JP2584752B2 - Liquid crystal device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal device, and more particularly, to a liquid crystal device using a chiral smectic liquid crystal having ferroelectricity.

[Description of Prior Art]

2. Description of the Related Art Conventionally, a liquid crystal display element in which a scanning electrode group and a signal electrode group are configured in a matrix, a liquid crystal compound is filled between the electrodes to form a large number of pixels, and an image or information is displayed is well known. I have. As a driving method of the display element, a time division drive in which an address signal is sequentially and selectively applied to the scanning electrode group and a predetermined information signal is selectively applied to the signal electrode group in parallel in synchronization with the address signal is used. Has been adopted.

Most of these have been put to practical use, for example, in “Applied Physik Letters”.
cs Letters "), 1971, 18 (4), pp. 127-128.
M. Schadt and W. Helfrich
Co-authored “Voltage Depende Optical Activity of a Twisted Nematic Liquid Crystal”
nt Optical Activity of a Twisted Nematic L
TN (twisted nematic) shown in iquid Crysttal ")
Type liquid crystal.

In recent years, as an improved type of the conventional liquid crystal element, the use of a liquid crystal element having bistability has been disclosed in both Clark and Lagerwall by JP-A-56-107216.
And US Patent No. 4367924. In general, a ferroelectric liquid crystal having a chiral smectic C phase (SmC ^* ) or an H phase (SmH ^* ) is used as the bistable liquid crystal. In these states, the first liquid crystal responds to an applied electric field. It takes one of an optically stable state and a second optically stable state, and has a property of maintaining the state when no electric field is applied, that is, has stability, and has a quick response to a change in the electric field, It is expected to be widely used in fields such as high-speed and storage type display devices.

[Problems to be solved by the invention]

However, a problem arises when the number of display pixels is extremely large and high-speed driving is required. That is, the threshold voltage for providing the first stable state in the ferroelectric liquid crystal cell having bistability for a predetermined voltage application time is -V.
_th1 and the threshold voltage for providing the second stable state is + V
_If the threshold voltage is set to _th2 , the display state (for example, white state) written in the pixel is changed to another display state (for example, black state) when the voltage is continuously applied for a long time without _exceeding these threshold voltages. May be reversed. FIG. 7 shows the threshold characteristics of a bistable ferroelectric liquid crystal cell.

FIG. 7 is a plot of the application time dependence of the threshold voltage (V _th ) required for switching when DOBAMBC (72 in the figure) and HOBACPC (71 in the figure) are used as chiral smectic liquid crystals exhibiting ferroelectricity. It was done.

As is clear from FIG. 7, it is understood that the threshold value _Vth has an application time dependency, and that the shorter the application time, the steeper the slope. From this fact, when the present invention is applied to an element having an extremely large number of scanning lines and driving at a high speed, even if a certain pixel is switched to a bright state at the time of scanning, an information signal which is always _Vth or less after the next scanning is obtained. It is understood that when the application of is continuously performed, there is a risk that the pixel is inverted to a dark state while the scanning of one screen is completed.

Therefore, when the multiplexing drive is applied to the ferroelectric liquid crystal element, a low voltage having a polarity opposite to that of the writing may be continuously applied to the non-selected pixels for a long time, which causes crosstalk. Had become.

In order to prevent this crosstalk, Kanbe et al., As disclosed in British Publication No. 2141279, used a data signal with a write signal and an auxiliary signal so that an AC voltage was applied to unselected pixels. It is proposed to apply to the line.

Although the problem of crosstalk could be solved by the above-mentioned method of Shinbe et al., The pulse at the time of writing (pulse width; Δt) and the non-selected pulse immediately after writing (pulse width; Δt) are continuous. When the pixels have the same polarity, the same polarity pulse is continuously applied to the pixels for at least 2Δt, and the screen flickers when the display panel is used (the display surface is periodically brightened or Darkening phenomenon).

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal device using a novel driving method which solves the above-mentioned problems in the conventional optical modulation element, particularly in a liquid crystal display element or a liquid crystal optical shutter.

[Means for Solving the Problems] and [Operation] The present invention provides a liquid crystal element having a chiral smectic liquid crystal arranged between a substrate having a scanning line and a substrate having a data line, and a scanning selection signal applied to the scanning line. And a means for applying a write signal of the first or second polarity to the data line in synchronization with the scan selection signal, wherein the n-th scan selection signal is applied to the data line. Comparing means for comparing the n-th write signal synchronized with the (n + 1) -th write signal synchronized with the (n + 1) -th scan selection signal, and the (n + 1) -th write signal after the n-th write signal Means for applying an auxiliary signal having a waveform in which a voltage having the same polarity as these write signals is not continuous before
The auxiliary signal has at least three different values depending on whether the n-th write signal and the (n + 1) -th write signal both have the first polarity, both have the second polarity, and the other have different polarities. It is characterized in that it is selected from two waveforms according to the output data of the comparing means.

The “write signal” described in this specification determines the write state of a pixel within an address period Ss including a period during which a scan selection signal for sequentially addressing a scan line is applied (the pixel is set to one of white and black). Information signal applied from the data line with a phase), and the "auxiliary signal" is a voltage applied from the data line with a phase that does not determine the pixel writing state within the address period Ss. It is.

Further, the “polarity” of the voltage applied to the scanning line and the data line described in this specification is based on the voltage applied to the unselected scanning line.

〔Example〕

FIG. 8 is a plan view of a ferroelectric liquid crystal cell 81 used in the present invention. The ferroelectric liquid crystal cell 81 has data lines 83 (I ₁ , I ₂ ,
..) And the scanning lines 82 (S ₁ , S ₂ ,...) Are wired so as to intersect. Further, 84 is a scanning circuit, 85 is a scanning side drive voltage generation circuit, 86 is a signal side drive voltage generation circuit, 87 is a line memory, 88
Represents a shift register.

FIG. 1 shows a driving waveform according to the present invention, wherein S1,
S2, S3 indicates a voltage waveform applied to the scan lines _{S 1, S 2, S 3} , in each scanning line, the scanning selection signal sequentially voltages 2Vo is applied. I1 and I2 indicate voltage waveforms applied to the data lines I ₁ and I ₂ , and the information signal of white-white-black-white-... Is continuously applied to the data line I _1. I ₂ is white-black-
Black-black -... information signals are continuously applied. or,
I1-S1 is a voltage waveform applied to the intersection between the scanning lines S ₁ and the data line I ₁ (pixel), the I2-S1 scan lines S ₁ and the data line
Is a voltage waveform applied to the intersection of the I _2.

In the driving example shown in FIG. ₁ , a voltage 3V ₀ exceeding the threshold voltage of the ferroelectric liquid crystal is applied to all or some pixels of the ferroelectric liquid crystal cell 61 in the erasing step T1, and the pixel The liquid crystal is reset to a first optical state (for example, “white”) based on the first stable state. Followed by the writing step T ₂ in the scanning lines S _1, S _2, sequentially applies a scanning selection signal voltage 2Vo to S _3, applies the information signal to the data lines I _1, I ₂ in synchronization with this, The display shown in FIG. 8 can be obtained.

The information signal applied to the data line I _M (M; M-th data line, M is an integer of 1,2,3, ...) is the n-th (n = 1,2,3, ...) write by comparing the signal W _n and the subsequent (n + 1) th write signal W _{n + 1,} the write signal W _n and W
determining the voltage of the auxiliary signal K _n to be applied between the _{n + 1.} First
Of the information signals applied to the data lines I ₁ and I ₂ in the figure, the shaded portions W ₁ ^W _, ⁽ ₂ ^B _, ⁾ _{3 ,} ... _N (the subscript W indicates a white write signal, and B indicates a black write signal) Is a write signal and K _{1
, 2 , 3 ,} ... _N are auxiliary signals. At this time, the n-th white write signal W _n ^W (+ V ₀ ) and the (n + 1) -th white write signal W _n ^W
₊₁ (+ V ₀₎ auxiliary signal K _n to be applied between the can, n-th white write signal W _n ^W opposite polarity voltage -V ₀ next to, n-th black write signal W _n ^B (-V ₀ ) And the (n + 1) th black write signal W _n ^B
Auxiliary signal K _n to be applied between the ₊₁ (-V ₀₎ is a n-th black write signal W _n ^B opposite polarity voltage + V _0. Furthermore, n
Th In the white write signal W _n ^W (or black write signal W _n ^B), in the case (n + 1) th subsequent thereto is black write signal W _n ^B (or white write signal W _n ^W), the voltage as an auxiliary signal K _n 0 is applied. For this reason, in the present invention, the time of 2Δt (referred to as 2Tb pulse) in which pulses of the same polarity are continuous does not occur between the time of selection and the time of non-selection immediately after selection, and the voltage applied to the pixel at the time of non-selection Can be made substantially zero. The present invention was able to prevent flicker on the display screen by eliminating the 2Tb pulse described above.

At this time, the voltage V ₀ is set to a voltage value that satisfies the relationship | 3V ₀ |> | V _th |> | V ₀ | (V _th is the threshold voltage of the ferroelectric liquid crystal).

Further, the phase t ₁ in FIG. 1 corresponds to a phase of applying a write signal W _n having a pulse width [Delta] n, the phase t ₂ is equivalent to the phase of applying an auxiliary signal K _n. Application time also the auxiliary signal K _n at this time, preferably also be set to Delta] t.

The driving example shown in FIG. 2 is different from the driving example shown in FIG. 2 in that a voltage 0, an alternating voltage having three alternating positive and negative pulses, and an alternating voltage having the opposite phase are used. ,
This is exactly the same as the driving example shown in FIG. or,
In the present invention, the alternating voltage having an odd number of positive and negative pulses is not limited to three alternating pulses.

FIG. 3 shows another preferred driving example of the present invention. In the driving example shown in Figure 3, by the erase pulses of uniform voltage 3V ₀ to all or part of the pixels on a selected scanning line in the phase t ₁ is applied, these pixels before write state uniformly can be reset, the subsequent address in phase t ₂ corresponding to the phase, black write signal from the data line to a pixel reset earlier W _n ^B (-V ₀₎ and white write signal W
_n ^W (+ V ₀ ) is selectively applied. Applying at subsequent auxiliary signal K _n in phase t ₃ and Figure 1 of the aforementioned method similar to the method described in Figure 2.

FIG. 4 shows another preferred driving example of the present invention. In the driving example shown in FIG. 4, the erasing pulse of the voltage −3V ₀ is uniformly applied to all or a part of the pixels on the scanning line whose phase t ₁ is selected, so that these pixels are written in the previous writing. The state can be reset uniformly. Phase t ₃ corresponds to the write phase, the black write signal from the data line in phase ^{_{t 3 W n B (V 0}} ) and the white write signal ^W _n W (-V ₀₎ is selectively applied, the phase t ₂ There corresponds to the phase of applying an auxiliary signal K _n. The auxiliary signal K _n are applied in a manner similar to that described in Figure 1.

 Next, a block diagram of the driving circuit is shown in FIG.

FIG. 5 is explained together with the time chart shown in FIG. 6. At the timing of t = 1, the shift register (S / R)
Is transferred to the line memory I at the timing t = 2. At time t = 3, the information in the line memory I is transferred to the line memory II, and at the same time, the information in the line memories I and II is compared by the comparator 51, and the result is transferred to the line memory III. The line memory II and the information of the line memory II are mixed by the drive mode processor 52 and the line decoder 53,
Each 1-bit signal is converted into 2 bits, and an output waveform is produced by the level converter 54 and the analog switch unit 55.

At t = 3, the contents of the shift register at the time of t = 1 are output, and then sequentially output.

In FIG. 5, CK ₁ and KC ₂ are clocks, LATH is a latch signal input, IN is an information data input to the shift register S / R, and V _DD , V _SS1 and V _SS2 are necessary for analog switch driving. The various voltage sources, V ₁ , V _C and V _2, are output level voltages.

The optical modulation substance used in the liquid crystal device of the present invention has at least two stable states, and particularly takes one of a first optical stable state and a second optical stable state according to an applied electric field. That is, a substance having a bistable state with respect to an electric field, particularly a liquid crystal having such properties is used.

As the liquid crystal having bistability that can be used in the driving method of the present invention, a chiral smectic liquid crystal having ferroelectricity is most preferable. Among them, a chiral smectic C phase (SmC ^* ) or an H phase (SmH ^* ) is used ^. A) liquid crystal is suitable.
This ferroelectric liquid crystal is described in “Le Jouranl de Physik Lutheran” (“Le Jouranl de physics”).
ove letter ") Volume 36 (L-69), 1975," Ferroelectric Liquid Crystals "(" Ferroelect
ric Liquid Crystals ”);“ Applied Physics Letter ”, Vol. 36 (No. 11),“ Submicron Second Bistable Electrooptic Switching in Liquid Crystals ”(1980) "Submicro Second Bist
able Electrooptic Switching in Liquid Crystal
s ");" Solid State Physics 16 (141) 1981, "Liquid Crystal", and the like, and the ferroelectric liquid crystal disclosed therein can be used in the present invention.

More specifically, examples of the ferroelectric liquid crystal compound used in the method of the present invention include desyloxybenzylidene-P'-
Amino-2-methylbutylcinnamate (DOBAMBC),
Hexyloxy benzylidene -P'- amino-2-chloropropyl cinnamate (HOBACPC) and 4 ₀ -
(2-Methyl) -butylresorsiliden-4'-octylaniline (MBRA8) and the like.

When an element is formed using these materials, in order to maintain the liquid crystal compound in a temperature state such that the liquid crystal compound becomes an SmC ^* phase or an SmH ^* phase, the element is, if necessary, provided with a copper block or the like in which a heater is embedded. Can be supported.

In the present invention, it is also possible to use ferroelectric liquid crystals that appear in the chiral smectic F phase, I phase, J phase, G phase or K phase in addition to the above-mentioned SmC ^* and SmH ^* .

FIG. 9 schematically illustrates an example of a ferroelectric liquid crystal cell. 91a and 91b are substrates (glass plates) coated with transparent electrodes such as In ₂ O ₃ , SnO ₂ and ITO (indium-tein-oxide), between which the liquid crystal molecular layer 92 is perpendicular to the glass surface The liquid crystal of the SmC ^* phase, which is oriented as described above, is sealed. A bold line 93 represents a liquid crystal molecule, and the liquid crystal molecule 93 has a dipole moment (P⊥) 94 in a direction perpendicular to the molecule. When a voltage above a certain threshold is applied between the electrodes on the bases 91a and 91b, the liquid crystal molecules
The helical structure of 93 is released, and the dipole moment (P⊥) 94
Can be changed in the direction of the orientation of the liquid crystal molecules 93 so that they all face the direction of the electric field. The liquid crystal molecules 93 have an elongated shape, exhibit a refractive index anisotropy in the major axis direction and the minor axis direction,
Therefore, it is easily understood that, for example, if polarizers arranged in a crossed Nicols positional relationship with each other above and below a glass surface are provided, a liquid crystal optical modulation element whose optical characteristics change depending on the polarity of applied voltage. Further, when the thickness of the liquid crystal cell is made sufficiently thin (for example, 1 μm), the helical structure of the liquid crystal molecules is unwound even when no electric field is applied as shown in FIG. Is in an upward (104a) or downward (104b) state. When such a cell is applied for a predetermined time of an electric field Ea or Eb having a different polarity or more than a certain threshold as shown in FIG. 10, the dipole moment is upward 104a or downward 104b with respect to the electric field vector of the electric field Ea or Eb. The orientation is changed, and the liquid crystal molecules are accordingly oriented in either the first stable state 103a or the second stable state 103b.

There are two advantages of using such a ferroelectric liquid crystal as the optical modulation element. First, the response speed is extremely fast, and second, the orientation of the liquid crystal molecules has a bistable state. The second point will be described with reference to FIG. 10, for example.
When the electric field Ea is applied, the liquid crystal molecules are oriented to the first stable state 103a, and this state is stable even when the electric field is turned off. or,
When an electric field Eb in the opposite direction is applied, the liquid crystal molecules are oriented in the second stable state 103b and change the direction of the molecules, but remain in this state even after the electric field is turned off. Electric field
As long as Ea does not exceed a certain threshold, each alignment state is also maintained. With such a fast response speed,
In order to effectively realize bistability, it is preferable that the cell is as thin as possible, and generally, 0.5 μm to 20 μm, particularly 1 μm to 5 μm is suitable.

〔The invention's effect〕

By determining the auxiliary signal by comparing the preceding and succeeding information signals as described above, the influence of the non-selected signal on the non-selected line can be minimized, and the display screen does not flicker. Excellent display quality can be realized.

[Brief description of the drawings]

FIGS. 1, 2, 3 and 4 are timing charts showing the drive waveforms used in the present invention in time series. FIG. 5 is an explanatory diagram showing a sequence up to output of an information signal used in the present invention, and FIG. 6 is a timing chart at that time. FIG. 7 is a characteristic diagram showing the application time dependency of the threshold voltage of the ferroelectric liquid crystal. FIG. 8 is a plan view of a matrix electrode structure used in the present invention. FIG. 9 and FIG. 10 are schematic perspective views of the ferroelectric liquid crystal element used in the present invention.

Claims (4)

(57) [Claims] A liquid crystal element having a chiral smectic liquid crystal disposed between a substrate having a scanning line and a substrate having a data line; a means for applying a scanning selection signal to the scanning line; Means for applying a write signal of the first or second polarity in synchronization with the signal, wherein the n-th write signal synchronized with the n-th applied scan selection signal and the (n + 1) th write signal Comparing means for comparing the (n + 1) th write signal synchronized with the scan selection signal, and a voltage having the same polarity as these write signals continues after the (n) th write signal and before the (n + 1) th write signal. Means for applying an auxiliary signal having a non-waveform waveform, wherein the auxiliary signal has the first polarity and the nth write signal and the (n + 1) th write signal both have the second polarity. Case and A liquid crystal device characterized in that at least three different waveforms are selected according to output data of the comparing means when the polarity is different. 2. The liquid crystal device according to claim 1, wherein the waveform of the auxiliary signal is selected from three waveforms: a single pulse of a second polarity, a single pulse of a first polarity, and a reference voltage. . 3. A waveform of the auxiliary signal includes a first pulse train composed of two pulses of a second polarity and one pulse of a first polarity, two pulses of a first polarity and one pulse of a second polarity. 2. The liquid crystal device according to claim 1, wherein the waveform is selected from three waveforms of a second pulse train composed of: and a reference voltage. 4. The auxiliary signal has a first waveform composed of a pulse of a second polarity and a reference voltage, a second waveform composed of a pulse of a first polarity and a reference voltage, and a third waveform composed of a reference voltage. 2. The liquid crystal device according to claim 1, wherein the liquid crystal device is selected from the following waveforms.