Abstract:
A multi-domain liquid crystal display and method of fabricating the same is disclosed in the present invention. More specifically, a liquid crystal display includes first and second substrates, a liquid crystal layer between the first and second substrates, wherein the liquid crystal layer a twist angle of at least 90 degrees, and an optical plate between the liquid crystal layer and the second substrate, wherein the optical plate has an optical axis horizontal to the first and second substrates.

Description:
[0001]    This application claims the benefit of Korean Application No. 2000-7152 filed on Feb. 15, 2000, which is hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to a liquid crystal display, and more particularly to a multi-domain liquid crystal display. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for a liquid crystal display that has a wide viewing angle and a simple structure.  
           [0004]    2. Description of the Related Art  
           [0005]    An active matrix liquid crystal display (LCD) requires a thin film transistor (TFT) as a switching device to display moving pictures. Since an LCD can be fabricated as a smaller dimension than a CRT, it has been extensively used in various applications such as a personal computer, a notebook computer, a copy machine, and a portable equipment, etc.  
           [0006]    A twisted-nematic (TN) liquid crystal having a twist angle of 90° is mainly used as a liquid crystal for the LCD. However, the TN-LCD has a limited viewing angle. In order to improve such a deficiency, a two-domain TN-LCD has been suggested.  
           [0007]    As shown in FIG. 1, a pixel of the two-domain TN-LCD includes two sub-domains having two different rubbing directions. A C-plate  2 , a first alignment film  3 , an O-plate  4 , a common electrode layer  3  formed of indium tin oxide (ITO), and a second alignment film  6  are disposed between a front transparent substrate  1  and a liquid crystal  7 . Similarly, a C-plate  12 , a first alignment film  11 , an O-plate  10 , a pixel electrode  9  formed of ITO, and a second alignment film  8  are disposed between a rear transparent substrate  13  and the liquid crystal  7 . The C-plates  2  and  12  have optical axes parallel to the Z-axis direction, so that they are vertical to the liquid crystal display panel. The O-plates  4  and  10  are patterned to have different tilt angles for each domain. The first alignment films  3  and  11  between the C-plates  2  and  12  and the O-plates  4  and  10  serve as an adhesive for attaching the C-plates  2  and  12  to the O-plates  4  and  10 , respectively. They are then rubbed to have different alignment directions for each domain, thereby determining alignment directions of the O-plates  4  and  10 . The second alignment films  6  and  8  have a liquid crystal align in different directions for each domain.  
           [0008]    As shown in FIG. 2, polarizers  14  and  15  having polarization directions perpendicular to each other are formed on the front and rear transparent substrates  1  and  13  for a two-domain TN-LCD. Light incident and outgoing sides of the liquid crystal cell  20  are parallel to the transmission axis.  
           [0009]    The conventional two-domain TN-LCD can improve a viewing angle by rotating a liquid crystal within a pixel to the opposite direction for each domain. The two-domain TN-LCD shown in FIG. 1 requires the C-plates  2  and  12  and the O-plates  4  and  10  on both the upper substrate and the lower substrate in order to improve a viewing angle. Thus, since the conventional two-domain TN-LCD employs a 90° TN, multi-layer optical films should be used for an optical compensation for each domain. Also, in the two-domain TN-LCD in FIG. 1, the first alignment films  3  and  11  arranged between the C-plates  2  and  12  and the O-plates  4  and  10  should be rubbed twice or have different alignment directions for each domain by a photo-alignment method. Furthermore, since a liquid crystal having a 90°-TN mode is used, the second alignment film  6  contacting the liquid crystal  7  should be aligned by twice rubbings to differentiate an alignment direction for each domain. As a result, the conventional two-domain LCD has problems in that the number of process increases and the process becomes complicated in an overall fabricating process.  
         SUMMARY OF THE INVENTION  
         [0010]    Accordingly, the present invention is directed to a multi-domain liquid crystal display and method of fabricating the same that substantially obviates one or more of problems due to limitations and disadvantages of the related art.  
           [0011]    An object of the invention is to provide a liquid crystal display that has a wide viewing angle and a simple structure.  
           [0012]    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 structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
           [0013]    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 includes first and second substrates, a liquid crystal layer between the first and second substrates, wherein the liquid crystal layer a twist angle of at least 90 degrees, and an optical plate between the liquid crystal layer and the second substrate, wherein the optical plate has an optical axis horizontal to the first and second substrates.  
           [0014]    In another aspect of the present invention, a method of fabricating a liquid crystal display having first and second substrates includes the steps of forming a liquid crystal layer between the first and second substrates, wherein the liquid crystal layer has a twist angle of at least 90 degrees, and forming an optical plate between the liquid crystal layer and the second substrate, wherein the optical plate has an optical axis horizontal to the first and second substrates. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention.  
         [0016]    In the drawings:  
         [0017]    [0017]FIG. 1 is a cross-sectional view illustrating a Z-Y plane of a liquid crystal pixel cell in a conventional liquid crystal display;  
         [0018]    [0018]FIG. 2 is a perspective view illustrating an optical axis of the liquid crystal pixel and an optical axis of a polarizer shown in FIG. 1;  
         [0019]    [0019]FIG. 3 is a cross-sectional view illustrating a structure of a multi-domain liquid crystal display device according to a first embodiment of the present invention;  
         [0020]    [0020]FIG. 4 is a cross-sectional view illustrating a structure of the multi-domain liquid crystal display device according to a second embodiment of the present invention;  
         [0021]    [0021]FIGS. 5 and 6 are cross-sectional views showing a structure of the multi-domain liquid crystal display device according to a third embodiment of the present invention; and  
         [0022]    [0022]FIG. 7 is a cross-sectional view illustrating a structure of the multi-domain liquid crystal display device according to a fourth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0024]    Initially referring to FIG. 3, a multi-domain liquid crystal display is illustrated according to a first embodiment of the present invention. The multi-domain liquid crystal display device includes an A-plate  32  having an optical axis horizontal to substrates  31  and  38  and provided between a front transparent substrate  31  and a common electrode  33 , and a low twisted-nematic (LTN) liquid crystal  35  injected between the common electrode  33  and a pixel electrode  37 . Alignment films  34  and  36  are formed on the common electrode  33  and the pixel electrode  37 , respectively. A twist angle of the LTN liquid crystal  35  is in the range of 1° to 89°. The LTN liquid crystal  35  is rotated by electric fields corresponding to a voltage difference between the voltages applied to the common electrode  33  and the pixel electrode  37 , thereby controlling an intensity of the incident light. Since the multi-domain liquid crystal display has a small twist angle of the liquid crystal, it can compensate a light incident to or coming out from the TN liquid crystal only by means of a single A-plate  32  without using the C-plates and the O-plates with a hybrid structure. Thus, in compensating the light, the optical axes have different directions similar to the conventional TN liquid crystal display. The A-plate  32  is formed of a polymer such as polyimide and has an optical axis horizontal to the substrates  31  and  38 , thereby compensating a phase difference of the LTN liquid crystal  35 . An electric filed is applied through the common electrode  33  and the pixel electrode  37  (formed of indium tin oxide (ITO)) to the LTN liquid crystal  35 . The alignment films  34  and  36  for determining an alignment direction of the liquid crystal may be rubbed in one direction. They may be however rubbed twice to differentiate an alignment direction of the liquid crystal for each domain or be subject to an alignment by a photo-alignment method, thereby generating different alignment directions to achieve a wide viewing angle.  
         [0025]    A multi-domain liquid crystal display according to a second embodiment of the present invention is illustrated in FIG. 4. The multi-domain liquid crystal display includes an A-plate  43  having an optical axis horizontal to substrates  42  and  49  and located between a front transparent substrate  42  and a common electrode  44 , a low twisted-nematic (LTN) liquid crystal  46  injected between the common electrode  44  and a pixel electrode  48 , and wide viewing angle films  41  and  50  attached to the side where the light comes out from the front transparent substrate  42  and the light incident side of a rear transparent substrate  49 , respectively. Alignment films  45  and  47  are formed on the common electrode  44  and the pixel electrode  48 , respectively. The A-plate  43  has an optical axis horizontal to the substrates  42  and  49 , thereby compensating for a phase difference of the LTN liquid crystal  46 . The common electrode  44  and the pixel electrode  48 , which are made of indium tin oxide (ITO), are applied by electric fields to the LTN liquid crystal  46 . The alignment films  45  and  47  for determining an alignment direction of the liquid crystal may be rubbed in one direction. However, they may be rubbed twice to differentiate an alignment direction of the liquid crystal for each sub-domain or be subject to an alignment by a photo-alignment method to have different alignment directions in achieving a wide viewing-angle. The wide viewing angle films  41  and  50  have optical axes vertical to optical axes of the light incident to and coming out from the LTN liquid crystal  46 , thereby improving a viewing angle.  
         [0026]    In FIGS. 5 and 6, a multi-domain liquid crystal display device according to a third embodiment is shown in the present invention. The multi-domain liquid crystal display device includes an A-plate  52  having an optical axis horizontal to front and rear transparent substrates  51  and  58  and provided between the front transparent substrate  51  and a common electrode  53 , a low twisted-nematic (LTN) liquid crystal  55  injected between the common electrode  53  and a pixel electrode  57 , and a slit  53   a  defined in the common electrode  53 . When a voltage is applied to the common electrode  53  and the pixel electrode  57  through the slit  53   a , the liquid crystal cells are aligned in different directions of the liquid crystal in each domain. When the slit  53   a  is formed in a straight-line direction or a diagonal direction, two domains are provided within one pixel.  
         [0027]    A data signal supplied from a data line  61  is applied to the pixel electrode  57  by a switching a thin film transistor  60 . In this case, the thin film transistor  60  turns on or off a channel between a source electrode and a drain electrode in accordance with a logical value of the gate pulse supplied from a gate line  62 .  
         [0028]    Meanwhile, an auxiliary electrode may be provided at the periphery of the pixel electrode  57  to differentiate an alignment direction of the liquid crystal for each domain within the liquid crystal pixel cell. The auxiliary electrode can be provided at the same layer as the gate electrode, the source/drain electrode and the pixel electrode. Alternatively, the slit  53   a  may be formed in a “+” shape, a “x” shape or a  
                         
 
         [0029]    shape. The slit  53   a  may be provided at the pixel electrode on the lower substrate. The alignment films  54  and  56  are formed on the common electrode  53  and the pixel electrode  57 , respectively. The A-plate  52  has an optical axis horizontal to the substrates  51  and  58  and compensates for a phase difference of the LTN liquid crystal  55 . The A-plate  52  is provided with a slit  53   a  in the diagonal direction.  
         [0030]    Alternatively, in the liquid crystal display shown in FIG. 5, wide viewing-angle films  59  and  60  may be formed on the front transparent substrate  51  and the rear transparent substrate  58 , as shown in FIG. 7.  
         [0031]    As described above, the multi-domain liquid crystal display and method of fabricating the same according to the present invention employs a LTN liquid crystal having a small twist angle to use only an A-plate having an optical axis horizontal to the substrates rather than using optical plates having a hybrid structure formed on the common electrode within the panel. Accordingly, the present multi-domain liquid crystal display is capable of improving the viewing angle and the contrast by the Aplate as well as simplifying the panel structure and reducing the number of fabrication processes.  
         [0032]    It will be apparent to those skilled in the art that various modifications and variations can be made in the multi-domain liquid crystal display and method of fabricating the same of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.