Patent Publication Number: US-2005128400-A1

Title: Liquid crystal display device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application claims priority to Taiwan Patent Application No. 92134924, filed Dec. 10, 2003, which is hereby incorporated by reference in its entirety.  
     TECHNICAL FIELD  
      This invention relates to a liquid crystal display device, and more particularly to a multi-domain homeotropic alignment mode liquid crystal display device.  
     BACKGROUND  
      Due to a viewing angle of the Twisted Nematic (TN) mode liquid crystal display being narrow and response times of gray-scale inversion and midtone being slow, applications of the liquid crystal display to flat panel display are limited, especially for the application to TV. For the problem of narrow viewing angle, it can be solved through the wide viewing angle technology of TN+Film. A special film attached outside the liquid crystal panel can raise the horizontal viewing angle from 90-degree angle to 140-degree angle. However, the technology can not improve two problems of low contrast and slow response time, and the color-shift problem is also occurred.  
      Another technology for improving viewing angle is IPS (In-Plane Switching). In IPS, the alignment direction of the liquid crystal molecules is parallel to a glass substrate, that is the difference between the TN+Film and IPS is. The viewing angle with IPS can achieve 170-degree angle as well as CRT display. Nevertheless, the technology still has some drawbacks. Due to the alignment of the liquid crystal molecules, pixel electrodes only are arranged on the array substrates, unlike TN mode. The electrodes are arranged as comb-shaped on a surface of the lower substrate. Nonetheless, that will cause the contrast to lower and so the brightness of the back light source must be increased. The contrast and the response time in IPS are not improved compared with the typical TFT-TN.  
      Hence, for improving the aforementioned problems of the contrast and the response time that do not solve yet, the VA (Vertical Alignment) is developed and expected that the display characteristics of high transparency, symmetrical wide viewing angle, short response time, without gray-scale inversion, and slight color shift can achieve. Recently, many technologies related to VA are developed, but the aforementioned display characteristics still can not entirely satisfy.  
      EP0884626 discloses the MVA (Multi-Domain Vertical Alignment). That is to form V-shaped bumps on the two glass substrates respectively to form different domains with different arrangement directions of nearby liquid crystals for improving the symmetrical arrangement of the liquid crystals and achieving the purpose of wide viewing angle. The horizontal and vertical viewing angle of the liquid crystal display manufactured according to MVA is more than 160-degree angle, even 170-degree angle. Furthermore, the response time can reduce to approach 25 ms due to the bumps and winding electric-power lines which is about a half of the response time of IPS and TN, the displaying colors can be closer to the true color.  
      U.S. Pat. No. 6,097,464 discloses a novel structure similar to the above-mentioned MVA structure. It integrates the advantage of photo-spacer and develops the wide viewing angle technology of MHA (Multi-domain Homeotropic Alignment). The method of MHA is to form a cruciform bump structure around each pixel on one glass substrate, and to form a square bump structure around each pixel on the other glass substrate. The bumps control the liquid crystal therein to overturn toward four directions for forming multi-domain. The aperture ratio of MVA is not high and the aperture ratio of MHA is more than MVA, nevertheless, the pixel size is limit to less than 350 μm. Therefore, if the MHA is applied to the liquid crystal display with larger pixel, the overturning time of the liquid crystals will increase and so movements&#39; result in long wakes being left on the screen.  
      In view of the prior arts, there are still problems of low contrast and slow response time in the conventional TN, TN+Film, and IPS technologies, low aperture ratio in MVA technology, and the pixel size limitation in MHA.  
     SUMMARY  
      One of objectives of the present invention is to provide a liquid crystal display device for overcoming the drawbacks of low contrast and slow response time, low aperture ratio, and pixel size limitation in the conventional arts.  
      Another objective of present invention is to provide a multi-domain homeotropic alignment mode liquid crystal display device. The spacers therein can be replaced with the intersections of the bumps or the contact points formed on bumps and so the problems of spacers non-uniformly sprinkling or spacers gathering can be avoided.  
      Still another objective of present invention is to provide a liquid crystal display device to divide pixels into a plurality of domains with appropriate dimensions to maintain the characteristic of fast response for large-size liquid crystal displays or liquid crystal displays with larger pixels.  
      A liquid crystal display device of the present invention comprises: a first substrate having a plurality of transistors on a first surface of the first substrate; a second substrate having a common electrode layer on a first surface of the second substrate; two polarizers, one of the two polarizers being attached to a second surface of the first substrate, the other polarizer being attached to a second surface of the second substrate; and bumps making a multi-domain formed on one of the first substrate and the second substrate dividing pixels complementary to the plurality of transistors into more than two domains, a plurality of strip patterns formed on the other one of the first substrate and the second substrate, when aid first substrate and the second substrate are fabricated and liquid crystals are injected into therein, the strip patterns and the bumps dividing the pixels to form a multi-domain homeotropic alignment mode liquid crystal display device.  
      The aforementioned strip patterns have a function of faster overturning liquid crystals, similar to that of the bumps, moreover, do not have the drawback of light leak. Therefore, the characteristics of high contrast, short response time, and wide viewing angle can be achieved by the present invention. Furthermore, the present invention can replace spacers with intersections of the bumps or the contact points formed on bumps and so the present invention doesn&#39;t have the problems of spacers non-uniformly sprinkling or spacers gathering. Further, to divide pixels into a plurality of domains with appropriate dimensions can maintain the characteristic of fast response for large-size liquid crystal displays or liquid crystal displays with larger pixels. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic diagram of a pixel unit in a liquid crystal display device;  
       FIG. 2A-2C  are schematic diagrams of bumps and slits according to a first preferred embodiment of the present invention;  
       FIG. 3A-3B  are vertical views of arrangements of liquid crystals under OFF state and ON state in a domain divided by bumps and slits according to the first preferred embodiment of the present invention;  
       FIG. 4A-4B  are 1 cross-sectional side view of arrangements of liquid crystals under the state with applying voltage and the state without applying voltage in a part of the domain divided by bumps and slits according to the first preferred embodiment of the present invention;  
       FIG. 5A-5B  are respectively the vertical view and the cross-sectional side view of the pattern of four aligned square formed by bumps according to a second preferred embodiment of the present invention;  
       FIG. 6A-6B  are respectively the vertical view and the cross-sectional side view of the bump of four aligned square and contact points on the bump according to a third preferred embodiment of the present invention;  
       FIG. 7A-7C  are respectively the vertical view and the cross-sectional side view of the H-shaped bump plus the square-shaped bump, slits complementary to the bumps, and the combined shape according to a fourth preferred embodiment of the present invention;  
       FIG. 8A-8B  are respectively the vertical view and the cross-sectional side view of the ++-shaped bump plus the square-shaped bump, and slits complementary to the bumps according to a fifth preferred embodiment of the present invention; and  
       FIG. 9A-9B  are respectively the vertical view and the cross-sectional side view of the #-shaped bump plus the square-shaped bump, and slits complementary to the bumps according to a sixth preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
      As shown in  FIG. 1 , it is a schematic diagram of a pixel unit in a liquid crystal display device. The region of the pixel is surrounded with the two adjacent gate lines  12  and the two adjacent source lines  14 . The pixel electrode  10  is in the region and electrically connects with the drain of the transistor  16 . The liquid crystal display device displays the predetermined image by controlling the pixel electrode  10  through the transistor  16 . The aforementioned plurality of strip patterns is formed on the pixel electrode and the pixel electrode is transparent.  
      One preferred embodiment of the present invention is to form bumps of four aligned square on one of the substrates. As shown in  FIG. 2A , multi-domain pattern  20  is composed of square (□)-shaped bumps  22  and +-shaped bumps  24 . The square-shaped bumps  22  and the +-shaped bumps  24  may be formed simultaneously, or first one of them is formed and then the other is formed.  FIG. 2A  shows that the +-shaped bumps  24  is first formed and then the square-shaped bumps  22  is formed. The cross-sectional side view of the bumps can be convex with rounded top, convex with rectangular top, or convex with triangular top, preferably an averaging tilt angle of the convex with triangular top is from 3° to 25°.  
      The strip patterns  28  are formed on the other substrate, as shown in  FIG. 2B . A multi-domain formed with the bumps  22  is divided into several domains which have an approximately same size by overlapping strip pattern  28 . The strip patterns can be formed on the pixel electrode or the common electrode layer, preferably the structure of the strip patterns is slit. The cross-sectional side view of the slits can be concave with rounded bottom, concave with rectangular bottom, or concave with triangular bottom, preferably the structure of the slits are square.  
       FIG. 2C  shows the liquid crystal display device after the two substrates was combined. After the two substrates was combined, the strip patterns  28  divides the domains formed by the multi-domain pattern  20 , preferably divides domains of multi-domain pattern  20  into equal parts. In general, the liquid crystal pixels are square with 1:3 aspect ratio. Therefore, the divided domains by the multi-domain pattern  20  are also square. Preferably, the strip patterns are parallel to one side of the square domain and the side is the long side thereof to improve the response time of the liquid crystals.  
       FIG. 3A  and  FIG. 3B  are the vertical views of the liquid crystal molecules  100  with a pre-tilted direction in the region A of  FIG. 2C  under the state without and with applying voltage respectively. One side of the drawing of the liquid crystal molecules  100  with a line represents the downward side thereof and the other side without the line represents the upward side. According to the pre-tilted state of the liquid crystal molecules  100 , it is recognized that the bumps  22 ,  24  and the slits  28  can tie in with each other. Under the state without applying voltage, the liquid crystal molecules  100  are perpendicular to a surface of the support and so the liquid crystal molecules  100  on the bumps pre-tilt with a certain angle. Under the state with applying voltage, due to the effect of the electric field, the liquid crystal molecules  100  change the tilted angle for changing the transmittance of pixels.  
       FIG. 4A  and  FIG. 4B  are the vertical views of  FIG. 3A  and  FIG. 3B  along the line a′-a respectively. The bumps  22  are in one substrate  102  and a layer structure  106  with slits  28  is on the other substrate  104 . Under the state without applying voltage ( FIG. 4A ), except the liquid crystal molecules  100  on the surface of bumps with a pre-tilted angle, all other liquid crystal molecules  100  are perpendicular to the surfaces of the substrates  102  and  104 . Under the state with applying voltage ( FIG. 4B ), the intermediate liquid crystal molecules  100  change the tilted angle due to the influence of the electric field, but the liquid crystal molecules  100  on the surface of the bumps  22  mainly are influenced by the bumps and almost maintains the pre-tilted angle near that under the state without applying voltage. The liquid crystal molecules  100  on the surface of the substrates also mainly are influenced by the substrates and almost perpendicular to the surface of the substrates. Similarly, the liquid crystal molecules  100  in the region above the slits  28  and perpendicular to the surface of the substrates are almost perpendicular to the surface of the substrate due to the influence of the slits. Hence, the arrangements of the liquid crystal molecules  100  in each domain have symmetrical arrangement directions and so it is expected that wide viewing angle can be achieved.  
      As aforementioned, the bumps  22 ,  24  can be formed on the substrate  102  during different steps. As shown in  FIG. 5A , it is the second preferred embodiment of the present invention. The bumps of four aligned square are formed with two steps: first forming +-shaped bumps  24  and then forming square-shaped bumps  22  to form bumps of four aligned square. Therefore, the cross-sectional side view of the B region in  FIG. 5B  shows that the bumps  22  and  24  are overlapped with each other and so the overlapped regions are higher. Hence, the cell gap can be supported with the overlapped regions of the bumps  22  and  24  to replace spacers for avoiding the problems of spacers non-uniformly sprinkling or spacers gathering. The forming sequence of the bumps of the present invention are not limited, namely, square-shaped bumps  22  can be first formed and then +-shaped bumps  24  are formed to achieve the function of replacing the spacers.  
      If the bumps  22  and  24  are formed on the substrate  102  with the same step, the overlapped regions are not occurred and so the height of the bumps  22  and  24  are the same. The third embodiment of the present invention is to form contact points  100  on the bumps  22  and  24 , e.g.: the intersection region C of the bumps  22  and  24  shown in  FIG. 6A . Therefore, the height of the contact point  110  on the bumps  22  and  24  is higher, as shown in  FIG. 6B  that is the cross-sectional side view of C region. Hence, the cell gap of the present invention also can be replace spacers with forming contact points  110  on the bumps  22  and  24  and the problems of spacers non-uniformly sprinkling or spacers gathering can be avoided.  
      The fourth preferred embodiment of the present invention is shown in  FIG. 7A  to  FIG. 7C . The manufacturing steps is to form the bumps  70  of the H-shaped pattern  74  and the square-shaped pattern  72  on one substrate, as shown in  FIG. 7A  and to form the slits  78  on the other substrate.  FIG. 7C  shows the combined shape of the two substrates. The bumps and the slits tie in with each other and so the slits  78  divides the domain formed by the bumps  70 . Preferably, the slits  78  divides the domains formed by the bumps  70  into equal parts and are parallel to the long side of the domains for improving the response time of the liquid crystals. The bumps  70  of H-shaped pattern  74  plus square-shaped pattern  72  divide a pixel into four domains of top, bottom, right, and left, preferably the shapes and dimensions of the four domains are the same. As shown in  FIG. 7A , the shapes and dimensions of the four domains are the same, but the difference of the arrangement directions between top (bottom) and right (left) is 90-degree angle. Therefore, the ratio of the overturned liquid crystals in every direction are more uniform and the best displaying effect and wide viewing angle can be achieved. Furthermore, for users using the liquid crystal display device according to the present invention, the contrast and brightness of viewing the display device from different directions is closer and so the effect of wide viewing angle is better that the conventional liquid crystal display device. The cell gap can employed that disclosed in the second and third embodiment of the present invention to support. That is to support the cell gap by the overlapped regions of the H-shaped pattern  74  and the square-shaped pattern  72  or the contact points on the intersections of the H-shaped pattern  74  and the square-shaped pattern  72 . The embodiment can make the ratio of the overturned liquid crystals in every direction uniformly for achieve the better effect of wide viewing angle (more than 160°/160°).  
      The present invention also aims at the application of large-size liquid crystal display. Except for the aforementioned embodiments, the present invention forms the bumps with different shapes on one substrate to divide pixels into more domains, and forms slits on the other substrate, wherein the amount of the slits are with respect to the domains divided by the bumps. The pixel is divided into a plurality of domains by both the bumps and the slits and the arrangement of the liquid crystals in different domains can complement with each other to achieve the wide viewing angle. For example, in the fifth preferred embodiment of the present invention, as shown in  FIG. 8A  and  FIG. 8B , the bumps  80  of square-shaped pattern  82  and ++-shaped pattern  84  are formed on one substrate, and the slits  88  are formed on the other substrate to divide the liquid crystal pixels into more domains.  
      In the sixth preferred embodiment of the present invention, as shown in  FIG. 9A  and  FIG. 9B , the bumps  90  of square-shaped pattern  92  and #-shaped pattern  94  are formed on one substrate, and the slits  98  are formed on the other substrate to divide the liquid crystal pixels into more domains. Hence, the present invention can divide pixels into a plurality of domains with suitable dimensions according to the dimension of pixels, preferably the dimensions of the divided domains are the same. Hence, except for providing wide viewing angle, the present invention can maintain the characteristic of fast response time due to each pixel divide into suitable domains. Therefore, the present invention does not limit to the dimension of the pixel that the present invention can apply to.  
      The present invention mainly provides a liquid crystal display device. The liquid crystal display device is a multi-domain homeotropic alignment mode, wherein pixels is divided into a plurality of domains having different arrangements of liquid crystals. The different arrangements of liquid crystals can complement with each other and so when users view the liquid crystal display device from different viewing angles, the difference in contrast and brightness is not large. Hence, the display device can achieve the effect of wide viewing angle.  
      The aforementioned liquid crystal display device comprises two substrates, and the material of the substrates may be glass or transparent plastics. Wherein one substrate has bumps for dividing pixels of said liquid crystal display device, and the other substrate has a plurality of strip patterns. When the two substrates are fabricated and liquid crystals are injected into therein, the strip patterns and bumps dividing said pixels to form a multi-domain homeotropic alignment mode liquid crystal display device.  
      One of the two substrates has a matrix composed of a plurality of transistors. The other substrate has a common electrode layer. In the present invention, the bumps and the plurality of strip patterns do not limit to form on the substrate having the common electrode layer or the substrate having the plurality of transistors. Preferably, the bumps only are formed on the substrate having the common electrode layer and the plurality of strip patterns are only formed on the substrate having the plurality of transistors. Therefore, to form bumps only on the substrate having the common electrode layer can solve a problem of bumps hard to form on the substrate having the plurality of transistors and so the yield can be raised and the cost can be reduced. Moreover, the plurality of strip patterns (in general, strip patterns are slits) have a function similar to that of the multi-domain pattern and so to add slits in the bumps can accelerate the overturning of liquid crystals. Further, the slits do not have the light leak of drawback of bumps and the contrast is not decreased.  
      The two substrates of the present invention can be attached polarizers respectively, and the difference of the polarizing directions thereof is 90-degree angle. At least a compensation film may be formed between one of polarizers and the substrate that the polarizer is attached on for improving the color shift and increasing the range of viewing angle.  
      Compared with the conventional arts, the liquid crystal display device of the present invention provides really has well advantages. The present invention employs two substrates. Wherein one substrate has a multi-domain pattern for dividing pixels of the liquid crystal display device, the other substrate has a plurality of strip patterns. When the two substrate are fabricated and liquid crystals are injected into therein, the strip patterns and the multi-domain pattern dividing the pixels to form a multi-domain homeotropic alignment mode liquid crystal display device.  
      The aforementioned strip patterns have a function of faster overturning liquid crystals, similar to that of bumps, moreover, do not have the drawback of light leak. Therefore, the characteristics of high contrast, short response time, and wide viewing angle can be achieved by the present invention. Furthermore, the present invention can replace spacers with intersections of the bumps or the contact points formed on bumps and so the present invention doesn&#39;t have the problems of spacers non-uniformly sprinkling or spacers gathering. Further, to divide pixels into a plurality of domains with appropriate dimensions can maintain the characteristic of fast response for large-size liquid crystal displays or liquid crystal displays with larger pixels.  
      Although specific embodiments have been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from what is intended to be limited solely by the appended claims.