Abstract:
A liquid crystal display (LCD) device has electrodes on barrier ribs that are adaptive for widening a viewing angle and improving an aperture ratio of the LCD device. In the device, barrier ribs are formed from an insulating material at the boundary portion of the pixel cells. First and second electrodes are provided at the front side and the rear side of the barrier ribs to apply an electric field to the liquid crystal. Accordingly, the viewing angle can be widened and the electrode area can be minimized, thereby improving the aperture ratio and the light transmissivity.

Description:
[0001]    This application claims the benefit of Korean Patent Application No. 1999-68074, filed on Dec. 31, 1999, which is hereby incorporated by reference for all purposes as if fully set forth herein.  
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device with electrodes on barrier ribs that is adaptive for widening a viewing angle and improving an aperture ratio.  
           [0004]    2. Discussion of the Related Art  
           [0005]    Generally, an active matrix liquid crystal display (LCD) of active matrix driving system uses thin film transistors (TFT&#39;s) as switching devices to display a natural moving picture. Since such a liquid crystal display can be made into a smaller-size device than the Brown tube or cathode ray tube (CRT), it is commercially available for a monitor such as a portable television or a lap-top personal computer, etc.  
           [0006]    The active matrix LCD displays a picture corresponding to video signals, such as television signals, on a pixel (or picture element) matrix having pixels arranged at each intersection between gate lines and data lines. Each pixel includes a liquid crystal cell for controlling a quantity of transmitted light in accordance with a voltage level of a data signal from a data line. The TFT is installed at an intersection between the gate line and the data line to switch a data signal to be transferred to the liquid crystal cell in response to a scanning signal (i.e., a gate pulse) from the gate line.  
           [0007]    Such a liquid crystal display device (LCD) can be largely classified into a twisted nematic (TN) mode, in which a vertical electric field is applied, and an in-plane switching (IPS) mode, in which a horizontal electric field is applied to have a wide viewing angle, depending on a direction of an electric field driving a liquid crystal.  
           [0008]    In a TN mode LCD as shown in FIG. 1, a TFT  30  is provided at an intersection between a data line  22  and a gate line  24 , and pixel electrodes  20  are arranged in a matrix type at a pixel area between the data line  22  and the gate line  24 . As shown in FIG. 2, the TFT  30  is provided on a rear substrate  2 . The TFT  30  includes a gate electrode  4  connected to the gate line  24 , a source electrode  14  connected to the data line  22 , and a drain electrode  16  connected to the pixel electrode  20 . A gate insulating film  6  made from SiN X  or SiO X , etc. is entirely deposited on the rear substrate  2  in which the gate electrode  4  is patterned. A semiconductor layer  8  made from amorphous silicon (a-Si) and an ohmic contact layer  10  made from a-Si doped with n+ions are sequentially disposed on the gate insulating film  6  in such a manner to cover the gate insulating film  6  on the gate electrode  4 . A source electrode  14  and a drain electrode  16  made from a metal are formed on the ohmic contact layer  10 . The source and drain electrodes  14  and  16  are patterned in such a manner to be spaced by a predetermined channel width from each other. Subsequently, the ohmic contact layer  10  is etched along a channel defined between the source electrode  14  and the drain electrode  16  to expose the semiconductor layer  8 . A protective film  18  made from SiN X  or SiO X , etc. is entirely deposited on the rear substrate  2  to cover the TFT  30 . The protective film  18  on the drain electrode  16  is etched away to define a contact hole  12 . The contact hole  12  and the pixel area are deposited with indium tin oxide (ITO) to connect the pixel electrode  20  to the drain electrode  16 .  
           [0009]    As, shown in FIG. 3, the rear substrate  2  provided with the TFT array is opposed to a front substrate  62  provided with black matrices  64 , color filters  66 , and a common electrode  68  of ITO with having a liquid crystal layer  70  therebetween. A gate high pulse is applied to the gate electrode  4  of the TFT, thereby applying an electric field corresponding to a difference voltage between a video data voltage and a common voltage between the pixel electrode  20  and the common electrode  68  opposed vertically to each other during a scanning interval when a channel is defined between the source electrode  14  and the drain electrode  16 . The liquid crystals of the liquid crystal layer  70  is driven with the vertical electric field to control a quantity of light input from a back light.  
           [0010]    Such a TN mode LCD has a drawback in that, since liquid crystal within the pixel cell has a large difference in refractive index and transmissivity depending on an observed angle, the viewing angle is limited. On the other hand, the IPS mode LCD has an advantage in the viewing angle since liquid crystal within the pixel cell is rotated on a basis of horizontal direction by a horizontal electric field.  
           [0011]    In an IPS mode LCD as shown in FIG. 4, a TFT  50  is provided at an intersection between a data line  52  and a gate line  54 , and pixel electrodes  48  are arranged in a matrix type at a pixel area between the data line  52  and the gate line  54 . As shown in FIG. 5, the TFT  50  is provided on a rear substrate  32 . The TFT  50  includes a gate electrode  34  connected to the gate line  54 , a source electrode  42  connected to the data line  52 , and a drain electrode  44  connected to the pixel electrode  48 . The gate electrode  34  and a common electrode  35  are formed on the rear substrate  32  by depositing a metal such as chrome (Cr), etc. and then patterning it. Herein, the common electrode  35  is patterned into a stripe shape within a pixel cell area. A gate insulating film  36  made from SiN X  or SiO X , etc. is entirely deposited on the rear substrate  32  provided with the gate electrode  34  and the common electrode  35 . A semiconductor layer  38  made from amorphous silicon (a-Si) and an ohmic contact layer  40  made from a-Si doped with n+ions are sequentially disposed on the gate insulating film  36  in such a manner as to cover the gate insulating film  36  on the gate electrode  34 . The source electrode  42  and the drain electrode  44  made from a metal are formed on the ohmic contact layer  40 . The source and drain electrodes  42  and  44  are patterned in such a manner as to be spaced by a predetermined channel width from each other. Then, ITO is deposited on the drain electrode  44  and the gate insulating film  36  and thereafter patterned to form the pixel electrode  48 . Herein, the pixel electrode  48  is connected to the drain electrode  44  and is patterned into a stripe shape in such a manner as to be alternated with the common electrode  35  within the pixel cell area. Subsequently, the ohmic contact layer  40  is etched along a channel defined between the source electrode  42  and the drain electrode  44  to expose the semiconductor layer  38 . A protective film  46  made from SiN X  or SiO X , etc. is entirely deposited on the rear substrate  32  to cover the TFT  50 .  
           [0012]    As shown in FIG. 6, the rear substrate  32  provided with the TFT array is opposed to a front substrate  72  provided with black matrices  74  and color filters  76 , with a liquid crystal layer  78  therebetween. A gate high pulse is applied to the gate electrode  34  of the TFT, thereby applying an electric field corresponding to a difference voltage between a video data voltage and a common voltage between the pixel electrode  48  and the common electrode  35  opposed horizontally to each other during a scanning interval when a channel is defined between the source electrode  42  and the drain electrode  44 . A liquid crystal of the liquid crystal layer  78  is driven with the horizontal electric field to control a quantity of a light input from a back light.  
           [0013]    However, the IPS mode LCD has an advantage in that it can achieve a wide viewing angle, but has a disadvantage in that, since the area occupied by the electrodes within the pixel cell area, particularly the common electrode  35  made from a metal is large, it has a low aperture ratio and transmissivity. The IPS mode LCD, as well as the TN mode LCD, has such a limitation in the aperture ratio and transmissivity caused by the electrode area as mentioned above. As the area of the electrode made from ITO or a metal is more enlarged so as to apply a strong enough electric field to drive the liquid crystal, the aperture ratio and the transmissivity become lower. Furthermore, the conventional TN mode and IPS mode LCD&#39;s have a problem in that, since a single pixel cell has to occupy more than a certain area in consideration of an area occupied by the electrodes, it is difficult to improve the resolution.  
         SUMMARY OF THE INVENTION  
         [0014]    Accordingly, the present invention is directed to a liquid crystal display device with electrodes on barrier ribs and a method of fabrication thereof that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.  
           [0015]    An object of the present invention is to provide a liquid crystal display device with electrodes on barrier ribs that is adaptive for widening the viewing angle of the display as well as improving the aperture ratio of the liquid crystal cells.  
           [0016]    Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structures particularly pointed out in the written description and claims hereof as well as the appended drawings.  
           [0017]    To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a liquid crystal display is provided having first and second electrodes to define pixel cells and a barrier member at the boundary portion of the pixel cells, the first and second electrodes being formed in a vertical structure between the first and second substrates;.  
           [0018]    A liquid crystal display device fabricating is also provided which includes: preparing first and second substrates; forming first and second electrodes to define pixel cells, the first and second electrodes being formed with a vertical shape between the first and second substrates; and forming a barrier member at the boundary portion of the pixel cells.  
           [0019]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.  
         [0021]    In the drawings:  
         [0022]    [0022]FIG. 1 is a plan view showing a structure of a conventional TN mode liquid crystal display device;  
         [0023]    [0023]FIG. 2 is a section view of the thin film transistor taken along the A-A′ line in FIG. 1;  
         [0024]    [0024]FIG. 3 is a section view representing a direction of an electric field applied to liquid crystals in the TN mode liquid crystal display device of FIG. 1;  
         [0025]    [0025]FIG. 4 is a plan view showing a structure of a conventional IPS mode liquid crystal display device;  
         [0026]    [0026]FIG. 5 is a section view of the thin film transistor taken along the B-B′ line in FIG. 4;  
         [0027]    [0027]FIG. 6 is a section view representing a direction of an electric field applied to liquid crystals in the IPS mode liquid crystal display device of FIG. 4;  
         [0028]    [0028]FIG. 7 is a plan view showing a structure of a liquid crystal display device with electrodes on barrier ribs according to a first embodiment of the present invention;  
         [0029]    [0029]FIG. 8 is a section view of the liquid crystal display device taken along the C-C′ line in FIG. 7;  
         [0030]    [0030]FIG. 9 illustrates a liquid crystal driving direction of a liquid crystal pixel cell shown in FIG. 7;  
         [0031]    [0031]FIG. 10 is a plan view showing a structure of a liquid crystal display device with electrodes on barrier ribs according to a second embodiment of the present invention; and  
         [0032]    [0032]FIG. 11 is a plan view showing a structure of a liquid crystal display device with electrodes on barrier ribs according to a third embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0034]    Referring to FIG. 7 and FIG. 8, there is shown a liquid crystal display device according to a first embodiment of the present invention. The liquid crystal display device includes barrier ribs  82  surrounding four sides of each pixel cell, and first and second electrodes  84  and  86  formed at the opposite surfaces of the barrier ribs  82  within the pixel cell. The barrier ribs  82  are provided at the boundary portions of the pixel cells in such a manner as to surround the respective pixel cells for displaying red, green and blue colors. An insulating material is used for the barrier ribs  82  so as to prevent a short or a electrical interference between the electrodes  84  and  86  formed at each side of the barrier rib  82 . The barrier ribs  82  are extended vertically between a front substrate  86  provided with black matrices  88  and color filters  90  and a rear substrate  94 . A liquid crystal material  92  is injected into each space surrounded with the barrier ribs  82 . The first and second electrodes  84  and  86  are made from a conductive material. Any one of the electrodes  84  and  86  is used as a common electrode to which a common voltage is applied while the other thereof is used as a data electrode to which video data is supplied.  
         [0035]    If a video data voltage and a common voltage are applied to each of the first and second electrodes  84  and  86 , then a horizontal electric field is applied to the liquid crystal  92  to rotate it around a vertical axis. Thus, the liquid crystal  92  goes from a state as shown in FIG. 9A into a state as shown in FIG. 9B, or vice versa, to control a transmissivity of an incident light. The liquid crystal  92  is driven with a horizontal electric field to widen the viewing angle as well as to reduce the area occupied by the electrodes within the pixel cell, so that the aperture ratio and light transmissivity can be increased. Furthermore, a distance D between the electrodes is narrowed to such an extent as to correspond to the increase in the aperture ratio and light transmissivity, so that the resolution can be improved.  
         [0036]    A height h of first or second electrodes  84  or  86  is set to be equal to or larger than a thickness d thereof (h≧d). And the height of the barrier ribs  82  is set to be equal to or larger than a thickness thereof.  
         [0037]    Meanwhile, when the liquid crystal display device shown in FIG. 7 is driven in an active matrix type, scanning electrode lines supplied with a scanning signal and switching devices driving the pixel cells in response to the scanning signal must be installed. For instance, when the pixel cells are driven with TFT&#39;s, a gate electrode line supplying the scanning signal is provided for each scanning line at each pixel cell. Also, the source electrode of the TFT is connected to any one of the first and second electrodes  84  and  86 , and the drain electrode thereof is connected to the other of the electrodes  84  or  86 .  
         [0038]    Referring to FIG. 10, there is shown a liquid crystal display device according to a second embodiment of the present invention. The liquid crystal display device includes barrier ribs  102  surrounding four sides of each pixel cell, and first and second electrodes  104  and  106  formed at the vertical surfaces of the opposed barrier ribs  82  within the pixel cell. The barrier ribs  102  are formed in a lattice shape at the boundary portions of the pixel cells in such a manner as to surround the respective pixel cells for displaying red, green and blue colors. An insulating material is selected for the barrier ribs  102  so as to prevent a short or an electrical interference between the electrodes  104  and  106  formed at the vertical surfaces of the barrier ribs  102 . The barrier ribs  102  are extended vertically between a front substrate  86  and a rear substrate  94  as shown in FIG. 8. A liquid crystal material  92  is injected into each space surrounded by the barrier ribs  102 . Any one of the electrodes  104  and  106  is used as a common electrode to which a common voltage is applied while the other electrode is used as a data electrode to which video data is supplied. The first and second electrodes  104  and  106  are supplied with voltage signals having a polarity contrary to each other. The first and second electrodes  104  and  106  are provided at four sides of the barrier rib  102  in such a manner to be symmetrical to the vertical surfaces of the barrier rib  102  in a diagonal direction. The first and second electrodes  104  and  106  have the same shape at the red, green and blue pixel cells adjacent to each other in a traverse direction, whereas they have an alternately different shape at the same color pixel cells adjacent to each other in a longitudinal direction. For instance, the first electrode  104  within the red, green and blue pixel cells arranged in the first row are formed equally at the left surface and the lower surface of the four surfaces of the barrier rib  102  surrounding the pixel cell. The first electrode  104  within the odd-numbered red pixel cells of the red pixel cells arranged in the first column is provided at the left surface and the lower surface of the four surfaces of the barrier rib  102 . On the other hand, the first electrode  104  within the even-numbered red pixel cells of the red pixel cells arranged in the first column is formed at the left surface and the upper surface of the barrier rib  102  in such a manner as to be opposed to the lower side of the first electrode  104  within the odd-numbered red pixels having the barrier rib therebetween.  
         [0039]    Referring to FIG. 11, there is shown a liquid crystal display device according to a third embodiment of the present invention. The liquid crystal display device includes barrier ribs  112  surrounding four sides of each pixel cell, and first and second electrodes  114  and  116  formed at three surfaces of the opposed barrier ribs  112  within the pixel cell in such a manner to be spaced by a desired gap for their mutual insulation. The barrier ribs  112  are formed in a lattice shape at the boundary portions of the pixel cells in such a manner as to surround the respective pixel cells for displaying red, green and blue colors. An insulating material is selected for the barrier ribs  112  so as to prevent a short or an electrical interference between the electrodes  114  and  116  formed at the vertical surfaces of the barrier rib  112 . The barrier ribs  112  are extended vertically between a front substrate  86  and a rear substrate  94  as shown in FIG. 8. Liquid crystal material  92  is injected into each space surrounded by the barrier ribs  112 . Any one of the electrodes  114  and  116  is used as a common electrode to which a common voltage is applied while the other electrode is used as a data electrode to which video data is supplied. The first and second electrodes  114  and  116  are supplied with voltage signals having the polarity contrary to each other. The first and second electrodes  114  and  116  are provided at the surfaces of the barrier rib  112  in such a manner as to be symmetrical to each other in the left and right direction. The first electrode  114  is provided at the left surface of the four surfaces of the barrier rib  112  and at a portion of the left sides of the upper and lower surfaces thereof. The second electrode  116  is provided at the right surface of the four surfaces of the barrier rib  112  surrounding the pixel cell, and is provided at a portion of the right sides of the upper and lower surfaces thereof in such a manner as to be opposed to the first electrode  114  with a desired gap therebetween.  
         [0040]    In the liquid crystal display devices as shown in FIG. 10 and FIG. 11, the electrode area is minimized to improve the aperture ratio and the light transmissivity. Also, the alignment directions of the liquid crystal at the center and the periphery of the pixel cell are different from each other when a horizontal electric field is applied to the liquid crystal and a voltage signal is applied to the first and second electrodes  104  and  114  or  106  and  116 . Therefore, the viewing angle can be increased. Such liquid crystal display devices can be driven in an active matrix system by the addition of switching devices and scanning electrode lines.  
         [0041]    As described above, according to the present invention, the barrier ribs of an insulating material are provided between the liquid crystal pixel cells, and electrodes are provided at the front side and the rear side of the barrier rib. Thus, an electric field is applied to the liquid crystal in the horizontal direction to differentiate an alignment direction of the liquid crystal at the center and the periphery of the liquid crystal cell, so that the viewing angle can be increased. Also, the electrode area is minimized, so that the aperture ratio and the light transmissivity can be improved.  
         [0042]    It will be apparent to those skilled in the art that various modifications and variation can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.