JPH03209216A - Liquid crystal element, driving method for the same and liquid crystal display device - Google Patents

Abstract

PURPOSE:To display a half tone and to enable multilevel display without increasing the number of electrodes by providing a pattern having one electrode lack part at the electrode in each picture element at least and impressing a prescribed pulse voltage. CONSTITUTION:On an upper glass base 1, stripe-shaped transparent electrodes Y1-Y4 equipped with an electrode lack part 5a are formed and on a lower glass base 2, stripe-shaped transparent electrodes X1-X4 without the electrode lack part are formed. When a matrix driving waveform is impressed to such a liquid crystal panel, for the dark/bright state of the picture element, the area executing hutching is turned to the dark state. In such a way, since the state of the electrode lack part 5a provided in the picture element is controlled by the voltage to be impressed to the electrode, the multilevel display can be obtained with the same number of electrodes as normal ferroelectric liquid crystal. Thus, the stable multilevel display is obtained by a pair of picture element electrodes.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a liquid crystal element having a ferroelectric liquid crystal as a liquid crystal layer, a driving method thereof, and a display device.

2. Description of the Related Art As a conventional ferroelectric liquid crystal element, there is, for example, a structured liquid crystal display panel as shown in FIG. One glass substrate 82
After forming a color filter 83 and a light-shielding layer 84 on top a and covering it with a smoothing layer 85, a transparent electrode 81 is formed, and an interlayer 86 is applied on the surface.

A transparent electrode 81 and an alignment film 8 are disposed on the other glass substrate 82b.
Add 6. These pair of substrates are opposed to each other by a spacer 88 at a certain distance of about 1.5 μm to 5 μIn, and a ferroelectric liquid crystal 80 is injected and aligned between them.

Furthermore, the glass substrates 82a and R2b are deflected to the outside and 87
, analyzer 89 (for example, Mura.1:., Ishikawa et al.:
"High-speed multicolor ferroelectric LCD," Proceedings of the 14th Liquid Crystal Conference, pp. 88-89).Thinned ferroelectric liquid crystals basically have two stable states as shown in Figure 10. In Fig. 10(a) and 10(a), the directions of the liquid crystal molecules are almost aligned, and the spontaneous polarization is directed above and below the normal line of the substrate. By sandwiching the liquid crystal cell, it is possible to create brightness and darkness using the uniform states shown in Figures 1O (a) and (b).A thin ferroelectric liquid crystal panel has such a stable state, and ,
Transitions between these states occur very rapidly depending on the applied voltage, and the characteristics of the applied voltage and amount of transmitted light exhibit steep threshold characteristics. Therefore, a high-capacity, high-contrast display can be obtained using only electrodes in a simple matrix configuration without providing a nonlinear element such as a thin film transistor.

However, ferroelectric liquid crystals can only take a limited stable state as shown in Figure 10, making it difficult to produce multiple gradations. In addition, Figure 10(a) and Figure 10(6) coexist, and a state showing intermediate brightness exists in a narrow voltage range where the state of Figure 10(a) changes to the state of Figure 10(b), but the liquid crystal panel Since there is non-uniformity in thickness, etc., it is difficult to actually achieve stable halftone display. Said FIG. 10(a) and FIG.
In order to display halftones using the mixed state shown in figure (b),
A system in which regions with different thicknesses of the liquid crystal layer are provided within each pixel has also been proposed (for example, Iwai, Wakita et al.: ``Gradation Display of Ferroelectric Liquid Crystals'', Proceedings of the 13th Liquid Crystal Symposium). , 13
(pp. 8-139), this method requires a complicated manufacturing process for the liquid crystal panel, leading to an increase in cost.

Therefore, surface-stabilized ferroelectric liquid crystals usually have basically two
In value display, gradation is produced by multiple picture elements or multiple scans (for example, Leroux et al.: Proceedings of the 1988 International Display Research Conference, 1).
Page 11 (T.LEROtlX.F.BAUMB.et.
al. : 1988 INTERNATIONAL
DISPl. AY RESEACH CONFEREN
CE, pll1-1133).

However, this method has problems such as an increase in the number of drive circuits. Therefore, in patent application No. 1-2422, we have disclosed a method for stably displaying halftones with a small number of drive circuits by applying a voltage to a region between picture elements through picture element electrodes.

Problems to be Solved by the Invention Conventionally, ferroelectric liquid crystals use multiple picture elements to display gradations, but this increases the number of electrodes, makes the electrode pattern finer, and increases the number of drive circuits. Therefore, the cost will increase. In addition, the method using pixel gaps requires a complicated driving method.
There are issues such as not being able to freely change the shape of the gap. Means for Solving the Problems In order to solve the above problems, the liquid crystal element of the present invention has a ferroelectric liquid crystal sandwiched between substrates having electrodes on opposing surfaces and forming matrix-like picture elements, and each picture element By applying a predetermined pulse voltage, the first electrode sandwiched between the opposing electrodes has a pattern in which at least one electrode is missing.
By switching the stable state of the region W41 and the second region on the missing electrode part, it is possible to display halftones by the combination of brightness and darkness of the region W41 and the second region, and it is possible to display many gray scales without increasing the number of electrodes. Gradation display is possible.

When a minute electrode missing part exists in the active picture element, the second area above the electrode missing part also responds to the electric field in the same way as the first area sandwiched between the upper and lower electrodes, and the second area responds to the electric field. It assumes a stable state similar to the first region. Although the threshold voltage of the liquid crystal in the second region is higher than the threshold 4m voltage in the first region, the stable state can be switched by applying a sufficient voltage and pulse width. The response of a ferroelectric liquid crystal is roughly proportional to the product of voltage and pulse width, but for simplicity, we assume a liquid crystal panel with one single-width electrode missing part in each pixel and fix the pulse width. The threshold voltage at which the stable state of the liquid crystal in the first region switches from bright to dark and from dark to bright when
, the voltages applied to the electrodes when the stable state of the second region switches from bright to dark and from dark to bright are −Vsd, Vs
b, there is a relationship of Vsd>Vpd and Vsb>Vpb. The threshold voltage ■sd of the second region,
Vsb increases as the width of the electrode missing portion increases. One Vs
After darkening both the first region and the second region with a voltage equal to or lower than d, the voltages applied to the picture elements during the selection period are set to v1 and v.
2. As v3, if there is a relationship of V1≧Vs b>V2>Vpb>V3, when the applied voltage is v1, the first region,
Both the second areas are in a bright state; at V2, only the first area is bright and the second area is dark; at (3), both are in a dark state. Therefore, when using v2, intermediate brightness can be obtained in one scan, and since V2 has a voltage range of Vsb>V2>Vpd, stable halftone display can be achieved even if there is unevenness in the liquid crystal panel. It is possible.

The intermediate brightness depends on the area of the electrode missing part provided within the picture element,
The area of the electrode missing part provided within the picture element is one-third of the picture element area.
By setting it to , evenly spaced halftones can be obtained. In addition, by providing N electrode missing parts with different widths within a picture element, it is possible to display N+2 gradations in one scan, and 2"-2" in N+1 scans.
'itl! In addition, if the width of the electrode missing part is large, the values of ■1 and ■3 are too far apart, so it cannot be controlled with one scan, but a scan to switch the second area on the electrode missing part By dividing the scanning for switching the first region sandwiched between the electrodes and the first region between the electrodes, writing can be realized by two scannings.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings regarding a liquid crystal element and its driving method.

1 and 2 are a plan view and a sectional view of a liquid crystal element according to an embodiment of the present invention. Electrode missing portion 5a on the upper glass substrate l
, 5b, strip-shaped transparent electrodes Y1 to Y4 have
The lower glass base 12 is provided with striped transparent electrodes X1 to X4 with no electrode missing parts. Electrodes XI-X4, Y1
~The pitch of Y4 is 18 μm, the gap between the electrodes is 2 μm, and the electrodes Y1 to Y4 of the upper glass substrate 1 have a length of 14 μm.
The electrode group was constructed so that each picture element had two electrode missing parts 5 with widths of 2 μm and 4 μm. SiO on both substrates
is deposited from a direction inclined at 82 degrees from the normal line of the substrate, with an orientation of 81
It resembles 113. Ester-based ferroelectric liquid crystal is sealed between the upper and lower substrates, and the thickness of the ferroelectric liquid crystal layer l4 is reduced to 2.
．． It was set to 0 μm. When a matrix driving waveform as shown in Fig. 3 is applied to this liquid crystal panel, the bright and dark states of the picture elements are as shown in Fig. 1, and the hunting area is in the dark state. Figures 4 and 5 are characteristic diagrams obtained by measuring the light transmittance of the liquid crystal panel with the structure shown in Figure 1.The voltage shown in Figure 6 was applied to the picture element, and the pulse width was 1 millisecond. After darkening the entire screen with a 25 volt alternating current pulse, the light transmittance in a stable state was measured after applying an alternating current test pulse with the reverse polarity order. Figure 4 a. b and c are the first region sandwiched between the electrodes, the electrode missing part, when the voltage is fixed at 25 volts and the test pulse width τ is varied! (
5a), the third region on the electrode missing part n(5b)
This is a characteristic curve that measures the light transmittance in the area of 20
The stable state changes at 0 μs, 350 μs, and 500 μs. 5IiJa, b, c are characteristic curves of the first region, second region, and third region when τ is fixed at 500 μs, and the respective threshold voltages are 10 volts and 14 volts.
Porto became 22 Porto. In this way, the first region sandwiched between the electrodes, the second head region and the third region above the electrode missing part both exhibit bistability, and the larger the width of the electrode missing part, the more
It was found that the threshold pulse width and threshold voltage increased.

An example will be described in which 8-gradation display is performed by scanning a plurality of times using the threshold characteristic. A driving waveform as shown in Fig. 3 is applied to the liquid crystal panel, and the first area, the electrode missing part 1 (5a
), and the brightness and darkness of the second region on the electrode missing part II (5b) were combined to perform gradation display. In Figure 3, first reset pulse 3 of ±25 volts, 1 millisecond.
0 is applied to bring the entire pulse area including the first, second, and third regions into a dark state, and then a threshold pulse is applied to the third, second, and first regions, respectively. Scanning was performed three times from 31 to 33 in order from the widest part, and the brightness and darkness of the three parts were independently applied, and a gradation display was made by combining them. For example, in the waveform of FIG. 3, A is the row electrode X of FIG.
B is the voltage applied to column electrode Y3, C is the voltage applied to Xi (Xi, Y3), and this causes the second
It is possible to make only the region in the dark state and the first region and the third region in the bright state.

In the first scan 34, the pulse width is 600 μs, and the polarity of the pulse applied to the picture element is reversed from the reset pulse, so the first, second, and third regions are all bright. become a state. By sequentially shifting this one scanning line at a time, data can be written in the third region on the electrode missing portion n (5b) of each picture element. Next, in the second scan 35, the pulse width is 400 μs, and the first region and the second region are changed to a dark state, but the third region maintains its previous bright state because the threshold voltage is high. do. Thereby, data in the second region on the electrode missing portion 1 (5a) can be written. After sequentially scanning this with each row electrode, 3
In the second scan 36, only the first region is changed to a bright state with a pulse width of 250 μsec, and since the threshold voltage of the first region and the third region is high, the previous state is maintained. This allows data in the first area to be written. These scans made it possible to write data independently in the first area, second area, and third area.

Next, we will show a second example that can display four gradations in one scan. The electrodes of the liquid crystal panel (x1~
X4, Y1 to Y4) pattern with an electrode pitch of 18 μm.
, it is assumed that the gap between the electrodes is 2 μm, and the lower glass substrate (1)
Electrode missing part r (5a) with a width of 1 μm on the upper electrode, 2 μm
A ferroelectric liquid crystal matrix panel having two electrode missing parts II (5b) was used. When the drive waveform shown in Fig. 6 is applied with a pulse width of 250 μs and the light transmittance characteristics of the entire panel are measured, the characteristic diagram shown in Fig. 7 is obtained, and the first region sandwiched between opposing electrodes, the electrode missing part 1 (5a) and the third region on the electrode missing portion II (5b) are added together, and the transmittance is plotted on the vertical axis. 2
At 0 volts the first region responds, at 26 volts the second region responds, and then at 28 volts the third region responds. Therefore pulse $51 250μsec, on voltage 29
volts, bias ratio 1/4, on voltage 29 volts, off voltage 18 volts, intermediate voltage 125 volts [If a selection voltage of 27 volts was applied, 4 gray scales could be displayed in one scan. .

At an intermediate voltage l, only the first region becomes a bright state, and at an intermediate voltage ■, only the first region and the second region become a bright state,
All areas become bright at on-voltage.

As described above, the liquid crystal element of the present invention is the same as the conventional ferroelectric liquid crystal by controlling the state of the electrode missing part provided in the picture element by the voltage applied to the electrode! Large number of poles
Achieve gradation display.

Furthermore, by using the liquid crystal element of the present invention and its driving method, an unprecedented high-definition, large-capacity display device can be realized. A block diagram of the display device is shown in FIG.

In particular, in the case of a pattern in which the pixel pinch is several tens of micrometers or less, by enlarging and projecting the image onto a screen, a large, high-definition, large-capacity, high-contrast, multi-gradation display device can be constructed.

Effects of the Invention The liquid crystal element of the present invention applies a predetermined voltage waveform to the picture element electrode, causes the ferroelectric liquid crystal molecules in the electrode missing part provided in the picture element to respond to the electric field, and switches the stable state. ,1
Stable multi-gradation display can be performed using a pair of picture element electrodes.

[Brief explanation of drawings]

FIG. 1 is a plan view and a cross-sectional view of a liquid crystal element according to an embodiment of the present invention, FIG. 3 is a waveform diagram of a driving method for a liquid crystal element according to the present invention, and FIGS. A characteristic diagram of the liquid crystal element of the present invention, FIG. 6 is a waveform diagram of the applied voltage during characteristic measurement, FIG. 7 is a characteristic diagram of the liquid crystal element of the present invention of the second embodiment, and FIG. FIG. 9 is a block diagram of a display device, FIG. 9 is a configuration diagram of a conventional ferroelectric liquid crystal panel, and FIG. 10 is a schematic diagram of a stable state of ferroelectric liquid crystal molecules. l...upper board, 2...lower board, 3...
...Column electrode group, 4... Row electrode group, 5...
...Electrode missing part, 13...Alignment film, l4...
... Ferroelectric liquid crystal layer, A... Voltage applied to row electrode X1, B... Voltage applied to column electrode Y3,
C... Voltage applied to picture element (Xi, Y3), 30
...Reset pulse, 31...First scan, 32...Second scan, 33...Third
scanning.

Claims (9)

[Claims] (1) By sandwiching a ferroelectric liquid crystal between substrates that have electrodes on opposing surfaces and forming matrix-like picture elements, and having a pattern in which the electrodes in each picture element have at least one electrode missing part. , switching the stable state of a first region sandwiched between opposing electrodes in each picture element and a second region above the electrode missing part,
A liquid crystal device characterized in that an intermediate tone is displayed by a combination of brightness and darkness of the first region and the second region. (2) The liquid crystal element according to claim (1), wherein the liquid crystal element can display multiple gradations by controlling the brightness of the electrode portions and electrode missing portions within the picture element in one scan. (3) Both the first region and the second region exhibit steep response threshold characteristics, the threshold voltages of the first and second regions are different, and stable halftones are displayed. The liquid crystal element according to claim 1, characterized in that: (4) The area ratio of the first region and the second region is 2:
1. The liquid crystal element according to claim 1, which is (5) Claim having a plurality of electrode missing parts with different areas (
1) The liquid crystal element described above. (6) In a method for driving a liquid crystal element in which a ferroelectric liquid crystal is sandwiched between substrates having electrodes on opposing surfaces and forming a matrix of picture elements, a selective scanning voltage is applied to the electrodes, and a selective scanning voltage is applied to the electrodes on the opposing surfaces. By applying a signal voltage corresponding to the image data of the picture element consisting of the electrode to which the selective scanning voltage is applied and the electrode missing part, the first area sandwiched between the opposing electrodes and the electrode missing part are A method for driving a liquid crystal element, characterized by controlling a stable state of a second region. (7) The method for driving a liquid crystal element according to claim (5), wherein the brightness and darkness of the electrode portion and the electrode missing portion within the picture element can be controlled in one scan to display multiple gradations. (8) The method for driving a liquid crystal element according to claim 5, wherein a second scan for controlling the stable state of the electrode portion is performed after the first scan for controlling the stable state of the electrode missing portion. (9) A liquid crystal display having a pattern in which a ferroelectric liquid crystal is sandwiched between substrates that have electrodes on opposing surfaces and form matrix-like picture elements, and each picture element has at least one electrode missing part. applying a selective scanning voltage to the electrode using an element, and applying a signal voltage corresponding to image data of a pixel consisting of the electrode to which the selective scanning voltage was applied and the electrode missing portion to the electrode on the opposing surface; 1. A liquid crystal display device comprising a circuit for realizing a method for driving a liquid crystal element, characterized in that the stable state of a first region sandwiched between opposing electrodes and a second region on an electrode missing portion is controlled by: