JPH03107920A - Driving method for liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal display device with more satisfactory response characteristic by improving the orienting state of the molecule of ferroelectric liquid crystal and a driving method. CONSTITUTION:A liquid crystal molecule at the interface on one side of a liquid crystal layer 10 and substrates 1, 1' is fixed weakly against the substrates 1, 1' than the liquid crystal molecule at the interface on the other side, and an initializing pulse is applied to all the picture elements before write, and the spontaneous polarization of the liquid crystal molecule is oriented at a spray state. Next, as for impression voltage to perform the switching of the write, the impression voltage higher than a voltage by which the molecule is inverted on the interface where the molecule is fixed weakly, and the one lower than the voltage by which the molecule is inverted on the interface where the molecule is fixed strongly are applied to a selected picture element. In such a way, since switching speed can be increased more than ever even when the same liquid crystal is used, it is possible to drive a display element with the picture elements more than ever.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of using a liquid crystal display device using a ferroelectric liquid crystal composition, and particularly to a method of using a liquid crystal matrix display device.

[Prior art] Ferroelectric liquid crystal display bag f'f (hereinafter referred to as liquid crystal display device)
In this method, the cell thickness (thickness of the liquid crystal layer sandwiched between two substrates) is reduced to provide electro-optical memory properties due to the molecular orientation bistability of the ferroelectric liquid crystal, and each of the devices is A method has been proposed in which display is performed by switching between two stable states by appropriately setting the wave height and polarity of an applied voltage pulse to a pixel (Japanese Patent Application Laid-Open No. 1986-10).
No. 7210).

In the above, in any stable state, the spontaneous polarization (Ps) of the liquid crystal molecules is oriented almost perpendicular to the substrate surface on the interface with the substrate, and the directions of the spontaneous polarization on the upper and lower substrates are almost parallel to each other. It has become.

Furthermore, switching between the two stable states is performed by applying an electric field (E) in a direction substantially opposite to the direction of spontaneous polarization.

[Problem to be solved by the invention] Generally, the time τ required for switching a ferroelectric liquid crystal is:
It can be expressed by the following equation (1).

η τ= (I) sE (η is the viscosity for reversal of spontaneous polarization) As is clear from equation (1), in order to shorten the response time (at) of the liquid crystal, the viscosity (η) must be low and the spontaneous polarization ( A high electric field (E) may be applied using a liquid crystal with a large Ps).

Therefore, although efforts are being made to develop such liquid crystal materials, there are limits to the improvement of such material properties alone, as in the case of nematic liquid crystals.

For example, when trying to time-divisionally drive a liquid crystal matrix display device with 2000 lines or more, the current situation is that its responsiveness is a problem.

An object of the present invention is to provide a liquid crystal display device with even more excellent response characteristics by devising the alignment state of the molecules of the ferroelectric liquid crystal and its utilization method.

[Means to solve the problem] The above object can be achieved by the invention described below.

That is, a cell is formed by opposing a pair of substrates with electrodes and at least one of which is transparent through a spacer, a ferroelectric liquid crystal layer sealed within the cell, and a ferroelectric liquid crystal layer that responds to changes in the orientation of the liquid crystal molecules. In the method of using a liquid crystal display device having an optical means for changing the intensity of light transmitted through the cell, the liquid crystal molecules at one interface between the liquid crystal layer and the substrate in the liquid crystal display device are replaced by the liquid crystal molecules at the other interface. The liquid crystal molecules are fixed weakly to the substrate than the molecules, and the spontaneous polarization of the liquid crystal molecules is oriented in a spray state by applying an initialization pulse to all pixels before writing.

Next, the applied voltage for switching the write is:
It is characterized by applying a voltage to the selected pixel that is higher than the voltage at which molecules are reversed on the interface where molecules are weakly fixed, and lower than the voltage at which molecules are reversed at the interface where molecules are strongly fixed. This is how to use a liquid crystal display device.

FIG. 2 is a perspective view showing the structure of a liquid crystal matrix display device to which the present invention is directed.

The ferroelectric liquid crystal layer 10 is sandwiched between transparent substrates 20.20' having electrodes 13.13'.

A spacer (not shown) is interposed between the upper substrate 20 and the lower substrate 20' to maintain the cell thickness, the periphery of the substrate is sealed (not shown), and the liquid crystal layer is isolated from the atmosphere. There is.

At the interface between the substrates 20, 20' and the liquid crystal layer 10, alignment means is provided which has an appropriate difference in the function of aligning the liquid crystal on the upper and lower sides.

Said LCD No. 10. Electrode 13.13' and substrate 20.
Polarizing plates 9 and 9' are provided so as to sandwich the cell constituted by 20' from above and below, and the polarizing axes 11 and 11 of the polarizing plates are
' are arranged almost orthogonally to each other.

The optical means described in the present invention includes, in addition to the polarizing plates 9 and 9' shown in FIG. 2, a dichroic dye added to the liquid crystal.
There is also a so-called guest-host method in which contrast is imparted by attaching one or two polarizing plates.

In the figure, electrodes 13 and 13' provided on the upper and lower substrates are matrix electrodes, and drive circuits 14 and 14' are connected so that an electric field is applied in a predetermined sequence to the pixels formed by the electrodes. Ru.

Next, a method of using the present invention will be explained with reference to FIG.

The figure shows the spontaneous polarization (
It is a schematic diagram showing the direction of Ps).

In the figure, vector 2 is a vector (C-director) that is a vector in the long axis direction of one molecule projected onto a plane parallel to the liquid crystal layer sandwiched between substrates. Vector 3 is a spontaneous polarization (Ps) that is orthogonal to vector 2. represents the direction of

In the present invention, liquid crystal molecules are weakly fixed at one interface 5 and strongly fixed at the other interface 6.

FIG. 1(a) shows a case where the molecular orientation direction at the interface 5 is almost equal to the molecular orientation direction at the interface 6. In this case, the orientation direction of all liquid crystal molecules between the upper and lower substrates is uniform.

In the case of FIG. 1(b) or (Q), when an electric field with a constant amplitude and polarity opposite to that in FIG. 1(a) is applied to the liquid crystal layer, the liquid crystal molecules at the weakly fixed interface 5 The spontaneous polarization of the liquid crystal molecules is reversed, and at the interface 6 where 1 is strongly fixed, the spontaneous polarization of the liquid crystal molecules does not change.

The strength of the above-mentioned reverse electric field is the electric field strength obtained by applying a voltage higher than the voltage at which the molecules on the interface 5 are reversed and lower than the voltage at which the molecules at the interface 6 are reversed. Accordingly, the state shown in (b) or (c) is obtained.

The interface on which liquid crystal molecules are weakly fixed, such as the interface 5 in FIG. 1, is, for example, one made of a polyimide polymer film, or one that has been lightly treated such as rubbing to weaken the regulating force.

On the other hand, a fixed interface refers to one in which an orientation control film such as a polyimide polymer is applied and a uniaxial alignment treatment such as rubbing is performed after curing, or one in which an SiO oblique evaporation film is formed. , these differ depending on the type of liquid crystal used, etc., and therefore need to be appropriately selected and controlled.

The method of fixing molecules on the interface (in the direction of the long axis of the molecule) is not only when they are parallel or antiparallel on the upper and lower interfaces, but also when they intersect with each other as long as the intersection angle is approximately twice the molecule tilt angle. .

Furthermore, in the present invention, the liquid crystal molecules at the upper and lower interfaces of the liquid crystal filled in the cell, which has been subjected to interface treatment so that molecules are fixed on one substrate and switched on the other substrate, are parallel to each other, Alternatively, it can be obtained by setting the two polarizing plates 9, 9' so that a dark state occurs when they are substantially parallel. A more desirable arrangement of the polarizing plates in this case is that the polarizing axes of the two polarizing plates 9 and 9' are at right angles to each other, and that the polarizing axis of one polarizing plate and the long axis direction of the molecules at the fixed interface are at right angles to each other. This is the case when it is set either parallel or at right angles.

[Function] First, in the present invention, we will explain the switching effect caused by using ferroelectric liquid crystals to differentiate the alignment control functions of the upper and lower substrates, strongly fixing one substrate and weakly fixing the other substrate. At the interface with the liquid crystal of the other substrate, an alignment film such as polyimide is provided, and the molecules on the interface are strongly fixed by applying a treatment such as rubbing to control the uniaxial alignment of the liquid crystal molecules, and at the interface with the liquid crystal of the other substrate, For example, a cell is formed in which the above-mentioned orientation treatment is not performed at all or a very weak rubbing treatment is performed to weaken the orientation control force.

When a ferroelectric liquid crystal is placed in this cell, an electric field is applied to stabilize the alignment direction of the liquid crystal on the former substrate, and S is slowly cooled to form an Sc phase, the alignment parallel to the rubbing direction becomes more stable. Once stabilized, the orientation obtained when an opposite polarity electric field is applied becomes relatively unstable.

The difference in the stability of these two orientations can be controlled by the method of orientation treatment of the upper and lower substrates. By appropriately controlling the difference in the alignment function between the upper and lower substrates, the alignment state during slow cooling is stable in the absence of an electric field, and the alignment obtained when reverse polarity is applied is unstable.

When the electric field is removed after applying a world of opposite polarity, a transition occurs to a splay state in which the direction of the spontaneous polarization vector on the ceiling board is almost the opposite. Such a spray state occurs more easily and is more stable as the cell thickness increases.

Due to the above-mentioned effects, a liquid crystal element is obtained which is stable in two states: the approximately --like alignment state (a) in the rubbing direction shown in FIG. 1, and the spray state (b) [or (C)].

Next, a description will be given of the switching effect when a predetermined electric field is applied to the electrodes of the liquid crystal element.

When an electric field is applied to the liquid crystal element such that only the spontaneous polarization of the liquid crystal molecules on the interface on the weakly fixed side is reversed, but the spontaneous polarization of the liquid crystal molecules on the interface on the strongly fixed side is not reversed, the one-sided interface Switching occurs only at

In this way, by switching only at one side of the interface, one of two states can be achieved: the orientation state (a), which is almost the same as the rubbing direction shown in Fig. 1, and the spray state (b) [or (C)]. A liquid crystal element that can be selected is obtained.

Next, a description will be given of the effect that when a cell having the characteristics (a), (b) (or (C)) is used, the switching speed becomes faster even with the same liquid crystal material.

As mentioned above, the switching time of the ferroelectric liquid crystal becomes faster as the spontaneous polarization and the applied voltage are larger.

This is because the torque that attempts to reverse the liquid crystal molecules generated by the interaction between the spontaneous polarization and the applied voltage increases. The magnitude of the molecular inversion torque varies not only depending on the spontaneous polarization and the magnitude of the applied voltage, but also on the angle (0) formed by these two vectors.

That is, it is maximum when the two vectors are orthogonal, and theoretically becomes zero when they are parallel or antiparallel.

In the conventional example, the spontaneous polarization is arranged almost perpendicularly to the interface with the substrate in the memory state.

Therefore, when an electric field is applied, the angle between the spontaneous polarization and the electric field is approximately 180 degrees, and the theoretical torque is zero.

In reality, the layer structure is not completely orthogonal to the substrate, but may be slightly tilted, its orientation locally disordered, or thermally fluctuated, resulting in non-zero torque. The inversion starts. Once the reversal begins, the angle between the spontaneous polarization and the electric field expands, and the torque increases accordingly, and switching progresses and is completed.

On the other hand, in the present invention, in the spray state shown in FIG. The torque is already significantly larger in the initial stage compared to the previous model, so even with the same material, the response speed is faster.

As described above, the switching speed from the spray state (b) to the uniform state (a) can be significantly improved, and in particular, the liquid crystal matrix display device can be driven in a shorter time.

In addition, the layer structure formed by ferroelectric liquid crystal molecules is not perpendicular to the substrate surface, but has a layer structure that is almost vertically symmetrical and deformed into a dogleg shape (T, P, Riekere et al.
, Physical Review Letters
, 59. No. 23 (1987) pp1257~
2661: Rieker et al., Commercial Review Letters]. Therefore, no matter how the liquid crystal molecules in one layer are arranged, the distribution of liquid crystal molecules in the thickness direction of the device cannot be in a uniform state, resulting in an ideal dark state and low contrast.

Therefore, in order to fully bring out the effects of the present invention.

It is desirable that the smectic layer be almost perpendicular and parallel to the thickness direction of the device (bookshelf structure). Such a bookshelf structure does not need to be formed from the beginning of the device. It can be formed by applying a relatively high voltage of . The above operation is particularly effective when using a liquid crystal material that passes through the smectic A phase.

In the present invention, after the direction of spontaneous polarization of the liquid crystal is set to the spray state, voltage pulses of opposite polarity are sequentially applied to each of a plurality of electrode lines to sequentially write data, from the spray state to the uniform state. Since the switching speed is more than twice as fast as that of conventional display devices, the time required to rewrite the entire screen can be significantly reduced.

[Example] Next, the present invention will be specifically explained with reference to Examples.

[Example 1] A polyimide-based alignment control film (PIQ) was deposited on one of two glass substrates provided with indium oxide-based transparent electrodes.
A varnish (manufactured by Hitachi Chemical Co., Ltd.) was spin-coded, heated and cured, and then rubbed.

The film thickness was measured using an ellipsometer manufactured by Mizojiri Optical Co., Ltd.
There were about 100 people. A liquid crystal cell was assembled using glass fiber powder as a spacer so that the distance between the two substrates was 3.2 μm, and a liquid crystal composition represented by the following formula was vacuum sealed.

(40% by weight) (40 heavy view%) (20 heavy view%) The phase series of the above composition is as follows.

angle of 32 degrees, viscosity coefficient 0.7Pa-8, spontaneous polarization 41n
C/cm".

After vacuum-sealing the present composition in the above-mentioned cell, it was heated to 61°C or higher, and then heated to about 0.0°C while applying a DC voltage of 20V.
．． It was slowly cooled to room temperature at 5°C/min.

Next, sandwich the above element between two polarizing plates, set the polarization axis of one polarizing plate almost parallel to the rubbing direction (shifted by about 10 degrees, which corresponds to the temperature change in the tilt angle), and use The polarization axis of the plate was arranged approximately perpendicular to the polarization axis of the polarizing plate.

A voltage pulse of 40 V and Iliτ is applied to this,
The minimum pulse widths τS and τU at which the molecules, that is, the spontaneous polarization is reversed, were measured only at one interface.

In the above, τS is the minimum pulse width for switching from the uniform state to the splay state, and τU is the minimum pulse width for switching from the splay state to the uniform state.

As a result, τs:=200us, tu:=70μs, and it can be seen that τU is more than twice as fast as τS.

Incidentally, the inclination of this composition at room temperature (25° C.) [Comparative Example] In an element having the same configuration as in Example 1, only the alignment film treatment was the same on the top and bottom, the film thickness was 50, and the rubbing direction was antiparallel on the top and bottom. And so. The minimum pulse width required for reversal when applying positive and negative voltage pulses was measured, and both were 220 μs.

[Example 2] A 3×3 liquid crystal matrix element with the same configuration as Example 1 except for the electrode structure as shown in FIG. 3(a).

A voltage waveform as shown in FIG. 3(b) was applied.

Here, first, in the initialization period 17, the state of the previous pixel is made uniform, and in the scanning period 18, each scanning electrode V x
z e V xz y V JI3), signal electrode V vl @ V v for each line
Sequential writing was performed using the voltage difference from the waveform carrying signal information from sp V vs.

In the drive waveform example shown in FIG. 3, the voltage during switching is set to V, and the pulse voltage applied when writing on other lines is set to V, /3.

In the second case, the initialization pulse 19 first puts all pixels into the spray state, and then the peak value of the write pulse 20 is vo, which becomes above the threshold value, or v, which becomes below the threshold value.
/3, and the splay state is maintained or the uniform state is rewritten, and two bright and dark states are appropriately written for each pixel.

In addition, during the initialization period, in order to complete the switching from the uniform state to the spray state,
This is achieved by making the pulse width sufficiently wide or by making the peak value sufficiently high.

[Effects of the Invention] According to the usage method of the present invention, even when using the same liquid crystal, the switching speed can be made faster.
It is possible to drive a display element with a larger number of pixels than ever before.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram illustrating the alignment state of liquid crystal molecules and spontaneous polarization of a liquid crystal device of the present invention, FIG. 2 is a perspective view of the structure of a liquid crystal device of the present invention, and FIG. Figure (b) is a diagram of the driving waveform. DESCRIPTION OF SYMBOLS 1...Substrate, 2...Vector showing the oblique shadow of liquid crystal molecules on a plane parallel to the liquid crystal layer (C-director), 3...Spontaneous polarization, 5...Free interface, 6...Fixed Interface, 9...
·Polarizer. lO...Liquid crystal cell, 11...Polarization axis of polarizing plate, 12
...Rubbing direction, 13...Matrix electrode, 14
... Drive circuit, 17... Initialization period, 18... Scanning period. 19...Initialization pulse, 20...Switching pulse. Figure 1 (a) (b) 12 2 Figure 1.1'...Substrate 9.9'...Polarizing plate 10...Liquid crystal ii, xi '... Polarizing axis of polarizing plate 12... Rapi/g direction 13.13'... Matrix 14...
...Drive circuit (b)

Claims (1)

[Claims] 1. A cell formed by opposing a pair of substrates, each of which has an electrode and at least one of which is transparent, with a spacer interposed therebetween; a ferroelectric liquid crystal layer sealed within the cell; In a method for driving a liquid crystal display device having an optical means for changing the intensity of light transmitted through the cell in response to a change in orientation, the method comprises: controlling liquid crystal molecules at one interface between the liquid crystal layer and the substrate in the liquid crystal display device; , fix the liquid crystal molecules weakly to the substrate than the liquid crystal molecules at the other interface, apply an initialization pulse to all pixels before writing to orient the spontaneous polarization of the liquid crystal molecules to a spray state, and then perform switching for writing. The applied voltage for is
It is characterized by applying a voltage to the selected pixel that is higher than the voltage at which the molecules are reversed on the interface where the molecules are weakly fixed, and lower than the voltage at which the molecules are reversed at the interface where the molecules are strongly fixed. A method for driving a liquid crystal display device. 2. A cell formed by opposing a pair of substrates, at least one of which has a matrix electrode and is transparent, with a spacer interposed therebetween; a ferroelectric liquid crystal layer sealed within the cell; In the method of driving a liquid crystal display device, the liquid crystal display device includes an optical means for changing the intensity of light transmitted through the cell, the liquid crystal molecules at one interface between the liquid crystal layer and the substrate in the liquid crystal display device being controlled by the liquid crystal molecules at the other interface. The liquid crystal molecules are fixed weakly to the substrate than the liquid crystal molecules, and before writing, the spontaneous polarization of the liquid crystal molecules is oriented to a splay state by applying an initialization pulse to all pixels configured by matrix electrodes, and then the writing is switched. The applied voltage for this is
Apply a voltage to the selected pixel that is higher than the voltage at which molecules are reversed on the interface where molecules are weakly fixed, and lower than the voltage at which molecules are reversed at the interface where molecules are strongly fixed. Features: A method for driving a liquid crystal display device. 3. In claim 2, by simultaneously applying a voltage pulse of a predetermined polarity to a plurality of electrode wires, the orientations of liquid crystal molecules at one interface and the other interface are initialized to a state where they intersect with each other, A method of using a liquid crystal display device, characterized in that writing is performed sequentially by applying a voltage pulse having a polarity opposite to the predetermined polarity to each of the plurality of electrode lines one by one. 4. The method for driving a liquid crystal display device according to claim 1, 2 or 3, characterized in that a uniaxially aligned liquid crystal alignment control film is provided on at least the side of the substrate where liquid crystal molecules are strongly fixed.