Abstract:
An IPS-LCD with a compensation structure for CD variation. The IPS-LCD panel includes a plurality of pixels wherein each pixel has parallel pixel electrodes and parallel common electrodes positioned such that a respective pixel electrode is disposed adjacent and parallel to a respective common electrode. This panel is characterized in that each spacing between any adjacent common electrode and pixel electrode in one pixel is equal to and different from that of the adjacent pixel.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an in-plane switching liquid display (IPS-LCD), more particularly, the present invention relates to an IPS-LCD with a compensation structure for critical dimension (CD) variation.  
           [0003]    2. Description of the Related Art  
           [0004]    Liquid crystal displays (LCDs) may be classified by the orientation of the liquid crystal molecules between the spaced glass substrates. In a conventional twisted nematic LCD (TN-LCD), the liquid crystal molecules are twisted between the two substrates. In contrast, in an in-plane switching LCD (IPS-LCD), common electrodes and pixel electrodes are formed on a lower glass substrate (TFT substrate) and an in-plane electrode field therebetween is generated to rearrange the liquid crystal molecules along the electrode field. Accordingly, the IPS-LCD has been used or suggested for improving drawbacks of the conventional TN-LCD, such as a very narrow viewing angle and a low contrast ratio.  
           [0005]    [0005]FIGS. 1A and 1B are sectional diagrams of a conventional IPS-LCD, in which FIG. 1A shows the alignment of the liquid crystal molecules in an off state and FIG. 1B shows the alignment of the liquid crystal molecules in an on state. The IPS-LCD has a lower glass substrate  10 , an upper glass substrate  12 , and a liquid crystal layer  14  disposed in a spacing between the two parallel glass substrates  10  and  12 . On the lower glass substrate  10 , serving as a TFT substrate, a plurality of strip-shaped common electrodes  16  is patterned on the lower glass substrate  10 , an insulating layer  18  is deposited on the common electrodes  16  and the lower glass substrate  10 , and a plurality of strip-shaped pixel electrodes  20  is patterned on the insulating layer  18 .  
           [0006]    As shown in FIG. 1A, before an external voltage is applied to the IPS-LCD, the negative liquid crystal molecules  14 A are aligned in a direction parallel to the lower glass substrate  10 . As shown in FIG. 1B, when an external voltage is applied to the IPS-LCD, an in-plane electric field is generated between the common electrode  16  and the pixel electrode  20 , resulting in a rotation of the liquid crystal molecules  14 B toward the in-plane electric field.  
           [0007]    Generally, the common electrode  16  and the pixel electrode  20  are formed on the same or different layers and arranged apart from each other by a predetermined distance, known as “spacing”. For example, FIG. 2 shows a cross-section of a glass substrate having common electrodes and pixel electrodes thereon. The common electrodes  16  and the pixel electrodes  20  have a width of about 4.0 μm. The common electrodes  16  in the edge have a width of about 8.0 μm. Each spacing between a respective common electrode  16  and a respective pixel electrode  20  is about 9.0 μm in the same pixel and the adjacent pixel.  
           [0008]    However, critical dimension (CD) variation is easily generated during formation of the common electrodes  16  and the pixel electrodes  20  caused by many parameters such as different substrate flatness, different resist thickness, and different etching recipe.  
           [0009]    [0009]FIG. 3 is a top view showing muras on an IPS-LCD panel caused by CD variation at area B. The IPS-LCD panel  100  having area A and area B is disposed in an outer frame  102 . A plurality of muras  104 , curved spots, are generated on the panel  100  caused by localized CD variation.  
           [0010]    Next, FIG. 4 shows a more detailed diagram to explain muras caused by CD variation and shows a pixel array including area A and area B having CD variation according to the prior art.  
           [0011]    As shown in area A of FIG. 4, the pixel array comprises a plurality of small rectangles having the same numeral (10.00). Each small rectangle denotes one unit pixel that has parallel pixel electrodes  20  and parallel common electrodes  16  positioned such that a respective pixel electrode  20  is disposed adjacent and parallel to a respective common electrode  16 . The numeral (10.00) in one small rectangle represents the spacing between any adjacent common electrode  16  and pixel electrode  20 . The spacing between any adjacent common electrode  16  and pixel electrode  20  in the same pixel is equal to that of the adjacent pixel. For example, the spacing between any adjacent common electrode  16  and pixel electrode  20  is 10.00 μm in the pixel  30 .  
           [0012]    Turning now to area B of FIG. 4, area B shows a pixel array, having spacing CD variation of about 0.30 μm. The pixel array comprises a plurality of small rectangles having numeral (10.30) respectively. Each small rectangle denotes one unit pixel that has parallel pixel electrodes  22  and parallel common electrodes  28  positioned such that a respective pixel electrode  22  is disposed adjacent and parallel to a respective common electrode  28 . The numeral (10.30) in one small rectangle represents the spacing between any adjacent common electrode  28  and pixel electrode  22 . The spacing between any adjacent common electrode  28  and pixel electrode  22  in the same pixel is equal to that of the adjacent pixel. For example, the spacing between any adjacent common electrode  28  and pixel electrode  22  is 10.30 μm in the pixel  40 .  
           [0013]    [0013]FIG. 5 is a three-dimensional diagram showing transmittance difference between area A and area B according to the prior art. In FIG. 5, Z-axle represents transmittance (%), X-axle and Y-axle mean pixel unit of the pixel array of FIG. 4 including area A and area B.  
           [0014]    [0014]FIG. 5 shows obvious transmittance difference between area A and area B so that an observer can perceive the apparent luminance difference.  
           [0015]    Therefore, improved IPS-LCD panels formed on an active matrix substrate with a compensation structure for CD variation are needed.  
         SUMMARY OF THE INVENTION  
         [0016]    In view of the above disadvantages, an object of the invention is to provide an IPS-LCD with a compensation structure for CD variation. According to the IPS-LCD, the transmittance difference between the two pixels can be reduced.  
           [0017]    In accordance with one aspect of the invention, there is provided an IPS-LCD with a compensation structure for CD variation. The IPS-LCD comprises a first substrate; a first pixel, formed on the first substrate, having first parallel pixel electrodes and first parallel common electrodes positioned such that a respective pixel electrode is disposed adjacent and parallel to a respective common electrode; and a second pixel adjacent to the first pixel, wherein the second pixel has second parallel pixel electrodes and second parallel common electrodes positioned such that a respective pixel electrode is disposed adjacent and parallel to a respective common electrode. This LCD is characterized in that each spacing between any adjacent first common electrode and first pixel electrode is equal and has a first distance, each spacing between any adjacent second common electrode and second pixel electrode is equal and has a second distance different from the first distance. Furthermore, the IPS-LCD comprises a second substrate being opposed to the first substrate and a liquid crystal material being interposed between the first substrate and the second substrate.  
           [0018]    In accordance with another aspect of the invention, the difference between the first distance and the second distance is preferably about 0.25*X μm, X=1, 2, 3, or 4. That is to say, the difference between the first distance and the second distance is 0.25, 0.50, 0.75 or 1.00 μm.  
           [0019]    Furthermore, the first parallel pixel electrodes and the first parallel common electrodes are separately formed on the different layers. Otherwise, the first parallel pixel electrodes and the first parallel common electrodes can be formed on the same layer.  
           [0020]    Furthermore, the first distance and the second distance can be about 10.00 μm to 11.30 μm, for example 10.00 μm, 10.25 μm, 10.50 μm, 10.75 μm, or 11.00 μm.  
           [0021]    In accordance with a further aspect of the invention, there is provided an IPS-LCD with a compensation structure for CD variation. The IPS-LCD comprises a plurality of pixels wherein each pixel has parallel pixel electrodes and parallel common electrodes positioned such that a respective pixel electrode is disposed adjacent and parallel to a respective common electrode. This IPS-LCD is characterized in that each spacing between any adjacent common electrode and pixel electrode in one pixel is equal to and different from that of the adjacent pixel.  
           [0022]    In accordance with yet another aspect of the invention, there is provided an IPS-LCD with a compensation structure for CD variation. The IPS-LCD comprises a pixel having a plurality of parallel pixel electrodes and a plurality of parallel common electrodes positioned such that a respective pixel electrode is disposed adjacent and parallel to a respective common electrode. This panel is characterized in that each spacing between any adjacent common electrode and pixel electrode in the pixel is not equal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    The preferred embodiment of the invention is hereinafter described with reference to the accompanying drawings in which:  
         [0024]    [0024]FIG. 1A is a cross-section showing the alignment of the liquid crystal molecules in an off state according to the conventional IPS-LCD.  
         [0025]    [0025]FIG. 1B is a cross-section showing the alignment of the liquid crystal molecules in an on state according to the conventional IPS-LCD.  
         [0026]    [0026]FIG. 2 is a cross-section showing a glass substrate having common electrodes and pixel electrodes thereon according to the prior art.  
         [0027]    [0027]FIG. 3 is a top view showing muras on an IPS panel caused by CD variation at area B.  
         [0028]    [0028]FIG. 4 is a diagram showing a pixel array including area A and area B having CD variation according to the prior art.  
         [0029]    [0029]FIG. 5 is a three-dimensional diagram showing transmittance difference between area A and area B according to the prior art.  
         [0030]    [0030]FIG. 6 is a diagram showing a pixel array including area A and area B having CD variation according to the first embodiment of the invention.  
         [0031]    [0031]FIG. 7 is a three-dimensional diagram showing transmittance difference between area A and area B according to the first embodiment of the invention.  
         [0032]    [0032]FIG. 8A is a diagram showing a glass substrate having common electrodes and pixel electrodes thereon in one pixel according to the second embodiment of the invention.  
         [0033]    [0033]FIG. 8B is a diagram showing a glass substrate having common electrodes and pixel electrodes thereon in another pixel according to the second embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0034]    [First Embodiment] 
         [0035]    [0035]FIG. 6 is a diagram showing a pixel array including area A and area B having CD variation according to the first embodiment of the invention.  
         [0036]    As shown in area A of FIG. 6, the pixel array comprises a plurality of small rectangles having numerals (10.00, 10.25, 10.50, 10.75, or 11.00) respectively. Each small rectangle denotes one unit pixel that has parallel pixel electrodes  200  and parallel common electrodes  160  positioned such that a respective pixel electrode  200  is disposed adjacent and parallel to a respective common electrode  160 . The numeral in one small rectangle represents the spacing between any adjacent common electrode  160  and pixel electrode  200 . In this embodiment, the spacing between any adjacent common electrode  160  and pixel electrode in the same pixel is equal to and different from that in the adjacent pixel. For example, the spacing between any adjacent common electrode  160  and pixel electrode  200  is 10.25 μm in the pixel  300 . The spacings of the pixels adjacent to the pixel  300  are 11.00 μm, 10.50 μm, 10.00 μm, and 10.75 μm respectively. Alternately, the spacing between any adjacent common electrode  160  and pixel electrode  200  is 11.00 μm in the pixel  310 . The spacings of the pixels adjacent to the pixel  310  are 10.00 μm, 10.00 μm, 10.25 μm, and 10.25 μm. That is to say, the spacings (10.00 μm, 10.25 μm, 10.50 μm, 10.75 μm, or 11.00 μm) in the plurality of pixels are randomly arranged. Also, the difference between any two spacings is about 0.25*X μm, X=1, 2, 3, or 4.  
         [0037]    Turning now to area B of FIG. 6, area B shows a pixel array, having spacing CD variation of about 0.30 μm. It is repeated based on area A. The pixel array comprises a plurality of small rectangles having numerals (10.30, 10.55, 10.80, 11.05, or 11.30) respectively. Each small rectangle denotes one unit pixel that has parallel pixel electrodes  202  and parallel common electrodes  162  positioned such that a respective pixel electrode  202  is disposed adjacent and parallel to a respective common electrode  162 . The numeral in one small rectangle represents the spacing between any adjacent common electrode  162  and pixel electrode  202 . In this embodiment, the spacing between any adjacent common electrode  162  and pixel electrode in the same pixel is equal to and different from that of the adjacent pixel. For example, the spacing between any adjacent common electrode  162  and pixel electrode  202  is 10.55 μm in the pixel  400  corresponding to the pixel  300  in area A. The spacings of the pixels adjacent to the pixel  400  are from 10.00 μm to 11.30 μm. For example, the spacings are 11.30 μm, 10.80 μm, 10.30 μm, and 11.05 μm respectively. The spacing between any adjacent common electrode  162  and pixel electrode  202  is 11.30 μm in the pixel  410  corresponding to the pixel  310  in area A. The spacings of the pixels adjacent to the pixel  410  are from 10.00 to 11.30 μm. For example, the spacings are 10.30 μm, 10.30 μm, 10.55 μm, and 10.55 μm, respectively. That is to say, the spacings (10.30 μm, 10.55 μm, 10.80 μm, 11.05 μm, or 11.30 μm) in the plurality of pixels are randomly arranged. Also, the difference between any two spacings is about 0.25*X μm, X=1, 2, 3, or 4.  
         [0038]    [0038]FIG. 7 shows transmittance difference between area A and area B according to the first embodiment of the invention. In FIG. 7, Z-axle represents transmittance (%), X-axle and Y-axle mean pixel unit of the pixel array of FIG. 6 including area A and area B.  
         [0039]    According to the embodiment of the invention, the localized transmittance difference between area A and area B with CD variation can be drastically reduced.  
         [0040]    [Second Embodiment] 
         [0041]    [0041]FIG. 8A is a diagram showing a glass substrate having common electrodes and pixel electrodes thereon in one pixel according to the second embodiment of the invention.  
         [0042]    In FIG. 8A, the pixel  500  has a plurality of parallel pixel electrodes  204  and a plurality of parallel common electrodes  164  positioned such that a respective pixel electrode  204  is disposed adjacent and parallel to a respective common electrode  164 . The common electrodes  164  have a width of about 4.0 μm in the central portion and a width of about 8.5 μm in edge portion. The pixel electrodes  204  have a width of about 4.0 μm. Each spacing between any adjacent common electrode  164  and pixel electrode  204  in the pixel  500  is not equal. The spacings in this pixel  500  are respectively 9.25 μm, 9.0 μm, 8.75 μm, 8.5 μm, 8.25 μm, and 8.0 μm so that the transmittance in the pixel  500  is variable at different positions.  
         [0043]    [0043]FIG. 8B is a diagram showing a glass substrate having common electrodes and pixel electrodes thereon in another pixel having CD variation in metal for common electrode.  
         [0044]    In FIG. 8B, the pixel  660  has a plurality of parallel pixel electrodes  208  and a plurality of parallel common electrodes  166  positioned such that a respective pixel electrode  206  is disposed adjacent and parallel to a respective common electrode  166 . The common electrodes  166  have a width of about 3.5 μm (CD variation) in the central portion and a width of about 8.0 μm in the edge portion. The pixel electrodes  206  have a width of about 4.0 μm. Each spacing between any adjacent common electrode  166  and pixel electrode  206  in the pixel  600  is not equal. The spacings in this pixel  600  are respectively 9.5 μm, 9.25 μm, 9.0 μm, 8.75 μm, 8.5 μm, and 8.25 μm so that the transmittance in the pixel  500  is variable at different positions. Therefore, the transmittance difference between the pixel  500  and pixel  600  with CD variation can be reduced.  
         [0045]    While the invention has been described with reference to various illustrative embodiments, the description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to those skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as may fall within the scope of the invention defined by the following claims and their equivalents.