JPS63168630A - Liquid crystal device and its driving method - Google Patents

Abstract

PURPOSE:To allow smectic liquid crystal to have a sufficiently large Ec (critical electric field or threshold electric field) by using the voltage applied to auxiliary electrodes. CONSTITUTION:Auxiliary electrodes are provided on the outer periphery of a pair of electrodes (main electrode, first and second electrodes 1 and 2), which are practically brought into contact with ferroelectric liquid crystal (FLC), as elements which determine the Ec, and an internal electric field is generated in FLC by the voltage applied to auxiliary electrodes (a third electrode 3 or the third and fourth electrodes 3 and 4), and FLC is oriented in one direction by itself with the internal electric field. A prescribed voltage is applied to the pair of main electrodes, and FLC between main electrodes is oriented in the direction opposite to said direction, where FLC is preliminarily oriented by the voltage applied to auxiliary electrodes, by the voltage applied to main electrodes. Thus, the transmission or non-transmission state is obtained by auxiliary electrodes, and the non-transmission or transmission state is obtained by the voltage of main electrodes.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] This invention relates to a liquid crystal device using smectic liquid crystal, particularly ferroelectric liquid crystal (hereinafter referred to as FLC), which is one of its representative examples, and improves contrast ratio. The present invention also relates to a liquid crystal device and a method for driving the same, which are intended to enable gray scale and to reduce the thickness of display units of microcomputers, word processors, televisions, and the like.

``Prior Art'' Conventionally, when attempting to fabricate a liquid crystal device using smectic liquid crystal, a method is known in which a pair of electrodes is provided inside a pair of substrates for the liquid crystal, and a symmetrical alignment film is provided on the liquid crystal side above the electrodes. It is being

However, in such a simple matrix structure or an active element structure in which nonlinear elements are connected in series to each pixel, the smectic liquid crystal described above has a sufficiently large Ec(R
It is most important to have an electric field or threshold electric field). This Ec is a phenomenon in which the liquid crystal maintains its initial state (for example, non-transparent) below a predetermined electric field, reverses extremely sharply and assumes another state (for example, transmissive) when the electric field exceeds a predetermined electric field, and vice versa. This refers to a phenomenon that becomes more opaque. That is, this Ec has Ec+ (critical electric field observed when a positive electric field is applied) and Ec- (an electric field that exists when a negative electric field is applied).

However, such Ec+ and Ec- are extremely scarce in the smectic liquid crystal itself, and especially in the liquid crystal that expresses the chiral smectic C phase, the electric field strength and pulse width of the pulsed electric field applied to this liquid crystal are greatly affected. dependent.

Therefore, in the matrix display, it is necessary to use a driving method known as rAC driving sound.

That is, when rewriting in the positive direction is desired, a negative pulse is applied once, and then a positive pulse is applied by precisely controlling the predetermined electric field strength and time. Conversely, when rewriting in the negative direction, a positive pulse must be applied once, and then a negative pulse must be applied under precise control of predetermined electric field strength and time.

``Problems to be Solved by the Invention'' When such a smectic liquid crystal is intended to be used, especially as a ferroelectric liquid crystal, it is difficult to use the above-mentioned rAC drive sound, and even surface-stabilized PLC (Surfac).
e 5tabilized FLC or 5SFLC
) technology must be used. However, it is difficult to produce gray scale using the darning method. Furthermore, it has a major drawback in that the physical properties of the interface where the alignment film and the FLC are in close contact, that is, the physical properties of the extremely unstable surface, must be directly used as a determining factor for the quality of alignment of the FLC. As a result, it has many drawbacks, such as the physical properties at the interface tend to become non-uniform when the area is increased, the physical properties tend to vary between lofts, and the physical properties tend to vary due to adsorption of water vapor in the atmosphere to the oriented surface. For this reason, a means that does not use 5SFLC technology has been sought. The present invention has been made to carry out such invention.

When such a ferroelectric liquid crystal is used, the present invention does not require the liquid crystal itself to have Ec, but rather a pair of electrodes (main electrodes) (first and second electrodes) provided outside the liquid crystal. (electrode of
This sub-electrode and an alignment film (axial alignment, that is, a process in which the central axis of the ferroelectric liquid crystal in all areas is arranged in a fixed direction)
The idea is to consider these as a single entity, and to obtain a substantially effective Ec for the whole.

In order to solve this problem, the present invention proposes a pair of electrodes (main electrodes) that are substantially close to the FLC (separated from each other while exerting an electrical influence on each other) as elements for determining He. , the first and second electrodes are indicated by ■ and ■ in FIG. and (indicated by ■) causes an internal electric field to be generated in the FLC. The internal electric field causes the FCC to orient itself in one direction. Then, a predetermined voltage (generally a pulsed voltage) is applied to the pair of main electrodes, and the voltage applied to the main electrodes causes
The purpose is to orient the FLC between the main electrodes in a direction opposite to the direction in which the FLC was oriented by a voltage previously applied to the sub-electrodes. Thus, a transmissive or non-transmissive state can be obtained by the sub-electrode, and a non-transmissive or transmissive state can be produced by the voltage applied to the main electrode.

The present invention changes the orientation of the FLC to one orientation (plane orientation, that is, one side of the cone) by applying a voltage (mainly DC voltage) to a sub-electrode provided in an area around the outer periphery of a pair of main electrodes where no main electrode is provided. or the other selected orientation).

In this way, the surface of this FLC (the surface in close contact with the alignment film)
With the sub-electrode located further away, the electric field applied to the FLC can provide the FLCO orientation in one direction (a fixed positive or negative orientation). One direction of the smectic liquid crystal is substantially determined by an electric field applied to the sub-electrode. In other words, as shown in the 5SFLC, the electric field is not determined by the surface, but by the internal electric field that exists inherently for the FLC due to the electrodes located away from the surface.

This sub-electrode can be defined so that the FLC is particularly strongly oriented in one direction in a region outside (outer periphery) of the main electrode where there is no pattern of the main electrode. Further, it is possible to provide a sub-electrode for this purpose on one or both of the outer sides of the pair of main electrodes. As a result, a state in which the FLC is oriented in one direction due to the direction of the internal electric field is used as the first stable orientation. Next, the FLC is oriented in the opposite direction by applying a voltage to the pair of main electrodes sandwiching it, and used as a second stable orientation. This method is not a so-called 5SFLC, but an internal electric field orientation (IFS).
ctric Field Stabilized) method.

Depending on the magnitude of the internal electric field generated in the FLC by this sub-electrode and the other internal electric field applied by the main electrode, it is determined which side the boundary between the two electrodes faces. The degree of orientation on either side can be identified as a so-called gray scale (halftone). That is, depending on the degree of voltage applied to the main electrode, it is possible to determine what percentage of the area of the main electrode can eliminate the influence of the electric field generated by the sub-electrode, and this degree can be identified as an intermediate tone.

An example of a longitudinal cross-sectional view of the present invention is shown in FIGS. 1(A) and 1(B).

In Figure 1 (A), the ferroelectric liquid crystal (FLC) has a gap (
1) is filled in the final process. In this drawing, the alignment film (
2), (2'), sub-electrode (8) for generating IFS
).

(9) (third and fourth electrodes), and a pair of light-transmitting main electrodes (on the insulating film (7) above (inside)
3), (4) (first and second electrodes), sub-electrode (8).

Transparent substrates (5) and (5') are provided on the outside of (9). One of the surfaces of the FLCO axis alignment film (2) or (2゛) in contact with the liquid crystal is rubbed and used as an alignment treatment surface.

The manufacturing process shown in FIG. 1(A) is abbreviated as follows. That is, transparent sub-electrodes (8) and (9) are formed on the entire surface of the transparent substrates (5) and (5') by sputtering. If the voltage applied here is DC voltage, the thickness should be 300 to 1000 (sheet resistance 300 to 100Ω) to save money.
/mouth) is sufficient.

An insulating film (7) of silicon oxide, silicon nitride, and alumina is continuously formed on this upper surface by another sputtering method. This insulating film (7) may be formed of polyimide resin by a spin method. Thereon, transparent conductive films are formed as main electrodes (3) and (4) by sputtering to a thickness of 1,000 to 5,000 wafers, and are patterned in a predetermined manner. A simple matrix structure can be achieved using a known photoetching technique.

In the next step, alignment films (2) and (2') are formed using polyimide or nylon. One of these alignment films is rubbed again, thoroughly washed, and then dried. After this, these are placed at a predetermined interval (generally 1 to 4
μm (for example, 2 μm) and glue them together as shown in Figure 1 (
The structure is A). This gap (1) in FIG. 1(A) is filled with a desired FLC to form a liquid crystal device.

In the present invention, when no voltage is applied to the main electrode and an electric field is applied so that one internal electric field is generated by the sub-electrode, F
The LCO direction naturally becomes oriented in one direction (planar orientation). That is, the FLC applies a negative voltage to the other sub-electrode (third electrode) (8) with respect to the sub-electrode (fourth electrode) (9).

Then, due to this electric field, on the area (20) of the main electrode (3)
Not only the FLC but also the region (21) between the main electrodes can be sufficiently oriented in one direction. In particular, as an FLC, the liquid crystal is filled at about 150°C, and then a constant DC voltage (10 to 30ν, e.g., 20V) is applied between the sub-electrodes, and the whole is lowered to room temperature to achieve uniform electric field alignment over the entire surface. It is possible to obtain.

In such a liquid crystal device, when aligning the FLC in the other direction, a voltage is applied between the main electrodes (3) and (4).

The training pole for generating IF5 is (8) in Fig. 1 (A).
.

(9), but as shown in Fig. 1 (B), one of them (
8) (the third electrode) only, and for IFS, a voltage may be applied between the third electrode and the second electrode (which also serves as the main electrode).

As a result of the configuration of the present invention, even when a liquid crystal device has a large area or a matrix configuration, this IFS
Due to the fixed orientation of FLC, a large margin can be made for the FLC filling process. Also F in the other direction
The voltage applied to reorient the LC can be applied to the main electrode (4) in the opposite direction, and in that case, for the FLC, the electric field generated by the IFS is used as the difference between the voltage and the electric field generated by the IFS. It even has the possibility of achieving gray scale, which was completely impossible in the past.

Such a gray scale corresponds to the main electrode (
3) can be determined by the orientation of the FLC in the peripheral portion (23).

Examples of the present invention are shown below.

“Example IJ FIG. 1 is a longitudinal sectional view of the configuration of the present invention.

In the drawing, transparent conductive films (8), (9) are deposited on glass substrates (5), (5') to a thickness of 800 mm by sputtering using, for example, ITO (indium tin oxide) as the main electrode. Formed. An insulating film (7) was formed on this upper surface by a polyimide spin method to a thickness of 1,500 mm. Next, a transparent conductive film (for example, rTo) was formed to a thickness of 2,500 mm, and a matrix structure was formed by a known photoetching method. In FIG. 1(A), the first main electrode (3) was set in the Y direction, and the second main electrode (4) was set in the X direction. Next, FLCO
For axial alignment, polyimide alignment film (2),
(2') was provided.

A rubbing treatment was applied to one of the two. A similar polyimide alignment film (2'') was formed on the other electrode. Rubbing treatment was omitted for this side surface, resulting in an asymmetric alignment film.

Next, the peripheral portions of the pair of substrates on which the alignment films were formed were sealed together (not shown) and filled with FLC using a known method. This FLC includes, for example, ester-based and bifel-based FLCs.
A blend product of LC 1:1 was used.

Also, for example, JP-A-56-107216, JP-A-59-9
8051 and JP-A-59-118744 may be used.

A main electrode (3) constituting each pixel of such a cell.

(4) That is, the intersection of the transparent conductive films is 1 mm x 1 mm.
The outer periphery (21) had a gap of 25 μm. Then, a 2×2 matrix was constructed. Sub-electrode (8),
When, for example, a voltage of -10 V was applied to (9), all the pixels in the system, that is, the outer periphery (21) of the pixels became black and non-transparent (depending on the orientation of the deflection film, all of them could be transparent). Then, a voltage different from the direction of the voltage on the sub-electrode, for example +20V, was applied to the main electrodes (3) and (4).

Then, only the pixels to which this voltage was applied became transparent. Furthermore, when the voltage applied to the main electrode was set to O, the voltage at the sub-electrode acted on it, making it non-transparent. That is, it has been found that the FLC can operate even when the voltage is Ov or positive (or Ov or negative electrode depending on the direction), that is, a bridge voltage.

The speed of transition from on to off in the drawing is a little slow, but
It can be assumed that this will become possible through improvements in liquid crystals. Also, when turning off, a slightly opposite large voltage may be applied to the sub-electrode to help rearrange the FLC.

This -polar driving method (a method in which the ferroelectric liquid crystal is driven by applying O and positive voltages, or zero and negative voltages to the liquid crystal device) can be used even for large-area displays having, for example, 720 x 480 pixels. It may be possible to perform display without crosstalk (crosstalk), and a blank matrix may be formed between the main electrodes.

In addition to the method of the present invention, it is possible to use a ferroelectric substance whose one pole or direction can be freely changed in the alignment film (2), (2') or in the organic material on the alignment treatment surface.

In the present invention, the sub-electrode is provided below the main electrode and between the main electrodes on the outside of the main electrode.

However, this sub-electrode may be provided only in some areas of the liquid crystal device as shown in FIG. 1, or may be provided in all areas of the display section. Further, the sub-electrode may be provided only between the main electrodes. In addition, it may be provided only between the main electrodes and a part of the back side of the main electrodes. Although such a case has the disadvantage that the auxiliary electrode must be patterned, it also has the advantage of providing flexibility in design depending on the application.

"Effect j" As shown above, the present invention can reduce F by applying a voltage to the sub-electrode.
It created an internal electric field for the LC, which essentially served the same function as an orienting membrane for the FLC. By providing one or two of these sub-electrodes, the E
A clear liquid crystal device with c.

This liquid crystal device is not only a display but also a speaker,
It can also be applied to shutters for printers, disk memories, and image sensors, and can be applied to all products to which the optical anisotropy of smectic liquid crystals can be applied.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a liquid crystal device of the present invention.

Claims (1)

[Claims] 1. First and second electrodes are provided inside a pair of substrates to face each other, and liquid crystal having ferroelectricity is filled between the pair of first and second electrodes. A liquid crystal device, characterized in that a third electrode, or third and fourth electrodes are provided around the outer periphery of the first or second electrode. 2. In claim 1, the third or third
and a liquid crystal device, wherein the fourth electrode is disposed between the first and second electrode groups having a matrix configuration. 3. In a liquid crystal device in which first and second electrodes are provided inside a pair of substrates to face each other, and a liquid crystal having ferroelectricity is filled between the first and second electrodes, the first
Alternatively, a third electrode, or third and fourth electrodes are provided around the outer periphery of the second electrode, and a third electrode is provided between the third electrode and the second or first electrode, or between the third electrode and the third electrode. 4. A method for driving a liquid crystal, characterized in that a voltage for orienting the liquid crystal in one direction is applied between the electrode and the electrode. 4. A liquid crystal driving method according to claim 3, characterized in that a voltage is applied between the first and second electrodes to drive the liquid crystal in the other direction.