JPH09127530A - Liquid crystal element and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a driving margin and a temperature margin and enable an analog gradational display of practical level without making a driving circuit complicated or increasing the cost by suppressing the number of analog gradations low. SOLUTION: A display which uses liquid crystal(FLC) is so constituted as to make a display of >=4 gradations in one pixel PX by arranging the FLC between a couple of substrates 1a and 1b having electrodes 22a and 22b on their opposite surface sides. For each pixel PX, the data electrode 22a is divided into an electrode A and an electrode B, whose division area ratio is controlled corresponding to the number of display gradations. When this FLC display is driven, the divided electrodes A and B are driven independently of each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention In the present invention, a liquid crystal is arranged between a pair of substrates each having an electrode on the opposite surface side (particularly,
A pair of substrates provided with a transparent electrode and an alignment film in this order are arranged to face each other with a predetermined gap, and a ferroelectric liquid crystal is injected into the gap) so that display of four or more gradations can be performed in one pixel. And a driving method thereof.

[0002]

2. Description of the Related Art A liquid crystal display (LCD) using a liquid crystal as a display has features of low power consumption, thinness and light weight, and taking advantage of this, from a clock and a calculator to a computer display and a television receiver. (T
Application to V) is progressing.

Conventionally, a nematic liquid crystal has been used as a liquid crystal in such an LCD. However, as a limit of the nematic liquid crystal, the response speed is slow, and the twisted nematic liquid crystal (TN)
With 100 lines, super twisted nematic liquid crystal (S
TN) also has a limit of 240 lines, and in active matrix driving, the thin film transistor (TF) used
Considering the increase in price due to T), it seems difficult to increase the screen size.

On the other hand, ferroelectric liquid crystal (FLC: ferroelect
R & D to apply ric liquid crystal to display devices has been actively pursued. Regarding FLC, a ferroelectric liquid crystal was first synthesized by Meyer in 1975, and a surface-stabilized ferroelectric liquid crystal capable of domain inversion by an electric field was invented in 1980 by Clark and Lagaard. FLC has a permanent dipole moment in the molecule itself, perpendicular to the long axis of the molecule,
A liquid crystal having spontaneous polarization and switchable by an electric field. An FLC display using the liquid crystal is an excellent one having mainly the following features (1) to (3).

(1) The switching speed is on the order of microseconds, the response is 1000 times faster than that of the TN liquid crystal display, and the high-speed response is excellent. (2) There is basically no twist structure in the molecular arrangement, and there is little viewing angle dependence. (3) Even if the power is turned off, the image is retained, the image has memory properties, and simple matrix driving is possible even for 1000 or more scanning lines that can support high definition.

Accordingly, the FLC display has a high definition,
It is a display that can pursue the performance of low cost and large screen.

Such an FLC display (ferroelectric liquid crystal display element) has a structure as schematically shown in FIGS. 13 and 14, for example. First, a transparent electrode is formed on a transparent glass substrate (Corning 7059, 0.7 mm thick) 1a, 1b.
(100 Ω / □ ITO: Indium tin oxide) 2a and 2b are provided. These transparent electrodes are patterned into stripes by etching, and are formed on the data electrodes 2a and the scanning electrodes 2b which intersect each other in a matrix.

On the transparent electrodes 2a, 2b, obliquely deposited SiO films 3a, 3b are formed as liquid crystal alignment films. In forming the oblique SiO vapor deposition film, the substrate was placed vertically above the SiO vapor deposition source in the vacuum vapor deposition apparatus, and the angle between the vertical line and the substrate normal was set to 85 degrees. SiO
Was vacuum-deposited at a substrate temperature of 170 ° C., and then baked at 300 ° C. for 1 hour.

In the pair of substrates 1a and 1b with the alignment film thus manufactured, the alignment treatment directions on the data electrode side and the scan electrode side are antiparallel on the opposite surfaces, and the electrode array of the data electrodes and the scan electrodes is arranged. Are assembled so that they are orthogonal. Glass beads corresponding to the target gap length as spacers (true sphere: diameter 0.8 to 3.0 μm (manufactured by Catalysts & Chemicals Co., Ltd.)) 4
Is used. Here, the orientation treatment directions are set antiparallel, but they may be set parallel.

Depending on the size of the transparent substrates 1a and 1b, the spacer 4 is placed in a sealing material (UV-curable adhesive (Photorec: manufactured by Sekisui Chemical Co., Ltd.)) 6 for adhering the periphery in the case of a small area. The gap between the substrates was controlled by dispersing about 0.3 wt%. When the substrate area is large, the above-mentioned true spheres on the substrate have an average density of 100 / mm ²
After spraying, a gap was formed, a liquid crystal injection hole was secured, and the periphery of the cell was bonded with a sealant 6.

A liquid crystal composition in which, for example, a ferroelectric liquid crystal (CS-1014 manufactured by Chisso Corporation) 5 is uniformly dispersed at an isotropic phase temperature using an ultrasonic homogenizer is injected between the pair of substrates 1a-1b. Have been. This ferroelectric liquid crystal composition is injected under reduced pressure while exhibiting fluidity at an isotropic phase temperature or a chiral nematic phase temperature. After the liquid crystal is injected, the liquid crystal is slowly cooled to remove the liquid crystal on the glass substrate around the injection hole, and then sealed with an epoxy adhesive to manufacture the FLC display 11.

As a driving method for the FLC display 11, an XY matrix method is used. 1H (1 horizontal scanning time or 1 line selection time) is 63.5 μs, and since the voltage is applied in bipolar, each selection pulse is 63.5 /
The width is 2 μs. A select pulse, which is a threshold value, is applied from the ROW side (electrode 2b), and a data pulse is applied from the COLUMN side (electrode 2a).

However, although the FLC display has the above-mentioned excellent features, it has been pointed out that it is difficult to display gradations. That is, the conventional ferroelectric liquid crystal display using the bistable mode is stable only in two states, and thus has been considered to be unsuitable for gradation display of video or the like. This is particularly remarkable in so-called surface-stabilized ferroelectric liquid crystals in which the helical structure is solved by the interaction with the alignment film, and there are only two stable states, and only binary display in black and white. It was

That is, a conventional ferroelectric liquid crystal element (for example, a surface-stabilized ferroelectric liquid crystal element) has an externally applied electric field E (Ps
15), the orientation direction of the molecule M switches between two states of state 1 and state 2 as shown in FIG. This change in the molecular orientation appears as a change in the transmittance when the liquid crystal element is placed between the orthogonal polarizing plates.
As shown in 16, the transmittance is the threshold voltage V _th for the applied electric field.
Suddenly changes from 0% to 100%. The voltage width at which the transmittance changes is generally 1 V or less. Furthermore, V _th changes due to minute fluctuations in the cell gap. Therefore,
In the conventional FLC liquid crystal element, it is difficult to give a stable voltage width to the curve of transmittance-applied voltage, and gradation display by voltage control is difficult or impossible.

Therefore, a method of performing gradation by providing sub-pixels and adjusting the pixel area (area gradation method)
Further, a method such as a method of performing gray scale by repeating switching during one field by utilizing a high-speed switching property of ferroelectric liquid crystal (time sequential or time integration gray scale method) has been proposed. However, these methods have a problem that gradation display is still insufficient.

In the case of the area gradation method, by dividing one pixel (pixel), the area of one pixel is controlled and halftone is displayed. However,
In order to display 64 gray scales or 256 gray scales required for a TV or the like by this method, one pixel is set to 6 pixels.
It is necessary to divide the pixel into eight and eight.

Therefore, when the pixel division of the six divisions and the eight divisions is actually performed, the number of wirings increases accordingly, and the mounting and the driving circuit are complicated (six times, eight times if the six divisions).
If it is divided, the number of external connections increases eight times). For this reason, the area required for one pixel is limited, which is not suitable for high-definition display. When the number of divisions increases, periodicity occurs in the image, and the image quality deteriorates.

In the case of the time-sequential gradation method, by utilizing the high-speed response of the ferroelectric liquid crystal, by switching black and white n times during one field, 2 ⁿ -level gradation display can be performed. However, when driving with a passive matrix (simple matrix), the time allocated to one line is limited,
For example, when performing video display with an NTSC signal,
Since interlacing is performed, the number of scanning lines is 25
If it is 6, 1H assigned to one line
Is 63 μsec. Using bipolar pulses to avoid electrolysis, the pulse width is 30 μsec.

Therefore, in order to perform the time sequential, it is necessary to perform the switching n times during the 30 μsec. However, when the temperature decreases, the viscosity increases, and the response speed tends to decrease. Therefore, in order to realize, for example, six or more switching operations in a wide temperature range, the response speed of 5 μsec or less is set to a wide temperature range. It must be realized over a range. This is obviously very difficult.

Therefore, as a method of performing analog gray scale display for each pixel, a local distance is changed by changing a distance between opposing electrodes in one pixel or changing a thickness of a dielectric layer formed between opposing electrodes. How to create an electric field strength gradient in
It has been proposed to provide a voltage gradient by changing the material of the counter electrode.

However, the production of a liquid crystal display device having a practical level of analog gradation display characteristics is complicated in terms of steps, the control of the production conditions becomes very difficult, and the production cost is high. was there.

[0022]

Therefore, in order to solve the problems of the prior art, the applicant of the present invention has realized a liquid crystal display element (especially a ferroelectric liquid crystal display) which realizes analog gradation display while maintaining high contrast. Element) has already been proposed as Japanese Patent Application No. Hei 5-262951 and the like (hereinafter, referred to as prior invention).

That is, in a liquid crystal display element in which an electrode layer is formed on the opposing surfaces of a pair of substrates, the effective electric field strength applied to the liquid crystal in one pixel is given a distribution so that It has been found that an analog gray scale display can be achieved by widening the threshold voltage width for switching between the bistable states of the liquid crystal. The prior invention based on this is characterized in that, in a liquid crystal element in which a liquid crystal is arranged between a pair of substrates, regions having different threshold voltages for switching the liquid crystal are finely distributed. Is.

In the liquid crystal device of the prior invention, a pair of substrates provided with a transparent electrode and an alignment film in this order are arranged to face each other with a predetermined gap, as in the display of FIGS. Although it can be configured as a liquid crystal element in which a ferroelectric liquid crystal is injected, it is fundamentally different in the following points.

That is, the above "fine distribution of regions having different threshold voltages" means that the transmittance due to the inversion domain (for example, black domain in white domain or vice versa).
At 25%, there are 300 or more (preferably 600 or more) domains (microdomains) with a size of 2 μmφ or more in the field of view of 1 mm ² , and the threshold voltage width within that domain. Means that the transmittance is 1 V or more in the range of 10 to 90%.

Therefore, as illustrated in FIG. 17, in the liquid crystal element of the invention of the prior application, the transmittance does not change sharply as shown in FIG. 16 but rather shows a relatively gradual change. . This is because, as described above, in particular, in one pixel, micro-domains having different threshold voltages (V _th ) are developed, and the transmittance of the micro-domains is changed according to the magnitude of the applied voltage. Is changed. Further, in one domain, when the liquid crystal molecules are bistable, it has a memory function, and one pixel is formed from domains of μm order with different threshold voltages, which enables continuous gradation display. .

In FIG. 17, when the threshold voltage at which the transmittance changes is _Vth1 when the transmittance is 10% and _Vth2 is when the transmittance is 90%, the change width of the threshold voltage ( ΔV _th =
V _th2- V _th1 ) is 1 V or more.

Regarding the micro domain, FIG. 18 (A)
As shown in (1), when the transmittance is 25%, the domain MD having a size of 2 μmφ or more exists at a rate of 300 or more / mm ² . Due to the fine light transmission part by such a micro domain, a halftone screen (transmittance) as a whole
However, since such a structure based on a microdomain has a so-called starry sky-like appearance, it will be referred to as a “starlight texture” below.

According to this starlight texture, the light transmitting portion MD by the micro domain is expanded (increased transmittance) or reduced according to the magnitude of the applied voltage as shown by the dashed line in FIG. 18 (A). The transmittance can be reduced, and the transmittance can be arbitrarily changed by the applied voltage. Contrary to this, in the elements of FIGS. 13 and 14,
As shown in FIG. 18 (B), since the threshold voltage width is extremely small, the light transmitting portion D due to the applied voltage only abruptly increases or disappears, and gradation display is extremely difficult. is there.

In the invention of the prior application, ultrafine particles can be dispersed in the liquid crystal 5 in the liquid crystal cell as a means for forming the above-mentioned microdomains.

The change in threshold voltage due to ultrafine particles will be described in principle with reference to FIG. When the particle size of the ultrafine particles 10 is d ₂ , the dielectric constant is ε ₂ , the thickness of the liquid crystal 5 excluding the ultrafine particles 10 is d ₁ , and the dielectric constant is ε ₁ , the electric field Eeff applied to the ultrafine particles is given by the following equation (1) ). Eeff = (ε ₂ / (ε ₁ d ₂ + ε ₂ d ₁ )) × Vgap (1)

Therefore, when ultrafine particles having a dielectric constant smaller than that of liquid crystal are added (ε ₂ <ε ₁ ), the total thickness dga of the liquid crystal layer is increased.
By introducing fine particles (d ₂ ) smaller than p (= d ₁ + d ₂ ), Eeff <Egap, and a smaller electric field Eeff acts on the liquid crystal as compared with the case where no fine particles are inserted (Egap). Conversely, by adding fine particles having a dielectric constant larger than that of the liquid crystal (ε ₂ > ε ₁ ), Eeff> Egap, and the electric field Eeff is larger than in the case where no fine particles are added to the liquid crystal (Egap). Works.

The above is summarized as follows. When ε ₁ > ε ₂ → Eeff <(Vgap / d ₁ + d ₂ )
= Vgap / dgap = Egap ε ₁ = ε ₂ → Eeff = Egap ε ₁ <ε ₂ → Eeff> Egap

In any case, the addition of the ultrafine particles changes the effective electric field Eeff applied to the liquid crystal itself, and the effective electric field applied to the liquid crystal differs between the region where the ultrafine particles exist and the region where the ultrafine particles do not exist. . As a result, even if the same electric field Egap is applied, there is a region where the inversion domain is generated and a region where the inversion domain is not generated.
The starlight texture structure as shown in (A) can be expressed.

From this, the starlight texture structure according to the invention of the prior application is suitable for realizing continuous gradation, and the applied voltage (size, pulse width, etc.) is controlled under the addition of ultrafine particles (ie, By applying two or more kinds of voltages, various transmittances (that is, two or more kinds of gradation levels) can be obtained. On the contrary, if only the fine particles are present, only the one as shown in FIG. 18 (B) can be obtained, and in particular, in a minute (about 2 μm) gap,
It is clear that the desired display performance cannot be obtained even when the 2 μm fine particles are present, and color unevenness is caused by the fine particle portions even if the gap is not a minute gap. In the invention of the prior application, the desired performance can be obtained without causing such a phenomenon.

In the liquid crystal element of the invention of the prior application, the fine particles added to the liquid crystal have the effective electric field strength applied to the liquid crystal 5 existing between the opposing transparent electrode layers 2a and 2b shown in FIGS. It is only necessary that the particles have a distribution, and, for example, particles of a plurality of materials having different dielectric constants can be mixed and used. The presence of fine particles having different permittivities in this way forms a permittivity distribution in each pixel. As a result, as described above, even when the external electric field is uniformly applied between the transparent electrode layers 2a and 2b of the pixel, the effective electric field strength applied to the liquid crystal in the pixel can be distributed, and the liquid crystal (especially strong liquid crystal) can be distributed. The distribution width of the threshold voltage for switching between bistable states of the dielectric liquid crystal) can be widened, and analog gray scale display can be performed within one pixel.

When fine particles having the same dielectric constant are used, the fine particles may have a size distribution. As described above, the presence of the fine particles having different dielectric constants but different sizes allows distribution in the thickness of the liquid crystal layer. As a result, even when an external electric field is applied uniformly between the transparent electrode layers 2a and 2b of one pixel, the effective electric field intensity applied to the liquid crystal in that pixel is distributed, and analog gradation display is performed in one pixel. Becomes possible. Regarding the distribution of the size of the fine particles, it is preferable that the spread of the distribution is large to some extent because excellent analog gradation display can be performed.

In the liquid crystal element of the prior invention, it is desirable that the fine particles added to the liquid crystal have a surface with a pH of 2.0 or more.
This is because when the pH is less than 2.0, the acidity is too strong and the liquid crystal is easily deteriorated by the protons.

The amount of the fine particles is not particularly limited and can be appropriately determined in consideration of the desired analog gradation, etc., but it is 50% by weight or less and 0.1% by weight or more in the liquid crystal. It is desirable that it is added. If the added amount is too large, the aggregated particles are less likely to form a starlight texture structure, and the injection of liquid crystal tends to be difficult.

The fine particles that can be used may be composed of carbon black and / or titanium oxide, the carbon black is carbon black produced by the furnace method, and the titanium oxide is preferably amorphous titanium oxide. The pyrolytic carbon black produced by the furnace method has a relatively wide particle size distribution of fine particles, and the amorphous titanium oxide has good surface properties and excellent durability.

The usable fine particles are in the state of non-aggregated primary fine particles and have a size of less than half the liquid crystal cell gap.
(0.4 μm or less, particularly 0.1 μm or less) is preferable. Also,
The gradation display characteristics can be controlled by the particle size distribution, but it is desirable that the standard deviation of the particle size distribution is 9.0 nm or more, since the change in transmissivity (transmittance) can be moderated. It is desirable that the specific gravity of the fine particles is 0.1 to 10 times that of the liquid crystal from the viewpoint of preventing sedimentation when dispersed in the liquid crystal,
Further, the fine particles are preferably surface-treated with a silane coupling agent or the like so as to exhibit good dispersibility.

In the invention of the prior application, the fine particles need to be present between the electrodes facing each other, but the location thereof is not particularly limited and may be in the liquid crystal, in the liquid crystal alignment film or on the liquid crystal alignment film. The configuration other than the presence of the fine particles between the electrodes facing each other can be the same as that of the liquid crystal display element (particularly the ferroelectric liquid crystal display element) of FIGS. 13 and 14. For example, a transparent glass plate is used as the substrate, ITO or the like is used as the electrode layer, and a rubbed polyimide film or S is used as the liquid crystal alignment film.
An iO orthorhombic vapor deposited film can be used. The drive system may be the same as that described above. However, in order to express the gray scale with the above-mentioned micro domain texture, since it is obtained by changing the voltage of the data pulse, it is always 1
The data pulse is applied to the entire frame.

The present inventor has studied the above-mentioned prior invention, and in order to effectively realize the various features described above, it is necessary to solve the following problems in driving the FLC display. I found that.

That is, regarding the driving margin at the time of driving the FLC display, for example, in order to perform 256 gradations with an analog signal, the margin of the signal level of each part constituting the element (the response speed of the liquid crystal, the electrode and its wiring, It is self-evident that the allowable range of conductivity etc.) becomes smaller than that when the number of gradations is small. Due to this, it is necessary to take measures such as limiting the parts to be used and suppressing the variation of parts between elements.

Further, the temperature dependence of the threshold voltage of the ferroelectric liquid crystal is larger by one digit than that of the conventional nematic liquid crystal, which means that the driving margin decreases as the number of gradations increases. Things are accelerating. Therefore, regarding the material problem, the lower the number of gradations, the less the influence of the change in threshold voltage due to temperature, the less the temperature dependence, and the greater the margin with respect to temperature.

However, in the invention of the prior application, since the gray scale display in the pixel can be controlled by the applied voltage as described above, when it is desired to increase the number of gray scales as the display, corresponding to this. It is necessary to change the applied voltage in various ways. However, as described above, there is a limitation in increasing the number of gray levels in a pixel, and in order to secure a driving margin and a temperature margin, change in applied voltage (the number of gray levels in a pixel) is reduced as much as possible. Is desired.

[0047]

SUMMARY OF THE INVENTION An object of the present invention is to increase the driving margin and the temperature margin by keeping the number of gray scales in a pixel low while making use of the features of the invention of the prior application described above. It is an object of the present invention to provide a liquid crystal element and a driving method capable of implementing gradation display without complicating a driving circuit and increasing costs.

[0048]

That is, according to the present invention, a liquid crystal is arranged between a pair of substrates each having an electrode on the opposite surface side, and four or more gradations (ie, 2 ⁿ (n ≧ n The number of gradations in 2): The same applies hereinafter), the electrode is divided in each pixel, and the division area ratio is controlled according to the number of display gradations. It is related to.

Further, according to the present invention, the liquid crystal is arranged between a pair of substrates each having an electrode on the opposite surface side, and a liquid crystal is arranged in one pixel.
The electrode is divided in each pixel so as to be capable of displaying more than the gradation, and the divided area ratio is divided when driving the liquid crystal element controlled according to the number of display gradations. The present invention also provides a method for driving a liquid crystal element, in which each electrode is independently driven.

[0050]

BEST MODE FOR CARRYING OUT THE INVENTION In the liquid crystal element and the method of driving the same according to the present invention, in each pixel formed by overlapping the data electrode and the select electrode, the data electrode is preferably divided into two.

Further, the divided area ratio of the electrodes is 1: 8, and the number of gray levels in the pixel is 8, and each of the divided electrodes can be independently driven to display 64 gray levels.

Alternatively, the divided area ratio of the electrodes is 1:16 and the number of gray levels in the pixel is 16, and each of the divided electrodes can be independently driven to display 256 gray levels.

Actually, the in-pixel gradation display is realized by giving a distribution to the effective electric field applied to the liquid crystal.

In this case, it is desirable to use the starlight texture structure as described above in which regions having different threshold voltages for switching the liquid crystal are finely distributed.

In particular, it is preferable to add ultrafine particles to the ferroelectric liquid crystal to realize gray scale display in the pixel.

In the pixel, a distribution can be provided in the effective electric field by providing a distribution in the distance between the electrodes of the pair of bases.

Alternatively, the effective electric field can be provided by providing a dielectric constant distribution in the pixel.

According to the desirable constitution of the liquid crystal element of the present invention, the constitution and material of the liquid crystal element, including the presence of the fine particles between the opposing electrodes, may be the same as those of the above-mentioned prior invention. , I will not explain it again here. Further, for example, a transparent glass plate can be used as the substrate, ITO or the like can be used as the electrode layer, and a rubbing-treated polyimide film or SiO oblique deposition film can be used as the liquid crystal alignment film.

[0059]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 The structure of the ferroelectric liquid crystal (FLC) display according to this example is basically the same as that based on the above-mentioned prior invention except for the shape of the data electrode. That is, CS-1014 manufactured by Chisso Corporation was used as the FLC. As ultrafine particles for forming the starlight texture structure,
1 wt% FL of amorphous titanium oxide with an average particle size of 17 nm
It was added to C, heated to 120 ° C. which is an isotropic temperature region, and sufficiently dispersed by an ultrasonic homogenizer. Then, it was gradually cooled.

Further, an ITO electrode (100 Ω / □) was coated on each of a pair of glass substrates each having a thickness of 3 mm and a size of 25 × 60 mm, and patterned in stripes to form a data electrode and a select electrode. SiO was vacuum-deposited on this by a resistance heating method at an incident angle of 85 °. This evaporated film thickness is
It was controlled to 60 nm. The substrates were made parallel to each other, and the periphery was screen-printed with a mixture of 1.6 μm silica spacers (true spheres) in an ultraviolet curable resin (Photorec: Sekisui Chemical Co., Ltd.) to make the cell gap 1.6.
μm.

In order to inject the above-mentioned FLC containing ultrafine particles into a cell, FLC is applied to the inlet of the cell at room temperature, the empty cell is heated to 140 ° C., and the FLC is allowed to undergo a phase transition to isotropic. , And was injected into the gap between the pair of substrates by decreasing the viscosity. Then, it was gradually cooled to SmC ^* , which is room temperature, for molecular orientation.

In the FLC display thus manufactured, the data electrode 22a is formed into a shape as shown in FIGS.
And select electrodes 22b are formed on each of the substrates 1a and 1b (however, in reality, a large number of each electrode is provided, but a part of the electrode is shown enlarged for simplification: hereinafter the same).

That is, the data electrode 22a provided on the substrate 1a is asymmetrically divided into the A electrode and the B electrode, and the area ratio of these is set to 1: 8 in one pixel. 2 shows the structure of the data side electrode, FIG. 3 shows the structure of the select side electrode, and
4 and 5 show the case where the data electrode is the front surface and the case where the data electrode is the back surface, respectively.
The method of combining b is shown. In an actual device, ITO electrodes (data electrode 22a and select electrode 22b)
Are assembled so as to face each other, and their intersections become pixels (PX) PX. An external connection portion for connecting each electrode to the drive circuit is led out at the end of each substrate.

When driving this FLC display, the applied voltage-contrast relationship shown in FIG. 7 was obtained by applying the pulse having the waveform shown in FIG. 6 (in the case where ultrafine particles are not added to the liquid crystal in FIG. 7). Also shown). It is understood that the range of the threshold voltage V _th is expanded by the addition of the ultrafine particles, and the tonality within the pixel due to the applied voltage is likely to be obtained accordingly.

That is, as shown in FIG. 7, by controlling the applied voltage, the transmittance or the contrast can be controlled in eight steps according to the data voltage. Therefore, by performing such control on each of the divided electrodes A and B, it is possible to independently drive 8 gradations with the A electrode and 8 gradations with the B electrode.

At this time, since the amount of transmitted light is determined according to the area ratio of the A electrode and the B electrode, it can be controlled as shown in FIG. That is, assuming that the electrodes A + B are one pixel PX, the total amount of transmitted light is first A when the B electrode of the larger size displays black, until the amount of light reaches 0.142.
The electrode can control in 8 steps. Next, the light intensity of the B electrode is increased by one step from the black side, and in this state, the same fine adjustment as above can be performed in eight steps by the A electrode until the light intensity becomes 0.285.

In this way, the maximum amount of light can be changed in 64 steps by combining the A electrode and the B electrode. That is, it can be seen that 8 × 8 = 64 gradations can be displayed.

From the above, according to the present embodiment, even with a material having a low gradation number of 8 gradations, a gradation display of 64 gradations of a practical level can be realized as a device.

By suppressing the number of analog gradations to a low level, it is possible to increase the driving margin and the temperature margin.

Further, since the electrodes are divided into only two in the pixel, the complication of the mounting and the driving circuit can be suppressed to the minimum and the cost of the driving circuit and the panel cannot be greatly increased.

Example 2 An FLC display was prepared and driven in the same manner as described in Example 1. However, the data electrode 32a is asymmetrically divided into the A electrode and the B electrode, and the area ratio of these is set to 1:16 in one pixel. FIG. 9 shows the structure of the data side electrode, FIG. 3 shows the structure of the select side electrode, and FIGS.
Shows the case where the data electrode 32a is the front surface and the case where the data electrode 32a is the back surface, and shows how to combine the data electrode 32a and the select electrode 22b.

When driving this FLC display, the same applied voltage-contrast relationship as shown in FIG. 7 was obtained by applying the pulse having the waveform shown in FIG.

As shown in FIG. 7, by controlling the applied voltage, the transmittance or contrast can be controlled in 16 steps according to the data voltage. Therefore,
By performing such control on each of the divided electrodes A and B, it is possible to independently drive 16 gradations with the A electrode and 16 gradations with the B electrode.

At this time, the amount of transmitted light is determined according to the area ratio of the A electrode and the B electrode, and can be controlled as shown in FIG. That is, assuming that the electrodes A + B are one pixel PX, the total amount of transmitted light is first A when the amount of light is 0.0666 when the larger B electrode displays black.
It can be controlled in 16 steps with electrodes. Next, the light intensity of the B electrode is increased by one step from the black side, and the same fine adjustment as above can be performed in 16 steps with the A electrode until the light intensity becomes 0.133 in this state.

In this way, the maximum amount of light can be changed in 256 steps by combining the A electrode and the B electrode. That is, it can be seen that 16 × 16 = 256 gradations can be displayed.

From the above, according to this embodiment, 16
Even with a material having a gradation and a low gradation number, a gradation display of 256 gradations of a practical level can be realized as a device.

As in the first embodiment, by suppressing the number of analog gray scales to a low level, it is possible to increase the driving margin and the temperature margin.

Further, since the electrodes in the pixel are divided into only two, the complication of the mounting and the driving circuit is suppressed to the minimum, and the cost of the driving circuit and the panel is not significantly increased.

Example 3 An FLC display was prepared and driven in the same manner as described in Example 1. However, the data electrode 42a is asymmetrically divided into an A electrode, a B electrode, and a C electrode as shown in FIG. 12A or 12B, and the area ratio of these is set to 1: 8: 3 within one pixel. I chose Here, the data electrode 42a of FIG.
Similarly, the data electrode of FIG. 12 (b) is extended to the external connection portion, and each pixel is individually led to the end portion of the substrate by wiring to be connected to the outside.

When driving this FLC display, the same applied voltage-contrast relationship as shown in FIG. 7 was obtained by applying the pulse having the waveform shown in FIG.

As shown in FIG. 7, by controlling the applied voltage, the transmittance or the contrast can be controlled in eight steps according to the data voltage. Therefore, by performing such control on the divided electrodes A, B, and C, respectively, the A electrode has 8 gradations, the B electrode has 8 gradations, and the C electrode has 8 gradations.
The electrodes can be independently driven in 8 gradations.

At this time, the amount of transmitted light is A electrode, B electrode and C
Since it is determined according to the area ratio of the electrodes, it can be controlled in the same manner as described above. That is, if the electrodes A + B + C are used as one pixel PX, the total amount of transmitted light can be controlled in eight steps for each of the A electrode and the C electrode when the B electrode of the larger size displays black. Next, increase the amount of light in the B electrode to the one side brighter than the black side, and in this state, perform the same fine adjustment as above with the A electrode or the C electrode.
It can be done in stages.

In this way, the maximum light amount can be changed in at least 64 steps by combining the A electrode, the B electrode, and the C electrode. That is, it can be seen that 8 × 8 = 64 gradations can be displayed.

However, in the present embodiment, when the A electrode and the B electrode are driven simultaneously, the result is basically the same as the case of the division area ratio of 1: 8 described in the first embodiment, but the A electrode and Since the B electrode can be driven separately, various combinations with the C electrode can be realized by driving only one of them or fixing one of them to a constant voltage as necessary, and the transmitted light level Can be changed.

Also in this embodiment, a material having a low gradation number can be used, and a gradation display of a practical level can be realized as a device.

As in the first embodiment, by suppressing the number of analog gray scales to a low level, it is possible to increase the driving margin and the temperature margin.

Furthermore, since the number of electrode divisions in the pixel is as small as three, the complication of the mounting and drive circuits is suppressed to the minimum, and the drive circuit and panel costs are not significantly increased.

Although the present invention has been described with reference to the embodiments, the embodiments described above can be further modified based on the technical idea of the present invention.

For example, the division area ratio of the data electrode, the number of gradations (the number of gradations in a pixel 2 ⁿ can be changed within a range of n ≧ 2), the division shape, the division pattern, the number, etc. are variously changed. Good. Further, in the driving method, the gray scale within one pixel can be realized not only by the modulation of the pulse voltage but also by the modulation of the pulse width or a combination of these.

In addition, the type of liquid crystal, the material, structure, shape and assembling method of each component of the liquid crystal element, and the physical properties of ultrafine particles used for forming fine microdomains,
The type and the like can be changed in various ways. Further, the method of adding the ultrafine particles may be changed, and the distribution position thereof may be not only in the liquid crystal but also on the alignment film or in the alignment film.
Further, a method other than the above, for example, stacking of a charge transfer complex such as a tetrathiafulvalene-tetracyanoquinodimethane complex can be used to form the microdomain.

It is also possible to provide a distribution in the distance between the electrodes of the pair of substrates in the pixel to give an effective electric field distribution, or to provide a dielectric constant distribution in the pixel to give an effective electric field distribution.

Although the liquid crystal element suitable for the display element has been described in the above-mentioned embodiments, the display element is preferable in that the gradation (halftone) can be realized.
However, the present invention is not limited to the display element, and can be applied to a liquid crystal element such as a filter or a shutter, a display screen of an OA device, a screen, a phase control element for wobbling, or the like. In any of these, it is possible to obtain a performance that has not been heretofore utilized by utilizing the fact that the above-described threshold voltage width exhibits the transmittance or the contrast ratio according to the drive voltage.

[0094]

According to the liquid crystal element and the driving method thereof of the present invention, the electrodes are divided in each pixel, and the division area ratio is controlled in accordance with the number of display gradations. It is possible to independently apply a voltage required for gradation display in a part and combine them to obtain a target number of display gradations. Therefore, the change in applied voltage to the electrodes,
That is, since the number of analog gray scales in a pixel can be kept low within a range of 4 gray scales or more, signal level margins of respective parts constituting the element (response speed of liquid crystal used when driving the element, electrode And the allowable range of the conductivity of the wiring) can be widened. Moreover, even if the threshold voltage of the liquid crystal used changes with temperature, it is possible to reduce the effect of this on the gradation, reduce the temperature dependence, and increase the temperature margin.

The number of electrode divisions in a pixel does not have to be increased as long as the required number of gray levels is satisfied, and two divisions are sufficient. Therefore, the mounting and drive circuit can be simplified and the cost increase can be suppressed. You can

[Brief description of the drawings]

FIG. 1 is a transmitted light amount-voltage characteristic diagram showing gradation level control of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a plan view showing a data electrode pattern of the liquid crystal display element.

FIG. 3 is a plan view showing a select electrode pattern of the liquid crystal display element.

FIG. 4 is a plan view of the data electrode side of the liquid crystal display element in a state where the data electrode and the select electrode are overlapped with each other.

FIG. 5 is a plan view on the select electrode side in a state where the data electrode and the select electrode of the liquid crystal display element are overlapped with each other.

FIG. 6 is a drive waveform diagram of the liquid crystal display element.

FIG. 7 is a contrast-voltage characteristic diagram showing a threshold voltage characteristic of the liquid crystal display element.

FIG. 8 is a transmitted light amount-voltage characteristic diagram showing gradation level control of a liquid crystal display device according to another embodiment of the present invention.

FIG. 9 is a plan view showing a data electrode pattern of the liquid crystal display element.

FIG. 10 is a plan view of the data electrode side of the liquid crystal display element in a state where the data electrode and the select electrode are overlapped with each other.

FIG. 11 is a plan view of the select electrode side in a state where the data electrode and the select electrode of the liquid crystal display element are overlapped with each other.

FIG. 12 is a data electrode pattern diagram in a pixel of a liquid crystal display device according to still another embodiment of the present invention.

FIG. 13 is a plan view of a select electrode side of a liquid crystal display element according to a conventional example.

14 is a sectional view taken along line XIV-XIV in FIG. 13.

FIG. 15 is a model diagram of a ferroelectric liquid crystal.

FIG. 16 is a transmittance-applied voltage characteristic diagram showing a threshold voltage characteristic of a liquid crystal display element according to a conventional example.

FIG. 17 is a transmittance-applied voltage characteristic diagram showing a threshold voltage characteristic of the liquid crystal display element based on the prior application.

FIG. 18 is a schematic diagram (A) for explaining a change in the transmittance of the liquid crystal display element at the time of switching, and the same diagram (B) is a similar schematic diagram when there is no gradation.

FIG. 19 is a schematic diagram for explaining an effective electric field in liquid crystal of the liquid crystal display element.

[Explanation of symbols]

1a, 1b ... Substrate 2a, 2b ... Transparent electrode layer 3a, 3b ... SiO oblique deposition layer 4 ... Spacer 5 ... Liquid crystal (FLC) 10 ... Ultra fine particle 11 ... FLC display 22a, 32a, 42a ... Data electrode 22b ... Select electrode PX ... Pixel (pixel) _Vth ... Threshold voltage MD ... Micro domain D ... Domain Eeff ... Effective electric field

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hiroaki Endo 6-735 Kitashinagawa, Shinagawa-ku, Tokyo Sony Corporation

Claims (18)

[Claims] 1. A liquid crystal is arranged between a pair of substrates each having an electrode on the opposite surface side, and is configured to display four or more gradations in one pixel, and the electrode is divided in each pixel. A liquid crystal element whose divided area ratio is controlled according to the number of display gradations. 2. The liquid crystal element according to claim 1, wherein in each pixel formed by overlapping a data electrode and a select electrode, the data electrode is divided into two. 3. The divided area ratio of the electrodes is 1: 8, the number of gray scales in a pixel is 8, and each divided electrode can be independently driven to display 64 gray scales. The liquid crystal element according to claim 1. 4. The divided area ratio of the electrodes is 1:16 and the number of gray levels in the pixel is 16, and each of the divided electrodes can be independently driven to display 256 gray levels. The liquid crystal element according to claim 1. 5. The liquid crystal element according to claim 1, wherein an in-pixel gradation display is realized by giving a distribution to an effective electric field applied to the liquid crystal. 6. The liquid crystal device according to claim 5, wherein regions having different threshold voltages for switching the liquid crystal are finely distributed. 7. The liquid crystal device according to claim 5, wherein ultrafine particles are added to the ferroelectric liquid crystal to realize gray scale display in a pixel. 8. The liquid crystal element according to claim 5, wherein a distribution is provided in an effective electric field by providing a distribution in a distance between electrodes of a pair of substrates in a pixel. 9. The liquid crystal element according to claim 5, wherein a dielectric constant distribution is provided in each pixel so that the effective electric field has a distribution. 10. A liquid crystal is arranged between a pair of substrates each having an electrode on the opposite surface side, and is configured to display four or more gradations in one pixel, and the electrode is divided in each pixel. A driving method of a liquid crystal element, wherein each of the divided electrodes is independently driven when driving the liquid crystal element whose divided area ratio is controlled corresponding to the number of display gradations. 11. The driving method according to claim 10, wherein the data electrode is divided into two in each pixel formed by overlapping the data electrode and the select electrode. 12. The divided area ratio of the electrodes is set to 1: 8, the number of gray levels in the pixel is set to 8, and each divided electrode can be independently driven to display 64 gray levels. Driving method described in 10. 13. The display device is capable of displaying 256 gray scales by independently driving each of the divided electrodes with a division area ratio of the electrodes of 1:16 and a gray scale number within a pixel of 16 gray scales.
Driving method described in 10. 14. The driving method according to claim 10, wherein gray scale display in a pixel is realized by providing a distribution in an effective electric field applied to the liquid crystal. 15. The driving method according to claim 14, wherein regions having different threshold voltages for switching the liquid crystal are finely distributed. 16. The driving method according to claim 14, wherein ultrafine particles are added to the ferroelectric liquid crystal to realize gray scale display in a pixel. 17. The driving method according to claim 14, wherein a distribution is provided in an effective electric field by providing a distribution in a distance between electrodes of a pair of bases in a pixel. 18. The driving method according to claim 14, wherein a dielectric constant distribution is provided in each pixel so that the effective electric field has a distribution.