JP2006058910A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent coloring and to improve image quality in a liquid crystal display element of a lateral electric field driving system which achieves a wide viewing angle and preferable multilevel display. <P>SOLUTION: Common electrodes 2 as comb-shaped electrodes and pixel electrodes 4 are formed parallel to each other into a dog leg shape. In pixel regions formed by the common electrodes and the pixel electrodes, regions 20, 21 are formed with an almost equal area to each other, the regions showing different directions where the orientation of liquid crystal molecules 6 changes when an electric field almost parallel to an array substrate and a counter substrate is applied between the pixel electrodes 4 and the common electrodes 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display element used as a flat display such as an AV apparatus and an OA apparatus, and more particularly to an active matrix type liquid crystal display element.

  Display elements using liquid crystals are applied in various fields such as video camera viewfinders, pocket TVs, high-definition projection TVs, personal computers, word display and other information display terminals. In particular, an active matrix type TN (Twisted Nematic) liquid crystal display device using a thin film transistor (TFT) as a switching element has a great feature that high contrast is maintained even when a large capacity display is performed. It is expected to be a large-scale, large-capacity full-color display for extremely demanding laptops, notebooks, and engineering workstations.

  In an active matrix liquid crystal display element, a TN (Twisted Nematic) NW (Normally White) mode is widely used as a liquid crystal display mode. The TN system has a structure in which liquid crystal molecules of a liquid crystal layer sandwiched between two transparent electrodes are twisted by 90 °, and a panel including the liquid crystal layer and the transparent electrodes is sandwiched between two polarizing plates. . In the NW mode, the polarizing axes of the two polarizing plates are orthogonal to each other, and the polarizing axes of one polarizing plate are arranged so as to be parallel or perpendicular to the major axis direction of the liquid crystal molecules in contact with one substrate. Has been. In this case, white display occurs when no voltage is applied or when a voltage equal to or lower than a predetermined threshold voltage is applied. When a voltage higher than the predetermined threshold is applied, the light transmittance gradually decreases, and black Display. Such display characteristics are obtained when a voltage is applied between the transparent electrodes on the panel, the liquid crystal molecules try to align in the direction of the electric field while unwinding the twisted structure. This is because the polarization state of the incoming light changes and the light transmittance is modulated.

  However, even in the same molecular arrangement state, the polarization state of the transmitted light changes depending on the incident direction of the light incident on the liquid crystal panel. Therefore, the light transmittance varies depending on the incident direction. That is, the characteristics of the liquid crystal panel have a viewing angle dependency. This viewing angle characteristic causes a luminance reversal phenomenon when the viewpoint is inclined obliquely with respect to the main viewing angle direction (the major axis direction of the liquid crystal molecules in the intermediate layer of the liquid crystal layer). In the case of this display mode, it means a phenomenon in which the display luminance when a certain voltage is applied becomes brighter than the luminance when a lower voltage is applied. In particular, the luminance reversal phenomenon when a high voltage is applied for black display is an important issue in terms of image quality of the liquid crystal panel.

In order to solve this problem, the electric field is not applied in the vertical direction of the substrate as in the TN liquid crystal display system, but the direction in which the liquid crystal is applied is changed to the substrate as shown in Patent Documents 1 and 2, for example. A method (transverse electric field method) in which the direction is substantially parallel to the above has been proposed. A structure of a thin film transistor substrate of a conventional horizontal electric field type liquid crystal display element is shown in FIG. As shown in FIG. 6, a plurality of scanning lines 1 and signal lines 3 are formed to be orthogonal to each other. A plurality of, for example, two pixel electrodes 4 are formed between two adjacent signal lines 3 forming one pixel. A plurality of, for example, three common electrodes 2 are formed between the signal wiring 3 and the pixel electrode 4 and between the adjacent pixel electrodes 4. The storage capacitor portion 5 is formed between the pixel electrodes 4 and above the scanning wiring 1. The pixel electrode 4 and the common electrode 2 are parallel to the signal wiring 3. Therefore, the alignment directions of the liquid crystal molecules 6 in the display regions 20 and 21 formed between the pixel electrode 4 and the common electrode 2 and disposed on both sides of the central wiring portion 2a of the common electrode 2 are the same.
Japanese Examined Patent Publication No. 63-21907 JP-A-6-160878

  Although the above-mentioned lateral electric field method is superior in viewing angle characteristics of the luminance reversal phenomenon, as shown in FIG. 7, when the screen is viewed at an angle of 45 °, 135 ° with respect to the comb-shaped electrode 2 or 4, it is inclined. , Each has the disadvantage of being colored blue and yellow, which is a problem in image quality.

  The present invention has been made to solve the above-described problems of the conventional example, and can realize a good multi-gradation display with a wide viewing angle, and prevent occurrence of coloring by a simple configuration and the same manufacturing process as the conventional one. It is an object of the present invention to provide an active matrix liquid crystal display element of a lateral electric field drive system that can display a high-quality image.

  In order to solve the above problems, a liquid crystal display element of the present invention includes a plurality of signal lines and scanning lines that intersect each other, a switching element provided corresponding to each intersection of the signal lines and the scanning lines, and the switching element. An array substrate having connected pixel electrodes and a common electrode, a counter substrate disposed opposite to the array substrate, and a liquid crystal layer sandwiched between the array substrate and the counter substrate A horizontal electric field type liquid crystal display element, wherein a pixel defined by two adjacent signal lines and two adjacent scanning lines generates an electric field between the pixel electrode and the common electrode In addition, the pixel electrode and the common electrode each have a substantially “<”-shaped portion in the pixel.

  In the above, one pixel may include a plurality of pixel electrodes and common electrodes having a substantially “<”-shaped portion.

  A portion of the pixel electrode and the common electrode having a substantially “<” shape may have a bending point, and may have a substantially symmetric shape with respect to a straight line passing through the bending point and parallel to the scanning wiring.

  The pixel electrode and the common electrode may have a bent point having a substantially “<” shape at the center.

  The areas of the plurality of regions that differ in the direction in which the alignment of the liquid crystal molecules changes may be substantially equal to each other.

  The pixel electrode and the common electrode may have a portion that is substantially parallel to each other and that is not parallel to any of the signal wiring and the scanning wiring.

  Either one of the signal wiring and the scanning wiring may be substantially parallel to the pixel electrode and the common electrode, and in this configuration, either the signal wiring or the scanning wiring has a substantially “<” shape. It may be formed.

  In the above configuration, the dielectric anisotropy of the liquid crystal molecules is positive, and an angle θ between the alignment direction of the liquid crystal molecules and the longitudinal direction of the pixel electrode and the common electrode is 0 ° <θ ≦. It is preferable to satisfy 30 °.

  Further, the dielectric anisotropy of the liquid crystal molecules is negative, and the angle θ formed by the alignment direction of the liquid crystal molecules with respect to the longitudinal direction of the pixel electrode and the common electrode satisfies 60 ° ≦ θ <90 °. It is preferable.

  According to the active matrix type liquid crystal display element of the present invention, as shown in FIG. 5, the yellow color change direction and the blue color change direction are overlapped to compensate for the color change with respect to the viewing angle, and an image with little color change can be obtained. . In addition, by forming the pixel electrode and the common electrode in a substantially "<" shape, the inclination direction is opposite above and below the inflection point of the substantially "<" shape. Almost complete compensation is possible.

  Furthermore, by making the areas of the regions where the alignment directions of the liquid crystal molecules change almost equal, the color changes with respect to the viewing angle can be completely compensated for each other, and an image with no color change can be obtained. Further, by configuring the pixel electrode and the common electrode to have a portion that is substantially parallel to each other and not parallel to either the signal wiring or the scanning wiring, when a voltage is applied between the pixel electrode and the common electrode, The liquid crystal molecules rotate at a portion not parallel to either the wiring or the scanning wiring. Thereby, the color change with respect to the viewing angle can be compensated.

  Further, even if one of the signal wiring and the scanning wiring is substantially parallel to the pixel electrode and the common electrode and has a portion inclined with respect to the other which is not substantially parallel, the color change with respect to the same viewing angle is compensated. be able to. Also in this case, it is preferable to form either one of the signal wiring and the scanning wiring, the pixel electrode, and the common electrode in a substantially “<” shape.

  In addition, since the dielectric constant anisotropy of the liquid crystal molecules is positive and the angle θ formed by the alignment direction of the liquid crystal molecules with respect to the longitudinal direction of the pixel electrode and the common electrode satisfies 0 ° <θ ≦ 30 °, The angular deviation between the polarization axis of the plate and the direction of the liquid crystal molecules can be reduced, and a modulation efficiency of 80% or more can be achieved. Further, when the dielectric constant anisotropy of the liquid crystal molecules is negative and the angle θ formed by the alignment direction of the liquid crystal molecules with respect to the longitudinal direction of the pixel electrode and the common electrode satisfies 60 ° ≦ θ <90 °, Similar effects can be obtained.

  As described above, the active matrix type liquid crystal display device of the present invention is provided with a thin film transistor array substrate (hereinafter abbreviated as an array substrate), a counter substrate facing the array substrate, and between the array substrate and the counter substrate. A liquid crystal layer and two polarizing plates provided outside the array substrate and the counter substrate are provided. A plurality of parallel signal lines and a plurality of parallel scanning lines are arranged on the array substrate so as to form a pixel matrix. For one pixel, at least one switching element is formed at the intersection of the signal wiring and the scanning wiring. A plurality of pixel electrodes and a plurality of common electrodes connected to the switching element are formed in parallel with each other between two adjacent signal lines defining one pixel or two adjacent scanning lines.

  One pixel defined by two adjacent signal lines and two adjacent scanning lines is divided into a plurality of display areas. One display area is defined by adjacent common electrodes and pixel electrodes. When an approximately parallel electric field is applied to the array substrate and the counter substrate, the alignment of the liquid crystal molecules moves so as to align with the direction of the electric field. In the case of the present invention, the orientation of liquid crystal molecules in one set (first) display region is different from the orientation direction of the liquid crystal molecules in another set (second) display region.

  Each display region has a display characteristic that an image is colored depending on the viewing angle. However, one pixel has a plurality of display areas having different display characteristics. For example, as shown in FIG. 5, when the direction colored yellow and the direction colored blue overlap each other, the yellow coloring is compensated by the blue coloring. As a result, an image without coloring depending on the viewing angle is obtained. In particular, by making the areas of the first display area and the second display area equal, the coloring of the image can be compensated almost completely.

  A voltage for generating an electric field is applied between the common electrode and the pixel electrode. The alignment direction of the liquid crystal molecules moves to align with the direction of the applied electric field. By forming the pixel electrode and the common electrode so as to have an inclined portion that is not parallel to the signal wiring and the scanning wiring, the direction of the electric field generated in the inclined portion follows the inclination of the inclined portion. By appropriately selecting the shapes of the pixel electrode and the common electrode, the alignment direction of the liquid crystal molecules in the display region formed between the pixel electrode and the common electrode can be arbitrarily controlled. More preferably, the pixel electrode and the common electrode are formed in a substantially “<” shape or a herringbone (herringbone) shape. With such a configuration, the inclination of each electrode is substantially symmetric with respect to the bending point of a substantially “<” shape or a herringbone shape. When the first display area is defined as being disposed on one side of the bending point and the second display area is defined as being disposed on the other side, the coloring of the image depending on the viewing angle is substantially reduced. Full compensation can be made.

  Further, either one of the signal wiring and the scanning wiring is formed substantially parallel to the pixel electrode and the common electrode, and the wiring and the electrode are inclined with respect to the other wiring that is not parallel to the pixel electrode and the common electrode. You may comprise so that it may have. Even with such a configuration, the same effect as in the above case can be obtained. Furthermore, the area of the non-display area between the adjacent signal wiring or scanning wiring and the common electrode can be reduced. Furthermore, it is preferable that either one of the signal wiring and the scanning wiring, the common electrode and the pixel electrode are formed in a substantially “<” shape or a herringbone shape.

  When the dielectric anisotropy of the liquid crystal molecules to be used is positive, the angle of the alignment direction of the liquid crystal molecules with respect to the longitudinal direction of the pixel electrode and the common electrode is θ, and the condition of 0 ° <θ ≦ 30 ° is satisfied. Thus, the deviation between the alignment direction of the liquid crystal molecules and the polarization axis of the polarizing plate can be reduced. As a result, the modulation efficiency can be 80% or more. Similarly, when the dielectric anisotropy of the liquid crystal molecules is negative, the angle θ formed by the alignment direction of the liquid crystal molecules with respect to the longitudinal direction of the pixel electrode and the common electrode satisfies 60 ° ≦ θ <90 °. The effect is obtained.

(First embodiment)
Hereinafter, a preferred first embodiment of an active matrix liquid crystal display element of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a configuration common to each embodiment of the liquid crystal display element of the present invention, and FIG. 2 is a TFT pixel portion of a thin film transistor (TFT) array substrate in the liquid crystal display element of the first embodiment of the present invention. FIG. 2 schematically shows a planar configuration. FIG. 5 is a diagram showing the principle of preventing the color dependent on the viewing angle of the liquid crystal display element.

  As shown in FIG. 1, the active matrix type liquid crystal display element of the present invention includes an array substrate 10, a counter substrate 11 disposed opposite to the array substrate 10, and a liquid crystal sandwiched between the array substrate 10 and the counter substrate 11. A layer 12 and two polarizing plates 13 and 14 disposed outside the array substrate 10 and the counter substrate 11 are provided. The polarizing plates 13 and 14 are arranged so that their polarization axes X and Y are orthogonal to each other.

  The array substrate 10 shown in FIG. 2 corresponds to a plurality of parallel signal wirings 3 and a plurality of parallel scanning wirings 1 arranged in a matrix and each intersection of the signal wiring 3 and the scanning wiring 1 for one pixel. At least one switching element 7 provided, a comb-shaped pixel electrode 4 connected to the switching element, and a comb-shaped common electrode 2 formed so as to mesh with the pixel electrode 4 are provided.

  As shown in FIG. 2, the plurality of scanning wirings 1 are formed in a pattern substantially parallel to each other at a predetermined interval on the array substrate 10 by photolithography using, for example, chromium. A common electrode 2 that is substantially parallel and has a substantially “<” shape or a herringbone shape is patterned between two adjacent scanning lines 1. The common electrode 2 has a width of 4 μm, and the material may be a conductive single layer film or a multilayer film such as aluminum or a metal mainly composed of aluminum in addition to chromium.

  On the scanning wiring 1 and the common electrode 2, a first insulator layer such as silicon nitride (SiNx), which functions as a gate insulating film of the TFT functioning as the switching element 7, is laminated (not shown). Further, on the first insulator layer, a semiconductor layer such as amorphous silicon (α-Si) for controlling the switching function of the TFT is laminated by a plasma CVD method (not shown). On the semiconductor, a plurality of signal lines 3 are patterned so as to be substantially orthogonal to the scanning lines 1 and substantially parallel to each other. The signal wiring 3 is formed by depositing two layers of titanium / aluminum (Ti / Al) on the semiconductor layer by sputtering, and then pattern-forming by dry etching.

  Between two adjacent common electrodes 2, a plurality of pixel electrodes 4 are formed in a substantially “<” shape or a herringbone shape so as to be substantially parallel to the common electrode 2. The width of the pixel electrode 4 is 4 μm, and the material may be titanium / aluminum (Ti / Al), or a conductive metal single layer film or multilayer film. On the scanning wiring 1 across the first insulating film layer and the semiconductor layer, the storage capacitor portion 5 is formed so as to overlap the two pixel electrodes 4. The storage capacitor unit 5 is provided to hold the voltage supplied to the pixel. The interval between the common electrode 2 and the pixel electrode 4 was 12 μm.

  An alignment film is applied to the thin film transistor array substrate 10 and the counter substrate 11 configured as described above, and a rubbing process is performed in a direction indicated by an arrow A in FIG. The thin film transistor array substrate and the counter substrate are bonded to each other with a gap of 3 μm, and a liquid crystal having a positive dielectric anisotropy is injected therebetween to form a liquid crystal layer 12. Further, two polarizing plates 13 and 14 are arranged outside the thin film transistor array substrate 10 and the counter substrate 11 so that the polarization axes X and Y are orthogonal to each other.

  As shown in FIG. 2, the common electrode 2 and the pixel electrode 4 are formed so as to be bent in a substantially “<” shape at about 5 ° with respect to the direction parallel to the signal wiring 3 at the center (bending point). ing. Therefore, when a voltage is applied between the common electrode 2 and the pixel electrode 4, an electric field is generated in a direction substantially orthogonal to the longitudinal directions of the common electrode 2 and the pixel electrode 4. The liquid crystal molecules 6a and 6b in the first and second display regions 20 and 21 located on both sides of the central wiring portion 2a of the common electrode 2 move so that their alignment directions are aligned with the direction of the electric field. The alignment direction of the liquid crystal molecules 6a in the first display region 20 and the alignment direction of the liquid crystal molecules 6b in the second display region 21 are opposite to each other. Furthermore, the area of the first display area 20 and the area of the second display area 21 are substantially equal. Therefore, as shown in FIG. 5, the yellow color change direction and the blue color change direction are overlapped, and the color change with respect to the viewing angle is compensated for each other, and an image having no color change can be obtained.

  Next, a description will be given of a case where the bending angle of the substantially “<” character of the common electrode 2 and the pixel electrode 4, that is, the orientation angle (θ) of the liquid crystal molecules 6 with respect to both electrodes is changed. Increasing this angle reduces the threshold value, but causes a shift in angle between the polarization axis of the polarizing plate and the direction of the liquid crystal molecules 6 and lowers the modulation efficiency. When θ exceeds 30 °, the modulation efficiency decreases rapidly. If θ is within 30 °, the modulation efficiency is 80% or more, which is a practical level. However, when θ = 0 °, the rotation direction of the liquid crystal molecules 6 when a voltage is applied is not determined. Therefore, the orientation angle (θ) is preferably 0 ° <θ ≦ 30 °. When a liquid crystal having negative dielectric anisotropy was used, the same result was obtained in the range of 60 ° ≦ θ <90 °. When the lighting image inspection of the liquid crystal display element was performed, it was confirmed that a liquid crystal display element having a wide viewing angle characteristic and having no color and an excellent image can be obtained.

(Second Embodiment)
Next, a second preferred embodiment of the active matrix liquid crystal display element of the present invention will be described with reference to FIG. FIG. 3 schematically shows a planar configuration of a TFT pixel portion of a thin film transistor (TFT) array substrate in a liquid crystal display device according to a second embodiment of the present invention. Note that the description of the parts common to the case of the first embodiment is omitted, and different parts are described.

  In the second embodiment, the signal wiring 3 is formed in parallel with the common electrode 2 and the pixel electrode 4 and in a substantially “<” shape or a herringbone shape. With this configuration, the non-display area 22 between the signal wiring 3 and the common electrode 2 can be significantly reduced as compared with the case of the first embodiment, and the aperture ratio (the area of the display area occupying one pixel) can be reduced. Ratio) can be improved. When a lighting image inspection of this liquid crystal display element was performed, it was confirmed that a liquid crystal display element having a wide viewing angle characteristic, no coloration, and a bright and excellent image can be obtained.

(Third embodiment)
Next, a third preferred embodiment of the active matrix liquid crystal display element of the present invention will be described with reference to FIG. FIG. 4 schematically shows a planar configuration of a TFT pixel portion of a thin film transistor (TFT) array substrate in a liquid crystal display device according to a third embodiment of the present invention. In addition, the description is abbreviate | omitted about the part which is common in the case of the said 1st or 2nd embodiment, and a different part is described.

  In the third embodiment, a plurality of regions having different directions in which the alignment of liquid crystal molecules changes are provided. That is, as shown in FIG. 4, the common electrode 2 and the pixel electrode 4 are formed twice in a substantially “<” shape so that it is common to the signal wiring 3 compared to the case of the first embodiment. The non-display area 22 between the electrodes 2 can be greatly reduced, and the aperture ratio (area ratio of the display area to one pixel) can be improved. When a lighting image inspection of this liquid crystal display element was performed, it was confirmed that a liquid crystal display element having a wide viewing angle characteristic, no coloration, and a bright and excellent image can be obtained.

The perspective view which shows the structure common to each embodiment of the liquid crystal display element of this invention. The top view which shows roughly the planar structure of the TFT pixel part of the thin-film transistor (TFT) array board | substrate in the liquid crystal display element of the 1st Embodiment of this invention The top view which shows roughly the planar structure of the TFT pixel part of the thin-film transistor (TFT) array substrate in the liquid crystal display element of the 2nd Embodiment of this invention The top view which shows roughly the planar structure of the TFT pixel part of the thin-film transistor (TFT) array substrate in the liquid crystal display element of the 3rd Embodiment of this invention The figure which shows the principle which prevents the coloring depending on the viewing angle of the liquid crystal display element The top view which shows roughly the plane structure of the TFT pixel part of the thin-film transistor (TFT) array board | substrate in the conventional liquid crystal display element Plan view of the liquid crystal display element showing the colored direction of the conventional liquid crystal display element

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Scan wiring 2 Common electrode 3 Signal wiring 4 Pixel electrode 5 Storage capacitor | condenser 6 Liquid crystal molecule 7 Switching element 10 Array substrate 11 Opposite substrate 12 Liquid crystal layer 13 Polarizing plate 14 Polarizing plate 20 The area | region 21 from which the direction in which the arrangement of liquid crystal molecules changes differs Region 22 in which the direction of change of the arrangement of liquid crystal molecules is different 22 Non-display region

Claims (5)

A plurality of signal lines and scanning lines crossing each other, switching elements provided corresponding to the respective intersections of the signal lines and the scanning lines, pixel electrodes connected to the switching elements, and an array substrate having a common electrode; ,
A counter substrate disposed to face the array substrate;
A horizontal electric field type liquid crystal display device comprising a liquid crystal layer sandwiched between the array substrate and the counter substrate,
When the electric field is generated between the pixel electrode and the common electrode, the pixels defined by the two adjacent signal lines and the two adjacent scanning lines have different directions in which the arrangement of liquid crystal molecules changes. Has multiple areas,
In the pixel, the pixel electrode and the common electrode have a substantially “<” shape.   The liquid crystal display element according to claim 1, wherein one pixel has a plurality of pixel electrodes and common electrodes each having a substantially “<”-shaped portion.   The portion of the pixel electrode and the common electrode having a substantially “<” shape has a bending point, and has a shape that is substantially symmetrical with respect to a straight line that passes through the bending point and is parallel to the scanning wiring. The liquid crystal display element as described.   4. The liquid crystal display element according to claim 1, wherein the areas of the plurality of regions having different directions in which the arrangement of the liquid crystal molecules is changed are approximately equal. 5. The liquid crystal display element according to claim 1, wherein the pixel electrode and the common electrode have a portion that is substantially parallel to each other and not parallel to any of the signal wiring and the scanning wiring.

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