JPH06138495A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To inexpensively produce the liquid crystal display device of an active matrix type having a high display contrast and good responsiveness. CONSTITUTION:Plural sets of first electrodes 2 and second electrodes 3 are disposed at <=1mum intervals in parallel with each other on a base substrate 1 and pixel electrodes 4 are formed by superposing the ends on one side thereof on the second electrodes 3. A ferroelectric high-polymer liquid crystal infitrates the spacings 9 between the first electrodes 2 and the second electrodes 3 from the display region. The spontaneous polarization of the ferroelectric high- polymer liquid crystal is inverted by the polarity inversion of the voltage impressed between both electrodes 2 and 3, by which the switching operation is executed. As a result, the pixel electrodes 4 connected to the second electrodes 3 are selected and are then subjected to display driving.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device used for a display such as a computer.

[0002]

2. Description of the Related Art In recent years, a flat panel display device having a screen composed of pixels arranged in a matrix has been widely used as a means for efficiently transmitting a large amount of information such as moving images and still images. . A typical example of such a display device is a matrix-type liquid crystal display device which performs display by applying a voltage to a liquid crystal layer enclosed between a pair of substrates to change the state of the liquid crystal layer. it can.

An example of this matrix type liquid crystal display device is a simple matrix type.

FIG. 4 shows a conventional simple matrix type liquid crystal display device. In this liquid crystal display device, a liquid crystal layer 25 is sandwiched between a base substrate 21 and a counter substrate 24 facing the base substrate 21,
The base substrate 21 has a plurality of scanning electrodes 22 ...
On the other hand, the counter substrate 24 is provided with a plurality of display electrodes 23 in a direction orthogonal to the electrodes 22. As a conventional example of this type of simple matrix type liquid crystal display device, there is one using a ferroelectric polymer liquid crystal or a ferroelectric liquid crystal as a display medium. In these, the liquid crystal molecules have spontaneous polarization peculiar to the ferroelectric substance, and the liquid crystal molecules are
Since it can be inverted by 80 °, screen display can be performed by utilizing this inversion of spontaneous polarization. Moreover, since the spontaneous polarization directly acts on the electric field, the response is significantly faster than that of the nematic liquid crystal having no spontaneous polarization. Of this,
Ferroelectric polymer liquid crystal is flexible and strong in impact resistance,
Since a thin and lightweight material such as a transparent film can be used for the substrate of the device, it is an optimal material for thin and lightweight displays. However, the ferroelectric polymer liquid crystal has a drawback that the polarization inversion speed is slower than that of the ferroelectric liquid crystal having the same ferroelectric substance because liquid crystal molecules are bonded to polymer side chains. On the other hand, the ferroelectric liquid crystal is inferior to the ferroelectric polymer liquid crystal in structural physical properties such as mechanical strength, but is extremely excellent in the above-mentioned high-speed response characteristic of the ferroelectric substance.

[0005]

Although the ferroelectric polymer liquid crystal and the ferroelectric liquid crystal have the above advantages, when they are used in a liquid crystal display device of a simple matrix type, they are time-shared. When driven, there is a problem that the ferroelectric polymer liquid crystal or the ferroelectric liquid crystal partly undergoes polarization reversal due to large voltage fluctuation during the non-selection period and the contrast is lowered.

The above problems can be solved by applying an active matrix type liquid crystal display device having a TFT (thin film transistor). In this method, time division driving is not performed, and a TFT is associated with each pixel of the screen, and each pixel is independently driven by this TFT.
Therefore, the responsiveness is fast, and there is no voltage fluctuation in the non-selected pixel region, so that high-contrast display is possible.

However, the number of masks for mounting the TFT is large,
Since high-density processing is required also in pattern formation, a new problem arises that the yield is poor and the cost is very high.

The present invention has been made in order to solve the problems of the prior art, and provides an inexpensive active matrix type liquid crystal display device capable of high-contrast display without providing a TFT. With the goal.

Another object of the present invention is to provide a liquid crystal display device which uses a ferroelectric polymer liquid crystal as a display medium and which is lightweight and thin.

Another object of the present invention is to provide a liquid crystal display device which uses ferroelectric liquid crystal as a display medium and has a high contrast and is capable of high-speed response display.

[0011]

A liquid crystal display device according to the present invention comprises an insulating base substrate in which a plurality of sets of first electrodes and second electrodes are arranged in parallel with each other with a slight gap therebetween. An insulative counter substrate that is arranged to face the base substrate with a light modulating material having ferroelectricity sandwiched between the base substrate and the base substrate in a direction intersecting the first electrode and the second electrode. A plurality of counter electrodes arranged in a plurality, and a plurality of picture elements provided on the base substrate at a portion where the counter electrodes face each other, a part of which is overlapped with a part of each second electrode. A liquid crystal display device having an electrode, wherein the light modulation material interposed between the first electrode and the second electrode functions as a switching element, whereby the above object is achieved.

Further, preferably, an alignment film is provided so as to cover the first electrode, the second electrode and the picture element electrode and to enter the space.

Preferably, a ferroelectric polymer liquid crystal is used as the light modulating material.

Further, preferably, a ferroelectric liquid crystal is used as the light modulating material.

Further preferably, the first electrode and the second electrode are made of the same material.

[0016]

In the above structure, when a signal voltage is applied to the first electrode, the ferroelectric polymer liquid crystal or the liquid crystal molecules of the ferroelectric liquid crystal interposed between the first electrode and the second electrode performs a switching operation. Then, each picture element electrode is selectively driven. That is, the ferroelectric polymer liquid crystal or the ferroelectric liquid crystal functions as an active switching element, and so-called active matrix driving is performed.

[0017]

【Example】

Example 1 An example of the present invention will be described below. Figure 1
As shown in (a) and (b), this liquid crystal display device has a structure in which a liquid crystal layer 5 is sandwiched between a base substrate 1 made of a transparent insulating film and an insulating counter substrate 7 facing the base substrate 1. It has become. The liquid crystal layer 5 is made of ferroelectric polymer liquid crystal. On the surface of the base substrate 1 in contact with the liquid crystal layer 5, a plurality of first electrodes 2 (signal electrodes) and second electrodes 3 made of Al are alternately arranged in parallel with each other. First
The distance between the electrode 2 and the second electrode 3 is set to 1 μm, and the film thickness of both electrodes 2 and 3 is set to 200 nm. On the inner surface of the counter substrate 7, a plurality of counter electrodes 6 ... Are provided in parallel to each other in a direction intersecting the first electrode 2.

Further, on the surface of the base substrate 1 which is in contact with the liquid crystal layer 5, under each counter electrode 6, it is sandwiched between the first electrodes 2 and 2 which are adjacent to each other and have a width smaller than the line width of the counter electrode 6. A pixel electrode 4 made of a transparent conductive film such as ITO is provided in each of the separated regions. The pixel electrode 4 is formed such that one end thereof is superposed on the second electrode 3 and the other end is in contact with the surface of the base substrate 1. A ferroelectric polymer liquid crystal is applied to the entire surface of the base substrate 1 so as to cover the first electrode 2, the second electrode 3 and the pixel electrode 4 and is subjected to an alignment treatment. 7 and 7 are attached to each other by using a sealing resin. At this time, the first electrode 2
Ferroelectric polymer liquid crystal penetrates into the gap 9 between the second electrode 3 and the second electrode 3. Alternatively, glass, quartz, or the like may be used as the substrate material.

Further, since the first electrode 2 and the second electrode 3 are simultaneously patterned, the first electrode 2 and the pixel electrode 4 are formed.
The second electrode 3 and the pixel electrode 4 are the same when both are formed of the same material. For example, in the case of a reflective type, both electrodes 3 and 4 are formed of a metal such as Al. You may. When used as a transmissive type, both electrodes 3 and 4 may be formed of transparent electrodes such as ITO. Thus, the first
By forming the electrode 2, the second electrode 3 and the pixel electrode 4 of the same material, the film forming process can be simplified and made more efficient.

In the present invention, the spontaneous polarization characteristic of the ferroelectric polymer liquid crystal is utilized to obtain the ferroelectric polymer liquid crystal.
The function of the terminal non-linear element is to be performed, and its principle is as follows.

The pitch of the spiral of the spiral structure of the ferroelectric polymer liquid crystal is usually several microns, but the distance between the electrodes is 1
By setting the thickness to about μm, when the ferroelectric polymer liquid crystal is interposed between the electrodes at this distance, the helical structure of the ferroelectric polymer liquid crystal is unraveled and the liquid crystal molecules are aligned in one direction. When a voltage is applied to the liquid crystal between the electrodes in this state, the orientation of the liquid crystal molecules can be switched depending on the positive or negative polarity of the voltage.

Further, the liquid crystal molecules whose orientation has been switched are maintained in orientation even when the applied voltage is turned off until an electric field in the opposite direction is applied. That is, it has a memory property, and if the polarity of the voltage is reversed and then applied, the direction of the molecule can be reversed again.

The liquid crystal display device of the present invention provided with the ferroelectric polymer liquid crystal having such a behavior in the non-linear element operates as follows. 2A and 2B show equivalent circuits of the liquid crystal display device of the present invention. In this embodiment, FIG.
As shown in (a), the liquid crystal capacitance C _{F of the} ferroelectric polymer liquid crystal that has penetrated into the gap 9 between the first electrode 2 and the second electrode 3.
And a liquid crystal capacitance C _LC between the pixel electrode 4 and the counter electrode 6 form a circuit connected in series. Of this, the liquid crystal capacitance C
_F operates as a two-terminal nonlinear element.

When one first electrode 2 and one counter electrode 6 are selected and a voltage is applied to each of them, the voltage V _S of the potential difference between the two electrodes 2 and 6 is changed to the first electrode 2. And a counter electrode 6 and a liquid crystal capacitor C _{S in a} path directly connecting the counter electrode 6 and liquid crystal capacitors C _F and C interposed in the path from the first electrode 2 to the counter electrode 6 through the second electrode 3 and the pixel electrode 4. _Applied to _LC . In the latter route, the voltage V _S is divided between the liquid crystal capacitance C _F between the first electrode 2 and the second electrode 3 and the pixel electrode 4 and the counter electrode 6 as shown in FIG. Liquid crystal capacity C between
It is capacitively divided and _LC, partial pressures V _F and the divided V _LC of V _S is applied to the liquid crystal capacitance C _F and the liquid crystal capacitance C _{L C,} respectively. At this time, the first
The partial pressure V _F applied to the liquid crystal capacitance C _F between the electrode 2 and the second electrode 3 is expressed by V _F = C _LC · V _S / (C _LC + C _F ), and the liquid crystal molecule of the liquid crystal capacitance C _F Are arranged in one direction based on the polarity of the partial pressure V _F. Further, the partial pressure V _LC applied to the liquid crystal capacitance C _LC between the picture element electrode 4 and the counter electrode 6 is V _LC = C _F · V _S / (C _LC + C
_F ). By setting C _F to about 1/20 of C _LC , most of the applied voltage V _S can be applied to the liquid crystal capacitance C _LC between the pixel electrode 4 and the counter electrode 6. This partial pressure V _LC
There is written as the signal voltage to the liquid crystal capacitance C _LC, the liquid crystal capacitance C _LC acts as a display element.

Now, when the applied voltage V _S is turned off in this state, the direction of the liquid crystal molecules of the liquid crystal capacitance C _F is kept in the direction when the applied voltage V _S is on, and the liquid crystal capacitance C _LC is shown in FIG. As shown in 2 (b), when the applied voltage V _S is on, the electric charge accumulated in the circuit holds the voltage of V ′ _LC . At this time, _V'LC is _V'LC = -S _f × P _r / (C _LC + C
_F ). (Here, S _f is a cross-sectional area of both electrodes 2 and 3 in a region where the first electrode 2 and the second electrode 3 face each other and apply a voltage to the liquid crystal capacitance C _F , and P _r is a unit area. The above is the behavior of the liquid crystal capacitance C _F and the liquid crystal capacitance C _LC in the first field.

[0026] during the next selection voltage over V _S of opposite polarity to the (second field) is applied, the partial pressure over V _F of the voltage over V _S,
-V _LC is applied to the liquid crystal capacitance C _F and the liquid crystal capacitance C _LC , respectively. At this time, the spontaneous polarization of the liquid crystal capacitance C _F is inverted, and a partial voltage −V _LC is applied to the liquid crystal capacitance C _LC to write the video signal. Even if the applied voltage −V _S is turned off in this state, the direction of the liquid crystal molecules of the liquid crystal capacitance C _F is still held in the direction when the applied voltage −V _S is on, and the applied voltage −V _S is applied to the liquid crystal capacitance C _LC. over V _S is the voltage of the magnitude of over V _'LC by the charges accumulated in the circuit when the oN is maintained. As described above, the liquid crystal is AC-driven over one frame (two fields).

On the other hand, the liquid crystal capacitance C _{S of the} path directly connecting the first electrode 2 and the counter electrode 6 has a small line width of the first electrode 2 and is sufficiently smaller than the area of the pixel electrode 4, It can be ignored as compared with the liquid crystal capacitance C _LC . Therefore, there is no possibility that this will cause crosstalk, and the liquid crystal capacitance C
_Since a high electric field can be applied to the _LC , it is possible to compensate for the slow polarization inversion speed of the ferroelectric polymer liquid crystal.

As described above, according to the present embodiment, since the liquid crystal in the selected pixel portion is directly driven by the electric charge accumulated in the selected pixel portion, the inversion of the ferroelectric polymer liquid crystal molecules occurs in the non-selected pixel portion. Can be suppressed, and high-contrast display over the entire screen can be realized even in a large-capacity display. Moreover, the response speed of the ferroelectric polymer liquid crystal is 1 to
Although it is relatively slow as 10 ms, the structure of this embodiment can compensate for the slow polarization reversal speed of the ferroelectric polymer liquid crystal, so that the ferroelectric polymer liquid crystal is flexible and has high impact resistance. It is possible to make full use of the physical properties and to manufacture a thin and lightweight liquid crystal display device at low cost.

(Embodiment 2) Embodiment 2 is shown in FIG. In the liquid crystal display device of Example 2, the alignment film 8 is formed on the first electrode 2, the second electrode 3 and the pixel electrode 4 on the base substrate 1 and on the counter electrode 6 of the counter substrate 7. To form
Example 1 described above except that a ferroelectric liquid crystal is used as the display medium.
Is the same as. Therefore, the same numbers are given to corresponding parts, and only different parts will be described.

The alignment film 8 is formed by a spin coating method. At this time, the thickness of the alignment film 8 is about 60 nm.
Since the gap between the first electrode 2 and the second electrode 3 is 1 μm and the thickness of both electrodes 2 and 3 is 200 nm, it is sufficiently small that the alignment film 8 does not fill the gap 9. There is no. Therefore, in the gap 9 between the first electrode 2 and the second electrode 3, the ferroelectric liquid crystal injected between the base substrate 1 and the counter substrate 7 enters after the alignment film 8 is formed. As in the first embodiment, the liquid crystal capacitance C _{F in the} gap 9 operates as a switching element.

The ferroelectric liquid crystal has a remarkably fast response, and in Example 2, a liquid crystal display device having a high display contrast and a high response can be realized at low cost.

[0032]

According to the above-described liquid crystal display device, the ferroelectric light modulating material interposed between the first electrode and the second electrode is caused to perform the switching operation, and each pixel electrode is made independent. Since it is driven by the liquid crystal display device, an active matrix type liquid crystal display device having a high display contrast over a large screen and a good response can be manufactured at a high yield and at a low cost.

Further, according to the liquid crystal display device of the second aspect, since the ferroelectric polymer liquid crystal is used as the display medium, the physical properties of the ferroelectric polymer liquid crystal which are flexible and have excellent impact resistance are utilized. Since a thin film can be used as the substrate material, it is possible to manufacture an active matrix type liquid crystal display device that is lightweight and thin, has high display contrast over a large screen, and has good responsiveness at high yield and at low cost. You can

Further, according to the liquid crystal display device of the fourth aspect, since the ferroelectric liquid crystal is used as the display medium and the ferroelectric liquid crystal has a high-speed response, a high-speed response and a large screen are obtained. Therefore, an active matrix type liquid crystal display device having a high display contrast can be manufactured at a high yield and at a low cost.

Further, according to the liquid crystal display device of the fifth aspect, the first electrode 2, the second electrode 3 and the pixel electrode 4 are formed of the same material, so that the film forming process is simplified. Efficiency and efficiency can be achieved.

[Brief description of drawings]

1A is a sectional view showing a first embodiment of a liquid crystal display device of the present invention, and FIG. 1B is a plan view.

FIG. 2A is an equivalent circuit diagram of the liquid crystal display device of the present invention in a switch ON state. FIG. 6B is an equivalent circuit diagram of the liquid crystal display device of the present invention in a switch OFF state.

3A is a sectional view showing a second embodiment of the liquid crystal display device of the present invention, and FIG. 3B is a plan view.

4A is a cross-sectional view showing a conventional simple matrix liquid crystal display device, and FIG. 4B is a plan view.

[Explanation of symbols]

 1 Base Substrate 2 First Electrode 3 Second Electrode 4 Pixel Electrode 5 Liquid Crystal Layer 6 Counter Electrode 7 Counter Substrate 8 Alignment Film 9 Gap

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Adachi 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka

Claims (5)

[Claims] 1. An insulative base substrate in which a plurality of first electrodes and a plurality of second electrodes are arranged in parallel with each other at a slight interval, and has ferroelectricity between the base substrate. An insulative counter substrate which is disposed to face each other with a light modulation material interposed therebetween; and a plurality of counter electrodes disposed on the counter substrate in a direction intersecting with the first electrode and the second electrode. A plurality of pixel electrodes are provided on the base substrate at opposite portions of the counter electrode, a part of which is overlapped with a portion of each second electrode. A liquid crystal display device in which the light modulation material interposed between the second electrodes functions as a switching element. 2. The liquid crystal display device according to claim 1, wherein an alignment film is provided so as to cover the first electrode, the second electrode and the picture element electrode and to enter the space. 3. The liquid crystal display device according to claim 1, wherein the light modulation material is a ferroelectric polymer liquid crystal. 4. The liquid crystal display device according to claim 2, wherein the light modulation material is a ferroelectric liquid crystal. 5. The liquid crystal display device according to claim 1, 2, 3, or 4, wherein the first electrode and the second electrode are formed of the same material.