JPS62160420A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To improve displayed gradation characteristic by inserting ferroelectric liquid crystals between confronting substrates and holding the liquid crystals at specified three conditions. CONSTITUTION:When ferroelectric liquid crystals are inserted between confronting substrates having an oblique deposited inorg. material on the surface of the substrates, the liquid crystal molecules are stabilized at an intermediate third state having a twisted structure with a different angle between the normal of the layer of molecules. Accordingly, the liquid crystals in the liquid crystal element are held at the first state where the liquid crystal molecules are almost parallel to the substrate but are inclined rightwards against the normal of the molecule layer, at the second state where the liquid crystals are inclined leftwards, and the third state where the liquid crystal molecules are in the intermediate stage, permitting sufficient display of gradation by the intermediate state. Thus, the display performance of the gradation is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a liquid crystal element having a ferroelectric liquid crystal as a liquid crystal layer, which can control the gradation of the amount of transmitted light.

Prior Art In recent years, reports have been made on ferroelectric liquid crystals with fast response speed and memory properties (for example, Hideo Takezoe, Atsuo Fukuda, and Sakae Kuze: "Industrial Materials", Vol. 31, No. 10, 22). ).

An example of a conventional ferroelectric liquid crystal panel will be described below with reference to the drawings. FIG. 6 shows the structure of a conventional smectic liquid crystal panel. In FIG. 6, 21 is a glass substrate, 22 is a transparent electrode made of ITO (indium tin oxide), 24 is a ferroelectric liquid crystal layer, 26 is a C director of liquid crystal molecules, and 126 is a dipole moment.

Ferroelectric liquid crystals generally have a dipole moment in the direction perpendicular to the long axis of the molecules, and as the film becomes thinner, they acquire spontaneous polarization. FIG. 7 shows how to describe ferroelectric liquid crystal using an example of a chiral smectoid phase exhibiting ferroelectricity. Figure 7 (IL) shows that the long axis of the molecule is +θ with respect to the normal 27 of the molecular layer.
FIG. 7('b) is a representation of a ferroelectric liquid crystal in a -θ degree tilted state. 27 is the normal to the layer, and 28 is the long axis direction n of the molecule.

29 is the dipole moment Ps, and 30 is the C director C131 when n is projected onto the xy plane, which is the inclination angle ±θ degrees with respect to the normal to the long axis of the molecule. The operating principle of the ferroelectric liquid crystal panel having the above structure will be explained below with reference to the drawings.

FIG. 8 shows a principle diagram of a conventional ferroelectric liquid crystal panel display method. 32 is a liquid crystal molecule whose long axis of the molecule is tilted by +θ degrees with respect to the layer normal, 33 is a liquid crystal molecule tilted by 10 degrees, 34 is a dipole moment in the direction of the front of the paper, 35 is a dipole moment in the direction of the back of the paper, 36 is the direction of the two polarizing plates. Now, Fig. 8 (&) shows the state where no voltage is applied, Fig. 8 (b) shows the case where a positive voltage is applied from the front to the back of the paper, and Fig. 8 (c) shows the case where the positive voltage is applied from the back to the front of the paper. This is the operating principle when applying .

In this way, the entire cell assumes two states tilted by ±θ degrees depending on the direction of applied voltage, and therefore, brightness and darkness can be expressed by utilizing birefringence or dichroism due to the electro-optic effect.

Problems to be Solved by the Invention Until now, there have only been reports on binary display based on the above two states. A method of using a mixture of two states within a picture element has been considered to display halftones, but there is no example of this being actually possible to display on a matrix panel. This is because the mixed state of the two states is easily influenced by the substrate surface, resulting in extremely poor controllability and requires very uniform alignment.

In view of the above problems, the present invention provides a liquid crystal element that is advantageous for gradation display.

Means for Solving the Problems In order to solve the above problems, the liquid crystal element of the present invention has a ferroelectric liquid crystal sandwiched between a pair of substrates having electrodes on opposing surfaces, so that the molecules are approximately parallel to the substrates. The first tilted to the right from the layer normal
, a second state that is approximately parallel to the substrate and tilted to the left from the molecular layer normal, and a third state in which the molecules form a twisted structure with different angles with the molecular layer normal on the opposing substrate. It can represent three gradations.

In order to produce even more gradations, one pixel of the above element can be arranged with multiple pixels with different areas, or by combining multiple scans, the gradations will increase as a power of 3. , which is much more advantageous than the case where there are only two states.

When a voltage is applied to the working ferroelectric liquid crystal molecules, the spontaneous polarization points uniformly upward or downward, and the director (macroscopic molecular force direction) uniformly tilts with respect to the layer normal.

If the spontaneous polarization points uniformly upward, fttIU(un
ifform up), if the uniformly facing downwards is U.
They will be referred to as D (uniform down) and are illustrated in FIGS. 1 (IL) and (b), respectively. -force,
In a cell with appropriate thickness and orientation treatment, when no voltage is applied, spontaneous polarization will be directed toward the substrate or in the opposite direction depending on the polarity of the substrate surface, so if the upper and lower substrates have the same polarity, spontaneous polarization will occur. The polarization spreads from top to bottom, and the gylefter exhibits a twisted structure (Tw) as shown in FIG. 1 (0). All of these three states are stable and have memory properties.

When the inclination angle θ of the molecule from the layer normal is around 22.6°,
A polarizer is installed parallel to the molecule on the incident light side substrate when the twisted structure is taken, and an analyzer is installed perpendicularly to the molecule. Assuming that the molecule is parallel to the polarizer during UD, the visible light range in each state is determined. FIG. 3 shows the calculated amount of transmitted light.

The horizontal axis is the product Δn of the refractive index anisotropy Δn of the liquid crystal and the distance d between the substrates.
od, the vertical axis is the ratio of transmitted light to incident light. U
It is clear that in D, it is always in a dark state, and in UTJ, equation (1) expressing the birefringence effect is used, and in the twisted state, equation (2) is used to express the amount of transmitted light when light passes through the twisted structure.

T = 5in2 (4θ) 5in2 (πΔnl/λ)
...Formula (1) T = 5 = n2 (20 towns〒〒u
” )/(1+ u2) ... complete set @) However, U=
π·Δnd/2θλ From the figure, it can be seen that when Δn@1 is around 0.3 and 0.8, halftones can be expressed by the twisted state.

Example Examples are shown below.

In my experiments, when ferroelectric liquid crystals are aligned by rubbing at a very low pressure or by obliquely depositing an inorganic material on the substrate surface, a twisted structure is very likely to appear and is stable. I found out. Figure 2(b)
Figure 2 (IL
), the first pulse resets the dark state.
The results were investigated by changing the second pulse voltage value.

At 0 to 6 volts it was in the dark state, at 6 to 8 volts it was in the intermediate state, and at 9 volts and above it was in the bright state. Observations revealed that the intermediate state is realized by the molecules adopting a twisted structure over the entire surface of the pixel. However, the distance between the substrates at this time was 3.2 μm.

Next, a matrix panel was prepared using the above-mentioned liquid crystal and alignment method, and a matrix drive waveform as shown in FIG. 4 was applied, and a uniform display was obtained in all three gradations. This is because there is a width of about 2 volts in the voltage that creates the twisted state as shown in Figure 2 (b), so it is not affected by the unevenness of the surface condition or the distance between the substrates, like the conventional mixed light and dark state. This is thought to be because it is difficult. In the drive waveform shown in FIG. 4, a reset pulse is applied to the scanning electrode during the non-selection period to keep it in a dark state, and the gradation is controlled by the voltage value during the selection period. In this case, the gradation can also be controlled by changing the pulse width. Since the amount of transmitted light per unit time can be adjusted by changing the timing at which the reset pulse is applied, more gradations can be displayed by using multiple frames in which the timing at which the reset pulse is applied is changed. Also, the area of 1 pixel is 1.1 /
Multiple gradations can also be expressed by configuring with electrodes different from 3 and 1/32.

In addition, as a drive waveform, one selection period as shown in Fig. 6 is set to 4.
A matrix driving method consisting of two pulses was also effective.

Effect of the invention The liquid crystal element of the present invention can be manufactured using an appropriate thickness and alignment method.

The twisted structure creates a stable panel, and in addition to the conventional untwisted two gradations of light and dark, it is possible to evenly realize halftones due to the twisted state.

[Brief explanation of drawings]

FIG. 1 is a state diagram showing the state of molecules at each gradation of the liquid crystal element of the present invention in the example, FIG. 2 is a characteristic diagram of the applied voltage versus transmitted light amount of the liquid crystal element, and FIG. Characteristic diagrams showing the amount of transmitted light in the molecular state, Figures 4 to 6 are waveform diagrams representing the ÷trix driving waveform in the example, Figure 6 is a cross-sectional view of the ferroelectric liquid crystal panel, and Figure 7 is the chiral smecte. FIG. 8 is a schematic diagram showing the notation of TsukuC liquid crystal, and FIG. 8 is a principle diagram showing the display principle of a conventional ferroelectric liquid crystal panel. 21... Glass substrate, 22... Transparent electrode, 23... Alignment film, 24... Ferroelectric liquid crystal layer, 25... C director of liquid crystal molecules
126...Dipole moment, 27...
・Normal to the layer, 28... Long axis direction of the molecule n129
......Dipole moment, 30...C director-131...Tilting angle of the long axis of the molecule ±θ degrees with respect to the layer normal, 32...Layer method Liquid crystal element whose long axis of the molecule is tilted by +θ degrees with respect to the line, 33...Liquid crystal element tilted by -θ degrees, 34...Dipole moment in the direction of the surface of the paper, 36... ...Dipole moment toward the back of the paper, 36...Direction of the two polarizing plates. Name of agent: Patent attorney Toshio Nakao, 1 person/-
--Kamidougan J Yatori Hoso 2--Ikushita. (α) (shi) (C) Fig. 2 600/"1566 Fig. 3 1O-UtJ 11--Ichizusa" arrival (optional) 0 0.2 0.4 06 0δf 1.2
1.4 1 koru ゛4 Fig. 4 (0-)-L: 1tJL (b rou
``5tL 2 YachiL ＼(0~

Claims (9)

[Claims] (1) A ferroelectric liquid crystal is sandwiched between a pair of substrates having electrodes on opposing surfaces, and a first state in which the molecules are approximately parallel to the substrates and tilted to the right from the molecular layer normal, and a first state in which the molecules are approximately parallel to the substrates and tilted to the right from the molecular layer normal. The second state is tilted to the left from the layer normal, and the third state is a twisted structure in which the angle between the molecules and the molecular layer normal on the opposing substrate is different, allowing three gradations to be expressed. liquid crystal element. (2) The liquid crystal element according to claim (1), wherein the angle of inclination of the molecules from the normal to the molecular layer of the ferroelectric liquid crystal is approximately 22.5. (3) A liquid crystal element according to claim (1) or (2), which is capable of expressing multiple gradations by arranging a plurality of picture elements having different areas in one picture element. (4) Apply a reset pulse during the non-selection period of the scanning electrode to reset the element to one of three constant states, and during the selection period, apply an AC grayscale signal with varying pulse width or voltage to the panel. A liquid crystal element according to any one of claims (1) to (3), comprising a drive circuit capable of applying a voltage to the liquid crystal element. (5) Claim No. 1 in which multiple gradations can be expressed by multiple scans with different timings of reset pulses.
) to (3). (6) Claim No. 1 (1) oriented by rubbing
) The liquid crystal element described in item 2. (7) A liquid crystal element according to claim (1), wherein an inorganic substance is oriented by obliquely vapor-depositing it on the surface of the substrate. (8) A liquid crystal element according to claim (1), comprising a drive circuit that applies four pulses during one selection period of the scanning electrode. (9) The product of the refractive index anisotropy of the ferroelectric liquid crystal and the substrate distance is 0
．． 1 to 0.45 or 0.7 to 0.96. The liquid crystal element according to claim (1).