JPS63284525A - Liquid crystal electrooptic device - Google Patents

Abstract

PURPOSE:To embody a change in transmittance to make display by using a liquid crystal which exhibits a ferroelectric characteristic, unraveling a spiral state by an electric field impressed to a cell and controlling the angle at which liquid crystal molecules incline by the positive and negative of the electric field and the impression time. CONSTITUTION:A spacing between substrates 2 is specified to about 10mum. Uniaxial orientational property to the liquid crystal is imparted to an oriented film 4 on one substrate by subjecting the film to a treatment. The ferroelectric liquid crystal of an ester system is injected into the cell. The liquid crystal has the angle theta of inclination of + or -19 deg. with the spiral axis in a temp. region where the ferroelectric characteristic is exhibited. The spiral pitch is 1.8mum. The polarization of a polarizing plate 1 is set at 19 deg. and a polarizing plate 7 is installed in the direction perpendicular to the plate 1. A diode 12 of in structure is sandwiched by thin Mo films 9 and 10 for light shielding and is isolated by a transparent insulator 8. The polarization direction of the plate 1 and the major axis direction of the liquid crystal molecules coincide with each other and light is not transmitted when a voltage is impressed on the electrodes 3, 9. The molecules are decreased in the voltage with the discharge by leakage and the state of transmitting the light is attained when the electric field is inverted.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of the Invention The present invention relates to a novel driving method for an electro-optical device using a ferroelectric liquid crystal and a novel electro-optical device.

``Conventional technology j Solid-state display devices that replace CRT are those that use liquid crystal materials,
A wide variety of devices have been developed, including those that utilize electrochromic phenomena and those that use gas discharge.

In particular, liquid crystal display devices are suitable for practical use due to their low power consumption and fast response speed, and their development has been particularly active.

However, recently, as the amount of information increases, the number of pixels in one screen continues to increase. In the case of a small number of pixels, display quality could be ensured even with display devices using TN liquid crystal materials, but
For example, in the case of a matrix liquid crystal display device that has a large number of pixels (about 640 x 400 pixels), image quality is inevitably degraded due to crosstalk, etc., and even if ferroelectric liquid crystal is used as the liquid crystal material or TN liquid crystal is used, SBE mode is not used. In addition, image quality has been improved by driving semiconductor elements as switches for each pixel.

In TN active matrix display devices using semiconductor elements, the production cost of forming the semiconductor elements is high;
Furthermore, since the manufacturing yield of the device is low, it has been difficult to reduce the price of the display device itself. However, although the display image quality itself was good and the production price could be reduced through efforts such as mass production, the response speed of the liquid crystal material was slow,
It was unsuitable for displaying content that required high speed.

In addition, instead of this TN-type liquid crystal, a liquid crystal electro-optical device using ferroelectric liquid crystal was proposed by N. A. C1ark et al. As shown in Figure 1,
The first layer tilted by +θ with respect to the normal direction of the smectic layer.
state (1) and a second state (n) tilted by -θ.

Display was performed by applying an external electric field to switch between these two states to switch the ferroelectric liquid crystal molecules, thereby making use of the difference in birefringence effect generated.

At this time, in order to change the ferroelectric liquid crystal molecules from the first state (I) to the second state (II), for example, a positive electric field is applied in a direction perpendicular to the smectic layer.

Conversely, in order to reverse the second state (I[) to the first state (1), it was accomplished by applying a negative electric field. That is, by changing the direction of an externally applied electric field, the two states of ferroelectric liquid crystal molecules are changed, and the resulting difference in electro-optic effects is utilized.

Furthermore, even when this externally applied electric field was removed, the ferroelectric liquid crystal molecules maintained their state stably and had the first and second bistable memory properties.

Therefore, the signal waveform that drives a liquid crystal electro-optical device using this ferroelectric liquid crystal is a bipolar pulse train, as shown in Figure 2, and the direction in which the pulse polarity switches changes the direction of the ferroelectric liquid crystal molecules. It was switching between two states.

This switching is performed much faster than in TN type liquid crystals, and even if this signal is removed, the state of the ferroelectric liquid crystal molecules is retained in memory.

However, in a liquid crystal electro-optical device using such a ferroelectric liquid crystal, the ferroelectric liquid crystal molecules must have bistability, so the structure of the device must also be modified to achieve bistability. Certain conditions had to be met. In other words, it was necessary to narrow the distance between the substrates that sandwich the ferroelectric liquid crystal to a distance that would achieve bistability.

When this ferroelectric liquid crystal is sandwiched between homogeneously aligned liquid crystal substrates, it forms a spiral if the distance between the substrates is wide. Conversely, if the spacing is made sufficiently small, the helix will unwind and the liquid crystal molecules will exhibit bistability, and conventional liquid crystal electro-optical devices using ferroelectric liquid crystals will achieve multistability. Therefore, it is necessary to reduce the distance between the substrates to about 1 to 3 μm, which is the helical pitch of the liquid crystal, and this small distance between the substrates has been a major problem in terms of mass production technology when mass producing liquid crystal electro-optical devices.

T Structure of the Invention j In order to solve the above-mentioned problems, the present invention provides a liquid crystal display using the wide spacing between substrates in an electro-optical device using a ferroelectric liquid crystal, that is, the state in which the ferroelectric liquid crystal forms a spiral. This is to ensure that this is carried out.

A ferroelectric liquid crystal is placed in the cell of an ordinary liquid crystal electro-optical device as shown in Figure 3. At this time, the spacing between the cell substrates (2) is wide enough to allow the liquid crystal (5) to take a spiral state. . In such a case, the liquid crystal molecules (5) will move toward the substrate (2) when no electric field is applied from the outside, as shown in FIG. 4(A).
) takes on a helical state with the helical axis in the parallel direction. In this state, when a voltage is applied between the upper and lower electrodes (3) to generate an electric field within the cell, the liquid crystal molecules (5) assume the state shown in FIG. 4(B) or (C). Next, when the electric field inside the cell is reversed, the liquid crystal molecules (8) change their direction as shown in FIG. 4(C) or (B). This liquid crystal molecule tilts (changes in transmitted light caused by differences in angle) are polarized by a polarizing means (11) installed outside the cell.
, (7), it is characterized in that it embodies and displays changes in transmission.

That is, the device is characterized in that the helix is unraveled by an electric field applied to the cell, and the angle at which the liquid crystal molecules are tilted is controlled by the sign of the electric field and the application time.

In addition, as shown in Figure 3, an element (13) exhibiting pixel rectification properties
When a voltage waveform as shown in Fig. 6(A) is applied between A and C of the liquid crystal device circuit shown in Fig. 5 by connecting them in series, the voltage between AB is as shown in Fig. 6(B). It will be like that.

That is, the potential across the liquid crystal is not reversed until the discharge of the capacitive part of the FLC due to the leakage of the system shown in FIG. 6(B) is completed.

Therefore, compared to the case where the rectifying element (13) is not connected, the time during which the selection voltage is applied to the liquid crystal is longer by t3-tz, and the ON time of the liquid crystal is also longer, so the apparent contrast is increased. This is a liquid crystal electro-optical device.

In addition, 1. -12 becomes longer as the area ratio of the pixel/rectifying element increases, and the ON time during which voltage is applied to the liquid crystal can also be increased.

The present invention will be explained below with reference to Examples.

Example j In this example, the liquid crystal electro-optical device cell shown in FIG. Orientation treatment is applied to impart this effect.

An ester-based ferroelectric liquid crystal having a helical pitch of 1.8 μm was injected into this cell. This liquid crystal had an inclination angle of approximately 19° with respect to the helical axis in the temperature range where it exhibits ferroelectricity.

At this time, the polarizing plate (11) on the outside of the substrate is set in the same direction as this tilt angle, that is, +19° or -19° with respect to the helical axis.
The polarizing plate (7) adjusts its polarization direction to the angle of (1).
) was installed in the direction perpendicular to the direction.

Diode (12) also includes an a-5t:H phosphorus-doped N layer, a non-doped layer, and a boron-doped P layer.
Di
I sandwiched the ode. Furthermore, a transparent electrode (1
Transparent insulator (8) is used to prevent short circuit between 1) and electrode (9).
)It was used.

In addition, the area ratio of the electrode (11) and the rectifying element (13) is 35.
:1.

In this state, the liquid crystal is in a spiral formation state within the cell.

Next, when a voltage is applied to the electrodes (31, (9) in the cell to generate an electric field in the cell, the liquid crystal molecules (8) assume the state shown in Figure 4 (B). At this time, the polarizing plate (1) Since the direction of polarization and the long axis direction of the molecules match, in this state no light is transmitted.

Next, when the electric field is reversed, the liquid crystal molecules (8) are discharged due to leakage, and after the voltage applied to the liquid crystal becomes small, as shown in Fig. 4 (C
) and becomes a state in which light is transmitted.

In this way, the liquid crystal display can be made transparent or non-transparent depending on the direction of the applied electric field.

For example, the voltage waveform shown in FIG.
), the transmitted light intensity of the cell was obtained as shown in (B) of the same figure. As is clear from the figure, it was also possible to control the transmitted light intensity by changing the application time of the applied voltage.

Next, when the voltage waveform shown in FIG. 8(A) was similarly applied, the transmitted light intensity of the cell as shown in FIG. 8(B) was obtained. As is clear from the figure, the transmitted light intensity could also be controlled by changing the voltage value of the applied voltage.

Therefore, the present invention has the feature that gradation display (bracesquel) can be performed in a liquid crystal display.

"Effect" The present invention provides a liquid crystal electro-optical device that uses a liquid crystal exhibiting ferroelectricity and utilizes the electro-optic effect generated due to the difference in states that the liquid crystal molecules can take. It does not have stability, and the state of liquid crystal molecules is changed by the electric field generated within the liquid crystal electro-optical device by an external voltage applied to the liquid crystal, and the electro-optic effect generated accordingly is utilized. It is characterized by this. That is, since bistability is not required, it has become possible to obtain a large industrial margin when manufacturing a liquid crystal electro-optical device.

Furthermore, even if the ferroelectric liquid crystal forms a spiral, due to the electric field,
In order to unwind the spiral, there is no need to narrow the spacing between the cell substrates, giving it a major advantage in mass production technology.

It also has the feature of being able to perform gradation display of a conventional liquid crystal display using ferroelectric liquid crystal.

Furthermore, a liquid crystal electro-optical device is characterized in that the apparent contrast is increased by connecting a rectifying element.

[Brief explanation of drawings]

FIG. 1 shows the appearance of ferroelectric liquid crystal molecules. FIG. 2 shows drive signals of a conventional liquid crystal electro-optical device. FIG. 3 shows a schematic diagram of the device of the invention. FIG. 4 shows possible states of the long axis of molecules of liquid crystal. FIG. 5 shows a circuit diagram of the device according to the invention. 6, 7, and 8 show the electro-optic effect on the drive signal waveform of the device of the present invention.

Claims (1)

[Claims] 1. Using a liquid crystal exhibiting ferroelectricity, an electric signal applied to the liquid crystal from the outside causes liquid crystal molecules that had formed a helix before the electric field was generated within the electro-optical device. In a liquid crystal electro-optical device, the liquid crystal molecules are aligned in a single direction, and the alignment direction of the liquid crystal molecules is changed depending on the direction of the generated electric field, and the resulting electro-optic effect is utilized. A liquid crystal electro-optical device characterized in that by connecting elements, the voltage applied across the liquid crystal can be maintained at a selected voltage for a predetermined period of time, and the contrast can be increased in appearance. 2. The liquid crystal electro-optical device according to claim 1, wherein the distance between the substrates is so wide that the liquid crystal forms a spiral. 3. A liquid crystal electro-optical device according to claim 1, characterized in that the intensity of transmitted light can be controlled by changing the intensity and application time of an externally applied electric field.