Abstract:
A thin film transistor array panel comprising an insulating substrate; a plurality of first signal lines formed on the insulating substrate; a plurality of second signal lines intersecting the first signal lines in an insulated manner to define pixel areas; a plurality of first pixel electrodes formed in each of the pixel areas; a plurality of thin film transistors having three electrodes respectively connected to the first signal line, the second signal line, and the first pixel electrode; and a plurality of second pixel electrodes formed in each of the pixel areas and electrically coupled with the first pixel electrodes, wherein the pixels include red, green, and blue pixels, and coupling capacitances between the first pixel electrodes and the second pixel electrodes are different among the red, green, and blue pixels. An LCD using such a thin film transistor array panel shows improved side visibility and has a wide viewing angle.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a liquid crystal display and a thin film transistor array panel.  
         [0003]     2. Description of the Related Art  
         [0004]     A liquid crystal display (LCD) is one of the most widely used flat panel displays. An LCD includes two panels provided with field-generating electrodes, and a liquid crystal (LC) layer interposed therebetween. The LCD displays images by applying voltages to the field-generating electrodes to generate an electric field in the LC layer, which determines orientations of LC molecules in the LC layer to adjust polarization of incident light.  
         [0005]     The LCD has a disadvantage of a narrow viewing angle. Various techniques for enlarging the viewing angle have been suggested, and a technique utilizing a vertically aligned LC and providing cutouts or protrusions at field-generating electrodes such as pixel electrodes and a common electrode is promising.  
         [0006]     To describe the method of providing cutouts in more detail, pixel electrodes and a common electrode respectively have cutouts, the cutouts induce a slanted electric field, and the slanted electric field controls falling directions of liquid crystals. Control of the falling direction of liquid crystals makes it possible to widen the viewing angle of liquid crystal display. To describe the method of providing protrusions in more detail, protrusions are formed on both of pixel electrodes and a common electrode, the protrusions induce a slanted electric field, and the slanted electric field controls falling directions of liquid crystals.  
         [0007]     Other methods in which pixel electrodes have cutouts and protrusions formed on a common electrode is also possible to control falling directions of liquid crystals. An LCD using cutouts or protrusions has an excellent viewing angle of over 80 degrees in any direction, in view of the contrast ratio where 1:10 is a standard contrast ratio and in view of gray scale inversion where a viewing angle of occurring brightness inversion is a standard angle. However, such an LCD shows poor visibility that is even inferior to a twisted nematic mode LCD. The poor visibility is caused by discordance of the gamma curve between the front view and side view. For example, in a vertically aligned mode LCD using cutouts, as the viewing angle is increased, the picture plane becomes brighter and the color shifts toward white. When this phenomenon is excessive, the image is distorted because the brightness difference between gray scales disappears. As the use of the LCD is widened to include multimedia displays, the visibility becomes more important.  
       SUMMARY OF THE INVENTION  
       [0008]     An object of the present invention is to provide an LCD having improved visibility. To achieve such an object, a pixel area includes two pixel electrodes, different voltages are applied to the two pixel electrodes, and a voltage difference between the two pixel electrodes is different among red, green, and blue pixels.  
         [0009]     Concretely, a thin film transistor array panel comprises: an insulating substrate; a plurality of first signal lines formed on the insulating substrate; a plurality of second signal lines intersecting the first signal lines in an insulated manner to define pixel areas; a plurality of first pixel electrodes formed in each of the pixel areas; a plurality of thin film transistors having three electrodes respectively connected to the first signal line, the second signal line, and the first pixel electrode; and a plurality of second pixel electrodes formed in each of the pixel areas and electrically coupled with the first pixel electrodes, wherein the pixels include red, green, and blue pixels and coupling capacitances between the first pixel electrode and the second pixel electrode are different among the red, green, and blue pixels.  
         [0010]     The thin film transistor array panel may further comprise a plurality of coupling electrodes connected to the first pixel electrode and overlapped with the second pixel electrodes in an insulated manner. At least one of the first and second pixel electrodes may have a domain dividing member. The coupling electrodes may be connected to and elongated from drain electrodes of the thin film transistors. The length of the coupling electrodes may decrease in an order of green, red, and blue pixels, and the width of the coupling electrodes may decrease in an order of green, red, and blue pixels. When the coupling capacitance between the first pixel electrode and the second pixel electrode in a green pixel is 1, the coupling capacitance of the first pixel electrode and the second pixel electrode in a red pixel preferably ranges from 0.95 to 1.0 and that of a blue pixel preferably ranges from 0.75 to 0.95.  
         [0011]     A thin film transistor array panel comprises: an insulating substrate; a plurality of first signal lines formed on the insulating substrate; a plurality of second signal lines intersecting the first signal lines in an insulated manner to define pixel areas; a plurality of first pixel electrodes formed in each of the pixel areas; a plurality of thin film transistors having three electrodes respectively connected to the first signal line, the second signal line, and the first pixel electrode; and a plurality of second pixel electrodes formed in each of the pixel areas and electrically coupled with the first pixel electrodes, wherein the pixels include red, green, and blue pixels and area ratios of the second pixel electrode with respect to the first pixel electrode are different among the red, green, and blue pixels.  
         [0012]     The thin film transistor array panel may further comprise a plurality of coupling electrodes connected to the first pixel electrode and overlapped with the second pixel electrodes in an insulated manner. The coupling electrodes may be connected to and elongated from drain electrodes of the thin film transistors. At least one of the first and second pixel electrodes may have a domain dividing member. The area ratios of the second pixel electrode with respect to the first pixel electrode may increase in an order of green, red, and blue pixels. The area ratios of the second pixel electrode with respect to the first pixel electrode in green, red, and blue pixels may be respectively 6:4, 5.5:4.4, and 5:5. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The above and other advantages of the present invention will become more apparent by describing preferred embodiments thereof in detail with reference to the accompanying drawings, in which:  
         [0014]      FIG. 1  is a layout view of a thin film transistor array panel for an LCD according to an embodiment of the present invention;  
         [0015]      FIG. 2  is a layout view of a color filter panel for an LCD according to an embodiment of the present invention;  
         [0016]      FIG. 3  is a layout view of an LCD according to the embodiment shown in  FIGS. 1 and 2 ;  
         [0017]      FIG. 4  is a sectional view of the LCD shown in  FIG. 3  taken along the line IV-IV′;  
         [0018]      FIG. 5  is a circuit diagram of the LCD shown in FIGS.  1  to  4 ;  
         [0019]      FIG. 6  is a layout view of a thin film transistor array panel for an LCD according to another embodiment of the present invention;  
         [0020]      FIG. 7  is a sectional view of the LCD shown in  FIG. 6  taken along the line VII-VII′;  
         [0021]      FIG. 8  is a layout view of a thin film transistor array panel for an LCD according to another embodiment of the present invention;  
         [0022]      FIG. 9  is a layout view of a thin film transistor array panel for an LCD according to another embodiment of the present invention;  
         [0023]      FIG. 10A  is a gamma curve front view.  
         [0024]      FIG. 10B  is a gamma curve upper side view.  
         [0025]      FIG. 10C  is a gamma curve diagonal side view. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein.  
         [0027]     In the drawings, the thickness of layers, films, and regions are exaggerated for clarity. Like numerals refer to like elements throughout. It is to be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.  
         [0028]     Now, liquid crystal displays and thin film transistor (TFT) array panels for LCDs according to embodiments of the present invention will be described with reference to the accompanying drawings.  
         [0029]      FIG. 1  is a layout view of a thin film transistor array panel for an LCD according to an embodiment of the present invention;  FIG. 2  is a layout view of a color filter panel for an LCD according to an embodiment of the present invention;  FIG. 3  is a layout view of an LCD according to the embodiment shown in  FIGS. 1 and 2 ; and  FIG. 4  is a sectional view of the LCD shown in  FIG. 3  taken along the line IV-IV′.  
         [0030]     An LCD according to an embodiment of the present invention includes a TFT array panel  100 , a common electrode panel  200 , and a LC layer  3  interposed between the panels  100  and  200  and containing a plurality of LC molecules aligned vertically to surfaces of the panels  100  and  200 .  
         [0031]     A structure of the TFT array panel  100  will now be described. A plurality of first and second pixel electrodes  190   a  and  190   b  made of indium tin oxide (ITO) or indium zinc oxide (IZO) are formed on an insulating substrate  110  made of a transparent material such as glass. The first pixel electrode  190   a  is connected to a thin film transistor and receives image data voltages. The second pixel electrode  190   b  is overlapped with a coupling electrode  176  which is connected to the first pixel electrode  190   a . Therefore, the second pixel electrode  190   b  is electrically coupled with the first pixel electrode  190   a . The overlapping areas between the second pixel electrode  190   b  and the coupling electrode  176  are different among red, green, and blue pixels.  
         [0032]     The thin film transistor connected to a gate line  121  transferring scanning signals and a data line  171  transferring image data signals. The thin film transistor switches the image data signals to be applied or to not be applied to the first pixel electrode  190   a  according to the scanning signals. The second pixel electrode  190   b  has cutouts  192 . A polarizer  12  is attached to the lower surface of the insulating substrate  110 . When a reflective LCD is considered, the first and second pixel electrodes  190   a  and  190   b  may be made of a non-transparent material. In this case, the polarizer  12  is omitted.  
         [0033]     A structure of the color filter panel will now be described. A light blocking layer  220  to prevent light leakage, red, green, and blue color filters  230 , and a common electrode  270  made of a transparent conductor such as ITO or IZO are formed on an insulating substrate  210  made of a transparent material such as glass. The common electrode  270  has cutouts  271 ,  272 , and  273 . The light blocking layer  220  may be formed on areas overlapping with the cutouts  271 ,  272 , and  273 , as well as around pixel areas to prevent light leakage due to the cutouts  271 ,  272 , and  273 .  
         [0034]     The TFT array panel  100  will now be described in more detail with reference to  FIGS. 1, 4 , and  5 . A plurality of gate lines  121  and a plurality of storage electrode lines  131  are formed on an insulating substrate  110 . The gate lines  121  extend substantially in a transverse direction and are separated from each other and transmit gate signals. Each gate line  121  has a plurality of gate electrodes  123  and expansions  125  for connecting to an external circuit.  
         [0035]     Each storage electrode line  131  extends substantially in the transverse direction and includes a plurality of sets of storage electrodes  133   a ,  133   b , and  133   c . Two storage electrodes  133   a  and  133   b  are extended in a longitudinal direction and are connected with a transverse storage electrode  133   c . The storage line  131  may include two or more transverse lines.  
         [0036]     The gate lines  121  and the storage electrode lines  131  may have a multi-layered structure including two films having different physical characteristics, i.e., a lower film (not shown) and an upper film (not shown). The upper film is preferably made of a low resistivity metal including an Al-containing metal such as Al or an Al alloy for reducing signal delay or voltage drop in the gate lines  121  and the storage electrode lines  131 . On the other hand, the lower film is preferably made of a material such as Cr, Mo, or a Mo alloy, which has good contact characteristics with other materials such as indium tin oxide (ITO) and indium zinc oxide (IZO). A good exemplary combination of the lower film material and the upper film material is Cr and an Al—Nd alloy. In addition, the lateral sides of the gate lines  121  and the storage electrode lines  131  are tapered, and the inclination angle of the lateral sides with respect to a surface of the substrate  110  ranges about 30-80 degrees.  
         [0037]     A gate insulating layer  140  preferably made of silicon nitride (SiNx) is formed on the gate lines  121  and the storage electrode lines  131 . A plurality of semiconductor stripes  151  that are preferably made of hydrogenated amorphous silicon (abbreviated to “a-Si”) are formed on the gate insulating layer  140 . Each semiconductor stripe  151  extends substantially in the longitudinal direction, and has a plurality of projections  154  branched out toward the gate electrodes  123 .  
         [0038]     A plurality of ohmic contact stripes  161  preferably made of silicide or n+ hydrogenated a-Si heavily doped with n type impurity are formed on the semiconductor stripes  151  and projections  154 . The ohmic contact stripes  161  have substantially the same pattern as the semiconductor stripes  151  except for around the projections  154 . Each ohmic contact stripe  161  has a plurality of projections  163 , and the projections  163  and the ohmic contact islands  165  are located in pairs on the projections  154  of the semiconductor stripes  151 .  
         [0039]     A plurality of data lines  171 , a plurality of drain electrodes  175 , a plurality of coupling electrode  176 , and a plurality of under-bridge metal pieces  172  are formed on the ohmic contacts  161 ,  163 , and  165  and the gate insulating layer  140 .  
         [0040]     Each data line  171  extends substantially in the longitudinal direction and has a plurality of source electrodes  173  extending toward the drain electrodes  175 . Each data line  171  includes an expansion  179  having a wider width for contact with another layer or an external device. The under-bridge metal piece  172  is disposed on the gate line  121 .  
         [0041]     The coupling electrode  176  is connected to the drain electrode  175  and is bent several times to have a “V” shape. The lengths of the coupling electrodes  176  are different from each other among red, green, and blue pixels. The length of the coupling electrode  176  in the green pixel is the longest, the length of the coupling electrode  176  in the red pixel is the second longest, and the length of the coupling electrode  176  in the blue pixel is the shortest.  
         [0042]     The data lines  171 , the drain electrodes  175 , the coupling electrodes  176 , and the under-bridge metal piece  172  may have a multi-layered structure including two films having different physical characteristics, i.e., a lower film (not shown) and an upper film (not shown). The upper film is preferably made of a low resistivity metal including an Al-containing metal such as Al or an Al alloy for reducing signal delay or voltage drop in the data lines. On the other hand, the lower film is preferably made of a material such as Cr, Mo, or an Mo alloy, which has good contact characteristics with other materials such as indium tin oxide (ITO) and indium zinc oxide (IZO). A good exemplary combination of the lower film material and the upper film material is Cr and an Al—Nd alloy.  
         [0043]     A passivation layer  180  made of an inorganic material such as silicon nitride or an organic material such as resin is formed on the data lines  171 , the drain electrodes  175 , and the under-bridge metal piece  172 . The passivation layer  180  has a plurality of contact holes  181  and  183  respectively exposing a portion of the drain electrode  175  and the expansion  179  of the data line  171 . The passivation layer  180  and the gate insulating layer  140  have a plurality of contact holes  182 ,  184 , and  185  respectively exposing the expansion  125  of the gate line  121  and two portions of the storage electrode line  131 .  
         [0044]     A plurality of pixel electrodes  190   a  and  190   b , a plurality of contact assistants  95  and  97 , and a plurality of storage bridges  91  are formed on the passivation layer  180 . The pixel electrodes  190   a  and  190   b , the contact assistants  95  and  97 , and the storage bridges  91  may be made of a transparent conductor such as ITO and IZO, or a light reflective material such as Al.  
         [0045]     The first pixel electrode  190   a  is connected to the drain electrode  175  through the contact hole  181 . The second pixel electrode  190   b  is electrically floated but is capacitively coupled with the first pixel electrode  190   a , since the second pixel electrode  190   b  is overlapped with the coupling electrode  176 . Therefore, the voltage of the second pixel electrode  190   b  varies dependant on the voltage of the first pixel electrode  190   a.    
         [0046]     The coupling capacitances formed between the first pixel electrode  190   a  and the second pixel electrode  190   b  are different among green, red, and blue pixels. The coupling capacitances formed between the first pixel electrode  190   a  and the second pixel electrode  190   b  become smaller step by step in an order of green, red, and blue pixels due to the length shortening of the coupling electrodes  176 .  
         [0047]     Differentiation of the coupling capacitances of the first pixel electrode  190   a  and the second pixel electrode  190   b  among green, red, and blue pixel may be achieved by other methods, such as width and disposition differentiation of the coupling electrode  176 , rather than by length differentiation.  
         [0048]     When the coupling capacitance of the first sup-pixel electrode  190   a  and the second pixel electrode  190   b  in the green pixel is 1, the coupling capacitances of the first sup-pixel electrode  190   a  and the second pixel electrode  190   b  in the red pixel preferably range from 0.95 to 1.0 and that of the blue pixel preferably ranges from 0.75 to 0.95.  
         [0049]     Cutouts  191 ,  193 , and  194  dividing the first pixel electrode  190   a  and the second pixel electrode  190   b  are classified into oblique portions  191  and  193  making an angle of about 45 degrees with the gate line  121 , and a longitudinal portion  194  making an angle of about 90 degrees with the gate line  121 . The two oblique portions  191  and  193  make an angle of about 90 degrees.  
         [0050]     The second pixel electrode  190   b  has a cutout  192  which initiates from the right side of the second pixel electrode  190   b  and extends toward the left side. The entrance of the cutout  191  is widened due to the comer cut of the second pixel electrode  190   b . The first pixel electrode  190   a  and the second pixel electrode  190   b  respectively make a mirror image with respect to a longitudinal center line of a pixel.  
         [0051]     The storage bridge  91  crosses over the gate line  121  and connects two storage lines that are disposed on both sides of the gate line  121 . The storage bridge  91  contacts the storage electrode  133   a  and the storage electrode line  131  through the contact holes  183  and  184 . The storage bridge  91  overlaps the under-bridge metal piece  172 . The storage bridges  91  electrically connect all the storage electrode lines  131  on the insulating substrate  110 .  
         [0052]     The storage electrode lines  131  may be used to repair defects of the gate lines  121  and the data lines  171 . Such repairs are done by illumination of a laser. The under-bridge metal piece  172  helps electrical connection of the gate line  121  and the storage bridge  91 .  
         [0053]     The contact assistants  95  and  97  are respectively connected to the expansion  125  of the gate line  121  and the expansion  179  of the data line  171  through the contact holes  182  and  183 .  
         [0054]     The color filter panel  200  will be described with respect to  FIGS. 2, 4 , and  5 . A black matrix  220  for preventing light leakage is formed on an insulating substrate  210  such as transparent glass. A plurality of red, green, and blue color filters  230  are formed on the black matrix and the substrate  210  and extend substantially along the columns of the pixel areas. An overcoat  250  is formed on the color filters  230  and the black matrix  220 . A common electrode  270 , preferably made of a transparent conductive material such as ITO or IZO, is formed on the overcoat  250 . The common electrode  270  has a plurality of cutouts  271 ,  272 , and  273 .  
         [0055]     A set of cutouts  271 ,  272 , and  273  include oblique portions and end portions. The oblique portions of the cutouts  271 ,  272 , and  273  are parallel with the oblique portions  191  and  193  of the cutout between the pixel electrodes  190   a  and  190   b . The oblique portions  191  and  193  are disposed between the oblique portions of the cutouts  271 ,  272 , and  273 . The end portions overlap the boundary line of the pixel area and include longitudinal end portions and transverse end portions.  
         [0056]     The LCD includes a TFT array panel  100 , a color filter array panel  200  facing the TFT array panel  100  and separated therefrom by a predetermined gap, and a liquid crystal layer  3  filled in the predetermined gap. When the two panels  100  and  200  are assembled, the cutouts  271 ,  272 , and  273  of the common electrode  270  partition the two pixel electrodes  190   a  and  190   b  into a plurality of sub-areas. In the present embodiment, as shown in  FIG. 3 , the two pixels  190   a  and  190   b  are respectively partitioned into four sub-areas. As shown in  FIG. 3 , each sub-area has two parallel long edges and several short edges. Therefore, the sub-areas have length direction and width direction.  
         [0057]     Each liquid crystal  3  portion disposed between each of the sub-areas of the pixel electrodes  190   a  and  190   b  and corresponding sub-areas of the common electrode  270  is a sub-region. The sub-regions are classified into four species according to the average long axis direction of liquid crystals disposed therein. The sub-regions will be called a domain from now on.  
         [0058]     The first pixel electrode  190   a  is physically and electrically connected to the drain electrodes  175  through the contact holes  181 . The second pixel electrode  190   b  is physically and electrically floated, but is overlapped with the coupling electrode  176  to form coupling capacitances with the first pixel electrodes  190   a . Therefore, the voltage of the second pixel electrode  190   b  depends on the voltage of the first pixel electrode  190   a . The voltage of the second pixel electrode  190   b  with respect to the common voltage is always smaller than that of the first pixel electrode  190   a . In the meantime, when a pixel area includes two sub-areas with somewhat different electric fields, lateral visibility is improved by the mutual compensation in the two sub-areas.  
         [0059]     The coupling relationship between the first pixel electrode  190   a  and the second pixel electrode  190   b  will be described later in detail with reference to  FIG. 5 .  FIG. 5  is a circuit diagram of the LCD shown in FIGS.  1  to  4 . In  FIG. 5 , Clca stands for liquid crystal (LC) capacitance formed between the first pixel electrode  190   a  and the common electrode  270 , and Cst stands for storage capacitance formed between the first pixel electrode  190   a  and the storage line  131 . Clcb stands for liquid crystal (LC) capacitance formed between the second pixel electrode  190   b  and the common electrode  270 , and Ccp stands for coupling capacitance formed between the first pixel electrode  190   a  and the second pixel electrode  190   b.    
         [0060]     The voltage Vb of the second pixel electrode  190   b  with reference to the common voltage and the voltage Va of the first pixel electrode  190   a  with reference to the common voltage are related by the voltage distribution law as follows:
 
 Vb=Va×[Ccp /( Ccp+Clcb )].
 
         [0061]     Since Ccp/(Ccp+Clcb) is always smaller than 1, Vb is always smaller than Va. The capacitance Ccp can be adjusted by overlapping an area or distance between the second pixel electrode  190   b  and the coupling electrode  176 . The overlapping area between the second pixel electrode  190   b  and the coupling electrode  176  can be easily adjusted by changing the width of the coupling electrode  176 . The distance between the second pixel electrode  190   b  and the coupling electrode  176  can be easily adjusted by changing the location of the coupling electrode  176 . That is, in the present embodiment, the coupling electrode  176  is formed on the same layer as the data line  171 , but the coupling electrode  176  may be formed on the same layer as the gate line  121 . By this change, the distance between the second pixel electrode  190   b  and the coupling electrode  176  is increased. In the meantime, voltage differences between the two pixel electrodes  190   a  and  190   b  are different among red, green, and blue pixels due to the difference of coupling capacitance. Through this, a bluish tinge is diminished to improve side visibility of an LCD.  
         [0062]     Now, the bluish tinge phenomenon will be described with reference to  FIGS. 10A  to  10 C and the reason why the present invention diminishes the bluish tinge will be described.  FIG. 10A  shows gamma curves of a front view,  FIG. 10B  shows gamma curves of an upper side view, and  FIG. 10C  shows gamma curves of a diagonal side view.  
         [0063]     As shown in  FIGS. 10A  to  10 C, when an LCD is viewed from directly in front, gamma curves of red, green, and blue almost correspond. However, when an LCD is viewed from the upper side or diagonal side, gamma curves of green and blue deviate from that of red as the gray level goes down. In particular, the gamma curve of blue severely deviates. This means that when an LCD is viewed from upper or diagonal sides, a ratio of blue light increases as the gray level goes down. This is the cause of the bluish tinge.  
         [0064]     In the present invention, a pixel area includes two pixel electrodes, different voltages are applied to the two pixel electrodes, and a voltage difference between the two pixel electrodes is different among red, green, and blue pixels.  
         [0065]     A coupling capacitance between the two pixel electrodes  190   a  and  190   b  of the blue pixel is smaller than that of the red and green pixels to alleviate an increase of the blue light ratio in the low gray level. When the coupling capacitance between the two pixel electrodes  190   a  and  190   b  is smaller, the voltage of the second pixel electrode  190   b  induced by electrical coupling with the first pixel electrode  190   a  is lower. Therefore, voltages applied to the second pixel electrode  190   b  in the same gray level are arranged in an order of blue&lt;red&lt;green according to their magnitude. Such voltage differences by colors increases as the gray level goes down. Accordingly, the ratio of blue pixel voltage with respect to green pixel voltage becomes smaller as the gray level goes down. The ratio of blue pixel voltage with respect to green pixel voltage also becomes smaller as the gray level goes down. As a result, the bluish tinge is alleviated.  
         [0066]     The present invention may be applied to a twisted nematic (TN) mode TFT. Such an embodiment will be described.  FIG. 6  is a layout view of a thin film transistor array panel for an LCD according to another embodiment of the present invention.  FIG. 7  is a sectional view of the LCD shown in  FIG. 6  taken along the line VII-VII′.  
         [0067]     A plurality of gate lines  121  and a plurality of storage electrode lines  131  are formed on an insulating substrate  110 . The gate lines  121  extend substantially in a transverse direction, and are separated from each other and transmit gate signals. The gate line  121  has a plurality of gate electrodes  123  and expansions  125  for connecting to external circuit.  
         [0068]     Each storage electrode line  131  extends substantially in the transverse direction, and includes a plurality of sets of storage electrodes  133   a ,  133   b , and  133   c . Two storage electrode  133   a  and  133   b  are extended in the longitudinal direction and are connected with a transverse storage electrode  133   c . The storage line  131  may include two or more transverse lines.  
         [0069]     The gate lines  121  and the storage electrode lines  131  may have a multi-layered structure including two films having different physical characteristics, i.e., a lower film (not shown) and an upper film (not shown). The upper film is preferably made of a low resistivity metal including an Al-containing metal such as Al or an Al alloy for reducing signal delay or voltage drop in the gate lines  121  and the storage electrode lines  131 . On the other hand, the lower film is preferably made of a material such as Cr, Mo, or an Mo alloy, which has good contact characteristics with other materials such as indium tin oxide (ITO) and indium zinc oxide (IZO). A good exemplary combination of the lower film material and the upper film material is Cr and an Al—Nd alloy.  
         [0070]     In addition, the lateral sides of the gate lines  121  and the storage electrode lines  131  are tapered, and the inclination angle of the lateral sides with respect to a surface of the substrate  110  ranges about 30-80 degrees.  
         [0071]     A gate insulating layer  140  preferably made of silicon nitride (SiNx) is formed on the gate lines  121  and the storage electrode lines  131 . A plurality of semiconductor stripes  151  preferably made of hydrogenated amorphous silicon (abbreviated to “a-Si”) is formed on the gate insulating layer  140 . Each semiconductor stripe  151  extends substantially in the longitudinal direction, and has a plurality of projections  154  branched out toward the gate electrodes  123 .  
         [0072]     A plurality of ohmic contact stripes  161  that are preferably made of silicide or n+ hydrogenated a-Si heavily doped with n-type impurities are formed on the semiconductor stripes  151  and projections  154 . The ohmic contact stripes  161  have substantially the same pattern with the semiconductor stripes  151 , except for around the projections  154 . Each ohmic contact stripe  161  has a plurality of projections  163 , and the projections  163  and the ohmic contact islands  165  are located in pairs on the projections  154  of the semiconductor stripes  151 .  
         [0073]     A plurality of data lines  171 , a plurality of drain electrodes  175 , a plurality of coupling electrodes  176 , and a plurality of under-bridge metal pieces  172  are formed on the ohmic contacts  161 ,  163 , and  165  and the gate insulating layer  140 . Each data line  171  extends substantially in the longitudinal direction, and has a plurality of source electrodes  173  extending toward the drain electrodes  175 . Each data line  171  includes an expansion  179  having a wider width for contact with another layer or an external device.  
         [0074]     The under-bridge metal piece  172  is disposed on the gate line  121 . The coupling electrode  176  is connected to the drain electrode  175 . The widths of the coupling electrodes  176  are different from each other among red, green, and blue pixels. The width of the coupling electrode  176  in the green pixel is the widest, the width of the coupling electrode  176  in the red pixel is the second widest, and the width of the coupling electrode  176  in the blue pixel is the narrowest.  
         [0075]     The data lines  171 , the drain electrodes  175 , the coupling electrodes  176 , and the under-bridge metal pieces  172  may have a multi-layered structure including two films having different physical characteristics, i.e., a lower film (not shown) and an upper film (not shown). The upper film is preferably made of a low resistivity metal including an Al-containing metal such as Al or an Al alloy for reducing signal delay or voltage drop in the data lines. On the other hand, the lower film is preferably made of a material such as Cr, Mo, or an Mo alloy, which has good contact characteristics with other materials such as indium tin oxide (ITO) and indium zinc oxide (IZO). A good exemplary combination of the lower film material and the upper film material is Cr and an Al—Nd alloy.  
         [0076]     A passivation layer  180  made of an inorganic material such as silicon nitride or an organic material such as resin is formed on the data lines  171 , the drain electrodes  175 , and the under-bridge metal pieces  172 .  
         [0077]     The passivation layer  180  has a plurality of contact holes  181  and  183  respectively exposing a portion of the drain electrode  175  and the expansion  179  of the data line  171 . The passivation layer  180  and the gate insulating layer  140  have a plurality of contact holes  182 ,  184 , and  185  respectively exposing the expansion  125  of the gate line  121  and two portions of the storage electrode line  131 .  
         [0078]     A plurality of pixel electrodes  190   a  and  190   b , a plurality of contact assistants  95  and  97 , and a plurality of storage bridges  91  are formed on the passivation layer  180 . The pixel electrodes  190   a  and  190   b , the contact assistants  95  and  97 , and the storage bridges  91  may be made of a transparent conductor such as ITO or IZO, or a light reflective material such as Al.  
         [0079]     The first pixel electrode  190   a  is connected to the drain electrode  175  through the contact hole  181 . The second pixel electrode  190   b  is electrically floated but is capacitively coupled with the first pixel electrode  190   a , since the second pixel electrode  190   b  is overlapped with the coupling electrode  176 . Therefore, the voltage of the second pixel electrode  190   b  varies depending on the voltage of the first pixel electrode  190   a.    
         [0080]     The coupling capacitances formed between the first pixel electrode  190   a  and the second pixel electrode  190   b  are different among green, red, and blue pixels. The coupling capacitances formed between the first pixel electrode  190   a  and the second pixel electrode  190   b  become smaller step by step in an order of green, red, and blue pixels due to the width narrowing of the coupling electrodes  176 .  
         [0081]     As described with respect to the embodiment of FIGS.  1  to  4 , differentiation of the coupling capacitances of the first sup-pixel electrode  190   a  and the second pixel electrode  190   b  among green, red, and blue pixels may be achieved by other methods. In the present invention, width differentiation of the coupling electrode  176  is applied.  
         [0082]     When the coupling capacitance of the first sup-pixel electrode  190   a  and the second pixel electrode  190   b  in the green pixel is 1, the coupling capacitance of the first sup-pixel electrode  190   a  and the second pixel electrode  190   b  in the red pixel preferably ranges from 0.95 to 1.0, and that of the blue pixel preferably ranges from 0.75 to 0.95.  
         [0083]     The first pixel electrode  190   a  and the second pixel electrode  190   b  are respectively disposed in the lower half and the upper half of a pixel area. The storage electrode  133   c  is disposed between the two pixel electrodes  190   a  and  190   b.    
         [0084]     The storage bridge  91  crosses over the gate line  121  and connects two storage lines that are disposed on both sides of the gate line  121 . The storage bridge  91  contacts the storage electrode  133   a  and the storage electrode line  131  through the contact holes  183  and  184 . The storage bridge  91  overlaps the under-bridge metal piece  172 . The storage bridges  91  electrically connect all the storage electrode lines  131  on the insulating substrate  110 .  
         [0085]     The storage electrode lines  131  may be used to repair defects of the gate lines  121  and the data lines  171 . Such repairs are done by illumination of a laser. The under-bridge metal piece  172  helps electrical connection of the gate line  121  and the storage bridge  91 .  
         [0086]     The contact assistants  95  and  97  are respectively connected to the expansion  125  of the gate line  121  and the expansion  179  of the data line  171  through the contact holes  182  and  183 . When a pixel area includes two sub-areas with somewhat different electric fields, lateral visibility is improved by the mutual compensation in the two sub-areas.  
         [0087]     In the meantime, voltage differences between the two pixel electrodes  190   a  and  190   b  are different among red, green, and blue pixels due to the differences of coupling capacitance. By this, the bluish tinge is diminished to improve side visibility of an LCD.  
         [0088]     Another embodiment for differentiation of the coupling capacitances of the first pixel electrode  190   a  and the second pixel electrode  190   b  among green, red, and blue pixel will now be described.  FIG. 8  is a layout view of a thin film transistor array panel for an LCD according to another embodiment of the present invention. In the embodiment of  FIG. 8 , the area ratio of the second pixel electrode  190   b  to the first pixel electrode  190   a  is different among red, green, and blue pixels, but the length of the coupling electrode  176  is the same among red, green, and blue pixels. The other aspects are very similar with the embodiment of FIGS.  1  to  4 .  
         [0089]     The area ratio of the second pixel electrode  190   b  to the first pixel electrode  190   a  of the green pixel is the smallest. The area ratios of the second pixel electrode  190   b  to the first pixel electrode  190   a  increase in an order of the red pixel and the blue pixel. That is, an area taken up by the second pixel electrode  190   b  in a pixel area increases in an order of green, red, and blue pixels. The area ratios of the second pixel electrode  190   b  with respect to the first pixel electrode  190   a  in the green, red, and blue pixels are preferably 6:4, 5.5:4.5, and 5:5. The area ratios of the second pixel electrode  190   b  to the first pixel electrode  190   a  may have various values as long as the area ratios become larger in an order of green, red, and blue pixels.  
         [0090]     According to the embodiments, though the same gray voltage is applied to red, green, and blue pixels, voltages of the second pixel electrodes  190   b  are different among red, green, and blue pixels to improve visibility of an LCD.  
         [0091]      FIG. 9  is a layout view of a thin film transistor array panel for an LCD according to another embodiment of the present invention. In the embodiment of  FIG. 9 , the area ratio of the second pixel electrode  190   b  to the first pixel electrode  190   a  is different among red, green, and blue pixels, but the width of the coupling electrode  176  is the same among the red, green, and blue pixels. The other aspects are very similar with the embodiment of  FIGS. 6 and 7 .  
         [0092]     The area ratio of the second pixel electrode  190   b  to the first pixel electrode  190   a  of the green pixel is the smallest. The area ratios of the second pixel electrode  190   b  to the first pixel electrode  190   a  increase in an order of the red pixel and the blue pixel. That is, an area taken up by the second pixel electrode  190   b  in a pixel area increases in an order of green, red, and blue pixels. The area ratios of the second pixel electrode  190   b  with respect to the first pixel electrode  190   a  in the green, red, and blue pixels are preferably 6:4, 5.5:4.5, and 5:5. The area ratios of the second pixel electrode  190   b  to the first pixel electrode  190   a  may have various values as long as the area ratios become larger in an order of green, red, and blue pixels.  
         [0093]     Although preferred embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that many variations and/or modifications of the basic inventive concepts herein taught which may appear to those skilled in the present art will still fall within the spirit and scope of the present invention, as defined in the appended claims. In particular, cutouts in the pixel and common electrodes may be rearranged in various ways.