JPH11101977A - Liquid crystal electro-optical element - Google Patents

Abstract

(57) [Object] To improve the reduction of the amount of transmitted light of a liquid crystal electro-optical element comprising a liquid crystal cell and a polarizing plate disposed so as to sandwich the liquid crystal cell. A liquid crystal electro-optical element includes a reflective liquid crystal cell and a polarizing element disposed on a light incident side of the liquid crystal cell.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a liquid crystal electro-optical element.

[0002]

2. Description of the Related Art As shown in FIG. 8, a conventional liquid crystal electro-optical device comprises a liquid crystal cell 1 and polarizing plates 3 and 4 disposed on both sides of the liquid crystal cell. In particular, in the case of the transmission type, the backlight 5 was provided outside the polarizing plate 4, and in the case of the reflection type, the reflection plate 5 was similarly provided.

[0003]

In recent years, with the increase in the number of pixels required for a display, the density of circuit elements formed on a substrate of a liquid crystal electro-optical element has increased rapidly, and the amount of transmitted light has been reduced. Inviting. For example, the aperture ratio defined by the displayable area occupied in the pixel area is about 40% in a current liquid crystal cell used for a projection television or the like, but will be increased in the future to the number of high-definition compatible pixels.
It is expected to drop to about 10%. For the purpose of improving this, the adoption of a backlight and an increase in the amount of the backlight, or the improvement of the structure and design of circuit elements have been performed, but the effect has been insufficient.

The present invention solves such a problem. The object of the present invention is to improve the aperture ratio to about 90% at once by introducing a new reflective liquid crystal mode, and to reduce the density of circuit elements. An object of the present invention is to provide a liquid crystal electro-optical element which does not cause a decrease in the amount of transmitted light even if the number increases.

[0005]

A liquid crystal electro-optical element according to the present invention is a liquid crystal electro-optical element comprising a liquid crystal cell having a liquid crystal sandwiched between two opposing substrates and one reflector. The liquid crystal has a twisted orientation of about 90 degrees and has no polarizing element between the liquid crystal and the reflector.

Further, a selective reflection member is provided on the opposite side of the liquid crystal with respect to the reflection plate.

Further, the reflection plate is a metal thin film formed on a substrate, and also functions as a pixel electrode.

[0008] Further, a circuit element such as a thin film transistor is provided on the substrate, and substantially the entire surface of the circuit element is covered with an electrode also serving as a reflector.

Further, the birefringence of the liquid crystal of the liquid crystal cell Δn
And the cell gap d, the retardation △ n × d
Is larger than 0.15 μm and smaller than 0.35 μm.

[0010]

[Function] A selective reflection member is formed, for example, by forming a multilayer thin film 22 made of a metal or a metal oxide on the slopes of two prism-shaped light transmitting bodies 21 as shown in FIG. It is a thing. 4 against the slope as shown in FIG.
When the light 51 is incident at an angle of 5 degrees, the P-polarized light component 52 (the polarized light whose light oscillating surface is perpendicular to the slope) goes straight out without being affected by the selective reflection member, and is emitted. 53 (polarized light whose light oscillation direction is parallel to the slope) is reflected in a direction at 90 degrees to the incident direction. Such a selective reflection member is particularly called a polarizing beam splitter (hereinafter abbreviated as PBS).

[0011] PBS has a similar effect to conventional polarizing films in that it selectively transmits polarized light. However, like the conventional liquid crystal electro-optical element,
Rather than having two polarizers, a polarizer and an analyzer, on both sides of the liquid crystal cell, a single PBS serves as both a polarizer and an analyzer, so it is necessary to use a new liquid crystal mode different from the conventional one.

Conventionally, for such an optical system, it has been proposed to use a homeotropically aligned n-type nematic liquid crystal. The display principle will be described with reference to FIG. Homeotropically aligned liquid crystals do not have birefringence in the cell normal direction. Therefore, it is incident from the direction A in the figure and the PBS
The S-polarized light 53 bent at a right angle by the light exits the cell in the state of the S-polarized light 56 as it is. The S-polarized light 56 is reflected at right angles by the PBS again and exits in the A direction, and is not observed from the B direction. On the other hand, a voltage is applied to the liquid crystal cell to tilt the liquid crystal molecules, and the retardation is λ / 4 (a quarter of the wavelength of light).
1. However, since it is a reflection type, the actual retardation is λ / 2).
The light is emitted in the state of P-polarized light 55. The P-polarized light 55 travels straight and is emitted in the B direction without being affected by the PBS. Thus, the homeotropic cell can be turned on / off with high contrast in the reflection mode combined with PBS. However,
The homeotropic liquid crystal cell is difficult to align and is not reliable.In addition, n-type liquid crystal materials are still under development and have not obtained sufficient characteristics, so this liquid crystal mode is practical. is not.

Conversely, a homogeneously aligned p-type nematic liquid crystal can be used without a twist. In this case, the light becomes bright when no voltage is applied, and becomes dark when the voltage is applied and the liquid crystal molecules stand sufficiently. Since the homogeneous alignment is different from the homeotropic alignment and has been widely used in the past, all the techniques are at a practical level. However, as the retardation is lost, a very high voltage is required to make the liquid crystal molecules stand, and a high contrast cannot be obtained with a normal voltage as in a homeotropic alignment cell. This is because, as shown in FIG. 6, the liquid crystal molecules in the vicinity of the substrate of the liquid crystal cell are hard to stand due to the surface regulation of the alignment film.

The liquid crystal electro-optical element of the present invention is characterized in that the twist angle is about 90 degrees while being homogeneously aligned. By setting the twist angle to about 90 degrees, the liquid crystal molecules near the upper and lower substrates that are orthogonal to each other optically compensate each other, and the retardation is lost at a relatively low voltage, so that a dark state is obtained. On the other hand, it is necessary to optimize the cell conditions for the reflectance (brightness) when no voltage is applied. FIG. 7 shows the angle θ between the polarization direction of the incident light and the rubbing direction of the upper substrate, and the retardation Δn of the liquid crystal cell.
The change in reflectivity when the value of xd is changed is shown. According to this figure, the reflectance is θ = 0 to 40 degrees and Δn × d = 0.15 μ
m to 0.35 μm, θ = 50 to 70 degrees, Δn × d = 0.60 μm
It can be seen that a high value is obtained under the two conditions of 0.75 μm. As described above, a dark state is always obtained when a voltage is applied, so that under these conditions, ON / OFF with high contrast is possible.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION

[0016]

The present invention will be described below in detail with reference to examples.

Example 1 FIG. 1 is a sectional view of a liquid crystal electro-optical element according to the present invention. In the figure, 1 is a liquid crystal cell and 2 is PBS. 11 is an upper substrate, 12 is a lower substrate, 13 is a transparent electrode, 14
Is a reflective film also serving as a pixel electrode, 15 is a thin film transistor (hereinafter referred to as TFT), 16 is an insulating film, and 17 is a liquid crystal. The liquid crystal uses ZLI-2359 (製 n = 0.0512) manufactured by Merck,
The liquid crystal cell having a cell gap of 4.9 μm was homogeneously aligned at a twist angle of 90 degrees left. The retardation is 0.25
μm. A nickel vapor deposition film was used for the reflection film, and a polyimide resin was used for the insulation film. The reflective film covers almost the entire surface of the TFT that caused the aperture ratio to decrease,
The aperture ratio has been improved to 92%.

FIG. 2 is a diagram showing the relationship between the axes of the liquid crystal electro-optical element according to the present invention as viewed from the light incident direction. 31 is the polarization direction of the incident light that has passed through the PBS, 32 is the rubbing direction of the upper substrate, and 33 is the rubbing direction of the lower substrate. 34 is 31
Is 32 (the counterclockwise direction is a positive value), and 35 is the twist angle of the liquid crystal. In Example 1, θ was set to 20 degrees.

FIG. 3 is a diagram showing the electro-optical characteristics of the liquid crystal electro-optical element manufactured under the above conditions. Its reflectivity is
76%, almost comparable to the conventional twisted nematic mode, combined with a high aperture ratio of 92%, a bright display was possible. The display contrast is up to 1:85.

Example 2 In Example 1, the twist angle of the liquid crystal was 95 degrees, the retardation was 0.20 μm, and the angle θ was
The procedure was the same as in Example 1, except that the temperature was changed to 105 degrees. Increasing the twist angle of the liquid crystal allows driving at a lower voltage, but reduces the reflectivity to 70%.
Note that the characteristics do not change even if an integer multiple of 90 degrees is added to the angle θ, so that θ = 105 degrees is the same as θ = 15 degrees.

Example 3 Example 1 was the same as Example 1 except that the retardation was 0.70 μm and the angle θ was 60 degrees.
Same as 1. This is another high reflectivity condition shown in FIG. Although it can be driven at a lower voltage and improves the sharpness of the threshold voltage as compared with the first embodiment, it has the disadvantage that the coloring of the display is increased.

Example 4 In this example, two polarizing plates were used instead of using PBS. FIG. 4 shows a cross-sectional view of the liquid crystal electro-optical element in Example 4. Light enters from a direction inclined about 10 degrees from the normal direction of the liquid crystal cell, and
The light is emitted in a direction inclined at an angle. A polarizer 3 and an analyzer 4 were placed on the optical paths of the incident light 51 and the output light 54, respectively, to substitute for PBS. Various conditions of the liquid crystal cell were set the same as in Example 1.

Since the polarizing plate has a higher degree of polarization than PBS,
A high display contrast of 1: 220 was obtained.

[0024]

As described above, according to the present invention, by introducing a new reflective liquid crystal mode, there is provided a liquid crystal electro-optical element which does not cause a decrease in the amount of transmitted light even if the density of circuit elements increases. be able to.

[Brief description of the drawings]

FIG. 1 is a sectional view of a liquid crystal electro-optical element according to the present invention.

FIG. 2 is a diagram showing a relationship between axes of the liquid crystal electro-optical element of the present invention.

FIG. 3 is a diagram illustrating electro-optical characteristics of the liquid crystal electro-optical element according to the first embodiment of the present invention.

FIG. 4 is a sectional view of a liquid crystal electro-optical element according to a fourth embodiment of the present invention.

FIG. 5 is a view showing the action of PBS.

FIG. 6 is a diagram schematically showing an arrangement of liquid crystal molecules when a voltage is applied to a liquid crystal cell.

FIG. 7 is a diagram showing how the reflectance of the liquid crystal electro-optical element of the present invention changes depending on Δn × d and the angle θ of the liquid crystal cell.

FIG. 8 is a sectional view of a conventional liquid crystal electro-optical element.

[Explanation of symbols]

 1． Liquid crystal cell 2. 2. Selective reflection member (here, PBS) Polarizing plate (polarizer) 4. Polarizing plate (analyzer) 5. Reflector or backlight 11. Upper substrate 12. Lower substrate 13. Transparent electrode 14. Reflective film that doubles as pixel electrode 15. Circuit elements (here TFT) 16． Insulating film 17. Liquid crystal 21. Prism 22. Multilayer thin film 31. 32. Polarization direction of incident light passing through PBS Rubbing direction of upper substrate The rubbing direction of the lower substrate 34. The angle θ formed by 31 to 32 35. Liquid crystal twist angle 41. Electro-optical characteristics of light with a wavelength of 450 nm (blue) 42. Electro-optical characteristics of light with wavelength of 550nm (green) 43. Electro-optical characteristics of light with a wavelength of 650 nm (red) 51. Incident light 52. P-polarized component of incident light 53. S-polarized component of incident light 54. Outgoing light 55. P-polarized component of emitted light 56. S-polarized component of emitted light

[Procedure amendment]

[Submission date] September 2, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction contents]

[0005]

According to the present invention, there is provided a liquid crystal electro-optical device having a reflective liquid crystal cell in which a liquid crystal is sandwiched between a pair of substrates. And the liquid crystal is twisted at about 90 degrees, and the product of the birefringence (屈折 n) of the liquid crystal and the cell thickness (d) of the reflection type liquid crystal cell (液晶). nd) is set in the range of 0.15 μm to 0.35 μm.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction contents]

The angle (θ) between the polarization direction of the incident light entering the reflection type liquid crystal cell and the rubbing direction applied to the light incident side substrate of the reflection type liquid crystal cell is 0 in the twist direction of the liquid crystal. It is characterized by being set in the range of degrees to 40 degrees.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction contents]

Further, according to the present invention, there is provided a liquid crystal electro-optical device having a reflective liquid crystal cell having a liquid crystal sandwiched between a pair of substrates, wherein the polarizing element is provided only on the light incident side of the reflective liquid crystal cell. And the liquid crystal is about 9
And the product (Δnd) of the birefringence Δn of the liquid crystal and the cell thickness d of the reflective liquid crystal cell is set in the range of 0.60 μm to 0.75 μm. It is characterized by becoming.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

Further, an angle (θ) between the polarization direction of the incident light incident on the reflection type liquid crystal cell and the rubbing direction applied to the light incident side substrate of the reflection type liquid crystal cell is in the twist direction of the liquid crystal. It is characterized by being set in the range of 50 to 70 degrees.

Claims (8)

[Claims] 1. A liquid crystal electro-optical element comprising a liquid crystal cell having a liquid crystal sandwiched between two opposing substrates and one reflector, wherein the liquid crystal has a twist orientation of about 90 degrees, and A liquid crystal electro-optical element having no polarizing element between the liquid crystal and the reflector. 2. The liquid crystal electro-optical element according to claim 1, wherein a selective reflection member is provided on the opposite side of the liquid crystal with respect to the reflection plate. 3. The liquid crystal electro-optical device according to claim 1, wherein the reflection plate is a metal thin film formed on a substrate and also serves as a pixel electrode. 4. The liquid crystal electro-optical device according to claim 1, further comprising a circuit element such as a thin film transistor on the substrate, and covering substantially the entire surface of the circuit element with an electrode serving also as a reflector. 5. The method according to claim 1, wherein the retardation Δn × d, which is the product of the birefringence Δn of the liquid crystal of the liquid crystal cell and the cell gap d, is larger than 0.15 μm and smaller than 0.35 μm. 2. The liquid crystal electro-optical element according to claim 1, wherein 6. An angle θ between a polarization direction of light incident on the liquid crystal cell and a rubbing direction of the upper substrate is 0 ° or more and 40 ° or less, or 90 ° or more and 130 ° or less. The liquid crystal electro-optical element according to claim 5, wherein: 7. A retardation Δn × d, which is a product of a birefringence index Δn of a liquid crystal of the liquid crystal cell and a cell gap d, is larger than 0.60 μm and smaller than 0.75 μm. 2. The liquid crystal electro-optical element according to claim 1, wherein 8. An angle θ between the polarization direction of light incident on the liquid crystal cell and the rubbing direction of the upper substrate is in the range of 50 to 70 degrees, or 140 to 160 degrees in the twist direction of the liquid crystal.
8. The liquid crystal electro-optical element according to claim 7, wherein the temperature is equal to or lower than the degree.