JPH06313878A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To provide easily controllable gradation drive. CONSTITUTION:This is a liquid crystal element with a liquid FLC clamped between a pair of electrodes 14 and 1903. A plurality of stripe type projections 12 formed with different intervals are provided on one of the electrodes 14 and 1903 within a picture element formed at an intersection with the other electrode. In addition, the liquid crystal element features that means 10 and 11 are provided to form the change of space between the projections 12 along a slope within the picture element, and further form field strength acting on the liquid crystal element distributed along the change of the space slope.

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 for imparting good display characteristics by using a ferroelectric liquid crystal having spontaneous polarization.

[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.
No. 3427, a method by spontaneously giving unevenness in the electrode substrate or intentionally providing a minute mosaic pattern as described in Japanese Patent Laid-Open No. 3427 or JP-A-61-1665.
There is a method for obtaining a gradation by providing a stepwise distribution in the thickness of the insulating layer described in JP-A-90. Further, Japanese Patent Application Laid-Open No. 64-77023 discloses a method by obtaining an alignment state with many defects. Further, in addition to the above, many ideas have been made such as giving patterned irregularities a periodic structure.

It has been confirmed that a halftone state is created by the above method, but it is further desired that the grayscale is made uniform in the pixel or the controlled grayscale characteristics.

In order to maintain a good contrast, it is desirable to have an alignment state in which no defects are observed.

The present applicant has further filed Japanese Patent Application Laid-Open No. 62-11952.
Japanese Patent Application Laid-Open No. 62-12533, which delays potential transmission in a pixel to provide gradation.
No. 0, etc., to form a forcible potential gradient in a pixel to provide gradation, or JP-A-62-1
In Japanese Patent No. 45216, there is proposed a method in which an inter-electrode distance (cell thickness) is provided with a gradient to provide gradation. Each of these controls the inversion area of the liquid crystal by utilizing the in-pixel gradient of the electric field intensity applied to the liquid crystal inside, and is as shown below.

What is represented by the above-mentioned JP-A-62-119521 or JP-A-62-125330 is basically composed of a low-resistance electrode line and a relatively high-resistance film connected to the electrode line. In the former, the potential supplied to the electrode line is delayed and transmitted in the high resistance film, and in the latter, at least two low resistance electrodes sandwiching the high resistance film in the plane are supplied with different potentials. By doing so, a potential gradient is forcibly formed in the high resistance film.

[0010]

Technical Problems to be Solved As technical problems to be solved by applying these potential gradients, there is usually a resistance which cannot be ignored in the low resistance electrode line, and when applying a potential from an external power source to the electrode line, Nonuniformity of the voltage applied to the liquid crystal due to delay and potential drop occurs in the electrode line between the power feeding portion and the portion away from the power feeding portion. For example, when constructing a matrix panel of about 1000 × 1000 pixels, There is a possibility that gradation unevenness that cannot be ignored is given.

Further, the one having a gradient in the distance between the electrodes, which is represented by the above-mentioned Japanese Patent Laid-Open No. 62-145216, has a large gamma characteristic as a gradation characteristic (typically, saturation voltage / threshold voltage value). May require a considerably large cell thickness difference, and at this time, a large difference in retardation due to the cell thickness difference may cause optical coloration, which may cause difficulty in color display, etc. There is.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned technical problems, and realizes a gradation drive which is easy to control and which has good orientation and uniform and stable halftone. It is intended to provide a liquid crystal element having

That is, the present invention is a liquid crystal element in which a liquid crystal is sandwiched between a pair of electrodes, and different spaces are formed on at least one of the electrodes in a pixel formed at the intersection with the other electrode. A plurality of stripe-shaped convex portions formed so as to form a gradient in the space between the convex portions, and the liquid crystal is formed along the gradient of the variation in the space along the gradient. The present invention is characterized in that a means for forming a distribution gradient of the electric field strength that acts is formed, and further that the change in the space forms a gradient over one pixel.

Further, the liquid crystal device of the present invention is a liquid crystal device in which a liquid crystal is sandwiched between a pair of electrodes, and at least one of the electrodes is a first low resistance striped electrode to which power is supplied and the other electrode. A plurality of second stripe-shaped electrodes independently formed so that the intervals are different from each other in one pixel formed at the intersection of the first and second stripe-shaped electrodes. It is characterized by comprising a film having a sheet resistance of ⁴ Ω / □ or more and 10 ⁸ Ω / □ or less.

Furthermore, the liquid crystal element of the present invention is a liquid crystal element in which a liquid crystal is sandwiched between a pair of electrodes, and a pixel formed on at least one electrode of the electrodes at the intersection with the other electrode. A plurality of stripe-shaped convex portions formed with different spaces in the interior, and the variation of the spaces between the convex portions is formed to have a gradient within the pixel, and along the gradient of the variation of the space A gradient is provided in the distance between the electrodes of the pair of electrode bases.

[0016]

FIG. 1 is a schematic view for explaining a liquid crystal device according to the present invention formed in a matrix type, showing a plane and a cross section of an upper substrate and a plane of a lower substrate which constitute a cell.

In the upper substrate in FIG. 1, 1901 is glass,
Transparent substrate such as quartz or plastic, 1902 is ITO,
A transparent electrode of SnO ₂ , In ₂ O ₃ or the like, and 1903 is a rubbed film of polyimide, nylon, other resin, or a film generally known as a conductive polymer material such as polyaniline or polypyrrole, or SiO or SiO _2.
Etc. is an alignment film obtained by oblique vapor deposition.

On the other hand, on the lower substrate side, stripe-shaped protrusions 12 are provided as constituent elements. The protrusion is, for example, 4
A convex portion with a width of μm is formed with a height of about 1500 Å as an example in a form in which a space (space) is continuously changed within a pixel width in 0.5 μm steps in a range of about 2 μm to 10 μm. When cells are formed by a cross matrix, pixels are formed at the intersections of the transparent electrodes on the upper substrate and the protrusion forming portions on the lower substrate.

As a material for forming the above-mentioned convex portion, especially A
1, metal such as Ti, Au, Pt, Cr or SnO ₂ ,
In ₂ O ₃ , transparent conductive oxides such as ITO are most preferable, but as another element for forming the protrusion, SiO _{2 and} other inorganic substances, further polyimide, polyamide, and other resins are known patterning elements, Alternatively, it is formed by a depot technique.

The alignment film provided on the protrusions as needed may be a rubbing film or an oblique deposition film similar to that of 1903, which imparts uniaxial alignment to the internal liquid crystal, or silane. A non-uniaxially oriented film formed of a coupling agent film or an inorganic simple vapor deposition film may be used.

It is better in terms of orientation that the direction of imparting uniaxiality due to the alignment treatment of the upper and lower substrates is close to the longitudinal direction of the stripe projections, but the effect of the present invention is obtained even if other directions are selected. Admitted enough. Polarizing plates arranged in crossed Nicols are provided outside the upper and lower substrates.

The structure of the liquid crystal device according to the embodiment of the present invention will be described in more detail with reference to the sectional views of three devices (cells) shown in FIGS. 2 (a), (b) and (c).

In the present invention, attention is paid to the tendency of continuous gradation due to the above-mentioned change gradient of the protrusion spacing space,
Furthermore, by adding a gradient to the electric field strength applied to the liquid crystal along the above-mentioned gradient, a better control effect is given to the gradation, and the gradient is applied to the electric field strength as shown in the conventional example. This is to simultaneously solve the problem of the gradation method.

In FIG. 2A, a forcible potential gradient is formed on the lower substrate together with the gradient of the change in the projection spacing, and the projection spacing variation gradient is formed in the liquid crystal sandwiched by the difference between the opposing upper substrate potential. The distribution gradient of the electric field strength along the is formed.

In the figure, 10 and 11 are electrodes to which electric power is supplied from the outside, and are formed of a low resistance metal such as Al, Cr and Au.

Further, 14 is a metal oxide such as SnO ₂ or Ta ₂ O _{3 and} has a sheet resistance of 10 ⁴ Ω / □ to 1
It is a transparent film adjusted to about 0 ⁸ Ω / □, and this can be formed by controlling the oxygen concentration during film formation. In this example, the stripe-shaped protrusions 12 are formed on the high resistance film.
However, it is desirable that the protrusion has a low resistance such as metal or ITO. Here, since the film 14 has a higher resistance than the metal of the projection 12 and ITO, it may be referred to as a high resistance film for convenience.

The illustration of the alignment film is omitted.

In the present invention, the high resistance film and the striped electrode may be arranged on the substrate 15, and the film 14 may be formed after the striped electrode 12 or the low resistance electrodes 10 and 11 are formed first.

In this case, polyaniline, polypyrrole,
A high resistance film 14 is formed by a film made of a conductive polymer such as polyacetylene, or a film obtained by dispersing and coating SnO ₂ , ITO or ultrafine particles of a metal or metal oxide on polyimide, polysiloxane, nylon or another resin matrix. May be formed, and in some cases, it may be used as an alignment film by rubbing itself.

When different potentials V ₁ and V ₂ are applied to the low resistance electrodes 10 and 11, a potential gradient as shown in FIG. 3 is formed. As a result, the electrode 19 on the upper substrate
A distribution gradient of electric field strength is formed in the liquid crystal portion with respect to the potential applied according to the gradation of 03.

The gradation effect due to the potential gradient formed in the entire pixel and the space variation gradient provided between the stripe protrusions as described above will be described below.

First, the protrusions, which are the protrusions, make the generation points of the gradation domain uniform in each pixel. A strong electric field acts directly on the liquid crystal in the protruding electrode portion as compared with the other portions, and when the electric field is applied, a clearly prioritized response is obtained. In addition, a slight change in the molecular arrangement may be considered in the vicinity of the protrusion, and the effect of being particularly susceptible to an electric field as torque is recognized.

Next, the formation effect of the gradation gamma due to the change in the space is accompanied by the factor of the effect of propagating the inversion response to the protrusion portion to the space portion, and the intensity of the electric field controlled and applied to the entire pixel. This is a major cause of overlapping gradients. That is, in a process in which liquid crystal molecules swung by an electric field are latched (immobilized) as domains, the space between the projection electrodes is small due to the effect of the propagation effect from the projection and the effect of the gradient of the electric field strength. , The liquid crystal molecules are more susceptible to inversion,
Further, at a position where the space is large, the reversal action becomes small due to the reduction of the propagation action and the reduction of the average electric field strength. As a result, the small portion of the space is fixed as an inversion domain at a low voltage as a whole, and as shown in FIG. 4, an area-controlled inversion portion having gradation is formed.

Further, the above-mentioned space variation and the gradient of the electric field strength are provided, so that the peak value of the driving pulse to be given,
The gradation control by modulating the pulse width and other pulse waveforms shows a smooth gamma characteristic. This is probably because the spread of the inversion domain area subtly picks up the propagation effect from the finest part of the space, creating a continuous gradation even with a gradual space change. .

On the other hand, the unevenness of the potential gradient due to the potential drop as described in the conventional example can be improved by the structure in which a plurality of low resistance stripe-shaped projections are provided on the high resistance film.

The dotted line in FIG. 5 shows the potential gradient values in the vicinity of the power feeding portion (end portion) and the portion (center portion) apart from the power feeding portion in the line (for example, the scanning side) which gives the potential gradient in the conventional potential gradient configuration. It shows unevenness. As shown schematically in FIG. 6, this unevenness has resistance in the low resistance power supply line,
Due to the interaction between this resistance and the resistance in the high-resistance film, the gradient value of the electric potential is from the end (between A and D in the figure, between C and F) to the central part (B
However, by forming the stripe-shaped protrusions 12 of the present invention with a low resistance, a plurality of independent stripes with a low resistance can be obtained even at a distance x from a low-resistance power supply line. It is considered that the protrusions reduce the apparent wiring resistance and try to maintain the equipotential surface, and as a result, the unevenness of the potential gradient value is improved as shown by the solid line in FIG.

Here, if a typical pulse width for high-speed driving of the display element is considered to be, for example, about 20 μsec, the above-described potential gradient and the gradation effect by the stripe-shaped protrusions can be well exhibited. In order to prevent an excessive current from flowing as the resistance condition of the high resistance film,
0 ⁴ Ω / □ or more, and about 10 ⁸ Ω / □ or less is desirable in order to achieve a desired potential gradient within the pulse width. On the other hand, a sheet resistance is 10
Ω / □ or less, or 1 as the resistance of the striped protrusions
It is desirable that it is about 0 ⁴ Ω / □ or less. The height of the stripe-shaped protrusions is set to 30 in order to suppress the disorder of the orientation.
Height less than 00Å, preferably 5% of cell thickness used
It is good to be about 15%. About 1.5 as an example
With the average cell thickness of μm, the projection height of about 1500Å had good characteristics.

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

As for the space width between the convex portions, it is preferable that the space width is equal to or more than the cell thickness in terms of the orientation, and the upper limit is changed in the range of about 20 μm, so that the gradation is excellent. Bring effect.

FIG. 7 shows a typical VT (voltage-transmittance).
Show the characteristics. The dotted line and the one-dot chain line in the figure show comparative examples, in which a stripe protrusion and a VT curve of a flat cell without a potential gradient means and a striped protrusion were provided on a normal ITO electrode and no potential gradient was provided. The VT curve in the case is shown.

On the other hand, in this example, the power supply electrodes 10 and 11 to which the potentials of 2 V and 0 V (ground) are applied and the potential gradient is applied are shown by the solid line graph.

Next, another embodiment of the present invention, FIG. 2B, will be described.

What is shown in FIG. 2B is structurally shown in FIG.
(A), only the power supply electrode indicated by reference numeral 20 is used.
The effect of delaying the transmission of the power supply potential by utilizing is used as a distribution gradient of the electric field strength applied to the liquid crystal.

The effect on the gradation in this example is as described in (a) above.
It is considered that it is almost the same as that by the forced application of the potential gradient, and the result as the gradation is similar to that of FIG. 7.

FIG. 2 (c) shows another embodiment, in which the cell thickness gradient is given to the shape of the lower substrate in order to have the distribution gradient of the electric field intensity. Reference numeral 30 is a normal low-resistance electrode such as ITO.

In the above-mentioned conventional example, in the case where the stripe-shaped projections having the space variation gradient are not provided as in the present embodiment, if the gamma value is about 1.5, the gradient of the cell thickness is assumed to be obtained. As a reciprocal of the electric field strength between the widest portion and the narrowest portion of the cell thickness, that is, a difference in cell thickness of about 30% with respect to the wide portion must be formed, whereas in the present example, the stripe-shaped protrusions are used. Since there is already a change in the threshold value, that is, a gradation effect, the cell thickness difference due to the overall cell thickness gradient can be reduced. As an example, when providing 1500 Å as the height of the stripe protrusion, sufficient gradation can be obtained even by providing a cell thickness difference of about 1500 Å. At this time, the diameter of the spacer beads arranged between the cells is about 1.4 μm.
I used the one. In this example, the tapered substrate and the substrate on which the stripe-shaped protrusions are provided may be different substrates. In this case, patterning and cell formation are performed paying attention to pixel alignment.

The stripe-shaped projections 12 provided in FIG. 2 (c) are effective even if they are made of a conductive material such as ITO or Cr or an insulating material such as SiO ₂ . As long as it is electrically conductive and is substantially in conduction with the transparent electrode 30, the illustrated feeding point 33 is any one of the stripe-shaped protrusions 12 (for example, the feeding point 34 of the feeding line shown by the dotted line), or It may be connected to multiple things.

As can be understood from the above description, good gradation characteristics are exhibited, but in the present invention, a gradient over one pixel is formed, and the area control of the domain in one direction is particularly preferable for gradation. As intended

Several embodiments will be described below.

(Example 1) After forming a resist pattern on a glass having a thickness of 1.1 mm, a SnO ₂ film was formed by a reactive sputtering method in an atmosphere of zero oxygen, and lift-off was performed to form a SnO ₂ film as shown in FIG. The pattern of the high resistance film 14 shown by is formed with a film thickness of about 200Å. In the same lot, gold electrodes were similarly vapor-deposited on the above-mentioned film formed on glass and the sheet resistance was measured, and it was found that the resistance was about 10 ⁷ Ω / □.

Next, the power supply electrodes 10 and 11 shown in FIG. 2A were formed to have a width of about 10 μm by a normal Al etching step, and then the stripe-shaped projection pattern 12 was formed by the lift-off method as described above. At this time, the protrusion height of the power supply electrode and the ITO pattern is about 1200Å, the protrusion width is 4 μm, and the space between the protrusions is 2 μm to 10 μm as described above.
It was assumed that a gradient of change was provided in 0.5 μm steps up to m.

Next, as an alignment film, polyimide LQ1802 is used.
Spin coating (concentration 0.9 wt% for spin condition solvent)
%, 2200 r. p. m. After 20 seconds), it was dried and baked to form a film having a thickness of about 100Å.

On the other hand, LQ1802 was similarly used as the alignment film on the upper substrate of FIG. 1, and the upper and lower substrates were rubbed.
A cell was formed through silica spacer beads of about 1.4 μm. As for the rubbing direction, the stripe protrusion forming side is made substantially parallel to the stripe longitudinal direction, while the other substrate side is
The direction was shifted by about −10 ° from the stripe direction. Ferroelectric liquid crystal having Ps of about 7 nC / cm ² was injected into the cell.

A scanning voltage having a difference of about 2 V is applied to the power supply electrodes 10 and 11 of the cell during gradation writing, and an information voltage including a panel width of about 20 μsec as a writing width is applied to the counter electrode. When gradation driving was performed with such a driving waveform, good gradation characteristics as shown by the solid line in FIG. 7 were obtained.

(Embodiment 2) The cell shown in FIG. 2B is formed by the same manufacturing method as in Embodiment 1, and a scanning voltage is applied to the power supply electrode 20 and a gradation information voltage is applied to the counter electrode 1903. Then, good gradation characteristics were obtained.

(Embodiment 3) The power supply electrode and the stripe-shaped protrusion pattern of Embodiment 1 or 2 are formed on a glass substrate by C by a normal photolithography (etching) process.
Directly formed with r (chromium). At this time, the stripe width is 3
μm.

After that, a solution of polyaniline known as a conductive polymer material is applied by printing, immersed in 1N dilute sulfuric acid, subjected to a conductive step, and dried to about 10 ⁶ Ω.
A film of about 100Å of / □ was obtained.

On the other hand, a conductive film of polyaniline similar to the above was formed on the other substrate (upper substrate), and the polyaniline film was rubbed on both upper and lower sides substantially parallel to the longitudinal direction of the stripe protrusions.

After this, ferroelectric liquid crystal SBF6 manufactured by Roche
After injecting 430 and performing AC application processing (10 Hz, ± 10 V, about 3 minutes) in a temperature environment of about 30 ° C., gradation driving was performed in the same manner as in Example 1 and Example 2, respectively. A tonality was obtained.

Example 4 A lower substrate (gradient shape 30) shown in FIG. 2C was formed by a step of transferring an acrylic UV curable resin from a metal mold master onto a glass substrate. After that, an ITO pattern 30 was formed by a normal photolithography process, and then a stripe-shaped projection pattern 12 was further formed by lift-off. The taper-shaped step of the substrate of this example is about 1500Å, and the step of the stripe-shaped protrusion is about 1
It was set to 500Å. The same alignment film and liquid crystal as in Example 1 were used.

Also in this example, good gradation characteristics were exhibited as described above.

FIG. 8 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 or both upper and lower sides of the matrix substrate, or one or both right and left sides of the matrix substrate. 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.

[0063]

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 diagram for explaining a configuration of a liquid crystal element according to the present invention.

FIG. 2 is a schematic cross-sectional view of a liquid crystal element according to three exemplary embodiments of the present invention.

FIG. 3 is a diagram showing a relationship between a position on an electrode and its potential.

FIG. 4 is a schematic view showing an inversion domain formed for explaining a gray scale display operation of a liquid crystal device according to the present invention.

FIG. 5 is a schematic diagram for explaining a potential change by a conventional potential gradient method.

FIG. 6 is an equivalent circuit diagram of electrodes for explaining the principle of potential change.

FIG. 7 is a diagram showing the relationship between the applied voltage and the transmittance of a liquid crystal element.

FIG. 8 is a block diagram of a display device using a liquid crystal element according to the present invention.

Front page continued (72) Inventor Masaaki Shibata 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Shinjiro Okada 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (8)

[Claims] 1. A liquid crystal element in which a liquid crystal is sandwiched between a pair of electrodes, wherein different spaces are formed on at least one of the electrodes in a pixel formed at an intersection with the other electrode. A plurality of stripe-shaped convex portions formed so as to change the space between the convex portions so as to form a gradient within the pixel, and act on the liquid crystal along the gradient of the change in the space. A liquid crystal element comprising means for forming a distribution gradient of electric field strength. 2. The liquid crystal device according to claim 1, wherein the change of the space has a gradient over one pixel. 3. The liquid crystal device according to claim 1, wherein the stripe-shaped convex portion has a height of 5 to 15% of a cell thickness used. 4. A liquid crystal element in which a liquid crystal is sandwiched between a pair of electrodes, at least one of the electrodes being supplied with power.
In one pixel formed at the intersection of the low-resistance striped electrode and the other electrode, and a plurality of independently formed second striped electrodes with different intervals are provided, and A liquid crystal element comprising a film having a sheet resistance of 10 ⁴ Ω / □ or more and 10 ⁸ Ω / □ or less between the first and second striped electrodes. 5. The liquid crystal device according to claim 4, wherein the change in the interval has a gradient over one pixel. 6. The liquid crystal device according to claim 4, wherein the striped electrode forms a convex portion having a height of 5 to 15% of a cell thickness used. 7. A liquid crystal element in which a liquid crystal is sandwiched between a pair of electrodes, wherein different spaces are formed on at least one electrode of the electrodes in a pixel formed at an intersection with the other electrode. It has a plurality of stripe-shaped convex portions formed, the change in the space between the convex portions is formed to have a gradient in the pixel, and along the gradient of the change in the space,
A liquid crystal element, characterized in that a gradient is provided in the distance between the electrodes of the pair of electrode bases. 8. The liquid crystal device according to claim 7, wherein the change of the space is formed so as to form a gradient over one pixel.