JPH06175101A - Driving method for ferroelectric liquid crystal display element - Google Patents

Abstract

PURPOSE:To clarify the display of gradation by applying an initialization voltage orienting a liquid crystal to either a first stable state or a second stable state in every selection period and thereafter applying a writing voltage. CONSTITUTION:When a ferroelectric liquid crystal display element is driven by using a gate signal and a data signal, the voltage-VD of a compensating pulse P11 (write compensation voltage), the voltage VR of a first resetting pulse P12 (a first resetting voltage) for orienting a liquid crystal to a first stable state, the voltage-VR of a second resetting pulse P13 (a second resetting voltage) for orienting the liquid crystal to a second stable state and the voltage VD of a writing pulse P14 (writing voltage) are successively applied on a pixel electrode through an active element(TFT) in every selection period TS. Namely, initialization voltages VR,-VR for orienting the liquid crystal to either the first or the second stable state and thereafter the writing voltage VD in accordance with displayed data are applied in every selection period TS.

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 ferroelectric liquid crystal display device.

[0002]

2. Description of the Related Art A ferroelectric liquid crystal display device using a ferroelectric liquid crystal has been noted for its high speed response and wide viewing angle as compared with a TN mode liquid crystal display device using a nematic liquid crystal. There is.

Research on the practical application of this ferroelectric liquid crystal display device has hitherto been called SS-F liquid crystal, in which the spiral pitch of the chiral smectic phase is larger than the substrate spacing (cell gap) of the display device and has bistability. It was conducted for ferroelectric liquid crystals.

The ferroelectric liquid crystal display device using the SS-F liquid crystal is one in which the SS-F liquid crystal is sealed between the substrates in a state where the helical structure is eliminated, and the spontaneous polarization of the liquid crystal with respect to an applied voltage causes The first stable state when a voltage of one polarity is applied and the second stable state when a voltage of the other polarity is applied
The stable state of the liquid crystal is obtained, and the light transmittance is controlled by the alignment state of the liquid crystal and the pair of polarizing plates arranged on the incident side and the outgoing side of the device for display.

However, the ferroelectric liquid crystal display element using the SS-F liquid crystal has only two stable liquid crystal alignment states, and either stable state is maintained even when no voltage is applied. It is said that it is difficult to change the ratio and display with gradation.

Therefore, recently, the development of a ferroelectric liquid crystal display device capable of displaying gray scales has been studied, and as one means therefor, the spiral pitch of the chiral smectic phase is smaller than the substrate interval of the display device and the bistability is small. It has been proposed to use a ferroelectric liquid crystal having The ferroelectric liquid crystal is called an SBF liquid crystal in distinction from the SS-F liquid crystal.

In the ferroelectric liquid crystal display element using the SBF liquid crystal, the SBF liquid crystal is enclosed between the substrates in a state of having a spiral structure, and the liquid crystal is divided into two depending on the polarity of the applied voltage and the voltage value. Since it is oriented in one stable state or in a state in which both stable states are mixed, the display element is an active matrix system in which a nonlinear element such as a TFT or MIM is an active element, and two stable states are maintained even during the non-selection period. It is said that gradation display is possible by holding a voltage for maintaining the alignment state of mixed liquid crystals.

Conventionally, as a driving method for causing the ferroelectric liquid crystal display element to perform gradation display, a voltage for orienting the liquid crystal in either a first stable state or a second stable state is selected every selection period. A method of applying a write voltage and then applying a write voltage has been considered.

[0009]

However, in the above-mentioned conventional driving method, the value of the write voltage and the transmittance do not correspond to each other, and therefore the gradation control is almost impossible, and the gradation display at the practical level is not possible. It could not be realized.

The present invention provides a clear gradation display on an active matrix type ferroelectric liquid crystal display device using a ferroelectric liquid crystal (SBF liquid crystal) having a spiral pitch smaller than a substrate interval and having bistability. The purpose is to provide a driving method that can be performed.

[0011]

According to the driving method of the present invention, the voltage for orienting the liquid crystal in the first stable state and the voltage for orienting the liquid crystal in the second stable state are alternately the same number of times for each selection period. It is characterized in that the voltages are applied in order and then the write voltage is applied.

[0012]

In this driving method, the write voltage is applied because the voltage for orienting the liquid crystal in the first stable state and the voltage for orienting the liquid crystal in the second stable state are applied in the same order every selection period. The alignment state of the liquid crystal immediately before is the same in any selection period. Therefore, since the value of the writing voltage and the transmittance correspond to each other, the transmittance is controlled by the writing voltage to realize a clear gradation display at a practical level. Can be realized.

In this driving method, the voltage for orienting the liquid crystal in the first stable state and the voltage for orienting the liquid crystal in the second stable state are alternately applied the same number of times for each selection period. There is no bias of electric charges between the electrodes, and therefore, a display burn-in phenomenon or liquid crystal deterioration does not occur.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

First, the structure of a ferroelectric liquid crystal display device driven for display by the driving method of the present invention will be described. FIG. 3 is a sectional view of a ferroelectric liquid crystal display device, and FIG. 4 is an equivalent circuit plan view of a substrate on which pixel electrodes and active devices of the liquid crystal display device are formed.

This ferroelectric liquid crystal display element is of the active matrix type, and of the pair of transparent substrates (eg glass substrates) 1 and 2, the lower substrate in FIG. 3 (hereinafter referred to as the lower substrate). 1, a transparent pixel electrode 3 and active elements 4 connected to the pixel electrode 3 are vertically and horizontally arranged.

The active element 4 is, for example, T
Although not shown, the structure of the TFT 4 is a FT (thin film transistor), a gate electrode formed on the substrate 1, a gate insulating film covering the gate electrode, and a semiconductor formed on the gate insulating film. And a source electrode and a drain electrode formed on the semiconductor layer.

Further, as shown in FIG. 4, on the lower substrate 1, gate lines 5 are arranged corresponding to the rows of the pixel electrodes 3 and data lines corresponding to the columns of the pixel electrodes 3 are arranged. A line 6 is wired, the gate electrode of the TFT 4 is connected to the gate line 5, and the drain electrode is connected to the data line 6. In FIG. 4, 5a is a terminal portion of the gate line 5, and 6a is a terminal portion of the data line 6.

The gate line 5 is covered with a gate insulating film (transparent film) of the TFT 4 except the terminal portion 5a, and the data line 6 is formed on the gate insulating film. The pixel electrode 3 is formed on the gate insulating film and is connected to the source electrode of the TFT 4 at one end thereof.

On the other hand, in FIG. 3, a transparent counter electrode 7 facing the respective pixel electrodes 3 of the lower substrate 1 is formed on the upper substrate (hereinafter referred to as the upper substrate) 2. The counter electrode 7 is a single electrode having an area covering the entire display area.

Alignment films 8 and 9 are provided on the electrode forming surfaces of the lower substrate 1 and the upper substrate 2, respectively. Each of these alignment films 8 and 9 is a horizontal alignment film made of an organic polymer compound such as polyimide, and its film surface is subjected to an alignment treatment by rubbing.

The lower substrate 1 and the upper substrate 2 are adhered to each other via a frame-shaped sealing material 10 at the outer peripheral edge thereof and surrounded by the sealing material 10 between the two substrates 1 and 2. Ferroelectric liquid crystal (hereinafter referred to as SBF liquid crystal) 11 having a spiral pitch of a chiral smectic phase smaller than the distance between the substrates 1 and 2 and having bistability is enclosed in the region. In FIG. 3, reference numeral 12 is a transparent gap member that regulates the distance between the substrates 1 and 2, and the gap members 12 are arranged in a scattered state in the liquid crystal enclosing region.

Since the spiral pitch of the SBF liquid crystal 11 is smaller than the distance between the substrates, the SBF liquid crystal 11 is enclosed between the substrates 1 and 2 in a spiral structure and is applied between the pixel electrode 3 and the counter electrode 7. Depending on the polarity of the voltage and the voltage value, the two stable states or both stable states are oriented.

Further, a pair of polarizing plates 13 and 14 are arranged on the lower surface side and the upper surface side of the liquid crystal display element, and the transmission axes of the polarizing plates 13 and 14 are oriented in two stable directions of the SBF liquid crystal 11. It is set according to the status.

That is, FIG. 5 shows the two stable states of the SBF liquid crystal 11 and the directions of the transmission axes of the pair of polarizing plates 13 and 14, and FIG. Hereinafter, the transmission axis 14a of the upper polarizing plate 14 is shown, and (b) shows two stable states 11a of the SBF liquid crystal 11,
11b, (c) shows the transmission axis 13a of the lower polarizing plate (hereinafter referred to as the lower polarizing plate) 13 in FIG.

As shown in FIG. 5, the SBF liquid crystal 1 is used.
1 is the first stable state 11a indicated by the solid line when a voltage of one polarity and a voltage equal to or higher than the threshold voltage of the liquid crystal 11 is applied.
The second stable state 1 indicated by the broken line when a voltage having the other polarity and having the other polarity and being equal to or higher than the threshold voltage of the liquid crystal 11 is applied.
Orient to 1b. The deviation angle θ between the first stable state 11a and the second stable state 11b varies depending on the type of the SBF liquid crystal 11 and the surface energy of the alignment films 8 and 9, but the deviation angle θ is about 45 °. It is desirable to choose.

Then, of the pair of polarizing plates 13 and 14, one polarizing plate, for example, the transmission axis 14a of the upper polarizing plate 14 is used.
Is the two stable states 11a, 11 of the SBF liquid crystal 11.
b, which is substantially parallel to the second stable state 11b, and the transmission axis 13a of the lower polarizing plate 13 of the other.
Is substantially orthogonal to the transmission axis 14a of the upper polarizing plate 14.

The ferroelectric liquid crystal display element in which the transmission axis directions of the polarizing plates 13 and 14 are set as shown in FIG. 5 has the highest transmittance when the liquid crystal 11 is oriented in the first stable state 11a ( The display becomes the brightest, and the transmittance becomes the lowest (the display becomes the darkest) when the liquid crystal 11 is oriented in the second stable state 11b.

That is, the liquid crystal 11 is in the first stable state 11
In the state of being aligned in a, the linearly polarized light that has passed through one of the polarizing plates is subjected to the polarization effect of the liquid crystal 11 to become non-linearly polarized light.
Light of a certain polarized component of the light passes through the other polarizing plate and is emitted. Further, when the liquid crystal 11 is aligned in the second stable state 11b, the linearly polarized light passing through one of the polarizing plates is hardly affected by the polarizing action of the liquid crystal 11 and is transmitted as it is through the liquid crystal layer, and Most of the light is absorbed by the other polarizing plate.

The SBF liquid crystal 11 is not limited to the two stable states 11a and 11b, but also the two stable states 11a and 11b depending on the polarity and voltage value (absolute value) of the applied voltage.
11b is also oriented in a mixed state.

FIG. 6 shows a general voltage-transmittance characteristic (characteristic of change of light transmittance with respect to applied voltage) of the ferroelectric liquid crystal display element. The light transmittance of this ferroelectric liquid crystal display element is shown in FIG. , As shown in the figure, depending on the applied voltage.

Since this ferroelectric liquid crystal display element is of the active matrix type, it holds a voltage for maintaining the alignment state of the liquid crystal 11 in which the two stable states 11a and 11b are mixed even during the non-selection period. You can keep it. For this reason, it is said that the ferroelectric liquid crystal display element using the SBF liquid crystal can display with gradation by changing the transmittance.

However, when the inventor conducted a drive test of the above-mentioned ferroelectric liquid crystal display element, it was almost impossible to control gradation by the drive method conventionally considered. The conventional driving method is, as described in the section [Prior Art], applying a voltage for aligning the liquid crystal to either the first stable state or the second stable state for each selection period. In the driving test conducted by the inventor, a voltage for orienting the liquid crystal 11 in the first or second stable state and a writing voltage having an absolute value smaller than that are alternately applied. Then, the change in transmittance was examined.

FIG. 7 is a waveform diagram of the gate signal and the data signal applied to the gate line 5 and the data line 6 of the liquid crystal display element in the above drive test. The data signal orients the liquid crystal 11 to the first stable state. A reset pulse P1 having a voltage value to be applied, a write pulse P2 having an arbitrary voltage value, a reset pulse P3 having a voltage value for orienting the liquid crystal 11 to the second stable state, and an arbitrary voltage value different from the write pulse P2. The write pulse P4 and the write pulse P4 are waveform signals which are alternately repeated. In this drive test, the reference voltage of the data signal (the same voltage as the voltage applied to the counter electrode 7) was set to 0V.

The reset pulses P1 and P3 are applied to the history effect peculiar to the liquid crystal display element, that is, to the change of the alignment state of the liquid crystal when the write pulse is applied, the alignment state of the liquid crystal by the write pulse applied before (hereinafter , The previous state) is a pulse for resetting the effect of
When the reset pulses P1 and P3 are applied, the previous state when the write pulse is applied next is determined.

If the reset pulses P1 and P3 have the same polarity, a direct current component exceeding the allowable value is applied to the liquid crystal 11 so that the charges are deviated, which causes a display burn-in phenomenon and deterioration of the liquid crystal. For this reason, the P1 reset pulse and the P3 reset pulse are of opposite polarity. This is also the case with the conventional driving method, and in the conventional method, the polarities of the voltages for orienting the liquid crystal in the first or second stable state are alternately reversed every selection period.

8 and 9 show that the ferroelectric liquid crystal display device is driven by using the gate signal and the data signal having the above waveforms, and after applying the respective pulses P1, P2, P3 and P4. 8 shows the results of examining the average charge amount (corresponding to the average alignment state of the liquid crystal 11) of spontaneous polarization of the liquid crystal 11 and the transmittance, and FIG.
Average charge amount of spontaneous polarization when voltage value of write pulse of 4 is 0V respectively (hereinafter referred to as average charge amount)
FIG. 9 shows the voltage value of the write pulse of P2 3.3.
The average charge amount and the transmittance of spontaneous polarization when the voltage values of the V and P4 write pulses are set to -3.3V are shown. In any case, the voltage values of the reset pulses P1 and P3 were set to P1 = 7.5V and P3 = -7.5V.

As can be seen from FIGS. 8 and 9, in the above drive test, the voltage values of the write pulses P2 and P4 did not correspond to the transmittance, so that the gradation control was almost impossible.

That is, if the transmissivities when the pulses of the same potential are applied as the write pulses P2 and P4 are the same, reproducible gradation display is possible, but in the above drive test, as shown in FIG. Moreover, even if the potentials of the write pulses P2 and P4 are the same (here, P2 = P4 = 0V), the transmittance is completely different and there is no gradation reproducibility.

Further, in the above drive test, as shown in FIG. 9, even if pulses having different voltage values (here, P2 = 3.3V, P4 = -3.3V) are applied as the write pulses P2 and P4, No clear difference in transmittance was obtained.

This is because the voltage-transmittance characteristic of the ferroelectric liquid crystal display element using the SBF liquid crystal has hysteresis as shown in FIG. That is, the previous state when the P2 write pulse is applied is the first alignment state (actually, the first alignment state corresponds to the holding voltage of the capacitor formed by the pixel electrode 3, the counter electrode 7 and the liquid crystal 11 therebetween). (Orientation state close to the orientation state of P4) and the previous state at the time of applying the writing pulse of P4 is the second orientation state (orientation state close to the second orientation state). The voltage values of the pulses P2 and P4 do not correspond to the alignment state of the liquid crystal 11, that is, the transmittance.

Therefore, in the present invention, in order to obtain the transmittance corresponding to the value of the write voltage, the voltage for orienting the liquid crystal in the first stable state and the orientation in the second stable state are selected for each selection period. The driving method in which the applied voltage and the write voltage are applied in the same order alternately and the same number of times is adopted.

Explaining one embodiment of this driving method, FIG. 1 shows the waveforms of the gate signal and the data signal applied to the gate line 5 and the data line 6 connected to the TFT 4 in the first row of the ferroelectric liquid crystal display device. And the average charge amount of spontaneous polarization of the liquid crystal 11 and the transmittance.

In FIG. 1, TF is one frame period, T
S is the selection period of the TFT 4 in the first row, and TO is the non-selection period. In this embodiment, each selection period TS is equally divided into four slots t1, t2, t3, t4 and the final slot t4 thereof. Is the application period of the write pulse P14,
The first slot t1 is the application period of the compensation pulse P11 with respect to the write pulse P14.

Further, the other slots t2 and t3 respectively have a reset pulse (hereinafter, referred to as a first reset pulse) P12 for orienting the liquid crystal 11 in the first stable state.
And a reset pulse (hereinafter referred to as a second reset pulse) P13 for orienting the liquid crystal 11 in the second stable state. In addition, each of the above-mentioned pulses P11, P12, P1
The application period of 3 and P14 (one slot time) is about 45 μsec in each case.

The compensation pulse P11 is the write pulse P14.
Is a pulse having a reverse polarity for compensating the bias of the DC component voltage applied to the liquid crystal 11 due to the application of the voltage.
Is the same as the voltage VD. The voltage VD of the write pulse P14 is controlled to various values according to the write data, and the voltage -VD of the compensation pulse P11 is also controlled correspondingly.

The second reset pulse P13 is a pulse for resetting the hysteresis effect of the liquid crystal display element, and the voltage value VR of the reset pulse P13 is a value sufficiently larger than the threshold voltage of the liquid crystal 11. The first reset pulse P12 is a reverse polarity pulse for compensating the bias of the DC component voltage applied to the liquid crystal 11 due to the application of the second reset pulse P13, and the voltage of the first reset pulse P12. -VR absolute value is the second reset pulse P1
It is the same as the voltage VR of 3.

Each of these pulses P11, P12, P13,
The polarity and voltage value of P14 are both the polarity and voltage of the data signal with respect to the reference voltage V0. This reference voltage V
0 is the same as the voltage applied to the counter electrode 7.

In this driving method, the write voltage V
The write voltage VD is controlled within the range of V0 to Vmax by setting the minimum value of D to V0 and the maximum value Vmax to a value slightly lower than the reset voltage VR of the second reset pulse P13.

When the ferroelectric liquid crystal display element is driven by using the gate signal and the data signal having the above waveforms,
For each selection period TS, the voltage of the compensation pulse P11 (hereinafter referred to as the write compensation voltage) -VD and the liquid crystal 11 are set to the first value.
Of the first reset pulse P12 (hereinafter referred to as the first reset voltage) VR for orienting the liquid crystal 11 to the stable state and the voltage of the second reset pulse P13 (hereinafter, the second reset voltage for orienting the liquid crystal 11 to the second stable state). -VR and the voltage of the write pulse P14 (hereinafter referred to as write voltage) VD are sequentially applied to the pixel electrode 3 through the TFT 4, and along with this, the average charge amount and the transmittance of the spontaneous polarization of the liquid crystal 11. And change as shown in FIG.

When the non-selection period TO has passed after the selection period TS has passed, the TFT 4 is turned off, and a voltage corresponding to the write voltage VD applied to the final slot t4 of the selection period TS opposes the pixel electrode 3. Electrode 7 and liquid crystal 1 between them
Is held in the capacitor formed by 1 and, during the non-selection period To,
The average charge amount of spontaneous polarization and the transmittance of the liquid crystal 11 are maintained at a value corresponding to the holding voltage of the capacitance, that is, a value corresponding to the write voltage VD applied during the selection period TS.

In this driving method, the selection period TS
Each time, the first reset voltage VR for orienting the liquid crystal 11 in the first stable state and the second reset voltage -VR for orienting the liquid crystal 11 in the second stable state are applied in the same order. The alignment state of the liquid crystal 11 immediately before the voltage VD is applied is the same (second stable state in this embodiment) in any selection period TS, and therefore the write voltage V
Since the value of D and the transmittance correspond to each other, the transmittance can be controlled by the write voltage VD to realize clear gradation display at a practical level.

That is, as shown in FIG. 1, for example, assuming that the liquid crystal 11 is in a certain alignment state (alignment state according to the write voltage applied previously), the write voltage VD applied in the next selection period TS is reset. Assuming that the voltage is 1/2 the voltage VR, the average charge amount of spontaneous polarization of the liquid crystal 11 in the non-selection period TO after applying the write voltage VD (VD = VR / 2) becomes almost zero. The alignment state of the liquid crystal 11 at this time is a state in which the first stable state and the second stable state are mixed in substantially the same proportion, and therefore the transmittance is such that the liquid crystal 11 is in the first stable state. The value is almost intermediate between the highest transmittance when aligned and the lowest transmittance when the liquid crystal 11 is aligned in the second stable state.

As shown in FIG. 1, the selection period T
Assuming that the write voltage VD applied in the next selection period TS of S is one fourth of the reset voltage VR, the liquid crystal in the non-selection period TO after application of the write voltage VD (VD = VR / 4). The average charge amount of the spontaneous polarization of 11 becomes a value in which the negative charge component is larger than the above-mentioned charge amount of almost zero. The alignment state of the liquid crystal 11 at this time is a state in which the first stable state and the second stable state are mixed in a proportion of the second stable state being larger, and therefore the transmittance is
The value is between the lowest transmittance and the intermediate transmittance when the liquid crystal 11 is aligned in the second stable state.

This is the same when a write voltage VD of another voltage is applied. For example, when the minimum voltage V0 is applied as the write voltage VD, as shown by the chain double-dashed line in FIG. The average charge amount of the spontaneous polarization of the liquid crystal 11 becomes a value in which the most negative charge component in the control range is the largest, that is, a value close to the charge amount when the liquid crystal 11 is aligned in the second stable state. Therefore, the transmittance becomes the lowest value in the control range.

When the maximum voltage Vmax is applied as the write voltage VD, the average charge amount of the spontaneous polarization of the liquid crystal 11 is the highest in the control range, as shown by the three-dot chain line in FIG. The value has the largest amount of positive charge components, that is, a value close to the amount of charge when the liquid crystal 11 is aligned in the first stable state, and the transmittance has the highest value in the control range.

As described above, according to the above driving method, the transmittance corresponding to the value of the writing voltage VD can be obtained. Therefore, by controlling the transmittance by the writing voltage VD, clear gradation display at a practical level can be achieved. Can be realized.

This is because the alignment state of the liquid crystal 11 immediately before the application of the write voltage VD is the same (the second stable state in this embodiment) in any selection period TS, and the write voltage VD is applied. If the alignment state of the liquid crystal 11 before the operation is always the same, the hysteresis of the voltage-transmittance characteristic which the ferroelectric liquid crystal display element using the SBF liquid crystal has does not appear in the operation, so that it corresponds to the value of the write voltage VD. The obtained transmittance is obtained.

That is, FIG. 2 is a voltage-transmittance characteristic diagram when the above-mentioned ferroelectric liquid crystal display element is driven by the driving method of the above-described embodiment. The voltage-transmittance characteristic has no hysteresis.

The voltage-transmittance characteristic shown in FIG.
This is the characteristic when the reference voltage VO of the data signal is 8 V (the voltage applied to the counter electrode 7 is also the same). In this case,
The first reset voltage VR is 10 V or more (preferably 11 V
V or more), the second reset voltage -VR is 6 V or less (preferably 5 V or less), and the write voltage VD is about 6.5 V or more.
It may be controlled in the range of about 10.5V.

In the above driving method, the first reset voltage VR for orienting the liquid crystal 11 in the first stable state and the second reset voltage -VR for orienting the liquid crystal 11 in the second stable state are selected every selection period TS. Since the and are alternately applied the same number of times (once in the above-described embodiment), the liquid crystal 11 is not biased by the direct current component of the allowable value or more, and therefore the display burn-in phenomenon and the deterioration of the liquid crystal are prevented. It never happens.

In the above embodiment, the reset voltage VR
, -VR are applied in the order of the first reset voltage VR and the second reset voltage -VR. The reset voltage VR,
The application order of -VR may be reversed, and the reset voltages VR and -VR are almost the same for the liquid crystal 11 as the first and second reset voltages.
If it is a voltage that orients to the stable state, it does not have to be a voltage to achieve a complete stable state.

Further, in the above embodiment, the first reset voltage VR and the second reset voltage -VR are applied once, but the number of times these reset voltages VR, -VR are applied may be arbitrary. , The first reset voltage VR and the second reset voltage −VR may be alternately applied at the same number of times.

Further, in the ferroelectric liquid crystal display device driven in the above embodiment, the transmission axis 14a of one polarizing plate 14 is SB.
Although the F liquid crystal 11 is made substantially parallel to the second stable state 11b, in the above driving method, the transmission axis 14a of one polarizing plate 14 is made substantially parallel to the first stable state 11a of the SBF liquid crystal 11. , The transmittance is highest when the liquid crystal 11 is oriented in the second stable state 11b (the display is brightest), and the transmittance is lowest when the liquid crystal 11 is oriented in the first stable state 11a ( It can also be applied to drive a ferroelectric liquid crystal display device in which the display becomes darkest.
The invention can be applied not only to the one using the TFT as the active element but also to the driving of the ferroelectric liquid crystal display element using the MIM as the active element.

[0065]

According to the driving method of the present invention, the selection period
Since the voltage for orienting the liquid crystal in the first stable state and the voltage for orienting the liquid crystal in the second stable state are alternately applied in the same order by the same number of times and then the write voltage is applied, the spiral smaller than the substrate interval is used. An active matrix type ferroelectric liquid crystal display device using a ferroelectric liquid crystal (SBF liquid crystal) having a pitch and bistability can display clear gradation.

[Brief description of drawings]

FIG. 1 is a diagram showing waveforms of a gate signal and a data signal, and an average charge amount and a transmittance of spontaneous polarization of liquid crystal according to an embodiment of the present invention.

FIG. 2 is a voltage-transmittance characteristic diagram when a ferroelectric liquid crystal display element is driven by the driving method of the example.

FIG. 3 is a sectional view of a ferroelectric liquid crystal display element.

FIG. 4 is an equivalent circuit plan view of a substrate on which pixel electrodes and active elements are formed.

FIG. 5 is a diagram showing two stable states of an SBF liquid crystal and directions of transmission axes of a pair of polarizing plates.

FIG. 6 is a general voltage-transmittance characteristic diagram of a ferroelectric liquid crystal display device.

FIG. 7 is a waveform diagram of a gate signal and a data signal applied in a drive test by a conventional drive method performed by the inventor.

FIG. 8 is a diagram showing a spontaneous polarization average charge amount and a transmittance of a liquid crystal when a drive test is performed with a voltage value of a write pulse set to 0V.

FIG. 9 shows the voltage value of the write pulse at 3.3V and -3.3V.
FIG. 6 is a diagram showing the spontaneous polarization average charge amount and the transmittance of the liquid crystal when the drive test is performed in the above manner.

[Explanation of symbols]

 3 ... Pixel electrode 4 ... Active element (TFT) 7 ... Counter electrode 8, 9 ... Alignment film 11 ... SBF liquid crystal 11a ... 1st stable state 11b ... 2nd stable state 13, 14 ... Polarizing plate 13a, 14a ... Transmission Axis P11 ... Compensation pulse P12, P13 ... Reset pulse VR, -VR ... Reset voltage P14 ... Write pulse VD ... Write voltage

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[Procedure amendment]

[Submission date] October 21, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

[0011]

The driving method of the present invention According to an aspect of, for each selection period, the liquid crystal of the first stable shape on purpose second stable state
The initializing voltage to orient one of the stable states
It is characterized in that the voltage is applied and then the writing voltage according to the display data is applied. The initialization voltage is
Voltage for orienting crystals in a first stable state and a second stable state
Multiple pulses that are applied in the same order, alternating the same number of times
Is preferably a voltage consisting of

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

[0012]

[Action] In this driving method, for each selected period, one of the stable and the liquid crystal first stable shape on purpose second stable state
Since the initialization voltage for aligning the liquid crystal is applied, the alignment state of the liquid crystal immediately before the application of the write voltage is the same in any selection period. Therefore, the value of the write voltage and the transmittance correspond to each other. The transmittance can be controlled by the voltage to realize clear gradation display at a practical level.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction content]

In this driving method, the initialization voltage
To align the liquid crystal in the first stable state and the second stable state
Voltage is applied alternately in the same order by the same number of times.
If the voltage is a pulse voltage, there is no deviation of the charges between the electrodes facing each other, and therefore, a display burn-in phenomenon or deterioration of the liquid crystal does not occur.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Name of item to be corrected] 0022

[Correction method] Change

[Correction content]

The lower substrate 1 and the upper substrate 2 are adhered to each other via a frame-shaped sealing material 10 at the outer peripheral edge thereof and surrounded by the sealing material 10 between the two substrates 1 and 2. Ferroelectric liquid crystal (hereinafter referred to as SBF liquid crystal) 11 having a spiral pitch of a chiral smectic phase smaller than the distance between the substrates 1 and 2 and having bistability is enclosed in the region. This SBF liquid crystal has a spiral pitch of visible light.
300 nm to 400 nm or less of band (400 nm to 700 nm) or less
Has a large spontaneous polarization and a large cone angle
It is a ferroelectric liquid crystal composition. In addition, in FIG.
Is a conservation cap member to regulate the distance between the substrates 1 and 2, the gap material 12 are arranged in a dotted state liquid crystal sealing area.

[Procedure correction 6]

[Document name to be amended] Statement

[Name of item to be corrected] 0029

[Correction method] Change

[Correction content]

That is, the liquid crystal 11 is in the first stable state 11
In the state of being aligned in a, the linearly polarized light that has passed through one of the polarizing plates is subjected to the polarization effect of the liquid crystal 11 to become non-linearly polarized light.
Light having a polarization component parallel to the transmission axis of the other polarizing plate passes through the other polarizing plate and is emitted. Further, when the liquid crystal 11 is aligned in the second stable state 11b, the linearly polarized light passing through one of the polarizing plates is hardly affected by the polarizing action of the liquid crystal 11 and is transmitted as it is through the liquid crystal layer, and Most of the light is absorbed by the other polarizing plate.

[Procedure Amendment 7]

[Document name to be amended] Statement

[Name of item to be corrected] 0032

[Correction method] Change

[Correction content]

Since this ferroelectric liquid crystal display element is of the active matrix type, it holds a voltage for maintaining the alignment state of the liquid crystal 11 in which the two stable states 11a and 11b are mixed even during the non-selection period. You can keep it. Thus, a ferroelectric liquid crystal display device using the SBF liquid crystal, Ru can der thereby the transmittance is varied by performing the display with a gray scale.

[Procedure Amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0033

[Correction method] Change

[Correction content]

However, when the inventor of the present invention conducted a drive test of the above-mentioned ferroelectric liquid crystal display element, it was not possible to control the gradation by the drive method conventionally considered . Na
In the drive test conducted by the inventor, a change in transmittance is investigated by alternately applying a voltage for orienting the liquid crystal 11 in the first or second stable state and a writing voltage having an absolute value smaller than that. It was

[Procedure Amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0036

[Correction method] Change

[Correction content]

If the reset pulses P1 and P3 have the same polarity, a direct current component exceeding the allowable value is applied to the liquid crystal 11 so that the charges are deviated, which causes a display burn-in phenomenon and deterioration of the liquid crystal. Therefore, P1 reset pulse and P3 reset pulse have opposite polarity.
It was

[Procedure Amendment 10]

[Document name to be amended] Statement

[Name of item to be corrected] 0037

[Correction method] Change

[Correction content]

8 and 9 show that the ferroelectric liquid crystal display device is driven by using the gate signal and the data signal having the above waveforms, and after applying the respective pulses P1, P2, P3 and P4. 8 shows the results of examining the average charge amount (corresponding to the average alignment state of the liquid crystal 11) and the transmittance due to the spontaneous polarization of the liquid crystal 11, and FIG. 8 shows the writing pulse of P2 and the writing pulse of P4. The average charge amount (hereinafter, referred to as the average charge amount) and the transmittance due to spontaneous polarization when the voltage values of P2 and P4 are set to 0 V, respectively. Voltage value is -3.3V
The average charge amount and the transmittance due to spontaneous polarization are shown. In either case, the reset pulse P1
, P3 have voltage values of P1 = 7.5V, P3 = -7.5.
It was set to V.

[Procedure Amendment 11]

[Document name to be amended] Statement

[Correction target item name] 0040

[Correction method] Change

[Correction content]

Further, in the above drive test, as shown in FIG. 9, even if pulses having different voltage values (here, P2 = 3.3V, P4 = -3.3V) are applied as the write pulses P2 and P4, difference clear transmittance was not obtained.

[Procedure Amendment 12]

[Document name to be amended] Statement

[Correction target item name] 0042

[Correction method] Change

[Correction content]

Therefore, in the present invention, in order to obtain the transmittance corresponding to the value of the write voltage, the voltage for orienting the liquid crystal in the first stable state and the orientation in the second stable state are selected for each selection period. The driving method in which the applied voltage and the write voltage are applied once and a plurality of times alternately in the same order is adopted.

[Procedure Amendment 13]

[Document name to be amended] Statement

[Correction target item name] 0043

[Correction method] Change

[Correction content]

Explaining one embodiment of this driving method, FIG. 1 shows the waveforms of the gate signal and the data signal applied to the gate line 5 and the data line 6 connected to the TFT 4 in the first row of the ferroelectric liquid crystal display device. And the spontaneous polarization of the liquid crystal 11.
Therefore, the average charge amount and the transmittance are shown.

[Procedure Amendment 14]

[Document name to be amended] Statement

[Name of item to be corrected] 0045

[Correction method] Change

[Correction content]

Further, the other slots t2 and t3 respectively have a reset pulse (hereinafter, referred to as a first reset pulse) P12 for orienting the liquid crystal 11 in the first stable state.
And a reset pulse (hereinafter referred to as a second reset pulse) P13 for orienting the liquid crystal 11 in the second stable state is applied , and these reset pulses P12 and P13 are used.
The reset pulse. In addition, each pulse P11,
The application period (one slot time) of P12, P13 and P14 is about 45 μsec.

[Procedure Amendment 15]

[Document name to be amended] Statement

[Correction target item name] 0047

[Correction method] Change

[Correction content]

The second reset pulse P13 is a pulse for eliminating the influence of hysteresis of the liquid crystal display element, and the voltage value VR of the reset pulse P13 is the liquid crystal 11
Almost all of the liquid crystal molecules in
It is a sufficiently large value. The first reset pulse P12 is applied to the liquid crystal 11 by applying the second reset pulse P13.
Is a pulse of opposite polarity for compensating the bias of the voltage of the DC component on the bias voltage. The absolute value of the voltage -VR of the first reset pulse P12 is the voltage V of the second reset pulse P13.
Same as R.

[Procedure Amendment 16]

[Document name to be amended] Statement

[Correction target item name] 0050

[Correction method] Change

[Correction content]

When the ferroelectric liquid crystal display element is driven by using the gate signal and the data signal having the above waveforms,
For each selection period TS, the voltage of the compensation pulse P11 (hereinafter referred to as the write compensation voltage) -VD and the liquid crystal 11 are set to the first value.
Of the first reset pulse P12 (hereinafter referred to as the first reset voltage) VR for orienting the liquid crystal 11 to the stable state and the voltage of the second reset pulse P13 (hereinafter, the second reset voltage for orienting the liquid crystal 11 to the second stable state). -VR and the voltage of the write pulse P14 (hereinafter referred to as write voltage) VD are sequentially applied to the pixel electrode 3 through the TFT 4, and along with this, the average charge amount and the transmittance due to the spontaneous polarization of the liquid crystal 11. And change as shown in FIG.

[Procedure Amendment 17]

[Document name to be amended] Statement

[Correction target item name] 0051

[Correction method] Change

[Correction content]

[0051] Further, when the selection period TS becomes to a non-selection period TO elapses, TFT 4 is Ri Do the OFF state, is kept to a value corresponding to a write voltage VD applied to the selected択期between TS.

[Procedure 18]

[Document name to be amended] Statement

[Correction target item name] 0053

[Correction method] Change

[Correction content]

That is, as shown in FIG. 1, for example, assuming that the liquid crystal 11 is in a certain alignment state (alignment state according to the write voltage applied previously), the write voltage VD applied in the next selection period TS is reset. Assuming that the voltage is 1/2 of the voltage VR, the average charge amount due to spontaneous polarization of the liquid crystal 11 in the non-selection period TO after applying the write voltage VD (VD = VR / 2) becomes almost zero. Liquid crystal 1 at this time
The orientation state of 1 is a state in which the first stable state and the second stable state are mixed in substantially the same proportion, and therefore,
The transmittance has an intermediate value between the highest transmittance when the liquid crystal 11 is aligned in the first stable state and the lowest transmittance when the liquid crystal 11 is aligned in the second stable state.

[Procedure Amendment 19]

[Document name to be amended] Statement

[Correction target item name] 0054

[Correction method] Change

[Correction content]

As shown in FIG. 1, the selection period T
Assuming that the write voltage VD applied in the next selection period TS of S is one fourth of the reset voltage VR, the liquid crystal in the non-selection period TO after application of the write voltage VD (VD = VR / 4). The average charge amount due to the spontaneous polarization of 11 becomes a value in which the negative charge component is larger than the above-mentioned charge amount of almost zero. The alignment state of the liquid crystal 11 at this time is a state in which the first stable state and the second stable state are mixed in a larger proportion in the second stable state. Therefore, the transmittance is the liquid crystal. This is a value between the lowest transmittance when 11 is oriented in the second stable state and the intermediate transmittance.

[Procedure amendment 20]

[Document name to be amended] Statement

[Correction target item name] 0055

[Correction method] Change

[Correction content]

This is the same when a write voltage VD of another voltage is applied. For example, when the minimum voltage V0 is applied as the write voltage VD, as shown by the chain double-dashed line in FIG. The average charge amount due to spontaneous polarization of the liquid crystal 11 is
The value of the most negative charge component in the control range is the largest, that is, the value is close to the amount of charge when the liquid crystal 11 is aligned in the second stable state, and the transmittance is within the control range. Is the lowest value of.

[Procedure correction 21]

[Document name to be amended] Statement

[Correction target item name] 0056

[Correction method] Change

[Correction content]

When the maximum voltage Vmax is applied as the write voltage VD, the average charge amount due to spontaneous polarization of the liquid crystal 11 is the highest in the control range, as shown by the three-dot chain line in FIG. The value has the largest amount of positive charge components, that is, a value close to the amount of charge when the liquid crystal 11 is aligned in the first stable state, and the transmittance has the highest value in the control range.

[Procedure correction 22]

[Document name to be amended] Statement

[Correction target item name] 0064

[Correction method] Change

[Correction content]

Further, in the ferroelectric liquid crystal display device driven in the above embodiment, the transmission axis 14a of one polarizing plate 14 is SB.
Although those substantially parallel to the second stable state 11b of F liquid crystal 11, the driving method, one of the transmission axis 14a of the polarizing plate 14 is substantially parallel to the first stable state 11a of the SBF liquid crystal 11 , The transmittance is highest when the liquid crystal 11 is oriented in the second stable state 11b (the display is brightest), and the transmittance is lowest when the liquid crystal 11 is oriented in the first stable state 11a ( It can also be applied to drive a ferroelectric liquid crystal display device in which the display becomes darkest.
The invention can be applied not only to the one using the TFT as the active element but also to the driving of the ferroelectric liquid crystal display element using the MIM as the active element.

[Procedure amendment 23]

[Document name to be amended] Statement

[Correction target item name] 0065

[Correction method] Change

[Correction content]

[0065]

According to the driving method of the present invention, the selection period
Any one of the first stable shape on purpose second stable state of the liquid crystal
Since an initialization voltage for orienting to one of the orientation states is applied and then a writing voltage is applied, a ferroelectric liquid crystal (SBF liquid crystal) having a spiral pitch smaller than the substrate interval and having bistability is used. The active-matrix ferroelectric liquid crystal display element can be made to perform clear gradation display.

[Procedure correction 24]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a diagram showing waveforms of a gate signal and a data signal, and an average charge amount and transmittance due to spontaneous polarization of liquid crystal according to an embodiment of the present invention.

FIG. 2 is a voltage-transmittance characteristic diagram when a ferroelectric liquid crystal display element is driven by the driving method of the example.

FIG. 3 is a sectional view of a ferroelectric liquid crystal display element.

FIG. 4 is an equivalent circuit plan view of a substrate on which pixel electrodes and active elements are formed.

FIG. 5 is a diagram showing two stable states of an SBF liquid crystal and directions of transmission axes of a pair of polarizing plates.

FIG. 6 is a general voltage-transmittance characteristic diagram of a ferroelectric liquid crystal display device.

FIG. 7 is a waveform diagram of a gate signal and a data signal applied in a drive test by a conventional drive method performed by the inventor.

FIG. 8 is a diagram showing an average charge amount and transmittance due to spontaneous polarization of liquid crystal when a drive test is performed with a voltage value of a write pulse set to 0V.

FIG. 9 shows the voltage value of the write pulse at 3.3V and -3.3V.
The figure which shows the average electric charge amount and the transmittance | permeability by the spontaneous polarization of the liquid crystal at the time of performing a drive test.

[Explanation of Codes] 3 ... Pixel electrode 4 ... Active element (TFT) 7 ... Counter electrode 8, 9 ... Alignment film 11 ... SBF liquid crystal 11a ... First stable state 11b ... Second stable state 13, 14 ... Polarizing plate 13a, 14a ... Transmission axis P11 ... Compensation pulse P12, P13 ... Reset pulse VR, -VR ... Reset voltage P14 ... Write pulse VD ... Write voltage

[Procedure correction 25]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

[Procedure Amendment 26]

[Document name to be corrected] Drawing

[Correction target item name] Figure 8

[Correction method] Change

[Correction content]

[Figure 8]

[Procedure Amendment 27]

[Document name to be corrected] Drawing

[Correction target item name] Figure 9

[Correction method] Change

[Correction content]

[Figure 9]

Claims (1)

[Claims] 1. A method of driving an active matrix type ferroelectric liquid crystal display device using a ferroelectric liquid crystal having a helix pitch smaller than a substrate interval and having bistability, wherein the liquid crystal is selected every selection period. A ferroelectric liquid crystal display device characterized by applying a voltage for orienting a first stable state and a voltage for orienting a second stable state alternately at the same number of times in the same order, and then applying a write voltage. Driving method.