Patent Publication Number: US-2019187522-A1

Title: Liquid crystal display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2017-244491 filed on Dec. 20, 2017, the contents of which are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to liquid crystal display devices. More specifically, the present invention relates to a horizontal alignment mode liquid crystal display device. 
     Description of Related Art 
     Liquid crystal display devices are display devices that utilize a liquid crystal composition for display. A typical display mode thereof is one applying voltage to a liquid crystal composition sealed between a pair of substrates to change the alignment state of liquid crystal molecules in the liquid crystal composition according to the applied voltage, thereby controlling the amount of light transmitted. These liquid crystal display devices, having characteristics such as thin profile, light weight, and low power consumption, have been used in a broad range of fields. 
     The display modes of liquid crystal display devices include horizontal alignment modes, which control the alignment of liquid crystal molecules by rotating the liquid crystal molecules mainly in the plane parallel to the substrate surfaces. The horizontal alignment modes have received attention because, with these modes, properties such as wide viewing angle characteristics can be easily achieved. For example, the in-plane switching (IPS) mode and the fringe field switching (FFS) mode, both are horizontal alignment modes, are widely used in recent liquid crystal display devices for smartphones or tablet terminals. 
     There is continuing research and development of the horizontal alignment modes to achieve a high transmittance and a high response speed, for example, to improve the display quality. JP 2014-232136 A, for example, discloses a display device as a technique to increase the response speed. The display device comprises a liquid crystal layer disposed between the first substrate and the second substrate facing each other. The first substrate has a first electrode and a second electrode. The first electrode or the second electrode includes an electrode base extending in a first direction, and a plurality of comb tooth portions, which extend in a second direction different from the first direction and protrude in a comb-tooth shape from the electrode base at a constant interval. In the initial alignment of liquid crystals in the liquid crystal layer, the major axes of the liquid crystal molecules are aligned in a third direction parallel to the second direction, and the angle formed by an electrode base-side portion of a long side of each of the comb tooth portions and the third direction is larger than an angle formed by an end-side portion of the long side of each of the comb tooth portions and the third direction. 
     The horizontal alignment modes offer the advantage of wide viewing angles, but have the problem of slow response as compared with vertical alignment modes such as the multi-domain vertical alignment (MVA) mode. JP 2014-232136 A discloses in  FIG. 19 , for example, a structure in which the ends of a comb tooth portion extending from one of adjacent electrode bases and the ends of a comb tooth portion extending from the other of the electrode bases are alternately arranged. JP 2014-232136 A also discloses in  FIG. 20 , for example, a structure in which the ends of a comb tooth portion extending from one of adjacent electrode bases and the ends of a comb tooth portion extending from the other of the electrode bases are arranged to face each other. In the liquid crystal display device disclosed in JP 2014-232136 A having such an electrode structure, application of voltage between the electrodes is likely to cause liquid crystal molecules in a region near the right long side of the comb tooth portion and in a region near the left long side of the comb tooth portion to be affected by opposite electric fields to rotate the liquid crystal molecules in opposite directions. Thus, the response speed can be increased in the horizontal alignment mode as well. However, liquid crystal molecules around the electrode bases do not respond or the response of the liquid crystal molecules is slow. Thus, in the case where an electrode base is disposed in an opening as in FIG. 19 of JP 2014-232136 A, the liquid crystal display device may have a low transmittance and a low response speed. Improvements can therefore still be made to increase the transmittance and response speed of the liquid crystal display device. 
     In response to the above issues, an object of the present invention is to provide a horizontal alignment mode liquid crystal display device that can achieve an increased response speed and an increased transmittance. 
     The present inventors made various studies on a horizontal alignment mode liquid crystal display device that can achieve an increased response speed and an increased transmittance, and focused on the shape of openings used to generate fringe electric fields. The inventors then found a structure in which an electrode is provided with a plurality of openings each having a long shape with two or more wide portions and one or more narrow portions. The two or more wide portions and the one or more narrow portions in each of the openings alternate with each other in the lengthwise direction of the opening. Adjacent two openings among the openings are formed such that a wide portion and a narrow portion of one of the openings are adjacent to a narrow portion and a wide portion of the other opening, respectively. This structure can reduce the distance between the adjacent two openings to reduce the space where liquid crystal molecules do not respond, further increasing the transmittance. The structure also can reduce liquid crystal molecules far from the electrode ends and slow to respond, further increasing the response speed. Thereby, the inventors achieved the above object, completing the present invention. 
     In other words, one aspect of the present invention may be a liquid crystal display device including: a first substrate; a second substrate facing the first substrate; and a liquid crystal layer being disposed between the first substrate and the second substrate and containing liquid crystal molecules, the first substrate including a first electrode, a second electrode closer to the liquid crystal layer than the first electrode is, and an insulating film between the first electrode and the second electrode, the liquid crystal molecules being aligned in a direction parallel to the first substrate with no voltage applied, the second electrode being provided with openings formed side by side, the openings each having a long shape with two or more wide portions and one or more narrow portions, the two or more wide portions and the one or more narrow portions in each of the openings alternating with each other in a lengthwise direction of the opening, each of the wide portions of one of adjacent two openings among the openings being adjacent to one of the narrow portions of the other of the adjacent two openings, each of the narrow portions of the one opening being adjacent to one of the wide portions of the other opening. 
     Each of the openings may be line-symmetrical about a straight line parallel to or perpendicular to an initial alignment azimuth of the liquid crystal molecules. 
     The liquid crystal molecules may have positive anisotropy of dielectric constant. 
     The two or more wide portions and the one or more narrow portions in each of the openings may alternate with each other at an initial alignment azimuth of the liquid crystal molecules. 
     The liquid crystal molecules may have negative anisotropy of dielectric constant. 
     The two or more wide portions and the one or more narrow portions in each of the openings may alternate with each other in a direction perpendicular to an initial alignment azimuth of the liquid crystal molecules. 
     The present invention can provide a horizontal alignment mode liquid crystal display device that can achieve an increased response speed and an increased transmittance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  and  FIG. 1B  are views of a liquid crystal display device of Embodiment 1 with voltage applied;  FIG. 1A  is a schematic cross-sectional view of the liquid crystal display device utilizing liquid crystal molecules having positive anisotropy of dielectric constant, and  FIG. 1B  is a schematic cross-sectional view of the liquid crystal display device utilizing liquid crystal molecules having negative anisotropy of dielectric constant. 
         FIG. 2  is a view of a pixel circuit in the liquid crystal display device of Embodiment 1. 
         FIG. 3  is a schematic plan view of a counter electrode in the liquid crystal display device of Embodiment 1. 
         FIG. 4A  and  FIG. 4B  are views of the liquid crystal display device of Embodiment 1;  FIG. 4A  is a schematic plan view illustrating the alignment of liquid crystal molecules with voltage applied, and  FIG. 4B  is a plan view illustrating an exemplary simulation result of the alignment distribution of the liquid crystal molecules with voltage applied. 
         FIG. 5A  and  FIG. 5B  are views of a liquid crystal display device of Reference Example 1;  FIG. 5A  is a schematic plan view of a counter electrode, and  FIG. 5B  is a plan view illustrating a simulation result of the alignment distribution of liquid crystal molecules with voltage applied. 
         FIG. 6A  and  FIG. 6B  are views of a liquid crystal display device of Comparative Example 1;  FIG. 6A  is a schematic plan view of a counter electrode, and  FIG. 6B  is a plan view illustrating a simulation result of the alignment distribution of liquid crystal molecules with voltage applied. 
         FIG. 7A ,  FIG. 7B , and  FIG. 7C  are views of liquid crystal display devices of Reference Examples 2-1 to 2-3; 
         FIG. 7A  is a schematic plan view of a counter electrode in Reference Example 2-1,  FIG. 7B  is a schematic plan view of a counter electrode in Reference Example 2-2, and  FIG. 7C  is a schematic plan view of a counter electrode in Reference Example 2-3. 
         FIG. 8A  and  FIG. 8B  are views of a liquid crystal display device of Example 1;  FIG. 8A  is a schematic plan view of a counter electrode, and  FIG. 8B  is a plan view illustrating a simulation result of the alignment distribution of liquid crystal molecules with voltage applied. 
         FIG. 9A  and  FIG. 9B  are views of a liquid crystal display device of Reference Example 3;  FIG. 9A  is a schematic plan view of a counter electrode, and  FIG. 9B  is a plan view illustrating a simulation result of the alignment distribution of liquid crystal molecules with voltage applied. 
         FIG. 10A  and  FIG. 10B  are views of a liquid crystal display device of Comparative Example 2-1;  FIG. 10A  is a schematic plan view of a counter electrode, and  FIG. 10B  is a plan view illustrating a simulation result of the alignment distribution of liquid crystal molecules with voltage applied. 
         FIG. 11A  and  FIG. 11B  are views of a liquid crystal display device of Comparative Example 2-2;  FIG. 11A  is a schematic plan view of a counter electrode, and  FIG. 11B  is a plan view illustrating a simulation result of the alignment distribution of liquid crystal molecules with voltage applied. 
         FIG. 12  is a schematic plan view illustrating the alignment of liquid crystal molecules with no voltage applied in a liquid crystal display device of Reference Example 4. 
         FIG. 13A  and  FIG. 13B  are views of the liquid crystal display device of Reference Example 4;  FIG. 13A  is a schematic plan view illustrating the alignment of the liquid crystal molecules with voltage applied, and  FIG. 13B  is a plan view illustrating a simulation result of the alignment distribution of the liquid crystal molecules with voltage applied. 
         FIG. 14A  and  FIG. 14B  are views of the liquid crystal display device of Reference Example 4 and a liquid crystal display device of Comparative Example 3;  FIG. 14A  is a schematic plan view of a counter electrode in the liquid crystal display device of Comparative Example 3, and  FIG. 14B  is a schematic plan view of a counter electrode in the liquid crystal display device of Reference Example 4. 
         FIG. 15A  and  FIG. 15B  are views of the liquid crystal display devices of Reference Example 4 and Comparative Example 3;  FIG. 15A  is a plan view illustrating a simulation result of the alignment distribution of liquid crystal molecules with voltage applied in the liquid crystal display device of Comparative Example 3, and  FIG. 15B  is a plan view illustrating a simulation result of the alignment distribution of the liquid crystal molecules with voltage applied in the liquid crystal display device of Reference Example 4. 
         FIG. 16A  and  FIG. 16B  are views of a counter electrode in a liquid crystal display device;  FIG. 16A  is a schematic plan view of the counter electrode in the liquid crystal display device of Comparative Example 1, and  FIG. 16B  is a schematic plan view of the counter electrode in the liquid crystal display device of Reference Example 1. 
         FIG. 17A  and  FIG. 17B  are views of a conventional FFS mode liquid crystal display device;  FIG. 17A  is a schematic plan view illustrating the alignment of liquid crystal molecules with no voltage applied, and  FIG. 17B  is a schematic plan view illustrating the alignment of the liquid crystal molecules with voltage applied. 
         FIG. 18A  and  FIG. 18B  are views of the liquid crystal display device of Comparative Example 1;  FIG. 18A  is a schematic plan view illustrating the alignment of the liquid crystal molecules with no voltage applied, and  FIG. 18B  is a schematic plan view illustrating the alignment of the liquid crystal molecules with voltage applied. 
         FIG. 19  is a schematic plan view illustrating the alignment of liquid crystal molecules with voltage applied in a conventional FFS mode liquid crystal display device. 
         FIG. 20  is a schematic plan view illustrating liquid crystal correlation lengths using the conventional FFS mode liquid crystal display device. 
         FIG. 21  is a schematic plan view illustrating the alignment of the liquid crystal molecules with voltage applied in the liquid crystal display device of Comparative Example 1. 
         FIG. 22A  and  FIG. 22B  are views of the liquid crystal display device of Comparative Example 1;  FIG. 22A  is a schematic plan view illustrating the alignment of liquid crystal molecules in the case where the left and right electrode ends are independent of each other, and  FIG. 22B  is a schematic plan view illustrating the alignment of the liquid crystal molecules with both the left and right electrode ends taken into consideration. 
         FIG. 23  is a view illustrating the relationship between the shape of a counter electrode and the response speed in a liquid crystal display device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the present invention is described below. The embodiment, however, is not intended to limit the scope of the present invention. The embodiment may appropriately be modified within the spirit of the present invention. 
     The same portions or portions having similar functions hereinbelow are provided with similar reference signs in different figures, and those portions are not described repeatedly. 
     The configurations in the embodiment may appropriately be combined or modified within the spirit of the present invention. 
     Embodiment 1 
     The present embodiment is described with an FFS mode liquid crystal display device taken as an example.  FIG. 1A  and  FIG. 1B  are views of a liquid crystal display device of Embodiment 1 with voltage applied;  FIG. 1A  is a schematic cross-sectional view of the liquid crystal display device utilizing liquid crystal molecules having positive anisotropy of dielectric constant, and  FIG. 1B  is a schematic cross-sectional view of the liquid crystal display device utilizing liquid crystal molecules having negative anisotropy of dielectric constant.  FIG. 2  is a view of a pixel circuit in the liquid crystal display device of Embodiment 1. Both  FIGS. 1A and 1B  show a cross section taken along the line L 1 -L 2  shown in  FIG. 2 . Liquid crystal molecules having positive anisotropy of dielectric constant are also referred to as positive liquid crystal molecules. Liquid crystal molecules having negative anisotropy of dielectric constant are also referred to as negative liquid crystal molecules. 
     As shown in  FIG. 1A  and  FIG. 1B  and  FIG. 2 , a liquid crystal display device  1  of the present embodiment includes a pair of substrates consisting of a first substrate  10  including thin-film transistors (TFTs) as switching elements and a second substrate  20  disposed to face the first substrate  10 , and a liquid crystal layer  30  containing liquid crystal molecules  31  between the substrates. A plane parallel to the main surface of at least one of the first substrate  10  and the second substrate  20  as used herein is also simply referred to as a “plane”. 
     The first substrate  10  has a structure including a first polarizer (not shown), an insulating substrate  11 , pixel electrodes (first electrodes)  12 , an insulating film  13 , and a counter electrode (second electrode)  14  sequentially stacked toward the liquid crystal layer  30 . The first substrate  10  is also referred to as an active matrix substrate. A backlight (not shown) is disposed at the side remote from the liquid crystal layer  30  of the first substrate  10 . These members may be disposed in the order of the first substrate  10 , the liquid crystal layer  30 , the second substrate  20 , and the backlight. 
     The first substrate  10  includes data lines  41 , scanning lines  42  crossing the data lines  41 , and TFTs  43 . Each of the TFTs  43  is connected to the corresponding data line  41  among the data lines  41  and the corresponding scanning line  42  among the scanning lines  42 . The TFT  43  is a three-terminal switch containing a thin-film semiconductor, a source electrode composed of part of the corresponding data line  41 , a gate electrode composed of part of the corresponding scanning line  42 , and a drain electrode connected to the corresponding pixel electrode  12  among the pixel electrodes  12 . 
     The second substrate  20  has a structure including a second polarizer (not shown), an insulating substrate  21 , a color filter layer  22  and a black matrix layer  23 , and an overcoat layer  24  sequentially stacked toward the liquid crystal layer  30 . The second substrate  20  is also referred to as a color filter substrate. The overcoat layer  24  flattens the surface close to the liquid crystal layer  30  of the second substrate  20  and may be, for example, an organic film (dielectric constant ε=3 to 4). 
     The liquid crystal display device  1  of the present embodiment includes display units arranged in a matrix form. The pixel electrodes  12  in the first substrate  10  are planar electrodes disposed in the respective display units. The “display units” are each a region corresponding to one pixel electrode  12 , and may be a “pixel” in the art of liquid crystal display devices. If one pixel is divisionally driven, the display unit may be a “sub-pixel”, “dot”, or “picture element”. 
     The counter electrode  14  supplies a common potential to the display units and is stacked on the pixel electrodes  12  with an insulating film  13  in between, covering substantially the entire surface (except for the openings for fringe electric field generation) of the first substrate  10 . The insulating film  13  can be, for example, an organic film (dielectric constant ε=3 to 4), an inorganic film (dielectric constant ε=5 to 7) such as silicon nitride (SiNx) or silicone oxide (SiO 2 ), or a stack of these films. The counter electrode  14  may be electrically connected to an external connection terminal in a peripheral portion (frame region) of the first substrate  10 . The counter electrode  14  is provided with openings  15  formed side by side in the row direction in which the scanning lines  42  extend. 
     The openings  15  formed in the counter electrode  14  are described with reference to  FIG. 3  and  FIG. 4A  and  FIG. 4B .  FIG. 3  is a schematic plan view of a counter electrode in the liquid crystal display device of Embodiment 1. FIG.  4 A and  FIG. 4B  are views of the liquid crystal display device of Embodiment 1;  FIG. 4A  is a schematic plan view illustrating the alignment of liquid crystal molecules with voltage applied, and  FIG. 4B  is a plan view illustrating an exemplary simulation result of the alignment distribution of the liquid crystal molecules with voltage applied.  FIG. 4A  is a view illustrating a region surrounded by the dashed quadrangle in  FIG. 3 , while  FIG. 4B  is a view illustrating a region near the center of  FIG. 4A .  FIG. 4A  and  FIG. 4B  are also views illustrating the liquid crystal molecules  31  having positive anisotropy of dielectric constant. The simulations mentioned herein are performed using LCD-Master 3D from Shintech, Inc. The state herein in which voltage is applied between any of the pixel electrodes (first electrodes)  12  and the counter electrode (second electrode)  14  is also simply referred to as “with voltage applied”. The state in which voltage is not applied between any of the pixel electrodes (first electrodes)  12  and the counter electrode (second electrode)  14  is also simply referred to as “with no voltage applied”. The alignment azimuth of the liquid crystal molecules  31  with no voltage applied is also referred to as the initial alignment azimuth of the liquid crystal molecules  31 . The alignment azimuth of the liquid crystal molecules  31  is a direction of the major axes of the liquid crystal molecules  31  projected on a plane parallel to the main surface of the first substrate  10  or the second substrate  20 . 
     In the present embodiment, the counter electrode  14  is provided with the openings  15  formed side by side. Each opening  15  has a long shape with two or more wide portions  151  and one or more narrow portions  152 . The two or more wide portions  151  and the one or more narrow portions  152  in each opening  15  alternate with each other in the lengthwise direction of the opening  15 . In this structure, with voltage applied, liquid crystal domains  32  are formed in respective regions A, B, C, D, E, F, G, and H which extend in the 45° directions from the center of a wide portion  151  or the center of a narrow portion  152 . This enables the liquid crystal molecules  31  in adjacent liquid crystal domains  32  to rotate at opposite azimuths. The liquid crystal molecules are therefore aligned in a bend- and splay-shaped manner in a narrow region, and the distortion force generated by this alignment enables a rapid response in the horizontal alignment mode without complicating the shape of the counter electrode  14 . Similar liquid crystal domains are formed also when utilizing the liquid crystal molecules  31  having negative anisotropy of dielectric constant, so that a rapid response is enabled. The case where the liquid crystal molecules  31  have negative anisotropy of dielectric constant is described in detail in the later-described Reference Example 4. 
     This structure also reduces the distance between adjacent electrode ends  14   a  and  14   b  formed at different angles in a plane, enabling an overlap between a region where the alignment of the liquid crystal molecules  31  is changed by the electrode end  14   a  and a region where the alignment of the liquid crystal molecules  31  is changed by the electrode end  14   b . In other words, the range where the long-range interaction of the liquid crystal molecules  31  is effective when an electric field is generated at the electrode end  14   a  can overlap the range where the long-range interaction of the liquid crystal molecules  31  is effective when an electric field is generated at the electrode end  14   b . In the overlap portion of ranges where the long-range interactions are effective, the alignment change of the liquid crystal molecules  31  by the long-range interactions are limited. Hence, when the ranges where the long-range interactions are effective overlap at a position far from the electrode ends, i.e., a position where the response of the liquid crystal molecules  31  is slow, the liquid crystal molecules  31  at the position far from the electrode ends do not, or substantially do not, respond. This seems to increase the response speed. The response speed is considered to be increased by the same mechanism also when the liquid crystal molecules  31  having negative anisotropy of dielectric constant are used. 
     In the present embodiment, each of the wide portions of one of adjacent two openings (hereinafter, the opening is also referred to as a first opening  15   a ) among the openings is adjacent to one of the narrow portions of the other of the adjacent two openings (hereinafter, the opening is also referred to as a second opening  15   b ), and each of the narrow portions of the first opening  15   a  is adjacent to one of the wide portions of the second opening  15   b . This structure can reduce the distance between the adjacent two openings  15  to reduce the space where the liquid crystal molecules  31  do not respond, further increasing the transmittance. The structure also can reduce the liquid crystal molecules  31  far from the electrode ends and slow to respond, further increasing the response speed. The response speed and the transmittance are considered to be increased by the same mechanism also when the liquid crystal molecules  31  having negative anisotropy of dielectric constant are used. 
     The width (width in the widthwise direction) of each opening  15  repeats a monotonic decrease and a monotonic increase in the lengthwise direction of the opening  15 . Each opening  15  alternately has the largest width in the lengthwise direction (hereinafter, also referred to as the maximum width) and the smallest width in the lengthwise direction (hereinafter, also referred to as the minimum width). A wide portion  151  and a narrow portion  152  adjacent to each other are in contact with each other at a boundary line where the opening  15  has the average width obtained by dividing the sum of the maximum width of the wide portion  151  and the minimum width of the narrow portion  152  by two. The boundary line defines the boundary between the wide portion  151  and the narrow portion  152 . The maximum width corresponds to the later-described maximum width a 1  of each wide portion  151 , and the minimum width corresponds to the later-described minimum width c 1  of each narrow portion  152 . 
     In each opening  15 , the two or more wide portions  151  preferably have substantially the same width as each other, but at least one of the wide portions  151  may have a different width. The wide portions  151  of each opening  15  preferably have substantially the same width as the wide portions  151  of the other openings  15 , but may have a different width. 
     In the case where each opening  15  includes two or more narrow portions  152 , the narrow portions  152  in each opening  15  preferably have substantially the same width as each other, but at least one of the narrow portions  152  may have a different width. The narrow portions  152  of each opening  15  preferably have substantially the same width as the narrow portions  152  of the other openings  15 , but may have a different width. 
     In each opening  15 , each wide portion  151  preferably has a maximum width a 1  of 5 μm or greater and 10 μm or smaller, more preferably 5.5 μm or greater and 9.5 μm or smaller. Each narrow portion  152  preferably has a minimum width c 1  of 1 μm or greater and 4 μm or smaller, more preferably 1.5 μm or greater and 3.5 μm or smaller. Each wide portion  151  preferably has a maximum width a 1  that is double or more and sextuple or less, more preferably triple or more and quintuple or less, the minimum width c 1  of the narrow portion  152  adjacent to the wide portion  151 . 
     In each opening  15 , a distance d 1  in the lengthwise direction between a maximum width a 1  portion of a wide portion  151  and a minimum width c 1  portion of an adjacent narrow portion  152  is preferably 2.5 μm or greater and 28.5 μm or smaller, more preferably 3 μm or greater and 28 μm or smaller. With a distance d 1  of 2.5 μm or greater and 28.5 μm or smaller, setting the initial alignment azimuth of the positive liquid crystal molecules  31  in the direction parallel to a straight line parallel to the lengthwise direction of the opening  15  enables inclination of an opening end  156  from the initial alignment azimuth of the liquid crystal molecules  31  by 5° or greater and 45° or smaller. In the case of using the positive liquid crystal molecules  31 , setting the angle formed by each opening end  156  and the initial alignment azimuth of the liquid crystal molecules  31  to 45° enables the response speed to be the highest. Decreasing the angle enables the transmittance to increase, although decreasing the response speed. Also with a distance d 1  of 2.5 μm or greater and 28.5 μm or smaller, setting the initial alignment azimuth of the negative liquid crystal molecules  31  in the direction parallel to a straight line parallel to the widthwise direction of the opening  15  enables inclination of the opening end  156  from the initial alignment azimuth of the liquid crystal molecules  31  by 45° or greater and 85° or smaller. In the case of using the negative liquid crystal molecules  31 , setting the angle formed by the opening end  156  and the initial alignment azimuth of the liquid crystal molecules  31  to 45° enables the response speed to be the highest. Increasing the angle enables the transmittance to increase, although decreasing the response speed. 
     Each opening  15  is preferably line-symmetric about a straight line parallel to the lengthwise direction of the opening  15  or a straight line parallel to the widthwise direction of the opening  15 , more preferably about a straight line parallel to the lengthwise direction of the opening  15  and a straight line parallel to the widthwise direction of the opening  15 . This structure can increase the symmetry of the liquid crystal domains  32  formed with voltage applied, further increasing the response speed. Each opening  15  being line-symmetric about a straight line parallel to the lengthwise direction of the opening  15  or a straight line parallel to the widthwise direction of the opening  15  includes cases where each opening  15  is perfectly line-symmetric or substantially line-symmetric about a straight line parallel to the lengthwise direction of the opening  15  or a straight line parallel to the widthwise direction of the opening  15 . 
     Each opening  15  preferably has a shape formed by repetitive opening units  153  having a predetermined shape. The opening units  153  are each a portion corresponding to the region surrounded by a dot-dashed line in  FIG. 3 . Each opening unit  153  preferably includes a main portion  154  and a pair of protruding portions  155  protruding in opposite directions from the center in the lengthwise direction of the main portion  154  of the opening  15 . With this structure, oblique electric fields can form stable liquid crystal domains  32 , further increasing the response speed. 
     Each opening  15  has a shape in which shapes each including the pair of protruding portions  155  protruding in the opposite directions from the center portion in the lengthwise direction of the shape overlap each other at at least one of their upper end and lower end. The shape is an ellipse or an ellipse-like shape such as an oval having two axes of symmetry. The protruding portions  155  protrude in the opposite directions (outward, widthwise direction) from the main portion  154  and are formed at the opposite ends of the main portion  154  in the lengthwise direction of the opening  15 . Each protruding portion  155  may have any size and may protrude from the main portion  154  significantly or slightly. Each protruding portion  155  has only to protrude from the main portion  154 , and the outline thereof may be arc- or elliptical arc-shaped, curved, or irregular. Each protruding portion  155  may also have a polygonal shape such as a triangular or trapezoidal (the longer base is adjacent to the main portion  154 ) shape, or a shape obtained by rounding at least one of the corners of such a polygon. 
     Each opening  15  preferably has the opening end  156  inclined from the initial alignment azimuth of the liquid crystal molecules  31 . Such an opening end  156  inclined from the initial alignment azimuth of the liquid crystal molecules  31  is also simply referred to as an “inclined portion” hereinbelow, and the inclined portion does not include the protruding portions  155 . This structure enables smooth rotation of the liquid crystal molecules  31  with voltage applied, further increasing the response speed. In the case where the liquid crystal molecules  31  have positive anisotropy of dielectric constant are used, the angle formed by the initial alignment azimuth of the liquid crystal molecules  31  and the inclined portion is, in a plan view, preferably 5° or greater and 45° or smaller, more preferably 10° or greater and 40° or smaller. In the case where the liquid crystal molecules  31  have negative anisotropy of dielectric constant are used, the angle formed by the initial alignment azimuth of the liquid crystal molecules  31  and the inclined portion is, in a plan view, preferably 45° or greater and 85° or smaller, more preferably 50° or greater and 80° or smaller. In the case where the angle formed by the initial alignment azimuth of the liquid crystal molecules  31  and the inclined portion is 45°, the liquid crystal molecules  31  can rotate smoothly and thus the response speed can be the highest. As the angle formed by the initial alignment azimuth of the positive liquid crystal molecules  31  and the inclined portion becomes closer to 0°, or as the angle formed by the initial alignment azimuth of the negative liquid crystal molecules  31  and the inclined portion becomes closer to 90°, the transmittance can be further increased. Hence, setting the angle formed by the initial alignment azimuth of the liquid crystal molecules  31  and the inclined portion to 5° or greater and 45° or smaller or to 45° or greater and 85° or smaller enables a further increased response speed and a further increased transmittance. 
     In each opening  15 , the number of the wide portions  151  and the number of the narrow portions  152  are not particularly limited, and may each appropriately be set according to the pixel size and the opening size of the black matrix layer  23 . For example, each opening  15  preferably includes two or more and seven or less wide portions  151  and one or more and six or less narrow portions  152 , more preferably three or more and six or less wide portions  151  and two or more and five or less narrow portions  152 . 
     In  FIG. 3 , the inside of a region X surrounded by a hexagon is a light transmissive region, i.e., a region without a black matrix layer, and the outside of the region X is a light blocking region Z, i.e., a region with a black matrix layer. At least one end (preferably both ends) in the lengthwise direction of each opening  15  is preferably within the light blocking region Z. The response of the liquid crystal molecules  31  outside each opening  15  is slow. Hence, the above structure can further increase the response speed in the display region. 
     In the present embodiment, the other opening  15  (second opening  15   b ) side opening end  15   al  of a wide portion  151  and the second opening  15   b  side opening end  15   a   2  of a narrow portion  152  in one of adjacent two openings  15  (first opening  15   a ) among the openings  15  are respectively alongside a first opening  15   a  side opening end  15   b   2  of a narrow portion  152  and a first opening  15   a  side opening end  15   b   1  of a wide portion  151  in the other of the adjacent two openings  15  (second opening  15   b ). Also, a wide portion  151  and a narrow portion  152  of the first opening  15   a  and a narrow portion  152  and a wide portion  151  of the adjacent second opening  15   b  are adjacent to each other, respectively. 
     The shortest distance between the first opening  15   a  and the second opening  15   b  adjacent to each other may differ at different positions, but is preferably within a range that is less than a double of the liquid crystal correlation length. This structure can reduce a portion with a small overlap of the liquid crystal correlation lengths between the first opening  15   a  and the second opening  15   b , further increasing the response speed. The liquid crystal correlation length can be adjusted using, for example, a physical property value such as anisotropy of dielectric constant or elastic constant of the liquid crystal material, or the degree of restriction (anchoring energy) of an alignment film. For example, the liquid crystal correlation length can be increased by increasing the anisotropy of dielectric constant of the liquid crystal material, increasing the elastic constant of the liquid crystal material, or lowering the degree of restriction of the alignment film. 
     The liquid crystal correlation length can be determined as follows, for example. When voltage is applied between a pixel electrode  12  and the counter electrode  14 , an electric field is generated at the electrode ends, so that the liquid crystal molecules  31  are re-aligned. In the region between the electrode ends, the liquid crystal molecules  31  are affected by multiple electrode ends and thereby re-aligned. In determination of the liquid crystal correlation length, however, a region where the alignment of the liquid crystal molecules  31  changes is determined by simulation, assuming that each electrode end is present alone. The distance from the electrode end to an end of the region where the alignment of the liquid crystal molecules  31  changes is measured, so that the liquid crystal correlation length can be determined. 
     At least two openings  15  are preferably formed in each display unit. The upper limit of the number of the openings  15  in one display unit is not particularly limited, but is preferably five or less, more preferably three or less. For an increase in the transmittance, the number of the openings  15  is preferably as small as possible. 
     Each opening  15  is preferably line-symmetric about a straight line parallel or perpendicular to the initial alignment azimuth of the liquid crystal molecules  31 . This structure can increase the symmetry of the liquid crystal domains  32  formed with voltage applied, further increasing the response speed. Each opening  15  being line-symmetric about a straight line parallel or perpendicular to the initial alignment azimuth of the liquid crystal molecules  31  includes cases where each opening  15  is perfectly line-symmetric or substantially line-symmetric about a straight line parallel or perpendicular to the initial alignment azimuth of the liquid crystal molecules  31 . 
     In the case where the liquid crystal layer  30  contains a liquid crystal material having positive anisotropy of dielectric constant and the liquid crystal molecules  31  have positive anisotropy of dielectric constant, the two or more wide portions  151  and the one or more narrow portions  152  of each opening  15  preferably alternate with each other at the initial alignment azimuth of the liquid crystal molecules  31 . This structure can fix crossing dark lines as shown in  FIG. 4B  in the wide portion  151  (especially in the protruding portions  155  in the wide portion  151 ) and give a high effectively applicable design voltage, further increasing the transmittance. In this case, the lengthwise direction of each opening  15  may be parallel to the initial alignment azimuth of the liquid crystal molecules  31 . 
     In the case where the liquid crystal layer  30  contains a liquid crystal material having negative anisotropy of dielectric constant and the liquid crystal molecules  31  have negative anisotropy of dielectric constant, the two or more wide portions  151  and the one or more narrow portions  152  of each opening  15  preferably alternate with each other in the direction perpendicular to the initial alignment azimuth of the liquid crystal molecules  31 . This structure can fix crossing dark lines as shown in  FIG. 4B  in the wide portion  151  (especially in the protruding portions  155  in the wide portion  151 ) and give a high effectively applicable design voltage, further increasing the transmittance. In this case, the widthwise direction (direction perpendicular to the lengthwise direction) of each opening  15  may be parallel to the initial alignment azimuth of the liquid crystal molecules  31 . 
     In the present embodiment, the alignment of the liquid crystal molecules  31  with voltage applied is controlled by the laminate of the pixel electrodes  12 , the insulating film  13 , and the counter electrode  14  formed on the first substrate  10 . In other words, the liquid crystal display device  1  of the present embodiment can control the alignment of the liquid crystal molecules  31  in the liquid crystal layer  30  by varying the voltage applied between the pixel electrodes  12  and the counter electrode  14 . In the present embodiment, the counter electrode  14  provided with the openings  15  is disposed on the planar pixel electrodes  12 . The positions of the pixel electrodes  12  and the counter electrode  14  may be switched to form pixel electrodes on a planar counter electrode and form the openings  15  in the pixel electrodes. Also, “with voltage applied” means a state where at least the minimum voltage (threshold voltage) required to rotate the liquid crystal molecules  31  under the influence of electric fields and change the alignment azimuth is applied, and may be a state where voltage for white display (white voltage) is applied. 
     Although not shown in  FIG. 1A  and  FIG. 1B , an alignment film is usually disposed on the liquid crystal layer  30  side surface of the first substrate  10  and/or the second substrate  20 . The alignment film controls the alignment of the liquid crystal molecules  31  with no voltage applied. The alignment film may be an organic or inorganic film. 
     In the present embodiment, a horizontal alignment film is used, which aligns the liquid crystal molecules  31  with no voltage applied in the direction parallel to the first substrate  10  and the second substrate  20 . The horizontal alignment film aligns the nearby liquid crystal molecules  31  in the direction parallel to the surface of the alignment film. Also, the horizontal alignment film can align the major axes of the liquid crystal molecules  31  aligned in the direction parallel to the first substrate  10  to a specific direction. A suitable horizontal alignment film is, for example, one on which an alignment treatment such as photo-alignment or rubbing has been performed. For example, in the case where the display units are quadrangular and the liquid crystal molecules  31  having positive anisotropy of dielectric constant are used, the photo-alignment or the rubbing can be performed on the alignment film in the lengthwise direction of the display units. In the case where the display units are quadrangular and the liquid crystal molecules  31  having negative anisotropy of dielectric constant are used, the photo-alignment or the rubbing can be performed on the alignment film in the widthwise direction of the display units. The horizontal alignment film may be a film formed of an inorganic material or a film formed of an organic material. 
     The “parallel” alignment of the liquid crystal molecules  31  includes the perfect parallel state and states equated with the parallel state (substantially parallel state) in the art. The pre-tilt angle (inclination angle with no voltage applied) of the liquid crystal molecules  31  is preferably smaller than 30, more preferably smaller than 1°, particularly preferably 0° using a photo-alignment film, from the surface of the first substrate  10 . Setting the pre-tilt angle to 0° eliminates the influence of the pre-tilt angle on the liquid crystal domains, enabling the four liquid crystal domains to be uniformly kept in a balanced state. 
     The liquid crystal molecules  31  may have negative or positive anisotropy of dielectric constant (Δε), which is calculated from the following formula. In other words, the liquid crystal molecules  31  may have negative anisotropy of dielectric constant or positive anisotropy of dielectric constant. 
       Δε=(dielectric constant in major axis direction)−(dielectric constant in minor axis direction)
 
     A liquid crystal material containing the liquid crystal molecules  31  having negative anisotropy of dielectric constant tends to have a relatively high viscosity. Thus, for a high response speed, a liquid crystal material containing the liquid crystal molecules  31  having positive anisotropy of dielectric constant is advantageous. However, even with a liquid crystal material having negative anisotropy of dielectric constant, the same effects can be achieved in the same manner as in the present embodiment as long as the viscosity of the liquid crystal material is as low as that of the liquid crystal material having positive anisotropy of dielectric constant. The initial alignment azimuth of the liquid crystal molecules  31  having negative anisotropy of dielectric constant is in the direction rotated by 90 degrees from the liquid crystal molecules  31  having positive anisotropy of dielectric constant. Also, the liquid crystal molecules  31  having positive anisotropy of dielectric constant with voltage applied are aligned such that the major axes thereof are perpendicular to the outline (opening end  156 ) of each opening  15 , whereas the liquid crystal molecules  31  having negative anisotropy of dielectric constant with voltage applied are aligned such that the major axes thereof are parallel to the outline of each opening  15 . 
     The definition of the liquid crystal display device  1  is not particular limited, but is preferably 300 ppi or higher and 1000 ppi or lower, more preferably 350 ppi or higher and 800 ppi or lower. The definition (pixel per inch: ppi) as used herein means the number of pixels per inch (2.54 cm). In the case of dividing one pixel into sub-pixels (display units) and divisionally driving the pixels, the definition may be calculated using the size of one pixel consisting of multiple sub-pixels. 
     The first polarizer and the second polarizer are each an absorptive polarizer, and are in crossed Nicols where the absorptive axes thereof are perpendicular to each other. One of the polarization axis of the first polarizer and the polarization axis of the second polarizer is in the direction parallel to the initial alignment azimuth of the liquid crystal molecules  31 , and the other of them is in the direction perpendicular to the initial alignment azimuth of the liquid crystal molecules  31 . 
     The liquid crystal display device  1  may include, as well as the above members, members such as optical films, including a retardation film, a viewing angle-increasing film, and a luminance-increasing film; external circuits, including a tape-carrier package (TCP) and a printed circuit board (PCB); and a bezel (frame). These members are not particularly limited, and may be those usually used in the field of liquid crystal display devices. The description of these components is thus omitted. 
     An embodiment of the present invention has been described above. Each and every detail described for the above embodiment is applicable to all the aspects of the present invention. 
     The present invention is described in more detail below based on an example, comparative examples, and reference examples. The example, however, is not intended to limit the scope of the present invention. 
     Reference Example 1 and Comparative Example 1 
     Liquid crystal display devices of Reference Example 1 and Comparative Example 1 have the same configuration as the liquid crystal display device of Embodiment 1 described above, except that the openings in the counter electrode have a different shape.  FIG. 5A  and  FIG. 5B  are views of the liquid crystal display device of Reference Example 1;  FIG. 5A  is a schematic plan view of a counter electrode, and  FIG. 5B  is a plan view illustrating a simulation result of the alignment distribution of liquid crystal molecules with voltage applied.  FIG. 6A  and  FIG. 6B  are views of the liquid crystal display device of Comparative Example 1;  FIG. 6A  is a schematic plan view of a counter electrode, and  FIG. 6B  is a plan view illustrating a simulation result of the alignment distribution of liquid crystal molecules with voltage applied. 
     Openings  15 R having the shape as shown in  FIG. 5A  were formed in the counter electrode  14 R of the liquid crystal display device of Reference Example 1. The openings  15 R in the counter electrode  14 R of the liquid crystal display device of Reference Example 1 each had wide portions  151 R and narrow portions  152 R alternating with each other at an initial alignment azimuth  31   a  of the liquid crystal molecules. Each wide portion  151 R included a pair of protruding portions  155 R such that the upper and lower liquid crystal domains are symmetrically defined. In Reference Example 1, one opening  15 R in the counter electrode  14 R was formed per display unit. Each wide portion  151 R in  FIG. 5A  had a maximum width ar of 8.5 μm, each opening  15 R had a length br in the lengthwise direction of 35.9 μm, and each narrow portion  152 R had a minimum width cr of 2.6 μm. The angle formed by an opening end  156 R inclined from the initial alignment azimuth  31   a  of the liquid crystal molecules and the initial alignment azimuth  31   a  of the liquid crystal molecules was set to 25°. The inside of a region XR surrounded by a quadrangle in  FIG. 5A  and  FIG. 5B  is a light transmissive region, i.e., a region without a black matrix layer, and the outside of the region XR is a light blocking region, i.e., a region with the black matrix layer. 
     The liquid crystal layer had a refractive index anisotropy (Δn) of 0.11, an in-plane retardation (Re) of 310 nm, and a viscosity of 70 cps. The liquid crystal molecules had an anisotropy of dielectric constant (Δε) of 7 (positive). The initial alignment azimuth of the liquid crystal molecules was set to be parallel to the lengthwise direction of the display units. Also, a pair of polarizing plates was disposed such that one polarizing plate was on the side remote from the liquid crystal layer of one of the substrates holding the liquid crystal layer in between, and the other polarizing plate was on the side remote from the liquid crystal layer of the other substrate. The polarizing plates were disposed in crossed Nicols, with the absorptive axis of one of the polarizing plates being parallel and the absorptive axis of the other being perpendicular, to the initial alignment azimuth of the liquid crystal molecules. The liquid crystal display device was therefore in the normally black mode where it provides black display with no voltage applied to the liquid crystal layer. 
     The liquid crystal display device of Comparative Example 1 has the same configuration as the liquid crystal display device of Reference Example 1, except that each opening  15 R in the counter electrode  14 R had the shape shown in  FIG. 6A . Each opening  15 R in Comparative Example 1 includes a main portion  154 R and the pair of protruding portions  155 R protruding in the opposite directions from the main portion  154 R. Each wide portion  151 R in  FIG. 6A  had a maximum width ar of 8.5 μm, and each opening  15 R had a length br in the lengthwise direction of 12.5 m. Also, the angle formed by each opening end  156 R inclined from the initial alignment azimuth  31   a  of the liquid crystal molecules and the initial alignment azimuth  31   a  of the liquid crystal molecules was set to 25°. The inside of the region XR surrounded by a quadrangle in  FIG. 6A  and  FIG. 6B  is a light transmissive region, i.e., a region without a black matrix layer, and the outside of the region XR is a light blocking region, i.e., a region with the black matrix layer. 
     The transmittance of each of the liquid crystal display devices of Reference Example 1 and Comparative Example 1 with a voltage of 4.5 V applied was simulated. The results are shown in the following Table 1. The transmittance of the liquid crystal display device of Reference Example 1 was determined with the transmittance of the liquid crystal display device of Comparative Example 1 taken as 100%. The sizes of the black matrix layer and the pixel electrodes in Reference Example 1 and Comparative Example 1 in the simulations were set to be the same as each other. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Comparative 
                 Reference 
               
               
                   
                 Example 1 
                 Example 1 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Transmittance 
                 100% 
                 108% 
               
               
                   
                   
               
            
           
         
       
     
     The results of Table 1 show that the transmittance of the liquid crystal display device of Reference Example 1 was higher than the transmittance of the liquid crystal display device of Comparative Example 1 by 8%. The liquid crystal display device of Comparative Example 1 caused a region between the openings  15 R (region surrounded by a dashed circle in  FIG. 6A  and  FIG. 6B ) to appear as dark lines and hardly increased the transmittance. Also, since the distance from each electrode end to the liquid crystal molecules is large between the openings  15 R, the response speed seems to be low. In contrast, in Reference Example 1, the openings  15 R formed in the counter electrode  14 R each include the wide portions  151 R and the narrow portions  152 R alternating with each other. The dark lines were therefore thinner than those in Comparative Example 1 as shown in the region surrounded by the dotted circle in  FIG. 5A  and  FIG. 5B , so that the transmittance seems to have been increased. As shown in the region surrounded by the dotted circle in  FIG. 5A  and  FIG. 5B , the distance from each electrode end to the liquid crystal molecules can be reduced in Reference Example 1 as compared with Comparative Example 1, and thus the response speed of the liquid crystal display device of Reference Example 1 seems to be further increased as compared with Comparative Example 1. 
     Reference Examples 2-1 to 2-3 
     Liquid crystal display devices of Reference Examples 2-1 to 2-3 have the same configuration as the liquid crystal display device of Reference Example 1 described above, except that the openings in the counter electrode have a different shape.  FIG. 7A ,  FIG. 7B , and  FIG. 7C  are views of liquid crystal display devices of Reference Examples 2-1 to 2-3;  FIG. 7A  is a schematic plan view of a counter electrode in Reference Example 2-1,  FIG. 7B  is a schematic plan view of a counter electrode in Reference Example 2-2, and  FIG. 7C  is a schematic plan view of a counter electrode in Reference Example 2-3. 
     In an opening including wide portions and narrow portions alternately, it is important that a line segment connecting the upper and lower vertexes in the lengthwise direction of the opening is parallel to the initial alignment azimuth of liquid crystal molecules and that the opening has a shape that is line-symmetrical about the initial alignment azimuth of liquid crystal molecules. As shown in  FIG. 7C , in the liquid crystal display device of Reference Example 2-3, a straight line passing an upper vertex V 1  in the lengthwise direction of the opening  15 R and being parallel to the initial alignment azimuth  31   a  of the liquid crystal molecules and a straight line passing a lower vertex V 2  in the lengthwise direction of the opening  15 R and being parallel to the initial alignment azimuth  31   a  of the liquid crystal molecules are shifted by 0 μm. This shows that the opening  15 R in Reference Example 2-3 is line-symmetrical about the initial alignment azimuth  31   a  of liquid crystal molecules. 
     The case where the opening is asymmetrical about the initial alignment azimuth of liquid crystal molecules is described based on Reference Examples 2-1 and 2-2. As shown in  FIGS. 7A and 7B , the liquid crystal display devices of Reference Examples 2-1 and 2-2 have the same configuration as a liquid crystal display device of Reference Example 2-3, except that the straight line passing the upper vertex V 1  in the lengthwise direction of the opening  15 R and being parallel to the initial alignment azimuth  31   a  of the liquid crystal molecules and the straight line passing the lower vertex V 2  in the lengthwise direction of the opening  15 R and being parallel to the initial alignment azimuth  31   a  of the liquid crystal molecules were shifted by 0.5 μm and 1.0 μm in the liquid crystal display devices of Reference Examples 2-1 and 2-2, respectively. In other words, in the opening  15 R in Reference Example 2-1, opening units  153   ar  and  153   br  constituting the opening  15 R in Reference Example 2-3 were shifted leftward and rightward by 0.25 μm, respectively, from the line segment connecting the upper vertex V 1  and the lower vertex V 2  in the opening  15 R in Reference Example 2-3. Also, in the opening  15 R in Reference Example 2-2, opening units  153   ar  and  153   br  constituting the opening  15 R in Reference Example 2-3 were shifted leftward and rightward by 0.5 μm, respectively, from the line segment connecting the upper vertex V 1  and the lower vertex V 2  in the opening  15 R in Reference Example 2-3. The opening  15 R in Reference Example 2-3 was line-symmetrical about a straight line parallel to the long sides of the pixel electrodes. 
     The response times of the liquid crystal display devices of Reference Examples 2-1 to 2-3 when voltage was changed from 0 V to 4.5 V were determined by simulation. The response time is the time required for the transmittance to change from 10% to 90% (the maximum transmittance with a voltage of 0 V applied is taken as 0% and the maximum transmittance with a voltage of 4.5 V applied is taken as 100%). The results are shown in Table 2. The response times of the liquid crystal display devices of Reference Examples 2-1 and 2-2 were determined with the response time of the liquid crystal display device of Reference Example 2-3 taken as 100%. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Reference 
                 Reference 
                 Reference 
               
               
                   
                 Example 2-1 
                 Example 2-2 
                 Example 2-3 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Response time 
                 104% 
                 114% 
                 100% 
               
               
                   
                   
               
            
           
         
       
     
     The results in Table 2 show that the response speed of the liquid crystal display device of Reference Example 2-3 was higher than that of the liquid crystal display devices of Reference Examples 2-1 and 2-2. The results therefore suggest that, for an increase in the response speed, the opening  15 R is preferably line-symmetrical about a straight line parallel to the initial alignment azimuth  31   a  of the liquid crystal molecules. 
     Example 1, Reference Example 3, and Comparative Examples 2-1 and 2-2 
       FIG. 8A  and  FIG. 8B  are views of a liquid crystal display device of Example 1;  FIG. 8A  is a schematic plan view of a counter electrode, and  FIG. 8B  is a plan view illustrating a simulation result of the alignment distribution of liquid crystal molecules with voltage applied.  FIG. 9A  and  FIG. 9B  are views of a liquid crystal display device of Reference Example 3;  FIG. 9A  is a schematic plan view of a counter electrode, and  FIG. 9B  is a plan view illustrating a simulation result of the alignment distribution of liquid crystal molecules with voltage applied.  FIG. 10A  and  FIG. 10B  are views of a liquid crystal display device of Comparative Example 2-1;  FIG. 10A  is a schematic plan view of a counter electrode, and  FIG. 10B  is a plan view illustrating a simulation result of the alignment distribution of liquid crystal molecules with voltage applied.  FIG. 11A  and  FIG. 11B  are views of a liquid crystal display device of Comparative Example 2-2;  FIG. 11A  is a schematic plan view of a counter electrode, and  FIG. 11B  is a plan view illustrating a simulation result of the alignment distribution of liquid crystal molecules with voltage applied. In Example 1, Reference Example 3, and Comparative Examples 2-1 and 2-2, the initial alignment azimuth of liquid crystal molecules was set in the lengthwise direction of the display units. 
     The openings  15  having the shape as shown in  FIG. 8A  and  FIG. 8B  were formed in the counter electrode  14  in the liquid crystal display device of Example 1. In other words, in Example 1, two lines of the openings  15  each including the wide portions  151  and the narrow portions  152  alternately were formed in each display unit. The center of each wide portion  151  of one of the adjacent openings  15  and the center of a narrow portion  152  of the other of the adjacent openings  15  were on a straight line perpendicular to the initial alignment azimuth of liquid crystal molecules and a straight line perpendicular to the long sides of the pixel electrode  12 . In Example 1, each of the wide portions  151  of one of the adjacent two openings  15  was adjacent to one of the narrow portions  152  of the other of the adjacent two openings  15 , and each of the narrow portions  152  of the one opening  15  was adjacent to one of the wide portions  151  of the other opening  15 . Each opening  15  has a shape in which elliptical shapes each including protruding portions, which are the center portion in the major axis direction of the elliptical shape protruding to form arcs, overlap each other at at least one of their upper end and lower end. Each opening  15  also has a shape in which elliptical shapes each including the pair of protruding portions  155  protruding in the opposite directions from the center portion in the lengthwise direction of the elliptical shape overlap each other at at least one of their upper end and lower end. 
     In Example 1, each wide portion  151  had a maximum width a 1  of approximately 7.3 m, each narrow portion  152  had a minimum width c 1  of approximately 1.8 m, and the angle formed by each opening end  156  inclined from the initial alignment azimuth of liquid crystal molecules and the initial alignment azimuth  31   a  of liquid crystal molecules was set to 25°. 
     The openings  15 R having the shape as shown in  FIG. 9A  and  FIG. 9B  were formed in the counter electrode in the liquid crystal display device of Reference Example 3. In other words, in Reference Example 3, two lines of the openings  15  each including the wide portions  151 R and the narrow portions  152 R alternately were formed in each display unit. The center of each wide portion  151 R of one of the adjacent openings  15  and the center of a wide portion  151 R of the other of the adjacent openings  15  were on a straight line perpendicular to the initial alignment azimuth of liquid crystal molecules and a straight line perpendicular to the long sides of a pixel electrode  12 R. In Reference Example 3, each wide portion  151 R of one of the adjacent two openings  15  was adjacent to one of the wide portions  151 R of the other of the adjacent two openings  15 R, and each of the narrow portions  152 R of the one opening  15  was adjacent to one of the narrow portions  152 R of the other opening  15 . 
     In Reference Example 3, each wide portion  151  had a maximum width ar of approximately 7.5 m, each narrow portion  152 R had a minimum width cr of approximately 1.8 m, and the angle formed by each opening end  156 R inclined from the initial alignment azimuth of the liquid crystal molecules and the initial alignment azimuth  31   a  of the liquid crystal molecules was set to 25°. 
     The openings  15 R having the shape as shown in  FIG. 10A  and  FIG. 10B  were formed in the counter electrode  14 R in the liquid crystal display device of Comparative Example 2-1. In other words, in Comparative Example 2-1, eight openings  15 R similar to those in Comparative Example 1 were formed separately in each display unit. The openings  15 R having the shape as shown in  FIG. 11A  and  FIG. 11B  were formed in the counter electrode  14 R in the liquid crystal display device of Comparative Example 2-2. In other words, in Comparative Example 2-2, eight openings  15 R were formed at a narrower interval than in Comparative Example 2-1. 
     In Comparative Example 2-1 and Comparative Example 2-2, each wide portion had a maximum width ar of approximately 7.5 m, and each opening  15 R had a length br in the lengthwise direction of approximately 10.9 m. The angle formed by each opening end  156 R inclined from the initial alignment azimuth of the liquid crystal molecules and the initial alignment azimuth of the liquid crystal molecules was set to 25°. 
     The transmittances of the liquid crystal display devices of Example 1, Reference Example 3, and Comparative Examples 2-1 and 2-2 were determined by simulation. Also, the liquid crystal display devices of the example, reference examples, and comparative examples herein take the longest time to respond in a change from display at a grayscale value of 0 to display at a grayscale value of about 128 as in a common FFS mode liquid crystal display device. Thus, the response time required to change display at a grayscale value of 0 to display at a grayscale value of 128 (gray to gray worst response time: the time required for the transmittance to change from 10% to 90% in transmittance change, where the transmittance of display at a grayscale value of 0 is taken as 0% and the maximum transmittance of display at a grayscale value of 128 is taken as 100%) was measured using an actual device capable of providing display at  256  grayscale vales. This response time is the longest among all the response times in grayscale changes including intermediate grayscale changes. The transmittances of the liquid crystal display devices of Comparative Example 2-2, Reference Example 3, and Example 1 were determined with the transmittance of the liquid crystal display device of Comparative Example 2-1 taken as 100%. The response times of the liquid crystal display devices of Comparative Example 2-2, Reference Example 3, and Example 1 were determined with the response time of the liquid crystal display device of Comparative Example 2-1 taken as 100%. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Comparative 
                 Comparative 
                 Reference 
                   
               
               
                   
                 Example 2-1 
                 Example 2-2 
                 Example 3 
                 Example 1 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Transmittance 
                 100% 
                 116% 
                 119% 
                 135% 
               
               
                 Response time 
                 100% 
                  84% 
                  79% 
                  76% 
               
               
                   
               
            
           
         
       
     
     The above results show that the response speed is increased by decreasing or eliminating the interval between adjacent openings  15  or between adjacent openings  15 R. The reasons thereof are presumably as follows. When voltage is applied between electrodes, the response of the liquid crystal molecules starts from the protruding portions formed in the widthwise direction of each of the openings  15  and  15 R, and thus the response of the liquid crystal molecules at the upper vertex and the lower vertex of each of the openings  15  and  15 R is relatively slow. Also, the alignment forced by the fringe electric field spreads to the outside of the openings  15  and  15 R, but the alignments of the liquid crystal molecules outside the openings  15  and  15 R do not collide or less collide with each other. These liquid crystal molecules therefore respond by their own viscoelasticity. The response of such liquid crystal molecules is slow. This is presumably why in Comparative Example 2-2 in which the interval between the openings  15 R was smaller than that in Comparative Example 2-1, the dark lines were thinner, the transmittance was higher, and the response speed was higher by 16%. 
     In Reference Example 3, the formation ratio of the openings  15 R was higher than those in Comparative Example 2-1 and Comparative Example 2-2. Hence, the transmittance was 119% of that in Comparative Example 2-1, and the regions where the response of the liquid crystal molecules was slow between the openings  15 R were eliminated. This is presumably why the response time shortened to 79%. 
     In Example 1, the formation ratio of the openings  15  was higher than that in Reference Example 3, and the alignment in the regions where the response of the liquid crystal molecules was slow outside the openings  15  was controlled by the electric fields. This is presumably why the transmittance was 135% of that in Comparative Example 2-1, the response time shortened to 76%, and a high transmittance and a high response speed were achieved. 
     Reference Example 4 and Comparative Example 3 
     A liquid crystal display device of Reference Example 4 has the same configuration as the liquid crystal display device of Reference Example 1, except that liquid crystal molecules having negative anisotropy of dielectric constant were used and the initial alignment azimuth of the liquid crystal molecules was set to be parallel to the widthwise direction of the display units. In Reference Example 4, the angle formed by each opening end inclined from an initial alignment azimuth  31   b  of liquid crystal molecules and the initial alignment azimuth  31   b  of the liquid crystal molecules was set to 65°. Also in the liquid crystal display device of Reference Example 4, the liquid crystal molecules  31 R in the liquid crystal layer had an anisotropy of dielectric constant (Δε) of −7 (negative). 
       FIG. 12  is a schematic plan view illustrating the alignment of liquid crystal molecules with no voltage applied in the liquid crystal display device of Reference Example 4.  FIG. 13A  and  FIG. 13B  are views of the liquid crystal display device of Reference Example 4;  FIG. 13A  is a schematic plan view illustrating the alignment of the liquid crystal molecules with voltage applied, and  FIG. 13B  is a plan view illustrating a simulation result of the alignment distribution of the liquid crystal molecules with voltage applied.  FIG. 13A  and  FIG. 13B  are views illustrating the region surrounded by the dashed square in  FIG. 12 . 
     In Reference Example 4 in which liquid crystal molecules having negative anisotropy of dielectric constant were used, as shown in  FIG. 12 , the initial alignment azimuth  31   b  of liquid crystal molecules was parallel to the widthwise direction of the display units. The liquid crystal molecules  31 R having negative anisotropy of dielectric constant with voltage applied were aligned with the major axes of the liquid crystal molecules  31 R being along the outline of the opening  15 R as shown in  FIG. 13A . 
     The alignment distribution of the liquid crystal molecules  31 R with voltage applied (4.5 V application) in the liquid crystal display device of Reference Example 4 is described based on  FIG. 13B . The liquid crystal molecules having negative anisotropy of dielectric constant in Reference Example 4 are in four liquid crystal domains formed in the respective 45-degree directions from each of the center of each wide portion  151 R and the center of each narrow portion  152 R as with the liquid crystal molecules having positive anisotropy of dielectric constant in Reference Example 1. This configuration sufficiently rotates the liquid crystal molecules  31 R aligned in the 45-degree directions from each of the centers at the initial voltage application. Thus, a high response speed can be achieved as in the liquid crystal display device of Reference Example 1. In other words, even in the case of using liquid crystal molecules having negative anisotropy of dielectric constant, the same effects as those achieved by liquid crystal molecules having positive anisotropy of dielectric constant can be achieved. 
       FIG. 14A  and  FIG. 14B  are views of the liquid crystal display device of Reference Example 4 and a liquid crystal display device of Comparative Example 3;  FIG. 14A  is a schematic plan view of a counter electrode in the liquid crystal display device of Comparative Example 3, and  FIG. 14B  is a schematic plan view of a counter electrode in the liquid crystal display device of Reference Example 4.  FIG. 15A  and  FIG. 15B  are views of the liquid crystal display devices of Reference Example 4 and Comparative Example 3;  FIG. 15A  is a plan view illustrating a simulation result of the alignment distribution of liquid crystal molecules with voltage applied in the liquid crystal display device of Comparative Example 3, and  FIG. 15B  is a plan view illustrating a simulation result of the alignment distribution of the liquid crystal molecules with voltage applied in the liquid crystal display device of Reference Example 4. The liquid crystal display device of Comparative Example 3 has the same configuration as that of Reference Example 4, except that the shape of the openings was changed to that in Comparative Example 1. The maximum width ar of each wide portion  151 R of each opening and the length br in the lengthwise direction of each opening  15 R in Comparative Example 4 were the same as those in Comparative Example 1. The maximum width ar of each wide portion  151 R and the minimum width cr of each narrow portion  152 R in each opening  15 R in Reference Example 4 were the same as those in Reference Example 1. 
     The transmittances of the liquid crystal display devices of Reference Example 4 and Comparative Example 3 with a voltage of 4.5 V applied were simulated. The results are shown in the following Table 4. The transmittance of the liquid crystal display device of Reference Example 4 was determined with the transmittance of the liquid crystal display device of Comparative Example 3 taken as 100%. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Comparative 
                 Reference 
               
               
                   
                 Example 3 
                 Example 4 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Transmittance 
                 100% 
                 106% 
               
               
                   
                   
               
            
           
         
       
     
     The results in Table 4 show that the transmittance of the liquid crystal display device of Reference Example 4 was higher than that of the liquid crystal display device of Comparative Example 3 by 6%. The portions not being taken into account for the transmittance between the openings  15 R are reduced in Reference Example 4 as compared with Comparative Example 3, which presumably led to a high transmittance. 
     The relationship between the liquid crystal correlation length and the response speed of liquid crystal molecules is further described below. 
       FIG. 16A  and  FIG. 16B  are views of a counter electrode in a liquid crystal display device;  FIG. 16A  is a schematic plan view of the counter electrode in the liquid crystal display device of Comparative Example 1, and  FIG. 16B  is a schematic plan view of the counter electrode in the liquid crystal display device of Reference Example 1. The regions each surrounded by a dashed square in  FIG. 16A  and  FIG. 16B  are opening units.  FIG. 16A  and  FIG. 16B  show that “the distance (length indicated by a solid arrow) between electrode ends facing each other at different angles in a plane” in an opening unit is the same in Reference Example 1 and Comparative Example 1, but “the distance (length indicated by a dashed arrow) between electrode ends facing each other at different angles in a plane” between adjacent opening units is shorter in Reference Example 1 than in Comparative Example 1. This difference between “the distances (lengths indicated by dashed arrows) between electrode ends facing each other at different angles in a plane” between opening units is presumed to be a cause of the high response speed of the liquid crystal display device of Reference Example 1. The reasons therefor are as follows. 
     Before comparison between the liquid crystal display devices of Reference Example 1 and Comparative Example 1, a conventional FFS mode liquid crystal display device is described.  FIG. 17A  and  FIG. 17B  are views of a conventional FFS mode liquid crystal display device;  FIG. 17A  is a schematic plan view illustrating the alignment of liquid crystal molecules with no voltage applied, and  FIG. 17B  is a schematic plan view illustrating the alignment of the liquid crystal molecules with voltage applied. In the conventional FFS mode liquid crystal display device, the openings  15 R shown in  FIG. 17A  and  FIG. 17B  are formed in the counter electrode  14 R, and a fringe field generated between parallel electrode ends facing each other is used as the driving force to change the alignment of the liquid crystal molecules  31 R.  FIG. 17B  shows that, with voltage applied, the fringe fields generated at the electrode ends in the same direction rotate all the liquid crystal molecules  31 R in the plane in the same direction. 
     Comparative Example 1 is described.  FIG. 18A  and  FIG. 18B  are views of the liquid crystal display device of Comparative Example 1;  FIG. 18A  is a schematic plan view illustrating the alignment of the liquid crystal molecules with no voltage applied, and  FIG. 18B  is a schematic plan view illustrating the alignment of the liquid crystal molecules with voltage applied. In Comparative Example 1, a fringe field generated at “electrode ends facing each other at different angles in a plane” re-aligns the liquid crystal molecules  31 R near the electrode ends by rotating them in the opposite directions between adjacent domains. At the boundary between the adjacent domains, the liquid crystal molecules  31 R do not rotate in the plane due to the torque balance (long-range interaction of liquid crystal molecules). In other words, at the dashed cross portion in  FIG. 18B , re-alignment of the liquid crystal molecules  31 R by the electric field does not occur and thus dark lines (virtual walls) are observed. The virtual walls caused by the long-range interaction balance are important in understanding the mechanism of increasing the response speed. 
     The liquid crystal long-range interaction is described.  FIG. 19  is a schematic plan view illustrating the alignment of liquid crystal molecules with voltage applied in a conventional FFS mode liquid crystal display device.  FIG. 20  is a schematic plan view illustrating liquid crystal correlation lengths using the conventional FFS mode liquid crystal display device.  FIG. 20  is an enlarged view of the region surrounded by the dotted square in  FIG. 19 . 
     In the FFS mode liquid crystal display device, fringe fields generated at the electrode ends re-align liquid crystal molecules. Dielectric torque (also simply referred to as torque) applied to the liquid crystal molecules by the electric fields is at the maximum near the electrode ends, and the deformation amount (amount of in-plane rotation) of the liquid crystal molecules is also at the maximum in the plane. As the alignment of liquid crystal molecules changes at the electrode ends, the alignment of liquid crystal molecules therearound also changes to conform to the changed alignment. This interaction is also referred to as the long-range interaction of liquid crystal molecules. The distance in which the long-range interaction is effective is referred to as the liquid crystal correlation length. 
     As described above, in the FFS mode liquid crystal display device, the alignment change of the liquid crystal molecules  31 R near the electrode ends spreads therearound, causing in-plane alignment change. This re-alignment dynamics of the liquid crystal molecules  31 R shows a viscoelastic behavior, and thus the timing of the alignment change of the liquid crystal molecules  31 R comes later at a position farther from the electrode ends. In other words, the alignment change of the liquid crystal molecules  31 R near the electrode ends causes alignment change of the liquid crystal molecules  31 R far from the electrode ends. Hence, the liquid crystal molecules  31 R farther from the electrode ends start to respond at a later time point and also stop responding at a later time point. 
     The reason why the response speed increases when the counter electrode has the electrode ends facing each other at different angles in a plane is described with Comparative Example 1 taken as an example.  FIG. 21  is a schematic plan view illustrating the alignment of the liquid crystal molecules with voltage applied in the liquid crystal display device of Comparative Example 1.  FIG. 22A  and  FIG. 22B  are views of the liquid crystal display device of Comparative Example 1;  FIG. 22A  is a schematic plan view illustrating the alignment of liquid crystal molecules in the case where the left and right electrode ends are independent of each other, and  FIG. 22B  is a schematic plan view illustrating the alignment of the liquid crystal molecules with both the left and right electrode ends taken into consideration. In other words,  FIG. 22A  is an image showing the liquid crystal correlation length of each of the left and right electrodes alone.  FIG. 22B  shows the alignment of liquid crystal molecules when the liquid crystal correlation length is limited due to an alignment change of liquid crystal molecules at the left electrode end and an alignment change of liquid crystal molecules at a right electrode end.  FIGS. 22A and 22B  are each an enlarged view of the region surrounded by the dotted square in  FIG. 21 . 
     As the distance between the electrode ends is reduced to a distance where the liquid crystal correlation lengths overlap as shown in  FIG. 22A , the alignment change by the long-range interaction is limited at a position that is far from the electrode ends and where the response speed is low as shown in  FIG. 22B . This causes the liquid crystal molecules far from the electrode ends to be irrelevant to the response property, meaning that the response speed is increased. The positions where the alignment change by the long-range interaction is limited are not taken into account for the transmittance either. 
     With the openings  15 R in Comparative Example 1 as shown in  FIG. 22A  and  FIG. 22B , the response speed increasing effect can be achieved in the inside of the opening units. However, as to the outside of the opening units, the distance between the opening units is large, and thus the response speed increasing effect seems to be difficult to achieve. 
       FIG. 23  is a view illustrating the relationship between the shape of a counter electrode and the response speed in a liquid crystal display device. The response time ratios shown in  FIG. 23  are the measured results. The response time is the above-mentioned response time (gray to gray worst response time) from display at a grayscale value of 0 to display at a grayscale value of 128, and the response time ratios are each a ratio relative to the response time of the configuration in Comparative Example 1 as shown in the design ( 1 ) in  FIG. 23 . As described above, in the FFS mode, liquid crystal molecules farther from the electrode ends are relatively slower to respond in a plane. In the case where each opening has the shape as shown in the design ( 1 ) in  FIG. 23 , which is the configuration in Comparative Example 1, virtual walls appear only in the opening units in the counter electrode, and the effect is small in the outside of the opening units. When the distance between the upper and lower openings in the design ( 1 ) is reduced to that in the design ( 2 ), the response speed can be increased. 
     The response speed can be higher than that in the design ( 2 ) when the openings in the design ( 2 ) are connected to each other to form the shape shown in the design ( 3 ). In addition, the response speed can be higher than that in the design ( 3 ) when each narrow portion of the left opening of the openings formed in two lines and one of the wide portions of the right opening are formed side by side in the widthwise direction of the openings so that the openings have the shape as shown in the design ( 4 ), i.e., the shape in the above embodiment. This is because the response of the liquid crystal molecules is slow in the regions (positions near the intersections of the crossed dark lines and those far from the electrode ends) surrounded by the solid or dashed circles in the design ( 3 ). Forming openings as shown in the design ( 4 ) enables reduction of the regions surrounded by the dashed circles in the design ( 3 ), i.e., reduction of the portions where the overlap between the liquid crystal correlation lengths is small. This is presumably why the response speed in the design ( 4 ) is higher than that in the design ( 3 ).