gate line GL and electrically connected to the gate line GL. The source electrode  206  is formed at the same time as the data line DL and electrically connected to the data line DL. 
         [0030]    The thin film transistor (TFT), as shown in  FIG. 1 , might be composed in a various shape such as “U” shape or island shape. 
         [0031]    A shielding pattern  212  of the thin film transistor TFT is formed at the same time as the pixel electrode  210 , and might be formed of the same material as the pixel electrode  210 . When light is illuminated from the backlight to the liquid crystal display panel inclusive of the array substrate for the liquid crystal display device, the shielding pattern  212  plays a role of shielding the light that is reflected from a liquid crystal cell, a color filter and a black matrix formed at a color filter substrate facing the array substrate for the liquid crystal display device and that is applied to the thin film transistor TFT. 
         [0032]      FIG. 2  is a sectional view of thin film transistors TFT of  FIG. 1 , taken along the line I-I′. 
         [0033]    As shown in  FIG. 2 , the thin film transistor TFT includes a gate electrode  202  extended from the gate line GL, a gate insulating film  203  formed on a substrate  201  where the gate electrode  202  is formed, a semiconductor layer  204  formed on the gate insulating film  203  to correspond to the gate electrode  202 , source and drain electrodes  206 ,  208  formed to be separated from each other on the semiconductor layer  204 , a passivation layer  205  formed on the substrate  201  where the source and drain electrodes  206 ,  208  are formed, and a shielding pattern  212  formed on the passivation layer  205  to correspond to the gate electrode  202 . 
         [0034]    On the other hand, the drain electrode  208  is electrically connected to the pixel electrode  210  through a contact hole on the passivation layer  205 . 
         [0035]    The semiconductor layer  204  includes an active layer  204   a  and an ohmic contact layer  204   b.    
         [0036]    The shielding pattern  212  is formed on the passivation layer  205  to correspond to the gate electrode  202  and might be formed of indium-tin-oxide (ITO) or indium-zinc-oxide (IZO) which is the same material as the pixel electrode  210 . The shielding pattern  212  might be formed of any one of molybdenum titanium alloy (MoTi), copper (Cu), molybdenum alloy (MoNb), molybdenum Mo, chromium (Cr), and Aluminum (AlNd). 
         [0037]    When light is illuminated from the backlight to the liquid crystal display panel including the array substrate for the liquid crystal display device having the thin film transistor TFT, the shielding pattern  212  plays a role of shielding the light that is reflected to the thin film transistor TFT by the liquid crystal cells, the color filter and the black matrix formed in the color filter array substrate which faces the array substrate for the liquid crystal display device. 
         [0038]    If the light illuminated from the backlight is reflected by the liquid crystal tells, the color filer and the black matrix of the color filter array substrate to enter into the channel layer of the semiconductor layer  204  of the thin film transistor TFT, a leakage current flows in the channel layer of the thin film transistor TFT. Accordingly, the shielding pattern  212  is formed on the passivation layer  205 , thus the light reflected by the liquid crystal cells, the color filter and the black matrix of the color filter array substrate is prevented from flowing into the channel layer of the thin film transistor TFT, thereby minimizing the leakage current. 
         [0039]    The shielding pattern  212  might be formed in various shapes in which the light is prevented from entering into the channel layer of the thin film transistor TFT by a structure formed in the color filter array substrate. 
         [0040]      FIGS. 3 to 8  are diagrams sequentially illustrating a fabrication process of the thin film transistor of  FIG. 1 . 
         [0041]    As shown in  FIG. 3 , a first mask process of the thin film transistor TFT according to an embodiment of the present disclosure selects and deposits any one of a conductive metal group inclusive of aluminum Al, aluminum alloy AlNd, Tungsten W, Chromium Cr, molybdenum Mo, and etc on the substrate  201 , and patterns it to form the gate electrode  202 . 
         [0042]    A gate insulating film  203  is formed, as shown in  FIG. 4 , in the entire surface of the substrate  201  where the gate electrode  202  is formed. The gate insulating film  203  is formed by selecting any one of an inorganic insulating group inclusive of silicon nitride SiNx, silicon oxide a-Si:H and etc and depositing it on the substrate  201 . As circumstances require, the gate insulating film  203  might be formed by depositing any one of organic insulating material inclusive of benzocyclobutane BCB, acrylic resin and etc. 
         [0043]    An amorphous silicon a-Si:H,  204 A is deposited to be formed on the substrate  201  where the gate insulating film  203 , and a doped amorphous silicon n+a-Si:H,  204 B is deposited to be formed on the amorphous silicon  204 A. A conductive metal film  207  is deposited to be formed on the substrate  201  where the amorphous silicon  204 A and the doped amorphous silicon  204 B are formed. 
         [0044]    The conductive metal film  207  might be formed of any one of a conductive metal group inclusive of aluminum Al, aluminum alloy AlNd, tungsten W, chromium Cr, molybdenum Mo, and etc. 
         [0045]    The amorphous silicon  204 A, the doped amorphous silicon  204 B and the conductive metal film  207  are patterned through a second mask process, as shown in  FIG. 5 . 
         [0046]    Specifically, a photosensitive film (not shown) is formed on the substrate  201  where the amorphous silicon  204 A, the doped amorphous silicion  204 B and the metal pattern  207 . If a mask (not shown) inclusive of a transmitting part, a semi-transmitting part and a shielding part is located on the substrate  201  where the photosensitive film is formed, light is illuminated to the upper part of the mask, the photosensitive film of the lower part is exposed and developed, then the photosensitive film is patterned on the substrate  201  in accordance with the area where the transmitting part, the semi-transmitting part and the shielding part of the mask are located. 
         [0047]    The substrate  201  where the patterned photosensitive film is formed goes through an ashing process and etching process sequentially. Through such processes, the conductive metal film  207  is formed to be the source and drain electrodes  206 ,  208  which are separated from each other, the doped amorphous silicon  204 B is formed to be the ohmic contact layer  204 B which is separated by the distance which separates the source and drain electrodes  206 ,  208 . The part of the amorphous silicon  204 B is exposed to the outside to be an active layer  204   a.    
         [0048]    A passivation layer  205  is, as shown in  FIG. 6 , formed on the substrate  201  where the source and drain electrodes  206 ,  208  are formed. The passivation layer  205  plays a role of protecting the source and drain electrodes  206 ,  208 , the active layer  204   a  and the ohmic contact layer  204   b  from the impurities which come from the outside. A contact hole is formed through a third mask process that the part of the drain electrode  208  is exposed on the substrate  201  where the passivation layer  205  is formed. 
         [0049]    The contact hole is formed on the passivation layer  205  to make the part of the drain electrode  208  exposed to the outside. 
         [0050]    A transparent metal film  209  is, as shown in  FIG. 7 , formed on the substrate  201  where the passivation layer  205  inclusive of the contact hole is formed. The transparent metal film  209  is formed in the entire surface of the substrate  201  to be connected to the drain electrode  208  of which is partly exposed. The transparent metal film  209  is formed of any one selected among the transparent conductive metal group inclusive of indium-tin-oxide (ITO) and indium-zinc-oxide (IZO). 
         [0051]    The transparent metal film  209  formed in the entire surface of the substrate  201  is, as shown in  FIG. 8 , patterned through a fourth mask process. 
         [0052]    Specifically, a photosensitive film (not shown) is formed on the upper part of the substrate  201  where the transparent metal film  209  is formed, and a mask (not shown) inclusive of a transmitting part and a shielding part is located at the upper part of the photosensitive film. Then, if light is illuminated to the upper part of the mask to expose and to develop the photosensitive film of the lower part, the photosensitive film is patterned in accordance with the area where the transmitting part and the shielding part of the mask are located. 
         [0053]    The patterned photosensitive film is respectively formed at a part where the drain electrode  208  is located and at a part where the gate electrode  202  is located. If the patterned photosensitive film is removed after eliminating the transparent metal film  209  which is exposed between the patterned photosensitive film, a shielding pattern  212  is formed at a location which corresponds to the gate electrode  202  and the pixel electrode  210  connected to the drain electrode  908  on the substrate  201  where the passivation film  205  is formed. 
         [0054]    The shielding pattern  212 , as described above, might be formed of indium-tin-oxide (ITO) or indium-zinc-oxide (IZO) which is the same material as the pixel electrode  210 . Further, the shielding pattern  212  might be formed of any one of molytitanium MoTi, copper Cu, molybdenum alloy MoNb, molybdenum Mo, chromium Cr, and aluminum alloy AlNd. 
         [0055]    When light is illuminated from the backlight to the liquid crystal display panel inclusive of the array substrate for the liquid crystal display device having the thin film transistor TFT inclusive of the shielding pattern  212 , the shielding pattern  212  plays a role of shielding the light that is reflected to the thin film transistor TFT by the liquid crystal cells, the color filter and the black matrix that are formed in the color filter array substrate facing the array substrate for the liquid crystal display device. 
         [0056]    If the light illuminated from the backlight is reflected by the liquid crystal cells, the color filter and the black matrix of the color filter array substrate and enters into the channel layer of the semiconductor layer  204  of the thin film transistor TFT, a leakage current flows in the channel layer of the thin film transistor TFT. Accordingly, the shielding pattern  212  is formed on the passivation layer  205 , thus the light reflected by the liquid crystal cells, the color filter and the black matrix of the color filter array substrate is prevented from entering into the channel layer of the thin film transistor TFT, thereby minimizing the leakage current. 
         [0057]    As the leakage current of the thin film transistor TFT is minimized, the pixel voltage charged in the pixel electrode connected to the thin film transistor TFT is not affected, thereby improving the picture quality. 
         [0058]      FIG. 9  is a graph comparing the leakage current of a related art thin film transistor with that of the thin film transistor according to the present disclosure. 
         [0059]    As shown in  FIG. 9 , the horizontal axis of the graph is a gate voltage Vg applied to the gate terminal of the thin film transistor, and the vertical axis of the graph is a leakage current Ioff of the thin film transistor. 
         [0060]    When the gate voltage Vg is applied at −5V, the leakage current of the related art thin film transistor is 692 pA and the leakage current of the thin film transistor according to the present disclosure inclusive of the shielding pattern  212  is 166 pA. Accordingly, the leakage current of the thin film transistor according to the present disclosure inclusive of the shielding pattern  212  is observed to decrease by 70% when compared with the leakage current of the related art thin film transistor. The graph shown in  FIG. 9  is an experimental data, but it is shown that the leakage current of the thin film transistor according to the present disclosure inclusive of the shielding pattern  212  decreases more than the leakage current of the related art thin film transistor. 
         [0061]    Accordingly, as in the present disclosure, the shielding pattern is included in the passivation layer, thus it is possible to minimize the leakage current by preventing the light illuminated from the backlight from entering into the channel layer of the thin film transistor by the color filter array substrate. As the leakage current of the thin film transistor is minimized, the pixel voltage charged in the pixel electrode connected to the thin film transistor TFT is not affected, thus it is possible to improve the picture quality by displaying the desired picture. 
         [0062]    As describe above, the present disclosure forms the shielding film on the passivation layer to correspond to the channel layer of the thin film transistor to intercept the light reflected by the liquid crystal cell, the black matrix and the color filter formed in the upper substrate and to minimize the leakage current of the channel layer, thereby improving the picture quality. 
         [0063]    Although the present disclosure has been explained by the embodiments described above, it should be understood to the ordinary skilled person in the art that the disclosure is not limited to the embodiments but rather that various changes or modifications thereof are possible without departing from the spirit of the disclosure. Accordingly, the scope of the disclosure shall be determined only by the appended claims and their equivalents.