JPS63133125A - Driving method for liquid crystal matrix panel - Google Patents

Abstract

PURPOSE:To realize high contrast display without degrading a liquid crystal by applying a DC component to most of a scanning period, and applying a pulse, which neutralizes the DC component, just before or a little before a selection period. CONSTITUTION:A ferroelectric liquid crystal 4 is held between a pair of substrates 1 whose counter faces electrodes are provided on to form matrix picture elements, and an asymmetrical memory is provided. In this case, the DC component is applied in most of the scanning period, and the pulse which neutralizes said DC component is applied just before or a little before the selection period. Only a scanning voltage is set to a prescribed waveform at the time of selecting another scanning electrode to apply said neutralizing pulse to a panel. Thus, the liquid crystal is prevented from being degraded by electrochemical reaction, and the panel having the asymmetrical memory is easily oriented as desired by the surface treatment like rubbing.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for driving a liquid crystal matrix panel having a ferroelectric liquid crystal as a liquid crystal layer.

Prior Art In recent years, reports have been made on ferroelectric liquid crystals with fast response speed and memory properties (for example, Hideo Takezoe, Atsuo Fukuda, Sakae Kuze; "Industrial Materials", Vol. 31, No. 10, 22). ).

An example of a conventional ferroelectric liquid crystal panel will be described below with reference to the drawings. FIG. 3 shows the structure of a conventional smectic liquid crystal panel. In Figure 3, 1 is a glass substrate, 2 is ITO (indium tin oxide)
4 is a ferroelectric liquid crystal layer, 5 is a C-dyle reflex of liquid crystal molecules, and 6 is a dipole moment. Ferroelectric liquid crystals generally have a dipole moment in the direction perpendicular to the long axis of the molecules, and as they become thinner, they come to have spontaneous polarization. FIG. 4 shows how to describe ferroelectric liquid crystal using an example of a chiral smectic phase exhibiting ferroelectricity. Figure 4 f
a) is a state in which the long axis of the molecules is tilted by ±θ degrees with respect to the normal to the molecular layer; Figure 4 is the notation for ferroelectric liquid crystal in a state in which the long axis is tilted by -θ degrees; 7 is the normal to the layer. , 8 is the long axis direction n of the molecule, 9
is the dipole moment) Ps, 10 is the C director when n is projected onto the xy plane -C111 is the tilt angle ±θ degrees with respect to the normal to the long axis of the molecule. The operating principle of the ferroelectric liquid crystal panel having the above structure will be explained below with reference to the drawings.

FIG. 5 shows a principle diagram of a conventional ferroelectric liquid crystal panel display method. 12 is a liquid crystal molecule whose long axis of the molecule is tilted by ±θ degrees with respect to the layer normal, 13 is a liquid crystal molecule whose molecular axis is tilted by 1θ degree, 14 is a dipole moment in the front direction of the paper, 15 is a dipole moment in the back direction of the paper, 16 is the direction of the two polarizing plates. Now, Figure 5 (al is the state where no voltage is applied, Figure 5 (b) is when a positive voltage is applied from the front to the back of the paper, Figure 5 (C1 is when a positive voltage is applied from the back to the front of the paper) This is the operating principle when

In this way, the entire cell assumes two states tilted by ±θ degrees depending on the direction of voltage application, and therefore brightness and darkness can be expressed by utilizing birefringence or dichroism due to the electro-optic effect. These two states are called uniform amplifier (UU) and uniform down (UD) based on the direction of spontaneous polarization.

The above is the display principle of a ferroelectric liquid crystal panel, but when matrix driving is performed, contrast can be achieved by retaining the pixel state set during the selection period using a memory effect. FIG. 6 shows a conventional driving method that has been successful in displaying matrix and 7x panels. The displayed panel was oriented by rubbing and has bistable memory.

The driving method is based on the intra-frame AC voltage averaging method; one scan consists of two frames, and white and black are written separately in each frame. (For example, Principles, Kawaguchi, Iwasa, Kai: Niss.I.D. 85 Digest, 1985
Year, 135 pages (T, HAI?ADA, M, TA-GU
CHI, Ni, IWASA, M, KAI:S10 '8
5 Digest (1985) p.

131] Problems to be Solved by the Invention As described above, the conventional driving method is based on the bistability of the liquid crystal panel. Therefore, in order to obtain a high-quality display in a ferroelectric liquid crystal panel, it is necessary to obtain uniform monodomain alignment and a stable memory effect. However, in order to obtain good orientation through surface treatments such as rubbing, it is necessary to give the surface uniaxial anisotropy so that the molecules are oriented in a fixed direction. This contradicts the bistable memory effect. Therefore, a surface treatment method that obtains as good alignment as possible with as weak uniaxial anisotropy as possible to obtain bistability, especially the industrially advantageous rubbing method, uses various alignment films and liquid crystal materials. Experiments are being conducted. Usually, when different types of alignment films are used on the upper and lower substrates, only one of UU and UD becomes stable in many cases.

In addition, even if the alignment film is vertically symmetrical, depending on the liquid crystal, the rubbing direction may deviate from the middle of the two molecular directions (UU and UD) (equal to the molecular layer normal), which may increase the memory property of one state and cause it to become monostable. Furthermore, it has been reported that when the electric field is turned off, the molecules are always oriented in the rubbing direction.

(For example, Murakami et al.: Proceedings of the 11th LCD Symposium, 144
page). Even in a conventional example in which a panel oriented by rubbing is displayed by matrix driving, the contrast is much lower than that obtained by cells oriented by shear stress or the like.

This is because although the bistability of the panel is utilized, its stability is shallow due to rubbing. As mentioned above, bistability often deteriorates or is lost due to rubbing, and if a conventional bistable panel is matrix-driven using the conventional AC driving method, a uniform high-quality display can be achieved. It's difficult to do.

In view of the above-mentioned problems, the present invention provides a driving method for a liquid crystal matrix panel that allows high-duty simple matrix driving to provide high-quality display even with a non-bistable ferroelectric liquid crystal panel, and that does not degrade the liquid crystal. be.

Means for Solving the Problems In order to solve the above problems, the method for driving a liquid crystal matrix panel of the present invention involves sandwiching a ferroelectric liquid crystal between a pair of substrates having electrodes on opposing surfaces, and driving a matrix-like liquid crystal panel. In a liquid crystal matrix panel that forms pixels and has memory for only one of the bright and dark states, a DC component is added to most of the scan, and a pulse is added to neutralize the DC component just before or slightly before the selection period. This enables high contrast display without deteriorating the liquid crystal.

Function Conventional ferroelectric liquid crystal panels have had the above-mentioned problems because they attempted to obtain bistable memory only through the interaction of molecules with the substrate surface. In the driving method of the present invention, the liquid crystal panel itself has only monostable memory, but by applying a DC bias voltage in the opposite direction to the direction of spontaneous polarization in the monostable memory state, it brings about bistability. A pulse for neutralizing the DC bias component is applied immediately before the selection period so as not to affect the display so as not to deteriorate the liquid crystal. When strong uniaxial anisotropy is imparted to the substrate surface, if the conditions for liquid crystal + olefin and reorientation are appropriately set, the orientation of the molecules in either the UD or UU state is aligned in the uniaxial direction. Good monodomain alignment can be easily obtained. If the molecular long axis direction of UD is uniaxial,
Since the panel has memory in UD, if an upward DC bias component (Vdc<O) is superimposed on the applied voltage,
By setting the voltage of Vdc appropriately, UU.

It is possible to have no memory of equal stability (dark value voltage) on both UDs. Apply ■dc for T seconds from the selection period, and a little before the selection period, the average voltage Vrs becomes Vdc-T+Vrs-1=Q, width t (Vrs>Q, t<<T)
When a neutralizing pulse of U is applied, the picture element becomes U due to the neutralizing pulse.
It is reset to the D state, and is inverted to UU or kept as UD depending on the voltage or pulse width of the applied pulse during the selection period. The waveform superimposed on Vdc may be a voltage averaging method used in nematics, but is not limited thereto.

Monostable panels can be obtained by changing the properties of the surfaces of the upper and lower substrates (alignment films), but this configuration prevents the twisted state in which molecules are twisted between the upper and lower substrates from becoming stable. Therefore, it is also advantageous to apply the driving method of the present invention to a panel having such a configuration. In addition, even in a bistable panel, when the dark value voltages are not symmetrical, the driving method of the present invention is applicable and it is effective to balance the dark value voltages without causing deterioration of the liquid crystal.

Also, if the waveform applied to the scanning electrode is set to a predetermined value,
Since the neutralization pulse can be applied to the picture elements while other scan electrodes are being selected, the scan time can be very short.

Example An embodiment of the present invention will be described below with reference to the drawings.

When a mixture of ester-based ferroelectric liquid crystals is injected into a rubbed matrix panel with a 2 μm space and slowly cooled from the iso-labor phase while applying a DC electric field, the chiral nematic phase changes from the chiral nematic phase to the chiral nematic phase. The membrane was oriented as shown in FIG. 2 through the mectink C phase. This panel had memory only in UD, but when a DC bias of 1.2 volts was applied, memory was generated in UU as well, and the dark value voltage characteristics were almost symmetrical between positive and negative, and very steep characteristics were obtained. When the driving waveform of the present invention shown in Fig. 1 was applied to this panel, the voltage was 1/40.
At 0 duty, a display with a contrast of approximately JO was obtained. 1 fa) to Fd) represent the scanning voltage, signal voltage, voltage applied to the picture element, and amount of transmitted light, respectively. A DC bias of Vdc=-1, 2pol 1- is superimposed on the signal voltage in accordance with the waveform of the intra-frame AC voltage averaging method of ]/7 Hias except for the scanning voltage of the phase where the neutralizing pulse is applied. The pulse width I] was 100 μsec, and Vo was 25 pol I·.

Next, Todoro phase → chiral nematic phase → smectic A
→A liquid crystal that had undergone a chiral smectic C phase was injected into a matrix panel with a space of 2.2 μm that had been rubbed with sufficient pressure, and when it was slowly cooled, a second-like orientation was obtained. When using this liquid crystal, a bistable panel could be obtained depending on the rubbing pressure and the conditions of the alignment film, but the panel of this example showed a more uniform alignment, and because of the uniform alignment, the dark value characteristic It was also steep. Therefore, when the bistable panel was driven using the driving method shown in FIG. 1, the contrast was higher than when the bistable panel was driven using the conventional driving method.

Effects of the Invention By superimposing a DC bias voltage on the applied voltage, the liquid crystal matrix panel driving method of the present invention enables display with an asymmetric memory, which has not been used in the past. This neutralizing pulse prevents the liquid crystal from deteriorating due to electrochemical reactions. Panels with asymmetrical memory can achieve a desired orientation more easily than conventional bistable panels through surface treatments such as rubbing, and can also provide stable memory with positive/negative symmetry and steep dark value characteristics through direct current bias, making them extremely useful. A high-quality display can be achieved.

[Brief explanation of the drawing]

Figure 1 is a waveform diagram of the driving method for the liquid crystal matrix panel of the present invention, Figure 2 is a plan view showing the orientation of liquid crystal molecules in the example, Figure 3 is a cross-sectional view of the ferroelectric liquid crystal panel, and Figure 4. is a schematic diagram showing the notation of chiral smectic C liquid crystal,
FIG. 5 is a plan view showing the principle of display of a conventional ferroelectric liquid crystal panel, and FIG. 6 is a driving waveform diagram of a conventional ferroelectric liquid crystal matrix panel. ■・・・Glass substrate, 2. Old transparent electrode, 3.
Old... Alignment film, 4... Ferroelectric liquid crystal layer, 5...
...C director of liquid crystal molecules 16...Dipole moment, 7...Normal of layer, 8...
...Long axis direction of molecule n, 9...Dipole moment, 10...C director-111...
・Inclination angle of the long axis of the molecule with respect to the layer normal ±θ degrees, 12...
...Liquid crystal molecules whose molecular long axes are tilted by +θ degrees with respect to the layer normal, 13...Liquid crystal molecules whose molecular long axes are tilted by -θ degrees, 14. Old.
・Dipole moment toward the front of the paper, 15...Dipole moment toward the back of the paper, 16...Direction of the two polarizing plates. Name of agent: Patent attorney Toshio Nakao 1 person 1-Glass 2-- ■Ding○ Electrode Figure 4 Figure 5

Claims (3)

[Claims] (1) In a liquid crystal matrix panel in which a ferroelectric liquid crystal is sandwiched between a pair of substrates having electrodes on opposing surfaces to form a matrix of pixels and has an asymmetric memory, a direct current component is added to most of the scanning, A method for driving a liquid crystal matrix panel, characterized in that a pulse for neutralizing the DC component is applied immediately before or slightly before a selection period. (2) A DC component neutralizing pulse can be applied to the panel by changing only the scanning voltage to a predetermined waveform at a time when another scanning electrode is selected.
1) Driving method of the liquid crystal matrix panel described in section 1). (3) The method for driving a liquid crystal matrix panel according to claim 1 or 2, wherein the pulses applied to the panel during the selection period are symmetrical in positive and negative directions.