JP2004333756A - Liquid crystal device and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize clear image display having no grittiness, in a vertical alignment type liquid crystal device. <P>SOLUTION: Slit-shaped aperture parts 21a are provided in positions corresponding to a non-pixel region of a common electrode 21 so that liquid crystal molecules L in the non-pixel region are not affected at all by the electric field generated by applying voltage between a pixel electrode 11 and the common electrode 21. The kernel of disclination generated in one pixel is made not to cross the non-pixel region and move to an another pixel region by fixing the alignment of the liquid crystal molecules L of the pixel peripheral part strongly to such an extent. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid crystal device and an electronic apparatus including the same, and more particularly, to an alignment control technique of a vertical alignment type liquid crystal device suitable for use in a light valve of a projector, a display unit of a mobile phone, a PDA, or the like. .
[0002]
[Prior art]
A liquid crystal device is required to have a display with a high contrast and a wide viewing angle, and in order to realize such a display, studies on a vertical alignment mode have been actively conducted (for example, see Patent Document 1).
In this vertical alignment type liquid crystal device, the initial alignment state of liquid crystal molecules (the alignment state when no voltage is applied) is set to be almost completely perpendicular to the substrate surface by the vertical alignment film, and this state is displayed in black. As a result, a high-contrast display with less black floating can be realized as compared with a TN-type liquid crystal device.
[0003]
[Patent Document 1]
JP-A-2002-202511
[Problems to be solved by the invention]
However, in this vertical alignment type liquid crystal device, the alignment regulating force is originally weak, and an unstable domain structure is likely to be formed due to various alignment states of liquid crystal molecules when a voltage is applied. A region where the liquid crystal molecules do not fall (disclination) is generated at the boundary between these adjacent domains. There is. This disclination area does not pose a significant problem as long as it always occurs at the same location, but if this disclination area moves over the entire panel, a grainy feeling is generated in the image display.
The present invention has been made in view of the above problems, and has as its object to provide a liquid crystal device capable of obtaining an image display without roughness, and an electronic apparatus including the liquid crystal device.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, a liquid crystal device according to the present invention includes an array substrate on which a plurality of pixel electrodes are arrayed, a counter substrate on which a common electrode is formed, and a substrate sandwiched between the two substrates, and the initial alignment state is vertical. A liquid crystal layer made of a liquid crystal having a negative dielectric anisotropy exhibiting alignment, wherein the common electrode is formed by conductively connecting a plurality of electrode portions arranged and formed corresponding to each pixel electrode. I do.
[0006]
In this configuration, an opening is provided at a position corresponding to a non-pixel region (a region between pixel electrodes) with respect to the common electrode so as to surround the outer periphery of each pixel electrode in a plan view, and the non-pixel region In this case, the alignment of the liquid crystal positioned at the position can be stably maintained. That is, in this configuration, since both the pixel electrode and the electrode portion of the common electrode are arranged in an island shape, the liquid crystal molecules located in the non-pixel region in the voltage applied state are caused by the pixel electrode-common electrode generated by the voltage application. The initial vertical alignment state is stably maintained without being affected by the electric field at all. As described above, in this configuration, the alignment state of the liquid crystal in the non-pixel region is firmly defined, so that the disclination generated in one pixel cannot move to another pixel beyond the non-pixel region. For this reason, a clear image display without roughness can be realized. In particular, the present inventors have confirmed that when the pixel pitch is 30 μm or less, the position at which the disclination occurs is fixed to the center of the pixel. Therefore, by applying this configuration to such a high-definition liquid crystal panel, the display quality can be further improved.
[0007]
In the above-described configuration, a projection or an opening may be provided at the center of each electrode portion of each pixel electrode or common electrode in order to reliably fix the position where disclination occurs. With this configuration, the position at which the disclination occurs is reliably fixed in the area where the protrusion or the opening is formed, and an image display with less roughness can be obtained.
Further, a chiral agent may be added to the liquid crystal layer. Thereby, the orientation of the liquid crystal molecules at the time of applying a voltage is stabilized, and a bright display is obtained.
[0008]
Further, the shape of the pixel electrode is preferably a polygon having no acute angle portion. Further, the shape may include a straight portion (including a bent portion having no acute angle) and a curved portion. With such a shape having no acute angle portion, disclination hardly occurs, and high-speed display with a wide viewing angle and high contrast can be realized. In particular, when the pixel shape is a shape having a rotational symmetry such as a regular polygon or a circle, the orientation of the liquid crystal molecules becomes an axially symmetric orientation, and the viewing angle characteristics are improved.
[0009]
According to another aspect of the invention, an electronic apparatus includes the above-described liquid crystal device. According to this configuration, it is possible to provide an electronic device including a display unit without a feeling of roughness.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
[First Embodiment]
Hereinafter, the liquid crystal device according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view illustrating a schematic configuration of a liquid crystal device according to the present embodiment, FIG. 2 is a plan view of a main part structure of the liquid crystal device viewed from a counter substrate side, and FIG. FIG. 4 is a plan view showing the alignment state of the liquid crystal in one pixel. In the following drawings, the scale of each layer and each member is different in order to make each layer and each member have a size recognizable in the drawings. Further, in this specification, a surface arranged on the liquid crystal layer side in each member constituting the liquid crystal device is referred to as an “inner surface”, a surface on the opposite side is referred to as an “outer surface”, and a region where a pixel electrode is formed is further defined. A pixel region and a region between pixel electrodes are referred to as a non-pixel region.
[0011]
As shown in FIG. 1, in the liquid crystal device of the present embodiment, a liquid crystal having a negative dielectric anisotropy is sealed between a pair of substrates 10 and 20 facing each other, and the sealed liquid crystal serves as a light modulation layer. The liquid crystal layer 30 of FIG.
A plurality of substantially rectangular pixel electrodes 11 made of a transparent conductive film such as ITO are arranged in a matrix on the inner surface side of a lower substrate 10 made of a translucent material such as quartz, glass, plastic, or the like. A vertical alignment film 12 is formed so as to cover 11. In the present embodiment, the lower substrate 10 is configured as a TFT array substrate on which switching elements such as TFTs and various wirings such as data lines and scanning lines are formed. However, in FIG. Illustration of the wiring is omitted.
[0012]
On the other hand, a common electrode 21 made of a transparent conductive film such as ITO is formed on the inner surface side of the upper substrate 20 made of a translucent material such as quartz, glass, plastic, or the like. An alignment film 22 is formed.
[0013]
As shown in FIG. 2, the common electrode 21 is provided with a plurality of openings 21a at positions corresponding to the non-pixel regions so as to surround the outer periphery of each pixel electrode 11 in plan view. Specifically, a slit-shaped opening 21a is provided along each edge of the pixel electrode 11, and the common electrode 21 is partitioned into a plurality of conductive regions by these openings 21a. The four openings 21a arranged so as to surround one pixel electrode 11 are not connected to each other, and the conductive region surrounded by these openings 21a is electrically connected to another conductive region. Has become. In the present embodiment, the conductive region surrounded by the four openings 21a at the position facing the pixel region is used as the electrode portion 210, and the conductive region surrounded by the four openings 21a at the position facing the non-pixel region is connected. The unit 211 is assumed. That is, the common electrode 21 is composed of a plurality of island-shaped electrode portions 210 arranged and formed to face the respective pixel electrodes 11, and the respective electrode portions 210 are conductively connected to each other via the connection portions 211.
Polarizing plates 15 and 25 are provided on the outer surfaces of the lower substrate 10 and the upper substrate 20, respectively.
[0014]
When a voltage is applied between the pixel electrode 11 and the common electrode 21 in such a configuration, the liquid crystal molecules L located in the pixel region are caused by the oblique electric field generated at the edge of the pixel electrode 11 as shown in FIG. Then, it falls radially from the periphery of the pixel toward the pixel center E1, and a disclination nucleus is stably formed in the pixel center E1. That is, in the pixel center portion E1, the tilt direction of the surrounding liquid crystal molecules L is concentrated in this region E1, so that the liquid crystal molecules L located in the region E1 cannot be tilted, and the initial vertical alignment state is stably maintained. You. At this time, the orientation directions of the liquid crystal molecules L are defined in four directions D1 to D4 perpendicular to the respective edges of the pixel electrode 11, and regions having four different orientation directions are formed in the pixel. As a result, orientation division is realized, and good viewing angle characteristics are obtained.
[0015]
On the other hand, in the non-pixel region E2, since neither the pixel electrode 11 nor the electrode portion 210 is formed, as shown in FIG. 3, the liquid crystal molecules L located in this region E2 generate an electric field between the electrodes 11 and 210 generated by applying a voltage. The initial vertical alignment state is stably maintained without being affected at all. Therefore, even if the applied voltage fluctuates within one pixel and the position of the disclination fluctuates, the alignment state of the pixel peripheral portion is firmly defined. It does not move to the pixel.
[0016]
Therefore, according to the liquid crystal device of the present embodiment, the moving range of the disclination generated in one pixel area can be limited to the pixel area, thereby realizing a clear image display without roughness. In particular, the present inventors have confirmed that, in a liquid crystal device having a pixel pitch of 20 μm or less, the position at which the disclination occurs is securely fixed in a narrow range at the center of the pixel. The display quality can be further improved by applying to such a high-definition liquid crystal panel.
[0017]
[Second embodiment]
Next, a liquid crystal device according to a second embodiment of the present invention will be described with reference to FIGS. In the present embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.
[0018]
In the present embodiment, a chiral agent is added to the liquid crystal layer 30 ', so that the alignment of the liquid crystal molecules L can be controlled more stably. That is, since the spirally tilted spiral orientation as shown in FIG. 6 is more stable than the simple radially inclined orientation, the chiral agent is added to the liquid crystal layer as in the first embodiment. Even in a configuration in which no liquid crystal is added, the liquid crystal molecules L fall in a helically twisted state along the thickness direction of the liquid crystal layer when a voltage is applied. The twist direction is not always constant but unstable, and the twist direction of the liquid crystal molecules L in one pixel is the same, but the twist direction is random between pixels. When a plurality of domains having different twisting directions are formed in the display area in this manner, disclination is likely to occur in the boundary area, leading to a reduction in response speed and transmittance. Therefore, by adding a chiral agent to the liquid crystal layer 30 'and setting the twist direction to be the same for all pixels, it is possible to prevent the occurrence of disclination between the pixels.
[0019]
In the simple radial tilt alignment, the liquid crystal molecules L aligned in the vertical or horizontal direction with respect to the polarization axes of the polarizers 15 and 25 do not give a phase difference to incident light. Incident light passing through the state region does not contribute to transmittance. On the other hand, when a chiral agent is added to the liquid crystal layer 30 'to change the liquid crystal molecules L spirally along the liquid crystal layer thickness direction as in the present embodiment, the polarization of the polarizing plates 15 and 25 is increased. Liquid crystal molecules L oriented in a direction perpendicular or parallel to the axis can also give a phase difference to incident light. Therefore, the incident light passing through the region in such an alignment state also contributes to the transmittance, so that a bright display is possible.
[0020]
In the present embodiment, the opening 21b is provided at the center of the electrode portion 210 '(that is, the pixel center E1). By providing such an opening 21b, the equipotential surface of this portion E1 is distorted when a voltage is applied, and the position where disclination occurs can be reliably fixed in this opening region.
Therefore, according to the present embodiment, it is possible to further reduce the feeling of roughness as compared with the first embodiment, and it is possible to provide a fast response and a bright display.
[0021]
[Third embodiment]
Next, a liquid crystal device according to a third embodiment of the present invention will be described with reference to FIG. In this embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.
[0022]
This embodiment is obtained by modifying the shapes of the pixel electrode and the electrode portion in the configuration of the first embodiment. That is, the pixel electrode 11 ′ of the present embodiment has a circular shape as shown in FIG. 7, and the electrode portion 210 ″ of the common electrode 21 ″ has a circular shape accordingly. In FIG. 7, reference numeral 211 'denotes a connecting portion, and each conductive portion 210''is conductively connected to each other via the connecting portion 211'.
An opening 21b 'is provided at the center of the electrode portion 210 "(that is, the pixel central portion E1), as in the second embodiment, and the position at which disclination occurs is determined by the pixel central portion E1. It can be fixed securely.
The rest is the same as the first embodiment.
[0023]
Therefore, in the present embodiment, since the pixel shape and the opening shape of the light-shielding film are circular, the liquid crystal molecules L in the pixel region are continuously tilt-aligned radially around the pixel center E1, resulting in a more rough feeling. A small display is possible.
[0024]
In addition, the shape of the pixel electrode 11 ′ and the electrode portion 210 ″ may be, for example, a polygon having no acute angle portion in addition to the circular shape. Further, the shape may be configured by a straight portion (including a bent portion having no acute angle) and a curved portion. For example, if the shape is an octagon, eight domains having different tilting directions of liquid crystal molecules are formed in one pixel when a voltage is applied. At this time, if there is an acute angle portion in the pixel shape, the liquid crystal molecules L tend to fall in substantially opposite directions in the two adjacent domains at the acute angle portion, so that disclination is likely to occur at this boundary portion. . On the other hand, when the pixel shape does not have an acute angle portion, the orientation direction of liquid crystal molecules between adjacent domains is almost parallel, and the occurrence of disclination is suppressed. Thereby, high-speed, wide viewing angle, and high-contrast display can be performed.
[0025]
In particular, when the shape is a shape having rotational symmetry (that is, a regular polygon or a circle), the orientation of the liquid crystal molecules L becomes an axially symmetric orientation, and the viewing angle characteristics are improved. In particular, when the shape is circular as in the present embodiment, the most favorable viewing angle characteristics and a stable alignment state can be obtained.
[0026]
Note that the present invention is not limited to the above-described embodiment, and can be implemented in various modifications without departing from the spirit of the present invention.
For example, in the first and second embodiments, the four openings 21a provided so as to surround one pixel electrode 11 are not connected to each other. However, according to the present invention, the conductive regions disposed inside and outside these openings are electrically connected to each other, so that there is no need to form an electrically isolated region in the common electrode. Two or three openings may be connected to each other. Further, in the above embodiment, the connection portion 211 is a corner portion of the electrode portion 210, but this position may be an edge of the electrode portion 210 and can be set arbitrarily.
[0027]
In the second and third embodiments, the opening 21b is provided in the common electrode 21 in order to more reliably fix the position where disclination occurs. However, such an opening may be provided in the pixel electrode. Good. Further, instead of providing the opening, a projection may be provided on the pixel electrode or the electrode portion, and the same effect as providing the opening can be obtained.
[0028]
Further, in each of the above embodiments, a transmissive structure is employed as the liquid crystal device of the present invention, but a reflective or semi-transmissive reflective structure may be employed. In the case of a reflective liquid crystal device, a metal reflective film of high reflectivity such as Al or Ag, or a laminated film of such a metal reflective film and a transparent conductive film can be used for the pixel electrode. For the lower substrate 10, an opaque material such as a semiconductor substrate can be used in addition to a light-transmitting material such as glass.
[0029]
(Electronics)
Next, a projection display device which is an example of the electronic apparatus of the present invention will be described.
FIG. 8 is a schematic configuration diagram showing an example of a so-called three-panel type liquid crystal projector using the liquid crystal device of the above embodiment as three liquid crystal light valves (light modulation means). In the figure, reference numeral 510 is a light source, 513, 514 are dichroic mirrors, 515, 516, 517 are reflection mirrors, 518, 519, 520 are relay lenses, 522, 523, 524 are liquid crystal light valves, and 525 is a cross dichroic prism (color). Reference numeral 526 denotes a projection lens system (projection means).
[0030]
The light source 510 includes a lamp 511 such as a metal halide and a reflector 512 that reflects light from the lamp 511. The dichroic mirrors 513 and 514 are color separation units that separate light emitted from the light source into a plurality of different color lights, and the dichroic mirror 513 that reflects blue light and green light reflects red light out of white light from the light source 510. While transmitting light, it reflects blue light and green light. The transmitted red light is reflected by the reflection mirror 517 and enters the red light liquid crystal light valve 522.
[0031]
On the other hand, among the color lights reflected by the dichroic mirror 513, green light is reflected by the dichroic mirror 514 that reflects green light, and is incident on the liquid crystal light valve 523 for green. On the other hand, the blue light also passes through the second dichroic mirror 514. For blue light, a light guide unit 521 including a relay lens system including an entrance lens 518, a relay lens 519, and an exit lens 520 is provided to compensate for a difference in optical path length from green light and red light. The blue light is incident on the liquid crystal light valve for blue light 524 via this.
[0032]
Then, each of the light valves 522 to 524 modulates the incident color light to form a corresponding color image light, and outputs the image light to the cross dichroic prism 525. The prism 525 is formed by bonding four right-angle prisms, and a dielectric multilayer film that reflects red light and a dielectric multilayer film that reflects blue light are formed in a cross shape on the inner surface.
The three image lights are combined by these dielectric multilayer films to form light representing a color image. Then, the combined light is projected on a screen 527 by a projection lens system 526, and an image is displayed in an enlarged manner.
[0033]
In the projection display device having the above configuration, since the liquid crystal device of the above embodiment is used as a light valve, a clear image display without a feeling of roughness can be realized.
Note that, as the electronic apparatus of the present invention, in addition to the above-mentioned projection display device, a mobile phone, a PDA, an electronic book, a personal computer, a digital still camera, a liquid crystal television, a viewfinder type or a monitor direct-view type video tape recorder, Examples include a car navigation device, a pager, an electronic organizer, a calculator, a word processor, a workstation, a videophone, a POS terminal, a device equipped with a touch panel, and the like. Apparatus can be applied.
[Brief description of the drawings]
FIG. 1 is a sectional view of a liquid crystal device according to a first embodiment of the present invention.
FIG. 2 is a plan view showing a main part structure of the liquid crystal device.
FIG. 3 is a cross-sectional view showing an alignment state when a voltage is applied to the liquid crystal device.
FIG. 4 is a plan view showing an alignment state when voltage is applied to the liquid crystal device.
FIG. 5 is a sectional view of a liquid crystal device according to a second embodiment of the present invention.
FIG. 6 is a plan view showing an alignment state when voltage is applied to the liquid crystal device.
FIG. 7 is a plan view illustrating a main structure of a liquid crystal device according to a third embodiment of the invention.
FIG. 8 is a diagram illustrating a projection display device as an example of the electronic apparatus of the invention.
[Explanation of symbols]
10, array substrate, 11, 11 ', pixel electrode, 20 counter substrate, 21, 21', 21 '', common electrode, 21a, 21a ', opening, 21b, 21b', opening, 30, 30 ' ... Liquid crystal layer, 210, 210 ', 210 "... Electrode part

Claims (7)

An array substrate on which a plurality of pixel electrodes are arranged and formed;
A counter substrate on which a common electrode is formed,
A liquid crystal layer made of a liquid crystal having a negative dielectric anisotropy sandwiched between the two substrates and exhibiting an initial alignment state of vertical alignment,
The liquid crystal device, wherein the common electrode includes a plurality of electrode portions arranged and formed corresponding to each pixel electrode, which are conductively connected to each other. The liquid crystal device according to claim 1, wherein a projection or an opening is provided at the center of each pixel electrode or each electrode portion. The liquid crystal device according to claim 1, wherein a chiral agent is added to the liquid crystal layer. The liquid crystal device according to claim 1, wherein the shape of the pixel electrode is a polygon having no acute angle portion. The liquid crystal device according to claim 4, wherein the shape of the pixel electrode has rotational symmetry. The liquid crystal device according to claim 1, wherein a pixel pitch is 30 μm or less. An electronic apparatus comprising the liquid crystal device according to claim 1.

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