JPH07168156A - Liquid crystal element driving method - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides an AC pulse component having a time width shorter than the response time of the spontaneous polarization component in the non-selected state with a flat voltage dependence of the light transmittance in the antiferroelectric liquid crystal. By superimposing on the DC bias component of the value and applying it, it is possible to completely prevent the leakage of light and the decrease in contrast due to the response of the spontaneous polarization component. [Structure] When driving the liquid crystal element main body, when the crossing electrodes are made to be in a ferroelectric state at the time of selecting the crossing electrodes, a writing pulse in a ferroelectric state is applied between the electrodes, and When the antiferroelectric state is set, the potential between the electrodes is set to zero, and when the crossing electrodes are not selected, the AC pulse component having a pulse width shorter than the pulse width of the writing pulse is selected. A state-holding pulse is formed by superimposing it on a DC bias component (Vo) of a constant polarity for holding the state, and this state-holding pulse is applied between the crossing electrodes to spontaneously polarize the antiferroelectric liquid crystal. Driving method of liquid crystal element that has blocked the response of.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a liquid crystal element sandwiching an antiferroelectric liquid crystal, and in particular, an AC pulse which is inverted in a time width shorter than the response time of a spontaneous polarization component when not selected. By applying the component by superimposing it on the DC bias component having a flat voltage dependency of the light transmittance of the antiferroelectric liquid crystal, it is possible to maintain the ferroelectric state or the antiferroelectric state at the time of selection. The present invention relates to a method for driving a liquid crystal element.

[0002]

2. Description of the Related Art Recently, in the field of display using liquid crystal, TF
A ferroelectric liquid crystal display (FLCD: FERRO-ELECTRIC L) is used for displaying a large-capacity and clear image in a matrix without using an active element such as a T (thin-film transistor).
IQUID CRYSTAL DISPLAY) and anti-ferroelectric liquid crystal display (AFLCD: ANTIFERRO-ELECTRIC LIQUID CRYSTA)
L DISPLAY) is being researched and developed.

This development situation is described in detail in Reference 1 (supervised by Atsushi Fukuda, "Next Generation Liquid Crystal Displays and Liquid Crystal Materials", CMC Co., Ltd.). In particular, the latter antiferroelectric liquid crystal display has a viewing angle. Is wide, there is little angular disparity, and there is a possibility of gradation display.

Here, an antiferroelectric liquid crystal (AFLC: ANTI)
FERRO-ELECTRIC LIQUID CRYSTAL) is a ferroelectric liquid crystal (FL).
C: FERRO-ELECTRIC LIQUID CRYSTAL) has the advantage of being easier to control the orientation and having self-healing property against layer change due to impact or stress.

Since the layer structure of this AFLC is described in the preliminary reference book, its detailed description is omitted here.
5 will be briefly described. This AFLC is shown in FIG.
As shown in (b), the antiferroelectric state (hereinafter, AF state or S state) in which the direction of the molecular axis 1 and the accompanying spontaneous polarization direction 2 are inverted for each layer without applying a DC electric field E in particular.
mC _A ^* ), and as shown in FIGS. 15A and 15C, the ferroelectric state in which the direction 2 of the spontaneous polarization corresponds to each layer according to the polarity of the applied DC electric field E (hereinafter, The F state can be roughly divided into two states. The F state has two spontaneous polarization directions 2 depending on the positive or negative polarity of the applied DC electric field E (voltage). The AF state is energetically stable when no voltage is applied, and corresponds to the degree to which the spontaneous polarization directions 2 are mixed, for example, SmCα ^* , SmCβ ^* , and SmCγ.
^{* It} is said that there are subspecies such as phases.

As described above, the AFLC has two F states corresponding to the application of a positive or negative voltage, and one F state corresponding to no voltage.
There will be a total of three states, one AF state.
Next, the electro-optical response of AFLC will be briefly described in relation to the driving method of AFLCD. FIG. 16 is a diagram showing the voltage dependence of the light transmittance in this AFLC. In the figure, the AFLC shows a double hysteresis characteristic in light transmittance corresponding to a change in applied voltage from zero level → positive polarity (plus) → negative polarity (minus) → zero level.

That is, first, an AFL for a display.
As shown in FIG. 17, C is arranged so that the average molecular axis direction in the AF state substantially coincides with the direction of one of the deflecting plates so that the no voltage applied state is turned off (dark). FIG. 16 is a graph in which a synchronized light transmittance is plotted by applying a triangular wave of about several tens Hz to this.

Here, when the applied voltage is raised from the zero level to the positive polarity side, the AF state is maintained up to the threshold value Vth, and when it exceeds Vth, one spontaneous polarization component is gradually inverted and finally becomes positive at Vst. To the F state on the side.

On the other hand, this F state is maintained up to a voltage Vth 'which is lower than Vth when the applied voltage is lowered, but the spontaneous polarization gradually includes a reverse component at this Vth'.
When the applied voltage has a negative polarity, it transits to the AF state again. Further, this AF state is maintained up to the applied voltage (-Vth) as the applied voltage decreases, but transitions to the negative F state at this (-Vth) boundary.

The molecular axis of the F state on the positive side shows the + θ direction in FIG. 17, and the molecular axis of the F state on the negative side is (−θ).
Indicates the direction. At this time, the positive-side and negative-side F states are used as the same state because the light transmittances are substantially equal, but they can also be used as different states.

FIG. 18 is a diagram showing a matrix driving waveform in the voltage modulation utilizing this type of double hysteresis characteristic (page 102 of the above-mentioned document 1). Each state formed during selection is bias voltage (DC component) during non-selection time
However, this DC component is eliminated by inverting the polarities of all the basic signals for each frame (first frame and second frame in FIG. 18). Even in this case, it is clear that there is no problem from the symmetry of the hysteresis characteristic of FIG. Although only one F state may be used, it is preferable to use both F states evenly from the viewpoint of the symmetry of the viewing angle and the mechanical pressure on the layer.

The write signal 3 in the F (on) state is │Vo + V
_D |> | satisfies the condition, the write signal 4 AF (off) state | | Vst meets the condition _{| Vo + V N | <|} Vth. In FIG. 18, a is a bias ratio. At the time of selection, the F state or the AF state is individually formed on each data electrode. Then, when not selected, the applied voltage is V
o (| Vth '| <Vo | <Vth |), but due to hysteresis, for example, the F state is maintained. However, the applied voltage at the time of non-selection is an amplitude Vs obtained by multiplying the voltage Vo of the non-selection signal by the same time width as the pulse width for writing.
The fluctuation due to is continued in an alternating manner. Therefore, the center voltage Vo
In addition, when the hysteresis curve corresponding to the amplitude Vs is not a flat region but is gently changing, the spontaneous polarization component responds to the fluctuation of the applied voltage and light leaks. This also applies to the AF state. If this light leakage is prevented, the contrast can be improved to about 80 to 100, but voltage modulation has a problem that it is difficult in principle to prevent the leakage and the contrast is reduced by about 20 to 30.

On the other hand, the present applicant has filed Japanese Patent Application No. 4-29577.
In No. 1, a specific AFLC having a positive dielectric anisotropy and retaining a chevron structure is subjected to a dielectric torque at the time of non-selection by using a drive waveform belonging to pulse width modulation drive, thereby improving this problem. The technology is disclosed.

That is, this is a technique for preventing the transition from the F state or the AF state to the other state at the time of selection by applying an AC pulse having a time width shorter than the pulse width of the writing pulse at the time of non-selection. .

[0015]

[Problems to be Solved by the Invention] However, Japanese Patent Application No. 4
The technique disclosed in No. 295771 has the following problems. In other words, the AC pulse applied in Japanese Patent Application No. 4-2957571 fluctuates the spontaneous polarization in the F state and the AF state because the voltage fluctuates around the zero level, but the F state changes to the AF state. There is a problem that the relaxation cannot be completely prevented. Especially, when the non-selection time (the number of scanning lines) is increased, the relaxation is extremely great and the flicker increases. Further, in order to lengthen the relaxation time, there is a problem that higher frequency pulses are required and power consumption is required. In addition, since the scanning signal uses a high frequency pulse having five output voltage levels as the scanning signal, there is a problem that the driving circuit becomes complicated.

The present invention has been made in consideration of the above-mentioned circumstances, and in the non-selected state, an AC pulse component having a time width shorter than the response time of the spontaneous polarization component is applied to the voltage dependence of the light transmittance of the antiferroelectric liquid crystal. An object of the present invention is to provide a method for driving a liquid crystal element, which can completely prevent leakage of light and reduction in contrast due to the response of a spontaneous polarization component by superimposing and applying on a DC bias component having a flat property. And

[0017]

According to a first aspect of the present invention, there is provided a method of driving a liquid crystal element, wherein an antiferroelectric liquid crystal exhibiting a chiral smectic C _A ^* phase is sandwiched between crossing electrodes. When the main body is driven, when the crossing electrodes are selected and when the crossing electrodes are brought into a ferroelectric state, a writing pulse for the ferroelectric state is applied between the crossing electrodes to change the crossing electrodes. When the anti-ferroelectric state is established between the crossing electrodes at the time of selection, a no-voltage state for writing the anti-ferroelectric state is formed between the crossing electrodes, and when the crossing electrodes are not selected, the writing is performed. An AC pulse component having a pulse width shorter than the pulse width of the input pulse is superimposed on a DC bias component having a constant polarity for maintaining the ferroelectric state or the antiferroelectric state at the time of selection to form a state holding pulse. Then
This is a method of driving a liquid crystal element in which the state-holding pulse is applied between the cross electrodes to prevent the spontaneous polarization component of the antiferroelectric liquid crystal from responding.

According to a second aspect of the present invention, in the method of driving a liquid crystal element according to the first aspect, when the pulse width of the writing pulse is τ, a unit pulse width τ / n
Positive and negative unit pulses having (n = 2, 3, 4, 5, ... Integer) and the unit pulse width τ /
By the combination of zero level states having the same time width as n,
An ON data signal for forming the writing pulse in the ferroelectric state, an OFF data signal for forming the anti-ferroelectric state, a scanning signal for selection for selecting the crossing electrode, and the crossing electrode. Non-selection scanning signals for non-selection are individually formed, and the number of output voltage levels in the ON data signal, the OFF data signal and the selection scanning signal is set to the unit pulse and the zero level. It is a method of driving a liquid crystal element, which is set to 3 in accordance with the state and includes the DC bias component in the non-selection scanning signal.

According to a third aspect of the present invention, in the liquid crystal element driving method according to the first or second aspect, the on-state is turned on for each frame in which the selection scanning signal and the non-selection scanning signal make one cycle. Is a method for driving a liquid crystal element in which the polarities of the data signal for scanning, the data signal for turning off, the scanning signal for selection, and the scanning signal for non-selection are inverted.

According to a fourth aspect of the invention, in the method for driving a liquid crystal element according to any one of the first to third aspects, the antiferroelectric state is formed between the cross electrodes during the selection. The time width of the non-voltage state for this purpose is a driving method of the liquid crystal element in which the pulse width of the write pulse for forming the ferroelectric state is made longer.

According to a fifth aspect of the invention, in the method for driving a liquid crystal element according to any one of the first to fourth aspects, a unit pulse included in the ON data signal between a plurality of cross electrodes. Is changed and the pulse width of the write pulse formed on the basis of the ON data signal is changed to display a gradation on the liquid crystal element body.

[0022]

Therefore, according to the invention corresponding to claim 1, by taking the above-mentioned means, when the liquid crystal element main body is driven, the cross electrodes are selected and the space between the cross electrodes is set to the ferroelectric state. At this time, a pulse for writing in the ferroelectric state is applied between the crossing electrodes, and when the crossing electrodes are selected and the antiferroelectric state is set between the crossing electrodes, for writing in the antiferroelectric state between the crossing electrodes. Of a constant voltage for maintaining the ferroelectric state or the antiferroelectric state at the time of selecting the AC pulse component having the pulse width shorter than the pulse width of the writing pulse when the cross electrode is not selected. A state-holding pulse is formed by superimposing it on the DC bias component of the polarity, and this state-holding pulse can be applied between the cross electrodes to block the response of the spontaneous polarization component of the antiferroelectric liquid crystal. Time shorter than the response time of the polarization component By applying the AC pulse component of the DC bias component having a flat voltage dependence of the light transmittance of the antiferroelectric liquid crystal, the leakage current and contrast of light caused by the response of the spontaneous polarization component The decline can be completely prevented.

In the invention corresponding to claim 2, when the pulse width of the write pulse is τ, a unit pulse width τ / n
A combination of positive and negative unit pulses having (n = one of 2, 3, 4, 5, ...) And a zero level state having the same time width as the unit pulse width τ / n gives a strong result. An on-data signal for forming a writing pulse in a dielectric state, an off-data signal for forming an antiferroelectric state,
Output voltage levels of the ON data signal, the OFF data signal, and the selection scan signal are formed by individually forming the selection scan signal for selecting the cross electrode and the non-selection scan signal for deselecting the cross electrode. Is set to 3 corresponding to each unit pulse and zero level state, and the non-selection scanning signal includes a DC bias component. Therefore, in addition to the function corresponding to claim 1, fast writing with high contrast can be performed. Since the number of output levels is small, the driving circuit becomes simple.

According to a third aspect of the invention, an ON data signal, an OFF data signal, a selection scanning signal and a non-selection scanning signal are provided for each frame in which the selection scanning signal and the non-selection scanning signal make one cycle. Since the polarity is inverted, in addition to the effect corresponding to the first and second aspects, the usage condition of the liquid crystal can be made uniform and the viewing angle dependency can be improved.

According to the fourth aspect of the invention, the time width of the no-voltage state for forming the antiferroelectric state between the cross electrodes at the time of selection is the pulse of the write pulse for forming the ferroelectric state. Since the width is made longer than the width, in addition to the action corresponding to the first to third aspects, the minimum writing time width can be set according to the characteristics of the liquid crystal material, and the writing speed can be further increased.

According to a fifth aspect of the present invention, the number of unit pulses included in the ON data signal is changed between a plurality of cross electrodes, and the pulse width of the write pulse formed based on the ON data signal is changed. Since the gradation is displayed on the liquid crystal element body by changing, the gradation can be displayed easily and stepwise in addition to the effect corresponding to the first to fourth aspects.

[0027]

Embodiments of the present invention will be described below with reference to the drawings, but before that, the principle of the present invention will be described. That is, since the present invention utilizes the layer structure of AFLC and the dielectric response to high frequency pulses, this relationship will be briefly described.

According to the X-ray diffraction experiment of the smectic layer in recent FLC and AFLC, the smectic layer is not the bookshelf structure shown in FIG.
As shown in FIG. 19 (a), the chevron structure is formed by bending a V-shape in the vicinity of the center of the layer (Tapee Leeker et al., Physical Review Letters, 59).
Vol., Page 2658 (1987)).

In the chevron structure, the smectic layer direction is inclined from the glass substrate by a finite angle α.
Further, the molecular axis 1 of the liquid crystal tends to be parallel to the substrate as much as possible, and finally, as shown in FIG. 20, the molecular axis 1 of the liquid crystal is stabilized at the inclinations of the positions S1 'and S2'. The angle α formed by the molecular axis 1 and the glass substrate is called a pretilt angle.

Further, the tilted positions S1 'and S2 of the molecular axis 1
′ Is the position S1 and S2 of maximum amplitude structurally allowed
More inside. Normally, molecular axis 1 is at maximum amplitude position S1
And the maximum contrast when tilted to S2,
The desired contrast cannot be obtained with the inclination of the molecular axis 1 at the positions S1 'and S2'.

By the way, the molecular axis 1 in each layer is constrained to S1 'or S2', or the pretilt angle α is changed to tilt the molecular axis 1 to an appropriate position and constrain (S1 '→ S1 or S2' → S2. Dielectric torque is utilized as the most reliable and general-purpose technique for achieving the above) (Japanese Patent Application Nos. 4-186715 and 4-219080).
issue). This dielectric torque is an important mode apart from the amplitude of the electric field when the AFLC responds to the DC electric field.

For example, a DC electric field E applied to the AFLC
When the amplitude (voltage) of is constant, a predetermined time width (pulse width) is required for complete inversion of spontaneous polarization. DC electric field E
When the pulse width is shorter than this pulse width, the spontaneous polarization is inverted only halfway, and when the DC electric field E is much shorter than this pulse width, the spontaneous polarization does not respond.

When a DC electric field E having a high frequency range is applied as described above, the dielectric response becomes dominant in AFLC. The direction of response of spontaneous polarization, that is, molecular axis 1
The moving direction of can be controlled according to the effective voltage.

In the frequency region where the dielectric response is dominant, the direction of movement of the molecular axis 1 is the dielectric tensor T = {εαβ, α,
Three components (ε ₁ , ε) in the eigenvalue of β = x, y, z}
₂ , ε ₃ ). ε ₁ , ε ₂ and ε
₃ is the value of the dielectric constant having the direction shown in FIG.

That is, the movement of the molecular axis so as to stand from the substrate surface is caused by ε ₃ and ε as in the following (a) and (b).
_At least one of the two is larger than the remaining two components. (B) ε ₃ > ε ₂ and ε ₃ > ε ₁ . (B) ε ₂ > ε ₃ and ε ₂ > ε ₁ .

The molecular axis is parallel to the substrate when (c) ε ₁ is the maximum, although it depends on the size of α. By analogy with nematic liquid crystals, it was considered that the molecular axis 1 stands when the dielectric anisotropy Δε = ε ₃ −ε ₁ is positive, but in consideration of biaxiality, the negative dielectric anisotropy is considered. Even if it has, the molecular axis may stand.

In FLC, the molecular axis is parallel to the substrate to improve the contrast in the case of having a bookshelf structure (Jepi-Les-Pezant et al., Liqu.
id crystal conference, dijest p17 (1984), JM Jari, SID85, dijest128 (1985)). In the bookshelf structure, it is not preferable that the molecular axis stands, but in the chevron structure, it is preferable that the molecular axis is tilted.

According to the experiments conducted by the present inventor, in AFLC, the initial orientation state, which is presumed to have a chevron structure, may change to a stable layer structure called bookshelf with the passage of current. In this case, an AFLC having the above-mentioned (b) dielectric property is desirable. On the other hand, when the chevron structure does not change, AFLC having the above-mentioned (a) or (b) dielectric characteristics is desirable.

However, in AFLC, the state of such a layer structure and the magnitude relationship of the eigenvalues of the dielectric tensor are not so important as in FLC. This is because it is experimentally confirmed that it is not important to apply a strong dielectric torque that tilts the molecular axis to match the layer structure.

For example, as inferred from the hysteresis characteristics shown in FIG. 16, in AFLC, in both the chevron structure and the bookshelf structure, when an appropriate DC bias component having a constant polarity is applied in both the AF state and the F state. , The molecular axis is automatically constrained at the position that gives almost maximum contrast. Further, as inferred from FIG. 16, in the AFLC, the AF state and the F state can be held by the DC bias components having the same polarity. In FLC, two states cannot be held with a DC bias of the same polarity.

Therefore, in the present invention, by applying a DC bias component corresponding to the AF state or the F state in the AFLC, the corresponding AF state or F state is held, and the DC bias component is superposed on this DC bias component. The principle of preventing the fluctuation of the molecular axis is applied by continuously applying an AC pulse component shorter than the time width in which the polarization component can respond in the non-selected state.

Next, a liquid crystal element according to an embodiment of the present invention using such a principle will be described. First, this liquid crystal element is formed by applying ITO (indium) on the first and second glass substrates.
tin oxide) film is formed by a sputtering method, and a pixel electrode in a stripe shape having a line width of 200 μm is formed by a conventional photo-etching method.

Here, in the first glass substrate, after the polyimide film is formed on the pixel electrode, the polyimide film is subjected to the uniaxial orientation treatment by rubbing to form the first transparent panel.

On the other hand, the second glass substrate had a photoresist solution (MP1400, Shipley Co., Ltd.) on the pixel electrode.
The second resist having a bonding layer is formed by spin coating, and linear resist portions are formed at the same pitch as the pixel electrodes so as not to come into contact with the pixel electrodes by the same photoetching method as in the conventional method. The transparent panel 8 is formed.
Next, the first and second transparent panels were adhered to each other so that the pixel electrode groups were orthogonal to each other, and were pressed at a pressure of 1 kg / cm ² , and the temperature was raised from room temperature to about 160 ° C. at a temperature rising rate of 5 ° C./min. The temperature is raised and maintained for 1 hour, then cooled and the pressure is released.

In this way, a matrix driving liquid crystal element having a gap of 1.8 μm between the first and second transparent panels is prepared. The liquid crystal device thus created is maintained at about 110 ° C. in a heating oven after the following AFLC is introduced between the substrates by capillary action from the filling port, SmC _A oriented gradually cooled to 60 ° C. ^{* A} phase was obtained and held at this temperature. Thereafter, the liquid crystal element is completely sealed with an epoxy resin at the sealing port.

[0046] (Φ means benzene ring) Phase transition of this liquid crystal
Is as shown below. Isotropic phase → 102 ° C → SmC^* → 70 ℃ → SmC_A ^* → 4
0 ℃ → SmX → Crystalline eigenvalue of the dielectric tensor of this liquid crystal and its frequency dependence
Is difficult to measure.

Further, this liquid crystal element has a double hysteresis characteristic in the voltage dependency of the light transmittance at 60 ° C. as shown in FIG. The applied voltage is 50Vp-p and 50H.
It is a triangular wave of z. As shown, | Vth | = 17
V, | Vth '| = 4V, | Vst | = 20V.

Further, in this liquid crystal element, as shown in FIG. 1, the response time of the spontaneous polarization component from the AF state to one F state and the response of the spontaneous polarization component from this one F state to the other F state. The time is about 0.4 ms, and the response time of the spontaneous polarization component from the other F state to the AF state is about 0.8 ms. That is, this liquid crystal element has F
It takes about 0.4 ms to write the state, and about 0.8 ms to write the AF state.

Further, in this liquid crystal element, the pulse width in which the dielectric response is dominant is 0.2 ms. This is determined by an experiment in which a high-frequency pulse (50 Vp-p) having a pulse width shorter than 0.4 ms described above is applied to a stable AF state. In the experiment, the light transmittance is measured when the pulse width is 0.2 ms or less. It has been obtained that the current does not follow the applied pulse.

Further, this experimental result shows that assuming that the pulse width during writing is 0.4 ms, the pulse width during non-selection is, for example, 1/3 or less (0.2 ms or less) of the pulse width during writing. This suggests that the fluctuation of the molecular axis can be completely prevented and the contrast can be significantly improved.

Next, a method of driving the above liquid crystal element will be described with reference to the drawings. FIG. 2 is a diagram showing a driving pulse formed by combining a scanning signal and a data signal for driving the liquid crystal element, and FIG. 3 is a time chart for explaining the driving of the liquid crystal element by the driving pulse.

This drive pulse is obtained by combining both signals of the data signal applied to the data electrode and the scanning signal applied to the scanning electrode with respect to the AFLC sandwiched between the data electrode and the scanning electrode which are substantially orthogonal to each other. It is applied as a potential difference.

The characteristic of this driving pulse is that both the data signal and the scanning signal are 1 / n of the shortest pulse width τ required for writing.
It is formed by combining a unit pulse composed of a pulse width of (= 3) and an amplitude V _D (= Vs). Therefore, the number of output voltage levels is three, that is, the positive level, the zero level, and the negative level. Here, n is called a pulse ratio,
It is defined as "pulse width of unit pulse / shortest pulse width τ required for writing".

The data signal and the scanning signal are combined at the time of selection to form the shortest pulse width τ and peak value for shifting the AF state or the F state to another state, and the DC bias voltage Vo is superposed at the time of non-selection. A state-holding pulse having a pulse width τ / n (= 3) is applied. In addition,
The polarity of the DC bias component Vo is the same as the polarity of the writing pulse in the ON state. Further, the non-selected state holding pulse is formed as a complete AC pulse that is inverted in a short time width in which the light transmittance cannot follow so as to increase the effect of suppressing the optical vibration. That is, the optical oscillation is suppressed by a short pulse having the same width, and further, since the complete alternating current pulse that does not take the zero voltage is used, the reduction of the effective value corresponding to the dielectric state is prevented, and the optical oscillation is surely suppressed. Can be made.

Further, when the F state is formed at the time of selection, bipolar pulses having a time width of 2τ are synthesized, but the effective portion for forming the F state is only the latter half single pulse. The single pulse in the first half is a reset pulse, and has a function of aligning the state with the other F state each time scanning is performed. Although this reset pulse can be omitted, it is inserted for gradation display.

On the other hand, when the AF state is formed, the pulse voltage is applied only to the first and last τ / 3 at the time of selection,
The transition from the F state to the AF state is realized by setting the voltage of 4τ / 3 in the middle to zero voltage. The reason why the zero voltage time is set longer than the pulse width τ is that the time required for writing the AF state is longer than the time required for writing the F state, as described above. Generally, the length of this zero potential is adjusted to the time width required for AF writing.

Here, the amplitude V _D = Vs = 25 V, the DC bias component Vo = 12 V, the pulse width τ = 0.45 ms,
When a pulse width ratio n = 3 and a voltage waveform in which (a) and (b) in FIG. 3 are connected is formed by a waveform generator and applied to a liquid crystal element, writing with a contrast of 80: 1 is possible. there were. Further, complete writing was possible even when the length of the non-selected portion was 2000 lines. Furthermore, the amplitude V
_{When D} (= Vs) was raised to 30V, writing was possible even with a pulse ratio n = 2.

Next, the gradation was controlled by changing the spontaneous polarization component ratio in accordance with the number of unit pulses included in the ON data signal for forming the F state. For example, in order to check the gradation, a signal train in which the number of pulses in the latter half portion of the ON data signal in FIG. 7 is reduced by 1 is generated in the same manner, and the light transmittance is checked. It was confirmed that the transmittance was reduced by 70% when another pulse was reduced.

As described above, according to the present embodiment, the voltage dependence of the light transmittance of the antiferroelectric liquid crystal is flattened when the AC pulse component having a time width shorter than the response time of the spontaneous polarization component is not selected. By superimposing and applying the DC bias component of various values, the F state or AF state at the time of selection can be stabilized by the dielectric torque, and the leakage of light and the deterioration of contrast due to the response of the spontaneous polarization component can be completely eliminated. Can be stopped.

Further, it has a high contrast which has never been obtained,
In addition, the AFLCD can be driven so that analog gradation display can be performed. The liquid crystal element is also inexpensive, and the driving part can be realized by using a commercially available low-voltage MOS LSI.

Further, according to this embodiment, the amplitudes V _D and V
Although s has the same value and three output level numbers, it is possible to change the dielectric torque by setting V _D and V s to different values within a writable range, and therefore, different reference numerals will be used for description. is doing. In addition, MOSLSI
Since a three-level output is performed by using, and a DC bias component Vo is superposed on the output from the outside, a simple structure can be obtained.
This can obviously be realized more easily than the conventional 5-level output from the inside of the MOSLSI.

Further, according to the present embodiment, the polarity of the waveform is inverted for each frame and one screen is displayed in two frames, so that it is possible to recover the bias of the charge due to the application of the DC bias component Vo, and The F state can be used evenly to improve the viewing angle dependency.

Further, according to the present embodiment, the gradation can be displayed stepwise by changing the number of unit pulses included in the ON data signal. It should be noted that the state in which the ratio of the spontaneous polarization components is different during gradation display is unstable, but according to the present embodiment, stabilization is promoted by the action of the dielectric torque.

Also for the AFLC having the shallow hysteresis characteristic shown by the broken line in FIG. 16, the F state or the AF state can be stably written by selecting the DC bias component in the flat portion of the hysteresis. .

In the above embodiment, one of the combinations of unit pulses with the pulse ratio n = 3 has been described, but the present invention is not limited to this, and various modifications of the pulse ratio n and combinations can be carried out. For example, in addition, there are 3 types of pulse ratios n = 2, 1 type of n = 3, 3 types of n = 4, and 2 of n = 5.
Two types, type and n = 6, are described in FIGS. 4 to 14, respectively. Here, FIG. 5, FIG. 6, FIG. 8, FIG.
The combination of unit pulses shown in (1) is a special type in which the selection signal and the non-selection signal cooperate to form the pulse width τ of the writing pulse.

Further, the time of zero voltage can be arbitrarily set corresponding to each pulse ratio n, and the minimum writing time width according to the characteristics of the liquid crystal material is set to achieve even higher speed writing. You can For example, as shown by the broken line in FIG. 10, when the pulse pair 11 is added to the data signal, the zero voltage section 12 is added to the selective write portion and the pulse 13 is added to the non-selected portion, and the time width of the zero voltage is increased by 50%. To do. However, there is a relation that a pair of pulses with large amplitude increases in the non-selection portion.

Further, when pulses of the same polarity are continuously applied with pulses of opposite polarity having a small amplitude, the effective voltage may shift from the DC bias component to alleviate the state. It has been confirmed that there is no problem until the ratio n = 6.

Further, for example, the last pulse of the OFF data signal may be deleted to further lengthen the zero voltage time width. Therefore, when the symmetry of the waveform is lost, the polarity may be inverted for each frame to restore the symmetry of the waveform.

Further, when the pulse ratio is an even number, the polarity inversion is performed for each frame by using only the waveform of the first half portion of the bipolar pulse 2τ, so that the present invention is similarly implemented and the scanning time is halved. be able to. However,
In this case, since the first half of the bipolar pulse 2τ has a reset function for gradation, gradation display is impossible.

Further, in the above embodiment, the case where the number of unit pulses included in the data signal is changed to display the gradation has been described, but the present invention is not limited to this, and the pulse width of the unit pulse is changed to write. Even if the gradation is expressed by changing the pulse width of the working pulse, the present invention can be similarly implemented and the same effect can be obtained. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

[0071]

As described above, according to the invention of claim 1, when the liquid crystal element main body is driven, when the crossing electrodes are selected and when the crossing electrodes are set to the ferroelectric state, the crossing electrodes are separated from each other. When a cross-electrode is selected and a cross-electrode is set to an anti-ferroelectric state by applying a write pulse in a ferroelectric state to, a no-voltage state for writing in the anti-ferroelectric state is set between the cross-electrodes. A DC bias component of constant polarity for maintaining the ferroelectric state or the antiferroelectric state when the AC pulse component having the pulse width shorter than the pulse width of the writing pulse is formed when the cross electrode is not selected. To form a state-holding pulse and apply this state-holding pulse between the cross electrodes to block the response of the spontaneous polarization component of the antiferroelectric liquid crystal.
By applying an AC pulse component with a time width shorter than the response time of the spontaneous polarization component to the DC bias component with a flat voltage dependence of the light transmittance in the antiferroelectric liquid crystal when not selected, It is possible to provide a method of driving a liquid crystal element that can completely prevent light leakage and reduction in contrast due to the response of the spontaneous polarization component.

According to the second aspect of the invention, when the pulse width of the write pulse is τ, the unit pulse width τ / n (n
= 1, 2, 3, 4, 5, ...) Positive and negative polarity unit pulses and unit pulse width τ / n and zero level state having the same time width ON data signal for forming the write pulse of
An off data signal for forming an antiferroelectric state, a selection scanning signal for selecting a crossing electrode, and a nonselection scanning signal for deselecting a crossing electrode are individually formed, and an on data signal is formed. The number of output voltage levels in the OFF data signal and the selection scanning signal is set to 3 corresponding to each unit pulse and the zero level state, and the non-selection scanning signal includes a DC bias component. In addition, it is possible to provide a driving method of a liquid crystal element capable of executing fast writing with high contrast.

According to the third aspect of the present invention, the ON data signal, the OFF data signal, the selection scanning signal and the non-selection scanning signal are included in each frame in which the selection scanning signal and the non-selection scanning signal make one cycle. Since the polarity is inverted, in addition to the effects of the first and second aspects, it is possible to provide a method of driving a liquid crystal element that can make the usage state of liquid crystal uniform and improve the viewing angle dependency.

According to the invention of claim 4, the time width of the no-voltage state for forming the antiferroelectric state between the cross electrodes at the time of selection is set to the pulse of the write pulse for forming the ferroelectric state. Since the width is longer than the width, in addition to the effects of the first to third aspects, it is possible to provide a method of driving a liquid crystal element in which a minimum writing time width is set in accordance with the characteristics of the liquid crystal material and further high speed writing can be achieved.

According to the fifth aspect of the invention, the number of unit pulses included in the ON data signal is changed between the plurality of crossing electrodes, and the pulse width of the writing pulse formed based on the ON data signal is changed. Since the gradation is displayed on the liquid crystal element body by changing the above, it is possible to provide a method of driving the liquid crystal element that can easily and stepwise display the gradation in addition to the effects of the first to fourth aspects.

[Brief description of drawings]

FIG. 1 is a time chart for explaining a response time of spontaneous polarization of a liquid crystal element according to an example of the present invention.

FIG. 2 is a diagram showing a drive pulse obtained by combining a scanning signal and a data signal for driving the liquid crystal element in the embodiment.

FIG. 3 is a time chart for explaining driving of a liquid crystal element by a driving pulse in the example.

FIG. 4 is a diagram showing drive pulses obtained by combining a scan signal and a data signal for driving a liquid crystal element according to a modification of the present invention.

FIG. 5 is a diagram showing drive pulses according to a modification of the present invention.

FIG. 6 is a diagram showing drive pulses according to a modification of the present invention.

FIG. 7 is a diagram showing drive pulses according to a modification of the present invention.

FIG. 8 is a diagram showing drive pulses according to a modification of the present invention.

FIG. 9 is a diagram showing drive pulses according to a modification of the present invention.

FIG. 10 is a diagram showing drive pulses according to a modification of the present invention.

FIG. 11 is a diagram showing drive pulses according to a modification of the present invention.

FIG. 12 is a diagram showing drive pulses according to a modification of the present invention.

FIG. 13 is a diagram showing drive pulses according to a modification of the present invention.

FIG. 14 is a diagram showing drive pulses according to a modification of the present invention.

15A and 15B are views for explaining the directions of molecules and the layer structure in the F state and the AF state which can be obtained by the conventional AFLC.

FIG. 16 is a diagram showing voltage dependence of light transmittance in a conventional AFLC.

FIG. 17 is a view for explaining the arrangement of a conventional liquid crystal and a polarizer.

FIG. 18 is a diagram showing a matrix driving waveform in conventional voltage modulation.

FIG. 19 is a cross-sectional view of a conventional SmC ^* layer or SmCA ^* layer.

FIG. 20 is a diagram for explaining the positions of molecules in a conventional chevron structure.

FIG. 21 is a diagram for explaining a geometrical relationship between a conventional chevron structure and three dielectric constants of liquid crystal molecules.

[Explanation of symbols]

1 ... Molecular axis, 2 ... Direction of spontaneous polarization, 3 ... Write signal in F state, 4 ... Write signal in AF state, E ... DC electric field, F ... Ferroelectricity, AF ... Antiferroelectricity, α ... Pretilt angle, Vo ... DC bias component.

Claims (5)

[Claims] 1. _A method of driving a liquid crystal device, wherein an antiferroelectric liquid crystal exhibiting a chiral smectic C _A ^* phase is sandwiched between crossing electrodes, wherein when the crossing electrodes are selected when driving the liquid crystal device body. And when the crossing electrodes are set to the ferroelectric state, a pulse for writing the ferroelectric state is applied between the crossing electrodes, and when the crossing electrodes are selected, the antiferroelectricity is applied between the crossing electrodes. In this state, a non-voltage state for writing the antiferroelectric state is formed between the crossing electrodes, and has a pulse width shorter than the pulse width of the writing pulse when the crossing electrodes are not selected. An AC pulse component is superposed on a DC bias component of a constant polarity for holding the ferroelectric state or antiferroelectric state at the time of selection to form a state holding pulse, and this state holding pulse is applied between the cross electrodes. Apply the anti-attack Method of driving a liquid crystal element, characterized in that blocked the response of spontaneous polarization components of sexual LCD. 2. The method of driving a liquid crystal element according to claim 1, wherein when the pulse width of the writing pulse is τ, a unit pulse width τ / n (n = 2, 3, 4, 5, ... A positive and negative polarity unit pulse and a zero level state having the same time width as the unit pulse width τ / n to form the writing pulse in the ferroelectric state. ON data signal for forming, an OFF data signal for forming the antiferroelectric state, a selection scanning signal for selecting the crossing electrode, and a non-selecting scanning signal for deselecting the crossing electrode Are individually formed, and the number of output voltage levels in the ON data signal, the OFF data signal, and the selection scanning signal is set to 3 corresponding to each unit pulse and the zero level state, and the non-selection is performed. Direct to the scanning signal for A method for driving a liquid crystal element, characterized in that a current bias component is included. 3. The method for driving a liquid crystal element according to claim 1, wherein the ON data signal and the OFF data signal are provided for each frame in which the selection scanning signal and the non-selection scanning signal make one cycle. A method of driving a liquid crystal element, which comprises inverting the polarities of a data signal, the selection scanning signal, and the non-selection scanning signal. 4. The method for driving a liquid crystal element according to claim 1, further comprising: a non-voltage state for forming the antiferroelectric state between the cross electrodes at the time of selection. The time width is longer than the pulse width of the write pulse for forming the ferroelectric state. 5. The method for driving a liquid crystal element according to claim 1, wherein the number of unit pulses included in the ON data signal is changed between a plurality of crossing electrodes, A method of driving a liquid crystal element, wherein a pulse width of the write pulse formed based on an ON data signal is changed to display a gradation on the liquid crystal element body.