JPH10186331A - Liquid crystal display - Google Patents

Abstract

(57) [Problem] To provide a plasma-addressed liquid crystal display device having excellent viewing angle characteristics and high contrast. SOLUTION: A counter substrate having a signal electrode, a plasma substrate having a plasma chamber for performing plasma discharge, and a liquid crystal layer sandwiched between the counter substrate and the plasma substrate are driven by the signal electrode and the plasma chamber. In the liquid crystal display device, the liquid crystal molecules are formed using liquid crystal molecules having negative dielectric anisotropy, and when no voltage is applied, the liquid crystal molecules are aligned perpendicular to the pair of substrates, When a voltage is applied, the liquid crystal molecules are configured to be axially symmetrically aligned for each of the plurality of picture element regions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display device, and more particularly to a large liquid crystal display device suitable for application to a high-definition television such as an HDTV, a CAD display, and the like.

[0002]

2. Description of the Related Art Currently, TFTs are used as flat displays.
-LCDs are widely used. However, a large T exceeding 20 inches, which is expected to be applied to wall-mounted TVs, etc.
FT-LCD has not yet been commercialized. Recently, as a candidate for realizing a large display device, Japanese Patent Application Laid-Open
Attention has been paid to a plasma addressed LCD (PALC) disclosed in, for example, Japanese Patent No. 17396.

FIG. 1 shows a sectional structure of a PALC. PAL
C100 has a liquid crystal layer 2 provided between a pair of substrates 1 and 11. A plurality of plasma chambers 13 are arranged between the substrate 11 and the liquid crystal layer 2. Each plasma chamber 13 is formed by the substrate 11, the dielectric sheet 16 facing the substrate 11, and the partition 12 provided therebetween. By applying a voltage to the anode 14 and the cathode 15 formed on the surface of the substrate 11 in the plasma chamber 13, the gas (for example, helium, neon, etc.) sealed in the plasma chamber 13 is ionized, and the plasma discharge is started. Occur.

The plurality of plasma chambers 13 extend in a stripe shape in a direction perpendicular to the plane of FIG. 1 and are orthogonal to the transparent electrodes 5 formed on the surface of the substrate 1 on the liquid crystal layer 2 side. In comparison with a simple matrix type liquid crystal display device, the transparent electrode 5 corresponds to a display electrode (signal electrode), and the plasma chamber 13 corresponds to a scanning electrode. The substrate 11, the dielectric sheet 16, the plasma chamber 13, and the like are collectively referred to as a plasma substrate 10.

[0005] The principle of operation of the PALC 100 will be described with reference to FIG. The plasma chamber 13 is sequentially turned on, and the gas in the selected plasma chamber 13 is in an ionized state. In a state where the plasma chamber 13 is ionized, as shown in FIG. 2, charges corresponding to the voltage supplied from the signal line to the transparent electrode 5 are accumulated and held on the back surface of the dielectric sheet 16 (the plasma chamber 13 side). Is done. The signal voltage supplied from the signal line is applied to the liquid crystal layer 2 located on the plasma chamber 13 ionized in this way. Plasma chamber 13
If is not ionized, no electric charge is supplied to the back surface of the dielectric sheet 16 (on the side of the plasma chamber 13), so that no signal voltage is applied to the region of the liquid crystal layer 2 located on the plasma chamber 13. In this way, the plasma chamber 13
Functions like a scanning electrode in a simple matrix type liquid crystal display device.

As a method for manufacturing a large-screen display at low cost, Japanese Patent Application Laid-Open No. 4-265931 discloses a technique of forming a plasma chamber structure on a glass substrate by a printing method using a glass paste. ing.

[0007] Also, JP-A-4-313788 discloses that
In order to solve the problem that the charge generated when using a thick dielectric sheet to improve the strength of the dielectric sheet separating the plasma chamber and the liquid crystal layer is diffused on the liquid crystal layer side and causes bleeding on the display, A configuration in which a transparent electrode is patterned in the direction of the plasma chamber is disclosed.

On the other hand, the conventional TN mode liquid crystal display device has a problem that the viewing angle characteristics are inferior (the viewing angle is narrow). FIG.
As shown in (a), in the halftone display state of the TN-LCD 200, the liquid crystal molecules 202 are tilted in a certain direction. As a result, when the TN-LCD 100 is observed from the viewing angle directions of the arrows A and B in FIG. 3, the apparent light transmittance differs depending on the direction. Therefore, the TN-LCD1
The display quality of 00 (for example, the contrast ratio) greatly depends on the viewing angle.

In order to improve the viewing angle characteristics of the liquid crystal display device by controlling the alignment state of the liquid crystal molecules, it is necessary to align the liquid crystal molecules in at least two directions in the picture element. For example, in the halftone state of the ASM mode liquid crystal display device 210 in which the liquid crystal region 214 is surrounded by the polymer region 212, the liquid crystal molecules are oriented in two different directions as shown in FIG. . This liquid crystal display device 210
When viewed from the viewing angle directions indicated by arrows A and B, the apparent light transmittance is averaged. As a result, A and B
, The light transmittance in the viewing angle direction becomes equal, and the viewing angle characteristics are improved as compared with the TN mode.

[0010] Specific examples of the wide viewing angle mode are as follows.
(1) to (5) can be mentioned.

(1) The liquid crystal cell has a polymer wall, does not require a polarizing plate, and does not require an alignment treatment.
There has been proposed a method of electrically controlling the transparent or opaque state by using the birefringence of liquid crystal. This method basically matches the ordinary light refractive index of liquid crystal molecules with the refractive index of the supporting medium, displays a transparent state when a voltage is applied, and aligns the liquid crystal, and displays a transparent state when no voltage is applied. The light scattering state due to the disorder of the orientation of the image is displayed.

[0012] As a proposed method, Japanese Patent Publication No. Sho 61
Japanese Patent Application No. -502128 discloses a method in which liquid crystal is mixed with a light or thermosetting resin, and then the resin is cured to deposit liquid crystal and form liquid crystal droplets in the resin. Further, a wide viewing angle mode in which the device and a polarizing plate whose polarizing axes are orthogonal to each other is combined is disclosed in JP-A-4-33.
No. 8923 and JP-A-4-212928.

(2) As a method for improving the viewing angle characteristics of a liquid crystal cell by using a non-scattering type polarizing plate, a method disclosed in Japanese Patent Application Laid-Open No. Hei 5-27242 is disclosed.
Japanese Patent Application Laid-Open Publication No. H11-139,086 discloses a method for producing a composite material of a liquid crystal and a polymer material by phase separation from a mixture of a liquid crystal and a photocurable resin. In this method, since the orientation state of the liquid crystal domains is in a random state due to the generated polymer, and the rising direction of the liquid crystal molecules is different in each domain when a voltage is applied, the apparent transmittance (d) seen from each direction is different. (Due to averaging n)), so that the viewing angle characteristic in the halftone state is improved.

(3) Recently, the present inventors have proposed a liquid crystal device in which liquid crystal molecules are omnidirectionally aligned in a picture element region (such as a spiral shape) by controlling the light with a photomask or the like during photopolymerization. It is disclosed in Japanese Unexamined Patent Publication No. Hei 7-120728. The operation of the liquid crystal is axially symmetrical when the voltage is OFF, and the liquid crystal is operated so as to approach the homeotropic alignment by applying a voltage, so that the viewing angle characteristics are remarkably improved. In the invention, a p-type liquid crystal is used. As an example of a manufacturing method, a lattice-shaped polymer wall having a thickness smaller than the cell thickness is formed for each pixel region, and a liquid crystal and a photocurable resin are formed in the manufactured cell. Is disclosed in Japanese Patent Application Laid-Open No. 8-9 / 1994, in which a mixture is injected to form an axisymmetric alignment using a two-phase region where a liquid crystal phase and a homogeneous phase are mixed.
No. 5012 discloses this. In the case of this manufacturing method,
No alignment film was used.

(4) Further, Japanese Patent Application Laid-Open No. 6-308496 discloses a wide viewing angle display mode using an axially symmetric alignment film having a spherulite structure which is a crystalline polymer on the substrate surface.

(5) Japanese Patent Application Laid-Open No. 6-194655 discloses a method in which an alignment film is coated on a substrate and liquid crystal molecules are aligned in a random direction without performing an alignment treatment such as rubbing.

The following (6) and (7) are disclosed as methods of dividing a picture element into a plurality of regions and arranging the liquid crystal molecules so that each region compensates for the viewing angle characteristics of each other. .

(6) Japanese Patent Laid-Open No. 63-106 discloses a method in which picture elements are divided for each picture element in the direction of orientation treatment such as a rubbing direction.
No. 624.

(7) Japanese Patent Application Laid-Open No. 7-199193 discloses a method in which the shape of the substrate surface is formed into a roof shape or a pyramid shape for each picture element, and the direction in which liquid crystal molecules fall is different in each divided area. And Japanese Patent Application Laid-Open No. 7-333612. Japanese Unexamined Patent Publication No. Hei 7-199193 discloses that an n-type (△ ε <0) liquid crystal material and a vertical alignment layer are used, and the liquid crystal molecules are vertically aligned with the substrate when the voltage is off, and the liquid crystal molecules are horizontally inclined when the voltage is on. An alignment type liquid crystal display device is also disclosed.

[0020]

However, the above-mentioned prior art has the following problems.

The display modes used for PALC are:
The TN mode is central. When a display mode in which the display quality depends on the viewing angle, such as the TN mode, is used in a large-screen display device, as shown in FIG. However, there is a problem that the display quality varies within the display surface.

Further, in the alignment division type display device using the p-type (positive dielectric anisotropy) liquid crystal material of the above (6) and (7), the orientation direction of the liquid crystal molecules on the division line when voltage is applied. Discontinuous disclination lines occur, causing a decrease in contrast ratio. Furthermore, the method of dividing the orientation of the inside of these picture elements has a problem that an orientation treatment is required for each region, the number of steps is increased, and the production stability is low.

In the case of the TN mode PALC, the polarization axis of the polarizing plate is adjusted with respect to the screen in order to adjust the viewing angle characteristics in the right and left directions viewed from the observer in consideration of the viewing angle dependency of the TN mode. It is set at 45 ° from the vertical and horizontal directions.
In this case, where there is a difference in the refractive index, such as the bonding surface between the plasma substrate and the thin glass, the junction is visible due to the difference in the birefringence and the reflectance of the polarized light at the bonding surface. Causes light leakage in the direction.

The display mode used for PALC is a display mode using a p-type liquid crystal material such as a NW (normally white) TN mode. PALC in these display modes has a problem that a sufficient contrast ratio cannot be obtained. This is because the non-uniform plasma discharge causes unevenness in the voltage (electric field) applied to the liquid crystal layer. p-type liquid crystal (△ ε>
In the NW display mode using 0), there is a problem that the black level is reduced particularly when the voltage is ON, and the contrast ratio is greatly reduced.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a plasma address type liquid crystal display device having excellent viewing angle characteristics and high contrast.

[0026]

A liquid crystal display device according to the present invention comprises a counter substrate having a signal electrode, a plasma substrate having a plasma chamber for performing a plasma discharge, a liquid crystal layer sandwiched between the counter substrate and the plasma substrate. A liquid crystal display device driven by the signal electrode and the plasma chamber,
The liquid crystal molecules of the liquid crystal layer have a negative dielectric anisotropy. When no voltage is applied, the liquid crystal molecules are oriented perpendicular to the pair of substrates. The orientation is axially symmetrical in each region, thereby achieving the above object.

The thickness (din) of the liquid crystal layer in the picture element region
Is larger than the thickness (dout) of the liquid crystal layer outside the pixel region, and is in a region corresponding to the pixel region on a surface of the at least one of the counter substrate and the plasma substrate on the liquid crystal layer side. It may have a vertical alignment layer.

[0028] At least one of the opposing substrate and the plasma substrate may have, on the surface on the liquid crystal side, a projection surrounding the picture element region.

It is preferable that the thickness of the liquid crystal layer in the picture element region is the largest at the center of the picture element region and decreases continuously toward the periphery of the picture element region.

It is preferable that the thickness of the liquid crystal layer in the picture element region changes axially symmetrically with respect to the center of the picture element region.

The liquid crystal layer has a pair of polarizing plates disposed on both sides of the liquid crystal layer in a crossed Nicols state, and the polarizing axis of one of the pair of polarizing plates is set to extend the signal electrode or the plasma chamber. Preferably, it is parallel to the direction.

It is preferable that the liquid crystal display device further includes an axially symmetric alignment fixed layer that gives an axially symmetric pretilt angle to the liquid crystal molecules on a surface in contact with the liquid crystal layer.

[0033] The axisymmetric alignment fixed layer may be made of a photocurable resin.

Since the liquid crystal display device of the present invention has a liquid crystal region which changes between the vertical alignment and the axially symmetric alignment depending on the voltage, it has excellent viewing angle characteristics. In addition, since a liquid crystal material having a negative dielectric anisotropy is used and a normally black mode display in which the liquid crystal material takes a vertical alignment state when no voltage is applied is provided, a high-contrast display can be provided.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle of operation of a liquid crystal display 300 according to the present invention will be described with reference to FIG. (A) and (b) show a state when no voltage is applied, (c) and (d) show a state when a voltage is applied, (a) and (c) are cross-sectional views,
(B) and (d) show the results of observing the upper surface with a crossed Nicol state polarizing microscope.

The liquid crystal display device 300 has a liquid crystal layer 40 sandwiched between a pair of substrates 32 and 34 and composed of liquid crystal molecules 42 having a negative (n) dielectric anisotropy (Δε). . One of the substrates 32 and 34 is a plasma substrate (10 in FIG. 1). Vertical alignment layers 38a and 38b are formed on the surfaces of the pair of substrates 32 and 34 that are in contact with the liquid crystal layer 40. In addition, a convex portion 36 is formed on at least one surface of the pair of substrates 32 and 34 on the liquid crystal layer 40 side. The convex portion 36 causes the liquid crystal layer 40 to have dout.
And din having two different thicknesses. As a result, as described later, a liquid crystal region exhibiting an axially symmetric orientation when a voltage is applied is defined as a region surrounded by the protrusion 36. In FIG. 5, electrodes and plasma chambers formed on the pair of substrates 32 and 34 for applying a voltage to the liquid crystal layer 40 are omitted.

When no voltage is applied, as shown in FIG.
The liquid crystal molecules 42 are aligned in a direction perpendicular to the substrate by the alignment control force of the vertical alignment layer. When observing the picture element region in the state where no voltage is applied with a polarizing microscope in a crossed Nicols state,
As shown in (b), a dark field is exhibited (normally black mode). When a voltage is applied, a force acts on the liquid crystal molecules 42 having negative dielectric anisotropy to orient the major axis of the liquid crystal molecules perpendicularly to the direction of the electric field, and as shown in FIG. From the right direction (halftone display state).
When the picture element region in this state is observed with a crossed Nicols polarizing microscope, an extinction pattern is observed in the direction along the polarization axis as shown in FIG.

FIG. 6 shows a voltage transmittance curve of the liquid crystal display device 300 of the present invention. The horizontal axis represents the voltage applied to the liquid crystal layer, and the vertical axis represents the relative transmittance. As the voltage is increased from the normally black state when no voltage is applied, the transmittance gradually increases. The voltage at which the relative transmittance becomes 10% is called Vth (threshold voltage). When the voltage is further increased, the transmittance further increases and reaches saturation. The voltage at which the transmittance is saturated is called Vst. The voltage applied to the liquid crystal layer 40 is changed from １ ／ Vth to Vs
If it is between t, the transmittance reversibly changes within the operating range shown in FIG. When a voltage of about 1/2 Vth is applied, the liquid crystal molecules are almost vertically aligned with the substrate, but the symmetry of the liquid crystal molecules with respect to the central axis of the axisymmetric alignment is recorded. It is considered that the application reversibly returns to the axisymmetric alignment state when applied. However, when the applied voltage is lower than 1/2 Vth, the liquid crystal molecules return to a substantially vertical alignment state. When a voltage is applied again, the direction in which the liquid crystal molecules fall is not uniquely determined. Are present, and the transmittance is not stable. Once a voltage of Ｖ Vth or more is applied, a plurality of central axes become one in a region surrounded by the convex portion 36 (corresponding to a pixel region), and the voltage transmittance characteristic shown in FIG. Show. At the stage when the n-type liquid crystal material is injected into the liquid crystal cell, the behavior is the same as when the applied voltage is lower than 1/2 Vth.

Therefore, in the present display mode, an axially symmetric state is produced by applying a voltage for producing an axially symmetric orientation at the initial stage of display, and after the display is started, it is used in a voltage range where the orientation is stable. Will be able to use it.

(Protrusion that Defines Pixel Region) The liquid crystal display device 300 of the present invention includes the projections 3 that surround the pixel region.
6. When there is no convex portion 36 and the thickness (cell gap) of the liquid crystal layer 40 is uniform, the position or size where the liquid crystal domain (continuously aligned region: a region where no disclination line occurs) is formed. Is not specified, a random alignment state is obtained, and the display becomes rough in halftone display.

By forming the convex portion 36, the position and size of the liquid crystal region exhibiting the axially symmetric alignment are defined.
The protrusion 36 controls the thickness of the liquid crystal layer 40 and is formed to weaken the interaction of liquid crystal molecules between picture element regions. The thickness of the liquid crystal layer is determined by the liquid crystal layer thickness (d
_out ) is smaller than the liquid crystal layer thickness (d _in ) _{in the} pixel region (opening) (d _in > d _out ).
It is preferable to satisfy the relationship of × d _in ≦ d _out ≦ 0.8 × d _in . That is, in the case of 0.2 × d _in > d _out , the effect that the convex portion 36 weakens the interaction of the liquid crystal molecules between the pixel regions is not sufficient, and a single axially symmetric alignment region is formed for each pixel region. It may be difficult to form. Furthermore, d _out >
At 0.8 × d _in , it may be difficult to inject the liquid crystal material into the liquid crystal cell.

The "picture element" is generally defined as a minimum unit for displaying. The term "picture element area" used in the present specification refers to a partial area of the display element corresponding to "picture element". However, in the case of a picture element having a large aspect ratio (long picture element), a plurality of picture element regions may be formed for one long picture element. The number of picture element regions formed corresponding to the picture elements is preferably as small as possible as long as the axially symmetric orientation can be stably formed.

(Control of the Position of the Center Axis of Axisymmetric Orientation) The position of the center axis of the axisymmetric alignment region generated when a voltage is applied greatly affects display quality. The relationship between the position of the central axis and the display quality will be described with reference to FIG. FIG. 7 (a)
When the central axis 44 is located at the center of the picture element area as shown in FIG. 7, all the picture element areas look the same as shown in FIG. . on the other hand,
As shown in (b), when there is a picture element area whose center axis is shifted from the center of the picture element area, as shown in (d), the picture element area shifted in center axis is different from other picture element areas. The display is uneven (grainy). This problem,
This is particularly noticeable in halftone display.

By adjusting the thickness din (x) of the liquid crystal layer in the picture element region, the position of the central axis of the axially symmetric orientation can be controlled. As shown in FIG. 8, x = 0 at the center of the pixel region, x = r at one end of the pixel region, and the thickness din (x = 0) of the liquid crystal layer at the center of the pixel region is maximized. The thickness din (x) of the liquid crystal layer may be continuously changed so that the thickness din (x = r) of the liquid crystal layer at one end of the picture element region is minimized. The derivative of din (x) is preferably always negative from x = 0 to x = r, and is preferably continuous. The thickness of the liquid crystal layer is preferably as symmetrical as possible with respect to the center of the picture element region from the viewpoint of the symmetry of the viewing angle characteristics.

By controlling the thickness of the liquid crystal layer as described above, an axially symmetric alignment is formed with good reproducibility. The mechanism will be described with reference to FIG. FIG. 9 is a sectional view schematically showing a picture element region of the liquid crystal display device of the present invention.

A display electrode 52 is formed in a picture element region on the surface of one substrate 32 (for example, a counter substrate), and a vertical alignment layer 58a is formed so as to cover the display electrode 52. The vertical alignment layer 58a has a cross-sectional shape such that the thickness din of the liquid crystal layer 40 changes as shown in FIG. Since the change in the thickness (df) of the vertical alignment layer 58a with respect to the position (x) is opposite to the change in the thickness of the liquid crystal layer 40, the differential coefficient of the thickness df (x) of the vertical alignment layer 58a is positive. Preferably, there is. The liquid crystal layer 4 of the other substrate 34 (plasma substrate)
On the 0-side surface, a vertical alignment layer 58b is formed.
The vertical alignment layer 58b has a flat cross section.

The liquid crystal molecules 42 present in the vicinity of the vertical alignment layer 58a are vertically oriented with respect to the surface of the vertical alignment layer 58a, and thus are inclined with respect to the substrate surface. Therefore, the electrode 5
When a voltage is applied between 2 and 54, the direction of the electric field (E)
In contrast, the major axis of the liquid crystal molecules is in an inclined state. As a result, the liquid crystal molecules 42 are tilted by the electric field E only in the directions indicated by the arrows in the figure. The tilt angle θ ′ of the liquid crystal molecules with respect to the normal direction of the substrate surface is preferably 0 <θ ′ ≦ 3 °. If θ ′ exceeds 3 °, a phase difference occurs due to liquid crystal molecules, light leakage occurs, and the contrast ratio decreases, which is not preferable.

As described above, by changing the cross-sectional shape (thickness) of the vertical alignment layer, as described with reference to FIG.
By changing the thickness of 0, the position of the central axis of the axisymmetric orientation can be controlled, and the axisymmetric orientation can be formed with good reproducibility. In the above example, the thickness of the liquid crystal layer 40 is controlled by the cross-sectional shape of the vertical alignment layer 58a, but the invention is not limited to this. For example, as shown in FIG. 9B, a solid dielectric layer 59 having a desired shape is separately formed under the vertical alignment layer 58a (substrate side), and a vertical alignment having a flat cross-sectional shape is formed thereon. The layer 58a may be formed. As the solid dielectric layer 59, a commonly used overcoating agent, specifically, an epoxy-based coating agent, an epoxy acrylate-based coating agent, or the like can be used.

When the thickness of the liquid crystal layer 40 is controlled using the solid dielectric layer 59, it is preferable that the solid dielectric layer 59 be formed on the display electrode 52. As shown in FIG. 9C, the display electrode 5 is formed on the solid dielectric layer 59 having a desired sectional shape.
When 2 is formed, the direction of the electric field E is inclined with respect to the substrate surface, so that the direction in which the liquid crystal molecules 42 are tilted is not uniquely determined, which is not preferable.

In the case of PALC, the voltage applied to the liquid crystal layer 2 is distributed between the liquid crystal layer 2 and the dielectric sheet 16 according to the capacitance (see FIG. 1). Generally, for PALC,
Since the thickness of the dielectric sheet is larger than the thickness of the liquid layer 2, the voltage applied to the liquid crystal layer 2 is smaller than the voltage applied to the dielectric sheet 16. Therefore, the dielectric sheet 1
Since the effect of the voltage drop due to the formation of the solid dielectric layer on the surface of the liquid crystal layer 2 on the side of No. 6 is relatively small, even if the solid dielectric layer having a thickness of about several μm is formed, there is a practical problem. There is no.

(Liquid Crystal Material) The liquid crystal material used in the present invention is a so-called n-type liquid crystal material having a negative dielectric anisotropy (Δε <0). The magnitude of the absolute value of Δε is
It can be set appropriately depending on the application. Generally, it is preferable to have a large absolute value from the viewpoint of lowering the driving voltage.

D · Δn (Retardation) at the time of voltage application
Is an important factor that affects important characteristics of the device, such as the transmittance and the viewing angle characteristics of the device. In the display mode of the present invention, it is not always necessary to limit the retardation specific to the liquid crystal cell, which is determined by the product of Δn specific to the liquid crystal material and the thickness d of the liquid crystal layer, to an optimum value.

Optimum value of retardation (first minimum condition for maximum transmittance: d · Δn = 450 nm)
FIG. 10 shows a voltage transmittance curve of a liquid crystal display device having a larger retardation value. For such a liquid crystal display device, it is not necessary to use a region beyond the maximum point of the relative transmittance, and the liquid crystal display device may be driven in a region where the relative transmittance monotonously increases. That is, in FIG. 10, the voltage at which the relative transmittance becomes maximum is changed to the maximum drive voltage (Vma
x).

In the present invention, retardation at the maximum drive voltage used is important. The range of the retardation is the product d · Δn (retardation) of the apparent Δn (anisotropy of the refractive index: the value at the maximum driving voltage) of the liquid crystal molecules when the liquid crystal cell is manufactured and the average thickness d of the liquid crystal layer. But about 3
It is preferably from 00 to 500 nm. There is a second minimum condition (retardation: 1000 to 1400 nm) at which the transmittance becomes maximum, but this is not preferable because the viewing angle characteristics when no voltage is applied are inferior. Also, depending on the viewing angle, the relationship between the magnitude of the applied voltage and the transmittance is reversed.
This is not preferable because a so-called gradation inversion (contrast inversion) phenomenon occurs.

The twist angle of the liquid crystal molecules in the liquid crystal layer is also one of the important factors for determining the transmittance of the liquid crystal display. In the present invention, as with retardation, the twist angle at the maximum drive voltage is important. In principle, the transmittance of a liquid crystal display device is such that the twist angle is 90 ° and 270 °.
° indicates the maximum value. However, in the case of a 270 ° twist, it is difficult to stably produce an axially symmetric orientation.
It is preferable to use the vicinity. Specifically, the twist angle when the maximum drive voltage is applied is 45 to 110 °. Since the present invention uses n-type liquid crystal molecules, the apparent twist angle of the liquid crystal molecules depends on the voltage. When no voltage is applied, the twist angle is almost 0 °, and the twist angle increases with an increase in the voltage. When a sufficient voltage is applied, the twist angle approaches the twist angle inherent to the liquid crystal material.

The twist angle and the retardation at the maximum driving voltage are more preferable when both are within the preferable ranges, because the transmittance can be more effectively brought close to the maximum value.

(Photocurable Resin) As described above with reference to FIG. 6, it is preferable that the liquid crystal display device of the present invention always apply a voltage of 1/2 Vth or more. When a voltage is applied to the liquid crystal molecules aligned perpendicular to the substrate, the direction in which the liquid crystal molecules fall cannot be uniquely determined. As a result, a phenomenon occurs in which a plurality of central axes are transiently formed. When the voltage is continuously applied, only one central axis is formed in the area defined by the convex portion, and as long as a voltage of 1/2 Vth or more is applied,
This state exists stably.

1/2 Vth for stabilizing the axially symmetric orientation
By curing the photocurable resin mixed in the liquid crystal material in advance with the above voltage applied, the axially symmetric alignment can be stabilized. After the photocurable resin is cured, even if the voltage of 1/2 Vth or more is removed, a plurality of central axes are not formed, and an axially symmetric orientation is formed with good reproducibility.

As the photocurable resin used in the present invention, acrylate, methacrylate, styrene, and derivatives thereof can be used. By adding a photopolymerization initiator to these resins, the photocurable resin can be more efficiently cured. Alternatively, a thermosetting resin can be used.

The optimum amount of the curable resin varies depending on the material, and the present invention is not particularly limited. However, the resin content (% based on the total weight including the liquid crystal material) is about 0.1 to 5%. Is preferred. If it is less than about 0.1%, the axisymmetric alignment state cannot be stabilized by the cured resin, and if it exceeds about 5%, the effect of the vertical alignment layer is hindered,
Since the liquid crystal molecules deviate from the vertical alignment, the transmittance increases (light leakage), and the black state when the voltage is turned off deteriorates.

(Phase plate) Between two orthogonal polarizing plates,
When a vertically aligned liquid crystal material is interposed, a good black state is obtained in the front direction, and high contrast is obtained. However, when observed at different viewing angles, (i) the viewing angle dependency of the characteristics of the polarizing plate, and (ii) the viewing angle dependency of the retardation of the liquid crystal layer (the retardation of vertically aligned liquid crystal molecules depends on the direction. Changes), light leakage is observed and a decrease in contrast ratio occurs. This phenomenon appears remarkably in a direction at 45 ° from the polarization axis of the polarizing plate (azimuth: in-plane direction of the substrate). To suppress this phenomenon,
It is effective to reduce the retardation of the vertically aligned liquid crystal material. Also, between the liquid crystal cell and the polarizing plate,
It is preferable to install a retardation plate having a Frisbee-type (refractive index _nx , _{y in the} display surface direction> refractive index _{nz in} the display surface vertical direction) refractive index ellipsoid. The phase difference of this phase plate is
It is preferable that the retardation is smaller than the retardation value unique to the liquid crystal cell, which is determined by the product of Δn specific to the liquid crystal material and the thickness d of the liquid crystal layer. More preferably, it is a value of about 30 to 80% of the retardation specific to the liquid crystal cell. Below about 30%
The effect of the retardation plate is small, and if it is about 80% or more, the coloring becomes large in the wide viewing angle direction, which is not preferable.

(Vertical Alignment Layer) It is only necessary to have a surface for vertically aligning liquid crystal molecules, and the material may be an inorganic material or an organic material. For example, polyimide type (JA
LS-204 (Nippon Synthetic Rubber), 1211 (Nissan Chemical), inorganic (EXP-OA003 (Nissan Chemical Industries)) and the like can be used.

(Arrangement of Polarizing Plate) If there is a difference in the refractive index between the bonding surface of the plasma substrate and the thin glass, light leakage occurs on the bonding surface due to the difference in the birefringence and the reflectance with respect to the polarized light. The phenomenon of seeing occurs. This phenomenon occurs when the angle between the polarization axis of the polarizing plate and the surface having a difference in refractive index is 4 degrees.
It is most pronounced at 5 ° and is minimal at 0 ° or 90 °. In the case of the TN mode device, in order to widen the viewing angle in the left-right direction as viewed from the observer in consideration of the viewing angle characteristics (FIG. 11A), as shown in FIG.
Generally, the polarizing plate is arranged so that the polarization axis of the polarizing plate is inclined by 45 ° from the vertical and horizontal directions of the display surface. PALC in TN mode
When such a polarizing plate is arranged in this manner, the plasma chamber structure that causes a difference in the refractive index extends in the vertical or horizontal direction of the display surface, so that the plasma chamber structure can be visually observed and reduced. However, the axisymmetric orientation mode (vertical ASM mode) used in the present invention
In this case, as shown in FIG. 12, since the viewing angle characteristics are highly symmetric, the polarization axes of the polarizing plates can be arranged in the vertical and horizontal directions of the display surface, and the structure of the plasma chamber can be made inconspicuous. . Also in this respect, there is an advantage of applying an axially symmetric orientation to PALC.

[0064]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples.

(Embodiment 1) FIG. 13 is a sectional view of a PALC 400 of this embodiment. PALC400 is a counter substrate 1
20; a plasma substrate 110; and a liquid crystal layer 102 sandwiched therebetween. The liquid crystal layer 102 is made of a sealant 1
06. The plasma substrate 110
Substrate 111 and dielectric sheet 11 facing substrate 111
6 and a plurality of plasma chambers 113 formed by partition walls 112 provided therebetween. The plasma chamber 113 is connected to the liquid crystal layer 1 via a dielectric sheet 116.
It faces 02. By applying a voltage to the anode 114 and the cathode 115 formed on the surface of the substrate 111 on the side of the plasma chamber 113, the gas sealed in the plasma chamber 113 is ionized and plasma discharge occurs.
The plurality of plasma chambers 13 extend in a stripe shape in a direction perpendicular to the paper surface of FIG.
The transparent electrode 1 formed on the surface on the liquid crystal layer 102 side
It is orthogonal to 05. A region where these are orthogonal defines a picture element region.

On the surface of the opposite substrate 110 on the liquid crystal layer 102 side,
Protrusions 132 are formed in a lattice shape so as to correspond to the picture element regions. The projection 132 forms an axially symmetric alignment region corresponding to the pixel region. Further, the surfaces of the plasma substrate 110 and the counter substrate 120 in contact with the liquid crystal layer 102 are provided on the vertical alignment layers 134a and 134a, respectively.
4b is formed.

A PALC400 was manufactured as follows. A plurality of electrode groups each including an anode electrode 114 and a cathode electrode 115 were formed on a glass substrate 111, and a partition 112 having a height of about 200 μm was formed using glass paste so as to separate each electrode pair. Next, the partition 112
A thin film glass substrate 116 having a thickness of about 50 μm was bonded thereon with a photocurable sealing agent. After that, the plasma chamber 113
Was filled with argon gas. JALS-204 (manufactured by Nippon Synthetic Rubber Co., Ltd.) was spin-coated on the entire surface of the thin film glass substrate 116 to form a vertical alignment layer 134a, and the plasma substrate 110 was obtained.

Referring to FIG. 14, a method for manufacturing the counter substrate 120 will be described. First, the stripe-shaped transparent electrode 1
05 (150 nm thick ITO) glass substrate 101
A spacer 1 made of photosensitive polyimide and having a height of about 6 μm
No. 35 was formed outside the picture element region. On top of that, OMR83
(Tokyo Ohka Co., Ltd.) was used to form a projection 132 having a height of about 2.7 μm (the size of the picture element region was 100 μm × 100 μm).
m). On top of that, JALS-204 (manufactured by Nippon Synthetic Rubber Co., Ltd.) is spin-coated to form a vertical alignment layer 134b,
A counter substrate 120 was obtained. The plasma substrate 110 and the opposing substrate 120 were attached to each other to produce a liquid crystal cell.

An n-type liquid crystal material (Δε =
−4.0, Δn = 0.077, 9 at a cell gap of 6 μm
(A twist angle unique to the liquid crystal material is set so as to be 0 ° twist), and a voltage of 7 V is applied. Immediately after voltage application,
In the initial state, a plurality of axially symmetric alignment axes existed. Further, when the voltage application state was continued, one axially symmetric alignment region (monodomain) was formed for each pixel region.

A polarizing plate was arranged on both sides of the liquid crystal cell so as to be in a crossed Nicols state, and a liquid crystal display device was manufactured. The structure of the obtained liquid crystal display device is substantially the same as that of the liquid crystal display device shown in FIG. 8, except that the cross-sectional shape of the vertical alignment layer 134b is mortar-shaped as shown in FIG. (Polarization plate is not shown). Vertical alignment layer 13
4b has a mortar-shaped cross-sectional shape, so that the derivative of the curve indicating the change in the thickness position (from the center of the picture element to the periphery) is positive, and the liquid crystal layer in the picture element region is positive. The derivative of the curve showing the change in thickness is negative.

The axial symmetric orientation of the cell of Example 1 was Ｖ V
It is stable when a voltage higher than th is applied.
If it is lower than / 2 Vth, the state of the axially symmetric orientation is broken and the state returns to the initial state. When a voltage was applied again, the state was changed to an axially symmetric alignment state in which a plurality of central axes of the initial axis symmetric alignment existed, and one central axis was provided for each pixel region.
This phenomenon did not change after 20 runs. Example 1
ＶV to measure the electro-optical characteristics of the liquid crystal cell of
After applying the voltage of th or more to form the axially symmetric state, the measurement was performed in a voltage range (1/2 Vth or more) where the axially symmetric orientation was stable during the measurement of the electro-optical characteristics.

FIG. 15 shows the obtained electro-optical characteristics. As is clear from FIG. 15, the liquid crystal display device according to the present invention has a low transmittance in the OFF state and a good contrast ratio (CR = 300: 1, 5V). The threshold voltage was about 2V. In addition, a high contrast ratio was obtained in a wide viewing angle range as shown in FIG. In FIG. 12, ψ indicates an azimuth angle (angle in the display surface), θ indicates a viewing angle (angle of inclination from the normal to the display surface), and hatching indicates a region where the contrast ratio is 10: 1 or more.

Comparative Example 1 In Comparative Example 1, the transparent electrode 105 formed on the surface of the substrate 101 in FIG.
The vertical alignment layer 134b was directly formed, and thereafter, a spacer 135 was formed using photosensitive polyimide in the same manner as in Example 1. That is, the protrusion 132 in FIG. 14 is not formed. The obtained opposite substrate 120 and the plasma substrate 110 formed in the same manner as in Example 1 were attached to each other to produce a liquid crystal cell. The thickness of the liquid crystal layer in the picture element region of this liquid crystal cell was constant.

When the same material as in Example 1 was injected into this liquid crystal cell, the liquid crystal molecules were in a random alignment state, and disclination lines were formed randomly. When a voltage was applied to the liquid crystal cell and the liquid crystal cell was observed, a rough display was observed in a halftone.

(Embodiment 2) In this embodiment, a method for stabilizing the axially symmetric orientation of liquid crystal molecules by curing a photocurable resin mixed in a liquid crystal material in advance will be described.

FIG. 16 is a schematic partial sectional view of the liquid crystal display device according to the second embodiment.

In the liquid crystal display device 500, a liquid crystal layer 80 including liquid crystal molecules 92 having a negative (n) dielectric anisotropy (Δε) is sandwiched between a pair of substrates 82 and 84. Substrate 82
And 84, a plasma substrate is used. Vertical alignment layers 88a and 88b are formed on the surfaces of the pair of substrates 82 and 84 that are in contact with the liquid crystal layer 80. In addition, a convex portion 86 is formed on at least one surface of the pair of substrates 82 and 84 on the liquid crystal layer 80 side. Since the dielectric sheet provided on the liquid crystal layer side of the plasma substrate is thin, it is preferable to form a convex portion on the opposite substrate (color filter substrate) from the viewpoint of strength.

The liquid crystal layer 80 is formed of two
It has different kinds of thickness. As a result, as described above, a liquid crystal region exhibiting an axially symmetric orientation when a voltage is applied is defined as a region surrounded by the protrusion 86. FIG.
In FIG. 6, the electrodes and plasma chambers formed on the pair of substrates 82 and 84 for applying a voltage to the liquid crystal layer 80 are omitted. The configuration so far is the same as that of the liquid crystal display device 400 according to the first embodiment. The liquid crystal display device 500 according to the present embodiment includes, on the vertical alignment layers 88a and 88b,
Axisymmetric alignment fixed layers 90a and 90b are formed. The liquid crystal molecules in the picture element region can be controlled by the axisymmetric alignment fixed layers 90a and 90b even when no voltage is applied.
Axisymmetric orientation can be maintained. As a result, when the liquid crystal display device of the present embodiment is driven, even if a voltage lower than 1/2 Vth is applied (no voltage is applied), the electro-optical characteristics shown in FIG. 6 are exhibited with good reproducibility. Axisymmetric alignment fixed layer 90a
And 90b maintain an axially symmetric alignment (pretilt) of liquid crystal molecules by curing a curable resin previously mixed in a liquid crystal material while a voltage of 1/2 Vth or more is applied to the liquid crystal layer. Axisymmetric alignment fixed layers 90a and 9
0b is formed. The details will be described below.

In the same manner as in Example 1, a counter substrate having a cross-sectional structure shown in FIG. 14 was manufactured. The transparent electrode 105 (I
(TO: 150 nm) A spacer 135 having a height of about 6 μm was formed out of the picture element region using photosensitive polyimide on a substrate provided with (TO: 150 nm). On this, a projection 132 having a height of about 2.7 μm was formed by OMR83 (manufactured by Tokyo Ohka Co., Ltd.) (the size of the pixel region was 100 μm × 100 μm). On top of that, the vertical alignment layer 13
4b (JALS-204: Japan Synthetic Rubber) was spin-coated. The same vertical alignment layer was applied on the plasma substrate as in Example 1, and the two were bonded to complete a liquid crystal cell. This liquid crystal cell is substantially the same as the liquid crystal cell of the first embodiment.

In the present embodiment, n
Liquid crystal material (Δε = −4.0, Δn = 0.077, set to 90 ° at a chiral angle of 6 μm), and as a photocurable resin,
0.4% by weight of a compound A represented by the following chemical formula 1, Irgac
ur651 0.1 wt% mixture was injected. After the injection, a voltage of 5 V was applied to form an axially symmetric orientation. The axially symmetric alignment region was formed in the picture element area surrounded by the convex portion 66, and the central axis was formed in the center of the picture element. Thereafter, while applying a voltage 0.5V higher than the threshold voltage 2.0V,
Ultraviolet irradiation (intensity at 365 nm: 6 mW / cm ² ) was performed at room temperature (25 ° C.) for 10 minutes to cure the photocurable resin in the mixture. As a result, as shown in FIG. 17, an axially symmetric alignment fixed layer 142a was formed so as to cover the vertical alignment layers of both substrates. The counter substrate 90b in FIG.
An axisymmetric alignment fixed layer (not shown) corresponding to the above was formed.
In this embodiment, a photocurable resin is used, but a thermosetting resin may be used.

[0081]

Embedded image

In the axially symmetric alignment of the liquid crystal cell of Example 2, even when the voltage applied to the liquid crystal layer is less than 1/2 Vth, the liquid crystal molecules do not return to the completely vertical alignment state, and the pretilt state in the axially symmetric alignment changes. It is considered that it is held by the axisymmetric alignment fixed layer 142a. As a result, once the axially symmetric alignment fixed layer 142a is formed, the central axis of the axially symmetric alignment is not drawn even when a voltage of Ｖ Vth or more is applied again after the liquid crystal layer is in a no-voltage application state. A plurality of phenomena did not appear in the element region, and it was possible to reversibly and electrically control the vertical alignment state (black state) and the axially symmetric alignment state (white state). The liquid crystal molecules of the liquid crystal display device of Example 2 are given a pretilt angle by the axially symmetric alignment fixed layer 92a when no voltage is applied, but the deviation from the vertical alignment is slight, and the black level at the time of OFF is small. Was substantially equivalent to the liquid crystal display device of Example 1, and the electro-optical characteristics and the viewing angle characteristics were the same as those in FIGS. 15 and 12, respectively.

In the liquid crystal display device of the present invention, the two polarizing plates were bonded so that the polarization axes were in the vertical and horizontal directions of the display surface. As shown in FIG. 12, a wide viewing angle characteristic was obtained in an axially symmetric shape, and light leakage was small because the direction of the plasma chamber coincided with the direction of the polarization axis of the polarizing plate.

The viewing angle characteristic in the direction of 45 ° from the polarization axis of the polarizing plate is such that a retardation plate (△ n · 有 す る) having a negative (in-plane refractive index> refractive index in the thickness direction) Frisbee-type refractive index ellipsoid. d =
(300 nm) between the cell and the polarizing plate can be further improved. Table 1 shows the results.

[0085]

[Table 1] With retardation plate Without retardation plate Transmittance at viewing angle 60 ° in 45 ° direction from polarization axis 7% 55%

(Comparative Example 2) A liquid crystal cell was manufactured in Example without forming a lattice-like convex portion formed on the opposite substrate. Form a horizontal alignment film on the liquid crystal layer side surface,
Rubbing treatment was performed to produce a TN mode liquid crystal cell. Inject liquid crystal material into liquid crystal cell
-PALC was prepared. The polarizing plate was bonded to the produced PALC in a direction in which the polarization axis of the polarizing plate was shifted by 45 ° from the vertical and horizontal directions with respect to the display surface. The viewing angle characteristics of the obtained liquid crystal display device are as follows:
This is the characteristic shown in FIG. 11, which is very narrow as compared with the first and second embodiments. In addition, light leakage from the joint surface was observed in a streak-like manner, resulting in a decrease in contrast.

[0087]

According to the present invention, a high-contrast PALC having excellent viewing angle characteristics has a liquid crystal region in which liquid crystal molecules are vertically aligned when no voltage is applied and liquid crystal molecules are axially symmetrically aligned for each pixel when a voltage is applied. A liquid crystal display device and a method of manufacturing the same are provided. INDUSTRIAL APPLICABILITY The liquid crystal display device of the present invention is suitably used as a large display device such as a high-definition television such as an HDTV and a display for CAD.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a conventional PLCA.

FIG. 2 is a schematic diagram showing the operation principle of PALC.

FIG. 3 is a schematic diagram for explaining viewing angle dependence of a liquid crystal display device.

FIG. 4 is a schematic diagram showing a difference in viewing angle in a large panel.

FIG. 5 is a diagram illustrating the operation principle of the liquid crystal display device 300 of the present invention. (A) and (b) show the results when no voltage is applied.
(C) and (d) show the state at the time of voltage application, and (a)
(C) is a cross-sectional view, and (b) and (d) show the results of observing the upper surface with a crossed Nicols polarizing microscope.

FIG. 6 is a diagram showing a voltage transmittance curve of the liquid crystal display device 300.

FIG. 7 is a diagram for explaining the relationship between the position of the central axis of the axially symmetric alignment region and the display quality.

FIG. 8 shows the thickness din of the liquid crystal layer of the liquid crystal display device of the present invention.
It is a typical sectional view explaining (x).

FIG. 9 is a cross-sectional view schematically showing a picture element region of the liquid crystal display device of the present invention.

FIG. 10 is a diagram showing a voltage transmittance curve of a liquid crystal display device having a liquid crystal layer with d · Δn = 450 nm.

FIG. 11 is a diagram illustrating viewing angle characteristics of a TN mode liquid crystal display device.

FIG. 12 is a diagram showing viewing angle characteristics of the liquid crystal display device of the present invention.

FIG. 13 is a cross-sectional view of the PALC according to the first embodiment.

FIG. 14A is a partial cross-sectional view of a substrate used for the PALC of Example 1, and FIG. 14B is a top view.

FIG. 15 is a view showing the electro-optical characteristics of the liquid crystal display device of Example 1.

FIG. 16 is a schematic partial cross-sectional view of the liquid crystal display device of Example 2.

FIG. 17 is a partial cross-sectional view of a substrate used in the liquid crystal display device of Example 2.

[Explanation of symbols]

 102 Liquid crystal layer 105 Transparent electrode 106 Sealant 110 Plasma substrate 111 Substrate 112 Partition wall 113 Plasma chamber 114 Anode 115 Cathode 116 Derivative sheet 120 Counter substrate 132 Convex parts 134a, 134b Vertical alignment layer 400 PALC

Claims (8)

[Claims] 1. A counter substrate having a signal electrode, a plasma substrate having a plasma chamber for performing a plasma discharge, and a liquid crystal layer sandwiched between the counter substrate and the plasma substrate. A liquid crystal display device to be driven, wherein liquid crystal molecules of the liquid crystal layer have negative dielectric anisotropy, and when no voltage is applied, the liquid crystal molecules are vertically aligned with respect to the pair of substrates. Sometimes a liquid crystal display device in which the liquid crystal molecules are aligned axially symmetrically for each of a plurality of picture element regions. 2. A thickness (di) of the liquid crystal layer in the picture element region.
n) is larger than the thickness (dout) of the liquid crystal layer outside the pixel region, and corresponds to the pixel region on the liquid crystal layer side surface of at least one of the counter substrate and the plasma substrate. The liquid crystal display device according to claim 1, further comprising a vertical alignment layer in the region. 3. The liquid crystal display device according to claim 2, wherein at least one of the counter substrate and the plasma substrate has a convex portion surrounding the picture element region on a surface on the liquid crystal side. . 4. The thickness of the liquid crystal layer in the picture element region is:
4. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is thickest at a central portion of the pixel region and continuously decreases toward a peripheral portion of the pixel region. 5. 5. The thickness of the liquid crystal layer in the picture element region is:
5. The liquid crystal display device according to claim 4, wherein the liquid crystal display device changes axially symmetrically about a central portion of the picture element region. 6. A liquid crystal layer comprising a pair of polarizing plates disposed on both sides of the liquid crystal layer in a crossed Nicol state, wherein the polarizing axis of one of the pair of polarizing plates is the signal electrode or the plasma chamber. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is parallel to an extending direction of the liquid crystal display. 7. The liquid crystal display device according to claim 1, further comprising an axis-symmetric alignment fixed layer that gives an axis-symmetric pretilt angle to the liquid crystal molecules on a surface in contact with the liquid crystal layer. 8. The liquid crystal display device according to claim 7, wherein the axis-symmetric alignment fixed layer is made of a photocurable resin.