JP5687372B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device operated by simple matrix driving.

  Liquid crystal display devices are widely used as information display units in, for example, various consumer and in-vehicle electronic devices. A general liquid crystal display device is configured by disposing a liquid crystal layer made of a liquid crystal material between two substrates arranged to face each other with a gap of about several μm. A vertical alignment type liquid crystal display device is known as one of such liquid crystal display devices. A vertical alignment type liquid crystal display device is a vertical alignment mode (hereinafter referred to as “VA mode”) in which liquid crystal molecules in a liquid crystal layer disposed between two substrates are aligned substantially perpendicular to the surface of each substrate. And a polarizing plate provided outside the liquid crystal cell as main components. Each polarizing plate is often in a crossed Nicol arrangement. In this way, since the transmittance of the liquid crystal display device when no voltage is applied becomes very low, a high contrast can be realized relatively easily.

  In order to realize a VA mode liquid crystal cell, it is important to control the alignment of liquid crystal molecules in the liquid crystal layer by applying a predetermined alignment treatment to the substrate surface. As the alignment treatment, for example, a metal oxide such as SiOx is vapor-deposited from a direction inclined with respect to the substrate normal, thereby forming a thin film having a saw-shaped surface on the substrate surface (so-called oblique vapor deposition method), An organic alignment film material such as polyimide is formed on the substrate surface and then irradiated with ultraviolet rays from a specific direction (so-called photo-alignment processing method; see Patent Document 1), or a vertical alignment film having a specific surface free energy An alignment process (see Patent Document 2) is mainly known in which a film is formed on a substrate surface and a rubbing process is performed on the surface. According to these alignment treatments, an alignment in which liquid crystal molecules in the liquid crystal layer are aligned in one direction when no voltage is applied (so-called monodomain alignment) can be obtained.

  A dot matrix method is known as one of display methods in a liquid crystal display device. In this dot matrix type liquid crystal display device, strip electrodes (stripe electrodes) are provided on the inner surfaces of an upper substrate and a lower substrate, and upper and lower substrates are arranged so that the strip electrodes intersect each other. In this liquid crystal display device, each intersection of the strip-shaped electrode on the upper substrate and the strip-shaped electrode on the lower substrate is a pixel portion. A dot matrix type liquid crystal display device can realize a good display state by operating by a simple matrix driving method (multiplex driving method) such as an optimum bias driving method or a multi-line addressing method. The dot matrix type liquid crystal display device has an advantage that the structure is simple and the cost is low as compared with an active matrix type liquid crystal display device in which a switching element such as a TFT is incorporated in each pixel portion.

  By the way, when driving a dot matrix type liquid crystal display device, an oblique electric field is generated near the edge of the pixel portion when a voltage is applied to each pixel portion, and this oblique electric field causes the liquid crystal layer to be vertically aligned and the dielectric of the liquid crystal material. When the rate anisotropy is negative, light leakage tends to occur near the edge of the pixel portion. In particular, when an off-voltage is applied, the transmittance at the off-voltage increases due to the occurrence of light leakage near the edge of the pixel portion even though a good black state can be achieved at the center of the pixel portion. Inconveniently, the contrast at the time of front observation is lowered.

Japanese Patent No. 2872628 JP 2005-234254 A

  A specific aspect of the present invention is to improve contrast by suppressing light leakage near the edge of a pixel portion when a vertical alignment type liquid crystal display device having an electrode structure for simple matrix driving is driven by a simple matrix driving method. One of the purposes is to provide a technology that can be used.

A liquid crystal display device according to an aspect of the present invention is a liquid crystal display device that is subjected to simple matrix driving (multiplex driving), and includes: (B) a first electrode in a strip shape provided on one surface side of the first substrate and extending in the first direction; (c) provided on one surface side of the second substrate; and A strip-shaped second electrode extending in the intersecting second direction; and (d) provided between the one surface side of the first substrate and the one surface side of the second substrate, and has a negative dielectric anisotropy. A liquid crystal layer containing a liquid crystal material and substantially vertically aligned; and (e) a pair of polarizing plates disposed with the first substrate and the second substrate interposed therebetween. Provided at at least one edge along the first direction in the crossing region with the two electrodes, and regularly arranged along the first direction (G) each of the plurality of first openings has two sides along the second direction in plan view, and (h) the pair of polarizing plates includes: Each of the absorption axes is a liquid crystal display device that is obliquely crossed so as to have an angle of approximately 45 ° between two sides of each of the plurality of first openings.

  According to the above liquid crystal display device, the pixel portion (intersection region between the first electrode and the second electrode) in the case where the vertical alignment type liquid crystal display device having an electrode structure for simple matrix driving is driven by the simple matrix driving method. Light leakage in the vicinity of the edge can be suppressed, and the contrast can be improved.

The polarizing plate of a pair as described above is arranged such that each of the absorption axes are substantially orthogonal to each other, it is also preferred.

  Each of the plurality of first openings preferably has a structure in which the edge is cut out in a substantially rectangular shape and opened at a portion corresponding to one side of the rectangle. It is also preferable that the plurality of first openings described above are provided on both the one edge and the other edge along the first direction in the intersection region.

  The first electrode may further include a second opening provided so as to overlap at least one edge of the second electrode along the second direction in a region intersecting with the second electrode. preferable.

  The second electrode preferably further includes a plurality of third openings provided at at least one edge along the second direction in a region intersecting with the first electrode.

  The liquid crystal layer preferably contains a chiral material.

It is the external appearance schematic diagram and partial enlarged view of the liquid crystal display device of one Embodiment. It is a fragmentary sectional view of the liquid crystal display device shown in FIG. It is a figure for demonstrating the simulation result of the pixel part provided with the several rectangular opening part. It is a figure for demonstrating the simulation result of the pixel part of a comparative example. It is a figure which shows the microscope observation image of the liquid crystal display device actually produced on the same conditions as the simulation of a comparative example. It is a top view which shows the structure of the pixel part in the liquid crystal display device of 1st Example. It is a figure which shows the microscope observation image of the pixel part at the time of the dark display of the liquid crystal display device of 1st Example. It is a figure which shows the microscope observation image of the pixel part at the time of the bright display of the liquid crystal display device of 1st Example. It is a figure which shows the microscope observation image of the pixel part at the time of the bright display of the liquid crystal display device of 2nd Example. It is a figure which shows the microscope observation image of the pixel part at the time of the bright display of the liquid crystal display device of a comparative example. It is a figure which shows the transmittance | permeability characteristic when each liquid crystal display device is driven on predetermined conditions. It is a figure for demonstrating the simulation result of the pixel part in which the some rectangular opening part was provided in each edge of upper and lower, right and left.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic external view and a partially enlarged view of a liquid crystal display device according to an embodiment. FIG. 2 is a partial cross-sectional view of the liquid crystal display device shown in FIG. Specifically, FIG. 2A is a partial cross-sectional view taken along line aa ′ of the liquid crystal display device shown in FIG. 1, and FIG. 2B is a partial cross-sectional view taken along line bb ′ shown in FIG. FIG. The liquid crystal display device 100 of this embodiment shown in each drawing includes an upper substrate (first substrate) 1, a plurality of upper stripe electrodes (first electrodes) 2, an alignment film 3, a lower substrate (second substrate) 4, A plurality of lower stripe electrodes (second electrodes) 5, an alignment film 6, a liquid crystal layer 7, an upper polarizing plate (first polarizing plate) 8, and a lower polarizing plate (second polarizing plate) 9 are included. Yes.

  The upper substrate 1 and the lower substrate 4 are transparent substrates such as a glass substrate and a plastic substrate, respectively. Between the upper substrate 1 and the lower substrate 4, spacers (granular bodies) are dispersed and arranged. By these spacers, the gap between the upper substrate 1 and the lower substrate 4 is kept at a predetermined distance (for example, about 4.0 μm).

  The plurality of upper stripe electrodes 2 are provided on one surface of the upper substrate 1. Each upper stripe electrode 2 is formed in a band shape, and extends in one direction on one surface of the upper substrate 1. In the present embodiment, each upper stripe electrode 2 extends in the vertical direction (first direction) in FIG. Each upper stripe electrode 2 is configured by appropriately patterning a transparent conductive film such as indium tin oxide (ITO), for example. Although not shown in FIGS. 1 and 2 for the sake of convenience, each upper stripe electrode 2 has a rectangular opening at its edge portion. This will be described in detail later.

  The plurality of lower stripe electrodes 5 are provided on one surface of the lower substrate 4. Each lower stripe electrode 5 is formed in a strip shape and extends in one direction on one surface of the lower substrate 4. In the present embodiment, each lower stripe electrode 5 extends in the left-right direction (second direction) in FIG. Each lower stripe electrode 5 is configured by appropriately patterning a transparent conductive film such as indium tin oxide (ITO), for example. As shown in the partial enlarged view of FIG. 1, in the liquid crystal display device 100 of this embodiment, each of the locations where the upper stripe electrode 2 and the lower stripe electrode 5 overlap in a plan view (intersection region location) is a pixel portion. 11 In FIG. 1, only one pixel portion 11 is shown colored.

  The alignment film 3 is provided on one surface side of the upper substrate 1 so as to cover the upper stripe electrodes 2. Similarly, the alignment film 6 is provided on one surface side of the lower substrate 4 so as to cover each lower stripe electrode 5. In the present embodiment, as the alignment film 3 and the alignment film 6, a film (vertical alignment film) that restricts the alignment state of the liquid crystal layer 3 in the initial state (when no voltage is applied) to the vertical alignment state is used. More specifically, as each of the alignment films 3 and 6, a substantially vertical alignment state in which a pretilt angle of 90 ° (for example, 89.9 °) is given to the liquid crystal molecules of the liquid crystal layer 3 is used.

  In the present embodiment, the alignment films 3 and 6 are each subjected to an alignment process such as a rubbing process. As shown in FIG. 1, the alignment direction of the liquid crystal molecules determined by the direction of this alignment treatment is 6 o'clock (downward in the figure) on the upper substrate 1 and 12 in the lower substrate 4. It is a time direction (upward direction in the figure). In other words, the upper substrate 1 and the lower substrate 4 are arranged to face each other so that the direction of the alignment treatment to each is antiparallel.

  The liquid crystal layer 7 is provided between the upper stripe electrodes 2 of the upper substrate 1 and the lower stripe electrodes 5 of the lower substrate 4. In the present embodiment, the liquid crystal layer 7 is configured using a liquid crystal material (nematic liquid crystal material) having a negative dielectric anisotropy Δε (Δε <0). A thick line 10 illustrated in the liquid crystal layer 7 schematically shows an alignment direction (director) of liquid crystal molecules when no voltage is applied. As shown in the figure, in the liquid crystal display device of the present embodiment, the alignment state of the liquid crystal molecules in the liquid crystal layer 7 is vertically aligned in the initial state (no voltage applied state) and restricted to the monodomain alignment.

  The upper polarizing plate 8 is disposed outside the upper substrate 1. The lower polarizing plate 9 is disposed outside the lower substrate 4. The upper polarizing plate 8 and the lower polarizing plate 9 are, for example, in a crossed Nicols arrangement. As shown in FIG. 1, in this embodiment, the absorption axis of the upper polarizing plate 8 is set in the 45 ° direction counterclockwise with reference to the 3 o'clock to 9 o'clock direction (extending direction of the lower stripe electrode 5). The absorption axis of the lower polarizing plate 9 is set in the 45 ° direction clockwise.

  Next, an example of a manufacturing method of the liquid crystal display device will be described in detail.

First, a substrate having a transparent electrode on one surface is prepared. As the substrate, for example, a glass substrate in which one surface is polished, SiO ₂ is coated on the surface, and a transparent conductive film made of ITO (indium tin oxide) is formed thereon can be used.

  A known photolithography process and etching process are performed on the substrate. For example, a positive photoresist is applied to the substrate with a roll coater or the like. Thereafter, using a photomask having a desired pattern formed of a chromium metal film or the like, the photoresist surface and the metal film surface of the photomask are brought into close contact with each other, and then the photoresist pattern is baked by irradiating ultraviolet rays. Thereafter, the photoresist is baked under a predetermined condition (for example, 120 ° C. for 10 minutes), and wet development is performed with a predetermined solution (for example, KOH aqueous solution), thereby removing the resist irradiated with the ultraviolet rays. Thereafter, the resist pattern strength is improved by baking under predetermined conditions (for example, 120 ° C. for 30 minutes), and the ITO film is etched using a predetermined solution (for example, a mixed aqueous solution of hydrochloric acid and sulfuric acid at 40 ° C.). . Finally, the resist is removed using a predetermined solution (for example, NaOH aqueous solution). Thereby, the upper substrate 1 having the upper stripe electrodes 2 and the second substrate 2 having the lower stripe electrodes 5 are formed.

  Next, the alignment film 3 is formed on one surface of the upper substrate 1, and the alignment film 6 is formed on one surface of the lower substrate 4. Specifically, after each substrate is washed with an alkali solution or the like, the material liquid of the vertical alignment film is applied onto one surface of each substrate by a method such as flexographic printing, and these are baked in a clean oven (for example, , 180 ° C., 30 minutes). Thereafter, alignment processing (for example, rubbing processing in the present embodiment) is performed on the alignment films 3 and 6. The pretilt angle of the liquid crystal layer 7 can be controlled by appropriately setting the alignment treatment conditions in this step.

  Next, spacers having a particle diameter of, for example, about 4 μm are dispersed on one substrate (for example, one surface of the upper substrate 1). The spacer is sprayed by, for example, a dry spraying method. Further, a sealing material is formed on the other substrate (for example, on one surface of the lower substrate 4). The sealing material is formed by applying a mixture of silica spacers having a particle size of about 4.2 μm by a method such as screen printing.

  Next, the upper substrate 1 and the lower substrate 4 are bonded together so that their one surfaces face each other and the alignment treatment directions for the alignment films 3 and 6 are antiparallel, and fired in a constant pressure state. To do. Thereby, the sealing material is cured, and the upper substrate 1 and the lower substrate 4 are fixed (an empty cell is completed). The upper substrate 1 and the lower substrate 4 are arranged so that the upper stripe electrode 2 and the lower stripe electrode 5 intersect each other (see FIG. 1).

  Next, a liquid crystal material (with a dielectric anisotropy Δε <0) is injected into the gap between the upper substrate 1 and the lower substrate 4 by a method such as vacuum injection, and the injection port used for the injection is sealed. Later, firing is performed (for example, 120 ° C., 1 hour). Thereby, the liquid crystal layer 7 is formed.

  Thereafter, the empty cell is appropriately washed and dried, and the upper polarizing plate 8 is bonded to the outside of the upper substrate 1, and the lower polarizing plate 9 is bonded to the outer side of the lower substrate 4. As described above, each of the upper polarizing plate 8 and the lower polarizing plate 9 has an angle of approximately 45 ° with respect to the alignment direction of the liquid crystal molecules at the center of the liquid crystal layer 7 and is mutually crossed Nicol. Placed in. Thus, the liquid crystal display device shown in FIGS. 1 and 2 is completed.

  Next, an electrode structure for suppressing light leakage near the edge of the pixel portion 11 will be described. As described above, in the present embodiment, a plurality of openings (first openings) cut out in a rectangular shape in plan view are provided at locations corresponding to the edges of the pixel portions 11 of the upper stripe electrodes 2. ing. Below, the effect by the several rectangular opening provided in the location corresponding to the edge of the pixel part 11 is demonstrated based on a simulation analysis result.

  FIG. 3 is a diagram for explaining a simulation result of a pixel portion provided with a plurality of rectangular openings. FIG. 3A shows the structure of the upper stripe electrode 2, and FIG. 3B shows the structure of the lower stripe electrode 5. Each colored portion corresponds to an electrode. As shown in FIG. 3A, the upper stripe electrode 2 is provided with a plurality of rectangular openings 20 at positions corresponding to the edges of the pixel portion 11 (in the figure, several openings are provided). Only 20 is labeled). Each opening (notch) 20 has a structure in which one and the other edges of the upper stripe electrode 2 are cut out in a substantially rectangular shape, and is opened at a portion corresponding to one side of the rectangle, The shape is defined by the portions corresponding to the remaining three sides. Each opening 20 is formed such that its two sides (long sides in the illustrated example) are substantially orthogonal to the extending direction (that is, the first direction) of the upper stripe electrode 2. In this simulation analysis, it is assumed that a plurality of regularly arranged openings 20 are provided at one end edge (left side in the figure) and the other end edge (right side in the figure) of the upper stripe electrode 2. . Also. The size of each opening 20 in this simulation analysis was set to 10 μm in the vertical direction (short side) and 20 μm in the horizontal direction (long side), and the distance between adjacent openings 20, that is, the arrangement pitch was set to 20 μm. . As shown in FIG. 3B, the lower stripe electrode 5 is not provided with an opening at a location corresponding to the edge of the pixel portion 11.

  The simulation conditions will be described. The simulation analysis area is 160 μm square, and the number of elements at the time of simulation analysis is set to 80 × 80 in the plane of the liquid crystal display device and 30 divisions in the thickness direction. The width of each of the upper stripe electrode 2 and the lower stripe electrode 5 was set to 140 μm. For the liquid crystal layer 7, the layer thickness (cell thickness) was set to 4 μm, and for the liquid crystal material, Δn was set to about 0.15 and Δε was set to about −3.5. The pretilt angle was set to 89.9 ° for both the upper substrate 1 and the lower substrate 4, and the rubbing direction was set to 12 o'clock for the lower substrate 4 and 6 o'clock for the upper substrate 1. The absorption axes of the upper polarizing plate 8 and the lower polarizing plate 9 are 45 ° clockwise for the lower polarizing plate 9 and 45 ° counterclockwise for the upper polarizing plate 8 based on the 9 o'clock to 3 o'clock direction. Set. Then, when the potential difference between the upper substrate 1 and the lower substrate 4, that is, the voltage applied to the liquid crystal layer 7 is set to a value near the threshold voltage, the steady state where the realignment of the liquid crystal molecules in the liquid crystal layer 7 is stable. The orientation distribution of liquid crystal molecules was calculated, and based on this, the in-plane transmittance distribution when observed from the normal direction of the liquid crystal display device was calculated. FIG. 3C shows the calculation result of the transmittance distribution for one pixel unit 11. As shown in the drawing, in the vicinity of the left and right edges of the pixel unit 11, although light leakage occurs, the luminance is significantly suppressed as compared with the comparative example shown below.

  FIG. 4 is a diagram for explaining the simulation result of the pixel portion of the comparative example. FIG. 4A shows the structure of the upper stripe electrode, and FIG. 4B shows the structure of the lower stripe electrode. Each colored portion corresponds to an electrode. As shown in FIGS. 4A and 4B, in this comparative example, both the upper stripe electrode 102 and the lower stripe electrode 105 are provided with openings at positions corresponding to the edges of the pixel portion 111. It is not done. Other simulation analysis conditions are the same as described above. FIG. 4C shows the calculation result of the transmittance distribution for one pixel unit 111. As shown in the figure, no light leakage occurs inside the pixel unit 111, but light leakage occurs near the top, bottom, left, and right edges of the pixel unit 111. In addition, the same result was obtained also in the liquid crystal display device actually produced on the same conditions as the simulation of a comparative example, and the microscope observation image is shown in FIG. One pixel portion 111 was 0.42 mm, and the interval between adjacent pixel portions was 0.03 mm.

  The reason why light leakage at the edge of the pixel portion is suppressed by providing a plurality of rectangular openings at positions corresponding to the edge of the pixel portion will be described below. In a portion where the stripe electrodes 102 and 105 cross in the comparative example (that is, the pixel portion), an oblique electric field is generated from the edge of one stripe electrode toward the other stripe electrode. In the region where the oblique electric field is generated, that is, in the vicinity of the edge of the pixel portion 111, the liquid crystal molecules tend to tilt toward the direction orthogonal to the electric field direction of the oblique electric field. On the other hand, in a region where an oblique electric field is not generated, that is, inside the pixel portion 111, liquid crystal molecules are tilted in a direction regulated by the alignment process. That is, the tilt angle of the director of the liquid crystal molecules near the edge of the pixel unit 111 is larger than the tilt angle of the liquid crystal molecules (director) inside the pixel unit 111. If the respective absorption axes of the upper polarizing plate 8 and the lower polarizing plate 9 are arranged at an angle of approximately 45 ° relative to the extending direction of the stripe electrodes 102 and 105, Changes in the liquid crystal molecules in the vicinity of the edge (director deformation) greatly affect the transmitted light intensity. For this reason, light leakage in the vicinity of the edge of the pixel portion 111 becomes significant. This is the cause of light leakage near the edge of the pixel unit 111 in the comparative example.

  On the other hand, in the present embodiment, since the plurality of rectangular openings 20 are provided at locations corresponding to the edges of the pixel portion 11 with respect to the stripe-shaped electrode 2, generation of oblique electric fields can be suppressed. it can. That is, since each opening 20 includes a side substantially parallel to a side substantially parallel to the extending direction of the stripe electrode 2, an electric field generated between each side and the other stripe electrode 5 is synthesized. Is done. As a result, the liquid crystal molecules in the vicinity of the edge of the pixel unit 11 are inclined in the direction of the absorption axis of the upper polarizing plate 8 or a direction close thereto. For this reason, light leakage near the edge of the pixel unit 11 is suppressed. Further, by arranging the openings 20 regularly, the distribution of the synthetic electric field generated by the openings 20 becomes uniform, so that the effect of suppressing light leakage can be made more uniform.

  Next, the effect of a plurality of rectangular openings provided at locations corresponding to the edges of the pixel unit 11 will be further described based on examples.

  FIG. 6 is a plan view showing the structure of the pixel portion 11 in the liquid crystal display device of the first embodiment. The overall configuration of the liquid crystal display device of the first embodiment is as shown in FIGS. 1 and 2, and various conditions are in accordance with the numerical examples described above. As shown in FIG. 6, the pixel portion 11 of the embodiment is provided in an intersecting region of each upper stripe electrode 2 and each lower stripe electrode 5. The upper stripe electrode 2 extends in the vertical direction in the drawing, and the lower stripe electrode 5 extends in the horizontal direction in the drawing. The pixel unit 11 is configured in a square shape with one side having a length R. In this embodiment, the length R is 0.42 mm. Note that the pixel portion 11 does not necessarily have a square shape, and may have a rectangular shape.

  Each upper stripe electrode 2 is provided with a plurality of openings 20 at locations corresponding to the left and right edges of the pixel portion 11 in plan view. In FIG. 6, only some of the openings 20 are denoted by reference numerals. Each opening 20 has a longitudinal direction substantially orthogonal to the extending direction of the upper stripe electrode 2 and has a long side having a length T1 and a short side having a width S1. In this embodiment, the length T1 is 0.05 mm and the width S1 is 0.007 mm. In this embodiment, the distance between the long sides of adjacent openings 20 (that is, the arrangement pitch of openings 20) A1 is set to 0.014 mm. In addition, each opening part 20 does not necessarily need to be rectangular shape, and square shape etc. may be sufficient as it.

  Further, the upper stripe electrode 2 of this embodiment is provided with a plurality of openings (second openings) 21 at positions overlapping with the upper edge of the pixel portion 11 (that is, the edge of the lower stripe electrode 5). It has been. In FIG. 6, only one opening 21 is denoted by a reference numeral. Each opening 21 is formed in a slit shape, and the longitudinal direction of each opening 21 is substantially orthogonal to the extending direction of the stripe electrode 2 and has a long side having a length T2 and a short side having a width S2. In this embodiment, the length T2 is 0.05 mm and the width S2 is 0.02 mm. In addition, each opening part 21 does not necessarily need to be rectangular shape, and square shape etc. may be sufficient as it. In the present embodiment, the distance between the short sides of adjacent openings 21 (that is, the arrangement pitch of the openings 21) A2 is set to 0.05 mm, and the edge of the stripe electrode 2 and the opening 21 closest to the edge are arranged. And the mutual distance B was set to 0.085 mm. Further, in this embodiment, each opening 21 is arranged so that the center of the short side of the opening 21 overlaps the edge of the pixel portion 11 (that is, the edge of the lower stripe electrode 5). By providing each opening 21 as described above, an oblique electric field in the forward direction is periodically generated with respect to the left-right direction in the vicinity of the upper edge in the plan view of the pixel unit 11. Thereby, an oblique electric field is generated in the vicinity of the upper edge of the pixel portion 11 in the direction opposite to the alignment direction of the liquid crystal molecules at the center of the liquid crystal layer 7, so that the alignment disorder of the liquid crystal layer 7 can be suppressed. Note that only one opening 21 may be provided depending on the size of the pixel portion 11 and the like.

  FIG. 7 is a diagram showing a microscope observation image of the pixel unit 11 during dark display of the liquid crystal display device of the first embodiment. In FIG. 7, one pixel portion 11 is shown. In FIG. 7, the brightness is adjusted for the sake of visibility of the drawing. Similar to the simulation analysis results described above, also in the liquid crystal display device of the embodiment, the light in the vicinity of the left and right edges of the pixel unit 11 is provided by providing a plurality of openings 20 at locations corresponding to the left and right edges of the pixel unit 11. It can be seen that omission is suppressed. Further, the occurrence of a dark region near the upper edge of the pixel unit 11 is also suppressed. This point will be further described later.

  FIG. 8 is a diagram showing a microscope observation image of the pixel unit 11 during bright display of the liquid crystal display device of the first embodiment. FIG. 8 shows three pixel portions 11 arranged side by side. In the liquid crystal display device according to the first embodiment, although light leakage of the pixel portion 11 during dark display is suppressed as described above, each of the openings is provided by providing a plurality of openings 20 on the left and right edges of the pixel portion 11. A dark region is observed around the opening 20, and it can be seen that the aperture ratio of the pixel 11 is somewhat reduced. This can be avoided by forming the liquid crystal layer 7 using a liquid crystal material to which a chiral material is added as described below.

  FIG. 9 is a diagram showing a microscope observation image of the pixel portion 11 during bright display of the liquid crystal display device of the second embodiment. The overall configuration of the liquid crystal display device of the second embodiment is the same as that of the first embodiment described above, except that a chiral material is added to the liquid crystal material for forming the liquid crystal layer 7. The chiral material was adjusted so that d / p was about 0.7 when the layer thickness of the liquid crystal layer 7 was d and the twist pitch was p. Further, with respect to the arrangement of the upper substrate and the lower substrate 4, the alignment treatment (rubbing treatment in this example) is performed so that the liquid crystal molecules of the liquid crystal layer 7 are twisted 180 ° clockwise (clockwise when viewed from the upper substrate 1 side). ) Direction. Compared to the case of the first embodiment (see FIG. 8), it can be seen that the dark regions at the left and right edges of the pixel portion 11 are eliminated by introducing a twisted structure into the liquid crystal layer 7. That is, it can be seen that the aperture ratio of the pixel portion 11 can be further increased in the liquid crystal display device of the second embodiment compared to the first embodiment. It has been confirmed that the d / p setting of the liquid crystal layer 7 is 0.5 or more and less than 0.8, preferably 0.5 or more and 0.74 or less.

  FIG. 10 is a diagram showing a microscope observation image of the pixel portion during bright display of the liquid crystal display device of the comparative example. The liquid crystal display device of the comparative example has the same configuration as that of the liquid crystal display device of the first embodiment, except that the openings 20 and 21 are not provided in the pixel portion 11. As shown in the figure, a dark region is generated near each edge of the pixel portion, and it can be seen that belt-like dark regions intersect each other near the upper edge. This intersection corresponds to so-called disclination. As shown in the drawing, the intersections (black crosses) of the dark regions occur at different positions for each pixel portion. That is, there is no regularity at the occurrence point of the intersection of the dark region. On the other hand, in the liquid crystal display device of the first embodiment shown in FIG. 8 described above, the location where the dark area intersection occurs is fixed corresponding to the arrangement of the openings 21, and the shape of the liquid crystal display device is also a pixel. It can be seen that there is little difference between parts.

  According to the observation results of the respective examples and comparative examples described above, it is considered that a difference in characteristics is observed particularly in the vicinity of the threshold voltage in the electro-optical characteristics. Therefore, (a) a liquid crystal display device having a comparative example structure in which no chiral material is added to the liquid crystal layer, (b) a liquid crystal display device having a comparative example structure in which a chiral material is added to the liquid crystal layer, (c) For the four types of liquid crystal display device of the first embodiment in which no chiral material is added to the liquid crystal layer, and (d) the liquid crystal display device of the second embodiment in which the chiral material is added to the liquid crystal layer, the electricity during frontal observation is shown. Optical properties were evaluated. The driving conditions of each liquid crystal display device were 1/64 duty, 1/9 bias, frame frequency 250 Hz, and the transmittance was measured when the driving voltage VLCD at the ON voltage was changed. The measurement results are shown in FIG. FIG. 11 (a) shows the characteristics of the comparative example and the examples (above, a and c) without addition of the chiral material, and FIG. 11 (b) shows the characteristics of the comparative example and the embodiment (above, b and d) with the addition of the chiral material. Indicates. In each figure, the “solid line” indicates the characteristic of the comparative example, and the “broken line” indicates the characteristic of the example. In FIG. 11A, in the liquid crystal display device of the example, the maximum transmittance is lower than that of the comparative example because the aperture ratio of the pixel portion 11 is somewhat lowered, but the steepness in the VLCD near the threshold is improved. You can see that On the other hand, in FIG. 11B, it can be seen that the liquid crystal display device of the example shows significantly superior steepness as compared with the comparative example.

  Incidentally, in each of the above-described embodiments, light leakage is suppressed by providing a plurality of openings 20 at the left and right edges of the pixel unit 11, but the same applies to the upper and lower edges of the pixel unit 11.

  FIG. 12 is a diagram for explaining a simulation analysis result of a pixel portion in which a plurality of rectangular openings are provided at each of the top, bottom, left, and right edges. FIG. 12A shows the structure of the upper stripe electrode 2, and FIG. 12B shows the structure of the lower stripe electrode 5. Each colored portion corresponds to an electrode. As shown in FIG. 12A, the upper stripe electrode 2 is provided with a plurality of rectangular openings 20 at positions corresponding to the left and right edges of the pixel portion 11 (in the figure, several openings are provided). Only the part 20 is provided with a reference numeral). Further, as shown in FIG. 12B, the lower striped electrode 5 is provided with a plurality of rectangular openings 22 (third openings) at locations corresponding to the upper and lower edges of the pixel portion 11. (In the figure, only some of the openings 22 are labeled). The size of each opening 20 in this simulation analysis was set to 10 μm in the vertical direction and 20 μm in the horizontal direction, and the distance between adjacent openings 20, that is, the arrangement pitch was set to 20 μm. The same applies to the size and arrangement pitch of the openings 22. Other simulation conditions are the same as described above. FIG. 12C shows the calculation result of the transmittance distribution for one pixel unit 11. As shown in the drawing, it can be seen that light is lost near the top, bottom, left, and right edges of the pixel unit 11 but the luminance is greatly suppressed. Therefore, by providing openings at the top, bottom, left, and right edges of the pixel unit 11, it is considered that light leakage near the threshold in the electro-optical characteristics is further suppressed and the steepness is further improved.

  In addition, this invention is not limited to the content of embodiment mentioned above, In the range of the summary of this invention, it can change and implement variously. For example, in the above description, the plurality of openings 20 are provided on the left and right edges of the pixel unit 11, but even when the plurality of openings 20 are provided only on one of the edges, compared to a case where these are not provided. Obviously, the effect of suppressing light leakage can be obtained. The same applies to the plurality of openings 22. In the above description, the plurality of openings 21 are provided only on the upper edge of the pixel unit 11. However, a plurality of openings 21 may be provided on the lower side.

  DESCRIPTION OF SYMBOLS 1 ... Upper substrate (1st substrate), 2 ... Upper stripe electrode (1st electrode), 3 ... Alignment film, 4 ... Lower substrate (2nd substrate), 5 ... Lower stripe electrode (2nd electrode) , 6 ... alignment film, 7 ... liquid crystal layer, 8 ... upper polarizing plate (first polarizing plate), 9 ... lower polarizing plate (second polarizing plate), 10 ... director, 11 ... pixel portion, 20, 21, 22 ... opening

Claims (7)

A liquid crystal display device driven by a simple matrix,
A first substrate and a second substrate disposed so as to face each other on one side;
A band-shaped first electrode provided on one surface side of the first substrate and extending in a first direction;
A belt-like second electrode provided on one surface side of the second substrate and extending in a second direction intersecting the first direction;
A liquid crystal layer provided between the one surface side of the first substrate and the one surface side of the second substrate, containing a liquid crystal material having a negative dielectric anisotropy and substantially vertically aligned;
A pair of polarizing plates disposed across the first substrate and the second substrate;
Including
The first electrode is provided at at least one edge along the first direction in a crossing region with the second electrode, and includes a plurality of first openings arranged regularly along the first direction. Have
Each of the plurality of first openings has two sides along the second direction in plan view,
The pair of polarizing plates obliquely cross so that each absorption axis has an angle of approximately 45 ° between each of the two sides of each of the plurality of first openings.
Liquid crystal display device. The pair of polarizing plates are disposed such that the absorption axes of the pair of polarizing plates are substantially orthogonal to each other.
The liquid crystal display device according to claim 1 . Each of the plurality of first openings has a structure in which the edge is cut out in a substantially rectangular shape and opened at a portion corresponding to one side of the rectangle.
The liquid crystal display device according to claim 1 or 2. The plurality of first openings are provided on both the one edge and the other edge along the first direction in the intersection region.
The liquid crystal display device according to any one of claims 1-3. The first electrode further includes a second opening provided so as to overlap with at least one edge of the second electrode along the second direction in a region intersecting with the second electrode.
The liquid crystal display device according to any one of claims 1-4. The second electrode further includes a plurality of third openings provided at at least one edge along the second direction in a region intersecting with the first electrode.
The liquid crystal display device according to any one of claims 1-4. It said liquid crystal layer contains a chiral agent, a liquid crystal display device according to any one of claims 1-6.