JPS62253126A - Driving method for liquid crystal element - Google Patents

Abstract

PURPOSE:To eliminate deterioration due to a DC component by making the width of a voltage pulse applied to liquid crystal invariably constant during a nonselection period and also setting the mean value of DC components of positive and negative voltages pulses to zero. CONSTITUTION:Scanning electrodes 23 and signal electrodes 24 are provided in a lattice shape on the opposite surfaces of a couple of substrates 21 and 22, and liquid crystal is oriented. The liquid crystal is ON in a selection period t10 and OFF in t20. In the selection periods, the 1st voltage pulses V2.t13 and (V2-V4).t24 larger than a saturation value are applied firstly. Then, the 2nd voltage pulse (V1-V4).t14 larger than the saturation value in one polarity direc tion in the ON state or (V1-V3).t24 less than the threshold value of the liquid crystal in the OFF state is applied. Further, the 3rd voltage pulses are applied in a selection period t15(t25). In nonselection periods t11 and t21, on the other hand, the ON or OFF waveform of a signal electrode waveform 202 in t10 or t20 is applied. Consequently, there is neither a contrast decrease nor a flicker as shown by optical response 204.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving a liquid crystal element, and particularly to a method for driving a ferroelectric liquid crystal.

[Prior art] As a conventional method for driving a ferroelectric liquid crystal, there is
No. 21499 and Japanese Unexamined Patent Publication No. 156046/1983, the drive waveforms were as shown in FIGS. 7 and 8, respectively. The drive waveform presented in Japanese Patent Application No. 60-021499 (
In Fig. 7), the scanning W pole (701 in Fig. 7) has an absolute value larger than the saturation value of the liquid crystal in order to orient the bistable liquid crystal to a stable state of ¥R1 during the selection period tlO and t20. A first voltage pulse (ML in FIG. 7) and a second voltage pulse (V in FIG.
2) is applied, and the non-selection periods tll and t21 are zero volts, while the signal voltage a (702 in FIG. 7) has a polarity on the second stable state side when combined with the second voltage pulse. A third voltage pulse (V3 in Figure 7) that can raise the liquid crystal saturation value or higher at A fourth voltage pulse (V4 in the TS7 diagram) having the same DC component is applied, and the third, !, ! A fifth voltage pulse (in FIG. 7) which has a polarity opposite to that of the voltage pulse s4, has an equal DC component, and which, when combined with the first voltage pulse, exceeds the saturation value of the liquid crystal on the polarity side of the first voltage pulse. This is a driving method that applies a voltage pulse of V3). With this driving method, when the LCD is not selected,
The structure is such that the average value of the DC components of the positive and negative voltage pulses is always zero below the threshold of the liquid crystal, regardless of the selection content and quantity of each pixel, and the voltage pulses are arranged in the same polarity direction. The second voltage pulse is characterized in that it is not applied continuously for a period longer than twice the pulse width of the second voltage pulse. This driving method is characterized in that it prevents, to some extent, the phenomenon that the threshold value of the liquid crystal varies depending on the pulse width of the applied pulse and the change in the selection content of the liquid crystal due to the cumulative response effect. Furthermore, JP-A-60
In the driving method described in No. 156046, a first voltage pulse is applied to a pixel on a scanning electrode to orient the liquid crystal in a first stable state at a phase of sl within a selection period (t10 in FIG. 8). A second voltage pulse is applied to select one of the pixels in a second phase to orient the liquid crystal in a second stable state to select the pixel on the scan electrode, It has a phase of 3 and has a non-selection period (
In FIG. 8, t11) is a driving method in which alternating voltage pulses are applied through zero. In this driving method, the voltage pulses applied during the non-selection period are continuously applied in the same polarity direction with a length that is more than twice the pulse width of the first and second voltage pulses by passing through zero. It is characterized by something that will never happen.

[Problems to be Solved by the Invention] However, in the conventional driving method, as shown in FIGS. 7 and 8, depending on the selection content of each pixel, the voltage pulses applied during the non-selection period may have the same polarity. It is known that 0 ferroelectric liquid crystals that are applied continuously in the same polarity direction or in the same polarity direction through zero respond cumulatively, and a voltage pulse that is apparently about twice as long is applied. In this case, the operation margin becomes narrow depending on the pixel selection due to the influence of the pulse width dependence, and the optical characteristics, especially the contrast, are likely to deteriorate and flicker, etc. As shown by tlG in FIGS. 7 and 8, The waveforms applied to the liquid crystal during the selection period have different DC components of positive and negative voltage pulses. It is well known that when a direct current component is applied to a liquid crystal element during operation, deterioration of the element is accelerated due to an electrochemical reaction, resulting in a shortened lifespan.

The present invention is intended to solve the above problems, and its purpose is to ensure that the voltage pulse width applied to the liquid crystal is always constant during the non-selection period, regardless of the selection content, and that the DC components of the positive and negative voltage pulses are By configuring the average value to be zero, deterioration of the liquid crystal element due to DC components can be prevented, and the voltage pulses applied during selection and non-selection periods can also be
The object of the present invention is to provide a good multiplexing driving method that fully takes into account the change in threshold physical properties due to the pulse width of the applied voltage and the cumulative response effect, which are unique to ferroelectric liquid crystals.

Means for Solving Problem E] In order to solve the above problem, the method for driving a liquid crystal element of the present invention provides a method for driving a liquid crystal element between two substrates in which electrode surfaces of a substrate having a scanning electrode and a substrate having a signal electrode are opposed to each other. In a method for driving a liquid crystal element formed by sandwiching a strongly electrostatic liquid crystal, a first voltage pulse of at least the saturation value of the liquid crystal is applied during the selection period to align the alignment direction of the liquid crystal molecules with one state number. Apply
Next, a 26th voltage pulse with the opposite polarity to the first voltage pulse and below the threshold voltage of the liquid crystal or above the saturation value of the liquid crystal is applied to select whether or not to align in the alignment direction of the other liquid crystal. then apply a third voltage pulse below the threshold voltage of the liquid crystal, while applying a voltage pulse of zero or a smaller absolute value than the threshold voltage of the liquid crystal during the non-selection period; The pulses are characterized in that they are applied continuously or not continuously through zero in at least the same polarity direction and with a length longer than the pulse width of the second voltage pulse.

[Example-1] Figure WS1 is a schematic view of an example of the configuration of a liquid crystal element in an example of the present invention, with Figure 1(a) being a cross-sectional view and Figure 1(b) being a plan view. Transparent electrodes 23 and 24 made of indium oxide and tin oxide are provided on opposing surfaces of a pair of substrates 21 and 22 made of glass or plastic.

These electrodes are each formed in a stripe shape, the electrodes are crossed at right angles, and are combined in a lattice shape. Here, 23 and 24 are a scanning electrode and a signal electrode, respectively. Furthermore, after providing an insulating layer such as 5io2 on this electrode as necessary, an obliquely deposited film such as SIO or an alignment film 25 made of polyimide, nylon, polyethylene, etc. is provided to orient the liquid crystal, and the liquid crystal is then rubbed. 26. Also, the upper and lower substrates 21.
The change plates 27 and 28 are installed on the surface where the electrodes 23 and 24 of 22 are not provided so as to be perpendicular to each other, and an electric field that is equal to or higher than the polarization axis of one polarizing plate and the saturation electric field of the ferroelectric liquid crystal is applied. The long sleeve direction of the liquid crystal molecules when

FIG. 2 shows the driving waveform and optical response of Example-1 of the present invention. The device shown in Figure 1 is used, and the device cap thickness is 1
3gm, nya crystal is. The threshold characteristic of this element is a pulse width of 200
At pLsec, the threshold voltage is 6.5V and the saturation voltage is 8V. This value remained almost the same even if the voltage polarity was changed.

201 is a scanning electrode waveform, 202 is a signal electrode waveform,
203 is a waveform applied to the liquid crystal element, and 204 is an optical response of the liquid crystal element. The selection period tlo, t is displayed on the LCD.
20, tlO is ON (temporarily four-state a), t2o
OFF (temporarily dark state) is selected. In the selection period, first, the fsl voltage bus jLz (7) V2 ・t 1 is equal to or higher than the saturation value in order to align the alignment direction of the liquid crystal in one direction.
3 and (V2-V4)It23 are applied. O
The peak value of the first voltage pulse is different between N and OFF, but since both are above the saturation value, there is no effect on the optical response.Next, when the f32 voltage pulse is ON, the peak value of the first voltage pulse is the saturation value of the other polarity direction. Above (7) (Vj-V4) ・
When t14 is 0FF (7), the threshold value of the liquid crystal (
Vl - V3 ) t24 is applied. Furthermore, a third voltage pulse is applied at t 15 (t 25) within the selection period. In this example, this! The voltage pulse 83 has a selection period tlO1t20, a non-selection period tll,
This is to prevent pulses of the same polarity from being applied continuously or continuously through zero at the beginning of t21 (signal waveform on the next scanning electrode).

On the other hand, in the valve selection period tll, t21, the signal electrode waveform 20
The ON or OFF waveforms in tlo and t20 of 2 will be applied depending on the pixel content of the liquid crystal element, but 2 in Fig. 2
As in 03, voltage pulses of the same polarity are not applied continuously through 9 or 0.

Therefore, in this example, as shown at 204 in FIG. 2, there is almost no contrast reduction and flicker □.
A good optical response was obtained. At this time, the contrast ratio between ON and OFF was 25:1, and the contrast ratio between different pixels was almost constant regardless of the display content.

[Example 2] FIG. 3 is a diagram showing a drive waveform and optical response according to a second example of the present invention. FIG. 3 301 is a scanning electrode waveform, 30
2 is a signal electrode waveform, 303 is a waveform applied to the liquid crystal element, and 304 is an optical response of the liquid crystal element. Example-
The difference from the driving waveform of No. 1 is that the DC component that appears during the selection period tlO is removed during the non-selection period tll. The DC component is removed. That is, lV2 l ·t13-IVI l
・t14=lV5l・t17. In this embodiment as well, as shown in FIG. 3 303, voltage pulses in the same polarity direction with the pulse width of the second voltage pulse are continuously applied to the liquid crystal element throughout the selection and non-selection periods, or continuously through zero. First, as shown in FIG. 3 304, a good optical response was obtained for a long period of time with almost no decrease in contrast or flickering.

[Example 3] FIG. 4 shows the drive waveform and optical response in Example 3.

Note that the cell thickness of the liquid crystal element is approximately 1.5 to 2 gm,
The liquid crystal is C81015 manufactured by Chisso Corporation.

FIG. 4 is a diagram showing a driving wave and an optical response according to an embodiment of the present invention part 3. FIG. 4 401 is a scanning electrode waveform, 402
is a signal electrode waveform, 403 is a waveform applied to the liquid crystal element, and 404 is an optical response of the liquid crystal element. For the liquid crystal, during selection periods tlG and t20, tlo is selected to be ON (temporarily in a bright state), and t20 is set to 0FF (temporarily in a dark state). In the selection period, the first voltage pulse (V2-V3
)·t13 and (V2-V4)-t23 are applied.

The peak value of the first voltage pulse is different between ON and OFF, but since both are above the saturation value, there is almost no difference in optical response.Next, the second voltage pulse is in the other polar direction when ON. (Vl - V4) greater than the saturation value of
・If t14 is 0FF (7), the threshold value of the liquid crystal (
Vl - V3 ) t24 is applied. Furthermore, a third voltage pulse is applied at t 15 (t 25) within the selection period.
This is to prevent pulses of the same polarity from being applied continuously or continuously through zero at the beginning of t 14 (signal waveform on the next scanning electrode), and an alternating current with a pulse width shorter than t 14 (t 24). It's a pulse. One-way valve selection period tll, t
21, 110 of the signal electrode waveform 402, O in t20
Although the N or OFF waveform is applied depending on the pixel content of the liquid crystal element, as shown in 403 in FIG. 2, voltage pulses of the same polarity are not applied continuously or continuously through zero. Therefore, in this example, as shown at 404 in FIG. 2, a good optical response was obtained with almost no decrease in contrast or flickering.

[Example 4] FIG. 5 is a diagram showing a driving waveform and optical response as an example of the present invention section 4. FIG. 5 501 is a scanning electrode waveform, 50
2 is a signal electrode waveform, 503 is a waveform applied to the liquid crystal element, and 504 is an optical response of the liquid crystal element. Example-
The difference from the drive waveform of No. 3 is that the DC component appearing within the selection period tlo is removed within the ratio selection period tll. The DC component is removed. That is, IV2 1 ・t13−IVI 1−
t14=lv51.・It is t17. In this embodiment as well, as shown in the TS5 diagram 503, voltage pulses in the same polarity direction with the pulse width of the second voltage pulse are not applied continuously or continuously through zero throughout the selection and non-selection periods. As shown in FIG. 5 504, a good optical response was obtained for a long period of time with almost no decrease in contrast or flickering.

[Example-5] FIG. 6 is a diagram showing a driving waveform and optical response as an example of ls5 of the present invention. FIG. 6 601 is a scanning electrode waveform, 6
02 is a signal electrode waveform, 603 is a waveform applied to the liquid crystal element, and 604 is an optical response of the liquid crystal element. The difference from the drive waveform of the third embodiment is that the signal electrode waveform 60
2, a voltage pulse v4 ・t14 (V3 ・t24) corresponding to the second voltage pulse when combined with the scanning electrode waveform 601 for selecting ON or OFF, and a voltage pulse v4 ・t14 (V3 ・t24) whose polarity is opposite to this and the peak value voltage pulse V3 with the same pulse width as
- Apply an AC pulse with a pulse width shorter than the second voltage pulse during a period other than t15 (V4/t23).

Moreover, the ON and OFF voltage pulses are applied from the same polarity and are made into AC pulses that end with the same polarity, so that, as shown in the composite waveform shown at 603 in FIG. 6,
Regardless of the pixel selection content, in this embodiment, the second voltage pulse of the signal electrode waveform is
An alternating current waveform with half the pulse width is used as a pulse shorter than the voltage pulse of , but in this case, the length of the second voltage pulse is 1.5 times longer than the second voltage pulse. Further, depending on the threshold individual properties of the liquid crystal, a higher frequency voltage pulse was applied, and the optical characteristics at this time are shown in FIG. 6 604, and the contrast was good with almost no decrease in contrast or flickering when OFF was selected.

[Effect of the invention] As described above, according to the driving method of the present invention, voltage pulses of the length for selecting ON/OFF of the liquid crystal element are not continuously applied in the same polarity direction at least during the non-selection period. , which is more effective against pulse width dependence and can reduce contrast deterioration and flickering of the liquid crystal element. Moreover, since it is possible to reduce the average value of the DC component applied to the liquid crystal element to zero, element deterioration due to the DC component can be prevented and stable liquid crystal elements can be realized, which can be used in various display devices, electronic shutters, polarizers, etc. can be applied.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of the configuration of a liquid crystal element in an embodiment of the present invention, FIG. 1(a) is a cross-sectional view, and FIG.
b) is a plan view. and Optical soil temperature diagram 2 are diagrams showing the first drive waveform and optical response of the present invention. The drive waveform of the second embodiment and! Figure s3 is a diagram showing the drive waveform and optical response of the second embodiment of the present invention. FIG. 4 is a diagram showing the drive waveform and optical response of the third embodiment of the present invention. FIG. 5 is a diagram showing the driving waveform and optical response of the fourth embodiment of the present invention. ! Figure s6 is a diagram showing the drive waveform and optical response of the fifth embodiment of the present invention. FIG. 7 is a diagram showing conventional drive waveforms. FIG. 8 is a diagram showing conventional drive waveforms. 21...Lower substrate 22...Upper substrate 23...Scanning electrode 24...Signal electrode 25...Alignment film 26... ...Liquid crystal 27.28...Polarizing plate 29...Sealing material 201, 301. 401. 501. 60
1°701.801...Scanning electrode waveform 202,
302. 402. 502. 602°702.8
02... Signal electrode waveform 203, 303. 4
03. 503. 603°703.803...
- Composite waveform 204, 304. 404. 504. 604°・
...Optical response of liquid crystal element Above 1st UA (α) Fig. 1(b) °C 4th diagram Fig. 15

Claims (2)

[Claims] (1) In a method of driving a liquid crystal element in which a ferroelectric liquid crystal is sandwiched between substrates with electrode surfaces of a substrate having a scanning electrode and a substrate having a signal electrode facing each other, at least liquid crystal molecules are generated during a selection period. Apply a first voltage pulse higher than the saturation value of the liquid crystal to align the alignment direction of the liquid crystal in one state, and then apply the first voltage pulse with the opposite polarity to align the alignment direction of the other liquid crystal or not. A second voltage pulse below the threshold voltage of the liquid crystal or above the saturation value of the liquid crystal is applied, and then a third voltage pulse below the threshold voltage of the liquid crystal is applied, while , during the non-selection period, apply a voltage pulse of zero or a voltage pulse with an absolute value smaller than the threshold of the liquid crystal,
Furthermore, the method for driving a liquid crystal element is characterized in that the voltage pulse is not applied continuously or continuously through zero in at least the same polarity direction with a length longer than the pulse width of the second voltage pulse. (2) In the method for driving the liquid crystal element, the voltage pulse is equal to the difference in absolute value between the first voltage pulse and the second voltage pulse in the polarity direction that eliminates the DC component within the selection period within the non-selection period. A method for driving a liquid crystal element according to claim 1, characterized in that a voltage pulse is applied.