JP2009168924A - Liquid-crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vertical alignment type liquid crystal display device capable of reducing deterioration in picture quality due to disclination. <P>SOLUTION: Pixel electrodes 11 arrayed in a matrix form are formed on a first substrate 10 on the side of a liquid crystal layer 30, and a common electrode 21 is formed on a second substrate 20 on the side of the liquid crystal layer 30; and liquid crystal molecules 31 constituting the liquid crystal layer 30 have negative dielectric constant anisotropy and are aligned substantially vertically in an initially aligned state while being pretilted in a predetermined direction on the whole. The second substrate 20 has a common electrode absent portion 22 which is formed correspondingly to a portion of an edge of the pixel electrode 10 which is orthogonal to the outline of the pixel electrode 11 and where an inward direction of the pixel electrode 11 and a direction indicated by the azimuth angle of the pretilt forms an angle exceeding a predetermined angle. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device that displays an image by controlling the transmittance of incident light. More specifically, the present invention relates to a vertical alignment type liquid crystal display device suitable for use in a light valve of a projection display device or a display unit of various electronic devices.

  Conventionally, a liquid crystal display device capable of displaying a high-quality image has been demanded, and development of a vertical alignment type liquid crystal display device excellent in display quality and responsiveness has been advanced.

  In the vertical alignment type liquid crystal display device, the liquid crystal layer is disposed between two polarizing plates disposed in crossed Nicols. The liquid crystal layer is sandwiched between the first substrate on which the pixel electrode is formed and the second substrate on which the common electrode is formed, and in a state where no electric field is applied to the liquid crystal layer, the liquid crystal molecules are applied to these substrates. It is oriented substantially perpendicularly to it. When an electric field (longitudinal electric field) in the thickness direction of the liquid crystal layer is applied, the liquid crystal molecules constituting the liquid crystal layer are tilted so that the major axis follows the substrate. In addition, when an electric field is applied to the liquid crystal layer, the direction of the polarization axis of one polarizing plate and the director form an angle of about 45 degrees. In the state where no electric field is applied to the liquid crystal layer, the light incident on the incident side polarizing plate reaches the output side polarizing plate with almost no retardation by the liquid crystal layer, and is absorbed by the output side polarizing plate (black). Display state). Therefore, the black display state can be almost equivalent to an ideal crossed Nicol that does not sandwich the liquid crystal layer. On the other hand, when the electric field is applied to the liquid crystal layer, the director makes an angle of approximately 45 degrees with respect to the linearly polarized light transmitted through the polarizing plate on the incident side, so that the liquid crystal layer acts as a half-wave plate. Then, the vibration direction of the linearly polarized light is rotated by 90 degrees. Thereby, the light which has passed through the liquid crystal layer is transmitted through the polarizing plate on the emission side (white display state).

  In the vertical alignment type liquid crystal display device, when the direction in which the liquid crystal molecules are tilted is not uniform in the state in which an electric field is applied to the liquid crystal layer, unevenness of brightness occurs in the displayed image. For this reason, in a state where no electric field is applied to the liquid crystal layer, the liquid crystal molecules are given a so-called pretilt so that the major axis of the liquid crystal molecules is inclined in a predetermined direction and a predetermined angle with respect to the normal direction of the substrate. Must be oriented substantially vertically. Generally, the direction indicated by the azimuth angle of the pretilt (the direction indicated by the azimuth angle of the liquid crystal molecules) is set to a direction in which the transmittance is maximized by a combination with an optical system such as a polarizing plate.

  An alignment film obtained by subjecting a film made of an organic material to a rubbing process is well known as an alignment film that gives a pretilt to liquid crystal molecules. Further, in a liquid crystal display device used in a projection display device irradiated with strong light from a light source, an alignment film made of an inorganic material having excellent light resistance is also used. The alignment film made of an inorganic material can be formed by vapor-depositing an inorganic material such as silicon oxide from an oblique direction with respect to the substrate (see, for example, JP-A-2005-274641 (Patent Document 1)). The pretilt direction and the tilt angle from the normal direction of the substrate are controlled by controlling the rubbing conditions in the case of the former alignment film, and the deposition conditions in the case of the latter alignment film. It is done by controlling.

  In a vertical alignment type liquid crystal display device, when different voltages are applied to adjacent pixel electrodes, an electric field (lateral electric field) in a direction following the substrate surface is generated between the pixel electrode and the adjacent pixel electrode. And the disturbance of the alignment of liquid crystal molecules occurs due to the transverse electric field. Disorders of liquid crystal molecules are generally called disclination.

  In a so-called line inversion driving method, the polarity of the voltage is inverted between odd lines and even lines. For example, if a voltage of 5 volts in absolute value is applied between the common electrode and the pixel electrode in the white display state, a potential difference between the pixel electrode belonging to the odd line and the pixel electrode belonging to the adjacent even line is present. The absolute value of reaches a maximum of 10 volts, and a strong transverse electric field is generated between the pixel electrodes. For this reason, in line inversion driving, disclination occurs along the arrangement of pixel electrodes. In a region where disclination occurs, particularly in a region where the azimuth angles of liquid crystal molecules are not uniform, the light transmittance changes remarkably. Therefore, the uniformity of luminance is impaired and the image quality is deteriorated.

  On the other hand, in the so-called frame inversion drive method, the polarity of the voltage is inverted for each frame. The absolute value of the potential difference between the pixel electrode and the adjacent pixel electrode is half that of line inversion driving in frame inversion driving. Therefore, the degree of disclination can be reduced by employing frame inversion driving.

JP-A-2005-274641

  However, even when frame inversion driving is employed, it is avoided that a strong lateral electric field is generated between the pixel electrode and the adjacent pixel electrode in a portion where the high luminance region and the low luminance region are adjacent to each other. It is not possible. For example, when a white window image is displayed on a black background on a liquid crystal display device, disclination occurs at the boundary portion of the white window, and a line-shaped dark portion or the like may be observed as shown in FIG. is there. If the part where the disclination occurs is shielded from light by a light shielding layer or the like, the influence of the disclination is not substantially a problem. However, the width of the light-shielding layer or the like has to be narrowed by design as the liquid crystal display device is improved in definition and the aperture ratio is improved, and deterioration of image quality due to disclination becomes a problem.

  Accordingly, an object of the present invention is to provide a vertical alignment type liquid crystal display device capable of reducing deterioration in image quality due to disclination.

In order to achieve the above object, a liquid crystal display device of the present invention is arranged between a first substrate, a second substrate disposed opposite to the first substrate, and between the first substrate and the second substrate. A liquid crystal display device comprising a liquid crystal layer,
Pixel electrodes arranged in a matrix are formed on the liquid crystal layer side of the first substrate.
A common electrode is formed on the liquid crystal layer side of the second substrate,
The liquid crystal molecules constituting the liquid crystal layer have a negative dielectric anisotropy, and in the initial alignment state, the liquid crystal molecules are substantially vertically aligned with a pretilt in a predetermined direction as a whole. And
The second substrate includes a common electrode lacking portion, and the common electrode lacking portion has a pretilt azimuth angle that is perpendicular to the contour line of the pixel electrode and toward the inner side of the pixel electrode. It is characterized in that it is formed so as to correspond to a portion that makes an angle exceeding a predetermined angle with the indicated direction.

  The pixel electrodes arranged in a matrix are arranged with an interval between adjacent pixel electrodes. There is a difference between the distribution of the equipotential surface between the pixel electrode and the common electrode and the distribution of the equipotential surface between the interval portion and the common electrode. Thereby, even if the voltage of the same value is applied to the pixel electrode, the electric field at the edge of the pixel electrode and in the vicinity thereof basically goes in a direction inclined with respect to the normal direction of the substrate. More specifically, the electric field at the edge of the pixel electrode and in the vicinity thereof is tilted away from the pixel electrode. The liquid crystal molecules having negative dielectric anisotropy are subjected to a force tilting in a direction perpendicular to the electric field. Accordingly, when a voltage is applied to the pixel electrode itself, the liquid crystal molecules located at the edge of the pixel electrode and in the vicinity thereof have a force in a direction inclined toward the inner side of the pixel electrode (hereinafter referred to as “inward force”). Will be added). When voltages having different values are applied to adjacent pixel electrodes, a horizontal electric field is generated between the pixel electrodes due to a potential difference between the adjacent pixel electrodes, and the liquid crystal molecules are also generated by the horizontal electric field. A force (hereinafter referred to as “force due to a potential difference”) is applied to. The inventors have determined that in a region where the “inward force” tends to turn the direction indicated by the azimuth angle of the liquid crystal molecules in the reverse direction (hereinafter, sometimes referred to as “reverse direction region”), It was noted that the occurrence of disclination becomes more prominent in this region when "" is added in the direction in which the direction indicated by the azimuth angle of the liquid crystal molecules is directed in the opposite direction. In the liquid crystal display device of the present invention, of the edges of the pixel electrode, the direction perpendicular to the contour line of the pixel electrode and toward the inside of the pixel electrode and the direction indicated by the azimuth angle of the pretilt form a predetermined angle. An electric field is formed so as to weaken the “inward force” in the reverse direction region by forming the common electrode lacking portion on the second substrate corresponding to the portion that makes an angle exceeding. Thereby, the force to reverse the azimuth angle of the liquid crystal molecules is reduced, and the degree of disclination can be reduced.

  In the liquid crystal display device of the present invention, the planar shape of the common electrode lacking portion is arbitrary as long as an electric field is formed so as to weaken the “inward force” in the reverse direction region. At least a portion of the common electrode lacking portion may be formed to face the pixel electrode, or all of the common electrode lacking portion may be formed to face the pixel electrode. It is preferable that the common electrode lacking portion is formed into a slit extending corresponding to the contour line of the pixel electrode because an electric field that weakens the “inward force” can be effectively formed in the reverse direction region.

  In the liquid crystal display device of the present invention including the various preferable configurations and forms described above, the planar shape of the pixel electrode can be appropriately set according to the design of the liquid crystal display device. As the planar shape of the pixel electrode, a triangular shape, a rectangular shape, or a hexagonal shape can be exemplified. When the pixel electrode has a polygonal shape, the corner portion may be rounded. From the viewpoint of manufacturing a liquid crystal display device or the like, it is convenient to make the pixel electrode rectangular. The common electrode lacking portion is a portion of the edge portion of the pixel electrode where the direction perpendicular to the contour line of the pixel electrode and inward of the pixel electrode and the direction indicated by the pretilt azimuth angle exceeds 90 degrees. It can be set as the structure formed correspondingly. In this case, the pixel electrode has a rectangular shape, each edge of the pixel electrode extends in a direction intersecting the direction indicated by the azimuth angle of the pretilt, and the common electrode lacking part corresponds to the two edges of the pixel electrode. It can be set as the structure currently formed in the substantially L shape.

  The liquid crystal display device of the present invention may be a monochrome liquid crystal display device or a color liquid crystal display device. Furthermore, a transmissive liquid crystal display device or a reflective liquid crystal display device may be used. Various members and materials constituting the liquid crystal display device can be formed of known members and materials. Examples of switching elements connected to the pixel electrodes include three-terminal elements such as MOS type FETs and thin film transistors (TFTs) formed on a single crystal silicon semiconductor substrate, and two-terminal elements such as MIM elements, varistor elements, and diodes. be able to. The pixel electrode and the common electrode can be formed by a widely known method, and the common electrode lacking portion can also be formed by a widely known method.

  As values of pixels of the liquid crystal display device, VGA (640, 480), S-VGA (800, 600), XGA (1024, 768), APRC (1152, 900), S-XGA (1280, 1024) , U-XGA (1600, 1200), HD-TV (1920, 1080), Q-XGA (2048, 1536), (1920, 1035), (720, 480), (1280, 960), etc. Some of the display resolutions can be exemplified, but are not limited to these values. In the case of a monochrome liquid crystal display device, basically, the same number of pixel electrodes as the number of pixels are formed in a matrix. In the case of a color liquid crystal display device, basically, three times as many pixel electrodes as the number of pixels are formed in a matrix. For example, the pixel electrodes may be arranged in a stripe shape or in a delta shape. The arrangement of the pixel electrodes may be appropriately set according to the design of the liquid crystal display device.

  In the liquid crystal display device of the present invention, of the edges of the pixel electrode, the direction perpendicular to the contour line of the pixel electrode and toward the inside of the pixel electrode and the direction indicated by the azimuth angle of the pretilt form a predetermined angle. An electric field is formed so as to weaken the inward force in the reverse direction region by forming the common electrode lacking portion on the second substrate corresponding to the portion that makes an angle exceeding. As a result, the degree of inversion of the azimuth angle of the liquid crystal molecules is reduced, so that the degree of disclination can be reduced.

  Hereinafter, the present invention will be described based on examples with reference to the drawings.

  FIG. 1 is a conceptual partial end view of a liquid crystal display device 1 of an embodiment. FIG. 2A is a schematic plan view for explaining the arrangement of the pixel electrodes 11 formed on the first substrate 10. FIG. 2B is a schematic plan view for explaining the arrangement of the common electrodes 21 and the like formed on the second substrate 20. First, the configuration and basic operation of the liquid crystal display device 1 according to the embodiment will be described with reference to FIGS. 1 and 2A and 2B.

  The liquid crystal display device 1 of the embodiment is a transmissive liquid crystal display device for monochrome display including, for example, 640 × 480 pixel electrodes 11. As shown in FIG. 1, the liquid crystal display device 1 includes a first substrate 10 made of a glass substrate or the like, a second substrate 20 made of a glass substrate or the like disposed opposite to the first substrate 10, and a first substrate. 10 and a second substrate 20 are provided with a liquid crystal layer 30.

  As shown in FIG. 1 and FIG. 2A, on the liquid crystal layer 30 side of the first substrate 10, for example, ITO (indium oxide-tin) arranged in a matrix with an interval 12 of about 1 μm. A pixel electrode 11 made of is formed. In FIG. 2A, 4 × 3 pixel electrodes 11 are shown in order to simplify the drawing. The size of each pixel electrode 11 is approximately 30 μm × 30 μm. Then, a first alignment film 13 made of, for example, silicon oxide is formed on the entire surface so as to cover the pixel electrode 11 and the like. The first alignment film 13 and the second alignment film 23 described later will be described in detail later. In the embodiment, the first substrate 10 is formed with switching elements such as TFTs connected to the pixel electrodes 11, various wirings such as data lines and scanning lines, various interlayer insulating films, light shielding layers, and the like. However, these are not shown in the drawing. Similarly, in the second substrate 20, illustration of components other than the common electrode 21, the common electrode lacking portion 22, and the second alignment film 23 is omitted.

  As shown in FIG. 1 and FIG. 2B, a common electrode 21 made of ITO or the like is formed on the liquid crystal layer 30 side of the second substrate 20. The second substrate 20 includes a common electrode lacking portion 22. In FIG. 2B, 4 × 3 common electrode lacking portions 22 are shown in order to simplify the drawing as in FIG. The common electrode lacking portion 22 will be described later. A second alignment film 23 made of, for example, silicon oxide is formed on the entire surface so as to cover the common electrode 21 and the like.

  The liquid crystal molecules 31 constituting the liquid crystal layer 30 disposed between the first substrate 10 and the second substrate 20 have a negative dielectric anisotropy, and in the initial alignment state, the liquid crystal molecules as a whole It is substantially vertically aligned with a pretilt applied in a predetermined direction. A spacer (not shown) for defining the thickness of the liquid crystal layer 30 is disposed between the first substrate 10 and the second substrate 20. In the example, the thickness of the liquid crystal layer 30 was set to 2.5 μm by design. Details of the pretilt will be described later.

  FIG. 3A is a schematic cross-sectional view for explaining the state of the liquid crystal molecules 31 in the initial alignment state (in other words, the state when no electric field is applied to the liquid crystal layer 30). FIG. 3B is a schematic plan view for explaining the relationship between the arrangement of the pixel electrodes 11, the alignment directions of the first alignment film 13 and the second alignment film 23, and the liquid crystal molecules 31 in the initial alignment state. FIG. In order to simplify the drawing, the display of the first substrate 10 and the second substrate 20 is omitted in FIG. 3A, and 3 × 3 pixel electrodes 11 are formed in FIG. Illustrated. The same applies to (A) and (B) of FIG. 5 and (A) and (B) of FIG.

  As shown in FIG. 3B, the pixel electrode 11 includes an edge portion 11a and an edge portion 11c that follow the X direction, and an edge portion 11b and an edge portion 11d that follow the Y direction. The first alignment film 13 and the second alignment film 23 are formed so that their alignment regulating directions are antiparallel to each other. Hereinafter, an azimuth angle is considered with the direction extending in the + X direction being 0 degrees and the direction extending in the + Y direction being 90 degrees on the XY plane. The first alignment film 13 is formed by obliquely depositing silicon oxide or the like in a direction having an azimuth angle of 225 degrees, and the second alignment film 23 is formed by obliquely depositing silicon oxide or the like in a direction having an azimuth angle of 45 degrees. Has been. The orientation direction (deposition direction) of the first alignment film 13 is indicated by an arrow with a reference numeral 13A. Similarly, the orientation direction (evaporation direction) of the second alignment film 23 is indicated by an arrow denoted by reference numeral 23A. The liquid crystal molecules 31 constituting the liquid crystal layer 30 are aligned by the first alignment film 13 and the second alignment film 23, and in an initial alignment state where no electric field is applied, the liquid crystal molecules as a whole have a predetermined direction (described later). Thus, the film is substantially vertically aligned in a state where a pretilt is given in a direction of 45 degrees in azimuth.

4A and 4B are schematic diagrams for explaining the elevation angle and the azimuth angle of the liquid crystal molecules 31 to which the pretilt is given. In a state where no electric field is applied to the liquid crystal layer 30, as shown in FIG. 4A, the liquid crystal molecules 31 are at an elevation angle θ _p (usually 83 _{p with} respect to the XY plane). In a range of more than 90 degrees and less than 90 degrees). Further, as shown in FIG. 4B, the azimuth angle θ _d of the liquid crystal molecules 31 is 45 degrees. When an electric field in the vertical direction (thickness direction of the liquid crystal layer 30) is applied to the liquid crystal layer 30, the liquid crystal molecules 31 basically have an azimuth angle θ as shown by broken lines in FIGS. While maintaining _d , the long axis is inclined so as to follow the XY plane.

  In FIG. 1, for example, a first polarizing plate (not shown) is disposed on the opposite side of the first substrate 10 to the liquid crystal layer 30 side so that the polarization axis follows the X direction. It is assumed that a second polarizing plate (not shown) is arranged on the opposite side so that the polarization axis follows the Y direction, and a light source is arranged on the first polarizing plate side. Note that the polarization axis of the first polarizing plate may follow the Y direction, and the polarization axis of the second polarizing plate may follow the X direction. When no electric field is applied to the liquid crystal layer 30, the liquid crystal molecules 31 are aligned in a substantially vertical direction, so that light incident on the first polarizing plate on the light source side hardly undergoes retardation by the liquid crystal layer 30. Without reaching, it reaches the second polarizing plate and is absorbed. Therefore, in principle, it is possible to obtain a black display state almost equivalent to an ideal crossed Nicol that does not sandwich the liquid crystal layer 30. On the other hand, in a state where an electric field is applied to the liquid crystal layer 30, the liquid crystal molecules 31 are tilted so that the major axis follows the XY plane. In addition, the azimuth angle of the liquid crystal molecules is approximately 45 degrees with respect to the linearly polarized light transmitted through the first polarizing plate on the incident side. Accordingly, the liquid crystal layer 30 acts as a half-wave plate and rotates the vibration direction of linearly polarized light by 90 degrees. As a result, the light that has passed through the liquid crystal layer 30 passes through the second polarizing plate and enters a white display state.

  Next, a manufacturing method of the liquid crystal display device 1 will be described. First, a scanning line, a light shielding layer, a transistor composed of a semiconductor layer, an interlayer insulating layer, and the like are appropriately formed on the first substrate 10 by a known method.

  Next, for example, an ITO film is formed and patterned by a known method to form pixel electrodes 11 arranged in a matrix. Thereafter, for example, silicon oxide is deposited from an oblique direction to form the first alignment film 13. Thus, a series of steps relating to the first substrate 10 is completed.

  Further, a black matrix, an interlayer insulating layer, and the like are appropriately formed on the second substrate 20 as necessary by a known method. Thereafter, for example, an ITO film is formed and patterned by a known method to form the common electrode 21 and the common electrode lacking portion 22. Thereafter, for example, silicon oxide is deposited from an oblique direction to form the second alignment film 23. Thus, a series of steps relating to the second substrate 20 is completed.

  And after making the 1st board | substrate 10 and the 2nd board | substrate 20 which passed the said process oppose and encapsulating liquid crystal material in the meantime, the circumference | surroundings are sealed and the liquid crystal display device 1 can be completed. Thereafter, the first polarizing plate may be attached to the first substrate 10 side and the second polarizing plate may be attached to the second substrate 20 side as necessary, and connection with an external circuit, attachment of a backlight, or the like may be performed.

  Next, the operation of the liquid crystal display device 2 of the comparative example in which the common electrode lacking portion 22 is not formed will be described with reference to FIGS. The liquid crystal display device 2 of the comparative example is different from the liquid crystal display device 1 of the embodiment only in that the common electrode lacking portion 22 is not formed. FIG. 5A shows a case where a constant voltage (for example, 0 volt) is applied to the common electrode 21 and the same voltage (for example, 5 volt) is applied to each pixel electrode 11 in the liquid crystal display device 2 of the comparative example. 2 is a schematic cross-sectional view for explaining the state of liquid crystal molecules 31. FIG. FIG. 5B is a schematic plan view for explaining the relationship between the arrangement of the pixel electrodes 11, the alignment directions of the first alignment film 13 and the second alignment film 23, and the liquid crystal molecules 31.

  The pixel electrodes 11 arranged in a matrix are arranged with an interval 12 between adjacent pixel electrodes 11. There is a difference between the distribution of the equipotential surface between the pixel electrode 11 and the common electrode 21 and the distribution of the equipotential surface between the interval 12 and the common electrode 21. As a result, the pixel electrode 11 and the common electrode 21 The electric field formed between them is curved at the edges 11a, 11b, 11c, 11d of the pixel electrode 11 and in the vicinity thereof. In FIG. 5A, the electric field at the center of the pixel electrode 11 is schematically indicated by reference numeral 41, the electric field at the edge 11b and its vicinity is indicated by reference numeral 41b, and the edge 11d and The state of the electric field in the vicinity is schematically indicated by reference numeral 41d. In addition, illustration of the electric field regarding the edge part 11a and the edge part 11c was abbreviate | omitted.

  As described above, the electric fields near the edges 11a, 11b, 11c, and 11d of the pixel electrode 11 and the vicinity thereof are inclined in the direction inclined with respect to the normal direction of the first substrate 10 (= the normal direction of the pixel electrode 11). More specifically, it tilts away from the pixel electrode 11 like an electric field 41b or 41d shown in FIG. Here, the liquid crystal molecules 31 constituting the liquid crystal layer 30 have negative dielectric anisotropy. For this reason, the edges 11a, 11b, 11c, 11d of the pixel electrode 11 and the liquid crystal molecules 31 located in the vicinity thereof receive a force in a direction in which they are inclined toward the inside of the pixel electrode. In this way, by applying a voltage to the pixel electrode 11 itself, the liquid crystal molecules 31 located at the edge of the pixel electrode 11 and in the vicinity thereof have a force (hereinafter referred to as “inclination”) toward the inner side of the pixel electrode 11. (Referred to as “inward force”).

FIG. 6A is a diagram schematically showing the direction of “inward force” at the edge of the pixel electrode 11 and in the vicinity thereof. Edge 11a of the pixel electrode 11, "inward force" and 11b are, (in other words, X-Y-direction of the azimuth angle of substantially 45 degrees in the plane) direction to follow the azimuth theta _d of the liquid crystal molecules 31 while containing component, the edge portion 11c of the pixel electrode 11, "inward force" is the 11d, in other words a direction (for inverting the azimuth angle theta _d of the liquid crystal molecules 31, substantially on the X-Y plane 225 Azimuth angle direction) component. Accordingly, as shown in FIG. 5B, at the edges 11c and 11d of the pixel electrode 11 and in the vicinity thereof, a force is applied in the direction in which the azimuth angle of the liquid crystal molecules 31 is reversed by the “inward force”. Join. Accordingly, disclination tends to be more conspicuous than the edges 11a and 11b.

Therefore, in the liquid crystal display device 1 according to the embodiment, the second substrate 20 includes the common electrode lacking portion 22, and the common electrode lacking portion 22 is the edge of the pixel electrode 11 in the pixel electrode 11. and a structure in which the direction indicated orthogonal and azimuth theta _d direction and pretilt toward the inside of the pixel electrode 11 in the contour line is formed corresponding to a portion at an angle exceeding a predetermined angle. FIG. 6B is a schematic plan view for explaining the relationship between the common electrode missing portion 22 formed on the second substrate 20 and the edge of the pixel electrode 11.

  As shown in FIG. 6B, at least a part of the common electrode lacking portion 22 is formed to face the pixel electrode 11. The common electrode lacking portion 22 has a slit shape extending corresponding to the contour line of the pixel electrode 11.

Common electrode Lack unit 22, among the edges of the pixel electrode 11, and the direction indicated by the azimuth angle theta _d direction and pretilt inwardly directed orthogonally and pixel electrodes 11 in the contour of the pixel electrode 11 is 90 degrees It is formed so as to correspond to the part that makes an angle exceeding. More specifically, the pixel electrode 11 has a rectangular shape, and each edge portion of the pixel electrode 11 extends in a direction intersecting the direction indicated by the azimuth angle θ _{d of the} pretilt, and the common electrode lacking portion 22 is formed of the pixel electrode. 11 are formed in a substantially L shape corresponding to the two edges 11c and 11d.

  With reference to FIGS. 7A and 7B, the operation of the liquid crystal display device 1 of the embodiment in which the common electrode lacking portion 22 is formed will be described. Similar to FIG. 5A, in FIG. 7A, as in FIG. 5A, a constant voltage (for example, 0 volts) is applied to the common electrode 21, and each pixel electrode 11 is identical. FIG. 5 is a schematic cross-sectional view for explaining the inclination of liquid crystal molecules 31 when a voltage (for example, 5 volts) is applied. 7B shows the relationship between the arrangement of the pixel electrodes 11, the alignment directions of the first alignment film 13 and the second alignment film 23, and the tilt of the liquid crystal molecules 31, as in FIG. It is a typical top view for demonstrating.

  Since the common electrode lacking portion 22 is formed corresponding to the edges 11 c and 11 d of the pixel electrode 11, the electric field formed between the pixel electrode 11 and the common electrode 21 is particularly the edge 11 c of the pixel electrode 11. , 11d and in the vicinity thereof. That is, there is a difference in equipotential surface distribution between the portion where the common electrode 21 is formed and the portion where the common electrode lacking portion 22 is formed, and as a result, the pixel electrode 11 and the common electrode 21 are formed. The applied electric field is curved in the direction toward the inside of the pixel electrode 11 at the edges 11 c and 11 d of the pixel electrode 11 and in the vicinity thereof. In FIG. 7A, the electric field at the center of the pixel electrode 11 is schematically indicated by reference numeral 42, the electric field at the edge 11b and its vicinity is schematically indicated by reference numeral 42b, and the edge 11d and its edge The state of the electric field in the vicinity is schematically indicated by reference numeral 42d. In addition, illustration of the electric field regarding the edge part 11a and the edge part 11c was abbreviate | omitted.

  In the liquid crystal display device 1 of the embodiment, the edges 11c and 11d of the pixel electrode 11 and the electric field in the vicinity thereof are curved in the direction toward the inside of the pixel electrode 11 by providing the common electrode lacking portion 22. To change. Accordingly, the “inward force” becomes weak at the edges 11c and 11d of the pixel electrode 11 and in the vicinity thereof (in some cases, the direction of the force is also reversed). This reduces the degree of disclination at the edges 11a and 11b and in the vicinity thereof.

  6B and 7A, it has been described that a part of the common electrode lacking portion 22 faces the pixel electrode 11, but the present invention is not limited to this. Although depending on the design of the liquid crystal display device, for example, as illustrated in FIG. 8, the common electrode lacking portion 22 may be configured to face the pixel electrode 11.

  With reference to FIGS. 9A and 9B, the disclination reducing effect will be described. FIG. 9A shows a line-shaped dark portion due to disclination generated at a boundary portion of a white window when a white window is displayed on a black background in the liquid crystal display device. The liquid crystal display device is driven by frame inversion, and the potential difference between the pixel electrode 11 and the common electrode 21 is 0 volt at the black background portion and 5 volt at the white window portion.

FIG. 9B is a schematic diagram for explaining a method for evaluating a line-shaped dark portion. The luminance on the AA line crossing the center of the pixel at the boundary of the white window was obtained and normalized with the luminance at the center of the pixel as a reference value. The vertical axis is normalized luminance, the horizontal axis is the position on the AA line, and the change in luminance is graphed. A position P ₁ where the luminance is reduced to 0.5 is obtained, and the distance L from the position P ₁ to the end of the pixel is obtained. ₂ was sought. The degree of the line-shaped dark portion was evaluated based on the ratio of the distance L _{2 to} the pixel width L ₁ (about 30 μm), that is, the magnitude of the value of L ₂ / L ₁ . In the liquid crystal display device in which the common electrode lacking portion 22 is not formed, the value of L ₂ / L ₁ was about 0.21.

10A and 10B are schematic diagrams for explaining the relationship between the pixel electrode 11 and the common electrode lacking portion 22 in the liquid crystal display device used when confirming the effect of reducing disclination. It is a top view. A liquid crystal display device in which the common electrode lacking portion 22 was formed as shown in FIGS. 10A and 10B was prepared, and the degree of the line-shaped dark portion was evaluated based on the above evaluation method. Note that the widths W ₁ and W ₂ of the common electrode lacking portion 22 in FIGS. 10A and 10B are both 1 μm.

In FIG. 10A, the common electrode lacking portion 22 is formed so as to oppose the edge portions 11c and 11d of the pixel electrode with a width of about 0.5 μm. In the liquid crystal display device having this configuration, the value of L ₂ / L ₁ was about 0.18. In FIG. 10B, distances D ₁ and D ₂ from the center of the interval 12 between the pixel electrode 11 and the adjacent pixel electrode 11 to the center of the common electrode lacking portion 22 are set to about 3 μm. In the liquid crystal display device having this configuration, the value of L ₂ / L ₁ was about 0.17, and it was confirmed that the degree of the line-shaped dark portion was all reduced.

  As mentioned above, although this invention was demonstrated based on the preferable Example, this invention is not limited to these Examples. The configurations and structures of the liquid crystal display devices described in the embodiments are examples and can be changed as appropriate.

  For example, in a region occupied by one pixel electrode, in a liquid crystal display device having a configuration in which the initial alignment state of liquid crystal molecules is different between a portion of one region and a portion of another region, the direction of the pretilt in each region portion The location where the common electrode lacking portion is provided may be determined based on the above.

FIG. 1 is a conceptual partial end view of a liquid crystal display device according to an embodiment. FIG. 2A is a schematic plan view for explaining the arrangement of the pixel electrodes formed on the first substrate. FIG. 2B is a schematic plan view for explaining the arrangement of common electrodes and the like formed on the second substrate. FIG. 3A is a schematic cross-sectional view for explaining the state of liquid crystal molecules in the initial alignment state. FIG. 3B is a schematic plan view for explaining the relationship between the arrangement of the pixel electrodes, the alignment directions of the first alignment film and the second alignment film, and the liquid crystal molecules in the initial alignment state. 4A and 4B are schematic diagrams for explaining the elevation angle and azimuth angle of liquid crystal molecules given a pretilt. FIG. 5A shows a liquid crystal when a constant voltage (for example, 0 volt) is applied to the common electrode and the same voltage (for example, 5 volt) is applied to each pixel electrode in the liquid crystal display device of the comparative example. It is typical sectional drawing for demonstrating the state of a molecule | numerator. FIG. 5B is a schematic plan view for explaining the relationship between the arrangement of the pixel electrodes, the alignment directions of the first alignment film and the second alignment film, and the liquid crystal molecules. FIG. 6A is a diagram schematically showing the direction of “inward force” at the edge of the pixel electrode. FIG. 6B is a schematic plan view for explaining the relationship between the common electrode missing portion formed on the second substrate and the edge of the pixel electrode. FIG. 7A shows a case where a constant voltage (for example, 0 volt) is applied to the common electrode and the same voltage (for example, 5 volt) is applied to each pixel electrode, as in FIG. FIG. 3 is a schematic cross-sectional view for explaining the inclination of liquid crystal molecules. FIG. 7B is a diagram for explaining the relationship between the arrangement of the pixel electrodes, the alignment directions of the first alignment film and the second alignment film, and the tilt of the liquid crystal molecules, as in FIG. 5B. It is a typical top view. FIG. 8 is a schematic plan view for explaining a configuration in which all of the common electrode lacking portion faces the pixel electrode. FIG. 9A shows a line-shaped dark portion due to disclination generated at a boundary portion of a white window when a white window is displayed on a black background in the liquid crystal display device. FIG. 9B is a schematic diagram for explaining a method for evaluating a line-shaped dark portion. FIGS. 10A and 10B are schematic plan views for explaining the relationship between the pixel electrode and the common electrode missing portion in the liquid crystal display device used for confirming the reduction effect of disclination. It is.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... 1st board | substrate, 11 ... Pixel electrode, 11a, 11b, 11c, 11d ... Edge of pixel electrode, 12 ... Space | interval, 13 ... 1st alignment film, 20 ... Substrate, 21 ... common electrode, 22 ... common electrode lacking portion, 23 ... second alignment film, 30 ... liquid crystal layer, 31 ... liquid crystal molecule, 41, 41b, 41d, 42, 42b 42d ... Electric field

Claims (5)

A liquid crystal display device comprising a first substrate, a second substrate disposed opposite to the first substrate, and a liquid crystal layer disposed between the first substrate and the second substrate,
Pixel electrodes arranged in a matrix are formed on the liquid crystal layer side of the first substrate.
A common electrode is formed on the liquid crystal layer side of the second substrate,
The liquid crystal molecules constituting the liquid crystal layer have a negative dielectric anisotropy, and in the initial alignment state, the liquid crystal molecules are substantially vertically aligned with a pretilt applied in a predetermined direction as a whole. And
The second substrate includes a common electrode lacking portion, and the common electrode lacking portion has a pretilt azimuth angle in a direction perpendicular to the contour line of the pixel electrode and toward the inside of the pixel electrode. A liquid crystal display device, characterized in that the liquid crystal display device is formed so as to correspond to a portion where the direction shown is an angle exceeding a predetermined angle.   The liquid crystal display device according to claim 1, wherein at least a part of the common electrode lacking portion is formed to face the pixel electrode.   The liquid crystal display device according to claim 1, wherein the common electrode lacking portion has a slit shape extending corresponding to the contour line of the pixel electrode.   The common electrode lacking portion is a portion of the edge portion of the pixel electrode where the direction perpendicular to the contour line of the pixel electrode and inward of the pixel electrode and the direction indicated by the pretilt azimuth angle exceeds 90 degrees. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is formed correspondingly.   The pixel electrode has a rectangular shape, each edge of the pixel electrode extends in a direction intersecting with the direction indicated by the azimuth angle of the pretilt, and the common electrode lacking portion is substantially L-shaped corresponding to the two edges of the pixel electrode. The liquid crystal display device according to claim 4, wherein the liquid crystal display device is formed in a shape.