JPS6371833A - Liquid crystal device - Google Patents

Abstract

PURPOSE:To enable a ferroelectric liquid crystal of a matrix electrode structure to perform time-sharing driving by setting a specified relation between the pulse width of each voltage signal to be impressed to a scanning electrode and a signal electrode, and the impression time of the voltage having the same polarity impressed to the crossing part of the both electrodes. CONSTITUTION:In a liquid crystal element 31 having a matrix electrode constituted of interposed ferroelectric liquid crystals, information selecting signals are impressed succeedingly to a scanning line 32 and information signals are impressed to a data line 33. Scanning selecting signals 2V0 are impressed to the scanning line S, information non-selecting signals IOFF and information selecting signals ION obtd. by adding alternate auxiliary signals are impressed to the data line I, and the information non-selecting signal and the information selecting signal are impressed to the picture element on the line where the scanning selecting signal is impressed. When a noted picture element at a crossing point is transferred from the selected state to the non-selected state IOFF(ION) is impressed in the selected state, the max. impression time of the voltage of the same polarity is regulated to 2DELTAT (DELTAT is a pulse width of the impressed signal), when ION(IOFF) is impressed in the non-selecting state.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to a liquid crystal device such as a liquid crystal display element or a liquid crystal-optical shutter array, and more particularly to a liquid crystal device using ferroelectric liquid crystal.

(Prior art) As a conventional liquid crystal element, for example, M-Shut (M,
5chadt) and Double Helfrich (W, He
Applied Physics Letters Volume 18, Number 4 (1971, 2, 1)
5), pages 127-128 (“Applied P
hysics Letters” Vo, 18, No 4 (
197t-2, 15), P, 127-128) "Voltage Dependent Optical Activity - Op a Twisted Nematic Liquid Crystal"("VoltageDependen
t 0pttcal Activty of
a Twisted Nematic Liq
TN (twisted nematic) shown in
nematic)) devices using liquid crystals are known. This TN liquid crystal has a problem in that crosstalk occurs during time-division driving using a matrix electrode structure with a high pixel density, so the number of pixels is limited.

Furthermore, a display element is known in which a switching element using a thin film transistor is connected to each pixel, and each pixel is switched. However, the process of forming the thin film transistor on the substrate is extremely complicated, and it is difficult to use a display element with a large area. There are some problems that make it difficult to create.

In order to solve these problems, Clark and Lagauer announced a ferroelectric liquid crystal device in US Pat. No. 4,367,924.

This ferroelectric liquid crystal has a memory effect, but if it incorporates a matrix electrode structure consisting of scanning lines and data lines and performs time-division driving, it is possible to reverse the polarity of the voltage during writing. If a voltage continues to be applied to the written pixel even if the voltage is below the threshold (e.g., more than 5 times the write pulse width), its written state will be reversed (e.g., a pixel written white This phenomenon was discovered through experiments by the present inventors.

[Summary of the invention]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a time-division driving method for a ferroelectric liquid crystal device using a matrix electrode structure having scanning lines and data lines.

Another object of the present invention is to provide a method for driving a ferroelectric liquid crystal device that prevents the above-mentioned inversion phenomenon.

Such an object of the present invention is to have the scan electrode have voltages of one polarity and the other polarity, and a voltage at the same level as the voltage applied to the scan non-selection electrode, based on the α voltage applied to the scan non-selection electrode. A first voltage signal that applies a scanning selection signal and applies a voltage exceeding one threshold voltage of the ferroelectric liquid crystal to the selected signal electrode in synchronization with the voltage of one polarity, and a voltage of the same level. a second voltage that exceeds the other threshold voltage of the ferroelectric liquid crystal in synchronization with the voltage of the other polarity to the other signal electrode by applying an information signal having an alternating voltage signal within the application period of An information signal having an alternating voltage signal is applied within the application period of the voltage signal and the voltage at the same level, and when the pulse width of the first voltage signal or the second voltage signal is ΔT, the voltage is applied to the intersection. A liquid crystal device in which the voltage of the same polarity is applied for a maximum of 2ΔT, or at the intersection of all or a predetermined number of scanning electrodes and all or a predetermined number of signal electrodes, exceeds the threshold voltage of one of the ferroelectric liquid crystals. applying a voltage to the scan electrode, and applying a scan selection signal having a voltage of one polarity and a voltage at the same level as the voltage applied to the scan non-selection electrode, based on the voltage applied to the scan non-selection electrode, A first voltage signal that applies a voltage exceeding the other threshold voltage of the ferroelectric liquid crystal to the selected signal electrode in synchronization with the voltage of one polarity, and an alternating voltage signal within the application period of the voltage of the same level. a second voltage signal that applies a voltage that does not exceed the threshold voltage of the ferroelectric liquid crystal to the other signal electrode in synchronization with the voltage of one polarity, and a voltage of the same level. Applying an information signal having an alternating current voltage signal within an application period,
The present invention is characterized in that the liquid crystal device has a maximum application time of 2ΔT for voltages of the same polarity applied to the intersection, where ΔT is the pulse width of the voltage signal.

[Detailed description of aspects of the invention]

Ferroelectric liquid crystals that can be used in the present invention include chiral smectic liquid crystals, particularly C phase (SmC''),
H phase (SmH”), I phase (SrnI*), J phase (SmJ
*), phase (SmK*), phase C (SmG*) or phase F (
SmF”) is suitable.For this ferroelectric liquid crystal,
(“LEJOURNAL DE PHYSIQ
UE LETTER3” )36 (L-69)1
975. "rFerroelectric Liquid Crystals"
dCrystals”; “Applied Physics Letters”
cs Letters”) 3B (11)!980 “Submicro Second Bistiple Electro-Optic Switching in Liquid Crystals J (rsubmicro 5econd B
tstable Electroopttc Sw
itching 1nLiquid Crysta
ls") H"Solid State Physics" 16 (141) 1981 r
ferroelectric liquid crystals disclosed in these documents can be used in the present invention.

FIG. 1 schematically depicts an example of a ferroelectric liquid crystal cell. 11 and 11' are In2O*.

5no2 and ITO (Indium-Tin Oxid
It is a substrate (glass plate) coated with a transparent electrode such as e), and a SmC* phase or SmH phase liquid crystal with 1112 oriented perpendicular to the glass surface is sealed between the substrates (glass plates). A thick line 13 represents a liquid crystal molecule, and this liquid crystal molecule 13 has a dipole moment 14 (on P) in a direction perpendicular to the molecule. When a voltage equal to or higher than a certain threshold is applied between the substrate 11 and the electrodes on tt', the helical structure of the liquid crystal molecules 13 is unraveled, and the liquid crystal molecules 13 change their alignment direction so that all the dipole moments 14 point in the direction of the electric field. Can be done. The liquid crystal molecules 13 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and the short axis direction,
Therefore, it is easy to understand that, for example, if crossed Nicol polarizers are placed above and below a glass surface, a liquid crystal modulation element whose optical characteristics change depending on the polarity of applied voltage can be obtained.

Furthermore, if the thickness of the liquid crystal cell is made sufficiently thin (for example, 1
μ), as shown in Figure 2, the helical structure of liquid crystal molecules is unraveled (non-helical structure) even when no electric field is applied.
, its dipole moment P or P' is either upward (24) or downward (24'). When such a cell is given an electric field E or E' with a different polarity above a certain threshold value as shown in FIG. 2, the dipole moment will move upward 24 or The direction is changed downward 24', and the liquid crystal molecules are oriented either in the first stable state 23 or in the second stable state 23' accordingly. There are two advantages to using such a ferroelectric liquid crystal as a light modulation element. Firstly, the response speed is extremely fast, and secondly, the alignment of liquid crystal molecules has bistability. To explain the second point with reference to FIG. 2, for example, when the electric field E is applied, the liquid crystal molecules are oriented in a first stable state 23, and this state remains stable even when the electric field is turned off. When an electric field E' in the opposite direction is applied, the liquid crystal molecules are oriented to a second stable state 23' and change their orientation, but they remain in this state even after the electric field is turned off.

Further, as long as the applied electric field E does not exceed a certain darkness 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 generally 0.5
-20μ, especially 1μ-5μ are suitable.

A liquid crystal electro-optical device having a matrix electrode structure using this type of ferroelectric liquid crystal has been proposed, for example, by Clark and Ragabal in US Pat. No. 4,367,924.

Preferred driving examples of the present invention will be described below with reference to the drawings.

FIG. 3 is a schematic diagram of a liquid crystal element 31 having a matrix electrode 8i structure with a ferroelectric liquid crystal sandwiched between them. 32 is a scanning line to which a scanning selection signal is sequentially applied, and 33 is a data line to which an information signal is applied.

FIG. 4 is a chronological representation of the preferred driving method of the present invention.

The mechanism of electric field-induced switching of ferroelectric liquid crystals in a bistable state is not necessarily clear microscopically, but in general, after switching to a predetermined stable state with a strong electric field for a predetermined time, no electric field is applied at all. It is possible to maintain this state semi-permanently if the switch is left in a state where it does not switch, but it is possible to maintain the state semi-permanently, but with a weak electric field that does not cause switching for a certain period of time (corresponding to the voltage below the threshold in the example explained earlier). Even if an electric field of opposite polarity is applied for a long time, the orientation state may be reversed again to the opposite stable state, resulting in a phenomenon in which correct information display or modulation cannot be achieved. . The present inventors have confirmed that the ease of occurrence of the transition reversal phenomenon (a type of crosstalk) of the orientation state due to the application of such a weak electric field for a long time is influenced by the surface condition of the substrate, the type of liquid crystal material, etc. Although this has been confirmed through experiments, its logical analysis has not been fully clarified. However, when fabricating a ferroelectric liquid crystal device, if a uniaxial substrate treatment is performed to align the liquid crystal molecules by rubbing the substrate or obliquely depositing SiO, etc., the above-mentioned inversion phenomenon may become more pronounced. found. especially,
It was also confirmed that the reversal phenomenon appears more strongly at high temperatures than at low temperatures.

In any case, it is preferable to avoid applying an electric field in a fixed direction for a long time in order to achieve correct information display or modulation.

FIG. 5 shows another preferred driving example of the present invention.

FIG. 4 shows a modified example of the alternating auxiliary signal used in the driving example of the one-time full erase/write method. 4(a) shows a 2Vo scanning selection signal applied to the scanning line S, and FIGS. 4(b) and 4(C) show an information non-selection signal 1 with an alternating auxiliary signal applied to the data line I, respectively. OFF and information non-selection signal engineering. It represents 8. Also, Fig. 4(d) and (e)
represent waveforms when an information non-selection signal and an information selection signal are applied to pixels on a line to which a scanning selection signal is applied, respectively.

In the waveform shown in Fig. 7, ΔT3-ΔT6=ΔT, Δ
T,=ΔT2=δ1. ΔT4=ΔT.

= δ2, the application time of the same polarity voltage is ΔT+6 for pixels on the scanning line to which the scanning selection signal S is applied.
2 (ΔT3+ΔT4) or δ1+6 (ΔT2+ΔT
3), and when the pixel of interest is non-selected - non-selected, I
OFF or I. When N is continuous, the application time of the same polarity voltage becomes ΔT1+ΔT6 and ΔT2+ΔT3, and when the pixel of interest changes from selected to non-selected, the process is performed at the time of selection. .

(ION) is applied, and lON(IOFF) is applied when not selected.
) is applied, and the application time of the same polarity voltage is ΔT
l+ΔT6. ΔT3+ΔT4 and ΔT2+ΔT.

Therefore, in the present invention, if δ1 × ΔT or δ2 × ΔT is set, the application time of the above-mentioned same polarity voltage is 2ΔT at maximum.
It can be done.

As shown in Fig. 4(b) and (c), the phase of the AC signal added before and after the information signal (applied to the data line in synchronization with the scanning selection signal) is different from that of the non-selection signal and the selection signal. Since they are different, the continuous application time of the same polarity does not exceed 2ΔT.

As shown in FIG. 4, the above-mentioned inversion phenomenon can be effectively prevented by applying the first alternating auxiliary signal and the second alternating auxiliary signal in phases before and after the phase in which the information signal is applied. .

Further, FIGS. 5 and 6 show modified examples of the line black and white sequential writing methods, respectively. That is, the methods shown in FIGS. 5 and 6 represent a mode in which a phase is provided in which the first alternating auxiliary signal and the second alternating auxiliary signal are applied before and after the information signal is applied.

In FIG. 5, 2Vo is applied to the scanning line with ΔT3 phase.

A scanning selection signal of -2Vo is applied at ΔT4 phase. On the data line I C0AIIX+, the black write information signal is the data line! (LIGHT), a white write information signal is applied in synchronization with the scan selection signal. Furthermore, by providing a phase in which the first auxiliary signal and a second auxiliary signal are applied before and after the phase in which this information signal is applied, the application time of the reverse voltage can be shortened to 2ΔT. At this time, the pulse width of the added AC waveform does not necessarily have to match the pulse width of the information signal.In addition, as shown in (d) in Figure 8, the S/I (on DAR) has pixels written in black. The waveform when the pixel is written, (e); S/In, is the waveform when the pixel is written white.

Further, FIG. 6 is a modification of the method shown in FIG. 5, in which the phases of the AC waveforms are different. In FIG. 6, (a) is a scanning selection signal, (b) is a black write signal, (c) is a white write signal, (d
) represents the waveform when the pixel is written in black, and (e) represents the waveform when the pixel is written in white.

In the embodiment described above, the voltage value Vo is: ■0<Vthl
<3Vo, -VO>-Vtrra>-3V.

(Vty: threshold voltage of first stable orientation state, Vthl:
The threshold voltage of the second stable orientation state is set to be satisfied.

The ferroelectric liquid crystals used in the present invention include desyloxybenzylidene-P'-amino-2-methylbutylcinnamate)-(DOBAMBC), hexyloxybenzylidene-P'-amino-2-chloropropylcinnamate (DOBAMBC), and hexyloxybenzylidene-P'-amino-2-chloropropylcinnamate
HOBACPC) and 4-o-(2-methyl)-butylresorsilitin-4'-octylaniline (MBRAS)
In addition, JP-A-59-98051, JP-A-59-11
Those disclosed in Japanese Patent No. 8744 and Japanese Patent No. 59-128357 can be used.

The method of the present invention can be widely applied to the field of optical shutters such as liquid crystal-optical shutters and displays such as liquid crystal televisions.

[Brief explanation of the drawing]

1 and 2 are perspective views schematically showing a liquid crystal element used in the driving method of the present invention. FIG. 3 is a plan view showing a matrix electrode structure used in the driving method of the present invention. FIG. 4, FIG. 5, and FIG. 6 are explanatory diagrams showing the driving method used in the present invention in chronological order.

Claims (2)

[Claims] (1) In a liquid crystal device in which a ferroelectric liquid crystal is arranged at the intersection of a scanning electrode group and a signal electrode group, voltages of one polarity and the other polarity are applied to the scanning electrodes with reference to the voltage applied to the scanning non-selection electrodes. , and a scan selection signal having the same voltage level as the voltage applied to the scan non-select electrode, and apply one threshold voltage of the ferroelectric liquid crystal to the selected signal electrode in synchronization with the one polarity voltage. A first voltage signal that gives a voltage exceeding the above voltage and an information signal having an alternating voltage signal are applied within the application period of the voltage of the same level, and the information signal having the alternating voltage signal is applied to the other signal electrode in synchronization with the voltage of the other polarity. applying a second voltage signal that provides a voltage exceeding the other threshold voltage of the dielectric liquid crystal and an information signal having an alternating voltage signal within the application period of the voltage at the same level; The pulse width of the voltage signal is Δ
A liquid crystal device characterized in that, where T is the same polarity voltage applied to the intersection, the maximum application time is 2ΔT. (2) In a liquid crystal device in which a ferroelectric liquid crystal is arranged at the intersection of a scanning electrode group and a signal electrode group, a ferroelectric liquid crystal is placed at the intersection of all or a predetermined number of scanning electrodes and all or a predetermined number of signal electrodes. Apply a voltage that exceeds the threshold voltage of one side of the liquid crystal, and apply a voltage to the scan electrode at the same level as the voltage of one polarity and the voltage applied to the scan non-select electrode, based on the voltage applied to the scan non-select electrode. applying a scanning selection signal having a polarity to the selected signal electrode in synchronization with the one-polarity voltage;
Applying a first voltage signal that gives a voltage exceeding the threshold voltage of the other ferroelectric liquid crystal and an information signal having an alternating voltage signal within the application period of the voltage at the same level, and applying the information signal having the alternating voltage signal to the other signal electrode. applying a second voltage signal that provides a voltage that does not exceed the threshold voltage of the ferroelectric liquid crystal in synchronization with the polarity voltage, and an information signal having an alternating current voltage signal within the application period of the voltage at the same level; The pulse width of the first voltage signal or the second voltage signal is set to Δ
A liquid crystal device characterized in that, where T is the same polarity voltage applied to the intersection, the maximum application time is 2ΔT.