JP4636057B2 - Liquid crystal display device, manufacturing method thereof, and driving method thereof - Google Patents

Description

  The present invention relates to a liquid crystal display device, a manufacturing method thereof, and a driving method thereof, and more particularly to a liquid crystal display device that is easy to manufacture and used as a display device having excellent viewing angle characteristics, a manufacturing method thereof, and a driving method thereof.

  The liquid crystal display device according to the present invention is a personal computer monitor, FA monitor, home TV, terminal monitor in hospitals, libraries, museums, etc., monitors in air traffic control towers, newspaper browsing, browsing in each office, etc. It is used for monitors for personal use, personal monitors at schools and private schools, terminal monitors for personal use of various media, and monitors at entertainment facilities such as pachinko. It can also be used for a light valve for a liquid crystal projector.

  In a twisted nematic (hereinafter abbreviated as “TN”) type liquid crystal display device that has been widely used, a “white” display state in which liquid crystal molecules are parallel to the substrate surface when no voltage is applied. Accordingly, the liquid crystal molecules change the orientation vector direction in the electric field direction in accordance with the applied voltage, so that the “white” display state gradually becomes “black” display. However, there is a problem that the viewing angle of the TN liquid crystal display device is narrow due to the specific behavior of the liquid crystal molecules to which voltage is applied. This problem of narrow viewing angle is particularly remarkable in the rising direction of liquid crystal molecules in halftone display.

  As a method for improving the viewing angle characteristics of a liquid crystal display device, a technique disclosed in Patent Literatures 1-3 has been proposed. In these techniques, as shown in FIGS. 15A, 15B, and 15C, an upper substrate in which a common electrode 502 having a slit 517 and an alignment film 503 are stacked on a color filter substrate 501 and a substrate 507 are provided. A liquid crystal cell 508 that is homeotropically aligned is sandwiched between the lower substrate on which the pixel electrode 504 and the alignment film 503 are stacked, and is sandwiched between two polarizing plates that are installed so that the polarization axes are orthogonal to each other. The slit 517 generates an oblique electric field in each pixel, whereby each pixel has two or more liquid crystal domains to improve viewing angle characteristics. There are various slits 517 such as a rectangular shape as shown in (b) and an x-shape as shown in (c).

  In Patent Document 1, in particular, high contrast is realized by controlling the direction in which the liquid crystal tilts when a voltage is applied. Further, as described in Patent Document 2, an optical compensator is used as necessary to improve the black viewing angle characteristics.

  Furthermore, in Patent Document 2, not only a homeotropically aligned liquid crystal cell but also a TN aligned cell, each pixel is divided into two or more domains by an oblique electric field to improve viewing angle characteristics.

  Further, in Patent Document 3, in order to prevent the effect of the oblique electric field generated by the common electrode having the opening from being affected by the electric field from the thin film transistor, the gate line, and the drain line, the thin film transistor, the gate line, and the drain line are provided. It is described that it is disposed below the display electrode.

  Further, in Patent Document 4, in a liquid crystal display device in which two or more kinds of micro regions coexist in a liquid crystal layer, one substrate has an opening, a second electrode is provided in the opening, and the second electrode A technique for generating an oblique electric field by applying a voltage to the liquid crystal, dividing the alignment direction of the liquid crystal in the pixel, and widening the viewing angle has been described mainly for TN-oriented cells.

  Further, in Patent Document 5, in order to rotate liquid crystal molecules while maintaining a horizontal direction with respect to the substrate, both electrodes are provided on one substrate, and a voltage is applied between the two electrodes to An In-Plane-Switching (IPS) type liquid crystal display device that generates a horizontal electric field has been proposed. In this method, the major axis of liquid crystal molecules does not rise with respect to the substrate when a voltage is applied. For this reason, the change in the birefringence of the liquid crystal when the viewing angle direction is changed is small and the viewing angle is wide.

  Furthermore, Journal of Applied Physics, Vol. 45, no. 12 (1974) 5466, or in Patent Document 6, a liquid crystal having positive dielectric anisotropy is homeotropically aligned in addition to the IPS mode described above, and the liquid crystal molecules are horizontally aligned with the substrate by an electric field in the horizontal direction. The method of defeating is described. At this time, liquid crystal molecules that are homeotropically aligned due to the direction of the electric field are divided into two or more regions having different directions of inclination, resulting in a liquid crystal display device having a wide viewing angle.

  In Patent Document 7, a square wall is formed using a photosensitive substance, a pixel is formed with this structure as a basic unit, and a liquid crystal having a negative dielectric anisotropy is divided in each pixel by applying a voltage. It is proposed to defeat it.

JP-A-4-261522 JP-A-6-43461 Japanese Patent Laid-Open No. 10-333180 Japanese Patent Laid-Open No. 10-20323 Japanese National Patent Publication No. 5-505247 JP-A-10-186351 Japanese Patent Laid-Open No. 10-186330

  However, in the above-described technique having the slits in the common electrode, a “microfabrication process such as a photoresist process for the common electrode 502” which is not required in the manufacturing process of a normal TN type liquid crystal display device is required. There is a problem that an advanced bonding technique for the upper and lower substrates 501 and 507 is required. This problem is particularly serious in the case of an active matrix liquid crystal display device using a switching element such as a TFT.

  That is, in a normal active matrix liquid crystal display device, an active element such as a thin film diode is manufactured on one transparent substrate, and therefore, a fine processing step such as a photoresist process is required. In other substrates, which are usually called “common electrodes”, it is not necessary to perform microfabrication, and only electrodes are formed on the entire surface.

  However, in the prior art, a “common electrode” that normally does not require microfabrication requires a microfabrication process such as a photoresist process, which increases the number of processes and increases the height of the upper and lower substrates 501 and 507. Therefore, a proper bonding technique is required.

  Further, as described in Japanese Patent Application Laid-Open No. 10-333180, when the thin film transistor, the gate line, and the drain line are arranged below the display electrode, there is a problem that the aperture ratio is lowered.

  Further, in the technique described in Patent Document 4: Japanese Patent Laid-Open No. 10-20323, there is a problem that special driving is required to apply a voltage to the second electrode during driving, and further, the orientation is divided. In addition, there is a problem that a step of applying a voltage to the second electrode is required.

  In addition, in the IPS system and the system in which vertically aligned liquid crystal is tilted by a lateral electric field, there are problems that the aperture ratio is lowered and that the drive voltage is increased if the cell gap is reduced for speeding up.

  In the IPS method and the method in which vertically aligned liquid crystal is driven by a lateral electric field, a color filter layer is conventionally disposed between the layer on which the liquid crystal is disposed and the counter substrate. When the switching element is formed in the above, the electric field formed by applying a potential between the source electrode and the common electrode drawn out affects the color filter layer and deteriorates the display characteristics. was there.

  That is, since the dye constituting the color filter layer contains sodium ions or the like as impurities, when an electric field is applied to the color filter layer, charges are accumulated therein and are charged up. When the color filter layer is charged up, an unnecessary electric field is always applied to the liquid crystal below the portion, and there is a problem that the display characteristics are particularly affected as color unevenness.

  Further, in the method of creating a wall disclosed in Patent Document 7: Japanese Patent Laid-Open No. 10-186330, it is necessary to create a wall using photolithography in order to perform alignment division of liquid crystal, which also increases the number of processes. There was a problem of doing.

  The present invention has been made in view of the above-mentioned problems, and without increasing the problems of the conventional techniques as described above, i.e., complicated processes such as a photoresist process, or requiring advanced bonding techniques. An object of the present invention is to provide a liquid crystal display device with excellent contrast and viewing angle characteristics. In particular, an object of the liquid crystal display device is to suppress the occurrence of color unevenness.

  Another object of the present invention is to provide a method of manufacturing a liquid crystal display device that can easily manufacture such a liquid crystal display device. Another object of the present invention is to provide a driving method that effectively utilizes the viewing angle characteristics of the liquid crystal display device of the present invention.

  In order to achieve the above object, a liquid crystal display device according to the present invention includes a liquid crystal layer sandwiched between a first substrate and a second substrate, and a common electrode on the first substrate and a second substrate. In a liquid crystal display device having a structure in which a voltage is applied between pixel electrodes, a liquid crystal layer is composed of a liquid crystal having a negative dielectric anisotropy, and is applied to the first substrate and the second substrate when no voltage is applied. The pixel electrode has a smaller area than the common electrode and is covered with the common electrode, and a plurality of electrodes having a good symmetry are connected. The electrodes having good symmetry adjacent to each other are connected to each other through at least one connection portion.

  According to the invention having such a configuration, the electric field when driving by applying a voltage between the common electrode and the pixel electrode is inclined with respect to the substrate, and the orientation of the liquid crystal in one pixel is naturally a plurality of regions. The viewing angle can be widened. Further, since the common electrode may be the same as the conventional one, the number of steps does not increase and no special technique is required.

  The liquid crystal display device according to the present invention is a liquid crystal display device according to the present invention in which three electrodes having a good symmetry are connected. According to the invention having such a configuration, even with a rectangular pixel, by using a pixel electrode having such a shape, the orientation of the liquid crystal in one pixel is naturally divided into a plurality of regions, and a wide viewing angle is obtained. Can be planned.

  The liquid crystal display device of the present invention is a liquid crystal display device characterized in that the shape having good symmetry is a circle or a regular polygon. According to the invention having such a configuration, by forming the pixel electrode with a good symmetry, the electric field when driving by applying a voltage between the common electrode and the pixel electrode is oblique with good symmetry with respect to the substrate. Thus, the orientation of the liquid crystal in one pixel is naturally divided into a plurality of regions, and a wide viewing angle can be achieved.

  The liquid crystal display device of the present invention is a liquid crystal display device characterized in that the common electrode is provided on substantially the entire surface of the first substrate. According to the invention having such a configuration, since it is not necessary to pattern the common electrode, complicated processes such as photoresist are not increased.

  The liquid crystal display device of the present invention is a liquid crystal display device in which the pixel electrode has a radial notch or protrusion from the center of a shape having good symmetry. According to the invention having such a configuration, it is possible to ensure the division position of the alignment of the liquid crystal and widen the viewing angle.

  The liquid crystal display device according to the present invention is a liquid crystal display device in which the pixel electrode has an electrodeless portion in which a radial electrode from the center of the shape having good symmetry toward the periphery is not formed. According to the invention having such a configuration, it is possible to ensure the division position of the alignment of the liquid crystal and widen the viewing angle.

  The liquid crystal display device of the present invention is a liquid crystal display device in which the pixel electrode has a radial concave portion from the center of the shape having good symmetry toward the periphery. According to the invention having such a configuration, it is possible to ensure the division position of the alignment of the liquid crystal and widen the viewing angle.

  The liquid crystal display device of the present invention is characterized in that the recess is formed in an interlayer insulating film or an overcoat layer. According to the invention having such a configuration, the concave portion can be formed deeply without complicating the manufacturing process, the liquid crystal can be more reliably fixed at the boundary portion, and a wide viewing angle can be achieved.

  In the liquid crystal display device of the present invention, the liquid crystal layer is formed by disposing at least one of an optically negative compensation film and an optically positive compensation film between the first or second substrate and the polarizing plate. A liquid crystal display device characterized in that the refractive index anisotropy of the compensation film is isotropic. According to the invention having such a configuration, the retardation of the liquid crystal when no voltage is applied is canceled, and excellent viewing angle characteristics can be obtained.

  The liquid crystal display device of the present invention has quarter-wave plates on both sides of the liquid crystal layer, and the optical axes of the quarter-wave plates are orthogonal to each other. It is. According to the invention having such a configuration, it is possible to effectively prevent a decrease in brightness in a transition region in which the direction in which the liquid crystal falls after applying a voltage is different.

  The liquid crystal display device of the present invention is a liquid crystal display device characterized in that the liquid crystal material contains a chiral agent.

  The liquid crystal display device driving method of the present invention is a liquid crystal display device driving method characterized by applying positive and negative voltages to each other in adjacent pixels of the liquid crystal display device. According to such an invention, the wide viewing angle can be surely widened even if the pixel is fine.

  The liquid crystal display device driving method of the present invention is a liquid crystal display device driving method characterized in that the liquid crystal display of the liquid crystal display device is returned to a black state before one frame is completed. According to such an invention, the cut in moving image display can be improved and the apparent response speed can be increased.

  The liquid crystal display device driving method of the present invention is characterized in that a voltage substantially equal to the threshold voltage of the liquid crystal is applied to the liquid crystal display device before one frame starts. It is. According to such an invention, especially when the pixel is large, the direction in which the liquid crystal is tilted is defined in advance, so that the time to settle in the divided state is shortened, and the response speed can be shortened.

  The liquid crystal display device of the present invention may have a configuration having a shield electrode around the pixel electrode. According to the invention having such a configuration, the influence of the electric field from the video signal line and the scanning signal line can be prevented, and a high-contrast liquid crystal display device can be obtained.

  The liquid crystal display device of the present invention has a common electrode for applying a reference potential across a plurality of pixels on the first substrate, and a plurality of scanning signal electrodes and a matrix on them on the second substrate. A plurality of video signal electrodes intersecting each other and a plurality of thin film transistors formed corresponding to respective intersections of these electrodes, and each region surrounded by the plurality of scanning signal electrodes and video signal electrodes At least one pixel is configured and has a pixel electrode connected to a thin film transistor corresponding to each pixel, and the pixel electrode, the scanning electrode, the video signal electrode, and the thin film transistor are separated via an interlayer insulating film It can be set as the structure currently made.

  According to the invention having such a configuration, a thin film transistor-driven liquid crystal display device having a wide viewing angle and a high contrast can be obtained.

  In the liquid crystal display device of the present invention, in the liquid crystal display device, a common electrode for applying a reference potential to a plurality of pixels is provided on the first substrate, and a plurality of scanning signals are provided on the second substrate. An electrode, a plurality of video signal electrodes intersecting with each other in a matrix, and a plurality of thin film transistors formed corresponding to respective intersections of these electrodes, and the plurality of scanning signal electrodes and video signal electrodes At least one pixel is formed in each surrounded region, and has a pixel electrode connected to a thin film transistor corresponding to each pixel, and the pixel electrode, the scan electrode, the video signal electrode, and the thin film transistor are interlayer A part of the pixel electrode or a seal is formed on at least one of the scanning signal electrode and the video signal electrode and separated by an insulating film May be configured to electrodes of use is located.

  According to the invention having such a configuration, the influence of the electric field from the video signal line and the scanning signal line can be prevented, and a high contrast thin film transistor driving liquid crystal display device can be obtained.

  The liquid crystal display device of the present invention includes the transparent first substrate, the second substrate, a liquid crystal layer sandwiched therebetween, and a color filter layer in the liquid crystal display device, wherein the color filter layer is The liquid crystal layer is disposed on the second substrate, the liquid crystal layer is disposed between the color filter layer and the first substrate, and a plurality of scanning signal electrodes and the second substrate under the color filter layer are disposed on the second substrate. A plurality of video signal electrodes intersecting with each other in a matrix and a plurality of thin film transistors formed corresponding to the intersections of these electrodes, and are surrounded by the plurality of scanning signal electrodes and the video signal electrodes Each region includes at least one pixel, and a pixel electrode connected to a thin film transistor corresponding to each pixel, and includes a plurality of pixels on the first substrate. A common electrode to provide a reference potential, the pixel electrode may be a structure which is disposed between the liquid crystal layer and the color filter layer.

  According to the invention having such a configuration, the color filter layer can be reliably prevented from being charged up, and a thin film transistor-driven liquid crystal display device having good display characteristics can be obtained.

  The liquid crystal display device of the present invention includes the first transparent substrate, the second substrate, a liquid crystal layer sandwiched therebetween, and a color filter layer in the liquid crystal display device, wherein the color filter layer is The liquid crystal layer is disposed on the second substrate, the liquid crystal layer is disposed between the color filter layer and the first substrate, and a plurality of scanning signal electrodes are disposed on the second substrate below the color filter layer. And a plurality of video signal electrodes intersecting with each other in a matrix, and a plurality of thin film transistors formed corresponding to respective intersections of these electrodes, and surrounded by the plurality of scanning signal electrodes and the video signal electrodes Each region includes at least one pixel and a pixel electrode connected to a thin film transistor corresponding to each pixel, and a plurality of pixels are provided on the first substrate. The pixel electrode is disposed between the color filter layer and the liquid crystal layer, and the pixel electrode is disposed on at least one of the scan electrode and the video signal electrode. It is possible to adopt a configuration in which a part of the electrode or a shielding electrode is arranged.

  According to the invention having such a configuration, the color filter layer can be reliably prevented from being charged up, and the influence of the electric field from the video signal line or the scanning signal line can be prevented, and the thin film transistor driving liquid crystal display device having good display characteristics. It can be.

  The liquid crystal display device of the present invention may be configured such that the liquid crystal includes a high molecular organic compound in the above liquid crystal display device. According to the invention having such a configuration, it is possible to give the pretilt angle according to the divided shape and to ensure the control of the initial orientation.

  The liquid crystal display device of the present invention is the above-described liquid crystal display device, wherein the liquid crystal layer is composed of a liquid crystal having a negative dielectric anisotropy, and the first substrate and the second substrate are not applied when no voltage is applied. Thus, the structure can be oriented substantially vertically. According to the invention having such a configuration, a liquid crystal display device having a wide viewing angle characteristic can be obtained without special treatment of the alignment film.

  The liquid crystal display device may be configured such that in the liquid crystal display device, a pretilt angle is formed in advance along a direction in which the liquid crystal is tilted when a voltage is applied. According to the invention having such a configuration, the control of the initial orientation can be ensured by controlling the pretilt angle according to the divided shape.

  In the liquid crystal display device of the present invention, in the liquid crystal display device described above, the liquid crystal layer may be configured by a liquid crystal having positive dielectric anisotropy and having a twisted nematic structure when no voltage is applied. According to the invention having such a configuration, the liquid crystal is naturally divided into portions having different twist directions and rising directions by the rubbing treatment of the alignment film, so that a liquid crystal display device having a wide viewing angle characteristic is obtained.

  In the liquid crystal display device of the present invention, in the liquid crystal display device described above, a plurality of minute regions having different twist directions and rising directions of liquid crystal molecules can coexist in the liquid crystal layer in each pixel. According to the invention having such a configuration, a liquid crystal display device having a wide viewing angle characteristic is obtained.

  In the liquid crystal display device of the present invention, in the liquid crystal display device described above, the liquid crystal layer may be composed of a liquid crystal having a positive dielectric anisotropy and have a homogeneous structure when no voltage is applied. According to the invention having such a configuration, the alignment direction of the liquid crystal can be defined by rubbing the alignment film, and the liquid crystal display device having a wide viewing angle characteristic can be obtained.

  In the liquid crystal display device of the present invention, in the liquid crystal display device described above, two types of micro regions having different rising directions of liquid crystal molecules coexist in the liquid crystal layer in each pixel. According to the invention having such a configuration, a liquid crystal display device having a wide viewing angle characteristic is obtained.

  The liquid crystal display device of the present invention may be configured such that, in the liquid crystal display device, a pretilt angle of the liquid crystal layer with respect to the first substrate and the second substrate is 1 ° or less. According to the invention having such a configuration, the direction in which the liquid crystal rises in the liquid crystal having a positive dielectric anisotropy can be set to an equal probability, so that the alignment division can be made accurate.

  The liquid crystal display device of the present invention can be configured such that, in the above-described liquid crystal display device, when a voltage substantially equal to the threshold voltage of the liquid crystal is applied, a portion that leaks light is shielded. According to the invention having such a configuration, even when a voltage equal to or higher than the threshold value is applied, it is possible to prevent a decrease in contrast due to a phenomenon such as light leakage or a change in the amount of transmitted light.

  According to the method for manufacturing a liquid crystal display device of the present invention, a liquid crystal composition containing a liquid crystal and a monomer and / or oligomer is covered with the first substrate having a common electrode, the area smaller than the common electrode, and the common electrode. And an injecting step of injecting between the second substrates having pixel electrodes with good symmetry and a polymerization step of polymerizing the monomer and / or oligomer.

  According to such a manufacturing method, the alignment of the liquid crystal in one pixel is naturally divided into a plurality of regions, and a liquid crystal display device with a wide viewing angle can be manufactured.

  In the method for producing a liquid crystal display device of the present invention, the polymerization step is performed while irradiating light, thereby forming a pretilt angle in the liquid crystal. According to such a manufacturing method, the pretilt angle can be reliably given to the liquid crystal.

  The method for manufacturing a liquid crystal display device of the present invention includes a step of irradiating light obliquely to the substrate. According to such a process, the pretilt angle can be reliably given to the liquid crystal.

  If the light irradiated is polarized, a pretilt angle can be reliably given to the liquid crystal.

  The pretilt angle of the liquid crystal is set to 1 ° or less by irradiating the polarized light from a direction substantially perpendicular to the substrate. According to such an invention, it is possible to ensure divisional alignment of a liquid crystal having positive dielectric anisotropy.

  As described above, according to the liquid crystal display device of the present invention, the liquid crystal layer is sandwiched between the first substrate and the second substrate, and the common electrode on the first substrate and the second substrate are arranged. In the liquid crystal display device having a structure in which a voltage is applied between the pixel electrodes, the pixel electrode is smaller than the area of the common electrode and covered with the common electrode, and has a good symmetry. The liquid crystal falls symmetrically, and one pixel is naturally divided into a plurality of regions. Therefore, a wide viewing angle can be achieved without increasing the number of steps such as photolithography. In particular, when the color filter is formed on the second substrate, it is not necessary to perform advanced alignment at the time of bonding the substrates, and a panel having high-definition pixels can be easily formed.

  Moreover, according to the manufacturing method of the liquid crystal display device of this invention, this liquid crystal display device can be manufactured easily.

  Furthermore, according to the driving method of the liquid crystal display device of the present invention, even when the pixel area in the liquid crystal display device is reduced, the alignment of the pixels can be more reliably performed, and the response speed can be increased. .

  Embodiments of the present invention will be described below with reference to the drawings. <First Embodiment> A liquid crystal display device according to a first embodiment of the present invention will be described with reference to FIGS. This liquid crystal display device is driven by a simple matrix, and a cross-sectional view of one pixel is shown in FIG. FIG. 1A shows a cross-sectional view taken along the line A-A ′ of the plan view of FIG.

  The upper substrate is configured by forming a transparent electrode (common electrode) 102 such as ITO on a glass substrate 101 and applying a vertical alignment film 103 thereon. In the case of simple matrix driving, the transparent electrode 102 is formed in a stripe shape as shown in FIG. In the lower substrate, transparent electrodes 111 orthogonal to the transparent electrode 102 of the upper substrate are formed in a stripe shape on the substrate 110, and an insulating film 112 such as silicon nitride is formed thereon, and is symmetrical via the through hole 113. It is connected to the pixel electrode 114 having a typical shape. A vertical alignment film 115 is applied thereon. The upper and lower substrates are pasted through a spacer, and liquid crystal 100 having a negative dielectric anisotropy is injected.

  The pixel electrode 114 is smaller than the common electrode 102 and is covered with the common electrode 102. Further, it has a shape having good symmetry, for example, a circular or elliptical shape, or a polygonal shape. Specifically, as shown in FIG. 1 (c), a circular or elliptical shape, a regular pentagon, a regular hexagon, The shape is a regular polygon such as a regular octagon or a square. In the case of a polygon, it does not need to be a regular regular polygon, and some deformation is allowed.

  Further, a shield electrode 116 is disposed around the pixel electrode 114 to prevent the liquid crystal alignment direction from being affected by the electric field from the lower transparent electrode 111.

  When no voltage is applied, the liquid crystal molecules 100 are aligned substantially perpendicular to the substrate because the alignment films 103 and 115 on the upper and lower substrates are vertical alignment films. When a voltage is applied between the common electrode 102 and the pixel electrode 114 on the upper and lower substrates, an electric field is induced between the pixel electrode 114 and the common electrode 102 arranged to face the pixel electrode 114. At this time, since the shape of the pixel electrode 114 is highly symmetric and the common electrode 102 is larger than the pixel electrode 114, the electric field generated between the two electrodes is not perpendicular to the substrate, as shown in FIG. An oblique electric field is directed from the periphery of the pixel electrode toward the center. Due to this electric field, as shown in FIG. 1 (a), the liquid crystal molecules 100 having negative dielectric anisotropy fall symmetrically toward the center of the pixel, and the symmetrical pixel as shown in FIG. 1 (c). Due to the shape, it is divided while maintaining symmetry. For this reason, the alignment direction of the liquid crystal in the pixel is naturally divided.

  As described above, in the present embodiment, the direction in which the liquid crystal falls can be automatically divided without specially processing the alignment film, and a wide viewing angle can be achieved. When sandwiched between polarizing plates arranged so that their transmission axes are orthogonal to each other, a normally black mode display that is black when no voltage is applied and bright when a voltage is applied is obtained, and exhibits a wide viewing angle characteristic.

  In the case of a normal liquid crystal display device, the pixel electrode is rectangular. However, as shown in FIG. 2, the pixel electrode is cut to form a pixel electrode having a shape in which several symmetrical shapes are connected. Thus, since the alignment division can be performed as described above at each portion having a good symmetry, the same effect as that of an electrode having a good symmetry can be obtained as a whole.

  In order to further ensure the division position where the liquid crystal falls, as shown in FIG. 3, a pixel electrode which is provided with a notch 114a at the corners in the case of a polygon, particularly in the case of a polygon, radially from the periphery of the shape having good symmetry It may be 114. Alternatively, as shown in FIG. 4, the pixel electrode 114 may be provided with a peripheral portion having a good symmetry, particularly, in the case of a polygon, a protrusion 114 b that protrudes radially from the center at each corner.

  Furthermore, as shown in FIG. 5, it is also effective to use a pixel electrode 114 having a structure in which an electrodeless portion 114c is provided so that no electrode is provided radially from the center to the periphery of a shape having good symmetry as indicated by a broken line. is there. Moreover, as shown in FIG. 6, you may form the recessed part 114d radially from the center of a shape with sufficient symmetry to a periphery. The recess may be on the pixel electrode or the pixel electrode itself may form a recess. Of course, these may be combined.

  In such a structure in which the concave portion 114d is provided, there is an interlayer insulating film made of an organic film or the like between the TFT and the pixel electrode, or a pixel electrode is disposed between the color filter layer and the liquid crystal layer. In this case, by forming a recess in the interlayer insulating film or overcoat layer, the recess 114d can be formed deeply without complicating the manufacturing process, and the fixing of the liquid crystal at the boundary can be made more reliable. .

  In the case of vertical alignment, when a voltage is applied, it is stabilized in a spiral alignment, but a chiral agent may be added to further stabilize this alignment and increase the response speed. Furthermore, the cut of a part of the pixel or the shape of the recess may be set spirally in the pixel.

  In addition, in the above description, these notches 114a, protrusions 114b, electrodeless portions 114c, and recesses 114d are provided radially from the center to the corners, but are particularly liquid crystals having a positive dielectric anisotropy. In the case of the homogeneous alignment in which the initial alignment of the liquid crystal on the upper and lower substrates is parallel or anti-parallel, it may be provided in parallel with the sides.

  The liquid crystal display device according to the present invention may further include at least one optical compensation plate between the polarizing plate and the liquid crystal cell in order to improve viewing angle characteristics. Since this compensation plate has homeotropic alignment when no voltage is applied, it is preferable to use an optically negative compensation plate from the viewpoint of canceling the change in retardation when viewed from an oblique direction. Such a compensation plate may be a single film prepared by a method such as biaxial stretching, or two or more uniaxially stretched films are stacked to form a substantially optically negative uniaxial film. The same effect can be obtained even when used as a compensation plate. As a result, the retardation of the liquid crystal when no voltage is applied is canceled out, and even when viewed from any direction, perfect black is obtained, and further excellent viewing angle characteristics are obtained.

  In addition, depending on the element, there may be a transition region in which the falling direction is different after applying a voltage, and this transition region is observed black under the orthogonal polarizing plate, causing a decrease in brightness. In some cases, the movement of the transition region is slow, and the apparent response speed may be slow. On the other hand, in particular, when the above-described uniaxially stretched film is a quarter-wave plate, it is possible to make the movement of the boundary portion invisible and obtain an apparently fast response. In other words, when this quarter-wave plate is arranged on both sides of the liquid crystal cell and arranged so that the optical axis forms an angle of 45 ° with the absorption axis of the orthogonal polarizer, respectively, the quarter-wave plate Therefore, a uniaxially stretched film may be overlapped and used as a substantially optically negative uniaxial compensation plate.

  Although the initial orientation is in principle vertical orientation, if there is a bias in a certain direction due to the characteristics of the element, a film with positive optical anisotropy is attached to compensate for this. Also good.

  Although the transmissive type is described as an example, the pixel electrode is made of a metal having a high reflectance such as Al, so that it can be used as a reflective type without any problem. At this time, white display can be made easier to see by forming irregularities on the surface of the pixel electrode or using a diffusion plate. Although the color filter layer is omitted here, color display can be obtained by providing a color filter layer between the upper substrate 101 and the transparent electrode 102.

  In the method for manufacturing a liquid crystal display device according to the present invention, a voltage is applied between the common electrode and the pixel electrode to control the initial alignment, and then polymerize a polymerizable monomer or oligomer mixed in a small amount in the liquid crystal. Thus, the initial liquid crystal alignment can be further ensured. When controlling the initial alignment, after the liquid crystal layer is made isotropic by heating, the temperature may be lowered while applying a voltage between the common electrode and the pixel electrode, or the common electrode and the pixel electrode at room temperature. Only a voltage may be applied between the two.

  In addition, the monomer reaction may be caused before heating to the isotropic phase, may be caused during heating, or may be caused after cooling. When controlling the initial orientation by applying a voltage between the common electrode and the pixel electrode at room temperature, a reaction may be caused before the voltage is applied, or a reaction may be caused after the voltage is applied. . At this time, since the alignment can be divided in a normal drive format, there is no need to apply a voltage to the second electrode (control electrode) as described in JP-A-10-20323.

  In the method for manufacturing a liquid crystal display device according to the present invention, the pre-tilt angle may be controlled in accordance with the divided shape by using a method such as photo-alignment on the substrate in advance, so that the initial alignment control can be made extremely reliable. Thereby, the effects of the oblique electric field and the pretilt angle work synergistically, and the split orientation can be realized much more effectively than either one of the processes.

  For example, a substance having a functional group capable of controlling the orientation of liquid crystal by polarized light such as a cinnamic acid group, or digest of technical papers (AM-LCD '96 / IDW ') of AMCD '96 / IDW '96. 96 Digest of Technical Papers) As shown in 337, a polymer such that a photosensitive group is polymerized by irradiation with polarized light is used for the alignment film, and a pretilt angle is formed in a direction along the divided shape through a mask on each part in an oblique direction. Irradiate polarized light. In this case, if the number of sides of the polygon is too large, the operation of photo-alignment increases, so an octagon to a quadrangular shape is desirable.

  Such split alignment methods are well known, but even in such a case, by polymerizing a polymerizable monomer or oligomer mixed in a small amount in the liquid crystal, the splitting can be performed more reliably even during driving. Can be maintained.

  As the monomer and oligomer used in the present invention, any of a photo-curable monomer, a thermosetting monomer, or an oligomer thereof can be used. May be. The “photo-curable monomer or oligomer” used in the present invention includes not only those that react with visible light but also ultraviolet-curing monomers that react with ultraviolet rays, and the latter is particularly desirable in terms of ease of operation.

  The polymer compound used in the present invention may have a structure similar to that of liquid crystal molecules including monomers and oligomers having liquid crystallinity, but is not necessarily used for the purpose of aligning liquid crystals. It may be flexible such as having a chain. Moreover, a monofunctional thing may be sufficient, and the monomer etc. which have a bifunctional thing, a trifunctional or more polyfunctionality, etc. may be sufficient.

  Examples of the light or ultraviolet curing monomer used in the present invention include 2-ethylhexyl acrylate, butyl ethyl acrylate, butoxy ethyl acrylate, 2-cyanoethyl acrylate, benzyl acrylate, cyclohexyl acrylate, 2-hydroxypropyl acrylate, 2-ethoxyethyl acrylate. , N, N-ethylaminoethyl acrylate, N, N-dimethylaminoethyl acrylate, dicyclopentanyl acrylate, dicyclopentenyl acrylate, glycidyl acrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, isodecyl acrylate, lauryl acrylate, morpholine Acrylate, phenoxyethyl acrylate, phenoxydiethylene glycol acrylate 2,2,2-trifluoroethyl acrylate, 2,2,3,3,3-pentafluoropropyl acrylate, 2,2,3,3-tetrafluoropropyl acrylate, 2,2,3,4,4 Monofunctional acrylate compounds such as 4-hexafluorobutyl acrylate can be used.

  Also, 2-ethylhexyl methacrylate, butylethyl methacrylate, butoxyethyl methacrylate, 2-cyanoethyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, 2-hydroxypropyl methacrylate, 2-ethoxyethyl acrylate, N, N-diethylaminoethyl methacrylate, N, N- Dimethylaminoethyl methacrylate, dicyclopentanyl methacrylate, dicyclopentenyl methacrylate, glycidyl methacrylate, tetrahydrofurfuryl methacrylate, isobornyl methacrylate, isodecyl methacrylate, lauryl methacrylate, morpholine methacrylate, phenoxyethyl methacrylate, phenoxydiethylene glycol methacrylate, 2, 2, 2- Li fluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, can be used monofunctional methacrylate compounds such as 2,2,3,4,4,4-hexafluoro-butyl methacrylate.

  Further, 4,4′-biphenyl diacrylate, diethylstilbestrol diacrylate, 1,4-bisacryloyloxybenzene, 4,4′-bisacryloyloxydiphenyl ether, 4,4′-bisacryloyloxydiphenylmethane, 3,9 -Bis [1,1-dimethyl-2-acryloyloxyethyl] -2,4,8,10-tetraspiro [5,5] undecane, α, α'-bis [4-acryloyloxyphenyl] -1,4- Diisopropylbenzene, 1,4-bisacryloyloxytetrafluorobenzene, 4,4'-bisacryloyloxyoctafluorobiphenyl, diethylene glycol diacrylate, 1,4-butanediol diacrylate, 1,3-butylene glycol diacrylate, dicyclopenta Nyl diacrylate, glycerol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, tetraethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, ditrimethylolpropane tetraacrylate , Dipentaerythritol hexaacrylate, dipentaerythritol monohydroxypentaacrylate, 4,4′-diacryloyloxystilbene, 4,4′-diacryloyloxydimethylstilbene, 4,4′-diacryloyloxydiethylstilbene, 4,4 '-Diacryloyloxydipropylstilbene, 4,4'-Diacryloyloxydibutylstilbene , 4,4'-Diacryloyloxydipentylstilbene, 4,4'-Diacryloyloxydihexylstilbene, 4,4'-Diacryloyloxydifluorostilbene, 2,2,3,3,4,4-hexafluoropentanediol Polyfunctional acrylate compounds such as -1,5-diacrylate, 1,1,2,2,3,3-hexafluoropropyl-1,3-diacrylate, and urethane acrylate oligomer can be used.

  Furthermore, diethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, 1,3-butylene glycol dimethacrylate, dicyclopentanyl dimethacrylate, glycerol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate , Tetraethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetramethacrylate, pentaerythritol trimethacrylate, ditrimethylolpropane tetramethacrylate, dipentaerythritol hexamethacrylate, dipentaerythritol monohydroxypentamethacrylate, 2, 2, 3, 3 , 4,4-Hexafluoropentanediol-1,5-dimeta Relate, polyfunctional methacrylate compounds and urethane methacrylate oligomer, other styrene, amino styrene, there are vinyl acetate, but is not limited thereto.

  Further, since the driving voltage of the element of the present invention is affected by the interface interaction between the polymer material and the liquid crystal material, a polymer compound containing a fluorine element may be used. As such a polymer compound, 2,2,3,3,4,4-hexafluoropentanediol-1,5-diacrylate, 1,1,2,2,3,3-hexafluoropropyl-1, 3-diacrylate, 2,2,2-trifluoroethyl acrylate, 2,2,3,3,3-pentafluoropropyl acrylate, 2,2,3,3-tetrafluoropropyl acrylate, 2,2,3 4,4,4-hexafluorobutyl acrylate, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 2,2,3,4,4,4-hexafluorobutyl Examples thereof include, but are not limited to, a polymer compound synthesized from a compound containing methacrylate, urethane acrylate oligomer or the like.

  When a light or ultraviolet curable monomer is used as the polymer compound used in the present invention, an initiator for light or ultraviolet light can also be used. As this initiator, various initiators can be used. For example, 2,2-diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenyl-1-one, 1- (4-isopropylphenyl)- Acetophenones such as 2-hydroxy-2-methylpropan-1-one and 1- (4-dodecylphenyl) -2-hydroxy-2-methylpropan-1-one, benzoin methyl ether, benzoin ethyl ether, benzyldimethyl ketal Benzoin such as benzophenone, benzophenone, benzoylbenzoic acid, 4-phenylbenzophenone, benzophenone such as 3,3-dimethyl-4-methoxybenzophenone, thioxanthone such as thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, Diazonium salt, sulfonium salt Iodonium salts, selenium salt, or the like can be used.

  Next, an example is concretely shown about 1st Embodiment. (Example 1) ITO was sputtered on glass substrates 101 and 110, and ITO electrodes 102 and 111 were formed in a matrix using a photolithography technique. A silicon nitride film 112 was deposited only on the lower substrate 110, and a through hole 113 was formed using photolithography. ITO was sputtered thereon, and a hexagonal pixel electrode 114 was formed using photolithography. Vertical alignment films (SE1211 manufactured by Nissan Chemical Industries, Ltd.) 103 and 115 were applied and dried by heating at 200 ° C. for 1 hour.

  After applying the sealing agent around the substrate and spraying the spacer agent, the upper and lower substrates were bonded together so that the matrix electrodes were alternately formed to form XY electrodes, and the sealing agent was cured by heating. A nematic liquid crystal 100 having a negative dielectric anisotropy was injected, and the injection hole was sealed with a photocurable resin. An optically negative compensation film having the same size as that of Δnd of the liquid crystal layer and having the opposite sign was attached, and then a polarizing plate was attached to the upper and lower substrates so that their transmission axes were orthogonal to each other.

  When the viewing angle characteristics of the panel thus obtained were measured, there was no gradation inversion and an excellent viewing angle characteristic with a very wide high contrast region was obtained.

  (Embodiment 2) Except that a shield electrode 116 is formed around a hexagonal pixel electrode 114 on a silicon nitride film 112 of a lower substrate 110 so as to be completely the same as that of Embodiment 1. Thus, a liquid crystal display device was produced. The shield electrode 116 could be created only by changing the mask. The shield electrode 116 was connected to 0V.

  When the viewing angle characteristics of the panel thus obtained were measured, there was no gradation inversion and an excellent viewing angle characteristic with a very wide high contrast region was obtained. Further, when the inside of the pixel was observed with a microscope, the abnormal disclination in the pixel rarely seen in Example 1 was not seen at all.

  <Second Embodiment> A second embodiment of the present invention will be described with reference to FIG. 7A is a cross-sectional view taken along line A-A ′ of the plan view of FIG. The second embodiment is a liquid crystal display device that uses a liquid crystal that uses simple matrix driving, has a positive dielectric anisotropy, and has a twisted nematic orientation when no voltage is applied.

  The upper substrate is configured by forming a transparent electrode (common electrode) 102 such as ITO on a glass substrate 101 and applying an alignment film 103a. By rubbing the alignment film 103a, the liquid crystal is aligned perpendicular to the rubbing direction, and the pretilt angle is almost 0 ° or very low (1 ° or less). In the case of simple matrix driving, the transparent electrode 102 is formed in a stripe shape. In the lower substrate, transparent electrodes 111 orthogonal to the transparent electrode 102 of the upper substrate are formed in a stripe shape on the substrate 110, and an insulating film 112 such as silicon nitride is formed thereon, and is symmetrical via the through hole 113. It is connected to the pixel electrode 114 having a typical shape. A vertical alignment film 115a is applied thereon. The upper and lower substrates are pasted through a spacer, and liquid crystal 100a having a positive dielectric anisotropy is injected.

  The pixel electrode 114 is smaller than the common electrode 102 and is covered with the common electrode 102. Further, a shield electrode 116 is disposed around the pixel electrode 114 to prevent the liquid crystal alignment direction from being affected by the electric field from the lower transparent electrode 111.

  In this embodiment, the upper and lower alignment films 103a and 115a are rubbed or photo-aligned to define the alignment direction of the liquid crystal. In FIG. 7B, the alignment direction of the liquid crystal on the substrate 101 side is represented by an arrow 117, and the alignment direction of the liquid crystal on the lower substrate 110 side is represented by an arrow 118. Such alignment can be easily obtained by, for example, irradiating polarized light from the normal direction of the substrate to an alignment film that is aligned in a direction perpendicular to the rubbing direction or a photo alignment film. Do not add any chiral agent.

  In the liquid crystal having positive dielectric anisotropy and twisted nematic alignment, there are two or more combinations of the twist direction and the rising direction, and the liquid crystal alignment in the pixel can be performed. In the case of twisted nematic alignment, the pretilt angle on the substrate surface of the liquid crystal is preferably as small as possible, preferably 1 ° or less, preferably 0 °, from the viewpoint that the rising direction of the liquid crystal has an equal probability.

  When no voltage is applied, the liquid crystal molecules 100a are aligned perpendicular to the rubbing direction of the alignment films 103a and 115a of the upper and lower substrates, and the pretilt angle is almost 0 ° or has a very low (1 ° or less) pretilt angle. When a voltage is applied between the common electrode 102 and the pixel electrode 114 on the upper and lower substrates, an electric field is induced between the pixel electrode 114 and the common electrode 102 arranged to face the pixel electrode 114. At this time, since the shape of the pixel electrode 114 is highly symmetric and the common electrode 102 is larger than the pixel electrode 114, the electric field generated between the two electrodes is not perpendicular to the substrate, as shown in FIG. An oblique electric field is generated from the periphery of the pixel electrode toward the center, and the oblique electric field is generated with good objectivity due to the shape characteristics of the upper and lower electrodes.

  In each part of the pixel, both right-handed twist and left-handed twist may occur. By this oblique electric field, for example, in each part of the pixel shown in FIG. An orientation state as shown in FIG. 7B is automatically generated. That is, the pixel electrode 114 on the lower substrate has a shape with good objectivity, the common electrode 102 on the upper substrate covers the pixel electrode 114, and the common electrode 102 is wider than the pixel electrode 114, so that the twisted nematic orientation is used. However, it is possible to divide pixels with good symmetry. For this reason, the alignment direction of the liquid crystal in the pixel is naturally divided, and a wide viewing angle can be achieved.

  It is sandwiched between polarizing plates arranged so that the transmission axes are orthogonal to each other, and arranged so that the alignment direction of the liquid crystal coincides with the transmission axis of the polarizing plate, it is white when no voltage is applied and black when a voltage is applied. A display with a wide viewing angle is obtained. Note that since the regions having different twist directions meet at the boundaries between the respective portions, light leakage does not occur, and high contrast can be maintained without providing a light shielding layer or the like.

  In order to further ensure the division position where the liquid crystal is tilted, as shown in FIG. 3, a pixel provided with notches 114 a at the corners in the case of a polygonal shape that is radial from the center, particularly in the case of a polygonal shape. The electrode 114 may be used. Alternatively, as shown in FIG. 4, the pixel electrode 114 may be provided with a peripheral portion having a good symmetry, particularly, in the case of a polygon, a protrusion 114 b that protrudes radially from the center at each corner.

  Furthermore, as shown in FIG. 5, it is also effective to use a pixel electrode 114 having a structure in which an electrodeless portion 114c is provided so that no electrode is provided radially from the center to the periphery of a shape having good symmetry as indicated by a broken line. It is. Further, as shown in FIG. 6, the concave portions 114d may be formed radially from the center of the shape having good symmetry to the periphery. The recess may be on the pixel electrode or the pixel electrode itself may form a recess. Of course, these may be combined.

  In addition, the device to further ensure the division by photo-alignment does not make sense in the case of twisted nematic, but it can be more effective even during driving by polymerizing a polymerizable monomer or oligomer mixed in a small amount in the liquid crystal. The division can be surely maintained as in the case where the dielectric anisotropy is negative.

  FIG. 8A shows an example in which the liquid crystal 100b has a positive dielectric anisotropy and has a homogeneous orientation when no voltage is applied. In this case, the upper and lower substrates are rubbed or photo-aligned to define the alignment direction of the liquid crystal. In FIG. 8B, the alignment direction of the liquid crystal on the substrate 101 side is represented by an arrow 117, and the alignment direction of the liquid crystal on the lower substrate 110 side is represented by an arrow 118. In this case as well, as in the case of twisted nematic orientation, the pretilt angle is desirably almost 0 °. Such orientation is polarized from the normal direction of the substrate to the orientation film oriented in the direction perpendicular to the rubbing direction or the photo-alignment film. Can be easily obtained. Do not add any chiral agent.

  When a voltage is applied between the upper and lower electrodes in such a state, an oblique electric field is generated with good symmetry due to the shape characteristics of the upper and lower electrodes. Thereby, since the alignment direction of the liquid crystal at the substrate interface is defined, two types of domains having different rising directions are generated. Further, in the case of homogeneous orientation, it is desirable that a recess 114e is provided at the center part, in particular, in order to stabilize the boundary region. Further, since the liquid crystal display device in FIG. 8 is otherwise the same as that in FIG. 7, the same reference numerals are given to the same members, and the description thereof is omitted.

  In addition, when liquid crystal having positive dielectric anisotropy is used and homogeneous alignment is performed when no voltage is applied, it is not divided into four but is divided into two divided only in the rising direction from the initial alignment direction. The uniaxial compensation film is arranged so that the optical axis coincides with the optical axis of the liquid crystal when no voltage is applied (normally black), or the negative compensation film is aligned in one region when the voltage is applied. The optical axis is gradually inclined in the film so as to simulate (normally white). Here, in the case of normally black, when the voltage is not applied, in the case of normally white, the liquid crystal in at least one region and the compensation film have a sufficiently wide retardation when the voltage is applied. Keratinization can be achieved.

  In this case, the notch shown in FIG. 3 of the part of the pixel display electrode on the lower substrate, the part without the electrode shown in FIG. 5, or the recess shown in FIG. The initial alignment of the liquid crystal should be set to be perpendicular to these. Further, it is desirable that the pretilt angle is almost 0 ° as in the case of TN.

  In addition, there is usually no problem if the distance between the pixels is sufficiently large in the division, but for the convenience of design, especially when the pixels are close to each other, the voltage applied to each adjacent pixel during driving is positive or negative. If so-called dot inversion driving is performed in which the reverse is true, the situation where the oblique electric field is generated becomes a more desirable direction and gives better driving.

  Furthermore, since the initial response of the liquid crystal is very fast, it is possible to drive by resetting it back to the black state in one frame for the purpose of using only this fast response for display. As described above, the driving for resetting is generally used for the purpose of improving the cut-off in moving image display. However, in the liquid crystal display device of the present invention, it is preferable to further increase the apparent response. Since the following effects can be obtained, better driving is given.

  Although the transmissive type is described as an example, the pixel electrode is made of a metal having a high reflectance such as Al, so that it can be used as a reflective type without any problem. At this time, white display can be made easier to see by forming irregularities on the surface of the pixel electrode or using a diffusion plate. Although the color filter layer is omitted here, color display can be obtained by providing a color filter layer between the upper substrate 101 and the transparent electrode 102.

  (Example 3) In the same manner as in Example 1, an ITO electrode and a silicon nitride film were formed using photolithography, and then a rectangular pixel electrode 114 was formed. A liquid crystal panel was prepared by changing the alignment film to JALS-428 manufactured by JSR and replacing the ZL14792 chiral agent with a positive dielectric anisotropy. However, rubbing was performed so that the alignment directions of the liquid crystals on the lower substrate and the upper substrate were orthogonal to each other, particularly in the direction of a square diagonal line. In JALS-428, the liquid crystal was aligned in the direction perpendicular to the rubbing direction, and the pretilt angle determined by the crystal rotation method was almost 0 °. The cell thickness was approximately 5 μm.

  As a compensation film, a New-Vac film manufactured by Sumitomo Chemical Co., Ltd. was used, and the viewing angle characteristics of the panel were measured. As a result, there was no gradation inversion over the entire surface, and excellent viewing angle characteristics were obtained.

  <Third Embodiment> A third embodiment of the present invention will be described with reference to FIG. 9A is a cross-sectional view taken along line B-B ′ of the plan view of FIG. In the third embodiment, the liquid crystal is driven by an active element.

  A color filter layer 202 and a light shielding layer 203 are formed on the upper transparent substrate 201, and a common electrode 204 is formed on almost the entire surface of the transparent substrate 201. A vertical alignment film 205 is applied on the common electrode 204.

  A thin film transistor 220 is provided on the lower substrate 211. In this transistor 220, a gate electrode (scanning signal electrode) 221 made of Cr is disposed, and a gate insulating film 222 made of silicon nitride is formed so as to cover the gate electrode 221. A semiconductor film 223 made of amorphous silicon is disposed on the gate electrode 221 with a gate insulating film 222 interposed therebetween, and functions as an active layer of the thin film transistor (TFT) 220. In addition, a drain electrode 224 and a source electrode 225 made of molybdenum are disposed so as to overlap a part of the pattern of the semiconductor film 223. A protective film 226 made of silicon nitride is formed so as to cover all of them.

  Note that the drain electrode 224 and the source electrode 225 are not illustrated, but overlap with part of the pattern of the semiconductor film 223 through an amorphous silicon film into which an n-type impurity is introduced.

  Further, as shown in FIG. 9B, the drain electrode 224 is connected to a data line (video signal electrode) 224a. In other words, the drain electrode 224 is formed as a part of the data line 224a. The gate electrode 221 also constitutes a part of the scanning signal line 221a. Further, a pixel electrode 212 connected to the source electrode 225 is provided on the edge film 222, and a vertical alignment film 213 is formed thereon.

  In this embodiment, a source electrode 225 is connected to the pixel electrode 212, and a video signal is applied to the pixel electrode 212. The on / off of the video signal is controlled by the scanning signal. The pixel electrode 212 has a highly symmetric shape. Here, a hexagon is illustrated, but as shown in FIG. 1C, the same effect can be obtained with a circle, pentagon, square, or the like. Note that liquid crystal molecules 200 having negative electric anisotropy are sandwiched between the upper and lower substrates.

  Since the alignment films 204 and 213 on the upper and lower substrates are vertical alignment films, the liquid crystal 200 is aligned substantially perpendicular to the substrates when no voltage is applied.

  When a voltage is applied to the gate electrode 221 to turn on the thin film transistor (TFT) 220, a voltage is applied to the source electrode 225, and an electric field is induced between the pixel electrode 212 and the common electrode 204 disposed opposite thereto. The At this time, since the shape of the pixel electrode 212 is highly symmetric and the common electrode 204 is larger than the pixel electrode 212, the electric field generated between the two electrodes is not perpendicular to the substrate but is oblique from the periphery of the pixel electrode toward the center. It becomes an electric field. Due to this electric field, the liquid crystal molecules 200 having a negative dielectric anisotropy are tilted symmetrically toward the center of the pixel as shown in FIG. For this reason, the alignment direction of the liquid crystal in the pixel is naturally divided.

  As described above, in the present invention, when a liquid crystal having a negative dielectric anisotropy is used, the direction in which the liquid crystal falls can be automatically divided without specially processing the alignment film. Viewing angle can be achieved.

  In particular, in the case of an active matrix liquid crystal display device, unnecessary disclination lines may enter the pixel electrode portion due to the influence of the lateral electric field from the scanning signal electrode 221a and the video signal electrode 224a, and the alignment of the liquid crystal may be disturbed. . Such a problem can be solved by increasing the distance between the scanning signal electrode 221a, the video signal electrode 224a, and the pixel electrode 212. However, if the distance is increased too much, the pixel size is reduced. From the viewpoint of aperture ratio, it is not desirable.

  Another method for solving this problem is to arrange a part of the pixel electrode 212 or a shielding electrode on at least one of the scanning signal electrode 221a and the video signal electrode 224a. That is, if all of the scanning signal electrode 221a and the video signal electrode 224a are shielded by the pixel electrode 212, the aperture ratio decreases.

  Therefore, by arranging the pixel electrode 212 or the shielding electrode on at least one of the scanning signal electrode 221a and the video signal electrode 224a, it is possible to prevent the aperture ratio from being lowered. Here, the best arrangement can be selected in consideration of the shape of the pixel, the arrangement of the scanning signal electrode 221a and the video signal electrode 224a, and the procedure for creating the shield electrode.

  Furthermore, in the case of a pixel design, when the aperture ratio is lowered and a sufficient distance cannot be taken, and when it is desired to control the direction in which the liquid crystal falls more completely, a photo-alignment film is used as the alignment film. Depending on the property, an operation such as irradiation with polarized light or non-polarized light from an oblique direction may be performed. Further, in order to prevent the alignment of the liquid crystal from being disturbed, a small amount of monomer may be introduced into the liquid crystal so as to memorize an appropriate alignment state.

  For the purpose of stabilizing the division boundary, a notch may be provided in a part of the pixel as shown in FIG. Further, as shown in FIG. 4, it is also effective to form a protruding portion in which the corner portion of the pixel electrode protrudes outward. Further, as shown by the broken line in FIG. The structure of the electrodeless portion 114c from which the portion is removed is also effective.

  Further, as shown in FIG. 10, concave portions 212 d as shown in FIG. 6 may be formed radially at each corner from the center of the pixel electrode 212 in a part of the square pixel electrode 212. The recess 212d may be on the pixel electrode, or the pixel electrode 212 itself may form a recess. Since the liquid crystal display device in FIG. 10 is the same as that in FIG. 9 except for the recess 212d of the pixel electrode 212, the same members are denoted by the same reference numerals, and the description thereof is omitted.

  Furthermore, in exactly the same manner as in the first embodiment, if an optically negative uniaxial compensation film is sandwiched between the polarizing plate and the glass substrate, the retardation of the liquid crystal when no voltage is applied is canceled and in which direction As a result, perfect black can be obtained, and further excellent viewing angle characteristics can be obtained.

  Furthermore, the initial orientation is in principle a vertical orientation, but if there is a bias in a certain direction due to the characteristics of the device, a film with positive optical anisotropy is attached to compensate for this. Also good.

  Further, in the above description, it is assumed that the dielectric anisotropy of the liquid crystal is negative and the liquid crystal is vertically aligned with respect to the substrate when no voltage is applied. Even when the dielectric anisotropy is positive and the twisted nematic alignment is taken when no voltage is applied, the liquid crystal alignment substantially the same as the liquid crystal alignment described in the second embodiment occurs, and a wide viewing angle can be achieved. In this case, the liquid crystal layer is divided into four as shown in FIGS. When using twisted nematic orientation, square pixels are desirable. The same applies to all the following embodiments.

  The present invention is particularly effective in the case of an active matrix liquid crystal display device using a switching element such as a TFT. That is, in the case of an active matrix liquid crystal display device, in a liquid crystal display device using a normal TN mode, a fine processing step such as a photoresist step is required only for a substrate on one side for producing an active element, Usually, other substrates called “common electrodes” do not need to be finely processed, and only electrodes are formed on the entire surface. Since the viewing angle is narrow as it is, if the alignment is divided into the liquid crystal in the pixel in order to widen the viewing angle, the photoresist process increases in the conventional technique. This increase in the photoresist process causes a load on production facilities and a decrease in yield, and therefore it is desirable to omit it. According to the present invention, the alignment process of the liquid crystal in the pixel can be performed without increasing the number of photoresist processes, and a wide viewing angle characteristic can be obtained.

  The liquid crystal manufacturing method of the liquid crystal display device of the third embodiment can be the same as that of the first embodiment.

  Next, examples of the third embodiment will be described. Example 4 A substrate having an amorphous silicon thin film transistor array (TFT) 220 was fabricated on a glass substrate 211 by repeating the film formation process and the lithography process. The TFT 220 includes a gate: chromium layer 221, silicon nitride: gate insulating layer 222, amorphous silicon: semiconductor layer 223, drain / source: molybdenum layers 224, 225 from the substrate 211 side. The source electrode 225 is connected to the pixel ITO electrode 212 having a square shape. A protective film 226 made of silicon nitride was formed so as to cover them.

  A color filter substrate with a black matrix on which ITO was sputtered over the entire surface was prepared and used as a counter substrate. Vertical alignment films (SE1211 manufactured by NISSAN CHEMICAL CO., LTD.) 205 and 213 were applied to both substrates, followed by heat drying at 200 ° C. for 1 hour. After applying a sealing agent around the substrate and spraying a spacer agent, the sealing agent was cured by heating, nematic liquid crystal having a negative dielectric anisotropy was injected, and the injection hole was sealed with a photocurable resin. An optically negative compensation film having the same size as that of Δnd of the liquid crystal layer and having the opposite sign was attached, and then a polarizing plate was attached to the upper and lower substrates so that their transmission axes were orthogonal to each other.

  When the viewing angle characteristics of the panel thus obtained were measured, there was no gradation inversion and an excellent viewing angle characteristic with a very wide high contrast region was obtained.

  (Example 5) A TFT substrate was prepared in exactly the same manner as in Example 4, and an electrodeless portion 114a having no electrode as shown in FIG. Otherwise in the same manner as in Example 4, a liquid crystal display panel was obtained.

  When the viewing angle characteristics of the panel thus obtained were measured, there was no gradation inversion and an excellent viewing angle characteristic with a very wide high contrast region was obtained. In addition, when the inside of the pixel was observed in detail with a microscope, the abnormal disclination observed in a very small number of pixels in Example 4 was not observed.

  (Example 6) A TFT substrate was prepared in exactly the same manner as in Example 4, and a part of the gate insulating film was etched into the shape shown in FIG. 10 using photolithography to form a recess 212d. A shape as shown in FIG. 10 was finally obtained by sputtering ITO here. That is, a recess was also formed in a part of the ITO 212. A liquid crystal display panel was produced in exactly the same manner as in Example 4.

  When the viewing angle characteristics of the panel thus obtained were measured, there was no gradation inversion and an excellent viewing angle characteristic with a very wide high contrast region was obtained. When the inside of the pixel was observed in detail with a microscope, the abnormal disclination movement at the time of driving, which was seen in the small number of pixels in Example 4, was not seen at all.

  Example 7 A TFT substrate and a color filter substrate were prepared in exactly the same manner as in Example 4. After applying JALS-428 as an alignment film and heating and drying at 200 ° C. for 1 hour, in the same manner as in Example 3, the direction of the diagonal line is set so that the alignment directions of the liquid crystals on the lower substrate and the upper substrate are orthogonal to each other. The alignment film 205a and the alignment film 213a are rubbed so that the respective orientations become arrows 231 and 232 as shown in FIG. 11B. As a liquid crystal having positive dielectric anisotropy, ZL14792 from which a chiral agent was removed was injected, and a liquid crystal panel as shown in FIG. In ZL14792, the liquid crystal was aligned in the direction perpendicular to the rubbing direction, and the pretilt angle determined by the crystal rotation method was almost 0 °. In FIG. 11, the same members as those in FIG.

  When the viewing angle characteristics of the panel thus obtained were measured, there was no gradation inversion and an excellent viewing angle characteristic with a very wide high contrast region was obtained.

  <Fourth Embodiment> A fourth embodiment of the present invention will be described with reference to FIG. The liquid crystal is driven by an active element in exactly the same manner as in the third embodiment. FIG. 12A shows a cross-sectional view taken along the line C-C ′ in FIG. The difference from the third embodiment is that the pixel electrode 312 and the source electrode 325 are connected via a through hole 327 instead of directly.

  A color filter layer 302 and a light shielding layer 303 are formed on the upper transparent substrate 301, and a common electrode 304 is formed on almost the entire surface of the transparent substrate 301. A vertical alignment film 305 is applied on the common electrode 304.

  A thin film transistor 320 is provided on the lower substrate 311. In the transistor 320, a gate electrode (scanning signal electrode) 321 made of Cr is disposed, and a gate insulating film 322 made of silicon nitride is formed so as to cover the gate electrode 321.

  A semiconductor film 323 made of amorphous silicon is disposed on the gate electrode 321 with a gate insulating film 322 interposed therebetween, and functions as an active layer of the thin film transistor (TFT) 320. In addition, a drain electrode 324 and a source electrode 325 made of molybdenum are disposed so as to overlap a part of the pattern of the semiconductor film 323. A protective film 326 made of silicon nitride is formed so as to cover all of these. The protective film 326 may be made of only silicon nitride, but an organic film such as an acrylic resin may be further coated on the silicon nitride.

  Note that the drain electrode 324 and the source electrode 325 are not illustrated, but overlap with part of the pattern of the semiconductor film 323 through an amorphous silicon film into which an n-type impurity is introduced. The pixel electrode 312 and the source electrode 325 are connected through a through hole 327. As shown in FIG. 12B, the drain electrode 324 is connected to a data line (video signal electrode) 324a. In other words, the drain electrode 324 is formed as a part of the data line 324a. The gate electrode 321 also constitutes a part of the scanning signal line 321a.

  A pixel electrode 312 connected to the source electrode 325 is provided on the protective film 326, and a vertical alignment film 313 is formed thereon.

  Also in the fourth embodiment, the source electrode 325 is connected to the pixel electrode 312, and a video signal is applied to the pixel electrode. The on / off of the video signal is controlled by the scanning signal. The pixel electrode 312 has a highly symmetric shape. Here, an octagon is illustrated, but as shown in FIG. 1C, the same effect can be obtained with a circle, a pentagon, a quadrangle, and the like.

  Liquid crystal molecules 300 having a negative dielectric anisotropy are sandwiched between the upper and lower substrates. Since the alignment films of the upper and lower substrates are vertical alignment films, the liquid crystal 300 is aligned perpendicular to the substrates when no voltage is applied.

  When a voltage is applied to the gate electrode 321 to turn on the thin film transistor (TFT) 320, a voltage is applied to the source electrode 325, and an electric field is induced between the pixel electrode 312 and the common electrode 304 disposed opposite thereto. The At this time, since the shape of the pixel electrode 312 is highly symmetric and the common electrode 304 is larger than the pixel electrode 312, the electric field generated between the two electrodes is not perpendicular to the substrate but from the periphery of the pixel electrode. It becomes an oblique electric field toward the center. Due to this electric field, the liquid crystal molecules 300 having negative dielectric anisotropy are tilted symmetrically toward the center of the pixel. For this reason, the alignment direction of the liquid crystal in the pixel is naturally divided.

  As described above, in the present invention, when a liquid crystal having a negative dielectric anisotropy is used, the direction in which the liquid crystal falls can be automatically divided without specially processing the alignment film. Viewing angle can be achieved.

  In particular, in the case of an active matrix liquid crystal display device, unnecessary disclination lines may enter the pixel electrode portion due to the influence of the horizontal electric field from the scanning signal electrode 321a and the video signal electrode 324a, and the alignment of the liquid crystal may be disturbed. . Such a problem can be solved by increasing the distance between the scanning signal electrode 321a and the video signal electrode 324a and the pixel electrode 312. However, if the distance is increased too much, the pixel size is reduced. From the viewpoint of aperture ratio, it is not desirable.

  Another method for solving this problem is to dispose a part of the pixel electrode 312 or a shielding electrode on at least one of the scanning signal electrode 321a and the video signal electrode 324a. That is, when the pixel electrode 312 shields all of the scanning signal electrode 321a and the video signal electrode 324a, the aperture ratio decreases. Therefore, by arranging the pixel electrode 312 or the shielding electrode on at least one of the scanning signal electrode 321a and the video signal electrode 324a, the aperture ratio can be prevented from decreasing. Here, the best arrangement can be selected in consideration of the shape of the pixel, the arrangement of the scanning signal electrode 321a and the video signal electrode 324a, and the procedure for creating the shield electrode.

  Furthermore, in the case of a pixel design, when the aperture ratio is lowered and a sufficient distance cannot be taken, and when it is desired to control the direction in which the liquid crystal falls more completely, a photo-alignment film is used as the alignment film. Depending on the property, an operation such as irradiation with polarized light or non-polarized light from an oblique direction may be performed. Further, in order to prevent the alignment of the liquid crystal from being disturbed, a small amount of monomer may be introduced into the liquid crystal so as to memorize an appropriate alignment state.

  For the purpose of stabilizing the division boundary, a notch may be provided in a part of the pixel as shown in FIG. Further, as shown in FIG. 4, it is effective to form a protruding portion in which the corner portion of the pixel electrode protrudes outward. Further, as shown by the broken line in FIG. 5, the structure of the electrodeless portion from which part of the pixel electrode is removed is also effective.

  Further, as shown in FIG. 10, a concave portion as shown in FIG. 6 may be formed in a part of the pixel electrode. The recess may be on the pixel electrode or the pixel electrode itself may form a recess.

  Furthermore, in exactly the same manner as in the first embodiment, if an optically negative uniaxial compensation film is sandwiched between the polarizing plate and the glass substrate, the retardation of the liquid crystal when no voltage is applied is canceled and in which direction As a result, perfect black can be obtained, and further excellent viewing angle characteristics can be obtained.

  Furthermore, the initial orientation is in principle a vertical orientation, but if there is a bias in a certain direction due to the characteristics of the device, a film with positive optical anisotropy is attached to compensate for this. Also good.

  Further, in the above description, it is assumed that the dielectric anisotropy of the liquid crystal is negative and the liquid crystal is vertically aligned with respect to the substrate when no voltage is applied. Even when the dielectric anisotropy is positive and the twisted nematic alignment is taken when no voltage is applied, the liquid crystal alignment substantially the same as the liquid crystal alignment described in the second embodiment occurs, and a wide viewing angle can be achieved. In this case, the liquid crystal layer is divided into four as shown in FIGS. When using twisted nematic orientation, square pixels are desirable.

  In particular, when the pixel is large, a voltage that is approximately equal to the threshold voltage (a voltage that is higher or lower than the threshold voltage) may be used in advance before applying a driving voltage and starting each frame. In this way, the direction in which the liquid crystal falls is defined, so that the liquid crystal can be divided more reliably and in a shorter time than when a sudden driving voltage is applied. In this way, when the response speed of the liquid crystal display device is shortened, and when a voltage higher than the threshold voltage is applied, the liquid crystal around the pixel starts to fall, and light leaks from this portion, In some cases, the contrast is lowered, but by shielding this portion, it is possible to prevent the contrast from being lowered.

  The liquid crystal manufacturing method of the liquid crystal display device of the fourth embodiment can be the same as that of the first embodiment.

  Next, an example of the fourth embodiment will be described. Example 8 A TFT 320 was formed on a glass substrate 311 in exactly the same manner as in Example 4. Similar to the fourth embodiment, the TFT 320 includes a gate-chromium layer 321, a silicon nitride-gate insulating layer 322, an amorphous silicon-semiconductor layer 323, and drain / source-molybdenum layers 324, 325 from the substrate 311 side. . A silicon nitride 326 was formed so as to cover all of these, and the pixel electrode 312 connected to the source electrode 324 was formed in an octagonal shape through the through hole 327 on the silicon nitride film 326.

  In the same manner as in Example 4, a color filter substrate with a black matrix in which ITO was sputtered on the entire surface was prepared and used as a counter substrate. Vertical alignment films (SE1211 manufactured by Nissan Chemical Co., Ltd.) 305 and 313 were applied to both the substrates, and heat-dried at 200 ° C. for 1 hour. After applying a sealing agent around the substrate and spraying a spacer agent, the sealing agent was cured by heating, a nematic liquid crystal 300 having a negative dielectric anisotropy was injected, and the injection hole was sealed with a photocurable resin. An optically negative compensation film having the same size as that of Δnd of the liquid crystal layer and having the opposite sign was attached, and then a polarizing plate was attached to the upper and lower substrates so that their transmission axes were orthogonal to each other.

  When the viewing angle characteristics of the panel obtained in this way were determined, there was no gradation inversion and an excellent viewing angle characteristic with a very wide high contrast region was obtained.

  (Example 9) In the same manner as in Example 8, a TFT substrate and a color filter substrate in which only the shape of the pixel electrode 312 was a square were prepared. A photo-alignment film was applied only to the TFT substrate side, and polarized ultraviolet rays were irradiated obliquely from four directions through a mask so as to divide the pixel into four. The division was performed so as to be divided at boundaries as shown in FIG. In exactly the same manner as in Example 8, application of a sealing agent, spraying of spacers, liquid crystal injection and sealing were performed, and an optically negative compensation film having a size equal to Δnd of the liquid crystal layer and an opposite sign was applied. Then, the polarizing plate was attached to the upper and lower substrates so that the transmission axes thereof were orthogonal.

  When the viewing angle characteristics of the panel thus obtained were measured, there was no gradation inversion and an excellent viewing angle characteristic with a very wide high contrast region was obtained. When the state of the pixel being driven was observed with a microscope, the abnormal disclination movement observed in a very small number of pixels in Example 8 was not seen at all.

  Example 10 In the same manner as in Example 8, a TFT substrate and a color filter substrate were prepared. A column (height 6 μm) serving as a spacer was formed by removing the pixel electrode by photolithography using a negative resist on the color filter substrate. In the same manner as in Example 8, a vertical alignment film (SE1211 manufactured by Nissan Chemical Industries, Ltd.) was applied to both substrates, and heat drying was performed at 200 ° C. for 1 hour. As in Example 6, the spraying of the spacer agent was omitted to prepare a panel.

  Next, nematic liquid crystal with negative dielectric anisotropy (trade name MJ95955 manufactured by Merck & Co., Ltd.) and UV curable monomer (trade name KAYARAD PET-30 manufactured by Nippon Kayaku Co., Ltd.) (0.2 wt% with respect to liquid crystal), start A liquid crystal solution composed of an agent (trade name: Irganox 907, 5 wt% with respect to the monomer) was injected, and the liquid crystal solution was sealed so as not to be exposed to light. While applying a voltage of 0 V to the common electrode and 3 V to the pixel electrode, the entire panel surface was irradiated with ultraviolet light from the TFT side to polymerize the monomer in the liquid crystal. An optically negative compensation film having the same size as that of Δnd of the liquid crystal layer and having the opposite sign was attached, and then a polarizing plate was attached to the upper and lower substrates so that their transmission axes were orthogonal to each other.

  When the viewing angle characteristics of the panel thus obtained were measured, there was no gradation inversion and an excellent viewing angle characteristic with a very wide high contrast region was obtained.

  Similarly to Example 9, when the state of the pixel being driven was observed with a microscope, in Example 8, the abnormal disclination movement seen in a very small number of pixels was not observed at all.

  (Example 11) In the same manner as in Example 8, a TFT substrate and a color filter substrate in which only the shape of the pixel electrode 312 was a square were prepared, and the response speed of a panel formed using these substrates was measured. As a driving method, when a bias voltage was not applied and a driving voltage of 5 V was applied suddenly from 0 V, the amount of transmitted light was not stable even after 40 ms had elapsed since the application of 5 V. On the other hand, when a bias voltage of 2.2 V was applied in advance and a drive voltage of 5 V was subsequently applied, the amount of transmitted light was stabilized after 20 ms had elapsed since the application of 5 V.

  Moreover, the alignment state of the liquid crystal of the test panel prepared under the same conditions as this panel was observed using a strobe. In this observation, when a voltage of 5 V was suddenly applied from 0 V, as shown in FIG. 13A, a disturbance in the liquid crystal alignment was observed even after 40 ms, and it was found that the amount of transmitted light was not stabilized due to this disturbance. In addition, when 5 V was applied after applying a bias voltage of 2.2 V, as shown in FIG. 5B, an alignment without disorder was observed after 20 ms. Thus, it was found that the response speed of the liquid crystal panel is increased if a bias voltage is applied in advance.

  However, when 5V is applied suddenly from 0V, there is 2300 contrast before and after application of 5V, whereas when 5V is applied by applying 2.2V bias voltage, 5V is applied. The contrast before and after application decreased to 130. This was caused by light leakage around the pixels as shown in the liquid crystal alignment state after 5 ms in FIG.

  To reduce this contrast, a contrast of 2000 could be obtained by blocking the light leaking portion (the peripheral portion of the pixel electrode) with a black matrix. By doing so, the response speed of the liquid crystal panel can be increased with almost no adverse effect on the decrease in contrast.

  <Fifth Embodiment> A fifth embodiment of the present invention will be described with reference to FIG. The liquid crystal is driven by an active element in exactly the same manner as in the third and fourth embodiments. 14A is a cross-sectional view taken along the line D-D 'in FIG. 14B. In the fifth embodiment, the color filter layer is provided on the lower substrate side.

  A common electrode 402 is formed on almost the entire surface of the transparent substrate 401 on the upper transparent substrate 401. A vertical alignment film 403 is applied on the common electrode 402. A thin film transistor 420 is provided over the lower substrate 411. In this transistor 420, a gate electrode (scanning signal electrode) 421 made of Cr is disposed, and a gate insulating film 422 made of silicon nitride is formed so as to cover the gate electrode 421. A semiconductor film 423 made of amorphous silicon is disposed over the gate electrode 421 with a gate insulating film 422 interposed therebetween, and functions as an active layer of a thin film transistor (TFT) 420. In addition, a drain electrode 424 and a source electrode 425 made of molybdenum are disposed so as to overlap a part of the pattern of the semiconductor film 423. A protective film 426 made of silicon nitride is formed so as to cover all of these.

  Note that the drain electrode 424 and the source electrode 425 overlap with part of the pattern of the semiconductor film 423 through an amorphous silicon film into which an n-type impurity is introduced, although not illustrated. As shown in FIG. 14B, the drain electrode 424 is connected to a data line (video signal electrode) 424a. In other words, the drain electrode 424 is formed as a part of the data line 424a. The gate electrode 421 also constitutes part of the scanning signal line 421a.

  Furthermore, in the fifth embodiment, a color filter layer 414 is formed on the protective layer 426, and a light shielding film 427 is formed on the protective layer 426 so as to cover the active layer 423 of the TFT. The color filter layer 414 and the light shielding layer 427 are covered with an overcoat layer 415. The overcoat layer 415 is made of a transparent insulating material that is difficult to charge up.

  A pixel electrode 412 connected to the source electrode 425 through a through hole 428 is provided on the overcoat layer 415, and a vertical alignment film 413 is formed thereon.

  Also in the fifth embodiment, the source electrode 425 is connected to the pixel electrode 412, and a video signal is applied to the pixel electrode. The on / off of the video signal is controlled by the scanning signal. The pixel electrode 412 has a highly symmetric shape. Although a square is illustrated here, as shown in FIG. 1C, a similar effect can be obtained with a circle, a pentagon, an octagon, or the like.

  Liquid crystal molecules 400 having negative dielectric anisotropy are sandwiched between the upper and lower substrates. Since the alignment films of the upper and lower substrates are vertical alignment films, the liquid crystal 400 is aligned perpendicular to the substrates when no voltage is applied.

  When a voltage is applied to the gate electrode 421 to turn on the thin film transistor (TFT) 420, a voltage is applied to the source electrode 425, and an electric field is induced between the pixel electrode 412 and the common electrode 402 disposed opposite thereto. The At this time, since the shape of the pixel electrode 412 is highly symmetric and the common electrode 402 is larger than the pixel electrode 412, the electric field generated between the two electrodes is not perpendicular to the substrate but is oblique from the periphery of the pixel electrode toward the center. It becomes an electric field. Due to this electric field, the liquid crystal molecules 400 having a negative dielectric anisotropy are tilted symmetrically toward the center of the pixel. For this reason, the alignment direction of the liquid crystal in the pixel is naturally divided.

  As described above, in the present invention, when a liquid crystal having a negative dielectric anisotropy is used, the direction in which the liquid crystal falls can be automatically divided without specially processing the alignment film. Viewing angle can be achieved.

  In the case of the fifth embodiment, because of the structure, the pixel electrode 412 is sufficiently separated from the gate line (scanning signal line) 421a and the drain line (video signal line) 424a. The alignment of the liquid crystal is hardly disturbed by the electric field. Nevertheless, for the purpose of preventing the adverse effect of the electric field from the outside, a shielding electrode may be provided on the upper part of one or both electrodes.

  In the fifth embodiment, the pixel electrode 412 is disposed between the color filter layer 414 and the liquid crystal layer 400. As a result, even the alignment between the color filter layer 414 and the pixel electrode 412 becomes unnecessary, and the overlay accuracy of the upper and lower substrates is greatly reduced. Obtaining such a remarkable effect is completely impossible in the technique having an opening in the common electrode. In addition, by arranging the pixel electrode 412 between the color filter layer 414 and the liquid crystal layer 400 in this way, the influence of the horizontal electric field from the scanning signal electrode 421a and the video signal electrode 424a can be greatly reduced. . Further, by adopting such a configuration, it is possible to solve the problem of color unevenness due to charge-up in the color filter layer 414, which has been a problem in the IPS method and the method in which vertically aligned liquid crystal is tilted by a lateral electric field. .

  Further, in the same manner as in the third and fourth embodiments, when it is desired to more completely control the direction in which the liquid crystal is tilted, a photo-alignment film is used as the alignment film, and the oblique alignment is performed according to the properties of the photo-alignment film. Operations such as irradiation with polarized light or non-polarized light may be performed. Further, in order to prevent the alignment of the liquid crystal from being disturbed, a small amount of monomer may be introduced into the liquid crystal so as to memorize an appropriate alignment state.

  In addition, when the polarization transmission axes are orthogonal to each other, a normally black mode is obtained, but a negative uniaxial compensation film and a positive uniaxial compensation film are used in combination in order to eliminate the observation angle dependency of the initial liquid crystal alignment retardation. be able to. This eliminates the dependency of the black state on the viewing angle, improving the image quality and widening the viewing angle.

  Further, in the above description, it is assumed that the dielectric anisotropy of the liquid crystal is negative and the liquid crystal is vertically aligned with respect to the substrate when no voltage is applied. Even when the dielectric anisotropy is positive and the twisted nematic alignment is taken when no voltage is applied, the liquid crystal alignment substantially the same as the liquid crystal alignment described in the second embodiment occurs, and a wide viewing angle can be achieved. In this case, the liquid crystal layer is divided into four as shown in FIGS. When using twisted nematic orientation, square pixels are desirable.

  The liquid crystal manufacturing method of the liquid crystal display device of the fifth embodiment can be the same as that of the first embodiment.

  Next, examples of the fifth embodiment will be described. (Example 12) In the same manner as in Example 4, a substrate having an amorphous silicon thin film transistor array (TFT) 420 was formed on a glass substrate 411 by repeating the film formation process and the lithography process. The TFT 420 includes a gate-chromium layer 421, a silicon nitride-gate insulating layer 422, an amorphous silicon-semiconductor layer 423, and drain / source-molybdenum layers 424, 425 from the substrate side. Next, a protective film 426 was formed over the gate insulating film 422 so as to cover the drain electrode 424, the source electrode 425, and the semiconductor film 423.

  Next, a color filter layer and a light shielding layer are formed on the protective film 426. The color filter layer 414 is made of, for example, a resin film containing a red, green, or blue dye or pigment. The light shielding layer 427 may be formed of a resin containing a black dye or pigment. Alternatively, the light shielding layer 427 may be formed using metal.

  The color filter layer 414 may be formed using, for example, a pigment dispersion resist in which a pigment capable of obtaining desired optical characteristics such as red is dispersed in an acrylic-based negative photosensitive resin. First, a pigment dispersion resist is applied on the protective film to form a resist film. Next, exposure is performed using a photomask so that light is selectively applied to a predetermined region of the resist film, that is, a pixel region arranged in a matrix. After this exposure, development is performed using a predetermined developer to form a predetermined pattern. The color filter layer 414 can be formed by repeating these steps three times for the number of colors, for example, three colors of red, blue, and green.

  Next, an overcoat layer 415 made of a transparent insulating material is formed over the color filter layer 414 and the light shielding layer 427. For this overcoat layer 415, for example, a thermosetting resin such as an acrylic resin may be used. Further, as the overcoat layer 415, a photocurable transparent resin may be used. Finally, a pixel electrode 412 having a quadrangular shape connected to the source electrode 425 through the through hole 428 was formed on the overcoat layer 415.

  As the counter substrate, a glass substrate having ITO coated on the entire surface was prepared. In the same manner as in Example 4, vertical alignment films (SE1211 manufactured by Nissan Chemical Industries, Ltd.) 403 and 413 were applied to both substrates, and heat drying was performed at 200 ° C. for 1 hour. After applying a sealing agent around the substrate and spraying a spacer agent, the sealing agent was cured by heating, nematic liquid crystal having a negative dielectric anisotropy was injected, and the injection hole was sealed with a photocurable resin. An optically negative compensation film having the same size as that of Δnd of the liquid crystal layer and having the opposite sign was attached, and then a polarizing plate was attached to the upper and lower substrates so that their transmission axes were orthogonal to each other.

  When the viewing angle characteristics of the panel thus obtained were measured, there was no gradation inversion and an excellent viewing angle characteristic with a very wide high contrast region was obtained. In addition, it was found that when the upper and lower substrates are bonded, no alignment is required, and there is no problem even if the pixel size is reduced.

  (Example 13) A panel was produced in the same manner as in Example 11 except that the shape of the pixel electrode was changed to a shape having a protruding portion as shown in FIG.

  When the viewing angle characteristics of the panel thus obtained were measured, there was no gradation inversion and an excellent viewing angle characteristic with a very wide high contrast region was obtained. In addition, the disclination curve observed in Example 11 with a very small number of pixels was not observed at all.

  (Example 14) A TFT substrate was prepared in the same manner as in Example 12, a color filter layer 414 and an overcoat layer 415 were formed, and a rectangular pixel electrode was formed. As in Example 3, the alignment film and the liquid crystal material were taken from the JAL JALS-428 and ZLI4792 chiral materials, and rubbed in the same manner as in Example 3 to produce a liquid crystal panel exactly as in Example 11. did.

  When the viewing angle characteristics of the panel thus obtained were measured, there was no gradation inversion and an excellent viewing angle characteristic with a very wide high contrast region was obtained. In addition, it was found that when the upper and lower substrates were bonded, alignment was not necessary, and there was no problem even if the pixel size was reduced.

  Example 15 A panel was prepared in exactly the same manner as in Example 13 except that the shape of the pixel electrode was changed to a shape having protrusions as shown in FIG. When the viewing angle characteristics of the panel thus obtained were measured, there was no gradation inversion and an excellent viewing angle characteristic with a very wide high contrast region was obtained.

1 shows a liquid crystal display device according to a first embodiment of the present invention, in which (a) is a cross-sectional view taken along line AA ′ of (b), (b) is a plan view, and (c) is a shape of a pixel electrode. It is a conceptual diagram which shows the example of. It is a conceptual diagram which shows the example of the shape of the pixel electrode which connected the shape with good symmetry. It is a conceptual diagram which shows the example of the shape of the pixel electrode which provided the notch. It is a conceptual diagram which shows the example of the shape of the pixel electrode which provided the projection part. It is a conceptual diagram which shows the example of the shape of the pixel electrode which provided the non-electrode part which does not form an electrode. It is a conceptual diagram which shows the example of the shape of the pixel electrode which provided the recessed part. The liquid crystal display device of 2nd Embodiment of this invention is shown, (a) is sectional drawing, (b) is a top view which shows the division | segmentation of the liquid crystal of a pixel. The liquid crystal layer shows a liquid crystal display device having a homogeneous structure when no voltage is applied, (a) is a cross-sectional view, and (b) is a plan view showing division of liquid crystal of a pixel. 4A and 4B show a liquid crystal display device according to a third embodiment of the present invention, in which FIG. 5A is a cross-sectional view taken along line B-B ′ in FIG. 5B, and FIG. 1 shows a liquid crystal display device having a pixel electrode provided with a recess, where (a) is a cross-sectional view taken along line B-B ′ in (b), and (b) is a plan view. The case where the dielectric constant anisotropy in 3rd Embodiment is used is shown, (a) is sectional drawing along the BB 'line of (b), (b) is a top view. is there. The liquid crystal display device of 4th Embodiment of this invention is shown, (a) is sectional drawing along the C-C 'line | wire of (b), (b) is a top view. FIG. 7A shows a transition change of the alignment state of the liquid crystal in the test panel of the eleventh embodiment of the present invention. FIG. 5A is a photograph showing the alignment state when a drive voltage is suddenly applied, and FIG. It is the photograph which shows the orientation state at the time of applying a drive voltage after that. The liquid crystal display device of 5th Embodiment of this invention is shown, (a) is sectional drawing along the D-D 'line | wire of (b), (b) is a top view. 1 shows a conventional liquid crystal display device, where (a) is a cross-sectional view, (b) is a plan view of a common electrode, and (c) is a plan view of a pixel electrode.

Explanation of symbols

100 Liquid crystal molecules 101 Transparent substrate 102 Common electrode 103 Alignment film 110 Lower substrate 111 Wiring electrode 112 Insulating film 113 Through hole 114 Pixel electrode 116 Shielding electrode 200 Liquid crystal 201 Transparent substrate 202 Color filter 203 Light shielding film 204 Common electrode 205 Alignment film 211 Lower substrate 212 Pixel electrode 220 Thin film transistor 221 Gate electrode 221a Scanning signal electrode 222 Gate insulating film 224 Drain electrode 224a Video signal line 225 Source electrode 300 Liquid crystal 301 Transparent substrate 302 Color filter 303 Light shielding film 304 Common electrode 305 Alignment film 311 Lower side Substrate 312 Pixel electrode 320 Thin film transistor 321 Gate electrode 321a Scanning signal electrode 322 Gate insulating film 324 Drain electrode 324a Video signal line 325 Source electrode 327 Through-hole 400 Liquid crystal 401 Transparent substrate 402 Common electrode 403 Alignment film 411 Lower substrate 412 Pixel electrode 414 Color filter 415 Overcoat layer 420 Thin film transistor 421 Gate electrode 421a Scan signal electrode 422 Gate insulating film 424 Drain electrode 424a Video signal line 425 Source electrode 427 Light shielding film 428 Through hole 501 Color filter substrate 502 Common electrode 503 Alignment film 504 Pixel electrode 507 Lower substrate (TFT substrate)
517 slit

Claims (14)

A liquid crystal display device having a structure in which a liquid crystal layer is sandwiched between a first substrate and a second substrate, and a voltage is applied between the common electrode on the first substrate and the pixel electrode on the second substrate. The first substrate has a common electrode for applying a reference potential across a plurality of pixels, and the second substrate has a plurality of scanning signal electrodes and a plurality of scanning signal electrodes crossing them in a matrix. It has video signal electrodes and a plurality of thin film transistors formed corresponding to the intersections of these electrodes, and at least one pixel is formed in each region surrounded by the plurality of scanning signal electrodes and video signal electrodes are have respective picture element electrode that is connected to the thin film transistors corresponding to the pixel, the pixel electrode and the scanning electrode, and the said picture signal electrode and the thin film transistor via the interlayer insulating film Is released,
The liquid crystal layer is composed of a liquid crystal having a negative dielectric anisotropy, and is aligned substantially perpendicular to the first substrate and the second substrate when no voltage is applied, and the pixel electrode is the common electrode An electrode having a smaller area than that of the electrode, covered with the common electrode, and having three rotationally symmetrical centers and having a good symmetry, adjacent neighboring symmetrically shaped electrodes are mutually rotationally symmetric. A liquid crystal display device having a shape connected at one place on a straight line connecting the centers.   2. The liquid crystal display device according to claim 1, wherein the shape having a rotational symmetry center and good symmetry is a circle or a regular polygon.   3. The liquid crystal display device according to claim 1, wherein the pixel electrode has a radial notch or protrusion from a rotationally symmetric center having a good symmetry. 4.   3. The liquid crystal display device according to claim 1, wherein the pixel electrode is radially formed with no electrode portion in which an electrode extending from a rotationally symmetric center having a good symmetry toward the periphery is not formed. A liquid crystal display device.   3. The liquid crystal display device according to claim 1, wherein the pixel electrode has a radial concave portion from a rotationally symmetric center having a good symmetry toward the periphery. 4.   6. The liquid crystal display device according to claim 5, wherein the recess is formed in an interlayer insulating film or an overcoat layer.   7. The liquid crystal display device according to claim 1, wherein at least one of an optically negative compensation film and an optically positive compensation film is interposed between the first or second substrate and the polarizing plate. A liquid crystal display device characterized in that the refractive index anisotropy of the liquid crystal layer and the compensation film is made isotropic by being installed.   8. The liquid crystal display device according to claim 1, wherein the liquid crystal layer has quarter-wave plates on both sides of the liquid crystal layer, and the optical axes of the quarter-wave plates are orthogonal to each other. A liquid crystal display device characterized by the above.   9. A liquid crystal display device according to claim 1, wherein the liquid crystal material contains a chiral agent.   10. The liquid crystal display device according to claim 1, wherein at least a part of the pixel electrode is a reflection portion.   11. The liquid crystal display device according to claim 1, wherein a part of the pixel electrode or a shielding electrode is disposed on at least one of the scanning signal electrode and the video signal electrode. Liquid crystal display device.   12. A method for driving a liquid crystal display device, comprising applying the voltages of adjacent pixels of the liquid crystal display device according to claim 1 in the opposite direction.   A method for driving a liquid crystal display device, comprising: returning the liquid crystal display of the liquid crystal display device according to any one of claims 1 to 11 to a black state before one frame ends.   12. A method of driving a liquid crystal display device according to claim 1, wherein a voltage substantially equal to a threshold voltage of the liquid crystal is applied to the liquid crystal display device according to claim 1 before one frame starts.