JPH0519267A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain the liquid crystal display element of a high display grade which is decreased in the vapor deposition defect points of oriented films to be generated by the hindrance of the vapor deposition flow of diagonally vapor deposited films by gap columns and can be thereby decreased in the orientation defect area of a liquid crystal and eliminates unequal display by uniformly maintaining a cell gap within the display surface. CONSTITUTION:The org. high-polymer gap columns 15 of a long circular cylindrical shape for maintaining the cell gap are provided within the display device of the liquid crystal display element constituted by having the diagonally vapor deposited oriented layers on a pair of transparent electrode substrates 13, 14 facing each other and crimping a liquid crystal compsn. therebetween, by which the cell gap can be uniformly controlled with good accuracy and, therefore, the unequal display and unequal colors occurring in the unequal gap are prevented. Since the gap columns are formed of the long circular cylindrical shapes, the vapor deposited defect points generated when the diagonally vapor deposited films are used as the oriented layers and, therefore, the orientation defect points occurring therein are minimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cell structure of a liquid crystal display device, particularly a ferroelectric liquid crystal display device.

[0002]

2. Description of the Related Art A surface-stabilized ferroelectric liquid crystal (Surface Stabi) proposed by Clark and Lagabal.
Lized Ferroelectric Liquid
d Crystal: Hereinafter referred to as SSFLC: App
l. Phys. Lett. , 36 (1980) 899)
Ferroelectric liquid crystal display element using the, has a high-speed response, memory effect, high contrast ratio that conventional liquid crystal element,
It is expected to be applied to next-generation display devices and spatial light modulators.

The ferroelectric liquid crystal and SSFLC will be briefly described with reference to the drawings. 5A and 5B are model diagrams showing a chiral smectic C liquid crystal phase showing ferroelectricity,
(A) is the cone model figure, (b) is a model figure which shows the arrangement | sequence state of a molecule | numerator. The chiral smectic C phase has a layered structure. The molecular axis 1 has an inclination angle 2 with respect to the layer normal direction. It has a spontaneous polarization 3 perpendicular to the molecular axis 1. The spontaneous polarization 3 rotates in a fixed direction for each layer. Therefore, the molecular axis 1 also rotates, and the liquid crystal molecules 4 have a helically arranged structure. The distance that the spiral makes one turn is the spiral pitch 5.

When this ferroelectric liquid crystal is sealed between the substrates having the alignment control layer, the alignment state shown in the alignment model diagram of FIG. 6 is obtained when the cell gap is thick. That is, since the binding force of the orientation control layer is strong at the interface between the substrate and the liquid crystal, the spiral structure in the vicinity can be solved, but the spiral structure is maintained at the center (bulk) of the cell gap. However, when the cell gap becomes thinner and falls below the spiral pitch, as shown in FIG.
As shown in the orientation model diagrams of (a) and (b), the binding force at the interface affects the entire cell gap, and the helical structure of the liquid crystal is completely released. Such an orientation is called a uniform state, (a) is a UR state,
(B) represents the UL state. (Note that, in FIGS. 6 and 7, according to the convention, the slant to the plane including the layer normal of the orientation vector is indicated by the nail 6 and the slant to the in-plane is referred to as the C-director by the arrow 7.)

The concept of SSFLC is to perform bistable inversion between two states (UR and UL) shown in FIGS. 7 (a) and 7 (b). That is, the electric field 8 applied from the outside in FIG.
The liquid crystal molecules 4 are inverted by utilizing the interaction between and the spontaneous polarization 3. 8 (a) and 8 (b) are inversion model diagrams of the ferroelectric liquid crystal due to the electric field seen from above the substrate. FIG. 8 (a) shows an on state, (b) shows an off state, 9 is a layer direction, and 10 is an alignment. The orientation control directions of the control film, 11 and 12 are the polarization directions of the upper and lower polarizing plates when they are used as display elements, respectively.
In the reversal between the uniform states, the uniform state itself is the orientation that minimizes the free energy consisting of the interfacial interaction energy and the liquid crystal elastic distortion energy.
The orientation is maintained immediately after reversal even in the non-electric field state. This is called the memory effect. Since this effect can be expected in SSFLC, it is not necessary to use an active matrix, and a low cost simple matrix system can be applied.

The above is the ideal operation principle of SSFLC. However, in reality, when a normal polyimide rubbing film, which is often used as an alignment control layer for nematic liquid crystals, is applied to a ferroelectric liquid crystal, as shown in FIGS. Inversion (UR-UL) cannot be obtained, and as shown in FIGS.
Between states or as shown in FIGS. 11 (a) and 11 (b), TL1
-Begin to exhibit inversion between two states called twist states between TL2 states. This is because the orientation control force of the substrate surface is strong, and the apparent tilt angle becomes small at the reversal between the twist 2 states, so that the contrast ratio becomes small, and when the external electric field is cut off, the twisting is caused by the strong orientation control force. , The contrast ratio in the memory state becomes smaller. Furthermore, when the same orientation control method is used,
Alignment defects called zigzag defects are often observed. When a general polyimide rubbing film is used for the orientation control layer, there is a selective pretilt of C-director (for example, K. Ishikawa et al .: Jp.
n. J. Appl. Phys. , 24 (1985) L2
30), it has been revealed by an X-ray diffraction method in recent years that there is a layer inclination and bending called a chevron structure as shown in the model diagrams of FIGS. (See, for example, T. P. Rieker et al .: Phys.
Rev. Lett. , 59 (1987) 2658) If the chevron structure is oriented in the same direction over the entire surface of the device, a uniform surface (monodomain) can be obtained. The chevrons will collide with each other. That is, <<<<>>>> or >>>> * <<<
Alignment defects occur in the * portion where a structure such as (<,> indicates chevron) is present. This alignment defect forms a zigzag defect as a continuous line and thus becomes an obstacle when used as a display element.

A method proposed as an orientation control method suitable for a ferroelectric liquid crystal which does not cause such defects is to use a silicon monoxide oblique vapor deposition film. The vapor deposition film is characterized in that a high pretilt angle can be obtained when the vapor deposition flow incident angle with respect to the substrate normal is increased, and at the same time, the interface restraining force is not so large. When the vapor-deposited film is used as the orientation control layer, the high pretilt angle reduces the selective pretilt of the C-director, the tilt of the layer is almost eliminated, and a monodomain is obtained. Since liquid crystal molecules in the vicinity can also be inverted, it is said that it is possible to invert between uniform states. (For example, T. Uemura et al .: J
APAN DISPLAY '86, (1986) 46
4)

On the other hand, the following two methods are mainly known as methods for maintaining the cell gap. The first method is to mix the glass fiber or silica spherical particles called a gap material in the adhesive of the seal part around the cell, and to hold the gap, and the second method is to display in the surface of the display element. This is a method of spraying a gap material of silica particles to maintain the gap on the entire surface. In the case of the liquid crystal display device having a small area, the former method can sufficiently maintain the gap,
Since there is a problem that the gap at the center of the cell cannot be maintained when the area is large, the latter gap maintaining method is mainly used when manufacturing a large-area liquid crystal display element.

As described above, in manufacturing a ferroelectric liquid crystal display element, the latter gap holding method is currently used to hold the gap over a large area.
There is a problem that liquid crystal orientation disorder occurs near the interface between the silica particles and the liquid crystal material, and as a result, from the viewpoint of display quality, many point-like orientation defects are observed in the display surface.

[0010]

In order to solve this problem, a method of keeping the gap over the entire surface of the cell without using a silica gap material has been studied. In this method, a column of organic polymer having a predetermined height is formed on a glass substrate in advance and used as a gap material, so that the gap can be maintained over a large area and there is little misalignment around the gap material. A ferroelectric liquid crystal display device can be obtained. However, if the alignment method using the SiO oblique deposition film as the alignment layer and the method of using this organic polymer column as a gap material are used together, after forming the organic polymer gap column on the glass substrate, SiO It becomes necessary to perform vacuum vapor deposition, and a vapor deposition defective portion is formed in the portion where the SiO vapor deposition flow is blocked by the gap column. As a result, the ferroelectric liquid crystal material has poor alignment in this portion, and when the display is performed, the image is not displayed. Observed as spotty. Further, in order to uniformly orient the ferroelectric liquid crystal material, the vapor deposition flow of SiO is set to 8 from the substrate normal direction.
It is necessary to enter from a direction of 5 °, and at this time, the length of the vapor deposition defective portion due to the vapor deposition flow being blocked by the above-mentioned gap column is about 10 times the height of the gap, which is large when the display is performed. There was a problem that it was observed as display unevenness.

The present invention has been made in order to solve the above problems, and reduces defective portions of alignment film vapor deposition caused by blocking the vapor deposition flow of an oblique vapor deposition film by a gap column, thereby reducing alignment defects of liquid crystal. The area can be reduced and
It is an object of the present invention to obtain a liquid crystal display device of high display quality in which the cell gap is kept uniform in the display surface and display unevenness is not caused.

[0012]

A liquid crystal display device according to the present invention is provided with an organic polymer gap column having a long cylindrical shape having a long axis in the vapor deposition flow incident direction of an oblique vapor deposition alignment layer in a display surface. Is.

[0013]

[Function] For example, an SiO 85 ° oblique vapor deposition film is used as an alignment layer,
In a ferroelectric liquid crystal display device in which a cell gap is held by an organic polymer gap column having an elliptic shape such as an ellipse having a long axis in the incident direction of SiO vapor deposition flow, a cell gap is formed by a circular organic polymer gap column. Since the amount of shielding the SiO vapor deposition flow is smaller than that in the case where the above condition is maintained, it is possible to reduce the vapor deposition defective portion of the SiO oblique vapor deposition film, and thus the orientation defective area of the liquid crystal material can also be reduced. Further, since the cross-sectional area of the elliptical gap column including the ellipse can be made larger than that of the circular gap column, the cell gap can be accurately maintained. Due to the above-mentioned two points, the defective area for vapor deposition of the alignment film is small, the area of defective alignment of the liquid crystal is small, and the cell gap can be uniformly maintained in the display surface, so that high display quality ferroelectric liquid crystal display without display unevenness can be obtained. An element can be obtained.

[0014]

【Example】

Example 1. In a ferroelectric liquid crystal panel with a pixel size of 960 x 720 and a screen size of about 7 inches, a pixel pitch of 150μ
m (display part 130 μm, interval 20 μm),
Gap columns were formed on this display surface. Gap pillar 15
2 has a thickness of 2 μm, 10 × 20 as shown in FIG.
It has an elliptical shape of μm, and the pitch of the gap columns 15 is 200 μm.
And The vertical to horizontal ratio of the ellipse is preferably 1: 1.5 to 1:10, most preferably 1: 2 to 1: 5. 1: 1.5
When the ratio is smaller, the area that blocks the SiO vapor deposition flow becomes wider, and thus the alignment defect portion becomes larger. When the ratio is larger than 1:10, the strength against the gap column gap axial displacement during cell crimping is weak, and the gap Can't hold. FIG. 1 is a perspective view showing a gap column formed on a glass substrate obtained by patterning ITO. In the figure,
13 and 14 are transparent electrode substrates, and 13a and 14a are I of the substrate.
It is a TO electrode pattern. The size and pitch of the gap columns 15 differ depending on the type of organic polymer material used.
In the case of the positive type photoresist used this time, 50 mm / mm ² is required to maintain the gap due to its strength.
0 .mu.m ² ～5000Myuemu is best cross-sectional area of the gap column 15 ^2, preferably 2000 .mu.m ² ～4000Myuemu ²
Is appropriate. When less than 1 mm ² per 500 [mu] m ² can not have sufficient strength to hold the gap, 5
When it exceeds 000 μm ² , the area occupied in the display surface becomes large and the display quality is remarkably deteriorated, which is not suitable. The height of the gap column 15 was set to 2.5 μm before the curing contraction and 2 μm after the curing contraction. The height of the gap column 15 after the curing shrinkage is not particularly limited because it varies depending on the cell gap after the intended cell fabrication.
Generally, in a ferroelectric liquid crystal display device, a cell gap of 1 to 4 μm is preferable. When the thickness is less than 1 μm, the interaction between the liquid crystal molecules and the interface is strong and it extends to the entire cell, so that a good response cannot be obtained. On the other hand, when it exceeds 4 μm, the orientation of the liquid crystal material is deteriorated, which is not suitable. On the other hand, the height of the gap column 15 before the curing shrinkage is obtained by adding the curing shrinkage amount determined by the type of the organic polymer material forming the gap column 15 to the target height of the gap column after the curing shrinkage. , It is necessary to measure and determine the amount of cure shrinkage inherent in the organic polymer material used.

The ITO electrode pattern is formed on the glass substrates 13 and 14.
After forming the electrodes 13a and 14a, the gap column 15 was prepared and the alignment film was vapor-deposited. For the deposition of the alignment film, first, SiO was vapor-deposited in the direction of the normal line of the substrate to about 250 Å, and then, about 250 Å was vapor-deposited from the direction of 85 ° from the normal line of the substrate. The thickness of the vapor-deposited film has been conventionally used, and 100 to 500 angstrom is suitable for both the vertical direction and the oblique direction. If it is less than 100 Å, the deposited film is not uniformly deposited, and if it exceeds 500 Å, the driving voltage becomes high. After depositing the alignment film, the glass substrates 13 and 14 were stacked. First, an adhesive was applied to the peripheral portion of one glass substrate, the other glass substrate was overlaid, and pressure-bonded while heating. A pressure of 0.03 to 3 kg / cm ² is suitable for the pressure, and 0.3 to 0.7 kg / cm ² is most preferable. 0.
Is less than 03Kg / cm ² can not be crimped to the cell gap of interest, also exceeds 3 Kg / cm ² would exceed the strength to hold the gap column, the cell gap becomes thinner than the target value.

When the ferroelectric liquid crystal material was injected into the cell manufactured as described above and the alignment state was examined, the location of misalignment due to the use of the gap column was about 200 μm ² per gap column, which was extremely high. It was small and did not deteriorate the display quality at all. On the other hand, the uniformity of the cell gap can be set to 2 μm ± 0.1 μm, which is the target, and it is possible to obtain a very good result without displaying unevenness.

Embodiment 2. In the ferroelectric liquid crystal panel having the same number of pixels and screen size as in Example 1, the pixel pitch is 1
When it is set to 50 μm (display portion 130 μm, interval 20 μm), the gap column 15 is formed within this interval. The size of the gap column 15 is 2 μm, as shown in FIG.
In order to form the gap pillars 15 between pixels in an oval shape of 0 × 20 μm, the pitch of the gap pillars 15 was set to 300 μm, which is a multiple of the pixel pitch. The ratio of the length and the width of the gap column 15 is 1: 1.5 to 1:10 for the same reason as in Example 1.
Is suitable, and 1: 2 to 1: 5 is most suitable. Gap pillars 1 are formed on the glass substrates 13 and 14 in which ITO is patterned.
FIG. 3 is a perspective view of the case where No. 5 is formed. Gap pillar 1
For the material of No. 5, since the same organic polymer material as in Example 1 was used, the area occupied by the gap column 15 on the display surface was 500 μm ^{2 to} 5000 per 1 mm ² for the same reason as in Example 1.
The cross-sectional area of the gap column 15 of μm ² is the best, and 2000 μm ^{2 to} 4000 μm ² is suitable. The pitch of the gap pillars 15 is a multiple of the pixel pitch in order to form the gap pillars 15 between pixels. If it is not a multiple of the pixel pitch, a gap column will be formed in the pixel, and the display quality will be degraded. Since the organic polymer material used for the gap column 15 is the same as that in Example 1, the curing shrinkage amount is the same, and the cell gap is also the same, the height of the gap column 15 is 2.5 μm before the curing shrinkage, It was set to be 2 μm after curing shrinkage.

The ITO electrode pattern is formed on the glass substrates 13 and 14.
After forming the electrodes 13a and 14a, the gap column 15 was prepared and the alignment film was vapor-deposited. The method of depositing the alignment film and the film thickness are the same as in Example 1.
Same as. After depositing the alignment film, the glass substrate 13,
Fourteen stacks were made. First, an adhesive was applied to the peripheral portion of one glass substrate, the other glass substrate was overlaid, and pressure-bonded while heating under the same conditions as in Example 1.

When the ferroelectric liquid crystal material was injected into the cell manufactured as described above and the alignment state was investigated, the location of misalignment due to the use of the gap pillar was about 200 μm ² per gap pillar, which was extremely high. In the case of the cell manufacturing method shown in this embodiment, the gap pillars are located between pixels, and therefore, the defective alignment portion is located only between pixels, and the display quality is not deteriorated at all. On the other hand, the uniformity of the cell gap can be set to 2 μm ± 0.1 μm, which is the target, and it is possible to obtain a very good result without displaying unevenness.

Comparative Example 1. A cell was produced with the same shape as in Example 1 except that the area occupied by the organic polymer material and the gap column in the display surface, the cell pressure bonding conditions, and the cell gap were the same, and the gap column shape was circular. When a cell was manufactured under the same conditions as in Example 1 with a gap column diameter of 15 μm and a gap column pitch of 200 μm, and a liquid crystal was injected, the SiO vapor deposition flow was blocked by the gap column, resulting in defective deposition points. The misaligned portion was about 300 μm ² , which was observed as a defect at the time of displaying, and good display quality could not be obtained.

In each of the above embodiments, the case where the shape of the gap column 15 is an elliptic column as shown in FIG. 2 has been described, but the present invention is not limited to this, and for example, FIG.
It may have a shape like (c). In addition, in FIG. 4, the arrow indicates the vapor deposition flow incident direction.

[0022]

As described above, according to the present invention, since the organic polymer gap column having a long columnar shape having the major axis in the vapor deposition incident direction of the oblique vapor deposition alignment layer is provided in the display surface, the gap is reduced. Since the area in which the vapor deposition flow of the alignment layer is blocked by the pillar can be reduced, the vapor deposition defective area of the alignment layer can be reduced, and accordingly, the alignment defective portion of the liquid crystal material can be reduced. Further, since the gap is maintained in the entire display surface of the cell, it is possible to reduce the unevenness of the gap in the display surface.

[Brief description of drawings]

FIG. 1 is a perspective view showing a cell configuration of a liquid crystal display element in Example 1 of the present invention.

2A and 2B are a top view and a side view showing a shape of a gap column according to the first embodiment of the present invention.

FIG. 3 is a perspective view showing a cell configuration of a liquid crystal display element in Embodiment 2 of the present invention.

FIG. 4 is a top view showing the shape of a gap column according to another embodiment of the present invention.

5A and 5B show a chiral smectic C liquid crystal phase exhibiting ferroelectricity, FIG. 5A is a cone model diagram thereof, and FIG. 5B is a model diagram showing a molecular alignment state.

FIG. 6 is a schematic diagram showing an alignment model of a ferroelectric liquid crystal injected into a cell having a thick gap.

FIG. 7 is a schematic diagram showing an alignment model of a ferroelectric liquid crystal injected into a cell having a thin gap, (a) of FIG.
State, (b) shows the UL state.

FIG. 8 is a schematic diagram showing an inversion model of a ferroelectric liquid crystal due to an electric field seen from above the substrate, FIG.
(B) shows an off state.

9A and 9B are schematic diagrams respectively showing an inversion model between two uniform states, where FIG. 9A shows a UR state and FIG. 9B shows a UL state.

10A and 10B are schematic diagrams showing a reversal model between two twisted states, where FIG. 10A shows a TR1 state and FIG. 10B shows a TR2 state.

11A and 11B are schematic diagrams showing a reversal model between twisted two states, where FIG. 11A shows a TL1 state and FIG. 11B shows a TL2 state.

FIG. 12 is a schematic diagram showing a model of a chevron structure, in which (a) shows a UR state, (b) shows a TR1 state, (c) shows a TR2 state, and (d) shows a UL state.

[Explanation of symbols]

 13: Transparent electrode substrate 13a: ITO electrode pattern of transparent electrode substrate 14: Transparent electrode substrate 14a: ITO electrode pattern of transparent electrode substrate 15: Gap column

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masaya Mizunuma 8-1-1 Tsukaguchihonmachi, Amagasaki City Mitsubishi Electric Corporation

Claims (1)

Claim: What is claimed is: 1. A liquid crystal display device comprising a pair of transparent electrode substrates which face each other and obliquely vapor-deposited alignment layers sandwiching a liquid crystal composition, wherein the alignment layers are vapor-deposited on a display surface. A liquid crystal display device, comprising: an organic polymer gap column having a long cylindrical shape having a long axis in a flow incident direction.