Abstract:
A pixel electrode structure for a liquid crystal display with a high aperture ratio increases the aperture ratio and eliminates Mura phenomenon. Any two adjacent pixel electrodes are disconnected to each other. Each pixel electrode comprises a first-lengthwise periphery that overlaps a first-adjacent data line to form a first overlapping portion, and a second-lengthwise periphery that overlaps a second-adjacent data line to form a second overlapping portion. The first-lengthwise periphery and the second-lengthwise periphery have an identical triangle-wave profile and are symmetrical to each other. The triangle-wave profile is formed by connecting a plurality of right-angled and equilateral triangles.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a liquid crystal display (LCD) that has a high aperture ratio (HAR), and more particularly, to a pixel electrode structure for the LCD with HAR.  
         [0003]     2. Description of the Related Art  
         [0004]     As resolutions of liquid crystal display (LCD) increase, aperture ratio of the LCD becomes more and more insufficient. Recently, color filter on array (COA) technology, has been developed to provide a LCD of high aperture ratio. In the HAR process, the color filter process is integrated with the TFT array process on the same glass substrate, thus the aperture ratio of the TFT-LCD device is increased to effectively improve brightness of the panel, and the step of attachment/alignment between a color filter substrate and a TFT array substrate is omitted to improve yield and decrease process costs. Moreover, in the HAR process, an overlapping portion is formed between a transparent pixel electrode and a data line to decrease the required area of a black matrix (BM) layer, resulting in a higher aperture ratio in the TFT-LCD device.  
         [0005]      FIG. 1  is a top view showing an electrode structure in a pixel of a conventional TFT-LCD device formed using a HAR process. FIG. 2  is a sectional diagram along line I-I of  FIG. 1  showing the rotating orientations of liquid crystal molecules in the conventional TFT-LCD device using a HAR process.  
         [0006]     The conventional TFT-LCD device comprises a plurality of traversing gate lines  12  and data lines  14  extending lengthwise to define a plurality of pixels  10  in a matrix, each pixel  10  comprising a pixel electrode  16  and a TFT. Using one data line  14  as the boundary, a first pixel  10 A is covered by a first pixel electrode  16 A, and a second pixel  10 B is covered by a second pixel electrode  16 B. Also, the periphery of the first pixel electrode  16 A overlaps one side portion of the data line  14 , the periphery of the second pixel electrode  16 A overlaps another side portion of the data line  14 , and a predetermined distance is kept to space the first pixel electrode  16 A from the second pixel electrode  16 B over the data line  14 . Further, an arrow P indicates a light-polarization planar direction on a polarizer, a light-entry direction.  
         [0007]     During a HAR process on a TFT array glass substrate  17 , a first metal layer is patterned as the gate lines  12 , and then an insulating layer  15  is deposited to cover the gate lines  12  and the glass substrate  17 . Next, processes corresponding to TFT are performed on a predetermined area of the gate line  12 , and a second metal layer is patterned as the data lines  14 . Next, a transparent conductive layer is patterned as the first pixel electrode  16 A and the second pixel electrode  16 B.  
         [0008]     In a case using TN-type (twisted nematic type) LCD, when an extra voltage exceeds a critical value, the liquid crystal molecules  18  originally parallel to the alignment film are rotated to become perpendicular to the alignment layer in accordance with the magnitude of the lengthwise electric field. However, a transverse electric field is generated between the periphery of the first pixel electrode  16 A and the periphery or the second pixel electrode  16 B, thus the inclined directions of the liquid crystal molecules  18 I and  18 II near the periphery of the pixel electrodes  16 A and  16 B are influenced by the lengthwise and transverse electric field. Also, when an included angle between the arrow P (a light-polarization planar direction on a polarizer) and the long-axis direction of the liquid crystal molecule  18 I is 45°, an ellipsoidal polarized light caused by birefringence effect may pass an analyzer perpendicular to the polarizer to result in light leakage. With regard to the rotating orientation of the liquid crystal molecules  1811  over the sidewall of the data line  14 , however, a Mura phenomenon occurs, manifesting as non-uniform color difference, to form a light leakage area L.  
         [0009]     In another attempt to solve the above-described problems, the width of the data line  14  is increased to shield the light leakage area L, but this decreases the aperture ratio of the TFT-LCD device.  
       SUMMARY OF THE INVENTION  
       [0010]     Accordingly, an object of the invention is to provide a pixel electrode structure in an LCD to increase the aperture ratio and eliminate Mura phenomenon near the overlapping portion between the pixel electrode and the data line.  
         [0011]     To achieve these and other aims, the invention provides a pixel electrode structure of a liquid crystal display with a high aperture ratio. A first substrate and a second substrate are disposed parallel to each other, such that an internal space is formed between the interior surface of the first substrate and the interior surface of the second substrate. A liquid crystal layer is formed in the internal space. At least one polarizer is formed on the exterior surface of the first substrate or the exterior surface of the substrate. A plurality of parallel gate lines is transversely formed on the interior surface of the first substrate. A plurality of data lines parallel and extends lengthwise on the interior surface of the first substrate. A plurality of pixels is defined by the gate lines and the data lines in a matrix, in which each pixel comprises at least one TFT formed on the interior surface of the first substrate and near the intersection of the gate line and the data line, a common electrode on the interior surface of the second substrate, covering the pixel, and a pixel electrode on the interior surface of the first substrate, covering the pixel.  
         [0012]     In one preferred embodiment, no two adjacent pixel electrodes are connected to each other. Each pixel electrode comprises a first-lengthwise periphery that overlaps a first-adjacent data line to form a first overlapping portion, and a second-lengthwise periphery that overlaps a second-adjacent data line to form a second overlapping portion. The first-lengthwise periphery and the second-lengthwise periphery have an identical triangle-wave profile and are symmetrical to each other. The triangle-wave profile is formed by connecting a plurality of right-angled and equilateral triangles.  
         [0013]     In another preferred embodiment, no two adjacent pixel electrodes are connected to each other. Each pixel electrode comprises a first-lengthwise periphery that overlaps a first-adjacent data line to form a first overlapping portion, and a second-lengthwise periphery that overlaps a second-adjacent data line to form a second overlapping portion. The first-lengthwise periphery and the second-lengthwise periphery have an identical square-wave profile, and the square-wave profile is formed by connecting a square protrusion and a square indentation in sequence. The square protrusion of the first-lengthwise periphery corresponds in position to the square indentation of the second-lengthwise periphery, and the square indentation of the first-lengthwise periphery corresponds in position to the square protrusion of the second-lengthwise periphery. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0014]     For a better understanding of the present invention, reference is made to a detailed description to be read in conjunction with the accompanying drawings, in which:  
         [0015]      FIG. 1  is a top view showing an electrode structure in a pixel of a conventional TFT-LCD device with high aperture ratio.  
         [0016]      FIG. 2  is a sectional diagram along line I-I of  FIG. 1  showing the rotating orientations of liquid crystal molecules in the conventional TFT-LCD device with high aperture ratio.  
         [0017]      FIG. 3A  is a sectional diagram of an electrode structure in a pixel of a TFT-LCD device according to the first embodiment of the present invention.  
         [0018]      FIGS. 3B and 3C  are top views of an electrode structure in a pixel of a TFT-LCD device according to the first embodiment of the present invention.  
         [0019]      FIG. 4  is a view of an electrode structure in a pixel of a TFT-LCD device according to the second embodiment of the present invention.  
         [0020]      FIG. 5  is a view of an electrode structure in a pixel of a TFT-LCD device according to the third embodiment of the present invention.  
         [0021]      FIG. 6  is a view of an electrode structure in a pixel of a TFT-LCD device according to the fourth embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
     First Embodiment  
       [0022]     A first embodiment of the present invention is now described with reference to  FIGS. 3A through 3C .  FIG. 3A  is a sectional diagram of an electrode structure in a pixel of a TFT-LCD device according to the first embodiment of the present invention.  FIGS. 3B and 3C  are top views of an electrode structure in a pixel of a TFT-LCD device according to the first embodiment of the present invention.  
         [0023]     In  FIG. 3A , the TFT-LCD device comprises a lower substrate  1  and an upper substrate  2  parallel to each other, and a liquid crystal layer  3  in the internal space between the lower substrate  1  and the upper substrate  2 . A lower polarizer  4  is formed on the exterior surface of the lower substrate  1 , an upper polarizer  5  is formed on the exterior surface of the upper substrate  2 , and a common electrode  7  is formed on the interior surface of the upper substrate  2 . An arrow L indicates a light-incident direction, and an arrow P indicates a light-entry direction (a light-polarization planar direction of the polarizer  4  and  5 ). The included angle between the arrow P and the X axis is 45°.  
         [0024]     In  FIGS. 3B and 3C , on the interior surface of the lower substrate  1 , a plurality of transverse-extending gate lines  22  and a plurality of lengthwise-extending data lines  24  are patterned to define a plurality of pixels  20  in a matrix. Each of the pixels  20  comprises a pixel electrode  26  and a TFT  6 . Using one data line  24  as the boundary, a first pixel area  20 A is covered by a first pixel electrode  26 A, and a second pixel area  20 B is covered by a second pixel electrode  26 B. Also, the periphery of the first pixel electrode  26 A overlaps one side portion of the data line  24 , the periphery of the second pixel electrode  26 A overlaps another side portion of the data line  24 , and a predetermined distance is kept to space the first pixel electrode  26 A from the second pixel electrode  26 B over the data line  24 .  
         [0025]     The first key feature of the first embodiment is that the periphery of the pixel electrode is a triangle-wave profile. Particularly, within one overlapping portion between the first pixel electrode  26 A and the data line  24 , the periphery of the first pixel electrode  26 A is a triangle-wave profile. Similarly, within the other overlapping portion between the second pixel electrode  26 B and the data line  24 , and the periphery of the second pixel electrode  26 B is a triangle-wave profile.  
         [0026]     Preferably, in  FIG. 3C , the triangle-wave profile is formed by connecting a plurality of right-angled and equilateral triangles. For example, each triangle constitutes a first hypotenuse  27 I (upper right toward lower left), a right angle θ 1 , and a second hypotenuse  27 II (upper left toward lower right). Thus, the angle θ 1  at the protruding portion of the triangle-wave profile is 90°, the included angle θ 2  between the first hypotenuse  27 I and the X axis is 45°, and the included angle θ 2  between the second hypotenuse  27 II and the X axis is 45°. Also, the first hypotenuse  27 I of the first pixel electrode  26 A is parallel to the first hypotenuse  27 I of the second pixel electrode  26 B, and the second hypotenuse  27 II of the first pixel electrode  26 A is parallel to the second hypotenuse  27 II of the second pixel electrode  26 B.  
         [0027]     The second key feature of the first embodiment is that the overlapping portion between the pixel electrode  26  and the data line  24  is larger than the total area of the triangles. Preferably, the width of the data line  24  is about 10 μm.  
         [0028]     In a case using TN-type (twisted nematic type) LCD with a parallel-treatment alignment film, when an extra voltage exceeds a critical value, the liquid crystal molecules  28  originally parallel to the alignment film are rotated to become perpendicular to the alignment layer in accordance with the magnitude of the lengthwise electric field. With regard to the rotating orientation of the liquid crystal molecules  28 I and  28 II near the overlapping portion between the data line  24  and the periphery of the first pixel electrode  26 A, a transverse electric field generated between the periphery of the first pixel electrode  26 A and the periphery of the second pixel electrode  26 B is influenced by the triangle-wave profile so as to incline. For example, an arrow E 1  indicates a first-inclined electric field generated between the first hypotenuse  27 I of the first pixel electrode  26 A and the first hypotenuse  27 I of the second pixel electrode  26 B. An arrow E 2  indicates a second-inclined electric field generated between the second hypotenuse  27 II of the first pixel electrode  26 A and the second hypotenuse  27 II of the second pixel electrode  26 B. Therefore, the first liquid crystal molecule  28 I rotates in the direction of the arrow E 1 , and the second liquid crystal molecule  28 II rotates in the direction of the arrow E 2 .  
         [0029]     Concerning the light-polarization planar direction on the polarizer shown by the arrow P, an included angle between the arrow P and the long-axis direction of the first liquid crystal molecule  28 I is 90°, and the long-axis direction of the second liquid crystal molecule  28 II is parallel to the arrow P. This avoids birefringence effect, that is, no ellipsoidal polarized light passes an analyzer. Thus, Mura phenomenon does not occur near the boundary of the data line  24 , eliminating light leakage.  
         [0030]     The rotating orientations of liquid crystal molecules near the overlapping portion between the data line  24  and the periphery of the second pixel electrode  26 B are similar to the above-described phenomenon, with no need for further description.  
       Second Embodiment  
       [0031]      FIG. 4  is a view of an electrode structure in a pixel of a TFT-LCD device according to the second embodiment of the present invention. Most of the electrode structure in the second embodiment is similar to the first embodiment, and the identical parts are omitted with no need for further description. The difference is that the width of the data line  24  is reduced to make the area of the overlapping portion equal to the total area of the triangles. This can achieve the same advantages as described in the first embodiment. Also, by reducing the width of the data line  24  to achieve 3˜10 μm, the aperture ratio of the TFT-LCD device is further improved.  
       Third Embodiment  
       [0032]      FIG. 5  is a view of an electrode structure in a pixel of a TFT-LCD device according to the third embodiment of the present invention. Most of the electrode structure in the third embodiment is similar to the first embodiment, and the identical parts are omitted with no need for farther description. The difference is that the periphery of the first pixel electrode  26 A is a square-wave profile, and the periphery of the second pixel electrode  26 B is a square-wave profile. The square-wave profile is formed by connecting a square protrusion and a square indentation in sequence. Particularly, the square protrusions of the first pixel electrode  26 A correspond in position to the square indentations of the second pixel electrode  26 B, and the square indentations of the first pixel electrode  26 A correspond in position to the square protrusions of the second pixel electrode  26 B.  
         [0033]     In a case using TN-type (twisted nematic type) LCD with a parallel-treatment alignment film, when an extra voltage exceeds a critical value, the liquid crystal molecules  28  originally parallel to the alignment film are rotated to become perpendicular to the alignment layer in accordance with the magnitude of the lengthwise electric field. With regard to the rotating orientation of the liquid crystal molecules  28 I and  28 II near the overlapping portion between the data line  24  and the periphery of the first pixel electrode  26 A, a transverse electric field, as shown by an arrow E, is generated between the periphery of the first pixel electrode  26 A and the periphery of the second pixel electrode  26 B. Therefore, the rotating orientations of the liquid crystal molecules  28 I and  28 II are influenced by the transverse electric field E and the lengthwise electric field.  
         [0034]     Concerning a light-polarization planar direction on the polarizer as shown by the arrow P, when an included angle between the arrow P and the long-axis direction of the liquid crystal molecule  28 I or  28 II is 45°, an ellipsoidal polarized light caused by birefringence effect may pass an analyzer to cause Mura phenomenon, resulting in a first light leakage area L 1  near the square indentation and a second leakage area L 2  near the square protrusion. However, since the data line  24  shields the second leakage area L 2 , Mura phenomenon is eliminated.  
         [0035]     The rotating orientations of liquid crystal molecules over the overlapping portion between the data line  24  and the periphery of the second pixel electrode  26 B is similar to the above-described phenomenon with no need for further description.  
       Fourth Embodiment  
       [0036]      FIG. 6  is a view of an electrode structure in a pixel of a TFT-LCD device according to the fourth embodiment of the present invention. Most of the electrode structure in the fourth embodiment is similar to the first embodiment, and the identical parts are omitted with no need for further description. The difference is that each sidewall of the data line  24  is a triangle-wave profile; with the features of the triangle-wave profile the same as the first pixel electrode  26 A and the second pixel electrode  26 B. Preferably, the triangle-wave profile is formed by connecting a plurality of right-angled and equilateral triangles. Each triangle constitutes a first hypotenuse  27 I (upper right toward lower left), a right angle, and a second hypotenuse  27 II (upper left toward lower right). Thus, the angle θ 1  at the protruding portion of the triangle-wave profile is 90°, the included angle θ 2  between the first hypotenuse  27 I and X axis is 45°, and the included angle θ 2  between the second hypotenuse  27 II and X axis is 45°.  
         [0037]     Also, the first hypotenuse  27 I of the data line  24  is parallel to the first hypotenuse  27 I of the first pixel electrode  26 A and parallel to the first hypotenuse  27 I of the second pixel electrode  26 B, and the second hypotenuse  27 II of the data line  24  is parallel to the second hypotenuse  27 II of the first pixel electrode  26 A and parallel to the second hypotenuse  27 II of the second pixel electrode  26 B.  
         [0038]     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 to the disclosed embodiments. To the contrary,, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.