JP2651842B2 - Liquid crystal element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a display element, an optical shutter, a light valve,
The present invention relates to a liquid crystal element applicable to an optical memory or the like.

[Conventional technology]

One of the liquid crystal devices using a ferroelectric liquid crystal having a memory property is disclosed in Japanese Patent Application Laid-Open No. 56-107216. This liquid crystal element is a surface-stabilized ferroelectric liquid crystal element (hereinafter referred to as SSFLCD). It is said that an ideal SSFLCD has two stable states, and switching can be performed between these two stable states depending on the polarity of an applied electric field. Figure 1
FIG. 4 is a schematic diagram showing a state of switching of liquid crystal molecules in an SSFLCD viewed from above a liquid crystal layer. In the figure, A and B indicate the directions of the long axes of the liquid crystal molecules in the two stabilized states. When an electric field is applied in a direction perpendicular to the paper surface, for example, in the direction of + on the top and-in the bottom, the molecular long axes are aligned in the direction of A, and the orientation state is maintained even after the electric field is cut off. On the other hand, when an electric field in the opposite direction is applied, the molecular long axes are aligned in the direction of B, and the orientation state is maintained even after the electric field is cut off.

At present, ferroelectric liquid crystal devices are manufactured by combining various alignment methods and liquid phase materials. In addition to the devices in which only two states are stabilized as described above, in addition to the apparent molecular long axis direction, We also propose devices with imperfect memory properties, such as devices that form different angles when an electric field is applied and when no electric field is applied, and devices that show different orientations when a high electric field is applied and when a low electric field is applied. Have been.

[Problems to be solved by the invention]

However, the above-mentioned conventional liquid crystal element has the following problems.

Since the above-mentioned liquid crystal element has a memory property, even if the drive circuit of the element is stopped by turning off the power supply or the like, the alignment state immediately before the alignment state or the alignment that has naturally transitioned from the alignment state. You will continue to take the state.

When such an element is left for a long time, the characteristics of the element change depending on the alignment state that has been taken for a long time. FIG. 2 shows the state of the change. FIG. 2 shows a relationship between an input signal and a light transmission intensity in a liquid crystal element having a structure in which a cell formed by sealing a ferroelectric liquid crystal between a pair of substrates having electrodes is sandwiched between two polarizing plates. It is a thing. The input signal is input to the electrode as a drive signal, and light is turned on and off. In FIG. 2, (a) shows the result of measurement within a few days after the liquid crystal was sealed, and (b) shows that the upper and lower electrodes were short-circuited after switching to a dark state so that no electric field was applied to the liquid crystal layer. The results after storage at room temperature for 3 weeks, (c) shows the results after the cell temperature was increased after the measurement of (b) and the liquid crystal was realigned, and (d) shows the results after switching to a bright state. This is the result after the electrodes were short-circuited and stored for 3 weeks. As can be seen from FIG. 2, after a long storage, the switching direction has a good memory property immediately before the storage, but the memory property in the opposite direction is partially impaired. Depending on the liquid crystal, the memory performance opposite to the above may be impaired. Possible reasons for the loss of memory properties include very hard-to-move liquid crystal molecules near the substrate interface that are realigned during a long non-driving period, and the migration of very small amounts of electrolyte components contained in the liquid crystal. However, it is not clear at present.

As described above, changing the characteristics depending on the alignment state during the non-driving period is very undesirable because it lowers the reliability of the device.

The present invention has been made in view of the above problems of the related art, and has as its object to provide a liquid crystal element which has high-speed response, high contrast, and high reliability, by eliminating a characteristic change due to an alignment state during a non-driving period. And

[Means for solving the problem]

According to the present invention, there is provided a liquid crystal display device comprising: a ferroelectric liquid crystal layer sandwiched between a pair of substrates having electrodes; and at least one polarizer disposed outside the substrate. When an electric field higher than the threshold electric field is applied to the liquid crystal layer, the orientation state of the liquid crystal molecules changes, and in a liquid crystal element having a plurality of pixels having a memory property when no electric field is applied,
Immediately before stopping the driving circuit unit for driving the element, the electric field value at which each pixel sequentially switches on and off states changes from the electric field value gradually decreasing to the electric field value at which each pixel does not perform the switching. There is provided a liquid crystal element characterized by comprising means for applying such an electric field to the liquid crystal layer.

As a specific example of the above means, for example, immediately before stopping the drive circuit unit for driving the liquid crystal element, an AC electric field having a magnitude equal to or larger than the threshold electric field at first and having a magnitude gradually decreasing is formed. A circuit to be applied is given. According to this circuit, immediately before the drive circuit is stopped, a sufficiently large AC electric field is initially applied, so that all the pixels are turned ON → OFF → ON → O
The switching is performed in the order of FF →..., The magnitude of the AC electric field is continuously reduced, and the switching is continued at a certain level, and no switching occurs when the level is smaller than the magnitude. Therefore, the drive circuit unit is set to a non-operating state.
In this way, each pixel does not take a definite memory state, or it is divided into small domains and becomes a memory state, so that characteristics do not change even if the non-driving period is long, and uniform characteristics are maintained. it can.

The waveform of the electric field applied to the liquid crystal layer immediately before stopping the driving circuit portion depends on the driving method.

In the above, a circuit for continuously decreasing the electric field value was used, but the present invention is not limited to this.For example, instead of continuously decreasing the electric field value, the frequency is continuously increased, and the switching is performed. The driving circuit unit may be set to the non-operation state at the time when the situation no longer occurs.

〔Example〕

 Next, the present invention will be described in more detail with reference to examples.

Using a ferroelectric liquid crystal CS-1011 manufactured by Chisso, a cell with a liquid crystal layer thickness of 2.0 was made.Polyimide was used as the alignment film, and the following glass substrate with ITO electrodes was used so that the rubbing direction was parallel. Bonded. When this cell was sandwiched between a pair of polarizing plates, an element in which an image was formed by an input signal was obtained. Since this liquid crystal element has a memory property, an image remains even when the input signal is turned off. Therefore, an element was made under the same conditions again, and immediately before stopping the drive circuit, a circuit for applying an AC electric field having a magnitude larger than the threshold electric field at first and having a magnitude gradually decreasing was provided, as described above. The following operation was performed. As a result, the characteristics of the device did not change even after long-term storage, and a uniform image was obtained.

〔The invention's effect〕

As described in detail above, according to the present invention, immediately before stopping the driving circuit unit for driving the elements, all the pixels are in the non-operating state while repeating the ON and OFF states sequentially, and thereafter the switching is performed. Since a means for applying an electric field such as stopping is provided, each pixel does not take a definite memory state during the non-driving period, or becomes a memory state after being divided into fine domains. And a liquid crystal element having high contrast, high contrast, and high reliability is provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing two stable states of liquid crystal molecules in an SSFLCD, and FIG. 2 is a diagram showing a relationship between an input signal and light transmission intensity in a conventional liquid crystal element. A, B ... Longitudinal direction of liquid crystal molecules in two stabilized states

Claims (1)

(57) [Claims] 1. A liquid crystal display device comprising: a ferroelectric liquid crystal layer sandwiched between a pair of substrates having electrodes; and at least one polarizer disposed outside the substrate. Is applied, the alignment state of the liquid crystal molecules changes,
In addition, in a liquid crystal element having a plurality of pixels having a memory property when no electric field is applied, just before stopping a driving circuit unit for driving the element, the value of an electric field value in which each pixel sequentially switches between an on state and an off state is determined. A liquid crystal device comprising: means for applying an electric field to the liquid crystal layer that gradually decreases and changes to an electric field value at which each pixel does not perform the switching.