JPH01273017A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To always obtain stable display quality by forming an inorganic thin film for optical compensation on a light transmitting substrate forming a super-twist nematic liquid crystal cell. CONSTITUTION:Incident light passes through a polarizer 1 and a driving STN liquid crystal cell 10 in that order. Since said cell 10 has birefringence, linear polarization is colored, and turns into elliptical polarization. It passes through the inorganic thin film 6 for optical compensation formed on the light transmitting substrate. However, the film 6 is set to possess birefringence opposite from the STN liquid crystal cell 10, the elliptical polarization returns to its original linear polarization, and its coloring is eliminated. The original linear polarization has the same vibrating direction regardless of color, and therefore it passes through a photodetector. As a result, a stable black and white display appears on an STN liquid crystal display device.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention simplifies the structure of a super twisted nematic liquid crystal display device, and is useful as a thin and lightweight liquid crystal color display device that has high contrast and excellent electro-optic properties. This invention relates to a liquid crystal display element.

[Prior Art] A liquid crystal display device uses an electro-optic effect, that is, a change in the optical properties of liquid crystal molecules that occurs when an electric field is applied. Among these electro-optic effects, twisted nematic (TN) Twisted nematic (hereinafter referred to as TN) type liquid crystal display devices that utilize this effect have been widely used. However, in liquid crystal display devices using this TN mode, high display contrast and sufficient visual range cannot be achieved due to the relatively smooth electro-optic characteristics peculiar to the large-capacity display using the XY71 helix electrode structure. I couldn't get it.

This led to the emergence of super twisted nematic (hereinafter referred to as STN) type liquid crystal display devices.

In a TN type liquid crystal display device, the polarization direction of linearly polarized light incident perpendicularly to the substrate is rotated by 90° along the internal twist of the liquid crystal molecules while passing through the cell, or by 80° in an STN type liquid crystal display device. It is set so that the light rotates within a range of ~270°. As a result, steep electro-optical characteristics can be obtained, which can meet the demand for larger capacity display devices.

On the other hand, an invention has been disclosed in which a phase control element and a reflecting mirror are integrally formed by vapor deposition on a transparent substrate of a liquid crystal element in a liquid crystal anti-glare mirror using a liquid crystal element.
1-84.625). In this invention, the phase control element and the reflecting mirror are made thinner, so that the structure is simple and the visibility is good, such as no double images.

“Invention or problem to be solved” However, for this STN type liquid crystal display device, S T
Since the N-type liquid crystal display device uses a sudden change effect due to an interference phenomenon using the birefringence of liquid crystal for display, there is a problem that the display is inevitably colored. That is, in general, in the STN type, depending on how the polarizing plate is attached, there are two display colors, yellow moat and blue moat, or even if the polarizing plate is attached at such an angle, it will appear colored.

Regarding the color tone of the display device, if possible, white/black display will have good contrast, and it can be applied to all kinds of display devices such as documents and charts, and furthermore, multi-color or full-color display is possible. For this reason, various methods have been developed for converting STN type liquid crystal display devices into black/white displays, and the two-layer method is the most superior (Nikkei Microchihs, 1987, 1).
(October, pp. 84-87). This method uses S]゛N as an optical compensation plate without a diagonal electrode structure to eliminate display coloration.
It consists of a 2W type panel structure with overlapping type liquid crystal cells. A schematic diagram of this 2WI type is shown in FIG.

In Fig. 4, it has an electrode structure (for driving) S TN
A 1111 conventional STN type liquid crystal cell 12 with exactly the same specifications except for the twisting direction of the liquid crystal molecules (which does not operate due to the electrode structure) is stacked on top of the 1111 conventional STN type liquid crystal cell 12, and polarizing plates 14. 16. When the incident light passes through the polarizer (polarizing plate on the incident side) 14, the colors of and also become linearly polarized light. Next, when passing through the driving STN type liquid crystal cell 10,
Due to birefringence, linearly polarized light changes to elliptically polarized light. The elliptically polarized light then passes through an STN type liquid crystal cell 12 for compensation. Here, the elliptically polarized light returns to its original linearly polarized light. Since the original linearly polarized light vibrates in the same direction regardless of color, if it is perpendicular to the analyzer (polarizing plate on the transmitted light side) 16 or the polarizer 14, no light can pass through it. In other words, a black display will be obtained.

However, this two-layer STN type liquid crystal display device is thicker and heavier than the conventional STN type liquid crystal display device due to the thickness of the STN type liquid crystal cell 12 for compensation, and it is difficult to obtain perfect white color. The retardation (direct (dΔ11, where d is the night crystal layer thickness,
Δ■] is the birefringence value of the liquid crystal. ), it was necessary to delicately control the liquid crystal material used and the cell gap.

The present invention was made in view of the above-mentioned problems of the two-layer STN liquid crystal display device, and it simplifies the structure and reduces the weight without reducing the thickness, and makes it easy to adjust the retardation value. An object of the present invention is to provide an STN type liquid crystal display element.

Means for Solving Problem 1] The present invention was completed based on the idea that an 8% substance-free obliquely deposited film has birefringence, and the liquid crystal display element of the present invention The gist is that an inorganic thin film of optical tHIiM was formed on the substrate on the transmitted light side forming a nematic liquid crystal cell.

The inorganic material deposited on the substrate is not particularly limited as long as it is transparent to visible light and exhibits birefringence when deposited obliquely. Examples of inorganic substances used for vapor deposition include SiC2, WO3, T a x Os
and other oxides. A known method is used for the oblique vapor deposition, such as an electron beam vapor deposition method or a method of sputter vapor deposition from an oblique lateral direction. The obliquely deposited film may be directly formed on the outside or inside of the glass substrate of the liquid crystal cell, or may be formed on another set of glass substrates and then combined.

It is desirable that the deposited film has a multilayer structure in which the deposition direction is varied, thereby alleviating the direction dependence of the birefringent anisotropy of incident light. The vapor deposited film is not limited to two layers, but may be alternately stacked in any number of layers. However, it is necessary that a sufficient columnar structure be grown in each layer, and therefore the thickness of each layer is required to be 500 Å or more. Appropriate values are selected for the film thickness and vapor deposition angle of each layer of the vapor deposited film depending on the desired dΔ11 value.

[Function] The incident light passes through a polarizer and becomes linearly polarized light, and the driving ST
Passes through an N-type liquid crystal cell. Since the STN liquid crystal cell has birefringence, linearly polarized light is colored and turns into elliptically polarized light. The elliptically polarized light then passes through a compensating inorganic thin film formed on the substrate on the transmitted light side.The inorganic thin film on the force plate is set to have birefringence opposite to that of the STN liquid crystal cell. returns to its original linearly polarized light and is either colored or eliminated. Since the original linearly polarized light has the same vibration direction regardless of color, it is displayed as white/black on the STN type liquid crystal display device by passing it through an analyzer.

[Example] A preferred embodiment of the present invention will be described below with reference to the drawings.

It should be noted that the present invention is not to be construed as being limited in any way by the description of the examples described below.

FIG. 1 is a sectional view of an embodiment of the present invention. Polarizing plates 14 and 16 are arranged on the incident light side and the transmitted light side of the STN type liquid crystal cell]0, and the polarizing plate (referred to as a polarizer) 14 on the incident light side and the polarizing plate (referred to as an analyzer) on the transmitted light side. )16 polarization directions are orthogonal.

Next, the structure of the STN liquid crystal cell 10 will be explained. A pair of glass substrates 2a and 21] are made of thin plate lime glass and are arranged to face each other, and transparent electrode layers 4a and 41] made of ITO, indium oxide, etc. are formed on the opposing surfaces, respectively. Alignment films 3a and 31] are formed thereon. The alignment film 3 is made by using an alignment agent such as polyimide, applying a solution to the substrate surface, heating and drying, and then performing an alignment treatment, and the alignment direction of the alignment film 3a on the incident light side is the same as the polarization direction of the polarizer 14. The alignment film 3b on the transmitted light side is parallel to the alignment film 3a on the incident light side.
The orientation direction is set to be twisted counterclockwise or clockwise within a range of 180 to 270°.

The two glass substrates 2a and 2+1 are held by spacers (not shown) so as to form a desired cell gap, and their peripheral edges are sealed with a sealing material 5 such as epoxy resin. In the space formed by the glass substrates 2a and 21), ZLI-1694, ZLI-1565,
The liquid crystal material 7 such as ZLI-3201 is filled and the STN
A 1° type liquid crystal cell is constructed.

An inorganic thin film 6 is formed on the outer surface of the glass substrate 2+1 on the transmitted light side, and this inorganic thin film 6 serves as a compensator and is transparent to visible light. Due to oblique deposition, it shows no birefringence and WO2, S i 0
Consisting of oxides of grade 2. This inorganic thin film 6 is formed by diagonal vapor deposition by dividing these oxides into many layers and changing the vapor deposition angle, as shown in the partially enlarged sectional view of the glass substrate 21 on which the inorganic thin film 6 is formed in FIG. The film thickness and deposition angle of each deposited film are STN type liquid crystal cell 1o and d△11.
are set so that they have birefringence of equal or opposite sign.

Next, regarding the operation of the STN type liquid crystal display device of this example,
This will be explained according to the schematic diagram in FIG. When the incident light (1) passes through the polarizer 14, the light of color (2) also becomes linearly polarized light. S'F
In the N-type liquid crystal cell 1o, all liquid crystal molecules are arranged parallel to the substrate surface 2, or the alignment axis 3A on the incident light side is parallel to the polarization axis 1.4A of the polarizer. On the other hand, the alignment axis 3B on the transmitted light side is shifted clockwise or counterclockwise in the range of 180 to 270°, so the alignment direction of the liquid crystal molecules changes continuously between both substrates, and 180~ at the cell interface of
It is twisted in the range of 27o°. The incident light is ST
When passing through the N-type liquid crystal cell 1o, the light undergoes optical rotation within the range of angles, and the linearly polarized light changes to elliptically polarized light, and the orientation and eccentricity of the long axis of the ellipse vary depending on the wavelength.

Next, the elliptically polarized light passes through the inorganic thin film 6, and the optical axis 6A of the inorganic thin film 6 forms a predetermined angle (for example, 45°) with respect to the polarization axis 1.6 A of the analyzer 16. As a result, the inorganic thin M6 exhibits birefringence with a magnitude equal to or opposite to dΔn of the STN liquid crystal cell, and the elliptically polarized light returns to its original linear polarization irrespective of the wavelength, and the polarization axis 16A of the analyzer Since they are perpendicular to each other, no light can pass through them, resulting in a black display. When a signal voltage is applied, light of each wavelength passes through the analyzer 16 with some difference in the amount of transmitted light, but a display that is almost indistinguishable from white to the naked eye is obtained.

Although the inorganic thin film 6 is not formed on the outer surface of the glass substrate 21 in this embodiment, it may be formed on the inside of the STN liquid crystal cell 0, or it may be formed on a separate set of glass substrates. You can assemble it later.

[Effects of the Invention] As explained above, the STN type liquid crystal display element of the present invention has the following effects:
In order to eliminate coloring in STN type liquid crystal display devices, an inorganic thin film for optical compensation is formed on the substrate of the STN type liquid crystal cell for driving, and coloring can be achieved without using an STN type liquid crystal cell for compensation. This makes it possible to reduce the thickness and weight of the liquid crystal display device. This makes it possible to display black and white with STN type liquid crystal display devices, which have high display contrast and steep electro-optic characteristics, making it possible to respond to larger capacity display devices and to be able to display documents, charts, and other types of display devices. Applicable to

Furthermore, if a color filter or the like is used, color display becomes possible (g), making it possible to manufacture a thin, lightweight, and high-quality liquid crystal color display device. In addition, in the present invention, since an inorganic thin film is directly formed as a retardation compensation plate on the liquid crystal cell, the structure is extremely simplified, the manufacturing cost is low, and dΔ11 can be easily adjusted by controlling the thickness of the formed film. Therefore, the optimum compensation film can be set for each individual liquid crystal cell, and stable display quality can always be obtained.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of an embodiment of the present invention, Fig. 2 is a schematic diagram for explaining the operation of the embodiment of Fig. 1, and Fig. 3 is a diagram showing an inorganic thin film formed thereon. FIG. 4 is a partially enlarged sectional view of the glass substrate, and is a schematic diagram for explaining the operation of a conventional STN type liquid crystal display device. 2a, 21] - Glass substrates 3a, 3b - Alignment film 4a, 4) - Transparent electrode 6 - Inorganic thin film 7 - Liquid crystal 10 - Driving STN type liquid crystal cell 12 -
Compensation STN type liquid crystal cell 14... Polarizer 16... Analyzer (O

Claims (1)

[Claims] (1) A liquid crystal display element characterized in that an inorganic thin film for optical compensation is formed on a substrate on the transmitted light side forming a super twisted nematic liquid crystal cell.