JPH0468312A - Driving device and method for ferroelectric liquid crystal device - Google Patents

Abstract

PURPOSE:To prevent the bistability from deteriorating with time by placing all picture elements uniformly in one stable state after an image is displayed, and applying an electric field in the opposite direction from a reverse electric field produced by self-polarization in the stable state. CONSTITUTION:Four scanning lines 112 are wired on one substrate of a panel 111 and four data lines 113 are wired on the other substrate; and the scanning lines 112 and data lines 112 cross each other and ferroelectric liquid crystal is arranged between the scanning lines 112 and data lines 113 at the intersections. Then, a scanning circuit 114, a scanning-side driving circuit 115, a signal-side driving voltage generating circuit 116, a line memory 117, a shift register 118, a scanning-side driving voltage generating power source 119, and a microprocessor unit 110 are provided. After the image is displayed, all the picture elements are placed uniformly in one stable state and the electric field is applied in the opposite direction from the reverse electric field produced by the self-polarization in the stable state. Consequently, one orientation state is left as it is to prevent the picture elements from entering a metastable state with time.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a driving device and a driving method for a ferroelectric liquid crystal device, and more specifically, to a driving device and a driving method for a ferroelectric liquid crystal device. The present invention relates to a driving device and a driving method for a ferroelectric liquid crystal device.

[Prior Art] Until now, regarding liquid crystal elements having bistability, Clark (C1ark) and Lagerwal (Lagerwal) have
1) was proposed by Teru (Japanese Unexamined Patent Publication No. 56-10721).
6, U.S. Pat. No. 4,367,924, etc.).

Liquid crystal elements having this bistability are generally used for chiral smectic C phase (SmC'') or H phase (SmH
'') is used.

This ferroelectric liquid crystal has a bistable state consisting of a first optically stable state and a second optically stable state in response to an electric field, and is different from optical modulation elements used in conventional TN-type liquid crystals. . For example, in a ferroelectric liquid crystal, the liquid crystal is oriented in a first optically stable state for one electric field vector, and the liquid crystal is oriented in a second optically stable state for the other electric field vector. .

Furthermore, this type of liquid crystal has the property of very quickly taking one of the above two stable states in response to an applied electric field, and maintaining that state when no electric field is applied. By utilizing such properties, many of the problems of the conventional TN type elements mentioned above can be improved in a flexible manner.

When manufacturing a liquid crystal display device using the above-mentioned strong octaelectric liquid crystal, a method is known in which a uniaxial alignment treatment is performed on the substrate surface in order to obtain uniform alignment performance. This -axial alignment treatment method includes rubbing the substrate surface in one direction with velvet, cloth, paper, etc., or rubbing the substrate surface with S
Examples include a method of obliquely depositing iO or 5i02.

By properly uniaxially aligning the substrate surface, a specified bistable state is achieved in the initial alignment.

[The problem that the invention tries to solve! ] However, depending on the orientation state, the two orientation states that were bistable at the initial orientation shift over time, that is, the realized orientation state (the one that was left alone) becomes It was found that the state is more stabilized than the conjugated orientation state. In other words, from the high temperature phase
It has been discovered that the bistable initial orientation state obtained by slow cooling to the c'' phase becomes monostable over time by being left in the Sc' phase.

Such monostabilization over time naturally has a strong influence on drive characteristics, leading to a decrease in drive margin and deterioration in display quality.

In view of the above-mentioned problems with the conventional type, the present invention aims to provide a driving device and a driving method for a ferroelectric liquid crystal device, which prevents monostabilization over time by leaving one orientation state as it is. purpose.

[Means and effects for solving the problem] In order to achieve the above-mentioned object, a driving device and a driving method for a ferroelectric liquid crystal device according to the present invention align all pixels to one stable state after image display is completed. , g In the stable state, an electric field in the opposite direction is applied to the anti-electric field generated by spontaneous polarization. This prevents monostabilization over time as described above.

[Example] Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a block diagram showing a driving device for a ferroelectric liquid crystal panel 111 having matrix electrodes used in the present invention.

Panel 111 in FIG. 1 has a pair of adjacent substrates. Four scanning lines 112 are wired on one board, and four data lines 113 are wired on the other board.

The scanning lines 1 and 2 and the data lines 113 are wired to cross each other. A high-pressure liquid crystal is disposed between the pair of substrates, that is, between the scanning line 112 and the data line 113 at the intersection thereof. S, -S4 indicate scanning signals applied to each of the four scanning lines 112, and (1) to I4 indicate information signals applied to each of the four data lines 113. Note that the reason why there are four scanning lines 112 and four data lines 113 is because
This is for convenience of explanation, and usually there are a large number of them.

Each rectangle that divides the panel 111 in FIG. 1 like the eyes of a substrate is the intersection of one scanning line 112 and one data line 113, and represents one pixel. Among the pixels, those with diagonal lines (for example, pixel A) indicate a portion in one alignment state, and those without diagonal lines (for example, pixel B) indicate a portion in the other alignment state.

In FIG. 1, 114 is a scanning circuit, 115 is a scanning side drive circuit, 116 is a signal side drive voltage generation circuit, 117 is a line memory, 118 is a shift register, 119 is a scanning side drive voltage generation power supply, and 110 is a microcontroller. A processor unit (MPU) is shown.

The scanning side drive voltage generation power supply 119 has voltages V+ and V2.
, Vc, and Vp are prepared. For example, voltage V1
and (2) can be used as the power supply for the scan selection signal, and the voltage (2)c (OV in this embodiment) can be used as the power supply for the scan non-selection signal.

In addition, (2) is when the strong galvanic panel 111 is not driven.
It can be used as a power source for a minute DC voltage that is applied to all pixels when the pixel is not in an image display state.

FIG. 2 shows time-series waveforms of the driving method used in the device of this example.

FIG. 2(A) is a time-series waveform diagram in the driving state. In the same figure, S+ to S3 are the waveforms of the scanning signals applied to the scanning line 112 in FIG. 1, II and I2 are the waveforms of the information signals applied to the data line 113 in FIG.
t) and (I2S1) indicate the composite waveforms applied to pixels A and B in FIG. Each waveform shown here corresponds to the display state (presence or absence of diagonal lines for each pixel) in FIG. 1.

These signal waveforms have been previously disclosed (U.S. Pat. No. 48
36656) drive waveform.

In the present invention, the driving state is no different from the conventional example, and of course other driving waveforms may be used.

FIG. 2(B) shows the last scan and subsequent voltage waveforms at the end of panel operation, that is, at the end of driving. Pulses RPI and RP2 are pulses (reset pulses) for aligning all pixels to one stable state,
It has a pulse width or voltage value that exceeds the switching threshold between bistable states.

Following reset pulses RPI and RP2, DC voltage VP
is applied. In the stable state set by reset pulses RP1 and RP2, this DCii: pressure vP
As a result, an electric field (compensation electric field) in the opposite direction to the direction of the anti-electric field generated by spontaneous polarization is applied. That is, this DC voltage (2) prevents the above-mentioned monostabilization over time.

Possible causes of monostabilization over time include uneven distribution of ions contained in the liquid crystal and changes in the alignment of liquid crystal molecules at the substrate interface, but the detailed cause is not known.

However, the inventor of the present invention found that an anti-electric field Ed generated by the spontaneous polarization PS peculiar to a strong electrostatic liquid crystal is involved, and came up with the concept of canceling this anti-electric field E by an external voltage (2). This significantly reduces monostabilization over time.

The liquid crystal material used in this example is a liquid crystal mixture containing a phenylpyrimidine skeleton that exhibits the following characteristics.

■Phase transition temperature CrySt4-5c″4-5A4-C10-I5°-1
4517579 ('C) ■ Spontaneous polarization 4 nc/cm' ■ Tilt angle 12 It was poured between a pair of substrates (glass plates) coated with an alignment film to form a ferroelectric liquid crystal panel (FLC panel) 111 shown in FIG.

The temperature of this FLC panel 111 was raised to a temperature at which the liquid crystal was in the isometric phase, and then slowly cooled to 30°C.

After slow cooling, almost bistable property was achieved, and when driven according to the time series waveform shown in Figure 2 (A), At = 50.
Good images could be displayed in the range of VOP-V2''v, = 20 to 23 V in μs.

Next, according to the time series waveform of Fig. 2 (B), VR = 2
0V, Δt4=80μ, vp==about 100mV
(preferably lomV to 1v, particularly preferably 20mV
A reset pulse of ~500 mV) and a compensation electric field were applied and left for about 24 hours. After that, when driving was started again, a good image could be displayed under almost the same driving conditions as after slow cooling.

The variations in conditions became significant, making it difficult to display good images.

[Effects of the Invention] As explained above, according to the present invention, after image display ends, all pixels are aligned in one stable state, and in the stable state, the anti-electric field generated by spontaneous polarization is applied in the opposite direction. Since the electric field is applied, deterioration of bistability over time can be prevented and high display quality can be maintained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a driving device for a ferroelectric liquid crystal device according to an embodiment of the present invention, and FIG. 2 is a time-series waveform diagram of driving waveforms used in this embodiment. Example 1 The FLC panel 111 was driven in exactly the same manner as in the example except that the reset pulse and the compensation electric field were not applied. As a result, the drive inside the panel 111: Strongly conductive liquid crystal panel, 112: Scanning line, 113: Data line, Engineering 14: Scanning circuit, 5: Scanning side drive circuit, 6. Signal side part! ! ! 7I voltage generation circuit, 7: line memory 8: shift register, 9: scanning side drive voltage generation power supply, 0: microprocessor unit, ~S4: scanning signal, ~I4: information signal.

Claims (6)

[Claims] (1) A pair of substrates with crossed electrodes formed thereon are arranged so that the distance between the substrates is sufficient to release the helical structure of the ferroelectric liquid crystal, and the ferroelectric liquid crystal is A driving device for a ferroelectric liquid crystal device in which a liquid crystal is arranged so that the ferroelectric liquid crystal has a bistable state, wherein after stopping the driving of the ferroelectric liquid crystal device, all pixels are brought into the bistable state. A stable state setting means for setting one of the stable states, and an electric field applying means for applying an electric field in the direction opposite to the direction of the counter electric field generated by spontaneous polarization in the stable state set in this way. A driving device for a ferroelectric liquid crystal device, characterized in that: (2) The device for driving a ferroelectric liquid crystal device according to claim 1, wherein the electric field applied by the electric field applying means has approximately the same magnitude as the counter electric field. (3) The electric field applied by the electric field applying means is an electric field smaller than the threshold electric field between the bistable states.
A driving device for a ferroelectric liquid crystal device according to. (4) A pair of substrates with crossed electrodes formed thereon are arranged such that the distance between the substrates is sufficient to release the helical structure of the ferroelectric liquid crystal, and the ferroelectric liquid crystal is A method for driving a ferroelectric liquid crystal device in which a liquid crystal is arranged so that the ferroelectric liquid crystal has a bistable state, the method comprising: after stopping driving of the ferroelectric liquid crystal device, all pixels are placed in the bistable state. A ferroelectric liquid crystal device characterized in that one of two stable states is set, and in the stable state thus set, an electric field is applied in a direction opposite to the direction of an anti-electric field generated by spontaneous polarization. Driving method. (5) The method for driving a ferroelectric liquid crystal device according to claim 4, wherein the applied electric field has approximately the same magnitude as the anti-electric field. (6) The method for driving a ferroelectric liquid crystal device according to claim 5, wherein the applied electric field is smaller than a threshold electric field between the bistable states.