Abstract:
The present invention is directed to prevent color shift in liquid crystal display devices and to improve their aperture ratio and transmittance. 
     High aperture ratio and high transmittance liquid crystal display preventing color shift comprising: an upper substrate and a lower substrate opposed to be separated by selected distance; a liquid crystal layer including a plurality of liquid crystal molecules and interposed between inner surfaces of the upper and lower substrates; a first electrode formed on the inner surface of the lower substrate; and a second electrode formed on the inner surface of the lower substrate, wherein the first electrode and the second electrode form an electric field for driving the liquid crystal molecules; wherein in the absence of electric field between the first and second electrodes, the liquid crystal molecules are aligned such that their long axis are parallel to surfaces of the substrates in a first direction; wherein after a selected voltage is applied therebetween, first and second diagonal electric fields are simultaneously formed in a pixel, the two diagonal electric fields are formed to be symmetrical with respect to the first direction; wherein the first and second electrodes are made of transparent materials; wherein the distance between the first and second electrodes is shorter than the distance between the upper and lower substrates; wherein widths of the first and second electrodes are determined such that liquid crystal molecules overlying the two electrodes are driven by the electric field generated between the first and second electrodes.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to a liquid crystal display, and more particularly to a liquid crystal display of wide viewing angle preventing color shift and simultaneously improving its aperture ratio and transmittance. 
     BACKGROUND OF THE INVENTION 
     Liquid crystal display devices have been used in various information display terminals and video devices. The major operating system for the liquid crystal display device is the twisted nematic(“TN”) mode and the super twisted nematic (“STN”) mode. Though they are commercially used in the market at present, the problems of narrow viewing angle remain unsolved. 
     An In-Plane Switching (“IPS”) mode liquid crystal display has been suggested to solve foregoing problems. 
     As described in FIG. 1, a plurality of gate bus lines  11  are formed on a lower insulating substrate  10  along an x direction shown in the drawings. The gate bus lines  11  are parallel to each other. A plurality of data bus lines  15  are formed along an y direction which is substantially perpendicular to the x direction. Therefore a pixel region is defined. At this time, a pair of gate bus lines  11  and a pair of data bus lines  15  are shown in the drawing so as to define the pixel region. The gate bus line  11  and the data bus line  15  are insulated by a gate insulating layer(not shown). 
     A counter electrode  12 , for example in the form of a rectangular frame, is formed within the pixel region and is disposed at the same plane with the gate bus line  11 . 
     A pixel electrode  14  is formed at each pixel region where the counter electrode  12  is formed. The pixel electrode  14  consists of a web region  14   a  which divides the region surrounded by the rectangular frame shaped counter electrode  12  in the y direction, a first flange region  14   b  connected to one end of the web region  14   a  and simultaneously overlapped with the counter electrode  12  of the x direction, and a second flange region  14   c  which is parallel to the first flange region  14  and is connected to the other end of the web region  14   a . Thus, the pixel electrode  14  appears like the letter “I”. Herein, the counter electrode  12  and the pixel electrode  14  are made of opaque metal layers. To ensure an appropriate intensity of electric field, the widths of both the counter and pixel electrodes are preferably in the range of 10˜20μm. 
     The pixel electrode  14  and the counter electrode  12  are insulated from each other by a gate insulating layer(not shown). 
     A thin film transistor  16  is disposed at the intersection of the gate bus line  11  and the data bus line  12 . This thin film transistor  16  includes a gate electrode extended from the gate bus line  11 , a drain electrode extended from the data bus line  15 , a source electrode extended from the pixel electrode  14  and a channel layer  17  formed on the upper portions of the gate electrode. 
     A storage capacitor(Cst) is disposed at the region where the counter electrode  12  and the pixel electrode  14  overlap. 
     Although not shown in FIG. 1, an upper substrate(not shown) equipped with a color filter(not shown) is disposed on the first substrate  10  opposite to each other with a selected distance. Herein, the distance between the upper substrate and lower substrate  10  is smaller than the distance between the counter electrode region in the y direction and the web region of the pixel electrode thereby forming an electric field which is parallel to the substrate surface. Further a liquid crystal layer(not shown) having a plurality of liquid crystal molecules is interposed between the upper substrate(not shown) and the lower substrate  10 . 
     Also, on the resultant structure of the lower substrate and on an inner surface of the upper substrate are formed homogeneous alignment layers respectively. By the homogeneous alignment layer, in the absence of electric field between the counter electrode  12  and the pixel electrode  14 , long axes of liquid crystal molecules  19  are arranged parallel to the substrate surface. Also, by the rubbing axis of the homogeneous alignment layer, the orientation direction of the molecules  19  is decided. The reference R in the drawings means the direction of rubbing axis for the homogeneous alignment layer formed on the lower substrate  10 . 
     A first polarizing plate(not shown) is formed on the outer surface of the lower substrate  10  and a second polarizing plate(not shown) is formed on the outer surface of the upper substrate(not shown). Herein, the first polarizing plate is disposed to make its polarizing axis to be parallel to the P direction of the FIG.  1 . That means, the directions of rubbing axis R and polarizing axis P are parallel each other. On the other hand, the polarizing axis of the second polarizing plate is substantially perpendicular to that of the first polarizing plate. 
     When a scanning signal is applied to the selected gate bus line  11  and a display signal is applied to the data bus line  15 , the thin film transistor  16  disposed adjacent to the intersection of the gate bus line  11  and the data bus line  15  is turned on. Then the display signal of the data bus line  15  is transmitted to the pixel electrode  14  through the thin film transistor  16 . Consequently, an electric field E is generated between the counter electrode  12 , where a common signal is inputted, and the pixel electrode  14 . At this time, as the direction of electric field E is referenced as x direction as described in the FIG. 1, it has a predetermined degree of angle with the rubbing axis. 
     Afterward, when no electric field is generated, the long axes of the liquid crystal molecules are arranged parallel to the substrate surface and parallel to the rubbing direction R. Therefore the light passing through the first polarizing plate and the liquid crystal layer is unable to pass the second polarizing plate, and the screen shows dark state. 
     On the other hand, when the electric field is generated, the long axes(or short axes) are rearranged parallel to the electric field. Therefore the incident light passing through the first polarizing plate and the liquid crystal layer, passes the second polarizing plate, and the screen shows white state. 
     At this time, the direction of the long axes of the liquid crystal molecules change according to the electric field, and the liquid crystal molecules themselves are arranged parallel to the substrate surface. Accordingly, the viewer can see the long axes of liquid crystal molecules from all directions, and the viewing angle characteristic is improved. 
     However, the IPS mode liquid crystal display as described above also includes the following problems. 
     It is well known that refractive anisotropy(or birefringence, n) occurs due to the difference in lengths of the long and the short axes. The refractive anisotropy  also varies according to the observer&#39;s viewing directions. Therefore a selected color can be shown in the region where the polar angle is of 0 degree and the azimuth angle is in the range of degrees 0, 90, 180 and 270, even in the white state screen. This is regarded as color shift and a more detailed description thereof is attached with reference to equation 1. 
     
       
         T≈T 0 sin 2 (2χ)·sin 2 (π·χnd/λ) . . .   equation 1 
       
     
     wherein, T: transmittance; 
     T 0 : transmittance to the reference light; 
     χ: angle between an optical axis of liquid crystal molecule and a polarizing axis of the polarizing plate; 
     : birefringence; 
     d: distance or gap between the upper and lower substrates(thickness of the liquid crystal layer); and 
     λ: wavelength of the incident light. 
     So as to obtain the maximum transmittance T, the χ should be π/4 or the nd/λ should be π/2 according to the equation 1. As the nd varies with the birefringence difference of the liquid crystal molecules depending on the viewing directions, the value of λ varies so as to make d/λ to be π/2. According to this condition, the color corresponding to the varied wavelength λ appears in the screen. 
     Accordingly, as the value of n relatively decreases at the viewing directions “a” and “c” toward the short axes of the liquid crystal molecules, the wavelength of the incident light for obtaining the maximum transmittance relatively decreases. Consequently, a blue color having a shorter wavelength than a white color can be looked in the screen. 
     On the other hand, as the value of n relatively increases at the viewing directions “b” and “d” toward the short axes of the liquid crystal molecules, the wavelength of the incident light relatively increases. Consequently, a yellow color having a longer wavelength than the white color can be looked in the screen. 
     Deterioration is caused in the resolution of IPS mode liquid crystal display. 
     Since the counter electrode  12  and the pixel electrode  14  of the IPS mode liquid crystal display are made of opaque metal layers, an aperture area of the liquid crystal display decreases, and the transmittance thereof also decreases. In addition, so as to obtain an appropriate brightness, a backlight with high intensity must often be used and thus electrical consumption increases, which is often undesirable. 
     To solve these limitations, a counter electrode  12  and a pixel electrode  14  made of transparent material have been proposed. In such a liquid crystal liquid display the aperture ratio is often increased, but the transmittance is often not improved. To produce an in-plane electric field, the distance l between the electrodes  12  and  14  must often be set to be greater than the cell gap d. To obtain an appropriate intensity of the electric field, the electrodes  12  and  14  have relatively large dimension of width, for example, 10 to 20μm. 
     However, if the electrodes have such a large dimension of width, the liquid crystal molecules positioned right above the upper surfaces of the electrodes  12  and  14  do not move thereby forming equipotential lines. As a result, since the liquid crystal molecules positioned right above the upper surfaces of the electrodes continue to hold an initial configuration even in the presence of the electric field, the transmittance is increased little. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a liquid crystal display which prevents the occurrence of color shift thereby improving picture quality. 
     It is another object of the present invention to provide a liquid crystal display capable of improving its aperture ratio and transmittance. 
     To accomplish the foregoing objects, the present invention provides a high aperture ratio and high transmittance liquid crystal display preventing color shift comprising: 
     an upper substrate and a lower substrate opposed and separated by selected distance; 
     a liquid crystal layer including a plurality of liquid crystal molecules and interposed between inner surfaces of the upper and lower substrates; 
     a first electrode formed on the inner surface of the lower substrate; and 
     a second electrode formed on the inner surface of the lower substrate, wherein the first electrode and the second electrode form an electric field for driving the liquid crystal molecules; 
     wherein in the absence of electric field between the first and second electrodes, the liquid crystal molecules are aligned such that their long axis are parallel to surfaces of the substrates in a first direction; 
     wherein after a selected voltage is applied therebetween, first and second diagonal electric fields are simultaneously formed in a pixel, the two diagonal electric fields are formed to be symmetrical with respect to the first direction; 
     wherein the first and second electrodes are made of transparent materials; 
     wherein the distance between the first and second electrodes is shorter than the distance between the upper and lower substrates; 
     wherein widths of the first and second electrodes are determined such that liquid crystal molecules overlying the two electrodes are driven by the electric field generated between the first and second electrodes. 
     The present invention, also provides a high aperture ratio and high transmittance liquid crystal display preventing color shift comprising: an upper substrate and a lower substrate opposed to be separated by selected distance; 
     a liquid crystal layer including a plurality of liquid crystal molecules and interposed between inner surfaces of the upper and lower substrates; 
     a gate bus line and a data bus line formed in the lower substrate in a matrix configuration thereby defining pixel regions; 
     a counter electrode formed at each pixel region in the lower substrate and the counter electrode having a body of a rectangular frame shape; a first branch disposed parallel to the gate bus line, connecting lengthwise sides of the body and dividing a region surrounded by the body into a first space and a second space; and a plurality of second and third branches diverged from the body or the first branch toward the first and second spaces as diagonal lines respectively; 
     a pixel electrode formed at each pixel region in the lower substrate, the pixel electrode forming an electric field together with the counter electrode, the pixel electrode having a first bar overlapped with one of those surfaces lengthwise sides of the body of the counter electrode and disposed parallel to the data bus line; a second bar diverged from the first bar and overlapped with the first branch of the counter electrode; a plurality of third and fourth bars diverged from the first and second bars toward the first and second spaces respectively as diagonal lines, wherein the third bar is interposed between the second branches and the fourth bar is interposed between the third branches; 
     a switching means formed adjacent to an intersection of the gate bus line and the data bus line for transmitting a signal from the data bus line to the pixel electrode; and 
     homogeneous alignment layers interposed between the lower substrate and the liquid crystal layer and between the upper substrate and the liquid crystal layer, wherein the counter electrode and the pixel electrode are formed in the lower substrate; 
     wherein the homogeneous alignment layer formed at the lower substrate has a rubbing axis which is parallel to the gate bus line and the data bus line, and the homogeneous alignment layer formed at the upper substrate has a rubbing axis which is anti-parallel to the rubbing axis of the homogeneous alignment layer formed at the lower substrate; 
     wherein the diagonal branches in the same space are disposed parallel to each other, and the second branch and the third bar in the first space make an angle θ with the first direction, the third branch and the fourth bar in the second space make an angle −θ with the first branch; 
     wherein the counter and pixel electrodes are made of transparent materials; 
     wherein the distance between the second branch of the counter electrode and the third bar of the pixel electrode, and the distance between the third branch of the counter electrode and the fourth bar of the pixel electrode are smaller than the distance between the upper and lower substrates; 
     wherein widths of the second, third branches and the third, fourth bars are determined such that liquid crystal molecules overlying the diagonal branches are substantially driven by the electric field. 
     The present invention further provides a high aperture ratio and high transmittance liquid crystal display preventing color shift comprising: 
     an upper substrate and a lower substrate opposed one another and separated by a selected distance; 
     a liquid crystal layer including a plurality of liquid crystal molecules, interposed between inner surfaces of the upper and lower substrates; 
     a gate bus line and a data bus line formed in the lower substrate in a matrix configuration thereby defining pixel regions; 
     a counter electrode formed at each of the pixel regions of the lower substrate and shaped as a rectangular plate; 
     a pixel electrode formed at each pixel region of the lower substrate, the pixel electrode forming an electric field together with the pixel electrode, the pixel electrode having a first bar overlapped with the counter electrode and disposed parallel to the data bus line; a second bar diverging from the first bar and overlapped with the counter electrode, wherein the second bar divides the counter electrode region into a first space and a second space; a plurality of third and fourth bars diverged from the first and second bars toward the first and second spaces respectively as diagonal lines wherein the third bar is interposed between the second branches and the fourth bar is interposed between the third branches; 
     a switching means formed at an intersection of the gate bus line and the data bus line for transmitting a signal from the data bus line to the pixel electrode; and 
     homogeneous alignment layers interposed between the lower substrate and the liquid crystal layer and between the upper substrate and the liquid crystal layer, wherein the counter electrode and the pixel electrodes are formed in the lower substrate; 
     wherein the homogeneous alignment layer formed at the lower substrate has a rubbing axis which is parallel to the gate bus line and the data bus line, and the homogeneous alignment layer formed at the upper substrate has a rubbing axis which is anti-parallel to the rubbing axis of the homogeneous alignment layer formed at the lower substrate; 
     wherein the diagonal branches in the same space are disposed parallel to each other, and the second branch and the third bar in the first space make an angle θ with the first branch of the counterdectrode, the third branch and the fourth bar in the second space make an angle −θ with the first branch of the counter electode; 
     wherein the counter and pixel electrodes are made of transparent materials; 
     wherein the distance between the second branch of the counter electrode and the third bar of the pixel electrode, and the distance between the third branch of the counter electrode and the fourth bar of the pixel electrode are smaller than the distance between the upper and lower substrates; and 
     wherein widths of the second, third branches and the third, fourth bars are determined such that liquid crystal molecules overlying the diagonal branches are substantially driven by the electric field. 
     Herein, the liquid crystal display is characterized in that a first polarizing plate is disposed at an outer surface of the lower substrate and a second polarizing plate is disposed at an outer surface of the upper substrate, and a polarizing axis of the first polarizing plate is coincided with a rubbing axis of the lower substrate and a polarizing axis of the second polarizing plate is perpendicular to the polarizing axis of the first polarizing plate. Furthermore, a liquid crystal of negative dielectric anisotropy can be used when the angle θ is set in the range of 0˜45°, wherein a liquid crystal of positive dielectric anisotropy can be used when the angle θ is set in the range of 45˜90°. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view showing a lower substrate of a conventional IPS mode liquid crystal display. 
     FIG. 2 is a perspective view showing a liquid crystal panel according to a first embodiment of the present invention. 
     FIG. 3 is a plan view showing a lower substrate according to the first embodiment of the present invention. 
     FIG. 4 is a plan view showing a counter electrode according to the first embodiment of the present invention. 
     FIG. 5 is a simulation result according to the first embodiment of the present invention. 
     FIG. 6 is a plan view showing a lower substrate according to a second embodiment of the present invention. 
     FIG. 7 is a simulation result according to the second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, the preferred embodiments of the present invention will be described with reference to the attached drawings. 
     First Embodiment 
     FIG. 2 is a perspective view showing a liquid crystal panel according to a first embodiment of the present invention, FIG. 3 is a plan view showing a lower substrate according to the first embodiment of the present invention, FIG. 4 is a plan view showing a counter electrode according to the first embodiment of the present invention, and FIG. 5 is a simulation result according to the first embodiment of the present invention. 
     Referring to FIGS. 2 and 3, a liquid crystal panel  100  is formed by disposing a lower substrate  20  and an upper substrate  30  opposite to each other with a selected distance. Herein, at least one of the lower substrate  20  and the upper substrate  30  is made of a transparent material. Further, the distance between both substrates  20 , 30  is referred as to a cell gap d and the cell gap in the present invention is approximately 3.9 μm. 
     As show in FIG. 3, a gate bus line  21  is extended in an x direction and a data bus line  25  is extended in a y direction, which is substantially perpendicular to the x direction, thereby defining a pixel PIX. Further, the pixel PIX has a rectangular shape that has a ratio of width to length of approximately 1:3. Although not shown in the drawing, an insulating layer is interposed between the gate bus line  21  and the data bus line  25  thereby electrically insulating therebetween. 
     A counter electrode  23  made of a transparent metal layer, for instance indium tin oxide(ITO), is formed in each pixel PIX. FIG. 4 illustrates only the counter electrode  23 . Referring to FIG. 4, the counter electrode  23  includes a body  23   a  of a rectangular frame shape. In the drawing, the reference numeral  23   a - 1  stands for a portion of the body  23   a  in the x direction and the reference numeral  23   a - 2  is a portion of the body  23   a  in the y direction. The counter electrode  23  also includes a first branch  23   c  which connects the portions  23   a - 2  in the y direction. Herein, the first branch  23   c  is parallel to the x direction and is disposed at the center of the body  23   a  thereby dividing a region surrounded by the body  23   a  into a first space AP1 and a second space AP2. Preferably, the first space AP1 and the second space AP2 are of an equal dimension. The counter electrode  23  further includes a plurality of second and third branches  23   e - 1 ,  23   e - 2  which are disposed in the form of diagonal lines with respect to the first branch  23   c  within the first space AP1 and the second space AP2. The second and third branches  23   e - 1 ,  23   e - 2  divide the first space AP1 and the second space AP2 respectively thereby dividing those spaces AP1,AP2 into a plurality of sub spaces s 1 ˜s 4 , s- 1 ˜s- 4 . Herein, the second branch  23   e - 1  and the third branch  23   e - 2  are disposed parallel each other with a regular distance or a random distance. The second branch  23   e - 1  and the second branch  23   e - 2  are disposed symmetrically with respect to the first branch  23   c  and have a selected angle θ with the first branch  23   c.    
     Furthermore, to prevent an edge electric field occurring at the corners of the first space AP1 and the second space AP2, which is not desired, a rib  23   g  is formed at a selected corner in the counter electrode  23 . A detailed description regarding the occurrence of edge electric fields, is disclosed in U.S. patent application Ser. No. 09/207,872. The rib  23   g  has a right-angled triangle shape. The rib  23   g  formed in the first space AP1 is inserted at right-angled corners of sub spaces  1  and  4 (s 1 ,s 4 ) so that the hypotenuse of the rib  23   g  is parallel to the second branch  23   e - 1 . Also, in the second space AP2 the rib  23   g  is inserted at right-angled corners of sub spaces  1  and  4 (s- 1 ,s- 4 ) so that the hypotenuse of the rib  23   g  is parallel to the third branch  23   e - 2 . 
     A pixel electrode  27  is also made of a transparent metal layer, such as ITO layer in each pixel PIX. As disclosed, the pixel electrode  27  is formed on the counter electrode  23  with intervening a gate insulating layer(not shown). The pixel electrode  27  includes a first bar  27   a  which is overlapped with a selected portion of the body  23   a  of the counter electrode  23 . The first bar  27   a  is overlapped with one of the body  23   a  which is parallel to the y direction. Preferably, the first bar  27   a  is disposed to overlap with the body  23   a - 2  adjacent to the data bus line  25  which applies signal voltages to the corresponding pixel PIX. The width of the first bar  27   a  of the pixel electrode  27  is equal to or smaller than that of the body  23   a - 2 . The pixel electrode  27  also includes a second bar  27   c  that is overlapped with the first branch  23   c  of the counter electrode  23  and one end thereof is connected to the first bar  27   a . The width of the second bar  27   c  is equal to or smaller than that of the first branch  23   c  of the counter electrode  23  and the second bar  27   c  is extended in the x direction. The pixel electrode  27  further includes a third bar  27   e - 1  and a fourth bar  27   e - 2  where their respective ends are connected to the first bar  27   a  or the second bar  27   c  and they are branched in the form of diagonal lines toward the first space AP1 and the second space AP2 respectively. The third bar  27   e - 1  and the fourth bar  27   e - 2  divide the sub spaces s 1 ˜s 4 , s- 1 ˜s- 4 . The third bar  27   e - 1  is parallel to the second branch  23   e - 1  of the counter electrode  23  and the fourth bar  27   e - 2  is parallel to the third branch  23   e - 2 . The respective third bars  27   e - 1  are interposed between the second branches  23   e - 1  and the respective fourth bars  27   e - 2  are interposed between the third branches  23   e - 2 . Herein, at least the ends of one of the third and fourth bars  27   e - 1 , 27   e - 2  of the pixel electrode  27  are bent to a selected direction so as to reduce the edge electric field being generated at corners of the sub spaces s 1 ˜s 4 , s- 1 ˜s- 4 . Preferably, the bending portions of the third and fourth bars  27   e - 1 , 27   e - 2  of the pixel electrode  27  are bent to greater angles between the angles made by intersecting the third bar  27   e - 1  and the body  23   a  of the counter electrode  23 , by intersecting the fourth bar  27   e - 2  and the body  23   a , by intersecting the third bar  27   e - 1  and the first branch  23   c  of the counter electrode  23 , and by intersecting the fourth bar  27   e - 2  and the first branch  23   c  respectively. The bending portions are turned along inner side of the body  23   a  or the first branch  23   c.    
     Herein, the second branch  23   e - 1  and the third bar  27   e - 1  make an angle θ° with respect to the first branch  23   c  of the counter electrode  23 , the third branch  23   e - 2  and the fourth bar  27   e - 2  make an angle −θ° with respect to the first branch  23   c  of the counter electrode  23 . 
     A distance l1 between the second branch  23   e - 1  and adjacent third bar  27   e - 1  of the pixel electrode  27  is almost equal to a distance 2 between the third branch  23   e - 2  of the counter electrode  23  and adjacent fourth bar  27   e - 2  of the pixel electrode  27 . The distances l1 and l2 are smaller than the cell gap d. Further, a ratio of the width of the second and third branches  23   e - 1 , 23   e - 2  or the width of the third and fourth bars  27   e - 1 , 27   e - 2  to the distances l1, l2 is 1 or more. In the present embodiment, the distances l1, l2 are preferably set in the range of 0.5˜1.5μm, or more preferably 1μm. 
     As noted above, if the distances l1, l2 are greater than the cell gap d, there may be formed a fringe field between the counter electrode  23  and the pixel electrode  27  that the fringe field affects upper portions of the electrodes  23 , 27 . 
     A storage capacitor is formed at each overlapping portion of the counter electrode  23  and the pixel electrode  27 . That is to say, the storage capacitor is formed between the body  23   a  of the counter electrode  23  and the first bar  27   a  of the pixel electrode  27 , between the first branch  23   c  of the counter electrode  23  and the second bar  27   c  of the pixel electrode  27 , and between the body  23   a  of the counter electrode  23  and the bending portions of the third and fourth bars  27   e - 1 , 27   e - 2  of the pixel electrode  27 . The reference numeral  26  in FIG. 3 stands for a common signal line for transmitting common signals to the counter electrode  23 . 
     Adjacent to the intersection of the gate bus line  21  and the data bus line  25 , a thin film transistor  280  is disposed as a switching means for transmitting a signal of the data bus line  25  to the pixel electrode  27  when the gate bus line is selected. Herein, the gate bus line  21  becomes a gate electrode for the thin film transistor  280  and the data bus line  25  becomes a source electrode for the thin film transistor  280 . Further, the first bar  27   a  of the pixel electrode  27  extends to the thin film transistor  280 , and becomes a drain electrode for the thin film transistor  280 . 
     A first alignment layer  29  is formed on a surface of a resultant structure as constituted above, as shown in FIG.  2 . At this time, the first alignment layer  29  is a homogeneous alignment layer having a pretilt angle of approximately below 5° and is rubbed in the x direction. The reason for rubbing the first alignment layer  29  in the x direction is that it is expected to obtain the maximum transmittance. 
     A color filter  32  is disposed at the inner surface of the upper substrate  30 , and a second alignment layer  34  is formed on a surface of the color filter  32 . The second alignment layer  34  is also a homogeneous alignment layer and is rubbed in a −x direction, i.e. it is rubbed in an anti-parallel manner with respect to the first alignment layer  29 . 
     A liquid crystal layer  35  is interposed between the upper substrate  30  and the lower substrate  20 . Dielectric anisotropy of the liquid crystal layer  35  is determined by an angle between the x direction and the electric field being formed between the second and third branches of the counter electrode, and between the third and fourth bars of the pixel electrode. When the angle between the electric field and the x direction is below 45°, a material of negative dielectric anisotropy is used, and then when the angle is 45°˜90°, a material of positive dielectric anisotropy is used thereby obtaining the maximum transmittance. 
     The transmittance of a general liquid crystal display can be described according to the equation 1 as above. That is to say, the maximum transmittance is obtained when the angle χ between the optical axes of liquid crystal molecules and the polarizing axis of the polarizer is 45°. Accordingly, to obtain the maximum transmittance, the twist angle of liquid crystal molecule should be over 45°. Therefore the liquid crystal material of negative dielectric anisotropy is used in the present embodiment, since if the angle θ is set, for instance, in the range of 60˜88°, the angle between the electric field and the x direction becomes 90−θ, i.e. 2°˜30°. 
     In addition, the refractive anisotropy of liquid crystal molecules within the liquid crystal layer  35  is set 0.05˜0.15 so that a value of phase retardation, i.e. the product of the refractive anisotropy and the cell gap becomes 0.2˜0.6μm. 
     A first polarizing plate  37  is disposed at an outer surface of the lower substrate  20 , and a second polarizing plate  39  is disposed at an outer surface of the upper substrate  30 . Herein, a polarizing axis P of the first polarizing plate  37  is disposed in the x direction which is coincided with the rubbing axis R 1  of the first alignment layer  29 , and a polarizing axis A of the second polarizing plate  39  is disposed in the y direction which is perpendicular to the polarizing axis P of the first polarizing plate  37 . 
     Operation of the liquid crystal display constituted as above is given below. 
     There is no electric field between the counter electrode  23  and the pixel electrode  27  when the gate bus line  21  is not selected since no signal is transmitted to the pixel electrode  29 . And then, the liquid crystal molecules  35   a  are arranged such that their long axes are parallel to surfaces of the substrates  20 , 30  under the influence of the first and second alignment layers  29 , 34 . Therefore, an incident light across the first polarizing plate  37  passes the long axes of the liquid crystal molecules and its polarizing state does not change. Consequently, the light to pass the liquid crystal layer  35  can not pass the second polarizing plate  39  whose polarizing axis A is perpendicular to the polarizing axis P of the first polarizing plate  37 . The screen shows a dark state. 
     On the other hand, when a scanning signal is applied to the gate bus line  21  and a display signal is applied to the data bus line  25 , the thin film transistor  280  formed adjacent to the intersection of the gate bus line  21  and the data bus line  25  is turned on thereby transmitting the display signal to the pixel electrode  27 . Electric fields E 1 ,E 2  are formed between the counter electrode  23  to which a common signal is continuously transmitted and the pixel electrode  27 . The electric fields E 1 ,E 2  are substantially formed between the second branch  23   e - 1  of the counter electrode  23  and the third bar  27   e - 1  of the pixel electrode  27 , and between the third branch  23   e - 2  and the fourth bar  27   e - 2  of the pixel electrode  27 . Herein, the electric field E 1  is formed in the first space AP1 and the electric field E 2  is formed in the second space AP2. Since the electric fields E 1 ,E 2  in the form of diagonal lines are formed as normal lines of the second and third branches  23   e - 1 ,  23   e - 2 . The electric fields E 1  and E 2  are symmetrically formed with respect to the first branch  23   c  of the counter electrode  23 . Herein, the intensity ratio of the electric field E 1  in the first space AP1 to the electric field E 2  in the second space AP2 is set in the range of 0.3˜1.3, preferably 1. 
     According to the electric fields E 1 ,E 2 , the liquid crystal molecules  35   a , arranged parallel to the x direction and the substrate, are twisted such that their long axes are arranged parallel to the electric fields E 1 ,E 2 . At this time, the electric fields E 1 ,E 2  are formed to make a symmetry within a pixel PIX in the form of diagonal lines, then the liquid crystal molecules  35   a  are rearranged to be parallel to the directions of the electric fields E 1 ,E 2 . 
     Accordingly, one pixel is divided into a first domain where the liquid crystal molecules are aligned in the form of the first electric field E 1 , and a second domain where the liquid crystal molecules are aligned in the form of the second electric field E 2  thereby forming two domains. When the liquid crystal molecules  35   a  are arranged as described above, the viewer at every azimuth angle can see the long and short axes of the liquid crystal molecules  35   a  simultaneously, therefore the refractive anisotropy of liquid crystal molecules is compensated. Consequently, there is no more color shift occurrence. 
     Further, the counter and pixel electrodes  23 , 27  are made of transparent metal layers, and the distance and width of the second(or third) branch and the third(or fourth) bar is adjusted such that the electric fields can affect the second and third branches  23   e - 1 , 23   e - 2  and the third and fourth bars  27   e - 1 , 27   e - 2 . Therefore, the liquid crystal molecules on the electrodes  23 , 27  are moved, and the aperture ratio and the transmittance are improved remarkably. 
     FIG. 5 is a simulation result when the liquid crystal display is constituted as described above. The reference symbol “S” means a section of the liquid crystal and the lower substrate in the liquid crystal display and the reference symbol “T” stands for the transmittance. Referring to FIG. 5, it is possible to obtain a transmittance of 43.44% which is regarded to as relatively high transmittance value in the lapse of approximately 70.81 ms. In addition, as shown in the drawing, the electric fields affect not only between the second branch  23   e - 1  and the third bar  27   e - 1  but also the upper portions of the second branch  23   e - 1  and the third bar  27   e - 1  thereby aligning all liquid crystal molecules. Accordingly, uniform transmittance is obtainable at every point in the screen. 
     Furthermore, a relatively high transmittance of 40% in the lapse of 31.17 ms is obtained due to a dense structure of the second branch  23   e - 1  and the third bar  27   e - 1 . 
     Second Embodiment 
     FIG. 6 is a plan view showing a lower substrate according to a second embodiment of the present invention. FIG. 7 is a simulation result according to the second embodiment of the present invention. 
     The present embodiment has a similar arrangement to the first embodiment as in the gate bus lines, the data bus lines, the thin film transistor, the common electrodes, the first and second alignment layers and the first and second polarizing plates except the arrangement of the counter electrode and the pixel electrode. 
     That is to say, as shown in FIG. 6, a counter electrode  230  according to the present embodiment is shaped of a rectangular plate and is made of a transparent material. 
     A pixel electrode  270  is disposed to overlap the counter electrode  230  and is made of a transparent metal layer. 
     The pixel electrode  270  includes a first bar  270   a  extended in the y direction at top edge of the counter electrode  230  adjacent to its corresponding data bus line, and a second bar  270   c  extended from the first bar  270   a  toward the x direction. Herein, an upper portion of the second bar  270   c  becomes a first space AP1 and a lower portion of the second bar  270   c  becomes a second space AP2. The pixel electrode  270  also includes a plurality of third and fourth bars  270   e - 1 ,  270   e - 2  which are extended from the first bar  270   a  or the second bar  270   c  toward a first space AP1 and a second space AP2 respectively. 
     Herein, the ratio(W11/l11) of the width w 11  of the third bar  270   e - 1  to the distance l11 between adjacent third bars  270   e - 1  is set preferably in the range of 0.2˜5, and the ratio(l11/d) of the distance l11 of the third bars  270   e - 1  to the cell gap d is set in the range of 0.1˜2. 
     In the present embodiment, the distance between the counter electrode  230  and the pixel electrode  270  is equivalent to the thickness of a gate insulating layer(not shown) and the thickness of the gate insulating layer is preferably smaller than the cell gap. 
     Additionally, an electric field is formed between the third or fourth bar  270   e - 1 , 270   e - 2  of the pixel electrode  270  and the counter electrode  230  exposed by the third and fourth bars  270   e - 1 , 270   e - 2 . 
     Operation of the liquid crystal display according to the present embodiment is the same as that in the first embodiment. 
     Further, as shown in FIG. 7, when the liquid crystal display is simulated, a uniform transmittance is obtained. When voltage is applied to the pixel electrode  270 , a relatively high transmittance of approximately 37.97% is obtained in the lapse of 31.30 ms. 
     As described in detail, according to the embodiments of the present invention, there are two diagonal electric fields which are disposed symmetrical to each other in a pixel. Therefore, liquid crystal molecules in the pixel are divided into two directions which are symmetrical to each other, in the presence of electric field, i.e. dual-domain is generated. Consequently, the viewer can see the long axes and short axes of liquid crystal molecules at all points in the screen, and the color shift is prevented. 
     Furthermore, according to the present invention the counter electrodes and pixel electrodes are made of transparent metal layers and their widths and distance are determined such that liquid crystal molecules on the electrodes are all driven by the fringe field. Accordingly, the liquid crystal display improves its transmittance and aperture ratio. 
     Further, a contrast distribution at a rubbing direction is improved. The rubbing direction in the present invention is at 90° or 180° which coincides with the viewer&#39;s viewing direction. Hence, the contrast in the viewer&#39;s direction is remarkably improved. 
     Various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the scope and spirit of the present invention.