JPS5820414B2 - liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a twisted nematic liquid crystal display device in which liquid crystal molecules are aligned by an oblique evaporation method using SiO)MgF2 or other inorganic materials, and particularly relates to setting of the evaporation angle.

The purpose of the present invention is to set the deposition angle differently from the conventional one, and to reduce the coloring of the display device peculiar to the conventional oblique deposition.Another purpose of the present invention is to provide a lower driving voltage. Yet another purpose is to completely eliminate the domain.

Before describing the contents, I will first explain the scope of the claims or the terms used below.

Evaporation angle: The angle between the perpendicular direction of the substrate surface and the direction from the evaporation source to the substrate.

Vapor deposition direction: Direction of vertical projection onto the substrate surface from the evaporation source toward the substrate.

Domain eraser: A liquid crystal that has the effect of unifying the twist direction to either left or right twist.

Clear vision direction: direction with the best contrast.

Domain: A region in which liquid crystal molecules that are asymmetric in the long axis direction and in contact with the substrate surface do not unify their asymmetric directions.

Molecular direction: Direction equivalent to the rubbing direction by the rubbing array processing method.

In order to align the liquid crystal molecules in a conventional twisted nematic liquid crystal display device, there is a rubbing method in which the substrate surface is rubbed in a certain direction.

Alternatively, an oblique evaporation method is used.

Since the rubbing method is unstable and has weak heat resistance, the oblique vapor deposition method, which has strong heat resistance and can provide inorganic sealing, is mainly used in Japan.

As a vapor deposition material for the oblique vapor deposition method, SiO has become mainstream due to its ease of vapor deposition and stability of alignment of liquid crystal molecules.

There are two types of deposition angles in conventional oblique deposition, one of which is a method in which the deposition angles are set around 85 degrees for both the upper and lower substrates.

This angle is the angle at which the liquid crystal molecules are aligned parallel to the deposition direction, and when the twist angle is set to 90 degrees or more, the liquid crystal molecules in contact with the substrate surface are completely unified not only in the long axis direction but also in their asymmetry.

Therefore, the problem of domains is solved, but on the other hand, a major disadvantage is that at such a deposition angle, the liquid crystal molecules in contact with the substrate surface are tilted by about 20 degrees, and when the display device is observed from the clear viewing direction, coloration due to birefringence is large. It becomes very unsightly as a display device.

Another conventional method of vapor deposition angle is to set the vapor deposition angle to about 60 degrees to 75 degrees for both the upper and lower substrates.

In the case of such an angle, the liquid crystal molecules are aligned perpendicularly to the deposition direction, and the liquid crystal molecules in contact with the substrate surface are almost parallel to the substrate surface, and coloring of the display device due to birefringence can be eliminated.

However, in this case, although the long axis directions of the liquid crystal molecules in contact with the substrate surface are unified, the asymmetry thereof is not unified, so a major problem of domains remains.

This is because liquid crystal molecules have asymmetry in the long axis direction, but when the deposition angle is about 60 degrees to 75 degrees, the groove structure grows perpendicular to the deposition direction, so there is asymmetry in the groove direction. do not have.

Therefore, in this case, four
A street domain occurs.

The broken line is the molecular direction on the lower substrate, and the solid line is the molecular direction on the upper substrate.

Therefore, a method of adding a domain erasing agent to the deposition angle has been proposed, but since the domain erasing agent itself determines only the twist direction, if the added domain erasing agent If it is something,
Domains 2 and 3 in FIG. 1 are generated, and if the domain eraser is of right twist, domains 1 and 4 in FIG. 1 are generated.

ELECTRO' 76 Professional
Prog-ramBoston, Mayl 1-1
4, 1976 (SESSION 7-3), Odawara et al. announced that the domain problem could be solved by depositing at a deposition angle of 72 degrees to 75 degrees, but it was confirmed through experiments that depending on the type of liquid crystal, It was found that the liquid crystal molecules were not aligned at all, and that conditions such as the deposition rate had to be extremely strict, which greatly affected the manufacturing yield.

The present invention can completely eliminate the above-mentioned drawbacks and also lower the driving voltage.

The present invention will be described in detail below, including examples.

FIG. 2 is a plan view of an embodiment of the present invention in which upper and lower electrode substrates are stacked on top of each other, and oblique vapor deposition is performed on the upper and lower substrates from directions 5 and 6, respectively.

The deposition angle in the deposition direction of No. 5 is about 65 degrees, and No. 6 is about 85 degrees.

The deviation 7 in the deposition direction is for making the twist angle different from 90 degrees, and is suitably about 5 degrees to 10 degrees.

Here, the vapor deposition direction 5 on the upper substrate may be reversed.

When a nematic liquid crystal is sandwiched between the upper and lower electrode substrates arranged in this way, the directions 8 and 9 become the molecular directions of the liquid crystal molecules in contact with the upper and lower substrate surfaces, respectively, as shown in Figure 3, and the domains are dissolved. Ru.

This is because the deposition angle on the lower substrate is set at about 85°, so the molecular direction on the lower substrate is determined in one way, and the molecular direction on the upper substrate is unified in the direction where the twist angle becomes larger, that is, the direction of 8. be done.

(Experimentally, the twist angle is more stable than 90 degrees.

) 10 is the clear vision direction.

11 is a twist angle of 90 degrees plus (deviation angle 7 in FIG. 2).

In this case, the twist direction is clockwise, but if the deposition direction is taken as shown in FIG. 4, it becomes counterclockwise.

Reference numerals 12 and 13 indicate the deposition directions on the upper and lower substrates, respectively, and the deposition angles are approximately 65 degrees and 85 degrees, respectively.

14 is the deviation in the deposition direction, which is preferably about 5 degrees to 10 degrees.

In this case as well, the vapor deposition direction 12 may be reversed as in the above embodiment.

FIG. 5 shows the molecular directions 15 and 16, the clear viewing direction 17, and the twist angle 18 when nematic liquid crystals are sandwiched between the upper and lower substrates arranged as shown in FIG.

The above embodiment shows the relationship between the vapor deposition direction and the clear viewing direction, and naturally the vapor deposition direction changes depending on where in the display device the clear viewing direction is placed.

In the above embodiment, the vapor deposition angle on the upper substrate is set at about 65 degrees, but it may be set at about 65 degrees on the lower substrate.

If a domain eraser is added, a more stable liquid crystal alignment can be obtained, and the deposition angle conditions can be made considerably gentler.

According to the present invention, the rubbing method or the deposition angle is
Compared to the oblique vapor deposition method in which the temperature was set at 0 degrees to 75 degrees, the drive saturation voltage was reduced by about 20% to 30%, making it possible to drive at a battery voltage of 1.5 cm.

As explained above, the present invention solves all the important issues for a liquid crystal display device, such as eliminating coloration in the display device, eliminating domains, and lowering the driving voltage.

[Brief explanation of drawings]

1.2, 3.4...4 types of domains in Figure 1. Fig. 2, Fig. 3, Fig. 4, Fig. 5... Examples of the present invention.

Claims (1)

[Claims] I In a twisted nematic liquid crystal display device in which liquid crystal molecules are aligned by an oblique evaporation method using SiO, MgF2, or other inorganic materials, the evaporation angles on the upper and lower electrode substrates are different, and one substrate is oriented in the evaporation direction. The evaporation angle is set so that the liquid crystal molecules are aligned in parallel, and the evaporation angle is set so that the liquid crystal molecules are aligned perpendicular to the evaporation direction on the other substrate, the twist angle is different from 90 degrees, and the nematic liquid crystal is A twisted nematic liquid crystal display device characterized in that a domain erasing agent is added to the liquid crystal display device.