JP2649389B2 - Phase compensator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a phase compensator for an optical element, and in particular, can completely eliminate coloring of a super twisted nematic liquid crystal element, and can perform white / black display. The present invention relates to a phase compensator having high contrast, excellent electro-optical characteristics, and useful as a thin and lightweight liquid crystal color display device.

[Related Art] A liquid crystal display device utilizes an electro-optic effect, that is, a change in optical properties of liquid crystal molecules caused by application of an electric field. Among these electro-optic effects, a twisted nematic (TN) effect is used. Twisted nematic (TN)
That. ) Type liquid crystal display devices have been widely used. However, in the liquid crystal display device using this TN mode, high display contrast and a sufficient visual range could not be obtained due to its unique comparatively gentle electro-optical characteristics compared to large capacity display using an XY matrix electrode structure. .

This is where the Super Twisted Nematic (hereinafter referred to as STN) liquid crystal display device comes in. In a TN-type liquid crystal display, the polarization direction of linearly polarized light that is perpendicularly incident on the substrate follows the twist of liquid crystal molecules while passing through the cell.
It rotates by 90 °, but 180 ° on STN-type LCDs.
It is set to rotate in the range of ゜ to 270 ゜. As a result, steep electro-optical characteristics can be obtained, and it is possible to meet a demand for a large capacity of a display device.

[Problems to be Solved by the Invention] However, in this STN type liquid crystal display device, a color change effect due to an interference phenomenon using birefringence of liquid crystal is used for display, so that the display is inevitably colored. There's a problem. That is, in general, the STN type is divided into two display colors, yellow mode and blue mode, depending on how the polarizing plate is attached. However, even if the polarizing plate is attached at any angle, it will appear colored.

Concerning the color tone of the display device, if white / black display can be performed, the contrast will be improved, and the display device can be applied to any display device such as a document and a chart, and further, a multi-color or full-color display can be performed. For this reason, various methods have been developed for the white / black display of the STN type liquid crystal display device, but the two-layer type is the most excellent (Nikkei Micro Devices, October 1987,
84-87). This method has a two-layer panel structure in which an STN-type liquid crystal cell as an optical compensator without an electrode structure is superposed to eliminate coloring of a display.

An STN liquid crystal cell with an electrode structure (for driving) is stacked with a compensation STN liquid crystal cell with exactly the same specifications except for the twisting direction of the liquid crystal molecules without an electrode structure (no operation), and the incident light side and transmitted light A polarizing plate is arranged on the side. When the incident light passes through the polarizer (the polarizer on the incident side), any color becomes linearly polarized light. Next, when the light passes through the driving STN-type liquid crystal cell, the linearly polarized light changes to elliptically polarized light because of birefringence. The elliptically polarized light then passes through a compensating STN-type liquid crystal cell. Here, the elliptically polarized light returns to the original linearly polarized light. Since the original linearly polarized light has the same vibration direction regardless of color, it is an analyzer (a polarizing plate on the transmitted light side)
If light is perpendicular to the polarizer, no light can pass.
That is, a black display is obtained.

However, this two-layer STN type liquid crystal display device has a compensation S
The thickness of the TN-type liquid crystal cell is greater than that of the conventional STN-type liquid crystal display device, and the weight increases.In addition, in order to obtain perfect white color, the retardation value of the driving STN-type liquid crystal cell and the compensation STN-type liquid crystal cell is required. (DΔn, where d is the thickness of the liquid crystal layer,
Δn is the birefringence value of the liquid crystal. In order to adjust) to the same value, delicate control of the liquid crystal material to be used and the cell gap was required.

It has been proposed to solve the above-mentioned drawbacks of the two-layer STN type liquid crystal display device by the unpublished prior art Japanese Patent Application No. 63-102988, in which the transmitted light side of the STN type liquid crystal cell is formed. An inorganic thin film for optical compensation is formed on a substrate.

However, the liquid crystal molecules of the STN-type liquid crystal parne have a 180-270 ° twisted alignment state, and the linearly polarized light that passes through this is not a simple elliptically polarized light after passing through a uniaxially stretched film, but is birefringent. It becomes a complex elliptically polarized light having two properties of light and optical rotation. Therefore, in the above proposal of forming an inorganic thin film for optical compensation on a substrate and performing phase compensation as shown by Δn · d (Δn; birefringence, d; thickness), the light passing through the STN type liquid crystal Pure white which cannot be returned to perfect linearly polarized light and is completely decolorized
There is a disadvantage that a black display cannot be obtained.

The present invention has been made in view of the above-described problems of the phase compensating plate of the STN type liquid crystal display element, and is a phase compensating plate capable of returning complicated elliptically polarized light transmitted through the STN type liquid crystal parene to perfect linearly polarized light. The purpose is to provide.

[Means for Solving the Problems] A phase compensating plate of the present invention is a phase compensating plate formed on a substrate on the transmitted light side of a super twisted nematic liquid crystal element, and a twist angle of the super twisted nematic liquid crystal element. The gist is that a large number of inorganic thin films are obliquely deposited by being shifted by a certain angle with respect to the in-plane azimuth of the deposition direction of the substrate by an angle equal to the above.

[Operation] In the present invention, since the phase compensator is formed by laminating the inorganic thin films which are obliquely vapor-deposited by being shifted by a certain angle with respect to the in-plane azimuth of the vapor deposition direction of the substrate by an angle equal to the twist angle of the liquid crystal cell, Optical rotation can be imparted in addition to birefringence, and it has optical properties equivalent to STN-type liquid crystal panels, so that perfect linearly polarized light can be obtained from light transmitted through STN-type liquid crystal panels.

In other words, the STN liquid crystal layer can be regarded as a cholesteric phase in which thin layers of homogeneous alignment parallel to the substrate are stacked with their alignment vectors sequentially shifted by a small angle. Focusing on this, if a structure equivalent to this can be reproduced with a phase compensator in which a large number of obliquely deposited films are stacked, the phase compensator exhibits optically similar birefringence and optical rotation.

While the above-mentioned undisclosed prior art (Japanese Patent Application No. 63-102988) does not particularly consider the angle of incidence of the obliquely deposited film in the longitudinal direction with respect to the substrate surface and the number of layers to be laminated, it is used in the present invention.
Considering the specifications of the STN type liquid crystal panel (Δn, thickness d, torsion angle and torsion direction of the liquid crystal, etc.), the obliquely deposited film that performs phase compensation is also multilayered by sequentially shifting the incident angle in the longitude direction. The feature is that the structure is such that the birefringence and optical rotation generated in the liquid crystal panel are just eliminated.

The inorganic material deposited on the substrate is not particularly limited as long as it is transparent to visible light and shows birefringence by oblique deposition. Examples of the inorganic substance used for vapor deposition include oxides such as SiO ₂ , WO ₃ , and Ta ₂ O ₅ . As a method of oblique deposition, a known method is used, for example, an electron beam evaporation method, a method of performing sputter deposition from an oblique lateral direction, or the like. The oblique deposition film may be formed directly on the outside or inside on the glass substrate of the liquid crystal cell,
After they are formed on another set of glass substrates, they may be combined.

Embodiment A preferred embodiment of the present invention will be described below with reference to the drawings. The present invention is not construed as being limited to the description of the embodiments described below.

FIG. 3 is a cross-sectional view when the phase compensator of the present invention is applied to an STN liquid crystal display device, and FIG. 4 is a three-dimensional view schematically showing the STN liquid crystal display device of FIG. STN-type liquid crystal cell 1
Polarizers 14 and 16 are disposed on the incident light side and transmitted light side of 0, and the polarization directions of the incident light side polarizer (referred to as polarizer) 14 and the transmitted light side polarizer (referred to as analyzer) 16. Are orthogonal.

Next, the structure of the STN type liquid crystal cell 10 will be described. The pair of glass substrates 2a and 2b are made of thin soda-lime glass, are arranged so as to face each other, and transparent electrode layers 4a and 4b made of ITO, indium oxide, etc. are formed on the facing surfaces, and further thereon. Have alignment films 3a and 3b formed thereon. The alignment film 3 is prepared by applying a solution to the substrate surface using an alignment agent such as polyimide, heating and drying, and then performing an alignment treatment. The alignment direction of the alignment film 3a on the incident light side is the same as the polarization direction of the polarizer 14. Parallel, the alignment film 3b on the transmitted light side,
The orientation direction of the orientation film 3a on the incident light side is set to a direction twisted clockwise or counterclockwise in the range of 180 to 270 °.

The two glass substrates 2a and 2b are held by a spacer (not shown) so as to form a desired cell gap, and a sealing material 5 such as an epoxy resin is sealed at the periphery.
In a space formed by the glass substrates 2a and 2b, a liquid crystal material 7 such as ZLI-1694, ZLI-1565, or ZLI-3201 is provided.
Is filled to form the STN type liquid crystal cell 10.

A phase compensating plate 6 is formed on the outer surface of the glass substrate 2b on the transmitted light side. The phase compensating plate 6 is formed by laminating a large number of inorganic thin films 8, and this inorganic thin film 8 is visible. It is made of an oxide such as WO ₃ or SiO ₂ which is transparent to light rays and shows birefringence by oblique deposition.

Next, a method for forming the phase compensator 6 will be described with reference to FIGS. 1 and 2 (A) and 2 (B). FIG. 2A is a three-dimensional view showing the direction of vapor deposition of the inorganic thin film 8 on the substrate 2b, and FIG. 2B is a plan view showing the direction of vapor deposition of the inorganic thin film 8 on the substrate 2b.

Here, a case where the molecular arrangement structure of the STN type liquid crystal cell 10 has a structure twisted by 240 ° will be described. In order to reproduce the twist of 240 ° by obliquely depositing a large number of the inorganic thin films 8 and laminating this 240 ° twist, as shown in FIG. 2 (B), the substrate surface longitude of the deposited particles of the first inorganic thin film 8 Angle of incidence ψ
Is made to coincide with the longitudinal direction of the substrate, and thereafter, the incident angles の of the second and subsequent layers in the longitudinal direction of the substrate are shifted by 30 ° to be stacked up to the ninth layer. FIG. 1 is a perspective view showing a state in which an inorganic thin film 8 is laminated on a substrate 2b to form a phase compensating plate 6. FIG.

At this time, the incident angle θ measured from the normal to the substrate surface varies depending on the material, but is usually around 70 °. The thickness of each layer of the inorganic thin film 8 is designed as follows. Note that the twist direction is opposite to that of the STN type liquid crystal cell 10.

d ₁ = {Δn ₀ · d ₀ ) × 1.2-1.3｝ / Δn ₁ · N where Δn ₀ ; birefringence of liquid crystal to be used, Δn ₁ : birefringence of inorganic thin film, d ₀ : STN type liquid crystal Cell thickness, d ₁ ; thickness of _one inorganic thin film, N: number of inorganic thin films. Further, although the coefficients 1.2 to 1.3 in the equation can be accurately obtained by experiments, they are corrections for loss of the birefringence effect of the inorganic thin film by twisting.

Next, regarding the operation of the STN type liquid crystal display device of the present embodiment,
This will be described with reference to the schematic diagram of FIG. The incident light L is a polarizer 14
, Light of any color becomes linearly polarized light. In the STN type liquid crystal cell 10, all the liquid crystal molecules are arranged in parallel to the substrate surface 2. However, while the incident axis 3A on the incident light side is parallel to the polarization axis 14A of the polarizer, the transmitted light Side orientation axis 3B is 1
Since the liquid crystal molecules are shifted clockwise or counterclockwise in the range of 80 to 270 °, the orientation of the liquid crystal molecules changes continuously between the two substrates, and is twisted in the range of 180 to 270 ° at the cell interface on the emission side. . Therefore, when the incident light passes through the STN type liquid crystal cell 10,
The light undergoes optical rotation and birefringence at an angle in that range, and the linearly polarized light is changed to elliptically polarized light.

Next, the elliptically polarized light passes through the phase compensator 6, which has birefringence and optical rotation optically equivalent to the STN liquid crystal panel 10. As a result, the transmitted light shows birefringence of the same size and opposite sign as the STN-type liquid crystal cell, so that the elliptically polarized light completely returns to the original linearly polarized light regardless of the wavelength,
Since it is orthogonal to the polarization axis 16A of the analyzer, no light can pass therethrough, and a black display can be obtained.

When a signal voltage is applied, the twist angle of the STN liquid crystal panel 10 is eliminated, and the liquid crystal is aligned in the normal direction of the panel surface. Therefore, the liquid crystal loses optical anisotropy with respect to incident light and becomes a mere isotropic medium. Accordingly, the linearly polarized light that has passed through the polarizing plate 14 becomes elliptically polarized light depending on the wavelength at the phase compensating plate 6, and only the polarized light component of the polarizing plate 16 is transmitted. At this time, if the thickness of the liquid crystal cell and the thickness of the phase compensator are properly adjusted, an approximately white display can be obtained.

In this embodiment, the phase compensator 6 is formed on the outer surface of the glass substrate 2b. However, the phase compensator 6 may be formed on the inner side of the STN type liquid crystal cell 10, or after being formed on another set of glass substrates,
They may be combined.

[Effect of the Invention] As described above, the phase compensator of the present invention eliminates the coloring of an optical element such as an STN liquid crystal display device by an angle equal to the twist angle of the optical element in the longitudinal direction of the substrate. It is characterized by being formed by laminating a large number of inorganic thin films that are obliquely deposited while being shifted by a fixed angle with respect to each other, and uses a separate optical compensation element such as a STN type liquid crystal cell for compensation. Since the coloring can be eliminated without any problem, the thickness of the liquid crystal display device can be reduced and the weight can be reduced. Moreover, according to the birefringence and optical rotation of the optical element, the phase compensator is given optical rotation in addition to the birefringence, and is set to be optically equivalent to that of the optical element. The complex elliptically polarized light received at the time of performing the above operation can be converted to perfect linearly polarized light. Therefore, complete phase compensation becomes possible, coloring is completely eliminated, and white / black display of an STN type liquid crystal display device having high display contrast and steep electro-optical characteristics becomes possible. And can be applied to any display device such as a document and a chart. In addition, since color display can be performed by using a color filter or the like, a thin, lightweight, high-quality liquid crystal color display device can be manufactured.

Further, the present invention is not limited to the STN type liquid crystal panel, but can be applied to all optical elements whose optical properties are to be controlled such as birefringence and optical rotation. Further, in the present invention, since an inorganic thin film as a phase difference compensating plate is formed directly on a liquid crystal cell, the structure is extremely simplified and the manufacturing cost is reduced.
In addition, since the phase compensator itself is an inorganic thin film, it is resistant to thermal and optical stress and can be used under severe environmental conditions. In terms of manufacturing technology, it is also suitable for mass production because a dry process called vapor deposition and a large vacuum layer can perform many processes at once.

[Brief description of the drawings]

FIG. 1 is a perspective view of one embodiment of the present invention, FIG. 2 (A) is a three-dimensional view showing a deposition direction of an inorganic thin film on a substrate, and FIG. 2 (B) is a plane showing a deposition direction of an inorganic thin film on a substrate. FIG. 3 is a cross-sectional view when the phase compensator of the present invention is applied to an STN type liquid crystal display device, and FIG. 4 is a three-dimensional view schematically showing the STN type liquid crystal display device of FIG. . 2a, 2b: Glass substrate 3a, 3b: Alignment film 4a, 4b: Transparent electrode 6: Inorganic thin film 7: Liquid crystal 8: Inorganic thin film 10: STN type liquid crystal cell 14: Polarizer 16 ... Analyzer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasukun Taga 41-Cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Laboratory, Inc. 41, Yokomichi, Toyota Central Research Institute, Inc.

Claims (1)

(57) [Claims] 1. A phase compensator formed on a substrate on a transmitted light side of a super twisted nematic liquid crystal device, wherein the substrate surface is in an evaporation direction of the substrate by an angle equal to a twist angle of the super twisted nematic liquid crystal device. A phase compensator characterized in that it is formed by laminating a large number of inorganic thin films which are obliquely deposited while being shifted by a certain angle with respect to an inner direction.