JPH06194655A - Liquid crystal display element and its production - Google Patents

Abstract

PURPOSE:To make visual angle characteristics nearly uniform in all bearings and to prevent the degradation in contrast by the specific position of an observer by constituting the liquid crystal display element in such a manner that the orientation directions of the liquid crystal molecules of a liquid crystal layer distribute at an equal probability in macroscopically nearly all directions with respect to the intra-surface direction of substrates and exhibit a nearly specified twist angle with respect to a direction perpendicular to the substrates. CONSTITUTION:The liquid crystal molecules 3 of a chiral nematic type are clamped between the transparent glass substrates 1 and 2. Macrossopically the orientation directions of the liquid crystal molecules 3 are randomly distributed with respect to the intra-surface direction of the substrates 1, 2. The chiral nematic liquid crystal rotates the axis of polarization of incident light at a prescribed angle as a whole with respect to the direction perpendicular to the plane of the substrates 1, 2. A positive display, etc., are realized if a pair of such polarizers are used. As a result, a rubbing treatment is not executed and, therefore, the destruction of elements and wirings by static electricity do not arise and the display defects by generation and pickup of dust are decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display element and a manufacturing method thereof, and more particularly to a liquid crystal display element capable of improving a viewing angle and a manufacturing method thereof.

[0002]

2. Description of the Related Art A liquid crystal display element used in a liquid crystal display or the like, a so-called liquid crystal cell, changes a specific molecular arrangement of liquid crystal into another different molecular arrangement by an action from the outside such as an electric field and causes an optical difference between them. The changes in characteristics are used as visual changes for display. In order to bring the liquid crystal molecules into a specific alignment state when there is no electric field (electric field off), it is usual to perform an alignment treatment on the surface of the glass substrate that holds the liquid crystal.

In a conventional twisted nematic (TN) type liquid crystal cell or the like, so-called rubbing in which a glass substrate sandwiching liquid crystal is unidirectionally rubbed with a glass cloth is used as an alignment treatment.

For example, a pair of substrates is assembled so that the rubbing directions are perpendicular to each other between the upper and lower substrates. When the liquid crystal cell is a negative display, the polarizing plates with parallel Nicols arrangement sandwiching the cell are arranged so that the polarization axis is parallel to one of the rubbing directions. The polarizing plate is arranged so that its polarization axis is parallel to the rubbing direction of the substrate.

[0005]

When the alignment treatment is carried out by such rubbing, the alignment direction of the liquid crystal molecules is uniform, so that when the screen is viewed from the observer, the angle at which the display is easy to see falls within a specific angle range. Limited viewing angle characteristics result.

FIG. 4A is an example of an equal contrast curve representing the viewing angle characteristics of the TN type liquid crystal cell. In FIG. 4 (A), the normal direction of the liquid crystal cell is θ = 0, and an angle θ from the normal is taken in a radial pattern centered there, and the azimuth angle φ indicates the observation position in the horizontal plane. The definition is shown in FIG.

The thick solid curve in FIG. 4A is an equal contrast line, and the contrast value is shown on each curve. As shown in FIG. 4A, it can be seen that the viewing angle region with high contrast is biased to a specific angle region. Therefore, such a liquid crystal cell has a viewing angle dependency that it is easy to see from one direction and hard to see from another direction.

When a liquid crystal cell having such a viewing angle dependency is used as a display device, the contrast becomes extremely extreme at a certain angle (around φ = 180 ° in the example of FIG. 4A) with respect to the display screen. When it is extremely low, the brightness of the display is reversed.

The view angle characteristic as shown in FIG.
This is because the rubbing causes pretilt of the liquid crystal molecules as shown in FIG. The direction in which the liquid crystal molecules have a pretilt coincides with the vector direction for rubbing indicated by the arrow in FIG.

When a voltage is applied to the liquid crystal cell, the liquid crystal molecules rise in the pretilt direction.
When observed from that direction, the optical activity tends to be eliminated. Therefore, the end direction of the vector is the easiest to see.

Further, during rubbing, static electricity may be generated due to friction to cause dielectric breakdown in the alignment film, or defective alignment may cause defective display. Further, in a liquid crystal cell adopting an active matrix (AM) driving method, when rubbing a substrate on which driving elements such as TFTs (thin film transistors) and wiring are formed, the elements and wiring are destroyed by static electricity due to rubbing. There is a case that Even in the case of a simple matrix, cutting of fine wiring may occur.

Further, a large amount of fine dust is generated during alignment film formation and rubbing, and the dust adheres to the substrate due to static electricity, which causes display defects such as gap defects in liquid crystal cells and black and white dots. There are cases.

The object of the present invention is to improve the characteristics of the viewing angle,
It is an object of the present invention to provide a liquid crystal display device and a manufacturing method thereof that can solve the problems caused by the rubbing process.

[0014]

A liquid crystal display device according to the present invention is a liquid crystal display device having a pair of substrates and a liquid crystal layer containing a chiral nematic liquid crystal or a nematic liquid crystal sandwiched between the pair of substrates. The orientation directions of the liquid crystal molecules of the liquid crystal layer are macroscopically distributed in almost all directions with equal probability in the in-plane direction of the substrate, and show a substantially constant twist angle in the direction perpendicular to the substrate.

[0015]

FUNCTION: Macroscopically, the orientation directions of liquid crystal molecules are randomly distributed in the in-plane direction of the substrate. In the direction perpendicular to the substrate surface, the chiral nematic liquid crystal rotates the polarization axis of incident light as a whole by a predetermined angle. Positive display and the like can be realized by using a pair of polarizers. Since no rubbing is performed, various problems based on rubbing do not occur.

[0016]

EXAMPLE An example of the present invention will be described below with reference to FIGS.
This will be described with reference to (C) and FIG. FIG. 1A is a schematic sectional view of a liquid crystal display cell according to an embodiment of the present invention.
Chiral nematic liquid crystal molecules 3 are sandwiched between transparent glass substrates 1 and 2.

In order to manufacture this liquid crystal cell, the conventional process can be used as it is. However, rubbing is not performed. When a positive alignment process such as rubbing is not performed, it is considered that liquid crystal molecules are aligned in parallel at least approximately in a certain direction when observing a minute area on one substrate surface. To be

When a wider range is viewed as a whole, a large number (multi) of these minute regions (microdomains) exist, the orientation directions in the multidomain are all directions, and all the directions are the same. It is thought to exist with a probability.

That is, when considering the orientation directions of the interface molecules of the entire cell, it means that they are oriented in all directions, and it can be approximated that they are oriented in a certain direction when viewed in each minute domain. become.

In the chiral nematic liquid crystal, as shown in FIG. 1 (B), the orientation direction of liquid crystal molecules is rotated by 360 degrees with a thickness p. The liquid crystal molecules have a twist structure in which the liquid crystal molecules gradually rotate with distance from the surface of one substrate, and on the surface of the other substrate, rotate to an angle defined by d / p. In the case of nematic liquid crystal, p = ∞. Since these show the same twist for each multi-domain, at the interface on the opposite side, the same multi-domain orientation is obtained in which the orientation direction is deviated by a certain twist angle.

When the chiral pitch of the chiral nematic liquid crystal is p and the thickness of the liquid crystal layer in the direction sandwiched by the glass substrates is d, 0 (<or ≈) d / p (<or ≈) 0.75. Meet the conditions. Preferably, the liquid crystal cell is formed so as to satisfy the condition of 0.15 <d / p <0.75. That is, when converted to an angle, 54
P and d are determined so as to have an optical rotatory power of 270 degrees to 270 degrees.

For example, a liquid crystal having a chiral pitch p of d / p = 0.25 (corresponding to a 90 ° twist) is injected between the transparent glass substrates 1 and 2 having a gap d arranged in parallel and sealed. Stop.

As the liquid crystal material, for example, any known nematic liquid crystal or cholesteric liquid crystal can be used. When it has a twist, a chiral agent may be added to the nematic liquid crystal.

Of course, in the case of the active drive system, as shown in FIG. 1C, a drive element Q such as a thin film transistor (TFT) using amorphous Si or polycrystalline Si and a metal such as Cr are used. Wirings W, transparent pixel electrodes P formed of indium-tin oxide (ITO), etc. are formed on the glass substrates 1 and 2. It is preferable to cover these surfaces with the insulating protective film 13. Further, black stripes, color filters, etc. may be formed. A common electrode is formed on the entire surface of the counter substrate. In the case of a simple matrix, a wiring group intersecting with each other is formed on a pair of substrates. It is not always necessary to form the insulating protective film or the alignment film on the substrates 1 and 2, but it may be formed. However, rubbing is not performed.

For example, when d / p = 0.25,
In each domain, liquid crystal molecules are twisted by 90 ° between two substrates. However, the orientation at interfaces within a multi-domain containing multiple domains is in all directions.

When injecting the liquid crystal, the liquid crystal is injected in the isotropic phase while maintaining the temperature of the liquid crystal at a temperature above the NI (N: nematic, I: isotropic) phase transition point of the liquid crystal, and N- When the liquid crystal cell is manufactured by gradually lowering the temperature to point I or lower, the display as a display element becomes clearer.

Further, it is preferable to inject the liquid crystal while maintaining not only the temperature of the liquid crystal but also the temperature of the substrate before injecting the liquid crystal above the NI point of the liquid crystal, and gradually lowering the temperature to below the NI point. The display quality is further improved by manufacturing the liquid crystal cell in this manner.

Considering that the property of the liquid crystal in bulk (a state in which no alignment regulating force is applied from the outside) forms a multi-domain, a multi-domain structure is generally adopted in a cell having no alignment regulating force. Expected to be deaf. In particular, it is considered that this tendency becomes stronger as the liquid crystal is injected while being kept above the NI point, and moreover the domain sizes of the multi-domains are more uniform.

The polarizing plate 1 arranged outside the liquid crystal cell
The positions of 1 and 12 are orthogonal Nicols for positive display and parallel Nicols for negative display. As can be seen from the fact that there is no reference direction such as the rubbing direction in the substrate surface, the in-plane angle of the polarization axis of the polarizing plate is arbitrary.

In the case of d / p = 0.25, among the multi-domains, the one in which the orientation direction of the liquid crystal molecules at the interface is parallel or perpendicular to the polarization direction of the incident polarized light is a normal T.
As with the N cell, the polarization direction of outgoing polarized light is twisted by 90 ° due to its optical rotatory power.

On the other hand, those that are not parallel or perpendicular to the incident polarization direction are twisted by the optical rotation plus retardation (Δn · d: Δn: refractive index anisotropy of liquid crystal) of the emitted light. The angle is fixed, and it becomes wavelength-dependent.

Therefore, the light passing through these multi-domains and the polarizing plate on the opposite side is colored. However, since the orientation directions in these multi-domains are present with equal probability in all directions, the wavelength dependence of the emitted light is almost canceled out as a whole, and in positive display, there is coloring when turned off. It is considered that the transparent state is shown.

FIG. 2 shows the viewing angle characteristics of the liquid crystal cell manufactured by the method described above. As a manufacturing condition, a general liquid crystal for TFT having a refractive index difference Δn = 0.093 of birefringence and a phase transition temperature T _NI = 98 ° C. was used, and a transparent electrode (indium tin oxide) having a gap of 5.5 μm was used. The liquid crystal was enclosed in a test cell provided with an (ITO) film.

The liquid crystal was injected without the alignment film while keeping both the liquid crystal and the substrate at a temperature of NI or higher. The polarizing plate of the neutral high-polarization type (Nitto Denko G-1220) has a crossed nicols, and the front and rear polarization axes are (0 °
The positive display was provided by arranging in the (-180 °) direction and the (90 ° -270 °) direction.

As is apparent from FIG. 2, the embodiment of the present invention has substantially the same viewing angle characteristics in all directions, and a specific liquid crystal cell as seen in the conventional liquid crystal cell of FIG. No deterioration in contrast is seen when viewed from an angle.

When the structure of this liquid crystal cell was observed with a polarization microscope, minute multi-domains were observed over the entire cell surface. It is considered that this is the reason why the viewing angle dependence disappeared.

That is, when a large number of domains are generated in the display surface and liquid crystal molecules of all orientations are distributed in the surface parallel to the substrate as a whole, no matter what the polarization axis of the incident light is, it will appear. The polarization axis of the emitted light is rotated by 90 degrees. A display is possible by a combination of 90 ° polarization axis rotation and a crossed polarizer. Also, the multi-domain eliminates the angle dependence.

The angle of the polarization axis is arbitrary because it has a multi-domain structure. Actually, even if the angle of the polarizing plate was changed, no difference in terms of characteristics was observed. In the case of the negative display of parallel Nicols, the wavelength dependence described above causes O
There was a tendency that black was not sufficiently produced at FF. That is,
Positive display is more preferable.

The embodiment described above is the case where the positive alignment treatment is not performed. However, in recent years, it has been found that the alignment treatment can be performed without the rubbing treatment. For example, when a polarization memory film is used, it is possible to perform alignment processing on a minute area by light irradiation. Even if a substrate subjected to such an alignment treatment is used, a multi-domain structure similar to that of the above-mentioned embodiment can be formed, and the same effect can be obtained.

As the optical polarization memory film, (1) one using a silicon polyimide doped with a diazoamine dye: Wayne M .; Gibbons
Others, NATURE Vol. 351 (1991) p. Four
9, (2) Using PVA (polyvinyl alcohol) doped with an azo dye: Yasufumi Iimura et al .: 18th Liquid Crystal Symposium-The 64th Annual Meeting of the Chemical Society of Japan-, p. 34, Published September 11, 1992, The Chemical Society of Japan. Or Jp
n. J. Appl. Phys. Vol. 32 (199
3) pp. L93-L96, (3) using photopolymerization photopolymer: Marti
n Schadt et al., Jpn. J. Appl. Phy
s. Vol. 31 (1992) pp. 2155-216
4 etc. can be used.

FIG. 3 (A) is a schematic enlarged view of the multi-domain structure in the above embodiment. FIG. 3A is an enlarged plan view of the cell. A large number of minute regions, that is, micro domains 4, are formed, and the liquid crystal molecules inside each domain 4 are aligned in parallel in a substantially uniform manner in a certain direction as indicated by the arrow. However, it can be understood that the cells as a whole have a random orientation when viewed macroscopically and the viewing angle characteristics are substantially isotropic.

In the manufacturing process of the liquid crystal cell in the above-described embodiment, the following alignment structure different from the multi-domain structure shown in FIG. 3A can be obtained by changing the manufacturing conditions.

For example, as shown in FIG. 3B, a structure is formed in which the liquid crystal molecules 3 continuously change their alignment directions. The orientation of the entire cell is random, and the liquid crystal molecules 3 are oriented in all directions with equal probability.

Further, as shown in FIG.
A structure like the combination of (A) and FIG. 3 (B) is also formed. That is, the micro domains 4 oriented in a certain direction are scattered in the minute region, and the liquid crystal molecules 3 are present while the orientation direction is continuously changed therebetween. Also in this case, the orientation direction of the cell as a whole is random.

Needless to say, the above effects can be obtained with any of the structures shown in FIGS. 3A, 3B and 3C. The present invention is not limited to the embodiments described above,
Various modifications and changes will be easily made by those skilled in the art based on the disclosure.

[0046]

According to the present invention, the viewing angle characteristics are substantially uniform in all directions, and the contrast does not decrease depending on the specific position of the observer.

Further, since the rubbing process is not performed,
It is possible to reduce display defects due to dust generation and adhesion without the destruction of elements and wiring due to static electricity. Further, if the alignment film is not formed, the problems such as afterimage and image sticking which are considered to be caused by the alignment film are eliminated.

If the rubbing treatment or the alignment film formation is not carried out, those steps are eliminated, so that the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal display cell according to an exemplary embodiment of the present invention.

FIG. 2 is a view angle characteristic of a liquid crystal display cell according to an embodiment of the present invention.

FIG. 3 is an enlarged schematic view of a part of a liquid crystal cell according to an embodiment of the present invention.

FIG. 4 is a view angle characteristic of a conventional liquid crystal display device.

FIG. 5 is a diagram illustrating pretilt by rubbing.

[Explanation of symbols]

 1, 2 Glass substrate 3 Liquid crystal molecule 4 Micro domain 11, 12 Polarizing plate 13 Insulating protective film Q Thin film transistor P Transparent pixel electrode W Wiring

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susuke Kobayashi 3-13-40 Nishioizumi, Nerima-ku, Tokyo

Claims (11)

[Claims] 1. A liquid crystal display device comprising a pair of substrates and a liquid crystal layer containing a chiral nematic liquid crystal or a nematic liquid crystal sandwiched between the pair of substrates, wherein the alignment direction of liquid crystal molecules of the liquid crystal layer is the substrate. A liquid crystal display element that is distributed macroscopically in almost any direction with equal probability in the in-plane direction and exhibits a substantially constant twist angle in the direction perpendicular to the substrate. 2. The liquid crystal display device according to claim 1, wherein the liquid crystal layer has a large number of minute regions in the in-plane direction of the substrate, and the alignment directions of the liquid crystal molecules are aligned in each of the minute regions. 3. The liquid crystal display element according to claim 2, wherein the liquid crystal layer includes a region in which the alignment direction of liquid crystal molecules changes substantially continuously in the in-plane direction of the substrate among a number of minute regions. 4. The liquid crystal display element according to claim 1, wherein the alignment direction of the liquid crystal molecules of the liquid crystal layer changes microscopically substantially continuously with respect to the in-plane direction of the substrate. 5. The liquid crystal display element according to claim 1, wherein the pair of substrates do not have a positive alignment structure for the liquid crystal molecules. 6. The liquid crystal display element according to claim 1, wherein the pair of substrates have a positive alignment structure for the liquid crystal molecules. 7. A condition in which the pair of substrates has a gap d, and 0 (<or ≈) d / p (<or ≈) 0.75, where p is the chiral pitch of the liquid crystal layer. The liquid crystal display element according to any one of claims 1 to 6 which is satisfied. 8. A step of preparing a pair of transparent substrates not having a positively oriented structure and a chiral nematic liquid crystal or a nematic liquid crystal, and a step of injecting the chiral nematic liquid crystal or the nematic liquid crystal between the transparent substrates. Liquid crystal display device manufacturing method. 9. The liquid crystal display element according to claim 8, wherein when the chiral nematic liquid crystal or the nematic liquid crystal is injected, the temperature of the liquid crystal is maintained at a temperature higher than the NI point of the liquid crystal. Production method. 10. The liquid crystal is injected by maintaining the temperature of the transparent substrate at the time of injecting the chiral nematic liquid crystal or the nematic liquid crystal at the NI point or higher of the liquid crystal. 9. The method for manufacturing a liquid crystal display element according to item 9. 11. When the chiral pitch of the chiral nematic liquid crystal or nematic liquid crystal is p and the thickness of the liquid crystal layer in the direction sandwiched by the pair of transparent substrates is d, 0 (<or ≈) d / The method for manufacturing a liquid crystal display device according to claim 8, wherein the p and d are selected so as to satisfy the condition of p (<or ≈) 0.75.