JPH0255328A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To attain the multigradation and high-speed display of a ferroelectric liquid crystal by using the electric field inducting tilt effect of a smectic A liquid crystal which itself has no memory effect and controlling the electric field inducting tilt by an active matrix. CONSTITUTION:The liquid crystal cell is basically constituted by inserting the liquid crystal 4 having a smectic A phase between the active matrix array 5 and a counter electrode 3. The liquid crystal cell is used by being held in place between a pair of polarizing plates 1 and 7 in case of using the cell with a double refraction mode. One of the polarizing plates can be removed in case of a GH mode added with a dichromatic dye to the smectic A liquid crystal. The voltaged to be impressed to the respective picture elements of such constitution, i.e. the tilt angles of the smectic A liquid crystal are controlled by electric fields and the electric field inducting tilt effect of the smectic A liquid crystal is applied to the active matrix, by which the video display having excellent high-speed response, high contrast, high visual field angle, and wide color reproducibility is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a liquid crystal display device that has excellent display speed, contrast, viewing angle characteristics, and gradation, and is therefore suitable for displaying images.

2. Prior Art Currently, liquid crystal display devices are available in black and white or in color.
There have been reports of commercialization or trial production of devices with sizes of up to 14 inches. Technically speaking, these liquid crystal video display devices can be broadly classified into two types.

Namely, they are active matrix type and simple matrix type. In the former case, as shown in FIG. 4, a rice stained nematic (TN) is used between an active matrix array 5 such as a thin film transistor array or a two-terminal nonlinear resistance element array with a metal-insulator-metal (MIM) configuration and a counter electrode 3.
) A liquid crystal 8 is sandwiched in between, and the active matrix array compensates for the insufficient dark value characteristics of the liquid crystal, making it possible to display high-quality images. However, the manufacturing cost of an active matrix array has the disadvantage of being expensive due to a decrease in yield. The latter constructs an X-Y matrix by sandwiching a liquid crystal between a pair of transparent band-shaped electrodes, and is simple in structure and therefore low in cost. Due to limitations, it has the disadvantage that it is inferior to the active matrix type in image quality.

In any case, both liquid crystals use nematic liquid crystals with positive dielectric constant anisotropy, and normally liquid crystals are placed between the two substrates.
Reisted nematic (TN) configurations are common, with the molecular axes initially oriented approximately parallel to the substrates and twisted approximately 90'' from one substrate to the other. TN configurations. The disadvantages of the above conventional liquid crystal display device are as follows.

(1) Since a nematic liquid crystal is used, the response speed is slow, and particularly in a display section where the applied voltage is low, the response is several tens of m5 or more, resulting in blurring of the display.

(2) The gradation is controlled by controlling the optical rotation by controlling the tilt angle of the liquid crystal with respect to the substrate using the effective value voltage applied to the pixel. In TN mode, the voltage margin between bright and dark is small, making it difficult to display multiple gradations comparable to CRT.

(3) The tilt angle of the liquid crystal with respect to the substrate is controlled by the effective value voltage applied to the pixel, and there is a drawback that contrast, brightness, chromaticity, etc. are highly dependent on viewing angle.

Recently, ferroelectric liquid crystals have been attracting attention as next-generation liquid crystal displays due to their high response speed and wide viewing angle characteristics.

The current development of ferroelectric liquid crystal displays mainly uses chiral smectic C phase because it has memory properties, high response speed, matrix properties, etc. However, those using chiral smectic C phase,
Although it has the above advantages, there are other problems such as bistability of liquid crystal molecules, difficulty in uniform alignment, instability of liquid crystal molecular alignment with respect to temperature, electric field, pressure, etc., and the lack of development of liquid crystal materials that exhibit chiral smectic C phase over a wide temperature range. The reality is that it has not yet been commercialized.

Furthermore, even if the above problems are solved, it is difficult to display halftones with ferroelectric liquid crystals, so a breakthrough in the cell structure or driving method is required to realize image display. Chiral smectic C liquid crystals are the basics. Because it has bistability and dark value characteristics, it does not require an active matrix.
It has the potential to realize a large-capacity display with high contrast and a wide viewing angle, and therefore can be expected at low cost.

In order to take advantage of the high-speed performance of ferroelectric liquid crystals, there are proposals to use them in active matrices, but chiral smectic C
With liquid crystals, there is still the problem of how to achieve gradation reproduction.

- In 1977, it was discovered that in the smectic A phase of ferroelectric liquid crystals, when an electric field is applied, the molecules tilt with respect to the layer, that is, the electric field-induced tilt effect (also called the electroclinic effect). Garof, S.
f & R, B, Meyer Phys, Rev, LeLt,
, vol. 38, p. 848, 1977). However, since there is no memory effect, dark value characteristic, etc., efforts to actively utilize this effect in displays have not been developed.

Problems that the invention aims to solve The problems to be solved by the present invention are as follows.

(1) Eliminate slow response speed, ie, display blur, of display devices using conventional nematic liquid crystals. (2)
Achieving multi-gradation display without the limitations of gradation display performance of conventional display devices using nematic liquid crystals. (3) Improving the narrow viewing angle of conventional display devices using nematic liquid crystal,
Achieves high viewing angle display.

(4) Solve the difficulty of gradation reproduction using chiral smectic C liquid crystal and realize multi-gradation, high-speed display.

In order to solve the problem more than means for solving the problem, the liquid crystal display device of the present invention has the following features:
A smectic A-phase liquid crystal is sandwiched between an active matrix array and a counter electrode, and gradation display is possible by controlling the voltage applied to each pixel, that is, the tilt angle of the smectic A liquid crystal using an electric field. It is characterized by the fact that

Operation The present invention achieves high-speed response, high contrast, high viewing angle, wide color reproduction, high magnification, and equivalent image display by applying the electric field-induced tilt effect of smectic A liquid crystal to the active matrix. It will become a reality.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, the liquid crystal display device of the present invention basically has a liquid crystal cell with a liquid crystal 4 having a smectic A phase sandwiched between an active matrix array 5 and a counter electrode 3. When used in birefringence mode, the liquid crystal cell is sandwiched between a pair of polarizing plates 1.7. In the case of the GH mode in which a dichroic dye is added to the smectic A liquid crystal, one of the polarizing plates can be removed. Although not shown in the drawings, a signal source for applying a scanning signal or a video signal to the active matrix, and a light source as necessary are provided to constitute the liquid crystal display device of the present invention.

The counter electrode (also the pixel electrode of the active matrix array 5 when used in a transmission type) is made of a transparent conductive film (hereinafter abbreviated as ITO) made of indium oxide, tin oxide, etc., made of glass or
It is provided on a transparent substrate made of a plastic film, during which smectic A liquid crystal 4 is aligned so as to be substantially parallel to the electrodes. The illustration of an alignment film for aligning liquid crystal molecules in a specific direction and at an appropriate tilt angle with respect to the electrode surface is omitted here. After drying and drying, the substrate is rubbed in one direction with a cloth, SiO or the like is obliquely deposited on the electrode surface, or a molecular alignment agent is adsorbed onto the substrate by dipping. If the active matrix array 5 is a 3-terminal element such as TPT, X-Y
The matrix is usually configured on the array side, and a scanning pulse is applied to the gate line and a signal pulse is applied to the source (or drain) line. When the active matrix array 5 is a two-terminal nonlinear resistance element, the opposing electrode is composed of a narrow strip-shaped electrode, and an XY matrix is formed between the array side and the opposing electrode side.

The electric field-induced tilt effect of smectic physiognomy is, for example, the DO
BAMBC((S)2-methylbutyJL/-P-(P-
N-tedyloxybenzylidene) amino) shear J-me)), DOBA-1-MPC (P tedyloxybenzylidene-P°-amino-1-methylpropyl cinnamate)
A ferroelectric liquid crystal of several microns in thickness is sandwiched between a pair of horizontally aligned electrodes, and the temperature of the cell is lowered from the isotropic liquid temperature to form a smectic A phase with the layer parallel to the electrode surface. Orient the molecules so that As shown in Figure 2, if the polarization axis of the first polarizing plate is made to coincide with the molecular axis when no voltage is applied, and the polarization axis of the second polarizing plate is made perpendicular to the polarization axis of the first polarizing plate, the voltage When no voltage is applied, the cell is in a dark state (normally black), but when, for example, a positive voltage is applied to the cell, the liquid crystal molecules are tilted by, for example, 10 degrees with respect to the layer normal due to the electric field-induced tilt effect, as shown in Figure 3. When the applied voltage is increased, θ increases, and when a negative voltage is applied, the liquid crystal molecules tilt in the direction of 10. In other words, the relationship between the voltage applied to the cell and the transmittance is as shown in Figure 3, and the optical characteristics does not depend on the polarity of the voltage, which is a characteristic suitable for use in active matrices.

This is because applying a DC component to the liquid crystal on average over a normal period of time causes deterioration of the liquid crystal, so it must be avoided. In the active matrix, it is advantageous to use the applied voltage holding function for low voltage driving, and a DC component is applied within each field time, but AC is applied in adjacent fields, so the deterioration of the liquid crystal is reduced. It can be prevented. At this time, if the optical properties are voltage polarity dependent as in chiral smectic C liquid crystal, it is necessary to apply a compensation pulse etc. to avoid applying the DC component, and the applied voltage waveform and timing become troublesome. In the case of the above-mentioned polarizing plate arrangement, the electric field-induced tilt effect has no voltage polarity dependence in the optical characteristics, so there is no concern that it will cause flicker. Furthermore, the electric field-induced tilt effect, that is, the tilt angle of the molecules, can be controlled by the magnitude of the applied voltage, and therefore the light transmittance can be modulated in an analog manner by the magnitude of the applied voltage. In other words, gradation display becomes possible.

The above-mentioned ferroelectric liquid crystal is just one example; generally, ferroelectric liquid crystals are Schiff base-based, azo-based, azoxy-based, biphenyl-based, aromatic, etc., with asymmetric sources such as amyl alcohol, secondary alcohol, lactic acid, and amino acids. A wide variety of molecular structures are known, including 7-quester, phenylpyrimidine, and polycyclic structures. The electric field-induced tilt effect of smectic A liquid crystals has been found in liquid crystal compositions having a chiral smectic C phase on the low temperature side. Practically speaking, it is easier to use a material whose smectic A phase is as close to room temperature as possible.

In addition, the electric field-induced tilt effect has a strong temperature dependence, so in some cases, the liquid crystal composition (or liquid crystal panel) may be kept at a constant temperature by temperature control, or the temperature of the panel may be sensed and fed back to the drive system. In order to achieve stable operation, it is necessary to change the voltage, period, etc. according to the temperature.

Effects of the Invention Conventional liquid crystal panels mainly operate in TN mode, resulting in (1) slow response speed, that is, blurring of the display. (2) Poor gradation display performance. (3) Magnitude of viewing angle dependence. On the other hand, when chiral smectin C ferroelectric liquid crystal is used, there is a problem in that it is difficult to reproduce gradations.

In the present invention, the electric field-induced tilt effect of the smectic A liquid crystal, which has no memory effect by itself, is used, and the gradation is controlled by controlling this electric field-induced tilt with an active matrix, which improves the response of the ferroelectric liquid crystal. In addition to achieving high speed, wide viewing angle, and good contrast,
Controlling the bistable orientation of conventional chiral smectic C liquid crystals was quite difficult in terms of uniformity, especially when the cell was large, but with smectic A liquid crystals, orientation control was extremely easy, and it was easy to mass-produce using rubbing techniques. Since the l-axis alignment treatment method can be adopted, a cell construction method that is almost the same as that for active matrix liquid crystal cells using conventional nematic liquid crystals can be adopted. Moreover, it has many advantages as a display device, such as responsiveness, contrast, wide viewing angle characteristics, and wide gradation reproduction, compared to active matrix cells using conventional nematic liquid crystals. In addition to direct-view video display devices such as pocket TVs and wall-mounted TVs, liquid crystal devices that utilize the atto effect of smectic A liquid crystals are transmissive or reflective, forming small high-definition panels, and are equipped with light sources and optical systems. Therefore, it can be effectively used as a so-called projection type high-definition TV device that enlarges and projects onto a screen.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the liquid crystal display device of the present invention, FIG. 2 is a conceptual diagram of the molecular arrangement and polarizing plate arrangement when used in birefringence mode, and FIG. 3 is the electric field induction of the chiral smectic A liquid crystal of the present invention. FIG. 4 is a characteristic diagram showing the transmittance-voltage characteristics of a liquid crystal cell using a tilt effect, and is a sectional view of an active matrix panel using a conventional TN liquid crystal. 1...First polarizing plate, 2...First substrate,
3... Transparent electrode, 4... Smectic A liquid crystal layer, 5... Active matrix array, 6... Active matrix forming second substrate,
7...Second polarizing plate, 8...TN liquid crystal layer. Agent's name Patent attorney Shigetaka Awano Haka 1 person 1 ---1 1st Rinko grade 2-11 7th t5 Saka 3- Irregular electrode 4 --- Sumekchi! riA Ri Kazusho 5-m-Active Ma) Refarray 6-m-Active Matrix f treatment 7---Kaya 2 Mercenary Rebellion 7---Mine 2 Butsuko treatment

Claims (6)

[Claims] (1) A smectic A-phase liquid crystal is sandwiched between an active matrix array and a counter electrode, and gradation is displayed by controlling the voltage applied to each pixel, that is, the tilt angle of the smectic A liquid crystal using an electric field. A liquid crystal display device characterized in that it enables. (2) Active matrix arrays are thin film transistors (TFTs) using semiconductors selected from amorphous silicon, polycrystalline silicon, cadmium selenide, tellurium, etc.
2.) The liquid crystal display device according to claim 1, comprising an array. (3) Active matrix arrays are made of amorphous silicon, polycrystalline silicon, cadmium selenide, tellurium,
PN junction elements, PIN junction elements composed of silicon nitride, chalcogenite compounds, and semiconductors selected from among them;
A metal-semiconductor-metal (MSM) element or a two-terminal nonlinear device with a metal-insulator-metal (MIM) configuration in which an insulator such as tantalum oxide, silicon nitride, aluminum oxide, or silicon oxide is sandwiched between a pair of metals. 2. The liquid crystal display device according to claim 1, comprising a resistive element array. (4) Smectic A liquid crystal is characterized in that the liquid crystal molecular layer is aligned between the active matrix array substrate and the counter electrode substrate so that it is substantially perpendicular to the substrate, and the molecular axis is substantially parallel to the substrate. (1) The liquid crystal display device described. (5) The liquid crystal display device according to claim (1), wherein the smectic A liquid crystal has a chiral smectic C phase on the low temperature side. (6) Claim (1) characterized in that the smectic A liquid crystal has a temperature sensing system for the panel, a temperature control system for the panel, and a feedback system for the drive system so as to maintain the temperature as constant as possible. The liquid crystal display device described.