JPS63306426A - Liquid crystal device - Google Patents

Abstract

PURPOSE:To maintain high display quality over the entire in-use temperature range by providing a means which superposes a DC component on a driving AC voltage and varying the value its DC component according to temperature variation. CONSTITUTION:A temperature sensor 112, a temperature compensating circuit 113, and a temperature control circuit 114 are provided, and a source voltage applied to a scan electrode driving circuit 105 or signal electrode driving circuit 104 is controlled by those circuit according to temperature. Namely, the value of a DC bias is set small on a low-temperature side and increased in response to the temperature rises. Thus, the DC bias is varied according to in-use temperature to widen the temperature range wherein the device can be driven to an extent where there is no problem in practical use.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a liquid crystal device exhibiting improved driving characteristics;
In particular, the present invention relates to ferroelectric liquid crystal devices that exhibit improved driving characteristics against temperature changes.

[Prior art]

Conventionally, liquid crystal display elements are well known in which a scanning electrode group and a signal electrode group are configured in a matrix, and a liquid crystal compound is filled between the electrodes to form a large number of pixels to display images or information. . The driving method for this display element is time-division driving, in which an address signal is selectively and periodically applied to a group of scanning electrodes, and a predetermined information signal is selectively applied in parallel to a group of signal electrodes in synchronization with the address signal. It has been adopted.

Most of these were put to practical use, for example, in “Applied Physics Letters” (“Applied Phys Letters”).
sics Letters”) 1971, 18
(4) published on pages 127-128 of M, Shut (M
, Schadt) and W. Helfrich (W.
“VoltageDependent 0pt
ical Activity of a Twist
TN (twisted nemati) shown in dNematic Liquid Crystal
c) type liquid crystal.

In recent years, as an improved version of conventional liquid crystal elements, the use of bistable liquid crystal elements has been proposed by both C1ark and Lagerwall in Japanese Patent Application Laid-open No. 107216/1982 and US Pat. No. 4,367,924.
It is proposed in the specification etc. As a bistable liquid crystal,
Generally, a ferroelectric liquid crystal having a chiral smectic C phase (SmC*) or H phase (SmH*) is used. In these states, the liquid crystal assumes either a first optically stable state or a second optically stable state in response to an applied electric field, and maintains that state when no electric field is applied. Because it has bistable properties and quick response to changes in electric field, it is expected to be widely used in fields such as high-speed and memory-type display devices.

For example, in the case of a rectangular pulse, switching between the first stable state and the second stable state in the ferroelectric liquid crystal is performed by applying a pulse that is equal to or greater than a threshold value determined by the pulse time width (pulse width) and voltage value. occurs when Therefore, among the pixels formed at the intersection of the scanning electrode and the information electrode,
Multiplexing driving is possible by applying appropriate pulses to the scanning electrodes and information electrodes so that pulses above the threshold are applied to the selected pixel and below the threshold to the other pixels.

Although there are various types of multiplexing drive methods, the 1/a bias method (eg, 1/3 bias method), which is a voltage averaging method with a small amount of crosstalk, is most commonly used. According to this l/a bias method, four states of the voltage applied to the pixel occur depending on the combination of the selected state and the non-selected state of the scanning line. That is, if both the scanning line and the information signal line are in a selected state (referred to as a selected state), the peak value of the drive voltage is V.

(However, V is a constant power supply voltage), and if the scanning line is selected and the information signal line is not selected (called a half-selected state), the peak of the drive voltage is (1-2/a)V,) , On the other hand, if the scanning line is not selected, regardless of the information signal line (
(referred to as a non-selected state), the peak of the driving voltage is V. /a. Therefore, one frame (
In one cycle time), the effective value of the driving voltage applied to the pixel in the selected state is larger than the effective value of the driving voltage applied to the pixel in the non-selected state, and the difference in effective values is the difference in the transmitted light of the liquid crystal. The difference in intensity or reflected light intensity, that is, the contrast, can be used for display.

By the way, in multiplexing driving, a write pulse of a threshold voltage or higher is applied in a selected state, and in a subsequent non-selected state, a pulse train having a voltage value of 1/a of the write pulse is applied in accordance with an information signal. However, depending on the application state of the pulse train under such a non-selected state, there may be a pixel that does not undergo inversion even though a write pulse is applied at the time of selection (in other words, if the application of the write pulse at the time of selection causes no inversion). However, it may continue (re-inversion occurs due to the application of a pulse train with a voltage value of 1/a applied when not selected).This phenomenon is generally called a crosstalk phenomenon, but such crosstalk The display screen where the phenomenon occurred did not have sufficient contrast and did not provide good display quality.

For this reason, in Japanese Patent Application Laid-Open No. 59-193426, the above-mentioned crosstalk phenomenon is prevented by superimposing a DC voltage component on the drive AC voltage applied between the electrodes corresponding to the intersection of the scanning line and the information line. A method has been proposed.

Furthermore, although ferroelectric liquid crystal elements have a memory effect, the memory effect is not necessarily symmetrical between the first and second alignment states, and in extreme cases, it may not be a bistable state. One orientation state becomes a stable monostable state,
This has been a cause of poor display quality during switching, but a method has been proposed to prevent this monostable state by superimposing a DC voltage component (DC bias).

However, if the above-mentioned DC bias value is too small, it will not improve the display quality, and if it is too large, the bistability of the ferroelectric liquid crystal will be completely destroyed, and on the contrary, it will become monostable. However, the alignment of the liquid crystal was destroyed.

For this reason, in the past, the value of the DC bias was optimized by taking the above into account, but the driving conditions depended on the temperature (with ferroelectric liquid crystals that change, there is a limit to the temperature range that can be driven). was.

[Summary of the invention]

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a ferroelectric liquid crystal device that enables high-quality display over a wide temperature range. In particular, another object of the present invention is to provide a temperature compensation method that can be operated over a wide temperature range.

The present inventors conducted various studies on the relationship between the DC bias and temperature described above in multiplexing drive of ferroelectric liquid crystal devices, and found that by changing the DC bias according to the operating temperature, drive is possible. We were able to widen the temperature range to a level that does not pose a practical problem. The present invention has been made based on this knowledge.

That is, the present invention provides a liquid crystal element having a scanning line and an information line, and a ferroelectric liquid crystal disposed between the scanning line and the information line, and a drive applied to the intersection of the scanning line and the information line. In a liquid crystal device having means for superimposing a DC component on an AC voltage,
The present invention is characterized by a liquid crystal device that changes the value of the DC component according to temperature changes. In particular, in the present invention, D
By setting the C bias value small and increasing the DC bias value as the temperature rises,
The above objectives can be achieved.

[Detailed description of aspects of the invention]

The present invention will be explained below with reference to the drawings.

FIG. 1 is a configuration diagram showing an example of a display device of the present invention. 1
01 is a display panel, which has scanning electrodes 102 and signal electrodes 103.
and ferroelectric liquid crystal filled between them, and at the intersection of the matrix consisting of the scanning electrode 102 and the signal electrode 103, the orientation of the ferroelectric liquid crystal is caused by the electric field caused by the voltage applied to the electrode. controlled.

104 is a signal electrode drive circuit, a video data shift register 1041 that stores serial video data from the information signal line 106, and a line memory 1O4 that stores parallel video data from the video data shift register 1041.
2. A signal electrode driver 1043 for applying a voltage to the signal electrode 103 according to the video data stored in the line memory 1042, and a signal from the control line 108 for switching the voltage vl+''C and -v1 to be applied to the signal electrode 103. It has an information side power switch 1044 that switches depending on the information.

105 is a scan electrode drive circuit, which connects the scan address data line 1
a decoder 1051 for receiving a signal from 07 and instructing one scanning electrode among all scanning electrodes;
A scanning electrode driver 1052 for applying a voltage to the scanning electrode 102 in response to a signal from the scanning electrode 102; It has a container 1053.

A CPU 109 receives clock pulses from an oscillator 110 to control the image memory 111 and control the transfer of signals to the information signal line 106, the scanning address data line 107, and the switching control line 108.

Next, the operation of the above configuration will be explained.

FIG. 2 is a timing chart of the switching control signal from the switching control line 108, the signal electrode drive voltages v++VC, V1, and the scan electrode drive voltages Vs, Vc, -Vs.

The timing at which the signal from the switching control line 108 is switched is during the period when no electric field is applied to the liquid crystal pixel, which in this embodiment is within the vertical synchronization period in the refresh drive, and when the signal from the switching control line 108 is high.
At i-level, the signal electrode drive voltage is +v11. -v
+0. +Vs+ and -Vsl are output as scan electrode drive voltages. Next, when the signal from the switching side control line 108 is at Lo- level, the signal electrode drive voltage is +v1□, -
V, , +VS2 to scan electrode drive voltage. -VS2 is output. In Figure 2, VI: +V+ 1>+VI 2 -Vl: -V
I 1> -Vl 2Vs: +Vs 1>+VS 2
-VS: -VS l> -VS 2 is shown, and when the signal from the switching control line 108 is at Hi- level, a higher voltage is applied to the liquid crystal pixel than when it is at LO- level. .

The apparatus shown in FIG. 1 is also provided with a temperature sensor 112, a temperature compensation circuit 113, and a temperature control circuit 114.

These circuits can control the power supply voltage input to the scan electrode drive circuit 105 or the signal electrode drive circuit 104 according to the temperature.

FIG. 3 is a drive waveform diagram used in the present invention.

In FIG. 3(A), Ss is the selection scanning waveform applied to the selected scanning line, SN is the unselected scanning waveform, and Is is the selection information waveform (black) applied to the selected data line. ), ■, represents a non-selection information signal (white) applied to an unselected data line. Also, in the figure (I
s Ss) and (IN ss) are the voltage waveforms applied to the pixels on the selected scanning line. The pixels to which the voltage (Is Ss) is applied display black, and the voltage (IN ss) is applied to the pixels on the selected scanning line.
The pixel to which ss) is applied assumes a white display state.

In the driving example shown in FIG. 3, the scanning selection signal Ss applied to the selected scanning line is an AC voltage set to a voltage of VSI and -v5□ (the positive polarity and negative polarity are based on the potential of the unselected scanning line). ), and the voltage with equal amplitude (lV
sl''lVs+1=lVs.1), and the voltage Vll(VI2) applied from the data line is IVs.
Each amplitude is set so that the value is 1 = 21V + 1 (7) (l VIl = l VI + l = I
Vl□1).

In addition, in the driving method shown in FIG. 3, one line clear phase t,
The voltage applied to the pixel (IN-3S) is set so that it exceeds the threshold voltage of the ferroelectric liquid crystal when the voltage application time is set to twice the minimum application time Δt. The voltage vs□+v1 applied at phase t2 is set to a voltage exceeding the other threshold voltage of the ferroelectric liquid crystal, and the voltage -v1 is set to a voltage 1 smaller than the threshold voltage.

Figure 4 shows the 3. It represents the drive waveform when the amplitude of the drive voltage is changed with respect to the amplitude of the drive voltage shown in j(A).

FIG. 4 shows a DC component V in the information signal 3 of FIG. 3(A) and IN. . (DC component V.0 based on the voltage of the scan non-selection signal) is given to the information signal 1g. Information signal shown in Figure 4■? and (8) are asymmetrical alternating waveforms to which VOC is applied, and the voltage -V? generates a DC component VDC of opposite polarity to the voltage polarity of the scan selection signal at the 1-line clear phase t1. have. (In other words, the ratio of the voltage amplitude (Vs) of the scan selection signal to the voltage amplitude (V+) of the information signal (vs /Vl)
is switched periodically. ) This voltage ■ is set to a value smaller than the threshold voltage of the ferroelectric liquid crystal determined by the write phase period Δt. In addition, the above-mentioned DC component VD
The polarity of C is not limited to the polarity described above, and may be the opposite polarity depending on the drive waveform.

FIG. 5(A) is an example of a driving waveform used in the present invention. FIG. 5(A) shows scan selection signals S2r+-1 applied to odd-numbered scan electrodes in odd-numbered frames FjJM-1 and even-numbered frames F2M (M=1, 2, 3, . . . ).
(n=1.2.3...) and scan selection signals 32a applied to even-numbered scan electrodes are shown.

According to FIG. 5(A), the scanning selection signals s, ts −1
is the odd frame F2 M −1 and the even frame FzM(
M=1°2.3. ) voltage polarity (
The voltage polarities (based on the voltage of the scan non-selection signal) are opposite to each other, and the same applies to the scan selection signal S2n. Furthermore, the scan selection signals s2n-1 and 32++ applied within one frame period have different voltage waveforms, and the voltage polarities of the same phase are opposite to each other.

In addition, in the scan drive waveform example shown in FIG. 5(A), a phase is provided at the third position for stopping the screen at once (for example, applying zero voltage to all pixels constituting the screen at once). , the third phase of the scan selection signal is set to voltage 0 (same level as the voltage of the scan non-selection signal).

Also, according to FIG. 5A, in the odd frame F2M-1, the information signal applied to the signal electrode is a white signal (scanning selection signal 52II-1) for the scanning selection signal 52m-1.
1, a voltage of 3 V exceeding the threshold voltage of the ferroelectric liquid crystal is applied in the second phase to form a white pixel) and the holding signal (scanning selection signal s2n -1), A voltage v0 smaller than the threshold voltage of the ferroelectric liquid crystal is selectively applied to the pixel, and a black signal (by combining with the scan selection signal S2n, a second black signal is applied to the scan selection signal 5211). A voltage of -3Vo exceeding the threshold voltage of the ferroelectric liquid crystal is applied in the phase to form a black pixel)
and a hold signal (by combining with the scan selection signal S2n, a voltage ±vo smaller than that of the ferroelectric liquid crystal is applied to the pixel) is selectively applied.

In the even frame F2M following the writing of the odd frame F2M-1 described above, the same black signal and hold signal as described above are selected as the information signals applied to the signal electrodes for the scan selection signal s2n-1. The same white signal and holding signal as described above are selectively applied to the scan selection signal 82n.

Figures 5(B), (C) and (D) are respectively shown in Figure 5(A).
), the voltage of the information signal +v.

VDC is added to the voltage of the scan selection signal ±2v
The voltage of the information signal ±vo is given ±VDC.

6(A)-(D) and FIG. 7(A)-(D) represent other drive waveforms used in the present invention.

FIG. 6(A) and FIG. 7(A) show the scanning selection signal 5n(n
=1. 2.3. . . ) represents a driving method in which two types of scan selection signal voltages whose polarities in the same phase are opposite to each other are applied alternately in odd-numbered frames and even-numbered frames. Figures 6 (B), (C) and (D) and Figure 7 (B)
), (C) and (D) are the drive waveforms shown in FIG. 6(A) with +VDC added to the voltage +v0 of the information signal and +VDC added to the voltage ±2v0 of the scan selection signal, respectively. and the information signal ±v0 with +VDC added to it.

FIG. 8 shows another preferred example of drive waveforms used in the present invention. In FIG. 8, voltage vc1 is a voltage for clearing all or a predetermined number of pixels at once prior to writing, and is applied to, for example, the scanning electrodes all at once. Ss is a scan selection signal having alternating voltages of 2V0 and -2V, and SN is a scan non-selection signal set to a reference voltage of 0. ■s is an information signal for inverting the cleared pixel, and IN is an information signal for holding the cleared pixel, and these information signals are synchronized with the scan selection signal that is sequentially applied to the scan electrodes. is applied to the signal electrode at the time of selection.

The information signals Is and ■ mentioned above each have a DC component V.
. An asymmetrical alternating voltage applied with C is formed. This DC component V. 0 can be a DC component VDC having the same polarity as the voltage Vc (3Vo), and it is also possible to superimpose this DC component VOC on the information signal voltage (+Vo) having the same polarity. At this time, in the present invention, the DC component VDC can be varied between 0 and a predetermined offset amount within the operating temperature range of the ferroelectric liquid crystal panel. Furthermore, the polarity of the DC component VDC described above is not limited to the polarity described above, and may be the opposite polarity.

Next, all pixels formed by the matrix electrode group shown in Fig. 9 are driven at temperatures of 15°C, 25°C, and 35°C by the 1/4 bias method using the waveform shown in Fig. 3. The contrast was measured when The driving conditions were Δt=28 μsec, the driving voltage was the optimum driving voltage at each temperature, and driving was performed by superimposing a DC bias voltage on this. Contrast was calculated as the ratio of transmittance when displaying an all-white pattern and an all-black pattern.

The results of plotting the contrast on the vertical axis and the temperature on the horizontal axis are shown in FIG. 1O.

In Figure 10, curve (A) shows the results when the VDC value is varied to obtain the maximum contrast at each temperature, and curve (B) shows the results when the VNC value is varied at a temperature of 25°C.
The value at which the maximum contrast was obtained when (Voc = 1
．． The results are shown when the voltage was fixed at 0 (V)).

In the curve (B) of Fig. 10, the contrast is thicker at 35°C (contrast decreases), whereas the optimal VOC value at each temperature (V at 15°C = 1.0 (V), 25
V at °C. o=1.0 (V), vDo at 35℃
= 0.5 (v)) (curve (A
) was able to maintain high contrast at all temperatures. Curve (C) in FIG. 10 is the result when V oc =O) (7) without ltDc bias. According to the temperature compensated driving method of the present invention, high contrast can be maintained even on the high temperature side where crosstalk is likely to occur, and contrast unevenness across the entire screen is reduced on the low temperature side, providing high quality display throughout the operating temperature range. was completed.

Further, in the present invention, the amount of amplitude change when switching the amplitude of the drive voltage is ±0.5% to ±10.0%, preferably ±1, with respect to the drive voltage amplitude during the first frame (first field).
．． Approximately 0% to 5.0% is suitable.

FIG. 9 is a plan view of the above-mentioned liquid crystal device, and a cell structure 90 shown in FIG.
and 91b are held at a predetermined distance by a spacer 94, and an adhesive 96 is applied around the periphery to seal the pair of substrates.
On the substrate 91a, an electrode group (for example, an electrode group for applying a scanning voltage in a matrix electrode structure) consisting of a plurality of transparent electrodes 92a is formed in a strip pattern, and on the substrate 91b Above the transparent electrode 9
An electrode group (for example, an information voltage application electrode group in a matrix electrode structure) is formed of a plurality of transparent electrodes 92b intersecting with the electrodes 2a. A 5i02 inorganic insulating film and polyvinyl alcohol (PV
The organic alignment film A) is formed, and its surface is subjected to a rubbing treatment. The liquid crystal used was an ester-based mixed liquid crystal having the phase series shown below, and had a chiral smectic phase.

Iso, Ch SmA ←--SmC*
←--Cry, 67.3°C 63.1°C47.7°
C-5.0°C (Iso: toyoyoshi phase, SmA: smectic A phase, Cry: crystalline phase) The above mixed liquid crystal was sealed in the cell shown in Fig. 9, and the temperature was once raised to the isoyoshi phase. Thereafter, it was slowly cooled to SmC*.

As the liquid crystal having bistability that can be used in the present invention, chiral smectic liquid crystal having ferroelectricity is most preferable, and among these, chiral smectic C phase (Sm
C*) or H phase (SmH wood) liquid crystals are suitable. Regarding this ferroelectric liquid crystal, please refer to “Le Journal de
"Le Journal"
de Physic Letter”) Volume 36 (L
-69) Ferroelectric Liquid Crystals J (r Ferroelectri) in 1975
cLiquid Crystalsj); “Applied Physics Letters” (“Applied
physics Letters") Volume 36 (No. 11) 1980 [Submicron Second Bistiple Electro-Optic Switching in Liquid Crystal J (rSubmicr.

5econd B15table Electroo
ptic Switchingin Liquid
Crystalsj) ; “Solid State Physics” 16 (141
), 1981, "Liquid Crystal", etc., and the ferroelectric liquid crystal disclosed therein can be used in the present invention.

More specifically, examples of ferroelectric liquid crystal compounds used in the present invention include decyloxybenzylidene-p'-amino-2-methylbutylcinnamate (DOBAMBC).
, hexyloxybenzylidene-p'-amino-2-'
Chloropropyl cinnamate (HOBACPC) and 4-o-(2-methyl)-butyl resol silidan-4'
-octylaniline (MBRA8) and the like.

When constructing an element using these materials, the element is supported by a copper block with a heater embedded, etc., as necessary, in order to maintain the temperature state such that the liquid crystal compound becomes the SmC* phase or SmH* phase. be able to.

Further, in the present invention, in addition to the above-mentioned SmC tree and SmH tree, it is also possible to use ferroelectric liquid crystals represented by chiral smectic F phase, ■ phase, J phase, G phase, or the like.

FIG. 11 schematically depicts an example of a ferroelectric liquid crystal cell. 131a (!: 131b, In203
．． It is a substrate (glass plate) coated with a transparent electrode such as 5n01 or ITO (indium tin oxide), between which a S m C* phase liquid crystal with a liquid crystal molecular layer 112 oriented perpendicular to the glass surface is formed. It is enclosed.

A thick line 113 represents a liquid crystal molecule, and this liquid crystal molecule 113 has a dipole moment (P) 114 in a direction perpendicular to the molecule. When a voltage equal to or higher than a certain threshold is applied between the electrodes on the substrates 111a and 111b, the helical structure of the liquid crystal molecules 113 is unraveled, and the alignment direction of the liquid crystal molecules 113 is changed so that all dipole moments (P) 114 are oriented in the direction of the electric field. can be changed. The liquid crystal molecules 113 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and the short axis direction. Therefore, for example, if polarizers are placed above and below the glass surface in a crossed nicol positional relationship, It is easily understood that this is a liquid crystal optical modulation element whose optical characteristics change depending on the polarity of applied voltage. Furthermore, if the thickness of the liquid crystal cell is sufficiently thin (for example, 1μ), the helical structure of the liquid crystal molecules will unwind even when no electric field is applied, as shown in Figure 12, and its dipole moment Pa or pb is upward (124a) or downward (12
Either state 4b) is taken. In such a cell, as shown in FIG.
When a or Eb is applied for a predetermined time, the dipole moment is directed upward 124 with respect to the electric field vector of electric field Ea or Eb.
a or downward 124b, and accordingly the liquid crystal molecules are aligned in either the first stable state 123a or the second stable state 123b.

There are two advantages to using such a ferroelectric liquid crystal as an optical modulation element. Firstly, the response speed is extremely fast, and secondly, the alignment of liquid crystal molecules has a bistable state. To explain the second point with reference to FIG. 12, for example, when the electric field Ea is applied, the liquid crystal molecules enter the first stable state 123a.
This state is stable even when the electric field is turned off.

Moreover, when an electric field Eb in the opposite direction is applied, the liquid crystal molecules are oriented to the second stable state 123b and the orientation of the molecules is changed.
It remains in this state even if the electric field is turned off. Further, as long as the applied electric field Ea does not exceed a certain threshold value, each orientation state is maintained. In order to effectively realize such fast response speed and bistability, it is preferable for the cell to be as thin as possible, and in general, the cell thickness is 0.5 μm.
~20μ, especially 1μ to 5μ is suitable.

〔Effect of the invention〕

As explained above, according to the temperature-compensated driving method according to the present invention, it is possible to reduce the uninverted portion during driving, reduce contrast unevenness on the entire screen, and reduce the difference in threshold voltage for each pixel. This makes it possible to maintain high display quality over the entire operating temperature range, even when the temperature is low.This temperature-compensated driving method is particularly effective for liquid crystal materials that are prone to crosstalk, and is also more effective for materials where the temperature dependence of the driving voltage is greater. It is.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a liquid crystal device of the present invention, and FIG. 2 is a timing chart of switching control signals, signal side drive voltages, and scanning side drive voltages used in the device. Figure 3 (A
) is a waveform diagram of the driving voltage used in the present invention, and Fig. 3(B)
is a timing chart thereof. Figure 4 is similar to Figure 3 (
FIG. 3 is a waveform diagram of a drive voltage whose amplitude is changed with respect to the drive voltage of A). Figures 5(A)-(D), Figures 6(A)-(D
) and FIGS. 7(A) to 7(D) are waveform diagrams showing other driving voltages used in the present invention. FIG. 8 is a waveform diagram showing another driving voltage used in the present invention. FIG. 9 is a plan view of the liquid crystal element used in the present invention. FIG. 10 is a characteristic diagram showing the temperature dependence of contrast. 11 and 12 are perspective views of the ferroelectric liquid crystal element used in the present invention. Patent applicant Canon Corporation 730 (A) SN O- 1st + [EI 5y □□ No. 3 (E3) Fig. 6 (8) Chestnut 7 (B) 3rd day SJ O□ - Vosu VDc

Claims (7)

[Claims] (1) A liquid crystal element having a scanning line and an information line, with a ferroelectric liquid crystal disposed between the scanning line and the information line, and a driving AC voltage applied to the intersection of the scanning line and the information line. 1. A liquid crystal device comprising means for superimposing a DC component on a liquid crystal device, characterized in that the value of the DC component is changed in accordance with temperature changes. (2) The voltage signal applied to the information line has one polarity voltage and the other polarity voltage based on the voltage applied to the unselected scanning line, and at least one of the one polarity voltage and the other polarity voltage. 2. The liquid crystal device according to claim 1, wherein a DC component is superimposed on the voltage. (3) The voltage signal applied to the selected scanning line has one polarity voltage and the other polarity voltage based on the voltage applied to the unselected scanning line, and the one polarity voltage and the other polarity voltage are different from each other. 2. The liquid crystal device according to claim 1, wherein a DC component is superimposed on at least one of the voltages. (4) The voltage signal applied to the information line has one polarity voltage and the other polarity voltage based on the voltage applied to the unselected scanning line, and the peak value of the one polarity voltage and the other polarity voltage. 2. The liquid crystal device according to claim 1, wherein the liquid crystals are asymmetrical with respect to each other. (5) The voltage signal applied to the selected scanning line has one polarity voltage and the other polarity voltage based on the voltage applied to the unselected scanning line, and the one polarity voltage and the other polarity voltage are different from each other. The liquid crystal device according to claim 1, wherein the peak values are asymmetrical to each other. (6) The liquid crystal device according to claim 1, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal. (7) The liquid crystal device according to claim 6, wherein the thickness of the chiral smectic liquid crystal is set to be sufficiently thin to eliminate the helical structure inherent in the chiral smectic liquid crystal in the absence of an electric field.