Abstract:
A liquid crystal display panel capable of preventing flicker and improving reflectance include a thin film transistor substrate having a gate line, a data line, a thin film transistor connected to the gage and data lines, and a reflective electrode connected to the thin film transistor and covering at least part of the gate line, a color filter substrate having a color filter and a common electrode forming an electric field with the reflective electrode. Liquid crystals are disposed between the thin film transistor substrate and the color filter substrate. The reflective electrode shields the liquid crystals from a gate signal.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to a thin film transistor substrate, and more particularly, to a thin film transistor substrate capable of preventing flicker and improving reflectance, a liquid crystal display panel including the same, and a method of manufacturing the liquid crystal display panel. 
         [0003]    2. Discussion of the Related Art 
         [0004]    A liquid crystal display (LCD) device displays an image by using electrical and optical properties of liquid crystals. The LCD device includes an LCD panel for displaying an image through a pixel matrix, a driving circuit for driving the LCD panel, and a backlight unit for supplying light to the LCD panel. The LCD device is widely used ranging from small-sized display devices to large-sized display devices, such as mobile communication terminals, notebook computers, monitors and LCD TVs. 
         [0005]    The LCD device may be classified according to a type of light source into a transmissive type using an internal light, a reflective type using an external light, and a transflective type using both the internal light and the external light. The transflective LCD device displays an image in a reflective mode if the external light is sufficient, and in a transmissive mode using a backlight unit if the external light is insufficient. Therefore, the transflective LCD device reduces power consumption and is not restricted to using external light. 
         [0006]    The transflective LCD device has a structure in which a lower substrate  1  faces an upper substrate  11  with liquid crystal molecules  20  of an optically compensated bend (OCB) mode disposed therebetween, as illustrated in  FIG. 1 . 
         [0007]    On the lower substrate  1 , a reflective electrode  8  and a pixel electrode  10 A of a first subpixel area face a pixel electrode  10 B of a second subpixel with a gate line  4  disposed therebetween, the gate line being covered by an insulation layer  6 . 
         [0008]    A black matrix  2  separating the respective subpixel areas from each other, a color filter  16  formed in each subpixel area, an overcoat layer  14  having different thickness in a reflective area and a transmissive area, and a common electrode  12  forming a vertical electric field with respect to the pixel electrodes  10 A and  10 B and the reflective electrode  8 , are formed on the upper substrate  11 . 
         [0009]    Due to an electric field formed between the common electrode  12  (or between the reflective electrode  8 ) and the gate line  4 , an arrangement of the liquid crystal molecules  20  is changed, for example, inverted, at an edge of the reflective electrode  8  (or of the gate line  4 ). Since an arrangement of the liquid crystal molecules  20  at an edge of the reflective electrode  8  is different than in the other areas, light leakage occurs at the edge of the reflective electrode  8 , resulting in flickering. Light leakage may be more severe in a line inversion scheme that supplies data voltages of different polarities to the adjacent pixel electrodes  10 A and  10 B with the gate line  4  disposed therebetween. 
         [0010]    If the black matrix  2  is widened to partially overlap the first subpixel area so that an edge of the reflective electrode  8  can be blocked in order to prevent the light leakage, reflectance is lowered due to a decrease in an effective area of the reflective electrode  8 . 
       SUMMARY OF THE INVENTION 
       [0011]    Embodiments of the present invention provide a thin film transistor (TFT) substrate capable of preventing flicker and improving reflectance, an LCD including the same, and a method of manufacturing the LCD panel. 
         [0012]    In accordance with an embodiment of the present invention, an LCD panel includes a TFT substrate including a gate line, a data line, a LCD connected to the gate line and data line, and a reflective electrode connected to the LCD and covering at least a part of the gate line, and a color filter substrate facing the thin film transistor substrate and including a color filter and a common electrode forming an electric field with the reflective electrode. Liquid crystals are disposed between the thin film transistor substrate and the color filter substrate. The reflective electrode shields the liquid crystals from a gate signal. 
         [0013]    The LCD panel further includes a pixel electrode connected to the TFT. 
         [0014]    The color filter substrate further includes an overcoat layer that has a first end and a second end overlapping the reflective electrode. The overcoat layer is formed on the color filter. 
         [0015]    The TFT substrate further includes a storage electrode forming a first storage capacitor by insulatedly overlapping a drain electrode of the TFT, a first storage line connected to the storage electrode and adjacent to a first end of the gate line, and a second storage line that forms a second storage capacitor by insulatedly overlapping the pixel electrode. The second storage line is adjacent to a second end of the gate line. 
         [0016]    The second storage line overlaps at least two pixel electrodes that are adjacent to each other in the direction of the length of the data line. 
         [0017]    The TFT substrate further includes a shield pattern overlapping the data line and having a wider width than that of the data line. 
         [0018]    The TFT substrate further includes a storage electrode forming a first storage capacitor by insulatedly overlapping a drain electrode of the TFT, a first storage line connected to the storage electrode and adjacent to a first end of the gate line, and a second storage line that forms a second storage capacitor by insulatedly overlapping the pixel electrode. The second storage line is adjacent to a second end of the gate line, wherein the shield pattern is electrically connected to the second storage line. 
         [0019]    In accordance with an embodiment of the present invention, a TFT substrate includes a gate line formed on a substrate, a data line insulatedly crossing the gage line, a TFT connected to the gate and data lines, and a reflective electrode connected to the TFT and formed to cover at least a portion of the gate line to shield the gate line. 
         [0020]    The second storage line is located between two pixel electrodes to which data signals having different polarities are supplied. 
         [0021]    In accordance with an embodiment of the present invention, a method of manufacturing a LCD panel includes providing a TFT substrate including a gate line, a data line, a TFT connected to the gate line and data line, and a reflective electrode connected to the TFT and covering at least a portion of the gate line to shield the gate line, providing a color filter substrate including a color filter and a common electrode forming an electric field with the reflective electrode, and bonding the TFT substrate and the color filter substrate with liquid crystals disposed therebetween. 
         [0022]    Providing the TFT substrate includes forming on the substrate the gate and data lines and the TFT connected to the gate and data lines, forming a passivation layer to cover the TFT, forming a pixel electrode connected to the TFT on the passivation layer, and forming the reflective electrode overlapping the gate line. 
         [0023]    Providing the TFT substrate further includes forming, on the same plane and with the same metal as the gate line, a storage electrode forming a first storage capacitor by insulatedly overlapping a drain electrode of the TFT, a first storage line that is connected to the storage electrode and adjacent to a first end of the gate line, and a second storage line that forms a second storage capacitor by insulatedly overlapping the pixel electrode and is adjacent to a second end of the gate line. 
         [0024]    Providing the TFT substrate further includes forming a shield pattern that overlaps the data line and has a wider width than that of the data line. The shield pattern is formed on the same plane and with the same metal as the gate line. 
         [0025]    The shield pattern is electrically connected to the second storage line. 
         [0026]    Providing the color filter substrate includes forming the color filter on the substrate, forming on the color filter an overcoat layer that has a first and a second end overlapping the reflective electrode, and forming the common electrode on the substrate on which the overcoat layer is formed. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    Exemplary embodiments of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0028]      FIG. 1  is a cross-sectional view illustrating a conventional transflective LCD panel; 
           [0029]      FIG. 2  is a plane view illustrating a TFT substrate of a transflective LCD panel according to an embodiment of the present invention; 
           [0030]      FIG. 3  is a cross-sectional view illustrating the TFT substrate taken along lines I-I′ and II-II′ in  FIG. 2 ; 
           [0031]      FIG. 4  is a plane view illustrating a TFT substrate of a transflective LCD panel according to an embodiment of the present invention; 
           [0032]      FIG. 5  is a cross-sectional view illustrating the LCD panel including the TFT substrate shown in  FIG. 3  and a color filter substrate according to an embodiment of the present invention; 
           [0033]      FIGS. 6A and 6B  are a plane view and a cross-sectional view for describing a process of manufacturing a first conductive pattern group of a TFT substrate according to an embodiment of the present invention; 
           [0034]      FIGS. 7A and 7B  are a plane view and a cross-sectional view for describing a process of manufacturing a second conductive pattern group and a semiconductor pattern group of a TFT substrate according to an embodiment of the present invention; 
           [0035]      FIGS. 8A and 8B  are a plane view and a cross-sectional view for describing a process of manufacturing an inorganic passivation layer and an organic passivation layer of a TFT substrate according to an embodiment of the present invention; 
           [0036]      FIGS. 9A and 9B  are a plane view and a cross-sectional view for describing a process of manufacturing a third conductive pattern group of a TFT substrate according to an embodiment of the present invention; and 
           [0037]      FIGS. 10A and 10B  are a plane view and a cross-sectional view for describing a process of manufacturing a fourth conductive pattern group of a TFT substrate according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0038]    Exemplary embodiments of the present invention will now be described with reference to the attached drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. 
         [0039]      FIGS. 2 and 3  are a plane view and cross-sectional views illustrating a TFT substrate of a transflective LCD device according to an embodiment of the present invention. 
         [0040]    Referring to  FIGS. 2 and 3 , a TFT substrate  160  includes a gate line  102  and a data line  104  that intersect each other, a TFT connected to the gate line  102  and to the data line  104 , a pixel electrode  122  formed in each subpixel area SPA, a reflective electrode  124  connected to the TFT, and first and second storage capacitors that maintain the stability of a video signal charged to the pixel electrode. The reflective and pixel electrodes  124  and  122  define a reflective area RA and a transmissive area TA of each subpixel area SPA. 
         [0041]    The data line  104  supplies a data signal to the pixel electrode  122  and to the reflective electrode  124  through the TFT. The gate line  102  supplies a gate signal to a gate electrode  106  of the TFT. One side of the gate line  102  is formed to be adjacent to a first storage line  132  and the other side thereof is formed to be adjacent to a second storage line  136 . 
         [0042]    The TFT includes the gate electrode  106  connected to the gate line  102 , an active layer  114  overlapping the gate electrode  106  with a gate insulating layer  112  disposed therebetween, a source electrode  108  connected to the data line  104  and to part of the active layer  114 , and a drain electrode  110  connected to another part of the active layer  114 . The TFT further includes an ohmic contact layer  116  for ohmic contact between the source electrode  108 , the drain electrode  110  and the active layer  114 . The gate electrode  106  and the gate line  102  are formed of the same metal on the lower substrate  101 . The active layer  114  and the ohmic contact layer  116  are deposited on the gate insulating layer  112 , and the source electrode  108  and the drain electrode  110  are formed of the same metal as the data line  104 . The source and drain electrodes  108 ,  110  may be formed on the same plane as the data line  104 . The TFT is connected to the pixel electrode  122  and to the reflective electrode  124  through a contact hole  120  penetrating an inorganic passivation layer  118  and an organic passivation layer  126  formed on the TFT. The TFT supplies the data signal of the data line  104  to the pixel electrode  122  and to the reflective electrode  124  in response to the gate signal of the gate line  102 . 
         [0043]    The pixel electrode  122  is formed on the organic passivation layer  126  of each subpixel area SPA and is connected to the drain electrode  110  through the contact hole  120 . The pixel electrode  122  is formed of a transparent conductive material with high transmittance and transmits an internal light from a backlight unit. Video signals of different polarities are charged to adjacent pixel electrodes  122  in up and down directions with the second storage line  136  disposed therebetween (see, e.g.,  FIG. 2 ). Therefore, adjacent pixel electrodes  122  may be separated from each other at prescribed intervals so that they do not affect each other. For example, the adjacent pixel electrodes  122  in up and down directions with the second storage line  136  disposed therebetween are separated from each other by about 7 μm to about 20 μm. 
         [0044]    The reflective electrode  124  is formed in a reflective area RA of each subpixel area SPA and is connected to the drain electrode  110  through the pixel electrode  122  formed thereunder. An area in which the reflective electrode  124  is formed in each subpixel area SPA is defined as the reflective area RA, and an area in which the reflective electrode  124  is not formed is defined as the transmissive area TA. The reflective electrode  124  is formed of a conductive material with high reflectance and reflects an external light. In order to improve reflective efficiency, the organic passivation layer  126  may have an embossed surface so that the reflective electrode  124  formed thereon also has an embossed surface. Referring to  FIG. 2 , for example, an outer part of the reflective electrode  124  overlaps a side of the data line  104  and overlap the TFT. Since a channel part of the TFT is protected by the reflective electrode  124 , no additional black matrixes are needed. The reflective electrode  124  overlaps the gate line  102  between the first and second storage lines  132  and  136  and overlaps a side of the second storage line  136  adjacent to the gate line  102 . Thus, since the gate signal of the gate line  102  is shielded by the reflective electrode  124 , an arrangement of liquid crystal molecules is not distorted throughout the entire area of the reflective electrode  124 . That is, since the LCD device according to the embodiments of the present invention does not need an additional black matrix for preventing the liquid crystal molecules from being distorted, reflectance is improved. In addition, when the reflectance is maintained constant, the LCD device of the embodiments of the present invention has improved transmittance compared to a conventional LCD device by, for example, about 20% or more. Furthermore, since the LCD device of the embodiments of the present invention can prevent light leakage, flicker caused by the light leakage is prevented. 
         [0045]    The first and second storage capacitors maintain the stability of the video signal charged to the pixel electrode  122  until the next signal is charged. 
         [0046]    The first storage capacitor is formed such that the drain electrode  110  connected to the pixel electrode  122  overlaps the storage electrode  134  with the gate insulating layer  112  disposed therebetween. The storage electrode  134  protrudes from the first storage line  132 . 
         [0047]    The second storage capacitor is formed such that the pixel electrode  122  overlaps the second storage line  136  with the gate insulating layer  112 , the inorganic passivation layer  118  and the organic passivation layer  126  disposed therebetween. The second storage line  136  is in parallel with the gate line  102  and overlaps the pixel electrodes  122  that are adjacent to each other in up and down directions, that is, in the direction of the data line  104 . 
         [0048]    The second storage line  136  is separated at given intervals from a shield pattern  138  overlapping the data line  104 . Since the shield pattern  138  overlaps the data line  104  with wider width than the data line  104 , light leakage between the data line  104  and the pixel electrode  122  can be prevented. 
         [0049]    The shield pattern  138  may include, as illustrated in  FIG. 4 , a shield part  138   b  overlapping the data line  104  and a second storage line part  138   a  parallel with the gate line  102 . The second storage line part  138   a  and the shield part  138   b  may be electrically connected to form a united shape. A common voltage that is a reference voltage during the driving of the LCD device or a storage voltage is supplied to the shield pattern  138  through the second storage line part  138   a . In this case, the shield pattern  138  prevents light leakage between the data line  104  and the pixel electrode  122  and shields the video signal of the data line  104 , thereby suppressing a coupling phenomenon caused by a parasitic capacitance between the data line  104  and the pixel electrode  122 . 
         [0050]    The area of the second storage line part  138   a  formed in an electrically united form with the shield part  138   b  is increased by the shield part  138   b . An overlapping area between the second storage line part  138   b and the pixel electrode  122  increases the capacitance of the second storage capacitor. As a result, a kickback voltage that is in inverse proportion to the increased capacitance of the second storage capacitor decreases. If the area of the storage electrode  134  decreases, the increased kickback voltage due to the decreased capacitance of the first storage capacitor is reduced by the second storage capacitor. 
         [0051]    The TFT substrate  160  illustrated in  FIG. 3  or  4  is bonded to the color filter substrate  150  including the color filter  152 , as shown in  FIG. 5 . A liquid crystal layer is disposed between the TFT and color filter substrates  160 ,  150 . Referring to  FIG. 5 , the TFT substrate  160  illustrated in  FIG. 3  is bonded to the color filter substrate  150 , thereby forming an LCD panel. 
         [0052]    The color filter substrate  150  includes the color filter  152  formed on the upper substrate  111 , and an overcoat layer  154  and a common electrode  156  deposited on the color filter  152 . 
         [0053]    The color filter  152  is formed on the upper substrate  111  in ref (R), green (G), and blue (B) subpixel areas SPA to define R, G and B subpixels. 
         [0054]    The overcoat layer  154  compensates for a difference in a light path between an external light emitted twice through the liquid crystal layer in the reflective area RA and an internal light emitted once through the liquid crystal layer in the transmissive area TA. To this end, the overcoat layer  154  has a through hole  158  for exposing the color filter  152  in the transmissive area TA. Alternatively, the overcoat  154  has the through hole  158  for penetrating a part of the overcoat  154  in order to compensate for a difference in the light path and to compensate for a stepped difference between the color filters  152 . 
         [0055]    An end of the overcoat layer  154  overlaps the reflective electrode  124  adjacent to the second storage line  136 , and the another end thereof is adjacent to the storage electrode  134  and overlaps the reflective electrode  124 . As a result, the arrangement of liquid crystals is similar to an up and down symmetrical structure. 
         [0056]    The common electrode  156  comprising, for example, a transparent conductive material is formed on the overcoat layer  154 . 
         [0057]      FIGS. 6A to 10B  are plane views and cross-sectional views illustrating a process of manufacturing a TFT substrate. A process of manufacturing the TFT substrate illustrated in  FIG. 2  will be described by way of example. 
         [0058]    As shown in  FIGS. 6A and 6B , a first conductive pattern group, including the gate line  102 , the gate electrode  106  connected to the gate line  102 , the first and second storage lines  132  and  136  adjacent to the gate line  102 , the storage electrode  134  connected to the first storage line  132 , and the shield pattern  138  adjacent to the second storage line  136 , is formed on the lower substrate  101 . 
         [0059]    More specifically, a gate metal layer is formed on the lower substrate  101  by a deposition method such as sputtering. The gate metal layer is formed in a single layer structure composed of a metal such as molybdenum (Mo), titanium (Ti), cupper (Cu), aluminum neodymium (AlNd), aluminum (Al), chrome (Cr), Mo alloy, Cu alloy or Al alloy, or in a multi-layered structure composed of a combination of these metals. Next, the gate metal layer is patterned by a photolithography process and an etching process, thereby forming the first conductive pattern group including the gate line  102 , the gate electrode  106 , the first and second storage lines  132  and  136 , the storage electrode  134  and the shield pattern  138 . 
         [0060]    Referring to  FIGS. 7A and 7B , the gate insulating layer  112  is formed on the lower substrate  101  on which the first conductive pattern group is formed. A second conductive pattern group, including the data line  104 , the source electrode  108  and the drain electrode  110 , is formed on the gate insulating layer  112 . A semiconductor pattern group, including the active layer  114  and the ohmic contact layer  116  overlapping the second conductive pattern group, is formed under the second conductive pattern group. The semiconductor pattern group and the second conductive pattern group are formed by one mask process using a diffraction exposure mask or a half-tone mask. 
         [0061]    Specifically, the gate insulating layer  112 , an amorphous silicon layer, an impurity (n+ or p+) doped amorphous silicon layer, and a source/drain metal layer are sequentially formed on the lower substrate  101  on which the first conductive pattern group is formed. An inorganic insulating material such as silicon oxide (SiOx) or silicon nitride (SiNx) is used as the gate insulating layer  112 . The source/drain metal layer is formed in a single metal layer structure composed of a metal such as Mo, Ti, Cu, AlNd, Al, Cr, Mo alloy, Cu alloy or Al alloy, or in a multi-layered structure composed of a combination of these metals. A photoresist is deposited on the source/drain metal layer, and the photoresist is exposed and developed by a photolithography process using a different exposure mask, thereby forming first and second photoresist patterns having a step coverage. The first photoresist pattern is located in an area in which the semiconductor pattern group and the second conductive pattern group are to be formed. The second photoresist pattern having a thinner thickness than the first photoresist pattern is located in an area in which the channel of the TFT is to be formed. The second conductive pattern group, and the semiconductor pattern group under the second conductive pattern group are formed by patterning the source/drain metal layer by an etching process using the photoresist patterns. The source electrode  108  and the drain electrode  110  of the second conductive pattern group are electrically connected to each other. 
         [0062]    The thickness of the first photoresist pattern is reduced by an ashing process using oxygen (O 2 ) plasma, and the second photoresist pattern is removed. By an etching process using the ashed first photoresist pattern, the second conductive pattern group exposed by removing the second photoresist pattern, and the ohmic contact layer  116  under the second conductive pattern group are removed, thereby separating the source electrode  108  and the drain electrode  110  from each other and exposing the active layer  114 . 
         [0063]    The first photoresist pattern remaining on the source/drain metal pattern is removed by a strip process. 
         [0064]    Referring to  FIGS. 8A and 8B , the inorganic passivation layer  118  is formed on the gate insulating layer  112  on which the second conductive pattern group is formed. Next, the organic passivation layer  126  having an embossed surface is formed on the inorganic passivation layer  118 . 
         [0065]    More specifically, the inorganic passivation layer  118  is formed on the gate insulating layer  112  on which the second conductive pattern group is formed. The inorganic passivation layer  118  may be formed of the same inorganic insulating material as the gate insulating layer. The organic passivation layer  126  having an embossed surface is formed on the inorganic passivation layer  118 . The organic passivation layer  126  comprises a resin including, for example, an alkali-soluble group, a photoactive compound (PAC), a solvent, and an additive (for example, an adhesion promoter or surfactant). By patterning the inorganic passivation layer  118  and the organic passivation layer  126  by a photolithography process and an etching process, the contact hole  120  exposing the drain electrode  110  by penetrating the inorganic passivation layer  118  and the organic passivation layer  126  is formed. 
         [0066]    Referring to  FIGS. 9A and 9B , a third conductive pattern group including a pixel electrode is formed on the organic passivation layer  126 . 
         [0067]    More specifically, a transparent conductive layer is formed on the organic passivation layer  126  by a deposition method such as sputtering to keep an embossed shape. The pixel electrode  122  is formed in each subpixel area by patterning the transparent conductive layer by a photolithography process and an etching process. The pixel electrode  122  is connected to the drain electrode  110  through the contact hole  120 . As he transparent conductive layer, for example, tin oxide (TO), indium tin oxide (ITO), indium zinc oxide (IZO), or indium tin zinc oxide (ITZO) may be used. 
         [0068]    Referring to  FIGS. 10A and 10B , a fourth conductive pattern group including the reflective electrode  124  is formed on the third conductive pattern group. 
         [0069]    More specifically, while maintaining an embossed shape, a reflective metal layer is deposited on the organic passivation layer  126  on which the pixel electrode  122  is formed. A metal with high reflectance such as Al or AlNd is used as the reflective metal layer. The fourth conductive pattern group including the reflective electrode  124  is formed in each subpixel area by patterning the reflective metal layer by a photolithography process and an etching process. 
         [0070]    While the embodiments of the present invention have been applied to a transflective LCD device, they are not limited thereto, and may be, for example, applicable to a reflective LCD device. The second storage line may overlap the reflective electrode. In addition, while the reflective electrode has been described as being formed on the pixel electrode, it is possible to form the pixel electrode on the reflective electrode or form the pixel and reflective electrodes on the same layer. 
         [0071]    As described above, the TFT substrate and the LCD device including the same according to embodiments of the present invention have the gate line covered by the reflective electrode. Therefore, an uneven arrangement of the liquid crystals occurring at the edge of the reflective electrode caused by the gate signal can be presented. As a result, flicker can be prevented and a reflective rate is improved. 
         [0072]    Moreover, since the TFT substrate and the LCD device including the same according to embodiments of the present invention prevent light leakage by using the reflective electrode, the storage line and the shield pattern, no additional black matrixes are needed. As a result, because a mask process for forming the black matrixes is unnecessary, a manufacturing process is simplified and a manufacturing cost is reduced. Also, yield and an aperture ratio are improved. 
         [0073]    While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.