Abstract:
A liquid crystal display includes a first substrate having a first electrode, a second substrate having a second electrode, a plurality of slits formed on said second electrode and including a plurality of first slits and a plurality of second slits to divide the second electrode into a plurality of fragmented electrode portions, wherein said plurality of first slits are alternate with said plurality of second slits, a plurality of third electrodes disposed under said plurality of first slits, and a liquid crystal layer having a plurality of liquid crystal molecules and interposed between the first substrate and the second substrate. Meanwhile, orientations of the respective liquid crystal molecules positioned out of a vicinity above the slit are respectively aligned at a first and a second angles with respect to surfaces of the first substrate and the second substrate while there are a first-level and a second-level electric fields respectively across the liquid crystal layer.

Description:
FIELD OF THE INVENTION  
         [0001]    This is a continuation-in-part application of U.S. patent application Ser. No. 10/020,262, filed on Dec. 13, 2001. The present invention is in relation to a liquid crystal display (LCD), and more particularly, the present invention is in relation to a biased bending vertical alignment mode liquid crystal display.  
         BACKGROUND OF THE INVENTION  
         [0002]    The liquid crystal display (or LCD) is made up of two substrates and a liquid crystal layer interposed therebetween. The light is transmitted under the control of the electric field intensity applied to the liquid crystal layer.  
           [0003]    The twisted nematic (TN) liquid crystal display, which is currently the most popular LCD, has a transparent matrix substrate and a transparent counter substrate, a pair of transparent electrodes respectively formed on the inner surface of the transparent substrates and opposite to each other so as to drive the liquid crystal layer interposed therebetween, and a pair of polarizing plates which are respectively attached to the outer surfaces of the transparent substrates. In the off state of the LCD, that is, in the state that the electric field is not applied to the transparent electrodes, the orientations of the liquid crystal molecules are aligned perpendicular to the substrates.  
           [0004]    Unfortunately, the contrast ratio of the conventional TN LCD in a normally black mode may not be so high because the incident light is not fully blocked in the off state. In order to obviate this problem and increasing the viewing angles of LCD, various LCD modes have been presented. An example of the new LCD mode is known as vertical alignment (VA) mode. As the name suggests, the liquid crystal molecules are normally aligned perpendicular to the inner surface of the substrates, swinging through 90° to lie parallel with substrates in the presence of electric field. This LCD mode produces a display with an ultra-wide viewing angle and high contrast ratio but with the added bonus of higher brightness and a response time of 25 milliseconds. In addition, this LCD mode also consumes less power.  
           [0005]    Following the advent of VA mode LCD, a new technique was proposed to align the liquid crystal molecules at a sub-level which uses UV light instead of the usual rubbing. This technique involves the addition of pyramid-shaped protrusions with each of liquid crystal cell, the surface of which each makes up a separate domain, in which the liquid crystal molecules are aligned differently from those in other domains. It produces increased viewing angles, at the expense of a reduction in brightness, by ensuring that each of the multiple domains within a pixel cell channel light at an angle to the substrates, instead of at right angles to it. The result is an all-round increase in viewing angle with no variation in color tone as the viewing angle increases and, requiring no rubbing, a simplified manufacturing process with a reduction in the possibility of liquid crystal contamination. When combined with the VA mode, the resultant display is known as a multi-domain vertical alignment (MVA) mode LCD and produces a viewing angle of 160° in all directions with a high contrast ratio of around 300:1.  
           [0006]    However, the pyramid-shaped protrusions which are applied to control the tilt direction of the liquid crystal molecules are the major reasons for the low yield and high cost of the LCD products. There is an inclination to develop an active matrix LCD which has an improved response time, an increased viewing angle, an enhanced yield and a lower cost.  
         SUMMARY OF THE INVENTION  
         [0007]    The foregoing objectives can be attained by providing a liquid crystal display including a first substrate having a first electrode, a second substrate having a second electrode, a plurality of slits formed on the second electrode and having a plurality of first slits and a plurality of second slits to divide the second electrode into a plurality of fragmented electrode portions, wherein the plurality of first slits are alternate with the plurality of second slits, a plurality of third electrodes disposed under the plurality of first slits, and a liquid crystal layer having a plurality of liquid crystal molecules and interposed between the first substrate and the second substrate, wherein orientations of the respective liquid crystal molecules positioned out of a vicinity above the slit are respectively aligned from a first angle to a second angle with respect to surfaces of the first substrate and the second substrate while there are a first-level and a second-level electric fields respectively across the liquid crystal layer.  
           [0008]    Certainly, orientations of the liquid crystal molecules in a vicinity above the slit can be aligned parallel to surfaces of the first substrate and the second substrate.  
           [0009]    Certainly, the first angle and the second angle can be ranged from 70 to 90 and from 0 to 45 respectively.  
           [0010]    Certainly, the first-level electric field can be a zero electric field.  
           [0011]    Preferably, the liquid crystal molecules have a negative dielectric anisotropy.  
           [0012]    Preferably, the liquid crystal display further includes a spacer for producing a gap between the first substrate and the second substrate.  
           [0013]    Preferably, the spacer includes one of a metal and an organic material.  
           [0014]    Preferably, the liquid crystal display further includes two polarizing plates respectively attached to the first substrate and the second substrate.  
           [0015]    Preferably, the liquid crystal display further includes a plurality of switching elements.  
           [0016]    Certainly, each of the switching elements can be a TFT.  
           [0017]    Certainly, the first electrode and the second electrode can be formed of a transparent conductive material.  
           [0018]    Certainly, the transparent conductive material can be an indium-tin-oxide.  
           [0019]    Certainly, the first-level electric field and the second-level electric field can be controlled by means of adjusting relative potential between the first electrode and the second electrode.  
           [0020]    Certainly, the first electrode and the second electrode and can be connected to a common voltage and a various voltage respectively.  
           [0021]    Certainly, the third voltage can be connected to one of an independent electrode and a gate line.  
           [0022]    According to the present invention, the liquid crystal display includes a first substrate having a first electrode, a second substrate having a second electrode, a plurality of slits formed on the second electrode and having a plurality of first slits and a plurality of second slits to divide the second electrode into a plurality of fragmented electrode portions, wherein the plurality of first slits are alternate with the plurality of second slits, a plurality of third electrodes disposed under the plurality of first slits, and a liquid crystal layer having a plurality of liquid crystal molecules and interposed between the first substrate and the second substrate.  
           [0023]    According to the present invention, the liquid crystal display includes a first substrate having a common electrode, a second substrate having a plurality of pixel electrodes separated from each other by a plurality of slits having a plurality of first slits and a plurality of second slits, wherein the plurality of first slits are alternate with the plurality of second slits, a plurality of third electrodes disposed under the plurality of first slits, and a liquid crystal layer comprising a plurality of liquid crystal molecules and interposed between the first substrate and the second substrate, with a plurality of pixel parts being defined therein in a matrix form, wherein orientations of the respective liquid crystal molecules positioned out of a vicinity above the slit are respectively aligned from a first angle to a second angle with respect to surfaces of the first substrate and the second substrate while there are a first-level and a second-level electric fields respectively across the liquid crystal layer.  
           [0024]    Certainly, the orientations of the liquid crystal molecules in a vicinity above the slit can be aligned parallel to surfaces of the first substrate and the second substrate.  
           [0025]    Certainly, the first angle and the second angle can be ranged from 70 to 90 and from 0 to 45 respectively.  
           [0026]    Certainly, the first-level electric field can be a zero electric field.  
           [0027]    Preferably, the liquid crystal molecules have a negative dielectric anisotropy.  
           [0028]    Preferably, the liquid crystal display further includes a spacer for producing a gap between the first substrate and the second substrate.  
           [0029]    Preferably, the spacer includes one of a metal and an organic material.  
           [0030]    Preferably, the liquid crystal display further includes two polarizing plates respectively attached to the first substrate and the second substrate.  
           [0031]    Certainly, the common electrode and the pixel electrodes can be formed of a transparent conductive material.  
           [0032]    Certainly, the transparent conductive material can be an indium-tin-oxide.  
           [0033]    Certainly, the first-level electric field and the second-level electric field can be controlled by means of adjusting relative potential between the common and the pixel electrodes.  
           [0034]    Preferably, the liquid crystal display further includes a plurality of switching elements.  
           [0035]    Preferably, the third electrode is connected to a gate line.  
           [0036]    Preferably, the second substrate further includes a gate insulating layer formed on the gate electrodes.  
           [0037]    Preferably, the second substrate further comprises a semiconductor layer formed on a portion of the gate insulating layer over the gate electrodes.  
           [0038]    Certainly, the common electrode and the pixel electrodes can be connected to a common voltage and a variable voltage respectively.  
           [0039]    According to the present invention, the liquid crystal display includes a first substrate having a common electrode, a second substrate having a plurality of pixel electrodes separated from each other by a plurality of slits having a plurality of first slits and a plurality of second slits, wherein the plurality of first slits are alternate with the plurality of second slits, a plurality of third electrodes disposed under the plurality of first slits, and a liquid crystal layer comprising a plurality of liquid crystal molecules and interposed between the first substrate and the second substrate, with a plurality of pixel parts being defined therein in a matrix form.  
           [0040]    Now the foregoing and other features and advantages of the present invention will be more clearly understood through the following descriptions with reference to the enclosed drawings, wherein: 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0041]    [0041]FIG. 1 shows the structure of electrodes and the alignment of the liquid crystal molecules of LCD in the dark state in accordance with the present invention;  
         [0042]    [0042]FIG. 2 shows the structure of electrodes and the alignment of the liquid crystal molecules of LCD in the white state in accordance with the present invention;  
         [0043]    [0043]FIG. 3 is a plan view showing the pixel region of LCD according to a preferred embodiment of the present invention;  
         [0044]    [0044]FIG. 4 shows a cross-sectional view of LCD according to a preferred embodiment of the present invention;  
         [0045]    [0045]FIG. 5 shows a software simulation result of LCD in dark state;  
         [0046]    [0046]FIG. 6 shows a software simulation result of the LCD in white state; and  
         [0047]    [0047]FIG. 7 is a plan view showing the pixel region of LCD according to another preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0048]    An exemplary embodiment of the present invention will now be described in detail by way of the following discussions with reference to the accompanying drawings. It is to be emphasized that the following descriptions of embodiments and examples of the present invention are only illustrative, and it is not intended to be exhaustive or not to be limited to the precise form disclosed.  
         [0049]    [0049]FIG. 1 shows the structure of electrodes and the alignment of the liquid crystal molecules of the LCD in the dark state in accordance with the present invention, and FIG. 2 shows the structure of electrodes and the alignment of the liquid crystal molecules of the LCD in the white state in accordance with the present invention. As indicated in FIG. 1 and FIG. 2, a matrix substrate  10  and a counter substrate  11  made of a transparent insulating material such as glass are spaced apart from each other. Two transparent electrodes  12  and  13  made of a transparent conductive material such as ITO (Indium-Tin-Oxide) are formed respectively on the inner surface of the glass substrates  10  and  11 . A liquid crystal layer  100  including the liquid crystal molecules  101  having a negative dielectric anisotropy is disposed between the matrix substrate  10  and the counter substrate  11 . On the outer surface of the substrates  10  and  11 , an analyzer and a polarizer are respectively attached to the outer surface of the matrix substrate  10  and the outer surface of the counter substrate  11  (both of which are not shown in the drawings). The polarizer polarize the light beam incident on the liquid crystal layer  100  and the light beam out of the liquid crystal layer  100  respectively. The polarizing directions of the polarizer are perpendicular to each other. A light source (back light) is disposed on the rear of the LCD to act as an optical shutter (not shown). On the other hand, the matrix substrate  10  is further provided with a color filter (not shown).  
         [0050]    Please refer to FIGS.  1 - 4 . As shown in FIG. 1 and FIG. 2, the liquid crystal display embodying the present invention is constructed with a matrix substrate  10  and a counter substrate  11 , and a liquid crystal layer  100  disposed between the matrix substrate  10  and the counter substrate  11 . A common electrode  12  is provided to cover the entire surface of the matrix substrate  10  and a pixel electrode  13  is provided on the inner surface of the counter substrate  11 . In accordance with a preferred embodiment of the present invention, the pixel region of LCD is constituted by a matrix consisting of a plurality of scanning electrodes  14  (gate electrodes) and a plurality of signal electrodes  17  (data electrodes) being arranged in a crossover form. Both the gate electrodes  14  and the signal electrodes  17  are part of a switching element such as a thin film transistor (or TFT), which is formed on the counter substrate  11  and connected to the pixel electrode  13 . Parts of slits  16  are created on the pixel electrode  13  over the center of the third electrode  18  but relative parts of slits  16 ′ are created on the pixel electrode without covering the third electrode  18 . When the slits  16  and the relative slits  16 ′ are created on the pixel electrodes  13 , the pixel electrode  13  is divided into a plurality of fragmented electrode portions. The same signal voltage must be applied to fragmented electrode portions, and an electric connection must be established to interconnect these fragmented electrode portions.  
         [0051]    [0051]FIG. 1 shows the dark state that the electric field is not applied to the liquid crystal layer  100 . The pixel electrode  13  having slits  16  formed over the third electrodes  18  is provided over the matrix consisting of the gate electrodes  14  and the orthogonal signal electrodes  17 . The liquid crystal molecules  101  in the liquid crystal layer  100  are aligned perpendicular to the inner surface of the first substrate  10  and the second substrate  11 , but the liquid crystal molecules  101  in the vicinity of slit  16  in the liquid crystal layer  100  are aligned parallel to the inner surface of the first substrate  10  and the second substrate  11 . The polarized light which is generated by the polarizer passes through the portion of the liquid crystal layer  100  where the liquid crystal molecules are aligned vertical with respect to the first substrate  10  and the second substrate  11 , so as to make a dark state.  
         [0052]    As discussed above, in the absence of electric field, i.e. there is no voltage difference between the first electrode  12  and the second electrode  13 , the liquid crystal molecules  101  are aligned perpendicular to the inner surface of the substrates  10  and  11 . However, the liquid crystal molecules in the vicinity of slit  16  on the pixel electrode  13  and over the third electrodes  18  are aligned parallel to the inner surface of the substrates  10  and  11 . Because the voltage difference between the third electrodes  18  and the common electrode  12  is maintained high enough to keep the oblique liquid crystal molecules  101  parallel to the inner surface of the substrates  10  and  11 , the electric field applied to the liquid crystal layer  100  can determine the direction in which the liquid crystal molecules  101  are tilted. The orientation of the liquid crystal molecules  101  is divided into different direction along a plane defined by each pair of fragmented electrode portions over the third electrode  18 .  
         [0053]    [0053]FIG. 2 shows the white state that the sufficient electric field is applied to the liquid crystal layer  100  by the first electrode  12  and the second electrode  13 , in which the liquid crystal molecules  101  in the liquid crystal layer  100  are tilted from the counter substrate  11  to the matrix substrate  10 , and the direction of the liquid crystal layer  100  varies continuously. The polarized light generated by the polarizer passes through the liquid crystal layer  100  and its polarization is rotated by 90° in accordance with the variation of direction of the liquid crystal layer  100 . In this way, the light passes through the analyzer will make a white state. It can be seen from FIG. 2 that if a predetermined voltage difference is applied to the common electrode  12  and the fragmented electrode portions  13 , the liquid crystal molecules  101  will easily and rapidly aligned parallel to the inner surface of the substrates  10  and  11 , and a white display will appear.  
         [0054]    [0054]FIG. 3 shows the pixel region of LCD according to a preferred embodiment of the present invention. As shown in FIG. 3, the gate lines  14  are extended horizontally or transversely and crisscross arranged with the signal lines  17  to from a matrix of pixels. A thin film transistor (or TFT) as a switching element is provided at the intersection of the gate lines  14  and the signal line  17 . The pixel electrodes  13  are provided in matrix and each connected to the TFT. A plurality of slits  16  are provided on the pixel electrodes  13  to divide the pixel electrodes  13  into a plurality of fragment electrode portions. The third electrodes  18  is connected to the gate electrode  14 . A spacer (not shown) is provided between the matrix substrate and the counter substrate to produce a gap. A liquid crystal material having a negative dielectric anisotropy is injected into the gap through an injection port (not shown) between the substrates to form a liquid crystal layer  100 . Subsequently the injection port is sealed, and a pair of polarizing plates are attached to their respective substrates to finish the production of a LCD.  
         [0055]    [0055]FIG. 4 shows a cross-sectional view of the LCD according to a preferred embodiment of the present invention. As shown in FIG. 4, a spacer  200  formed of a metal or an organic material is formed on the TFT  30  to produce a gap between the matrix substrate  10  and the counter substrate  11 . A liquid crystal layer  100  is disposed between the counter substrate  11  having a TFT  30  and a matrix counter having a color filter (not shown). The TFT  30  formed on the counter substrate  11  includes a gate electrode  14 , a gate insulating layer  32  formed thereon, an a-Si semiconductor layer  33  formed on a portion of the gate insulating layer  32  over the gate electrode  14 , and source/drain electrodes  341  and  342  formed on the a-Si semiconductor layer  33 . A passivation film  50  covers the enter surface of counter substrate  1 . A pixel electrode  13  is formed in the pixel region and electrically coupled to the drain region  342  through a contact hole in the passivation film  50 . Parts of the slits  16  are created on the pixel electrodes  13  over the third electrodes  18  but relative parts of the slits  16 ′ are created on the pixel electrodes  13  without covering the third electrodes  18 , wherein the slits  16  and the relative slits  16 ′ divide the pixel electrodes  13  into a plurality of fragmented electrode portions.  
         [0056]    [0056]FIG. 5 and FIG. 6 respectively exhibits the software simulation results of the alignment of the liquid crystal molecules of LCD in the dark state and in white state. It can be clearly understood from FIG. 5 that the liquid crystal molecules are aligned perpendicular to the surfaces of substrates to make dark display, except for the liquid crystal molecules in the vicinity of the slits which are lay parallel to the surfaces of substrates. In FIG. 6, it is readily known that the liquid crystal molecules are lay parallel to the surfaces of the substrates to make white display. It should be noted that the software simulation results of alignment of the liquid crystal molecules in FIG. 5 and FIG. 6 respectively has the same profile as those shown in FIG. 1( a ) and FIG. 1( b ), which further proves the practicability of the function of LCD according to the present invention.  
         [0057]    [0057]FIG. 7 shows the pixel region of LCD according to another preferred embodiment of the present invention. As shown in FIG. 7, the gate lines  14  are extended horizontally or transversely and crisscross arranged with the signal lines  17  to from a matrix of pixels. A thin film transistor (or TFT) as a switching element is provided at the intersection of the gate lines  14  and the signal lines  17 . The pixel electrodes  13  are provided in matrix and each connected to the TFT. Parts of slits  16  over the third electrodes  18  are provided on the pixel electrodes  13  but relative parts of slits  16 ′ are provided on the pixel without covering the third electrodes  18 , wherein the slits  16  and the relative slits  16 ′ divide the pixel electrodes  13  into a plurality of fragment electrode portions. In FIG. 3, the third electrode  18  is connected to the gate electrode  14 , but the third electrodes  18  in FIG. 7 is connected to an independent electrode  19 , which is not connected to the gate electrodes  14 . The various case of bias voltage pairs according to FIG. 7 of the present invention could optimize LC tilt angle in surround slit ITO over the third electrode.  
         [0058]    As described above, the orientations of the liquid crystal molecules of the LCD according to the present invention is determined by the electric field intensity across the liquid crystal layer. By way of dividing the pixel electrode on the counter substrate into a plurality of fragmented electrode portions so as to create parts of slits  16  over the third electrode and relative parts of slits  16 ′, the dark state and the white state of the LCD can be readily and easily achieved by controlling the orientations of the liquid crystal molecules through the electric field across the fragmented electrode portions and the common electrode. In comparison with the prior MVA technology, the present invention substantially removes the protrusions on the matrix substrate, and the liquid crystal alignment method of the liquid crystal display can be accomplished by appropriately applying electric field across the common electrode and fragmented pixel electrodes overlapping the third electrode to make the dark state and the white state. Owing to the removal of the protrusions, it is known that the present invention is advantageous in terms of response time, viewing angle, yield and manufacturing cost.  
         [0059]    Those of skill in the art will recognize that these and other modifications can be made within the spirit and scope of the present invention as further defined in the appended claims.