JPH0588154A - Ferroelectric liquid crystal element - Google Patents

Abstract

PURPOSE:To improve display quality by suppressing the movement of a liquid crystal molecule in a cell when a liquid crystal element is driven. CONSTITUTION:In a liquid crystal display element in which a pair of electrode substrates 1a and 1b having at least three layers such as a layer constituted of plural belt-like display electrodes 11a, 12a, 11b, and 12b in parallel, insulating layers 13a and 13b, and oriented films 14a and 14b on their surfaces is opposed, and ferroelectric liquid crystal 16 is sealed between both substrates, a wall 18 higher than the height of the display electrode is provided on the interval 17 between the picture elements of at least one electrode substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device using a ferroelectric liquid crystal.

[0002]

2. Description of the Related Art Regarding a display element using a ferroelectric liquid crystal, as shown in Japanese Patent Laid-Open No. 94023/1986, a cell gap of about 1 to 3 microns is maintained on two inner surfaces. It is known that a ferroelectric liquid crystal is injected into a liquid crystal cell formed by facing glass substrates on which transparent electrodes are formed and subjected to orientation treatment.

The characteristics of the above-mentioned display device using the ferroelectric liquid crystal are that the ferroelectric liquid crystal has spontaneous polarization, so that the coupling force between the external electric field and the spontaneous polarization can be used for switching, and that the long-axis direction of the ferroelectric liquid crystal molecule is Since the polarization direction of the spontaneous polarization has a one-to-one correspondence with the polarization direction, switching can be performed depending on the polarity of the external electric field.

Since the ferroelectric liquid crystal is generally a chiral smectic liquid crystal (SmC * .SmH *), the long axis of the liquid crystal molecules exhibits twisted alignment in the bulk state. The twist of the long axis of the liquid crystal molecule can be eliminated by putting it in the cell of (P213-P234 N.A. LARKet).
al, MCLC, 1983, Vol 94).

The actual structure of a ferroelectric liquid crystal cell uses a simple matrix substrate as shown in FIG. In the figure, 31 is a glass substrate, 32 is a stripe display electrode of ITO, 33 is an insulating film of SiO ₂ , 34 is an alignment film of polyimide, 35 is a seal member, and 36 is a ferroelectric liquid crystal. The ferroelectric liquid crystal is hereinafter referred to as FLC.

[0006]

When the conventional cell structure is used, the durability of the liquid crystal cell has the following problems.

That is, it is known that FLC molecules move to some extent even by a non-selection signal during matrix driving. This is also clear from the fact that when the optical response of the pixel to which the non-selection signal is applied is taken, the light amount varies in synchronization with the applied pulse. So-called splay orientation (orientation with a large twist in the angle of the molecular long axis between the upper and lower substrates)
Then, such a fluctuation of the molecule can hold the display content unless the stable position of the molecule is changed (switched) by it, so that it is not a problem other than a slight decrease in contrast. However, in a cell with an alignment (hereinafter referred to as a uniform alignment) in which the change in the angle of the molecular long axis direction between the upper and lower substrates is relatively small, liquid crystal molecules are said to move in the layer by applying a voltage (for example, a non-selection signal). You can see the phenomenon.

This phenomenon will be described in detail with reference to FIGS. 2 and 3. FIG. 3A shows a cell state before voltage application, and FIG.
Indicates the cell state after voltage application. The FLC 36 is sealed in the seal member 35 between the glass substrates 31 having the alignment film 34 formed on the surface. A polyimide thin film is used as the alignment film 34, and the rubbing direction is parallel to the upper and lower substrates from the bottom to the top in both FIGS. When such treatment is performed, the smectic layer is formed as shown in FIG.
It is generated in a direction orthogonal to the rubbing direction as shown in (c).

When the cell thickness is made thin enough to release the helical pitch, the FLC molecule can take two stable states, but one of the FLC molecules has the same orientation of all molecules in the cell. ..

Assuming that this state is the + θ state (FIG. 3D), another stable state exists at the −θ position almost symmetrically with respect to the layer normal.

When an electric field (for example, a rectangular wave of 10 Hz and ± 8 V) is applied to the entire surface of the cell in this state (+ θ), the liquid crystal molecules are maintained in the inclination with respect to the layer normal line of + θ.
Start moving in the layer from point A to point B in (a).

As a result, when the voltage application is continued for a long time, as shown in FIG.
As shown in (b), a portion E having no liquid crystal is generated at the end A, and the cell thickness of the portion B is thicker than that of the portion A. Such a phenomenon occurs when liquid crystal molecules are in the state of −θ, liquid crystal moves in the layer from the B end to the A end, and a void portion without liquid crystal such as the E portion occurs at the B end.

Such a phenomenon occurs in a relatively short time of 20 hours to 50 hours. The presence of a portion that cannot be controlled electro-optically such as the portion E is not desirable in terms of display quality, and it is difficult to control the driving of the entire liquid crystal panel if the cell thickness of the portions A and B changes with time. , Has been a serious problem as an optical element using FLC.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide a liquid crystal display device in which the movement of liquid crystal molecules in a cell is suppressed when the liquid crystal is driven and the display quality is improved. ..

[0015]

In order to achieve the above object, according to the present invention, a pair having on its surface at least three layers of a layer composed of a plurality of parallel strip-shaped display electrodes, an insulating layer and an alignment film. In the liquid crystal display element in which the electrode substrates are opposed to each other and the ferroelectric liquid crystal is sealed between both substrates, a wall having a height higher than that of the electrodes is provided between pixels of at least one of the electrode substrates.

Here, the term “between pixels” refers to a portion above and below the liquid crystal layer, where at least one has no display electrode, and the term “within a pixel” refers to a portion where display electrodes above and below the liquid crystal layer.

[0017]

That is, the present invention aims to prevent the movement of the liquid crystal molecules by providing a wall between the pixels in order to prevent the movement of the liquid crystal molecules in the pixel from expanding to other pixels.

Since the wall is provided for the purpose of suppressing the movement of FLC molecules, it is necessary to set the wall higher than the display electrode (transparent electrode such as ITO film). If this height is lower than (height of display electrode + 0.4 μm), movement of FLC cannot be prevented. The higher the height, the better as long as it suppresses the movement of liquid crystal molecules. If the surface of the alignment film above the wall is in contact with the counter substrate, the movement can be completely suppressed over a long distance. However, in this case, a serious defect occurs in that it is made into cells. That is, it is impossible to uniformly inject and fill the FLC throughout the cell in the step of injecting the FLC. Unless the current vacuum injection system allows for a completely different future, for example, printing technology and laminating technology in the future, it is practically extremely inconvenient to provide a wall such that the substrate surface contacts the counter substrate. Therefore, as a result of studying the interval at which the injection can be efficiently performed by the current technology, it has been found that the interval should be 0.2 μm or more.
From the above, in the present invention, the height of the wall is set to 0.
At least 4 μm higher, 0.2 μ between the surfaces of both substrates
A distance of m or more was set as a desirable range.

With the above structure, movement of the FLC can be prevented.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the structure of a ferroelectric liquid crystal display device according to an embodiment of the present invention. In FIG. 1, reference numerals 1a and 1b are glass substrates, 11a and 11b are transparent electrodes (display electrodes) 12a and 12b, each of which is an ITO pattern of about 150 nm formed in a stripe shape on the glass substrate by a sputtering method.
Is a metal auxiliary electrode (Al or Mo or the like) of about 100 to 200 nm formed on at least a part of the ITO pattern by a sputtering method, and 13a and 13b are insulating films (Ta ₂ O ₅ ) of about 200 nm formed on the electrodes. Etc.), 14a, 14b
Is an alignment film of about 20 nm for aligning FLC, 15
Is a gap material (SiO 2) for obtaining a uniform cell gap.
₂ ), 16 is an FLC material, 17 is a wall formed between pixels, and 18 is a wall formed between pixels characterized by the present invention. The values of materials, film thicknesses, etc. shown above are examples of a number of combinations and are not particularly limited to the numerical examples.

The wall shown by 18 is made of a photosensitive polyimide / polyamide having excellent heat resistance and is 0.4 μm higher than the ITO film of the display electrode (that is, 0.55 μm from the glass surface).
m height), and was formed along the space 17 between pixels. The reason for using a material having excellent heat resistance is that the alignment of FLC is better when the alignment film is formed at a high temperature (250 ° C. or higher).

The substrates 1a and 1b on which the ITO pattern, the metal auxiliary electrode, and the alignment film are formed are opposed to each other so that the cell gap is 1.3 μm in the pixel, and a liquid crystal display element in which FLC is injected is manufactured. Driven, 50
The cell thickness did not change even after a lapse of 0 hours, and it was an element with good display quality.

[0024]

Other Embodiments In the same structure as in Embodiment 1, the cell gap is set to 1.5 μm. The distance between the surface of the alignment film above the wall provided between the pixels and the surface of the counter substrate is 0.2 μm.
The height was set in advance so that

Compared to the cell of the first embodiment, this cell has FLC
It took a long time (about 2 days) to inject, but there was no injection defect, and even if the cell was driven, the cell thickness did not change even after 1000 hours had passed, and the device had good display quality. became.

[0026]

As described above, according to the present invention,
By providing the wall for preventing the movement of FLC between pixels, there is an effect of preventing a change in cell thickness, which is a defect of reliability of the FLC display element.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a ferroelectric liquid crystal display element according to an embodiment of the present invention.

FIG. 2 is a sectional view and an electrode pattern view of a conventional liquid crystal cell.

FIG. 3 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

1a and 1b: glass substrates, 11a and 11b: transparent electrodes (display electrodes), 12a and 12b: metal auxiliary electrodes, 13
a, 13b: insulating film, 14a, 14b: alignment film, 15:
Gap material, 16: FLC material, 17: between pixels, 18:
FLC migration prevention wall, 31: glass substrate, 32: ITO stripe electrode, 33: SiO ₂ insulating film, 34: polyimide alignment film, 35: seal member, 36: liquid crystal.

Claims (2)

[Claims] 1. A pair of electrode substrates having on their surfaces at least three layers of a plurality of parallel strip-shaped display electrodes, an insulating layer and an alignment film are opposed to each other, and a ferroelectric liquid crystal is sealed between both substrates. A liquid crystal display element, wherein a wall having a height higher than that of the electrode is provided between pixels of at least one of the electrode substrates. 2. The height of the walls is at least 0.4 μm higher than the height of the display electrodes, and the distance between the surfaces of both electrode substrates is at least 0.2 μ above the walls.
The ferroelectric liquid crystal element according to claim 1, wherein the ferroelectric liquid crystal element is separated by m or more.