JPS58198092A - Liquid crystal display - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an I-type liquid crystal display device that takes full advantage of the thermal and electro-optic effects of liquid crystal, and particularly to improving the reliability thereof.

In recent years, supported by the development of semiconductor technology, information processing devices are rapidly becoming popular. Along with this, the demand for H-I fltt as a man-machine interface is increasing, and at the same time, the required performance is also becoming more sophisticated. Currently, CRTs hold an overwhelming position as display devices that can meet these demands; however, on the other hand, CRTs
has the major drawback of being bulky. In this respect, liquid crystal display devices have the advantage of being thin, but they have the disadvantage that it is difficult to increase basic display performance, such as increasing the display capacity. It was extremely difficult to compete with RT.

The present invention overcomes the limitations of conventional liquid crystal display devices and relates to a liquid crystal display device based on a novel display method with high display capacity and high contrast.

The display principle of the liquid crystal display device according to the present invention will be explained below.

FIG. 1 is a block diagram showing one embodiment of the configuration of a liquid crystal display device according to the present invention. 11.12°13 indicates the electrodes of the liquid crystal panel. 21°22.23 indicates column electrodes. Both are substantially orthogonal to each other, and the intersection becomes the display pixel. The row electrode group, the electrode group, and the column electrode group are each formed on the inner wall surface of a separate substrate, and are opposed to each other with a liquid crystal layer interposed therebetween.

The substrate is omitted here. In addition, in Fig. 1, there are only three row electrodes and two column electrodes for simplicity, but in reality, the number of these electrodes may be large depending on the display capacity required for the display device. is normal.

The row electrode groups are all connected at their right ends, so they are usually all wired the same way. It is ranked 5th. Also, the column electrode group is normally connected to the row electrode 2 via the column electrode drive circuits 41, 42, 43'i.
It has the same rank as Shigun. Therefore, an electric field is normally applied to the liquid crystal layer that is located between the row and column electrodes.

There is a liquid crystal layer between the row electrode group and the column electrode group.

The liquid crystal used is a thermotropic liquid crystal that changes from a smectic phase to a nematic phase to an isotropic liquid phase as the temperature rises. Also, LCD lightning.

It is necessary that the anisotropy be positive. Examples of liquid crystals having such characteristics include Ni-24 and Ni-27 manufactured by BDI (British company).

Reference numerals 51, 52, and 55 denote row electrode drive circuits, which are controlled by the row electrode drive control circuit 51 and cut off the electrical connection between the row electrode drive power source 52 and each row electrode.

41, 42, and 43 are column electrode drive circuits, which are controlled by the column electrode drive control circuit 53 and apply signals from the column electrode drive power supply 54 to each column electrode, or apply signals to the right end of the row electrodes. A selection is made as to whether to apply the same electric potential as .

55 is a control circuit for the entire display device, which receives display data from an external device and performs a series of controls for displaying the data.

A series of operations for actually performing display will be described below.

When the control circuit 55 receives a display command from an external device, it first sends a signal to the row electrode control circuit 51 to start driving the rows, cities, and poles. In response to this, the march and polar drive control circuits
First, the row seven-pole drive circuit 31 is brought into operation. As a result, a current flows through the row electrode 11 from the row electrode driver VIJ source 52, generating heat, and the liquid crystal near the row electrode 11 is heated. Heating is continued for a period of time sufficient to bring the nearby liquid crystal layer into an isotropic liquid phase. After this time has passed, the row electrode drive circuit 31 becomes inactive. At the same time, the row electrode drive circuit 62 becomes operational. Thereafter, in the same manner, the row electrode groups are driven line-by-line in the order of 11, 12, and 13.

On the other hand, the humidity of the liquid crystal layer in the vicinity of the row electrode 11 that has been heated decreases, changing from an isotropic liquid phase to a nematic phase and a smectic phase. During this cooling, each pixel on the row electrode 11 is written.

Data to be displayed is sent from an external device to a control circuit 555-, and the control circuit 55 transfers data of pixels on the row electrodes 11 to the column electrode drive circuit 53 when the row electrodes 11 are heated.
Transfer to. According to this data, the column electrode control circuit 55 controls the column electrode drive circuits 41, 42, and 43.

For example, when it is desired to turn on the pixel at the intersection with the column electrode 21, the column electrode drive circuit 41 applies the same potential as the right end of the row electrode. Then, no electric field is applied to the liquid crystal layer of the pixel at the intersection. When the humidity decreases in this state, the random state of the isotropic liquid phase is carried over to the smectic phase and stabilized. Such a random smectic phase exhibits a light scattering phenomenon and appears cloudy.

Further, for example, when it is desired to turn off a pixel at the intersection with the column electrode 22, the column electrode drive circuit 42 switches the column electrode drive power supply 5 to a non-lighted state.
Apply the signal from 4. Since the dielectric anisotropy of liquid crystal is positive, when the liquid crystal layer is in a nematic phase, it becomes vertically aligned by an electric field. When the humidity decreases and the state becomes smectic, the vertical alignment becomes stable. This state is transparent in appearance.

6- In this way, visually different states such as a cloudy state and a transparent state can be created, and display becomes possible. After the writing of the pixels on the row electrodes 11-H is completed by the above operations, the writing of the pixels on the row electrodes 12 and 13 is also performed in the same manner.

I'm going to go.

The above is the display principle of the liquid crystal display device according to the present invention j.

One of the advantages of the liquid crystal display device based on the above principle is
In some cases, the display contrast is essentially unrelated to the multiplicity of multiplex driving. This is, for example, a conventional twisted nematic liquid crystal display device (TN-TJO).
This is a very large advantage compared to the case of multiplex driving (D), in which the -C contrast ratio inevitably decreases as the degree of multiplicity increases.

However, on the other hand, there are also problems that do not exist in conventional TN-LCDs. One of them is that it is difficult to ensure reliability. The main reason for this is that every time a display is written, a mixed shock of rapid temperature rise and fall is applied to the liquid crystal display panel.

Therefore, in terms of ensuring reliability, conventional TN-LCD
Much more consideration needs to be taken than that.

The present invention provides one of the important means for ensuring such reliability.

As described above, the liquid crystal display device according to the present invention not only applies a temperature shock every time writing is performed, but also applies an electric field. In principle, this applied electric field can be either alternating current or direct current, but as a result of experiments, it has been found that there is a large difference in the deterioration rate between alternating current and direct current. That is, when a direct current field is applied, the display performance deteriorates quite rapidly, whereas when an alternating current field is used, the deterioration rate is very slow.

Based on this fact, the liquid crystal display device according to the present invention uses an alternating current electric field as the electric field applied to the liquid crystal layer from the column electrode drive circuit. To explain this based on FIG. 1, the signal output from the column electrode drive power supply 54 is alternating current, and the row electrode drive power supply 52 is a power supply for heating the row electrode group. This is because the electric field from the lightning source is applied to the liquid crystal in the trench. Furthermore, the ratio of the time applied to each row electrode becomes smaller as the degree of multiplex driving increases. For this reason, it does not have as big an impact on deterioration as the Retsuichi and Gokusenkan Power Sources 54,
Reliability is also improved by using an alternating electric field.

Examples will be described below.

BDI (a mixture of Ni-24 and Ni-60 manufactured by Co., Ltd.) was used in a liquid crystal display cell made using an aluminum film formed by vapor deposition on a glass substrate as a row electrode, and an indium oxide film as a column electrode. A liquid crystal display device having the structure shown in FIG. 1V was manufactured by fully encapsulating the liquid crystal.

There are 50 row, electrode, and column electrodes. Vertical alignment treatment was performed using a silane-based surface treatment agent.

The row electrode driving TJtjJt source 52 was a 15 volt DC power source, the column electrode driving power source 54 was also a 15 volt DC power source, and the heating time per row electrode line was 9 to 20 milliseconds, and writing was performed repeatedly. However, after about 50,000 cycles, the alignment deteriorated and clear display became impossible.

Similarly, for this liquid crystal panel, a column electrode drive power source 54 is connected.
Using an alternating electric field with a voltage of 15 volts and a frequency of 100 hertz, and other conditions being the same, writing was repeated repeatedly, and no noticeable deterioration was observed until about 2 million times.

Furthermore, when a 100 Hz alternating electric field was used for the signal from the row electrode drive power source 52, the degree of change in appearance was even better than in the previous experiment.

As described above, the present invention has made it possible to greatly improve the reliability of liquid crystal display devices.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the configuration of a liquid crystal display device according to the present invention. 11.12,13...Row electrode 21.22.2
3... Column city, pole -10- 31.32.33... Row electrode drive circuit 41
,42.43... Column electrode drive circuit 51...
... Row electrode drive control circuit 52 ... Row electrode drive power supply 56 ... Column electrode drive control circuit 54 ... Column electrode drive power supply 55 ... Liquid crystal This is a control circuit for a display device. Applicant: Suwa Seikosha Co., Ltd.

Claims (1)

[Claims] (1) At least a liquid crystal layer that changes from a smectic phase to a nematic phase to an isotropic liquid phase as the temperature rises, a pair of substrates sandwiching the liquid crystal layer, and an inner wall surface of one of the substrates. A row electrode group formed on the substrate that generates heat when a current flows and heats the entire nearby liquid crystal layer, a row electrode drive circuit that supplies current to the row electrode group, and a substrate facing the substrate on which the row electrode group is formed. In a liquid crystal display device comprising a column electrode group formed on the inner wall surface of another substrate in a direction substantially perpendicular to the row electrode group, and a column electrode drive circuit that applies a display signal to the column electrode group. . A liquid crystal display device, wherein a display signal applied to the column electrode group by the column electrode drive circuit is an alternating current signal. (2. The liquid crystal display device according to claim 1, wherein the signal applied to the row electrode group is an alternating current.