JPH02214820A - Driving method of ferroelectric liquid crystal electro-optical device - Google Patents

Abstract

PURPOSE:To attain fast writing by carrying out 2nd write scanning, wherein a light put off state can be written regardless of a signal applied to a signal electrode, for an electrode where 1st write scanning is to be performed next in a selection time wherein the 1st write scanning wherein a light put-on state is written. CONSTITUTION:One scanning electrode is selected and applied with a select signal 1 and the write scanning 1 for placing respective picture elements on the scanning electrode in a light put-on state when a light put-on signal is supplied is carried out. In the selection time of the write scanning 1, a scanning electrode where the write scanning 1 is to be performed is applied with a select signal 2 and the write scanning 2 wherein all picture elements on the scanning electrode are turned off regardless of the signal applied to a signal electrode is carried out, thus driving the electrooptic element. Those write scannings consist of the former half period T1 and latter half period T2 of the selection time T. Consequently, the fast writing is enabled to obtain a display which makes a high-definition and large-capacity display.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for driving a ferroelectric liquid crystal electro-optical element that uses a ferroelectric liquid crystal and is used in matrix display devices, optical shutters for printers, etc. be.

[Prior Art] Liquid crystal electro-optical devices using ferroelectric liquid crystals have a response that is 10 to 1000 times faster than conventional liquid crystal electro-optic devices using nematic liquid crystals, and can be applied to high-speed optical shutter devices. Furthermore, since it exhibits bistability with respect to electric fields, it is expected to be applied to large-sized, high-density display devices.

In simple matrix driving of a ferroelectric liquid crystal electro-optical element that exhibits bistability with respect to the polarity of an electric field, it is generally necessary to write into one bistable state and write into the other. On the other hand, in view of the reliability of the liquid crystal electro-optical element, it is preferable that the voltage applied to the liquid crystal during such a writing operation be an alternating current without a direct current component.

As a driving method for a ferroelectric liquid crystal electro-optical element, the two-field method (SID '85 DIGEST) is a driving method that eliminates or reduces the direct current component.

p, 131), 4-pulse method (Japanese Patent Application Laid-Open No. 62-17343
6), 2-slot method (EURODISPLAY “87
PROCEEDINGS.

Several proposals have already been made, such as p. 152).

The former two of these driving methods write each pixel on two scanning electrodes in state 1 (one of the bistable states).
It takes time to apply voltage to write to state 2 (the other bistable state), time to apply voltage to write to state 2 (the other bistable state), and time to convert each write to AC, and as a result, the response speed of the liquid crystal There was a problem in that the writing time was four times longer than that of the conventional method, and the scanning time for writing all pixels was increased.

Furthermore, the two-slot method has the effect of shortening the scanning time for writing to all pixels compared to the former two methods, but requires a higher driving voltage. For this reason, when using a driving IC with the same withstand voltage, the reduction in scanning time is only 578 yen (in the typical case) compared to the former two methods. The voltage applied to each pixel during the selection time has a DC component.Therefore, this DC component is canceled out by the DC component applied during the non-writing time to convert the drive voltage to AC. However, in this method, at high duty, the pulse widths of the DC component applied during the selection time and the DC component applied during the non-selection time are significantly different, which is unfavorable in terms of device reliability. However, when the duty is low, the direct current component applied during the non-selection time becomes large and there is a problem that the device cannot be driven.

[Problems to be Solved by the Invention] FIGS. 11(a) and 11(b) show an example of a specific driving method of the two-field method. In this driving method, one cycle of writing is made up of two scans: one to bring the ferroelectric liquid crystal into a stable state, and another to bring it into the other stable state. The two-field method will be described below with two stable states in which one is lit and the other is non-lit.

For write scanning in the lighting state, when one scanning electrode is selected, the voltage Vo + Vl (7) is applied during the first half T3 of the selection time 1/2 T3, and the voltage Vo - Vl is applied during the second half T3. , and when not selected, vO -.
Apply constant voltage. On the other hand, for write scanning in the non-lighting state, the first period 1/4T3 of the selection time 1/2T3 is V
Apply a-vll chisel, and apply vo + to 1/4T3 described later.
A voltage of Vl is applied, and a constant voltage of VO is applied when not selected.

When a pixel on a selected scan electrode is turned on, the signal electrode is set to a voltage of V during the first half Ta of the selection time 1/2T3 for both lighting and non-lighting writing scans.
o -V2 voltage is applied, and Vo
Apply a voltage of +v2. In addition, when the pixel on the selected scan electrode is set to a non-lighting state, both the lighting and non-lighting write scans are performed within the selected time 1/2T3.
A voltage of VO+V2 (7) is applied to the first 1/4T3, and a voltage of vo-V2 is applied to the second 1/4Tz.

Here, vl and v2 are the pulse width of ferroelectric liquid crystal 1/4T
If the threshold voltage that changes from one stable state to the other stable state in the square wave of No. 3 is Vth, then lV11V
21>VLh>lV+V21 This is a voltage that satisfies the relationship (7). In particular, it is preferable that V1=3XV2.

FIGS. 12(a), (b), (c), and (d) show this driving method. The voltage waveform applied to the pixel at point A1 in FIG. 2 is shown when it is used in the case (n·8) composed of regular electrodes.

Fig. 12 (al) shows that when all pixels at Aol (low 1 to 8) points are turned on, Fig. 12 (b) shows An
When all the pixels at points t in 1 to 8) are turned off, the pixels at points Ant (n-odd) are turned on, and the pixels at points Anti (even) are turned off. When the pixels at the An+in=odd number) point are set to the non-lighting state, and when the pixels at the An+tn=even number) point are set to the lighting state, the voltage applied to the pixel at the Al1 point is shown in Fig. 12 fd). The voltage waveform is shown.

Writing the ferroelectric liquid crystal of each pixel into a lit or non-lit state is based on the voltage applied to 1/4T3 in the latter half of the selection time, and the voltage applied to 1/4T3 in the first half of the selection time is This is a voltage of opposite polarity to the voltage applied during the latter half of the selection time, 1/4T, and is applied for the purpose of alternating the applied voltage waveform.

In this manner, in the two-field method, writing in the lit state and writing in the non-lit state each require twice the writing time as the time required to change the state of the ferroelectric liquid crystal. Furthermore, writing to all pixels requires two scans: a write scan in a lit state and a write scan in a non-lighted state. Therefore, writing to all pixels takes four times the time to change the state of the ferroelectric liquid crystal (1/4T,
4 = Ta) was required.

The two-slot method has the effect of reducing the writing time required to write to all pixels compared to the two-field method. FIG. 13 shows an example of a specific driving method of the two-slot method. In this driving method, within the scanning electrode selection time T,
In the first half T4, all pixels on the selected scanning electrode are brought into one stable state, and in the second half T4, a voltage is applied to bring only the necessary pixels into the other stable state depending on the content of the display. One period of writing is formed by scanning.

The two-slot method will be explained below with one of the two stable states being a lighting state and the other being a non-lighting state.

In write scanning, when one scanning electrode is selected, a voltage of Vo-V is applied during the first half T of the selection time T, and a voltage of VO+V2 is applied during the second half T4. is applied, and V when not selected. Apply a voltage of +v3.

When the pixels on the selected scanning electrode are turned on, V is applied to the signal electrode during the first half T4 of the selection time T4. A voltage of +v4 is applied, and V is applied in the latter half of 1/2T4.

-V4 voltage is applied. Furthermore, in order to turn the pixel on the selected scanning electrode into a non-lighting state, a voltage of V1=V4 is applied during the first 1/2T of the selection time T, and during the second half 1/2T of the selection time T. V. Apply a voltage of +V4.

Here, Vl, V2, V3, ■ are threshold voltages at which the ferroelectric liquid crystal changes from one stable state to the other stable state in a rectangular wave with a pulse width of 1/2 T, and Vth is the threshold voltage of the ferroelectric liquid crystal with a pulse width of 1/2T.
, +vFlag>1-V4+V, l>Vth, V4-V
21 >V,, >l L-V21. And when the number of scanning poles is N, V3 = fVz - V11/ (2x f
This is the voltage that satisfies Nl)). In particular, L = 5 x
V4, preferably v23×v4.

FIG. 14 shows that when this driving method is used at fn=81 in the case of eight scanning electrodes in the dot matrix in which the scanning electrode group and the signal electrode group are combined shown in FIG. The voltage waveform applied to the pixel is shown. 14th
Figure fa) shows A when all pixels at An+ (n=1 to 8) points are turned on, and Figure fbl shows A. +
When all pixels at points fn=1 to 8) are turned off, the pixels at points Anl (n-odd) are turned on, and the pixels at points An+fn-even are turned off. In this case, Fig. 14fdl shows the voltage waveform applied to the pixel at point Al1 when the pixel at point An+fn=odd number is in the non-lighting state and the pixel at point An+fn=even number) is in the lighting state. .

The ferroelectric liquid crystal of each pixel is 1/2T of the previous period within the selection time.
In step 4, the non-lighting state is written regardless of the lighting signal or non-lighting signal applied to the signal electrode. Also, in the latter half of the selection time, l/2T4, if a lighting signal is applied to the signal electrode, the lighting state is written, and if a non-lighting signal is applied to the signal electrode, the non-lighting state does not change. .

In this way, in the two-slot method, the writing time is twice the time to change the state of the ferroelectric liquid crystal (1/2T4
= T4), it is possible to write the lighting state and non-lighting state.

However, in order to set the pixel to a non-selected state regardless of the voltage applied to the signal electrode during the first half T of the selection time, for example, if the voltage value having the above-mentioned preferable relationship is used, the non-selected The amplitude of the voltage waveform that is five times the amplitude of the voltage waveform that is sometimes applied to the pixel is required at the time of selection.

In the 2-field method, the amplitude of the voltage waveform when selected is four times the amplitude of the voltage E applied to the pixel when not selected.In this respect, the 2-slot method is superior to the 2-field method.
Requires twice as much driving voltage.

For this reason, when a drive IC with the same breakdown voltage is used in the 2-slot method and the 2-field method, the scan time reduction in the 2-slot method is not approximately half that of the 2-field method, but is 57.
It remained at around 8. Furthermore, in the two-slot method,
The voltage applied to each pixel within the selection time is the voltage (V2-
V, l), and there is a DC component with a pulse width of 1/2Tn. This DC component is canceled by the DC component of the voltage (V2- V+) / (2X (N-1)) and pulse width T4X (N-1) applied during the time when no writing is performed, and the AC drive voltage is is being transformed. However, N is the number of scanning electrodes. However, in this method, at high duty (N large), the pulse widths of the DC component applied during the selection time and the DC component applied during the non-selection time are significantly different. This direct current component with a large pulse width causes polarization due to the movement of ions in the liquid crystal, or oxidation or reduction reactions of the electrodes, which is unfavorable in terms of device reliability. Furthermore, when the duty is low (N is small), the direct current component applied during the non-selection time becomes large, and there is a problem that the device cannot be driven.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and includes the following: between a substrate on which a group of scanning electrodes is provided and a substrate on which a group of signal electrodes is provided; A pair of polarizing plates was installed outside the liquid crystal cell, in which a ferroelectric liquid crystal exhibiting a bistable state depending on the polarity of an electric field was sandwiched, and the intersection of the scanning electrode group and the signal electrode group was used as a display pixel. In the ferroelectric liquid crystal electro-optical element, the scanning electrodes of the scanning electrode group are sequentially selected, and each of the scanning electrodes on the scanning electrode is In a driving method for a ferroelectric liquid crystal electro-optical element that performs write scanning to put pixels into a bistable state depending on the content to be displayed, one scanning electrode is selected and each pixel on the scanning electrode is displayed. A selection signal (selection signal l) for writing to one of the bistable states (state 1) is applied depending on the content to be performed, and selection signal 1 is sequentially applied to the scanning electrodes to write to all pixels. , selects at least one scan electrode other than the scan electrode to which the selection signal l is applied within the time period in which the selection signal 1 is applied to at least one scan electrode, and doubles all pixels on this scan electrode. A selection signal (selection signal 2) different from selection signal 1 for writing to the other stable state (state 2)
) is applied, and a selection signal l is applied to at least one scan electrode of the scan electrodes to which the selection signal 2 is applied after the selection signal 2 is applied, and the selection signal l and the selection signal 2 are applied.
At least one selection signal consists of two times T1 and T2 in which the voltages applied are different, and the voltage of the selection signal l within the time T1 is VC++, the voltage of the selection signal 2 is VO2+, and the selection signal is The voltage applied to the scan electrode that is not applied is V(31, and the voltage applied to the signal electrode corresponding to the pixel to be written to state 1 is selected as VS, , by the combination of the selection signal l and the voltage applied to the signal electrode. VS2 + is the voltage applied to the pixel that does not change the stable state due to the combination of the signal l and the voltage applied to the signal electrode, and the voltage of selection signal 1 within the time T2 is VC + 2, and the voltage of selection signal 2 is VS2 +. VO22, the voltage applied to the scanning electrode to which no selection signal is applied is VO32, the voltage applied to the signal electrode corresponding to the pixel to be written into state l by the combination of the selection signal 1 and the voltage applied to the signal electrode is VSI2, Assuming that the voltage applied to the pixel that does not change the stable state due to the combination of the selection signal l and the voltage applied to the signal electrode is vs22, then VS11XTl+VS12XT2=VS21XTl+
VS22XT2= (VCIl+vC21) XTl
+ (VC12+VC22) XT2=VC31XT
The present invention provides a method for driving a ferroelectric liquid crystal electro-optical element, characterized in that the voltage of 1+VC32XT2 is almost fully satisfied.

FIG. 1 is a cross-sectional view of a ferroelectric liquid crystal electro-optical element driven by the present invention. On the surfaces of the two transparent substrates 1a and 1b,
Transparent conductive films 2a, 2b and alignment control films 3a, 3, respectively.
b. The conductive films 2a and 2b are electrodes for applying an electric field to the liquid crystal layer 4 held between the substrates, and constitute a scanning electrode group and a signal electrode group, respectively, and are provided for the purpose of generating an electro-optic response. It is l11203-
3nT.

(ITO), 5n02, etc., and is formed into a predetermined pattern.

The alignment control films 3a and 3b align liquid crystal molecules generally horizontally. Typical examples include organic polymer membranes,
In particular, it is preferable to form a polyimide polymer film and rub it in a certain direction with a cloth, but in addition, it is preferable to use a polymer film formed by rubbing a polyamide polymer film, polyimide amide polymer film, polyparaxylylene, etc. Also effective are obliquely deposited films such as SiO and SiO. It is also possible to directly rub the conductive films 2a and 2b to form an alignment control film without forming these films.

After performing such orientation control, spacers such as organic beads or alumina particles are sandwiched so that the substrates are held parallel and with a constant gap, and the periphery is fixed with a sealing material 5 to form a cell. . At this time, the orientation control directions of the two substrates are made to be approximately parallel to each other.

Thereafter, the ferroelectric liquid crystal composition is heated to a cholesteric phase or an isoreal phase, injected into a cell, and then sealed.

A pair of polarizing plates 6a and 6b are arranged on both sides of the cell so that their polarization axes are substantially orthogonal to each other and form a constant angle with the orientation control direction of the substrate. The angle of intersection of the polarization axes and the angle with the alignment control direction vary depending on the liquid crystal material and the operating temperature of the device, and the angle that provides the best contrast characteristics may be selected.

A light source 7 is placed on the back side of the substrate lb so that light is transmitted to the opposite side. In addition, when using a reflective type, a reflective plate may be provided outside the polarizing plate 6b on the back side.

FIG. 2 shows an example of a pattern of conductive films 2a and 2b used in a dot matrix display element. One substrate is patterned with horizontally striped scanning electrode groups C1-cn, and the other substrate is patterned with vertically striped signal electrode groups S1-Sl. The intersections All to An11 of the two sets of electrode groups become display pixels.

FIG. 3 shows an example of a pattern of the conductive films 2a and 2b used in an optical shutter for a printer head. This example shows a pattern example when driven at 1/4 duty.

A1□ to A4° indicate openings, and the other portions are used by forming a light-shielding film.

As the ferroelectric liquid crystal used in the driving method of the present invention, a liquid crystal having a liquid crystal phase exhibiting bistability depending on the polarity of the electric field can be used. Liquid crystal is preferred.Specific examples include:
Examples include 4-(4-n-decyloxybenzylideneamine) cinnamic acid-2-methylbutyl ester.

Further, as the liquid crystal used in the present invention, a liquid crystal having a smectic A phase (SmA phase) in a temperature range higher than that of a liquid crystal phase exhibiting ferroelectricity is preferable from the viewpoint of symmetry of bistability. Isoreal phase (■ phase) or nematic phase (Ne phase)
Alternatively, when using a liquid crystal that undergoes a direct phase transition from a cholesteric phase (Ch phase) to a ferroelectric liquid crystal phase such as an SmC' phase without passing through the SmA phase, the layer direction of the smectic phase is usually aligned with respect to the orientation control direction. Takes two different states. If these two types of layer directions coexist, this will lead to a decrease in contrast, so when cooling from the I phase, Ne phase, or Ch phase to a ferroelectric liquid crystal phase such as SmC'' phase, a DC electric field with a polarity in one direction is applied. It is necessary to take measures such as applying a current to the layer and aligning it in only one of the two types of layer directions.The device created in this way has two stable states: the first stable state and the second stable state. Among the stable states, the stable state that matches the polarity of the electric field applied during cooling is more stable, leading to a decrease in bistability.

On the other hand, in a liquid crystal having an SmA phase, the layer direction generally coincides with the orientation control direction, and the bistability with respect to the electric field is also symmetrical.

Furthermore, it is preferable for the liquid crystal used in the present invention to have a Ch phase in a higher temperature range than a liquid crystal phase exhibiting ferroelectricity, from the viewpoint of uniformity of alignment. Regarding the method of controlling the alignment of this liquid crystal, by using the method disclosed in Japanese Patent Application No. 59-274073, an element with extremely good alignment can be produced.

As a ferroelectric liquid crystal composition, it has an SmC phase and a Ch phase at higher temperatures, and the length of the helical pitch (p) in the Ch phase is the distance between the substrates 1a and 1b (
d) Use a liquid crystal that is at least four times longer. Also, Ch phase and SmC
It is desirable to have an SmA phase between 2 and 3 from the viewpoint of alignment uniformity.Such a liquid crystal can be obtained by mixing an optically active substance, a smectic liquid crystal compound, and a nematic liquid crystal compound in appropriate proportions. Non-liquid crystal additives may be added as necessary.In particular, in order to lengthen the helical pitch in the Ch phase, an optically active substance that produces a left-handed helix and an optically active substance that produces a right-handed helix are mixed together. It is effective to mix according to the force used.

Typically, the length of the helical pitch in the Ch phase changes with temperature. In order to obtain uniform orientation, it is preferable to satisfy the condition p)) 4b immediately above the Ch-3mA phase transition point.

However, if the temperature range that satisfies this condition is limited to the vicinity of the transition point, and if the rate of temperature drop is fast, the helical structure will not unravel and will transition to the SmA layer.

In this case, uniform orientation cannot be obtained, so l11Xi
It is necessary to maintain the temperature at a temperature that satisfies p))4d until the spiral structure unravels, or to slow down the temperature drop rate. For this reason, the temperature range in which the helical pitch p is four times or more the inter-substrate distance d is preferably 5°C or more above the Ch-SmA phase transition point, and more preferably over the entire temperature range of the Ch phase. .

Note that the Ch phase referred to herein also includes a phase in which an optically active substance is added to a nematic liquid crystal so that it has a specific pitch.

Next, the driving method of the present invention will be explained according to a specific example. In the driving method of the present invention, one scanning electrode is selected and a selection signal is applied, and each pixel on this scanning electrode is turned on when a lighting signal is applied to the signal electrode. During the selection time of write scan 1 for each tree of scan l (k≧1 integer), select signal 2 is applied to the tree scan electrode to perform write scan 1 next. Consisting of write scan 2 in which all pixels on the scan electrode are turned off regardless of the signal applied to the signal electrode,
These write scans are composed of the first half T and the second half T2 of the selected time T, and one cycle of writing for all pixels is constructed by performing write scan 1 for all scan electrodes.

FIG. 4 shows an example of a combination of a selection signal 1, a selection signal 2, a non-selection signal applied to the scanning electrodes, a lighting signal, and a non-lighting signal applied to the signal electrodes used in the present invention. ■1,
v2, v3, v4, v5, v6, ■2, V8, v9, L
(l is the threshold voltage that changes from one stable state with a rectangular wave with a pulse width T1 to the other stable state in order to enable the above writing scan, and Vtl+1 is the threshold voltage that changes from one stable state with a rectangular wave with a pulse width T2 to the other stable state. The key [t[fwoVth2.!:, tru,!::,1-
v8-v21 >Vt112, l -V9+L l <
Lh+, IVIOV21<Vt112, l Va +
V41 > Lhz, l VIO+V41 >Vt1
12, L−V5<Vt,,l, −Vs+V6<
Vthz, V9 VS l < VthI, l Lo
+ Vs 1 < Vth2, and from the condition of changing the voltage applied to each pixel to AC, V7” V8X T2/
TI, V9=V,. ×T2/T1, v5V6 X T2
/ TI, (Vl+V3) ×T1+ (V2 V4
) ×T, = 0 should be satisfied.

This example is an example in which writing is performed using the applied voltage only during the latter period T2 of the scanning electrode selection time, but there is also a method of writing using the applied voltage during the earlier period T1 of the selection time. An example thereof will be described later as an explanation of FIG. 9.

According to the driving method of the present invention, the DC component applied to the pixel in write scan 1 is canceled in write scan 2, and the applied voltage waveform is changed to AC, so that the DC component applied to the pixel is applied to the pixel regardless of the number of scan electrodes. The pulse width of the DC component is at most within the scanning electrode selection time T=T, +T2.

FIG. 5 shows a preferable example that satisfies the conditions described in the explanation of FIG. In this example, the threshold voltage Vt changes from one stable state to the other stable state in a rectangular wave with a pulse width T2.
L7 indicates the case where h2 is 2xVa or more and 4xVa or less
, is an example when TI = 1/2T2,
V+=2Va, V2=3Va, V3=2Va
, %14=5Va, V5=0l-V6=
O11/7=2Va, Vs=Va,
Vg=-2V6. This is an example in which V+o=Va.

Figures 6(a) and (b) show the driving method shown in Figure 5 when there are three scanning electrodes and three signal electrodes in the dot matrix in which the scanning electrode group and the signal electrode group are combined as shown in Figure 2. The voltage waveform applied to each electrode and the pixel Arm (m=1) when used in

It shows the voltage waveform applied to 2.3).

According to this drive waveform, the required voltage amplitude is 1
oxva, which is larger than 8XVa in the two-field method, but the time required to write a pixel is 3l2 times the time T2 for changing the state of the ferroelectric liquid crystal, which is shorter than four times the two-field method. be able to. Comparing drive ICs with the same breakdown voltage, the drive method shown in Figure 5 shows that 2
．． It becomes possible to write at a speed 13 times faster, which is 1.3 times faster than the two-slot method.

It is preferable to set TI=1/2T2 since it is possible to shorten the writing time to all pixels.

The driving method shown in Fig. 5 requires four different voltage output voltages to drive the scan electrode and four different output voltages to drive the signal electrode, and also requires four different output voltages to drive the scanning electrode and the signal electrode. Pulse @l/3T and 2/3 to change the applied voltage
Two control signals with different T are required.

FIG. 7 shows another preferable example that satisfies the conditions described in the explanation of FIG. This example assumes TI = 72,
Threshold voltage V1. that changes from one stable state to the other stable state with a rectangular wave with pulse width TI=72. h is 2xV
This is an example of a case where it is more than a, 4XV, and less than 1 = Vl
=-3V, V2=3Va, 13=5Va, V
a= 5Va, V5= 0l-V6=O1v7=
V81=va--va1=17q--1/,,VIO=
This is an example of Va.

Comparing the amplitude of the voltage waveform applied to the pixel, the time required for writing is the same as in the two-slot method. On the other hand, in this example, different five-value voltage outputs are required to drive the scan electrodes, and different two-value output voltages are required to drive the signal electrodes, and the applied voltage is changed between the first half T and the second half T within the selected time. In order to do this, a control signal with a pulse width of 1/2T is required.

This has the advantage that the control signal is simplified and the number of output voltage values required to drive the signal electrodes is smaller than in FIG. 5.

FIG. 8 shows another preferable example that satisfies the conditions described in the explanation of FIG. This example assumes T, = T2, and the threshold voltage Vth for changing from one stable state to the other stable state with a rectangular wave of pulse width TI = T2 is 2XV or more, 4XV or less. Another example is 1=V,=
V,,L=3V,,V3=V,1=L=-5V,,
V5= 01=V, =O1V7=V, 1=V8=-
This is an example in which V, 1=V9=-V, and Lo=Va.

A comparison of the amplitudes of the voltage waveforms applied to the pixels reveals that the time required for writing is the same as in the two-slot method. On the other hand, in this example, 4 different voltage outputs are required to drive the scanning electrodes, and 2 different output voltages are required to drive the signal electrodes, and the applied voltage is changed between the first half T and the second half T within the selected time. In order to do this, a control signal with a pulse width of 172T is required.

This has the advantage that the control signal is simplified and the number of output voltage values required to drive the signal electrodes is smaller than in FIG. 5.

Among the driving methods of the present invention, FIG. 9 shows a method in which writing using an applied voltage is used during the first period T1 of the selected time in the driving method of FIG.

Figure 4 Nioite v1. v2, v3, ■4, v5, V6,
Vl, va, v9, VIO are the threshold voltages that change from one stable state to the other with a pulse width TI (7) square wave teno. If the threshold voltage that changes to the stable state is Vth2, 1-Vs-V21>Vth2, I
−V9+ Vl l <Vthl, IVIO−V21<
Vth2,l Vl-Va 1 >Vthl,1-Vs
+ Val<Vth2.1-Vq-Vs1>
Vthl, l VIO+ Va l <Vth2.1V
7-V5l<Vthl, I-V8+V6
+ <Vth2.1-v9V51 <Vtr11, I
VIO+V61 <Vth2, and from the conditions of alternating the voltage applied to each pixel, v7V8XT2/Tl,
V9 = Vlo x T2/ Tl, v5-v6 x T
2/T+, (-Vl+V3) XTl+(V2 V4
) This is a driving method that satisfies XT2 = O, and Tl =
72, and the threshold voltage V+h for changing from one stable state j fish to the other stable state with a square wave of pulse width TI = T2 is 2×Va or more and 4×■8 or less. Yes 1=1/1=Va, V2=3V6,
V3=-5V, l, -V4=Va, v5=01=
V6=O1V7=Va1=va--Va1=v9=
This is an example in which va, Vlo = Va.

A comparison of the amplitudes of the voltage waveforms applied to the pixels reveals that the time required for writing is the same as in the two-slot method. On the other hand, in this example, four different voltage outputs are required to drive the scanning electrodes, and two different output voltages are required to drive the signal electrodes, and the applied voltage is changed between the first half T and the second half T within the selected time. A pulse @ 1/2T control signal is required to do this. This is preferable because the control signal is simplified and the number of output voltage values required to drive the signal electrodes is smaller than in FIG. 5.

As described above, according to the driving method of the present invention, regardless of the number of scan electrodes, the AC voltage waveform applied to the pixel does not have a DC component with a long pulse width, and within the writing time of the scan electrodes, By changing the ratio between the first period T1 and the second period T2, it is possible to shorten the writing time to all pixels.

[Function 1] First, the bistable state of the ferroelectric liquid crystal electro-optical element used in the present invention and its response to applied voltage will be explained with reference to FIG. Ferroelectric liquid crystal has liquid crystal molecules 4
1 has a layered structure, and the direction of the long axis of its molecules is inclined at a certain angle with respect to the direction of the layer line. It has spontaneous polarization 43 in a direction perpendicular to this molecule and included in the layer plane 42.

When a ferroelectric liquid crystal with such a structure is sandwiched between two substrates as shown in Figure 1, if the cell thickness is relatively thin, the liquid crystal molecules are tilted with respect to the layer structure. And it comes to show two stable states almost parallel to the substrate.

The following two effects can be considered as the effect of changing the direction of the liquid crystal molecules by an external electric field. One is the combined action of spontaneous polarization and an electric field, and in this action, the orientation of molecules changes so that the direction of spontaneous polarization aligns with the polarity of the electric field. That is, in the direction of the positive electric field and the direction of the negative electric field, the direction in which the molecules are inclined from the stacking line is opposite. 10th
As shown in the figure, for the electric field polarity E, they are arranged like fal, and for the electric field polarity E2, they are arranged like (bl).

There is a threshold value depending on the pulse width of the applied electric field for the change from one stable state to the other stable state due to the combined effect of this spontaneous polarization and electric field, and this threshold value depends on the orientation control method. In one type of orientation control, the product of the pulse width of the applied electric field and the intensity of the electric field generally tends to be approximately equal.

Another effect is the coupling effect between the dielectric anisotropy and the electric field. In this action, the direction in which the molecules are arranged does not depend on the polarity of the electric field, but is determined only by the direction. When liquid crystal molecules have negative dielectric constant anisotropy, they tend to take either (a) or fbl alignment state with respect to the electric field direction of E3.

In the driving method of the present invention, the former effect is used in particular to change between the lit and non-lit states, but when a liquid crystal with negative dielectric anisotropy is used as the ferroelectric liquid crystal, the latter This effect increases bistability and reduces changes in light intensity due to crosstalk voltage waveforms during the period when non-selection signals are applied to the scan electrodes.

Next, the operation of the ferroelectric liquid crystal electro-optical element according to the driving method of the present invention will be explained with reference to FIG. FIG. 4 shows an example in which a non-lighting state occurs when an electric field is directed from a signal electrode to a scanning electrode and is above a threshold value, and a lighting state is brought about when an electric field from a scanning electrode to a signal electrode is above a threshold value. In write scan 2, a voltage is set to the scan electrode so that an electric field equal to or higher than the threshold is applied from the signal electrode to the scan electrode within the selected time, regardless of the lighting signal or non-lighting signal applied to the signal electrode. be done.

There are two methods for this, one is the first period T within the selection time T.
1 is a method of applying an electric field higher than a threshold value from a signal electrode to a scanning electrode, and FIG. 9 corresponds to this method. In this case, during the latter half of the selection time T, an electric field higher than the threshold value is not applied from the scanning electrode to the signal electrode.

Another method is to apply an electric field equal to or higher than the threshold from the signal electrode to the scanning electrode during the later period T2 of the selection time T, as shown in Figures 5, 7, and 8. .

In this case, any electric field may be applied to the pixel during the first period T1 of the selection time T.

Write scan 1 is replaced by write scan 2.

Thereafter, a writing scan 1 is performed on the scan electrodes that have not been performed yet. Therefore, the scanning is performed on a scan electrode in which all pixels on the scan electrode are in a non-lighted state.

In writing scan l, depending on whether a lighting signal or a non-lighting signal is applied to the scanning electrode and the signal electrode, the pixel to which the lighting signal is applied has a threshold value from the scanning electrode to the signal electrode within a selected time. The electric field above is applied. In addition, a voltage is set to the pixel to which the non-lighting signal is applied so that an electric field equal to or higher than the threshold value is not applied from the scanning electrode to the signal electrode within the selection time.

There are two methods for applying an electric field equal to or higher than a threshold value from the scanning electrode to the signal electrode within a selected time period to turn on the signal electrode.

One method is to apply an electric field equal to or higher than a threshold value from the scanning electrode to the signal electrode during the first period T1 of the selection time T.

In this case, during the latter period T2 of the selection time T, an electric field higher than the threshold value is not applied from the signal electrode to the scanning electrode.

Another method is to apply an electric field equal to or higher than the threshold value from the scanning electrode to the signal electrode in the later period T2 of the selection time T, as shown in FIGS. 5, 7, 8, and 9. This is illustrated in the figure. In this case, any electric field may be applied to the pixel during the first period T1 of the selection time T. Furthermore, an electric field greater than a threshold value is not applied from the scanning electrode toward the signal electrode within the selection time to the pixel to which the non-selection signal is applied.

The non-selected state is a state in which write scan 1 and write scan 2 are not performed, and a non-select signal is applied to the scan electrode in the non-selected state. The non-selection signal is set to a voltage such that an electric field equal to or higher than the threshold electric field is not applied to the pixel in combination with either a lighting signal or a non-lighting signal applied to the signal electrode.

The voltage/waveform applied to the pixel is changed to AC by applying a lighting signal, a non-lighting signal, and a non-selection signal applied to the scanning electrode within a selection time T, as shown in FIG. The time integral of the voltage waveform is V. XT, and the voltage is set so that the sum of the time integrals of the voltage waveforms of the selection signal 1 and the selection signal 2 applied to the scanning electrodes becomes LX T X 2.

[Example] Liquid crystal composition C manufactured by Chisso Corporation, which has an SmA phase on the high temperature side of the SmC'' phase and a ch phase on the high temperature side as a ferroelectric liquid crystal.
3-1014 was used to form a liquid crystal cell with 32 scanning electrodes and a cell gap of 2 μm.

Using this liquid crystal cell, at 30°C, as the driving method of the present invention, T2 = 100 μsec in FIG.
The figure shows the voltage applied to the pixel at 1/32 duty to 1/1024 duty using the drive waveforms shown in Figures 7, 8, and 9 (maximum value of voltage applied to the pixel: 30 cm) When I wrote while changing the voltage, for every drive waveform, it went from around V, = 4.9V to V, = 6.6V.
Normal display was obtained at nearby voltages regardless of the duty ratio. At this time, in the drive waveform shown in Fig. 5, flicker was observed at a duty of 1/120 or more, and in Figs.
In the drive waveforms shown in FIGS. 9 and 9, flicker was observed at a duty of 1780 or more.

On the other hand, as a comparative example, 174
When writing was performed while changing the voltage applied to the pixel with T3 = 100 μsec and L = 3 Although a display was obtained, flicker was observed at a duty of 1/40 or more.

In addition, as a comparative example, 1/2T4 is
=lOOgsec, ■, = 5 XV4, V2
= 3 x L, and when writing was performed while changing the voltage applied to the pixel, normal display was possible at high duty from around V4 = 4.9V to around V4 = 6.6V, but at low duty In case of 1/200 duty or less where v3 exceeds 50 mV, the voltage range at which normal display can be performed gradually narrows, and at 1/60 duty where v3 approaches 200 mV, normal display cannot be performed.

The driving results of these examples are summarized in Table 1.

Table 1 As described above, according to the driving method of the present invention, a normal display can be obtained regardless of the duty ratio, and in particular, the driving waveform shown in FIG. The number of lines can be increased.

[Effects of the Invention] In the driving method of the present invention, in write scan 2, a non-lighting state is written regardless of the signal applied to the signal electrode, and in the subsequent write scan 1, a lighting state is written by a signal applied to the signal electrode. Get the required display by writing. In addition, since writing scan 2 can turn the pixel into a non-lighting state regardless of the signal applied to the signal electrode,
It can be performed during the selected time when writing scan l is being performed, and compared to the 2-field method, writing can be performed 2113 times faster with the same drive voltage, and uniform display can be achieved when the display content changes rapidly. It will be done. In addition, since high-speed writing can be performed, the number of scanning electrodes that can be scanned can be increased when the display screen switching speed is high, and this has the effect of increasing display definition and display capacity. These effects result in a display capable of high-definition, large-capacity display.

Further, according to the driving method of the present invention, the pulse width of the DC component of the voltage waveform applied to the pixel is at most less than the selection time, and the DC component of the voltage waveform applied to the pixel is completely AC in write scan 1 and write scan 2. The drive voltage range can be widened regardless of the number of scanning electrodes, and the width of the allowable gap variation in the display surface during cell manufacturing and the illumination device installed on the back of the cell can be adjusted. It is possible to widen the allowable range of temperature distribution within the display surface.

In addition, in the driving method of the present invention, by shortening the selection time in the first half or the second half of the selection time that is not used for switching between pixel lighting and non-lighting, and by making a large voltage swing, it is possible to When a material with negative dielectric anisotropy is used as the material, it has the effect of increasing bistability and increasing contrast.

The driving method of the present invention provides a procedure for applying an external field to an element in which elements exhibiting bistability depending on the direction of the applied external field are arranged in a matrix. In addition to electric fields, it is valid for things that have magnitude and direction, such as magnetic fields and temperature gradients, and for example, has a threshold value and exhibits bistability depending on the polarity of the applied electric field. It also enables high-speed state control in electronic devices.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the element driven by the present invention, and the second
FIG. 3 is a plan view of an example of an electrode pattern in a preferred application example of the driving method of the present invention. FIG. 4 is a basic waveform diagram showing the driving method of the present invention,
5, 6, 7, 8, and 9 are waveform diagrams showing actual examples of the driving method of the present invention. FIG. 10 is a schematic diagram illustrating the principle of the driving method of the present invention. FIGS. 11, 12, 13, and 14 are waveform diagrams of conventional driving methods. la, lb: transparent substrate 2a, 2b = conductive film 3a, 3b; alignment control film 4: liquid crystal layer 5: sealant 6a, 8b: polarizing plate signal electrode group S, S2 signal electrode group 182S3 Sl, l

Claims (4)

[Claims] (1) A ferroelectric liquid crystal exhibiting a bistable state depending on the polarity of an electric field is sandwiched between a substrate provided with a scanning electrode group and a substrate provided with a signal electrode group, and the scanning electrode group A ferroelectric liquid crystal electro-optical element has a pair of polarizing plates installed on the outside of a liquid crystal cell in which the intersection of the signal electrode group and the signal electrode group is used as a display pixel.The scanning electrodes of the scanning electrode group are sequentially selected, and a voltage is applied to the scanning electrodes. A ferroelectric device that performs writing scanning to place each pixel on the scanning electrode into either a bistable state depending on the content to be displayed by combining the voltage applied to the signal electrode and the voltage applied to each signal electrode of the signal electrode group. In a method of driving a liquid crystal electro-optical element, one scanning electrode is selected, and a selection signal (selection signal) is used to write each pixel on the scanning electrode into one of the bistable states (state 1) according to the content to be displayed. 1) and the selection signal 1 is applied to the scanning electrodes sequentially to write to all pixels, the selection signal 1 is applied within the time during which the selection signal 1 is applied to at least one scanning electrode. A selection signal (selection signal 2) different from selection signal 1 for selecting at least one scan electrode other than the scan electrode and writing all pixels on this scan electrode into the other bistable state (state 2). ), and the selection signal 1 is applied after the selection signal 2 is applied to at least one of the scan electrodes to which the selection signal 2 is applied, and at least one of the selection signal 1 and the selection signal 2 is selected. The signal has two different applied voltages.
VC_1_1 is the voltage of selection signal 1 within time T_1, VC_2_1 is the voltage of selection signal 2, VC_3_1 is the voltage applied to the scan electrode to which no selection signal is applied, and VC_3_1 is the voltage of selection signal 1 and the selection signal 1 and the signal In combination with the voltage applied to the electrode, the voltage applied to the signal electrode corresponding to the pixel to be written to state 1 is set to VS_1_1, and in combination with the selection signal 1 and the voltage applied to the signal electrode, the pixel does not change its stable state. The applied voltage is VS_2_1
, and voltage VC_1_2 of selection signal 1 within time T_2
, the voltage of selection signal 2 is VC_2_2, the voltage applied to the scanning electrode to which no selection signal is applied is VC_3_2, and the combination of selection signal 1 and the voltage applied to the signal electrode is state 1.
When the voltage applied to the signal electrode corresponding to the pixel to be written to is VS_1_2, and the voltage applied to the pixel whose stable state does not change due to the combination of selection signal 1 and the voltage applied to the signal electrode is VS_2_2, VS_1_1 ×T_
1+VS_1_2×T_2=VS_2_1×T_1+V
S_2_2×T_2=(VC_1_1+VC_2_1)
×T_1+(VC_1_2+VC_2_2)×T_2=
A method for driving a ferroelectric liquid crystal electro-optical element, characterized in that VC_3_1×T_1+VC_3_2×T_2 is substantially satisfied. (2) In claim 1, the T_1 and T_2 are T_1
=1/2T_2. A method for driving a ferroelectric liquid crystal electro-optical element. (3) In claim 1, the T_1 and T_2 are T_1
=T_2. (4) In claim 1, 2 or 3, in the writing scan, the selection signal 2 is applied to one scan electrode within a given writing time, and the selection signal 1 is applied within the writing time. A method for driving a ferroelectric liquid crystal electro-optical element, characterized in that the scanning electrode is adjacent to a scanning electrode to which an applied voltage is applied.