Abstract:
A pixel electrode structure including a first electrode and a second electrode is provided. The first electrode has a first stripe electrode extended along a first direction and pleural first branch electrodes connected to the first strip electrode. The first branch electrodes include pleural first branch domain electrodes extended along a second direction and pleural second branch domain electrodes extended along a third direction substantially perpendicular to the second direction. The second electrode has a second stripe electrode extended along the first direction and pleural second branch electrodes connected to the second stripe electrode. The second branch electrodes include pleural third branch domain electrodes extended along the second direction and pleural fourth branch domain electrodes extended along the third direction. The first and the third branch domain electrodes are alternated to each other. The second and the fourth branch domain electrodes are alternated to each other.

Description:
This application claims the benefit of Taiwan application Serial No. 101112114, filed Apr. 5, 2012, the subject matter of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates in general to a liquid crystal display, and more particularly to a multi-domain horizontal alignment (MHA) liquid crystal display panel and a pixel electrode structure thereof. 
     2. Description of the Related Art 
     Having the features of low voltage operation, no radiation, light weight and small size, the liquid crystal display (LCD) has gradually replaced the conventional cathode ray tube (CRT) display and become a mainstream product in the display market. 
     However, the liquid crystal display still encounters some problems such as the viewing angle being too narrow and the liquid crystal response time being too long. Therefore, how to enlarge the viewing angle and shorten the response time are prominent tasks for the industries. Currently, several solutions for wide-viewing angle LCD such as multi-domain vertical alignment (MVA) LCD, in-plane switching (IPS) LCD and fringe field switching (FFS) LCD are already provided. The IPS LCD generates a lateral electric field between the pixel electrode and the common electrode to drive the liquid crystal molecules to twist horizontally. The multi-domain horizontal alignment (MHA) LCD makes the liquid crystal molecules arranged in multiple directions to obtain pleural domains with different polarizing angles to increase the viewing angle of the LCD. Due to the restriction in electrode pattern, the liquid crystal molecules located between two adjacent domains are not driven by the electric field to twist. Consequently, the transmittance in the domain boundary region may easily deteriorate and image contrast is low. 
     SUMMARY OF THE INVENTION 
     The invention is directed to a liquid crystal display (LCD) panel and a pixel electrode structure thereof capable of increasing the transmittance in the domain boundary region and accordingly increasing image contrast. 
     According to an embodiment of the present invention, a pixel electrode structure including a first electrode and a second electrode is provided. The first electrode has a first stripe electrode extended along a first direction and a plurality of first branch electrodes connected to the first strip electrode. The first branch electrodes include a plurality of first branch domain electrodes extended along a second direction and a plurality of second branch domain electrodes extended along a third direction substantially perpendicular to the second direction. In addition, the second electrode has a second stripe electrode extended along the first direction and a plurality of second branch electrodes connected to the second stripe electrode. The second branch electrodes include a plurality of third branch domain electrodes extended along the second direction and a plurality of fourth branch domain electrodes extended along the third direction. The first branch domain electrodes and the third branch domain electrodes are alternated to each other. The second branch domain electrodes and the fourth branch domain electrodes are alternated to each other. 
     According to another embodiment of the present invention, a LCD panel including an active element array substrate, an opposite substrate and a liquid crystal layer is provided. The opposite substrate is opposite and parallel to the active element array substrate. The liquid crystal layer is disposed between the active element array substrate and the opposite substrate. The active element array substrate has a pixel electrode structure. The pixel electrode structure includes a first electrode and a second electrode. The first electrode has a first stripe electrode extended along a first direction and a plurality of first branch electrodes connected to the first strip electrode. The first branch electrodes include a plurality of first branch domain electrodes extended along a second direction and a plurality of second branch domain electrodes extended along a third direction substantially perpendicular to the second direction. In addition, the second electrode has a second stripe electrode extended along the first direction and a plurality of second branch electrodes connected to the second stripe electrode. The second branch electrodes include a plurality of third branch domain electrodes extended along the second direction and a plurality of fourth branch domain electrodes extended along the third direction. The first branch domain electrodes and the third branch domain electrodes are alternated to each other. The second branch domain electrodes and the fourth branch domain electrodes are alternated to each other. 
     The above and other aspects of the invention will become better understood with regard to the following detailed description of the preferred but non-limiting embodiment(s). The following description is made with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic diagram of a LCD panel according to an embodiment of the invention; 
         FIG. 2  shows a partial diagram of an active element array substrate according to an embodiment of the invention; 
         FIG. 3  shows a schematic diagram of a pixel electrode structure according to an embodiment of the invention; 
         FIG. 4  shows a schematic diagram of a pixel electrode structure according to an embodiment of the invention; and 
         FIG. 5  shows a partial diagram of an active element array substrate according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention provides a liquid crystal display (LCD) panel and a pixel electrode structure thereof. By changing the electrode pattern in the domain boundary region, the liquid crystal molecules located between two adjacent domains are driven by an electric field to twist, such that more lights pass through domain boundary region and the transmittance of the LCD panel is increased. Let the polarizing directions of the upper polarizer and the lower polarizer of the LCD panel be respectively 0 degree and 90 degrees. Considering the polarizing directions of the polarizers, in the following embodiments, the branch electrodes of the pixel electrode structure respectively are arranged at a predetermined angle (such as 45 and 135 degrees), such that in each domain, the direction of the electric field respectively forms an angle of 45 degrees and an angle of 135 degrees with the polarizing direction of the upper polarizer and the polarizing direction of the lower polarizer, and the transmittance of the LCD panel is thus increased. 
     A number of embodiments are disclosed below for elaborating the invention. However, the embodiments of the invention are for detailed descriptions only, not for limiting the scope of protection of the invention. 
     Referring to  FIG. 1 , a schematic diagram of a LCD panel according to an embodiment of the invention is shown. The LCD panel  100  includes an active element array substrate  110 , an opposite substrate  120 , a liquid crystal layer  130 , a first polarizer  140  and a second polarizer  150 . The opposite substrate  120  is opposite and parallel to the active element array substrate  110 . For example, the opposite substrate  120  is a color filter substrate, and the active element array substrate  110  is a thin film transistor (TFT) array substrate or a diode array substrate. The liquid crystal layer  130  is disposed between the active element array substrate  110  and the opposite substrate  120 , and is realized by a polymer-stabilized blue phase (PSBP) liquid crystal layer or a cholesterol liquid crystal layer. The blue phase liquid crystal has three phases, namely, the first blue phase (BP I), the second blue phase (BP II) and the third blue phase (BP III). The first blue phase liquid crystal and the second blue phase liquid crystal form a double twist cylinder (DTC) structure, that is, double twist cylinders in space are perpendicular to each other. The first blue phase liquid crystal is a body-centered cubic (BCC) structure, the second blue phase liquid crystal is a simple cubic (SC) structure, and the third blue phase liquid crystal is an amorphous structure. When no lateral electric field E is added to the positive type blue phase liquid crystal, ideally the positive blue phase liquid crystal is optical isotropic, has zero variation in the refractive index (that is, Δn=0), presents a normally black state and is impermeable to the light. When a lateral electric field E is added to the positive type blue phase liquid crystal, the blue phase liquid crystal is optical anisotropic, and its refractive index varies (that is, Δn&gt;0), such that the light may penetrate the blue phase liquid crystal and present a bright state. 
     The first polarizer  140  and the second polarizer  150  are respectively disposed on a lower surface of the active element array substrate  110  and an upper surface of the opposite substrate  120 , and the polarization axes P and A of the first polarizer (polarizer)  140  and the second polarizer (analyzer)  150  vertically intersect with each other. 
     First Embodiment 
     Referring to  FIG. 2 , a partial diagram of an active element array substrate according to an embodiment of the invention is shown. As indicated in  FIG. 2 , the active element array substrate  110  has a substrate  110   a , a scan line  111 , at least one data line  112 , a first electrode  113 , a second electrode  116 , at least one common wire  119  and two active elements  123  and  124 . The active element  123  is electrically connected to the scan line  111  and a data line  112 . The active element  124  is electrically connected to the scan line  111  and another data line  112 . The first electrode  113  and the second electrode  116  are co-planar and located within a pixel region defined by the scan line  111  and two data lines  112 , wherein the first electrode  113  and the second electrode  116  are pixel electrodes with different voltages, such that a first electric field E 1  and a second electric field E 2  are formed between the first electrode  113  and the second electrode  116  for driving the liquid crystal molecules  132  to twist. 
     In the present embodiment, the first electrode  113  has a first stripe electrode  114  extended along a first direction D 1  and a plurality of first branch electrodes  115  connected to the first stripe electrode  114 . The first branch electrodes  115  includes a plurality of first branch domain electrodes  115   a  extended along a second direction D 2  and a plurality of second branch domain electrodes  115   b  extended along a third direction D 3 . The second direction D 2  and the third direction D 3  form an angle of 90±10 degrees and preferably the angle is 90 degrees. In addition, the second electrode  116  has a second stripe electrode  117  extended along the first direction D 1  and a plurality of second branch electrodes  118  connected to the second stripe electrode  117 . The second branch electrodes  118  includes a plurality of third branch domain electrodes  118   a  extended along the second direction D 2  and a plurality of fourth branch domain electrodes  118   b  extended along the third direction D 3 . 
     In  FIG. 2 , the first direction D 1  is the polarizing direction of the second polarizer (analyzer)  150  of  FIG. 1 , such that the two data lines  112 , the first stripe electrode  114 , the second stripe electrode  117  are aligned in the same direction with the polarization axis A of the second polarizer  150 . Moreover, the first direction D 1  and the second direction D 2  substantially form an angle of 45 or 135 degrees, and the first direction D 1  and the third direction D 3  substantially form an angle of 45 or 135 degrees. 
     As indicated in  FIG. 2 , in order to form a multi-domain alignment distribution of electric fields, the pixel region is sequentially divided into a first domain P 1 , a second domain P 2  and a third domain P 3 , and one domain boundary region is between the first domain P 1  and the second domain P 2  and another domain boundary region is between the second domain P 2  and the third domain P 3 . For example, a first electric field E 1  is formed in the first domain P 1  and the third domain P 3 , and the direction of the first electric field E 1  is parallel to the third direction D 3  or differs with the third direction D 3  by less than 10 degrees. Also, a second electric field E 2  is formed in the second domain P 2 , and the direction of the second electric field E 2  is parallel to the second direction D 2  or differs with the second direction D 2  by less than 10 degrees, for example. 
     In addition, in domain boundary region between the first domain P 1  and the second domain P 2 , the first branch domain electrodes  115   a  and the second branch domain electrodes  115   b  vertically intersect with each other, and are sawtooth-like and extended between the first stripe electrode  114  and the second stripe electrode  117  in the domain boundary region. In domain boundary region between the second domain P 2  and the third domain P 3 , the third branch domain electrodes  118   a  and the fourth branch domain electrodes  118   b  vertically intersect with each other in a domain boundary region, and are sawtooth-like and extended between the first stripe electrode  114  and the second stripe electrode  117  in the domain boundary region. 
     The first branch domain electrodes  115   a  and the third branch domain electrodes  118   a  are alternated to each other, and the second branch domain electrodes  115   b  and the third branch domain electrodes  118   b  are alternated to each other. When a voltage is applied to the first branch domain electrodes  115   a  and the third branch domain electrodes  118   a , the first branch domain electrodes  115   a  and the third branch domain electrodes  118   a  form a first electric field E 1  in the first domain P 1  and the third domain P 3 . Likewise, when a voltage is applied to the second branch domain electrodes  115   b  and the fourth branch domain electrodes  118   b , the second branch domain electrodes  115   b  and the fourth branch domain electrodes  118   b  form a second electric field E 2  in the second domain P 2 . The rate of penetration is maximized when the angles between the first electric field E 1  and the second electric field E 2  and the polarization axis A of the second polarizer  150  are equal to 45 degrees and 135 degrees respectively, and the transmittance of the LCD panel  100  can thus be increased. Similarly, the liquid crystal molecules  132  located in two domain boundary region are driven by the first electric field E 1  or the second electric field E 2  to twist, and the rate of penetration can further be increased. 
     Second Embodiment 
     Referring to  FIG. 3 , a schematic diagram of a pixel electrode structure according to an embodiment of the invention is shown. Like the active element array substrate  110  used in the first embodiment, the pixel electrode structure  210  includes a first electrode  213  and a second electrode  216 . The first electrode  213  has a first stripe electrode  214  extended along a first direction D 1  and a plurality of first branch electrodes  215  connected to the first stripe electrode  214 . The first branch electrodes  215  includes a plurality of first branch domain electrodes  215   a  extended along a second direction D 2  and a plurality of second branch domain electrodes  215   b  extended along a third direction D 3 . The second direction D 2  and the third direction D 3  are substantially perpendicular to each other or the difference is less than 10 degrees. In addition, the second electrode  216  has a second stripe electrode  217  extended along the first direction D 1  and a plurality of second branch electrodes  218  connected to the second stripe electrode  217 . The second branch electrodes  218  includes a plurality of third branch domain electrodes  218   a  extended along the second direction D 2  and a plurality of fourth branch domain electrodes  218   b  extended along the third direction D 3 . The first branch domain electrodes  215   a  and the third branch domain electrodes  218   a  are alternated to each other. The second branch domain electrodes  215   b  and the fourth branch domain electrodes  218   b  are alternated to each other. 
     Like the first embodiment, when a voltage is applied to the first branch domain electrodes  215   a  and the third branch domain electrodes  218   a , a first electric field E 1  is formed between the first branch domain electrodes  215   a  and the third branch domain electrodes  218   a  due to voltage difference. When a voltage is applied to the second branch domain electrodes  215   b  and the fourth branch domain electrodes  218   b , a second electric field E 2  is formed between the second branch domain electrodes  215   b  and the fourth branch domain electrodes  218   b  due to voltage difference. The rate of penetration is maximized when the angles between the first electric field E 1  and the second electric field E 2  and the polarization axis A of the second polarizer  150  are equal to 45 degrees and 135 degrees respectively, and the transmittance of the LCD panel can thus be increased. 
     Third Embodiment 
     Referring to  FIG. 4 , a schematic diagram of a pixel electrode structure according to an embodiment of the invention is shown. Like the active element array substrate  110  used in the first embodiment, the pixel electrode structure  310  includes a first electrode  313  and a second electrode  316 . The first electrode  313  has a first stripe electrode  314  extended along a first direction D 1  and a plurality of first branch electrodes  315  connected to the first stripe electrode  314 . The first branch electrodes  315  includes a plurality of first branch domain electrodes  315   a  extended along a second direction D 2  and a plurality of second branch domain electrodes  315   b  extended along a third direction D 3 . The second direction D 2  and the third direction D 3  form an angle of 90±10 degrees, and preferably the angle is 90 degrees. In addition, the second electrode  316  has a second stripe electrode  317  extended along the first direction D 1  and a plurality of second branch electrodes  318  connected to the second stripe electrode  317 . The second branch electrodes  318  includes a plurality of third branch domain electrodes  318   a  extended along the second direction D 2  and a plurality of fourth branch domain electrodes  318   b  extended along the third direction D 3 . The first branch domain electrodes  315   a  and the third branch domain electrodes  318   a  are alternated to each other. The second branch domain electrodes  315   b  and the fourth branch domain electrodes  318   b  are alternated to each other. 
     Like the first embodiment, when a voltage is applied to the first branch domain electrodes  315   a  and the third branch domain electrodes  318   a , a first electric field E 1  is formed between the first branch domain electrodes  315   a  and the third branch domain electrodes  318   a  due to voltage difference. When a voltage is applied to the second branch domain electrodes  315   b  and the fourth branch domain electrodes  318   b , a second electric field E 2  is formed between the second branch domain electrodes  315   b  and the fourth branch domain electrodes  318   b  due to voltage difference. The rate of penetration is maximized when the angles between the first electric field E 1  and the second electric field E 2  and the polarization axis A of the second polarizer  150  are equal to 45 degrees and 135 degrees respectively, and the transmittance of the LCD panel can thus be increased 
     Fourth Embodiment 
     Referring to  FIG. 5 , a partial diagram of an active element array substrate according to an embodiment of the invention is shown. As indicated in  FIG. 5 , the active element array substrate  410  has a substrate  410   a , a scan line  411 , at least one data line  412 , a first electrode  413 , a second electrode  416 , at least one common line  419  and an active element  420 . The present embodiment is different from the first embodiment in that: the first electrode  413  is a pixel electrode, and the second electrode  416  is a common electrode, for example. The active element  420  is electrically connected to the scan line  411  and the data line  412 . The first electrode  413  and the second electrode  416  are co-planar and located within a pixel region defined by the scan line  411  and the data lines  412 . 
     Descriptions and disposition relationships related to the first stripe electrode  414 , the first branch electrodes  415 , the first branch domain electrodes  415   a , the second branch domain electrodes  415   b , the second branch electrodes  418 , the third branch domain electrodes  418   a  and the fourth branch domain electrodes  418   b  are similar to the disclosure in the first embodiment, and the similarities are not repeated here. Moreover, descriptions and disposition relationships of the pixel electrode structures  210  and  310  disclosed in the second embodiment and the third embodiment can also be used in the present embodiment, and the similarities are not repeated here. 
     When a voltage is applied to the first branch domain electrodes  415   a  and the third branch domain electrodes  418   a , a first electric field E 1  is formed between the first branch domain electrodes  415   a  and the third branch domain electrodes  418   a  due to voltage difference. When a voltage is applied to the second branch domain electrodes  415   b  and the fourth branch domain electrodes  418   b , a second electric field is formed between the second branch domain electrodes  415   b  and the fourth branch domain electrodes  418   b . The first electric field E 1  and the second electric field E 2  is realized by an in-plane switching (IPS) lateral electric field or a fringe field switching (FFS) lateral electric field for driving the liquid crystal molecules  432  to twist horizontally to control the rate of penetration of the liquid crystal layer, such that the light may penetrate the liquid crystal layer and present a bright state. The rate of penetration is maximized when the angles between the first electric field E 1  and the second electric field E 2  and the polarization axis A of the second polarizer  150  are equal to 45 degrees and 135 degrees respectively, and the transmittance of the LCD panel  100  can thus be increased 
     Although lateral electric fields are exemplified in the above embodiments, the pixel electrode structure and the LCD panel of the invention are not limited thereto, and may also be used in vertical electric fields such that the transmittance of the LCD panel can further be increased. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.