Patent Publication Number: US-2003234901-A1

Title: Liquid crystal display with wide viewing angle and high brightness uniformity

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a liquid crystal display and, more particularly, to a liquid crystal display with wide view angle and high brightness uniformity.  
       [0003] 2. Description of the Related Art  
       [0004] To obtain a high image quality as good as the traditional CRT display (Cathode Ray Tube display) in LCD (Liquid Crystal Display) for large-screen display products, many properties, such as high contrast ratio, fast response time and wide view angle, need to be improved. Therefore, many types of LCD, like MVA-LCD (Multi-domain vertical alignment LCD), ECB-LCD (electrically controlled birefringence-LCD) that can provides high contrast ratio, fast response time and wide view angle, are disclosed.  
       [0005]FIG. 1 is a top view showing a ECB-Liquid crystal display. FIG. 2 is a sectional view showing the structure along to line I-I of FIG. 1. A plurality of liquid crystal molecules  24  are held between color filter substrate  20  and TFT (thin film transistor) substrate  18  and are aligned vertically to the TFT substrate  18 . A plurality of scanning electrodes  10  and a plurality of signal electrodes  12  are formed on the TFT substrate  18  to define a plurality of pixel areas  15  being arranged in a matrix form. A TFT device  14  and a plurality of block pixel electrode  16 I are formed in each pixel area  15 . The first alignment film  22 I is deposited on the liquid crystal layer  24  side of the TFT substrate  18 . A common electrode  16 II is formed on the liquid crystal layer  24  side of the color filter substrate  20 . The second alignment film  22 II is deposited on the common electrode  16 II. When applying the voltage to the common electrode  16 II and the pixel electrode  16 I, electric fields E are generated to drive the liquid crystal molecules  24  rotating. Therefore, BCE-LCD can improve viewing angle and response time.  
       [0006] However, the position of the disconnected line is easily affected by process in vertical alignment LCD. It will result in the brightness anuniform (multiformity) as FIG. 3.  
       SUMMARY OF THE INVENTION  
       [0007] The object of the present invention is to provide a wide view angle LCD having uniform brightness. The brightness uniformity of the display is improved by a protrusion structure and slits which induce LC molecules toarrange at a pretilt angle.  
       [0008] A liquid crystal display has a pair of transparent substrates disposed opposite to each other sandwiching a liquid crystal layer therebetween, and the liquid crystal layer comprises a plurality of liquid crystal molecules and chiral components. A plurality of scanning electrodes and signal electrodes are patterned on the first substrate to define a plurality of pixel areas, wherein each pixel area has a first area and a second area. A plurality of switching devices are formed on the plurality of pixel areas and connected to the scanning electrodes, the signal electrodes and the pixel electrodes. A protrusive structure with a plurality of protrusions formed in each pixel area to produce the pretilt angle for liquid crystal molecules.  
       [0009] According to the present invention, LCD has infinite-domain in the pixel area by producing a protrusive structure to generate the fringe electrode field. LCD with infinite-domain has super wide view angle. At the same time, the position of the disconnected line is fixed on the protrusive structure or on the first area. It can successfully increase the brightness uniformity.  
       [0010] Moreover, because the present invention can be fabricated using normal TN manufacturing method, the process is simple and has high production yield that will decrease the manufacturing cost.  
     
    
    
     BRIFE DESCRIPTION OF THE DRAWINGS  
     [0011]FIG. 1 is a top view showing a ECB-Liquid crystal display.  
     [0012]FIG. 2 is a sectional view showing the structure along to line I-I′ of FIG. 1.  
     [0013]FIG. 3 is a diagram showing the image quality of a vertical alignment LCD.  
     [0014]FIG. 4 is a top view showing a LCD according to first embodiment of the present invention.  
     [0015]FIG. 5 is a sectional view showing the structure along to line II-II′ of FIG. 4.  
     [0016]FIG. 6 is a diagram showing the image quality of a LCD of the present invention.  
     [0017]FIG. 7 is a top view showing a LCD according to second embodiment of the present invention.  
     [0018]FIG. 8 is a sectional view showing the structure along to line III-III′ of FIG. 7.  
     [0019]FIG. 9 is a top view showing a LCD according to third embodiment of the present invention.  
     [0020]FIG. 10 is a sectional view showing the structure along to line VI-VI′ of FIG. 9. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS FIRST EMBODIMENT  
     [0021]FIG. 4 is a top view showing a LCD according to the first embodiment of the present invention. FIG. 5 is a sectional view showing the structure along to line II-II′ of FIG. 4. On the lower insulating substrate  180 , serving as a TFT array substrates  180 , a plurality of scanning electrodes  100  are patterned and then covered by a gate insulating layer  110 . Next, a plurality of signal electrodes  120  are patterned on the gate insulating layer  110 . Thus, the scanning electrodes  100  and the signal electrodes  120  are arranged in a matrix form to define a plurality of pixel areas  150  which each of the pixel area  150  has a first area  280  and a second area. A plurality of pixel electrode  160 I are formed on the second area of the plurality of pixel areas  150 . A plurality of switching devices  140  are formed on the neighboring intersection of the scanning electrodes  100  and the signal electrodes  120  and are connected to the scanning electrodes  100 , the signal electrodes  120  and the pixel electrodes  160 I. The insulating substrate  180  is made of a material selected from a group comprising glass, quartz or the like. The scanning electrodes  100  and the signal electrodes  120  are made of non-transparent conductivity material, such as aluminum, tungsten, chromium, copper, and the combination thereof. The gate insulating layer  110  are made of transparent non-conductivity material, such as silicon nitride, silicon oxide, silicon oxynitride and the combination thereof. The pixel electrodes  160 I are made of a transparent conductivity material, such as indium tin oxide (ITO), indium zinc oxide(IZO) or the like.  
     [0022] Moreover, the wall-shape protrusive structure  260  is formed on the pixel area  150  and are covered by the pixel electrodes  160 I. The wall-shape protrusive structure  260  encircled the first area  280  in predetermined distance divides the pixel area  150  into a plurality of block regions. The height of the wall-shape protrusive structure  260  ranges from 0.6 to 1.0 um. The wall-shape protrusive structure  260  is stacked up by the non-transparent conductivity materials and the transparent non-conductivity materials. The non-transparent conductivity materials are formed simultaneaisly with the scanning electrodes  100  and signal electrodes  120 . The transparent non-conductivity materials are formed simultaneaisly with the gate insulating layer  110 . Thus, the production yield is not be decreased and the cost is lower because of no additional process step to form the wall-shape protrusive structure  260 . Finally, a first alignment layer  220 I of poly imide (PI) is formed on the liquid crystal layer  250  side of the lower insulating substrate  180 .  
     [0023] On the upper insulating substrate  200 , serving as a color filter substrates  200 , a common electrode layer  160 II are formed. Finally, a second alignment layer  220 II of poly imide (PI) is formed on the liquid crystal layer  250  side of the upper insulating substrate  200 . The common electrode layer  160 II is made by transparent conductivity material, such as indium tin oxide (ITO), indium zinc oxide(IZO) or the like.  
     [0024] A liquid crystal layer  250  comprises a plurality of liquid crystal molecules  240  and chiral components (not shown) is held between the lower insulating substrate  180  and the upper insulating substrate  200 . Liquid crystal molecules  240  are negative dielectric anisotropy material and are aligned vertically to the TFT substrate  180 . When applying the voltage to the common electrode  160 II and the pixel electrode  160 I, as FIG. 5 shown, the electric fields are generated to drive liquid crystal molecules  240 . The direction of the long axis of liquid crystal molecules  240  are vertical to the direction of the electric fields. Because of the fringe electrode field E 1  and the wall-shape protrusive structure  260 , liquid crystal molecules  240  rotate in the predetermined direction in the Y-Z plane. At the same time, liquid crystal molecules  240  also rotate in the X-Y plane because of the chiral components (not shown). Liquid crystal molecules  240  tilt to pixel electrodes and counter-clockwise rotate simultaneously shown by arrow in FIG. 4. So that, liquid crystal molecules  240  can be aligned in 360 degree to form infinite-domain with the pixel area  150  to obtain super wide view angle. In FIG. 5, it is easy to observe the disconnection line of the liquid crystal molecules  240  between two adjacent wall-shape protrusion  260  appear in the first area  280 . Thus, the disconnection line is successfully fixed in the first area  280 , as show in FIG. 6, to improve the brightness uniformity.  
     SECOND EMBODIMENT  
     [0025]FIG. 7 is a top view showing a LCD according to second embodiment of the present invention. FIG. 8 is a sectional view showing the structure along to line III-III′ of FIG. 7. Comparing to the first embodimen of the present invention, a floating electrode  300  is formed in the center of the first area  280 . A floating electrode  300  and the pixel electrode  160 I are separated in the same plane. The design of second embodiment can achieve the same result as the first embodimen. The floating electrode is made of a transparent conductivity material, such as indium tin oxide (ITO), indium zinc oxide(IZO) or the like.  
     THIRD EMBODIMENT  
     [0026]FIG. 9 is a top view showing a LCD according to the third embodiment of the present invention. FIG. 10 is a sectional view showing the structure along to line VI-VI′ of FIG. 9. Comparing to the first embodiment of the present invention, a plurality of block-shape pixel electrodes  160 I are formed in the second area (not shown) of the pixel area  150 . Each block-shape protrusion  320  is formed at the center of each block-shape pixel electrode  160 I and is covered by the pixel electrode  160 I. The height of the block-shape protrusions  320  ranges from 0.6 to 1.0 um. The block-shape protrusions  320  are stacked up by the non-transparent conductivity materials and the transparent non-conductivity materials. The non-transparent conductivity materials are formed simultaneaisly with the scanning electrodes  100  and signal electrodes  120 . The transparent non-conductivity materials are formed simultaneaisly with the gate insulating layer  110 . Therefore, the production yield is not be decreased and the cost is lower because of no additional process step to form the block-shape protrusions  320 .  
     [0027] When applying the voltage to the common electrode  160 II and the pixel electrode  160 I, as show in FIG. 10, the electric fields are generated to drive liquid crystal molecules  240 . The direction of the long axis of liquid crystal molecules  240  are perpendicular to the direction of the electric fields. Because of the fringe electrode field E 1  and the block-shape protrusions  320 , liquid crystal molecules  240  rotate in the predetermined direction in the Y-Z plane. At the same time, liquid crystal molecules  240  also rotate in the X-Y plane because of the chiral components (not shown). Liquid crystal molecules  240  tilt to pixel electrodes and counterclockwise rotate simultaneously shown by arrow in FIG. 9. In FIG. 10, it is easy to observe the disconnection line of the liquid crystal molecules  240  on the block-shape pixel electrodes  160 I appears at the protrusions  320 . Thus, each disconnection line is successfully fixed at the center of each block-shape pixel electrode  160 I, as show in FIG. 6, to improve the brightness uniformity.  
     [0028] While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.