JPH0713519A - Driving method for ferroelectric liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain images of a high contrast in a stable orientation state even in the case of using of such a ferroelectric liquid crystal which does not exhibit a memory characteristic by inverting the first orientation state to the second orientation state and maintaining the second orientation state by a high-frequency electric field. CONSTITUTION:Voltage values Vs, -Vs are given to both of a data signal S1 and data signal S2 which are pulselike signals of the same high frequency (fH) inverted in polarity from each other. A common signal C1 is a signal to which the voltage values Vc, -Vc of the same period as the period of the data signal S1 are given in a first period to third period quadrisecting one frame (tw). This signal is completely synchronized with the data signal S1 in the first signal, is precedent by a quarter period from the data signal S1 in the second period and recedes by a quarter period from the data signal S1 in the third period. A specified value -Vo is given to the common signal in the fourth period. The voltage waveforms impressed in such a manner are C1-S1 (at the time of on) or C1-S2 (at the time of off).

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 device.

[0002]

2. Description of the Related Art For example, chiral smectic C (SmC
^* ) Liquid crystal display devices using ferroelectric liquid crystals such as phases have been reported to have the effects of being capable of high-speed response and having memory properties. Such characteristics are realized by the Sm layer of the liquid crystal being in a uniform alignment state so as to have a complete bookshelf structure.

However, even when a rubbing film made of polyimide, for example, is used as the alignment film, the Sm layer of the ferroelectric liquid crystal does not actually have a bookshelf structure but has a chevron structure as shown in FIG. . In the figure, 1
1 and 12 are glass substrates, 13 and 14 are transparent electrodes, 15 and 16 are alignment films, 17 and 18 are sealing materials, and 19 is a ferroelectric liquid crystal. Therefore, it is difficult for the liquid crystal display device using the ferroelectric liquid crystal to obtain the sufficient memory property in the uniform alignment state as described above.

Also, when a liquid crystal display device using a ferroelectric liquid crystal is used as a liquid crystal shutter, charge clusters are generated by impurity ions in the ferroelectric liquid crystal, and due to this cluster of charges, continuous ON or OFF selection is performed. At times, it was difficult to obtain stable shutter characteristics because the light amount changed with time.

[0005]

As described above, in the liquid crystal display device using the ferroelectric liquid crystal, in reality, since impurities or the like are generated in the ferroelectric liquid crystal, its orientation is poor and the memory property is poor. There was a problem that it would be low.

The present invention has been made in view of the above circumstances, and an object thereof is to use a ferroelectric liquid crystal which is relatively easy to obtain and which does not exhibit a memory property because it has impurities. Even in such a case, it is an object of the present invention to provide a driving method of a ferroelectric liquid crystal device capable of obtaining a high-contrast image in a stable alignment state.

[0007]

That is, the present invention uses a ferroelectric liquid crystal having a negative dielectric anisotropy and applies a high-frequency electric field after applying a positive or negative biased electric field. The dielectric liquid crystal is maintained in the first alignment state, a positive or negative biased electric field is applied, and then a non-electric field or a weak electric field is applied to cause spontaneous polarization due to internal charges due to ions in the liquid crystal. The state is reversed from the state to the second orientation state, and the second orientation state is maintained by the high frequency electric field. Ferroelectricity that is relatively easy to obtain and does not show memory property due to the presence of impurities. Even with liquid crystal, a high-contrast image can be obtained in a stable alignment state.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a cell structure of a ferroelectric liquid crystal device, in which 21 and 22 are glass substrates, 23 and 24 are glass substrates 21,
Transparent electrodes arranged and formed on 22; transparent electrodes 23 and 25;
An alignment film made of polyimide, which is coated on 24 and rubbed to make the alignment directions parallel, 27,
28 is a sealing material, 29 is a sealing material 27, 28 and the above alignment film
Ferroelectric liquid crystal enclosed between 25 and 26, 30 is a transparent electrode 23,
It is a power supply that drives 24. The figure shows a state in which the ionic impurities in the ferroelectric liquid crystal 29 cause the bending around the transparent electrodes 23, 24 due to the driving of the power supply 30.

Here, the cell thickness of the above structure, that is, the distance between the alignment films 25 and 26 is 2 [μm], and the physical characteristic values of the ferroelectric liquid crystal 29 enclosed between the alignment films 25 and 26 are shown in FIG. The value is as shown in.

When a bipolar pulse voltage (Vop = 20 [V]) as shown in FIG. 3 (A) is applied to the ferroelectric liquid crystal 29 containing impurity ions and having a chevron structure, As shown in FIG. 3 (B), the ferroelectric liquid crystal 29 does not have a memory property, and the amount of transmitted light changes with time.

However, this ferroelectric liquid crystal 29 is also used.
A high frequency electric field (fH = 50) as shown in FIG.
It is understood that when [kHz]) is applied, it has a memory property as shown in FIG. 4B and maintains the orientation state of the biased DC electric field applied immediately before.

Utilizing this point, a signal having a time division drive waveform as shown in FIG. 5 is supplied to the ferroelectric liquid crystal device having the cell structure. Here, the duty ratio is set to 1/4, and FIG.
The data signal S1 for turning on all the shutters on all four scanning electrodes is shown in (2), and the data signal S for turning off all the shutters on all four scanning electrodes is shown in FIG. 5 (3).
2 and the common signal C1 is shown in FIG. Both the data signal S1 and the data signal S2 have a voltage value V
S and -VS are given pulse signals of the same high frequency (fH) whose polarities are inverted. Further, the common signal C1 has a voltage value V of the same cycle as the data signal S1 in the first period to the third period in which one frame (tw) is divided into four.
C, -VC (VC <VS), which is completely synchronized with the data signal S1 in the first period, precedes the data signal S1 by a quarter period in the second period, and In the period, the data signal S1 is retracted by a quarter cycle. In the fourth period, the common signal has a constant value -V0 (V0
<VC) is given.

However, the voltage waveform actually applied to the ferroelectric liquid crystal 29 is C1-S1 (when ON) shown in FIG. 5 (4) or C1-S2 (when OFF) shown in FIG. 5 (5). ). Then, the signal of this waveform is actually transferred to the ferroelectric liquid crystal 29.
FIG. 6 shows the response obtained by applying to the. In the figure, the duty ratio is 1/4 as described above, the cycle tw of one frame is 1.44 [ms], VC = 16 [V], V0 = 5.
[V], VS = 20 [V], fH = 50 [kHz]. -V0 given in the fourth period of the common signal C1 is applied to reset the state, and this electric field causes a bias of ionic impurities in the ferroelectric liquid crystal 29. Immediately after that, the spontaneous polarization is inverted by the electric field due to the accumulation of electric charges, that is, the ON state is realized, and the high frequency electric field thereafter stabilizes this state. The off state is realized by directly stabilizing the state reset by -V0 by the high frequency electric field.

In FIG. 2 of the above embodiment, the ferroelectric liquid crystal is used.
The value of the specific resistance ρ of 29 is 2.2 × 10 ¹¹ , which is 1
It is more desirable that it is 0 ¹⁰ or less, that is, the more ionic impurities are.

[0015]

As described above in detail, according to the present invention, a high frequency electric field is applied after a positive or negative biased electric field is applied to maintain the ferroelectric liquid crystal in the first alignment state. After applying a negatively biased electric field, a non-electric field or a weak electric field is applied to reverse the spontaneous polarization from the first alignment state to the second alignment state by the internal charge due to the ions in the liquid crystal,
Since the second alignment state is maintained by the high-frequency electric field, the stable alignment state is obtained even when using a ferroelectric liquid crystal which is relatively easy to obtain and which does not show a memory property because it has impurities. It is possible to provide a driving method of a ferroelectric liquid crystal device capable of obtaining a high-contrast image.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a liquid crystal cell structure according to an embodiment of the present invention.

FIG. 2 is a diagram showing physical property values of the ferroelectric liquid crystal of FIG.

FIG. 3 is a diagram showing a response characteristic of the ferroelectric liquid crystal of FIG. 1 to application of a bipolar pulse voltage.

FIG. 4 is a diagram showing response characteristics of the ferroelectric liquid crystal of FIG. 1 to an application of a high frequency electric field.

FIG. 5 is a timing chart showing a drive voltage waveform according to an embodiment of the present invention.

FIG. 6 is a diagram showing response characteristics corresponding to the drive waveforms in FIG.

FIG. 7 is a cross-sectional view showing a cell structure of a ferroelectric liquid crystal having a chevron structure having ionic impurities.

[Explanation of symbols]

11, 12, 21, 22 ... Glass substrate, 13, 14, 23, 24 ... Transparent electrode, 15, 16, 25, 26 ... Alignment film, 17, 18, 27, 28 ... Sealing material, 19, 29 ... Ferroelectric Liquid crystal, 30 ... Power supply.

Claims (1)

[Claims] 1. A ferroelectric liquid crystal having a negative dielectric anisotropy is used,
After applying a positive or negative biased electric field, a high frequency electric field is applied to maintain the first alignment state, and a positive or negative biased electric field is applied, followed by a non-electric field or a weak electric field. A method for driving a ferroelectric liquid crystal device, comprising reversing from the first alignment state to the second alignment state by the internal charge of the ions and maintaining the second alignment state by a high frequency electric field.