Abstract:
An IPS-LCD panel includes first and second substrates, and a liquid crystal interposed therebetween. An electro-conductive polarizer is formed on the second substrate of the IPS-LCD panel, and a ground electrode surrounds the electro-conductive polarizer. The electro-conductive polarizer and ground electrode prevent exterior static electricity from affecting the liquid crystal layer.

Description:
[0001]    This application claims the benefit of Korean Patent Application No. 2000-7711, filed on Feb. 18, 2000, which is hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a color liquid crystal display device, and more particularly to a color liquid crystal display device implementing in-plane switching (IPS) where an electric field to be applied to liquid crystal is generated in a plane parallel to a substrate.  
           [0004]    2. Discussion of the Related Art  
           [0005]    Recently, liquid crystal display (LCD) devices with light, thin, and low power consumption characteristics are used in office automation equipment and video units and the like. Such LCDs typically uses optical anisotropy and spontaneous polarization of a liquid crystal (LC). The LC has thin and long LC molecules, which causes an orientational alignment of the LC molecules. Therefore, alignment direction of the LC molecules is controlled by applying an electric field to the LC molecules. When the alignment direction of the LC molecules is properly adjusted, the LC molecules are aligned and light is refracted along the alignment direction of the LC molecules to display image data. By now, an active matrix (AM) LCD, in which a plurality of thin film transistors and pixel electrodes are arranged in an array matrix, is of particular interest because of its high resolution and superiority in displaying moving pictures. Driving methods for such LCDs typically include a twisted nematic (TN) mode and a super twisted nematic (STN) mode.  
           [0006]    Although TN-LCDs and STN-LCDs have been put to practical use, they have a drawback in that they have a very narrow viewing angle. In order to solve the problem of narrow viewing angle, IPS-LCD devices have been proposed. A color IPS-LCD device typically includes a lower substrate where a pixel electrode and a common electrode are disposed, an upper substrate having a color filter, and a liquid crystal interposed between the upper and lower substrates. The color IPS-LCD device has advantages in its improved viewing angle property, such as contrast, gray inversion, and color dispersion properties.  
           [0007]    [0007]FIG. 1 is a plan view illustrating a conventional color IPS-LCD device. As shown, on a lower substrate or an array substrate (reference  33  of FIG. 2), gate line  13  and data line  15  are formed perpendicular to each other with a pixel region “P” defined thereby. At a cross point between the gate and data lines  13  and  15 , a switching device  12  is formed. The switching device  12  conventionally employs a thin film transistor (TFT). On the pixel region P, a plurality of pixel electrodes  17  and common electrodes  19  are formed. The pixel and common electrodes  17  and  19  are parallel with and spaced apart from each other on the same plane. Therefore, when a voltage source  10  generates a voltage difference between the pixel and common electrodes  17  and  19 , an in-plane electric field  23  is induced therebetween. The in-plane electric field  23  operates a liquid crystal layer  21  that is interposed between the lower substrate  33  and an upper substrate (reference  25  of FIG. 2).  
           [0008]    At this point, liquid crystal molecules arranged in the gap between the adjacent pixel and common electrodes  17  and  19  are aligned in the same direction as the in-plane electric field  23 . Because each pair of adjacent pixel and common electrodes  17  and  19  involves a corresponding domain of the liquid crystal  21 , a plurality of domains are present in the pixel region “P” such that a wide viewing angle is achieved.  
           [0009]    With reference to FIG. 2, structure of the conventional color IPS-LCD device is explained in detail. As shown, between the upper and lower substrate  25  and  33 , the liquid crystal layer  21  is interposed. On the lower substrate  33 , the pixel electrodes and common electrodes  17  and  19  are alternately formed with gaps therebetween. On an inner surface of the upper substrate  25 , a color filter  29 , including color filter layer  29   a  and black matrix  29   b , is formed, and a planar layer  45  is formed to cover the color filter  29 . On exterior surface of the upper substrate  25 , a ground electrode  27  is formed of a transparent conductive material such as indium tin oxide (ITO). The ground electrode  27  prevents exterior static electricity from affecting the liquid crystal layer  21 . Without the ground electrode  27 , the exterior static electricity may electrify the upper substrate  25  and the electrified upper substrate affects the alignment of the liquid crystal molecules. In that case, switching operation of the liquid crystal layer  21  cannot be controlled by data signals and image quality of the LCD device becomes poor.  
           [0010]    [0010]FIGS. 3A to  3 E illustrate a sequence of fabricating process for the upper substrate of the conventional IPS-LCD device. At first, as shown in FIG. 3A, the upper substrate  25  is prepared. In later steps, the color filter  29  will be formed on a first surface  25   a  of the upper substrate  25  while the ground electrode  27  will be formed on a second surface  25   b  thereof.  
           [0011]    Thereafter, as shown in FIG. 3B, the ground electrode  27  is formed on the second surface  25   b  of the upper substrate  25 . As explained previously, to form the ground electrode  27 , the transparent conductive material such as indium tin oxide (ITO) is deposited on the upper substrate  25 . Then, the upper substrate  25  including the ground electrode  27  is transferred via a carrier  41 , as shown in FIG. 3C. At this point, the first surface  25   a , where the color filter will be formed in a subsequent step, contacts a plurality of loaders  43  of the carrier  41 . The loaders  43  are spaced apart from each other, and each of them rotates to move the upper substrate  25 . Since the first surface  25   a  directly contacts the rotating loader  43 , scratches or defects may occur on the first surface  25   a.    
           [0012]    Next, as shown in FIG. 3D, the black matrix  29   b , color filter layer  29   a , and planar layer  45  are sequentially formed on the first surface  25   a  of the upper substrate  25 , which is transferred via the carrier  41  shown in FIG. 3C. In detail, chromium oxide (CrO x ) and chromium (Cr) are deposited on the first surface  25   a  and patterned to form the black matrix  29   b . Thereafter, the color filter layer  29   a  including red, green, and blue resins “R”, “G”, and “B” is formed on the first surface  25   a  of the upper substrate  25 , using photolithography. The color filter layer  29   a  and black matrix  29   b  are adjacent to each other in an array matrix shape. Then, an insulating material of a transparent polymer or the like is deposited over the first surface  25   a  to form the planar layer  45 .  
           [0013]    Next, as shown in FIG. 3E, the upper substrate  25  is attached to the lower or array substrate  33  via a sealant  51  such that the IPS-LCD panel  31  is completed. Then a polarizer  47  is formed on the ground electrode  27  of the IPS-LCD panel  31 . The ground electrode  27  is made of the transparent conductive material and attracts contaminants or extraneous matters more than the upper substrate does. That is to say, to prevent the exterior static electricity, the ground electrode  27  is interposed between the upper substrate  25  and the polarizer  47 . However, because the ground electrode  27  of the transparent conductive material attracts extraneous matter more than the upper substrate  25  of a glass material does, the extraneous matter  49  is easily interposed between the polarizer  47  and upper substrate  25  during forming the polarizer  47  on the upper substrate  25 .  
         SUMMARY OF THE INVENTION  
         [0014]    Accordingly, the present invention is directed to an IPS-LCD device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.  
           [0015]    An object of the present invention is to provide an IPS-LCD device that is protected from exterior static electricity without interposing a ground electrode between a polarizer and an upper substrate of the IPS-LCD device.  
           [0016]    In order to achieve the above object, the first preferred embodiment of the present invention provides a fabricating method for an in-plane switching color liquid crystal display device. The method includes: forming a color filter layer on a first surface of a first substrate; forming an array matrix including a plurality of common electrodes, pixel electrodes, and switching devices on a second substrate such that each common electrode is parallel to a corresponding pixel electrode with a gap therebetween; attaching the first and second substrates via a sealant; forming a ground electrode on side edge portions of a second surface of the first substrate; and forming an electro-conductive polarizer on the second surface of the first substrate such that the electro-conductive polarizer contacts the ground electrode.  
           [0017]    The ground electrode is selected from a group consisting of indium tin oxide (ITO) and indium zinc oxide (IZO).  
           [0018]    The step of forming the ground electrode includes: covering the second surface of the upper substrate with a mask; depositing a transparent conductive material on the second surface of the upper substrate such that the ground electrode are formed only on side edge portions of the second surface of the first substrate.  
           [0019]    In another aspect, the present invention provides an in-plane switching liquid crystal display device, which includes: a color filter on a first surface of a first substrate; a common electrode and a pixel electrode on a second substrate; a liquid crystal layer between the first and second substrates; a ground electrode on side edge portions of a second surface of the upper substrate; and an electro-conductive polarizer on the second surface of the upper substrate, the polarizer contacting the ground electrode.  
           [0020]    The ground electrode is selected from a group consisting of indium tin oxide (ITO) and indium zinc oxide (IZO).  
           [0021]    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 DRAWING  
       [0022]    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.  
         [0023]    In the drawings:  
         [0024]    [0024]FIG. 1 is a plan view illustrating a liquid crystal display device according to the related art;  
         [0025]    [0025]FIG. 2 is a cross-sectional view taken along a line “II-II” of FIG. 1;  
         [0026]    [0026]FIGS. 3A to  3 E illustrate a sequence of a fabricating process for the conventional IPS-LCD device;  
         [0027]    [0027]FIGS. 4A to  4 D illustrate a sequence of a fabricating process for a color filter substrate and an IPS-LCD panel according to a preferred embodiment of the present invention; and  
         [0028]    [0028]FIGS. 5A to  5 C illustrate a sequence of forming an electro-conductive polarizer on the IPS-LCD panel according to the preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    Reference will now be made in detail to the preferred embodiment of the present invention, an example of which is illustrated in the accompanying drawings.  
         [0030]    [0030]FIGS. 4A to  4 D illustrate a sequence of fabricating a color filter  115  on an upper substrate  111 , according to the preferred embodiment. At first, as shown in FIG. 4A, chromium oxide (CrO x ) and chromium (Cr) are sequentially deposited on the upper substrate  111  and patterned to form a black matrix  113 . Thereafter, as shown in FIG. 4B, the color filter layer  115  including red, green, and blue resins “R”, “G”, and “B” is formed on the upper substrate  111 , using photolithography with the same mask. Then, as shown in FIG. 4C, acryl based or polyimid based resin is deposited over the upper surface  111  to form a planar layer  117 . The planar layer  117  not only levels but also protects the color filter layer  115  and black matrix  113 .  
         [0031]    Next, as shown in FIG. 4D, the upper substrate  111  including the color filter layer  115  is attached with a lower substrate or array substrate  123  via a sealant  125  such that an IPS-LCD panel  131  is completed. Though not shown in FIG. 4D, an array of common electrode, pixel electrode, and gate and data lines are formed on the lower substrate  123  (see FIG. 1).  
         [0032]    Now, with reference to FIGS. 5A to  5 C, a process of forming a polarizer  217  on the IPS-LCD panel  131  is explained. At first, as shown in FIG. 5A, a mask  213  covers a middle portion of the upper substrate  111  of the IPS-LCD panel  131 . Preferably, the mask  213  is selected from a group consisting of a metal and a shadow mask. Then, as shown in FIG. 5B, a transparent conductive material is deposited on the upper substrate  111  of the IPS-LCD panel  131  such that a ground electrode  215  is formed. Since the mask  213  covers the middle portion of the upper substrate  111 , the ground electrode  215  is formed only on side portions of the upper substrate  111 . The ground electrode  215  is preferably selected from a group consisting of indium tin oxide (ITO) and indium zinc oxide (IZO), and the upper substrate is preferably a glass substrate.  
         [0033]    Thereafter, as shown in FIG. 5C, a polarizer  217  is formed on the upper substrate  111  such that portions of the polarizer  217  overlap inner sides of the ground electrode  215 . Further, a ground line  219  is electrically connected to the ground electrode  215 . One end of the ground line is grounded. At this point, the polarizer  217  preferably includes a conductive material such that electric charges are easily discharged via the ground electrode  215  and ground line  219  when the polarizer is electrified by exterior static electricity.  
         [0034]    In the preferred embodiment of the present invention, the electro-conductive polarizer is directly formed on the upper substrate, and the ground electrode surrounds the side edges of the electro-conductive polarizer. Therefore, the problem of extraneous matter interposed between conventional polarizer and ground electrode, as shown in FIG. 3E, is prevented. In addition, because the upper substrate of the preferred embodiment does not need to be transferred via a carrier, as in with the conventional upper substrate shown in FIG. 3C, scratches or defects on a surface of the upper substrate are prevented.  
         [0035]    It will be apparent to those skilled in the art that various modifications and variation can be made in the method of manufacturing a thin film transistor 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.