JPH06313900A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To enable high orientation characteristics to be obtained and stable intermediate gradation display to be performed. CONSTITUTION:This liquid crystal element is composed of liquid crystal FLC clamped between electrodes 1902 and 1905 as a pair, and features that at least one electrode 1905 on an electrode substrate has a plurality of stripe type projections 1906 formed at a different gap in one picture element at an intersection with the other electrode 1902, and a lower resistance layer 1907 of electric conductivity equal to or above 10<-8>/cm formed over the projections 1906. According to this construction, an inversion domain allowing the easy control of area is formed, and hysteresis is reduced, thereby enabling good intermediate gradation display to be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal element used in a display device or a liquid crystal printer, and more particularly to a liquid crystal element which is preferable for realizing good display characteristics by using a ferroelectric liquid crystal having a memory characteristic.

[0002]

2. Description of the Related Art Ferroelectric liquid crystal (FLC) has high speed,
Attention has been paid to advantages such as memory properties, and it is actively used for display devices, light valves, and the like.

Targets that take advantage of the above advantages include an optical shutter array, a high-definition display device driven by a simple matrix, and a light valve for high-density recording combined with a photoconductor. Furthermore, thin film transistors (TF
There are also expectations for moving image display by active matrix driving using T).

Further, as an indispensable subject for enhancing the display capability of FLC, great efforts have been made to obtain good halftone.

For example, Japanese Patent Laid-Open No. 59-19 discloses a method for creating a mixed state of black and white domains in one pixel.
3427 A method by spontaneously giving unevenness in the electrode substrate or intentionally providing a minute mosaic pattern as described in the specification, or providing a stepwise distribution in the insulating layer thickness described in JP-A-61-166590. There is a method of obtaining gradation by the method. Furthermore, JP-A-64-77
023 discloses a method by obtaining an alignment state with many defects.

[0006]

It has been confirmed that a halftone state is created by the above method, but it is further desired to have uniform halftones or controlled gradation characteristics in the pixel. There is.

In order to keep the contrast even better, it is desirable to have an alignment state in which no defects are observed as much as possible in the halftone display state.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above technical problems and provides a liquid crystal device which achieves good orientation, uniform and stable halftone, and a gradation design which is easy to control. The purpose is to

Therefore, the present invention is a liquid crystal element in which a liquid crystal is sandwiched between a pair of electrodes, and within one pixel formed on at least one electrode of the substrate at the intersection with the other electrode, A plurality of stripe-shaped convex portions formed with different spaces, and 10 ⁻⁸ S / cm provided on the convex portions.
It is characterized by having a low resistance layer having the above conductivity.

The space change is formed so as to form a gradient over one pixel to provide an optimum gradation element.

[0011]

In the present invention, a stripe-shaped uneven structure is formed so that the pitch or space thereof has a gradient of change within one pixel. By doing so, the FLC inversion threshold has a gradient within the pixel, a linear inversion domain extending in a predetermined direction is formed in accordance with the grayscale signal, and good inversion area control is unsuccessful. A tonality characteristic is obtained.

Furthermore, since unnecessary ions do not remain during gradation driving, hysteresis is reduced.

[0013]

【Example】

Description of Preferred Embodiments FIG. 1 is a schematic view showing an example of the structure of a liquid crystal element according to an embodiment of the present invention.

Ferroelectric liquid crystal is used as a sandwiching element between a pair of substrates shown in the figure.

Then, for gradation display, a stripe convex portion is provided so that the inversion domain is linearly spread in a predetermined direction by changing the inversion threshold value so that the threshold value has a gradient in a predetermined direction. In addition, electric field due to inversion, residual ion,
Conductivity is 10 ^-8 S / to prevent adverse effects due to movement, etc.
A low resistance film of cm or more is provided.

This structure will be described in detail below.

FIG. 1 shows an electrode structure on one side (a lower substrate which is the scanning electrode side in FIG. 1) of a matrix substrate which is driven by multiplex, and the uneven shape having the above-mentioned pitch is provided by patterning or mask deposition. As an example, the line width of the convex portion is 4 μm, and the space width between the lines is from about 2 μm to 10 μm.
A schematic configuration diagram of the layers formed by sequentially changing the thickness of 5 μm is shown, and pixels are formed by the transparent electrode intersections of the upper and lower substrates in the figure.

Reference numeral 1901 is an upper substrate, which is a transparent substrate such as glass, quartz, or plastic, and 1902 is ITO, SnO ₂ ,
It is a transparent electrode such as In ₂ O ₃ . Reference numeral 1903 denotes a rubbing film of polyimide, nylon or other resin, or an alignment film obtained by oblique vapor deposition of SiO, SiO ₂ or the like.

On the other hand, the lower substrates 1904 and 190 are formed.
Reference numeral 5 denotes a transparent substrate and a transparent electrode similar to those in the above 1901 and 1902, and stripe convex portions 1906 are provided on the transparent electrode. Further, in the present invention, the low resistance layer 1 is formed on this.
907 is provided.

Next, if necessary, an alignment film 1908 is provided. The alignment film may be a riving film similar to the above 1903 or an oblique vapor deposition film to give uniaxial alignment to the internal liquid crystal. Alternatively, a non-uniaxially oriented film formed of a film of a silane coupling agent or an inorganic simple vapor deposition film may be used. Alternatively, the alignment film 1908 may be omitted by directly subjecting the low resistance layer 1907 to an alignment treatment as needed.

It should be noted that the direction of imparting uniaxiality due to the alignment treatment of the upper and lower substrates should be close to the longitudinal direction of the stripe protrusions in terms of the orientation, but the other directions should be taken. You may choose.

On the outer sides of the upper and lower substrates, polarizing plates arranged in crossed Nicols are provided.

As a material for forming the above-mentioned convex portion, in particular, A
1, metal such as Ti, Au, Pt, Cr or SnO ₂ ,
Although transparent conductive oxides such as In ₂ O ₃ and ITO are most preferable, SiO _{2 and} other inorganic substances as well as polyimide, polyamide, and other resins are known as deposition elements for forming other protrusions. It is formed by a patterning technique.

The line width of the stripe protrusions is preferably in a range larger than the thickness of the liquid crystal cell used, and is preferably 2 μm to 10 μm. Further, the protrusion stripe length is longer than the maximum space width, more preferably about one pixel length or more than one pixel length, and for example, it may be continuous over the entire electrode length of the scanning electrode. Good.

It is preferable that the space width between the convex portions is equal to or larger than the cell thickness in terms of orientation, and the upper limit is changed in the range of about 20 μm, so that the gradation is improved. Bring a good effect.

The gradation effect due to the stripe unevenness in which the above-mentioned space has a change gradient will be described below.

First, the protrusions make uniform the generation points of the gradation domain in each pixel. The protrusion has a stronger working electric field than the other parts with respect to the liquid crystal, and gives a clearly prioritized response when the electric field is applied. This effect is particularly great when the projection is formed of a conductive member, but even if it is relatively insulating, a similar electric field effect due to the capacitance ratio with other parts can be considered.

Further, a slight change in the molecular arrangement may be considered in the vicinity of the protrusion, and in particular, the formation of a portion that easily receives an electric field as torque is also effective.

Next, it is considered that the effect of forming the linearity (gamma) of the gradation by changing the space is largely due to the effect of propagating the inversion response to the space portion, which is prioritized to the protrusion portion. That is, in a process in which liquid crystal molecules swung by an electric field are latched (immobilized) as domains, a strong propagation effect is exerted, and the portion with a small space width is first immobilized as an inversion domain as a whole. As a result, it is considered that an inversion portion having an area-controlled gradation is formed in the pixel as shown in FIG.

Further, since the space change is provided with a gradient, the gradation control by modulating the peak value of the applied pulse, the pulse width, and the pulse waveform has a smooth gamma characteristic. This is because the spread of the inversion domain area is dependent on the propagation effect from the finest part of the space to create a continuous gradation with respect to the stepwise change of the space. .

The present invention pays attention to the tendency of formation of continuous gradation due to the above-mentioned gradient, and further, the present invention enhances the above effect by providing the low resistance film 1907.

FIG. 3 shows again the enlarged sectional shape of the pixel of the cell of the present invention. It is considered that the low resistance film 1907 makes the threshold gradient distribution due to the above-described propagation effect clearer.

That is, particularly known organic conductive films of polypyrrole, polyaniline, polyacetylene, etc., or polyimide nepolysiloxane, other resins, etc. as a matrix are dispersed SnO ₂ , In ₂ O ₃ , and other conductive fine particles. When a film is formed by spin coating or dipping from a solution state to an appropriate film thickness (50 Å or 1000 Å, preferably 100 Å or 500 Å), there are small spaces in the space due to factors such as surface tension, It is considered that there is a difference in the film coverage in a wide space, and the height of the concave and convex portions becomes large on average in a small space.

As a result, the threshold value in the small space portion is further lowered, and the edge portion of the original protrusion portion due to the film coating is smoothed, and at the same time the orientation is improved. Therefore, since the height of the protrusion can be further increased, the electric field effect can be sufficiently large, and very good gradation can be realized.

FIG. 4 shows a typical gradation characteristic obtained by the constitution of the present invention as a VT characteristic (solid line).
The dotted line in the figure shows the VT characteristics in the case where the low resistance film is not provided in this configuration as a comparative example,
The gradation characteristics are obviously improved by the present invention. The pulse width of the drive voltage applied here is about 20 μse.
c.

The low resistance film provided in the present invention is optimally one having a conductivity of about 10 ^-4 S / cm to 10 ^-8 S / cm. When the film has a conductivity of more than 10 ⁻⁴ S / cm, electrical conduction between pixels cannot be ignored, and the film needs to be patterned as a pixel electrode in the same manner as the underlying transparent electrode.

Further, when the conductivity is less than 10 ^-8 S / cm, in order to obtain good gradation characteristics, for example, a time width for resetting a pixel needs to be several hundreds μsec or more on the driving waveform. Cause obstacles.

The thickness of this film is preferably not too thick in consideration of the partial pressure of the liquid crystal when a voltage is applied, at most 1000 Å or less, preferably 50 in consideration of the transmittance and the like.
0 Å or less is desirable.

On the other hand, the height of the stripe protrusions in the case of providing the low resistance film is preferably in the range of 500Å to 4000Å because of the effect of the protrusions or the one not disturbing the orientation.

Further typical examples will be described below.

(Example 1) As an example of the basic structure of the concavo-convex pattern in the element (cell) of the present example, the stripe-shaped convex portions are ITO having a height of about 2000 Å, and the spaces between the convex portions are Concavities and convexities were formed by gradually changing the space width with a gradient from a minimum of 2 μm to a maximum of 10 μm in 0.5 μm steps.

Next, as a low resistance film, polyaniline and an organic strong acid having a molecular weight of about 200 to 300 (eg, CSA) are used.
(Camphorsulfonic acid)) was dissolved in a mixed liquid medium of N-methylpyrrolidone (NMP) and rubutyl cellosolve (nBC) in an amount of about 0.7 wt% and about 0.3 wt%, respectively. p. m. It was formed on the irregularities by spin coating for 20 sec. Note that the same material can be formed with an appropriate thickness by dipping. Further, as another method, a known electrolytic polymerization film can be formed. The optimum film thickness under the above conditions is about 40 when coated on another glass substrate with ITO.
It is 0Å, and the conductivity of this film was measured to be about 10 ^-7
A conductivity of S / cm was obtained.

On the other hand, on the substrate facing the above-mentioned concavo-convex pattern substrate, the above-mentioned polyaniline provided on ITO by adjusting the solution concentration to provide about 50Å is arranged through a silica bead spacer having a diameter of about 1.2 μm to form a cell. And

The liquid crystal alignment treatment in this cell is as follows.
Both the uneven pattern substrate or the counter substrate,
Alternatively, the liquid crystal filled in the cell could be aligned by subjecting only the counter substrate to a rubbing treatment in a direction substantially parallel to the longitudinal direction of the stripe.

The gradation characteristic of the above-mentioned cell is shown by the solid line in FIG. 4 and shows good gradation characteristics.

Example 2 A polyimide alignment film (LQ1802) was formed as an LB film on the polyaniline film on the concavo-convex pattern formed in Example 1 by about 30Å, while the opposite substrate was directly formed on ITO by the above polyimide. An alignment film was formed, and both were roughly rubbed in the direction parallel to the stripe longitudinal direction in the same manner as above to obtain cells. A liquid crystal different from that in Example 1 was injected into this and aligned. Gradation results were similarly good.

Example 3 SnO ₂ was used as the low resistance film.
The conductive fine particles having a particle size of about 100Å subjected to antimony-doped by coating type SnO ₂ mixed with polysiloxane to form a film on the uneven pattern. The conductivity of this film is about 10 ⁻⁷ S / cm.

Furthermore, the LB film (LQ180
2) was formed by 30Å and rubbed. Other configurations are the same as those in the first and second embodiments.

The orientation was very good and the gradation was also better than that shown by the solid line in FIG.

The short-period surface irregularities due to the fine particles in this example seem to add a further effect to good orientation and gradation characteristics.

(Example 4) In Example 3, a large number of types of substrate samples each having a film formed thereon were formed by changing the doping amount of antimony, the size of conductive fine particles, the mixing ratio of polysiloxane and the particles, and the like.

Of these, the conductivity is 10 ^-10 S / c
A sample in the range of m to 10 ^-2 S / cm was selected and a similar liquid crystal element sample was prepared. Then, halftone display was performed to evaluate the hysteresis characteristic. The results are shown in Tables 1 and 2 below.

[0053]

[Table 1]

[0054]

[Table 2] Here, ⊚ is particularly good as an element for displaying a halftone from the viewpoint of hysteresis characteristics, ○ is good, Δ is applicable, ×
The mark is inappropriate.

Therefore, as the low resistance film, 10 ^{−8 to} 10
^It can be seen that a film having a conductivity of ⁻⁴ S / cm is particularly preferable.

FIG. 5 shows the structure of an image display device having a liquid crystal display element according to this embodiment. The device is a panel 1801 of a 500 × 500 matrix as a liquid crystal display element,
A scanning waveform generator 1806 including a clock 1802, a synchronizing circuit 1803, a shift register 1804, an analog switch 1805, and the frame memory 1, for example.
And an information signal generator 1808 for converting and outputting video information from 807 or the like into a drive signal. In terms of mounting, these may be distributed by being connected to one side or both sides above and below the matrix substrate and one side or both sides on the left and right sides. As a method of applying an information signal waveform as a halftone signal, there is a voltage modulation which is usually considered as a method of giving gradation information, but in the present embodiment, especially in the elastic propagation in the layer direction of the chiral smectic C phase. In order to control the propagation time of the combined domain, pulse width modulation,
Driving methods such as phase modulation are also effective.

[0057]

As described above, according to the present invention,
It is possible to maintain good reproducibility of halftone display and perform halftone display having a desired applied signal-transmittance characteristic (γ characteristic). In addition, good halftone display can be performed at higher speed, with a higher number of gradations, and with higher definition, without complicating the structure of the element so much.

[Brief description of drawings]

FIG. 1 is a schematic view showing a structure of a liquid crystal element according to an embodiment of the present invention.

FIG. 2 is a schematic view showing a state of domain inversion of a liquid crystal element according to the present invention.

FIG. 3 is a schematic cross-sectional view of a liquid crystal device according to the present invention.

FIG. 4 is a diagram showing the relationship between the applied voltage and the transmittance of the liquid crystal element according to the present invention.

FIG. 5 is a block diagram of a display device using a liquid crystal device according to an embodiment of the present invention.

[Explanation of symbols]

 1901 Transparent substrate 1902 Transparent electrode 1903 Alignment film 1904 Transparent substrate 1905 Transparent electrode 1906 Striped convex portion 1907 Low resistance film 1908 Alignment film

Claims (3)

[Claims] 1. A liquid crystal element in which liquid crystal is sandwiched between a pair of electrodes, wherein different spaces are formed in at least one electrode of the substrate at one pixel formed at an intersection with the other electrode. A liquid crystal element comprising: a plurality of stripe-shaped convex portions formed by the above-described method, and a low resistance layer having a conductivity of 10 ⁻⁸ S / cm or more provided on the convex portions. 2. The liquid crystal device according to claim 1, wherein the change of the space has a gradient over one pixel. 3. The conductivity of the low resistance layer is 10 ⁻⁴ S / cm.
The liquid crystal element according to claim 1, wherein: