Abstract:
An In-Plane Switching mode liquid crystal display device includes a first substrate and a second substrate, a plurality of gate lines and data lines defining a plurality of pixels on the first substrate, a driving device disposed in each of the plurality of pixels, at least one pair of a first electrode and a second electrode arranged in each of the plurality of pixels to generate a horizontal electric field, a black matrix formed on the second substrate and having a slot around the plurality of pixels, and a liquid crystal layer formed between the first substrate and the second substrate.

Description:
[0001]    This application claims the benefit of Korean Patent Application No. 2003-043979, filed on Jun. 30, 2003, which is hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a liquid crystal display (LCD) device and a method of fabricating an LCD device, and particularly, to an In-Plane Switching mode LCD device and a method of fabricating the same.  
           [0004]    2. Discussion of the Related Art  
           [0005]    Recently, with the development of various portable electronic devices, such as mobile phones, PDAs, notebook computers, etc., a light, thin, small flat panel display device has been in great demand. Research and development are actively conducted for the flat panel display devices, such as an LCD, a PDP (Plasma Display Panel), an FED (Field Emission Display), a VFD (Vacuum Fluorescent Display), etc. Among these devices, the LCD attracts much more attention because of its simple mass-production technique, easy driving system, and implementation of a high picture quality.  
           [0006]    There are various display modes for the LCD device according to arrangement of liquid crystal molecules. Currently, a TN (twisted nematic) mode LCD device is being generally utilized because of its easy black and white display, short response time, and low driving voltage. When a voltage is applied to the TN mode LCD device, liquid crystal molecules aligned to be horizontal to a substrate are aligned to be nearly perpendicular to a surface of the substrate. Accordingly, there is a problem in that a viewing angle is narrowed by refractive anisotropy of the liquid crystal molecules in applying of the voltage.  
           [0007]    In order to solve this problem, LCD devices of various modes having wide viewing angle characteristics have been proposed. Among those, an In-Plane Switch (IPS) mode LCD device is applied to actual mass-production, and thus is being fabricated. This IPS mode LCD device forms a horizontal electric field that is substantially parallel to a surface of a substrate by forming at least one pair of electrodes arranged parallel in a pixel, so that liquid crystal molecules are aligned along the plane.  
           [0008]    [0008]FIG. 1 is a schematic view of a structure of the above-mentioned IPS mode LCD device according to the related art. As shown in FIG. 1, a liquid crystal panel  1  has a pixel defined by a gate line  3  and a data line  4  that are disposed along lengthwise and widthwise directions. Although only the (n, m) th  pixel is shown in FIG. 1, N (&gt;n) gate lines  3  and M (&gt;m) data lines are disposed in an actual liquid crystal panel, thereby forming N×M pixels over the entire liquid crystal panel  1 . A thin film transistor  10  is formed at an intersection of the gate line  3  and the data line  4  in the pixel. The thin film transistor  10  includes a gate electrode  11  to which a scan signal is applied from the gate line  3 , a semiconductor layer  12  formed on the gate electrode  11  and activated to form a channel layer when the scan signal is applied thereto, and a source electrode  13  and a drain electrode  14  formed on the semiconductor layer  12 , to which an image signal is applied through the data line  4 , thereby applying an image signal input from the outside to a liquid crystal layer.  
           [0009]    A plurality of common electrodes  5  and a plurality pixel electrodes  7  are arranged substantially parallel to the data line  4  in the pixel. In addition, a common line  16  connected with the common electrode  5  is disposed in the middle of the pixel, and a pixel electrode line  18  connected with the pixel electrode  7  is disposed on the common line  16  and is thus overlapped with the common line  16 .  
           [0010]    As discussed above, in the related art IPS mode LCD device, the liquid crystal molecules are aligned substantially parallel to the common electrode  5  and the pixel electrode  7 . When the thin film transistor  10  is operated and thus a signal is applied to the pixel electrode  7 , an horizontal electric field that is substantially parallel to the liquid crystal panel  1  is generated between the common electrode  5  and the pixel electrode  7 . The liquid crystal molecules are rotated along the same plane by the horizontal electric field, thereby preventing a gradation inversion due to refractive anisotropy. Here, a black matrix  32  serves to prevent light from being transmitted to an unwanted area, namely, an image non-displayed area.  
           [0011]    The related art IPS mode LCD device having such a structure will now be described in more detail with reference to FIGS. 2A and 2B. Here, FIG. 2A is a cross-sectional view taken along I-I′ of FIG. 1 to show a structure of the thin film transistor  10  according to the related art. FIG. 2B is a cross-sectional view taken along  11 - 11 ′ of FIG. 1 to show a structure of a pixel according to the related art. In FIG. 2A, the thin film transistor  10  (in FIG. 1) includes the gate electrode  11  formed on a first substrate  20 , a gate insulating layer  22  laminated over the entire surface of a first substrate  20 , the semiconductor layer  12  formed on the gate insulating layer  22 , the source electrode  13  and the drain electrode  14  formed on the semiconductor layer  12 . In addition, a passivation layer  24  is formed over the entire surface of the first substrate  20 . In FIG. 2B, the plurality of common electrodes  5  are formed on the first substrate  20  in a pixel, and the pixel electrode  7  and the data line  4  are formed on the gate insulating layer  22 , so that a horizontal electric field is generated between the common electrode  5  and the pixel electrode  7 .  
           [0012]    The black matrix  32  and a color filter layer  34  are formed at a second substrate  30 . The black matrix  32  serves to prevent light from leaking to an area where the liquid crystal molecules are not operated (namely, undesired area where an image is not displayed), and is usually formed at the thin film transistor  10  area (in FIG. 1) and between pixels (i.e., gate line and data line areas). The color filter layer  34  includes R (Red), B(Blue) and G(Green) colors to implement an actual color. A liquid crystal layer  40  is formed between the first substrate  20  and the second substrate  30 , and then the liquid crystal panel  1  is thus completed. In addition, a black resin is usually utilized for the black matrix  32 , and the reason thereof will now be described next.  
           [0013]    The black matrix  32  made of metal, such as Cr or CrOx, that is usually utilized for the TN mode LCD or the like may form an electric field between the data line  4  and itself by its characteristic low resistance. Such an electric field is a vertical electric field that is formed between the first substrate  20  and the second substrate  30 . Meanwhile, another electric field is formed between the pixel electrode  7  on the first substrate  20  and the common electrode  5  on the second substrate  30 . As a result, the vertical electric field may not greatly affect the electric field between the pixel electrode  7  and the common electrode  5 .  
           [0014]    On the contrary, in the IPS mode LCD device, an electric field applied to the liquid crystal layer  40  is a horizontal electric field that is substantially parallel to a surface of the substrate  20  or  30 . Accordingly, when the horizontal electric field is formed by the black matrix  32 , the vertical electric field affects the horizontal electric field, thereby distorting the horizontal electric field. Such distortion may cause a vertical cross talk on a screen as a main factor of image quality deterioration. Accordingly, in the IPS mode LCD device, a black resin with high resistance is usually utilized as the black matrix  32  to prevent distortion of the horizontal electric field. However, there exist several problems because of disadvantages of the black resin itself.  
           [0015]    First, since the resin has a bad anisotropy etching characteristic compared to metal in a photolithography, it is difficult to form the black matrix  32  with a fine pattern to make good resolution. Accordingly, it is difficult to fabricate an IPS mode LCD of high resolution.  
           [0016]    Second, since the black matrix  32  has a low light blocking rate compared to Cr or CrOx (because transmittance of light is high), its thickness has to be thick compared to Cr or CrOx in order to completely block light transmitted to the image non-displayed area. Accordingly, a step is generated at the color filter layer  34  and makes it difficult to be flat.  
           [0017]    Finally, since the black resin has a bad dispensability compared to the metal, such as Cr or CrOx, a protrusion is easily formed at a surface of the black matrix  32  compared to Cr or CrOx. Thus, defection occurs at the black matrix  32 , thereby degrading a yield of the LCD.  
         SUMMARY OF THE INVENTION  
         [0018]    Accordingly, an object of the present invention is to provide an In-Plane Switching mode LCD device and a method of fabricating the same that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
           [0019]    An object of the present invention is to provide an In-Plane Switching mode LCD device and a method of fabricating the same capable of forming a fine pattern and improving a yield by forming a black matrix as a metal layer.  
           [0020]    Another object of the present invention is to provide an In-Plane Switching mode LCD device and a method of fabricating the same capable of preventing a vertical cross talk from occurring by electrically isolating a black matrix formed at each pixel from a neighboring pixel and thus minimizing distortion of a horizontal electric field.  
           [0021]    To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided an In-Plane Switching mode LCD device including a first substrate and a second substrate, a plurality of gate lines and a data lines formed on the first substrate and defining a plurality of pixels, a driving device disposed in each pixel of the first substrate, at least one pair of a first electrode and a second electrode arranged in each pixel of the first substrate and forming a horizontal electric field, a black matrix formed at the second substrate and having a slit around the pixel, and a liquid crystal layer formed between the first substrate and the second substrate.  
           [0022]    In another aspect, an In-Plane Switching mode LCD device includes a first substrate and a second substrate, a plurality of gate lines and data lines defining a plurality of pixels on the first substrate, a driving device disposed in each of the plurality of pixels, at least one pair of first electrode and second electrode arranged in each of the plurality of pixels to generate a horizontal electric field, a black matrix formed on the second substrate and electrically isolated from a neighboring pixel, and a liquid crystal layer formed between the first substrate and the second substrate.  
           [0023]    In another aspect, a method of fabricating an In-Plane Switching mode LCD device includes forming a plurality of gate lines and data lines defining a plurality of pixels on a first substrate, deposing a driving device on each of the plurality of pixels, arranging at least one pair of a first electrode and a second electrode on each of the plurality of pixels to generate a horizontal electric field, forming a black matrix having a slit around the plurality of pixels on a second substrate, and forming a liquid crystal layer between the first substrate and the second substrate.  
           [0024]    The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a unit of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:  
         [0026]    [0026]FIG. 1 is a schematic plane view of an IPS mode LCD device according to related art;  
         [0027]    [0027]FIG. 2A is a cross-sectional view taken along I-I′ of FIG. 1 according to related art;  
         [0028]    [0028]FIG. 2B is a cross-sectional view taken along II-II′ of FIG. 1 according to related art;  
         [0029]    [0029]FIG. 3A is a schematic plan view of an exemplary black matrix of an IPS mode LCD device according to the present invention;  
         [0030]    [0030]FIG. 3B is a schematic plan view of an exemplary black matrix of an IPS mode LCD device according to the present invention;  
         [0031]    [0031]FIG. 4 is a schematic plan view of an exemplary IPS mode LCD device according to the present invention; and  
         [0032]    [0032]FIG. 5 is a cross-sectional view taken along III-III′ of FIG. 4 according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0034]    [0034]FIG. 3A is a schematic plan views of an exemplary black matrix of an IPS mode LCD device according to the present invention. In FIG. 3A, a black matrix  132  formed on a second substrate  130  (of FIG. 5) is integrally formed over the entire surface of the second substrate  130 . Thus, in a case where the black matrix  132  made of metal of low resistance is integrally formed over the entire pixel, the entire black matrix  132  operates as one metal layer, thereby forming relatively large parasitic capacitance. Accordingly, an intensity of a vertical electric field formed by the black matrix  132  and a data line  104  (of FIG. 4) is increased, thereby distorting a horizontal electric field. Furthermore, during a vertical blanking period of an image signal input to the data line  104 , a time for an electric charge at the parasitic capacitance to be discharged is lengthened. Hence, the vertical electric field that distorts the horizontal electric field during a next image signal period becomes stronger.  
         [0035]    In addition, if the metal black matrix  132  is integrally formed over the entire pixel, the pixels are mutually affected by each other. For example, when an image signal is applied along the data line  104  (in FIG. 5), a vertical electric field is formed even at a pixel to which a weak image signal is currently applied by a strong signal of another pixel, thereby distorting the vertical electric field.  
         [0036]    According to the present invention, the above-mentioned problems can be solved by electrically isolating the black matrix  132  made of metal pixel by pixel. That is, by limiting the influence of the vertical electric field in each pixel to only a corresponding pixel, intensity of the vertical electric field is minimized. Accordingly, the distortion of the horizontal electric field due to the vertical electric field can be prevented. Thus, the vertical electric field is formed in the corresponding pixel by the black matrix  132 . However, the influence due to other pixels is excluded, so that the generated vertical electric field almost does not affect the horizontal electric field.  
         [0037]    [0037]FIG. 3B is a schematic plan views of an exemplary black matrix of an IPS mode LCD device according to the present invention. In FIG. 3B, the black matrix  132  formed at an edge of each pixel (i.e, an area where data and gate lines are formed) is electrically insulated from the black matrix  132  at a neighboring pixel. The black matrix  132  may be formed by removing a predetermined central portion of the black matrix  132  (in FIG. 3A). Since the black matrix  132  is formed by laminating a metal layer and then patterning it, the central portion is not substantially removed. Thus, the central portion where the black matrix has been removed may be referred to as a removal area or slit  133  formed at the black matrix  132 .  
         [0038]    [0038]FIG. 3B, a width of the black matrix  132  (including width of slit  133 ) is formed to be almost the same as that of the black matrix  132  (in FIG. 3A). Accordingly, in view of the slit  133 , the actual area of the black matrix  132  is decreased, thereby decreasing intensity of a vertical electric field formed between itself and the data line. Accordingly, the distortion of the horizontal electric field can be minimized.  
         [0039]    [0039]FIG. 4 is a schematic plan view of an exemplary IPS mode LCD device according to the present invention, and FIG. 5 is a cross-sectional view taken along III-III′ of FIG. 4. In FIG. 4, a gate line  103  and the data line  104  defining a pixel are arranged in a liquid crystal panel  101 . A thin film transistor  110  is formed at an intersection of the gate line  103  and the data line  104  in the pixel. At least one pair of a common electrode  105  and a pixel electrode  107  arranged substantially parallel to the data line  104  are disposed in the pixel, and form a horizontal electric field that is substantially parallel to a surface of the liquid crystal panel between the common electrode  105  and the pixel electrode  107  when a signal is applied to the pixel electrode  107  through the thin film transistor  110 . Also, a common line  116  connected with the common electrode  105  and a pixel electrode line  118  connected with the pixel electrode  107  are disposed in the pixel. The common line  116  and the pixel electrode line  118  are overlapped with each other, thereby forming storage capacitance.  
         [0040]    The black matrix  132  made of metal, such as Cr, CrOx, Cr/CrOx or the like is formed at an edge of the pixel, where the gate and date lines  103 ,  104  and the thin film transistor  110  are formed. The slit  133  (in FIG. 5) with a predetermined width is formed in the black matrix  132 , thereby separating the black matrix  132  of a corresponding pixel from the black matrix  132  of a neighboring pixel. In FIG. 4, the width of the slit  133  is not limited if the black matrix  132  of the corresponding pixel can be electrically isolated from that of the neighboring pixel. Since the black matrix  132  is made of metal having good etching anisotropy, a desired width of the slit  133  may be formed.  
         [0041]    In FIG. 5, the common electrode  105  and the pixel electrode  107  are respectively formed on a first substrate  120  and a gate insulating layer  122  made of a transparent insulating material, such as glass or the like. Even though not shown in FIG. 5, a gate electrode  111  is formed on the first substrate  120 , a semiconductor layer  112  is formed on the gate insulating layer  122 , and a thin film transistor  110  is formed on the semiconductor layer  122  when a source electrode  113  and a drain electrode  114  are formed. A passivation layer  124  is formed on the source electrode  113  and the drain electrode  114 .  
         [0042]    The black matrix  132  and a color filter layer  134  are formed on the second substrate  130  made of glass or the like. As mentioned above and shown in FIG. 5, the black matrix  132  ( 132   a ,  132   b ) is formed by etching Cr, CrOx, Cr/CrOx or the like by photolithography, forming the slit  133  with a predetermined width, so that a corresponding pixel is electrically isolated from other pixels. By such electrical isolation, an actual black matrix-formed area is decreased, and the black matrix  132   a  of the corresponding pixel is not affected by the black matrix  132   b  of the neighboring pixel. Accordingly, a vertical electric field between the data line  104  and the black matrix  132   a  of the corresponding pixel is decreased.  
         [0043]    In FIG. 5, the slit  133  is formed around the pixel. Since the slit  133  is an area where no black matrix is formed, light is directly leaked. Therefore, preferably, the slit  133  is formed along the gate line  103  and the data line  104  that define a pixel, to thereby prevent leakage of light. In FIG. 5, the black matrix  132  is formed so as to block only the data line  104  (or the gate line  103 ). But the black matrix  132  may be formed to block the data line  104  and the common electrode  105  disposed near the data line  104 . The common electrode  105  is disposed near the data line  104  in order to prevent distortion of the horizontal electric field due to the data line  104  and the pixel electrode  107  by shielding therebetween with the common electrode  105 . Accordingly, since a space between the data line  104  and the common electrode  105  becomes an image non-displayed area where the horizontal electric field is not applied, the black matrix  132   a  may be enlarged to the common electrode  105 . Even though not shown, an overcoat layer may be formed on the color filter layer  124  in order to protect the color filter layer  124  and improve flatness. Finally, by forming a liquid crystal layer  140  between the first substrate  120  and the second substrate  130 , an IPS mode LCD device is thus completed.  
         [0044]    In general, since Cr, CrOx or the like has a good light blocking property, light can be effectively blocked even with a film having a thin thickness. Accordingly, in the IPS mode LCD device in accordance with the present invention, the black matrix  132  can be formed to have a thin thickness, so that flatness of the second substrate  130  can be improved. In addition, a step between the slit  133  and the black matrix  132  ( 132   a ,  132   b ) can be minimized.  
         [0045]    The black matrix  132  in accordance with the present invention may be made of metal other than Cr, CrOx, Cr/CrOx or the like. That is, any kind of metal may be used for the black matrix in accordance with the present invention, if it has a good light blocking property and processability (etching anisotropy). In addition, while a specific structure of the IPS mode LCD device has been described, those descriptions are for explaining the present invention, not for limiting the present invention. For example, in FIG. 5, the common electrode  105  and the pixel electrode  107  are respectively formed on the first substrate  120  and the gate insulating layer  122 . However, the common electrode  105  and the pixel electrode  107  may be respectively formed on the gate insulating layer  122  and the first substrate  120 . In addition, both of the common electrode  105  and the pixel electrode  107  may be formed on the passivation layer  124  or on the first substrate  120 . Metal for forming the common electrode  105  and the pixel electrode  107  is not also limited to a specific metal. Also, the data line  104 , the common electrode  105  and the pixel electrode  107  may be shaped as a zigzag form.  
         [0046]    As described above, in the IPS mode LCD device in accordance with the present invention, the black matrix  132  for preventing leakage of light is formed as a metal layer, so that the black matrix  132  can be formed with a fine pattern. Accordingly, the IPS mode LCD device having a high resolution can be fabricated.  
         [0047]    In addition, since Cr, CrOx or the like used for the present invention has a good light blocking rate compared to a black resin, even though a metal layer made of Cr, CrOx or the like has a relatively thin thickness, light transmitting a liquid crystal layer can be effectively blocked. Accordingly, the black matrix  132  with a thin thickness can be realized, and a step can be prevented from being generated.  
         [0048]    Furthermore, in the present invention, the distortion of the horizontal electric field applied to the liquid crystal layer  140  can be minimized by separating the black matrix  132   a  formed in one pixel from the black matrix  132   b  formed in a neighboring pixel. Hence, the vertical cross talk due to the distortion of the horizontal electric field can be prevented from occurring.  
         [0049]    In the present invention, a fine pattern can be formed, a color filter layer can be flattened, no step is generated, and the quality of a black matrix is not degraded. Further, a black matrix which can prevent a vertical cross talk from being generated by a horizontal electric field distortion between a common electrode and a pixel electrode is provided. Furthermore, since such a black matrix is formed, an IPS mode LCD device having improved quality and an improved yield can be fabricated.  
         [0050]    Therefore, in the present invention, a black matrix is formed as a metal layer of Cr, CrOx, Cr/CrOx or the like. Since the metal has good etching anisotropy, a fine line width may be formed and thus the black matrix having a fine pattern may be formed by being made of Cr, CrOx, Cr/Ox or the like. In addition, since the metal layer of Cr, CrOx, Cr/CrOx or the like has a good light blocking rate, light transmitting a liquid crystal layer may be effectively blocked even with the metal layer having thin thickness. Accordingly, the black matrix with a thin thickness can be formed. Meanwhile, in the present invention, by separating the black matrix formed in one pixel from another black matrix formed in a neighboring pixel, the black matrix in each pixel is electrically isolated from the outside.  
         [0051]    As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to be embraced by the appended claims.