JP2576818B2 - Driving method of electro-optical element - Google Patents

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 an electro-optical element which can be used as a display element, a transmitted light amount control element, and the like.

[0002]

2. Description of the Related Art Conventionally, various electro-optical elements have been developed. Among them, a liquid crystal electro-optical element using a liquid crystal has a relatively simple structure, and is widely used as a display element, an optical shutter, and the like because of its features such as small size, light weight, and low power consumption.

In the production of a liquid crystal electro-optical element, a liquid crystal electro-optical element using a simple matrix is more advantageous than a liquid crystal electro-optical element using an active matrix when a large capacity / large area is used. In, it is difficult to produce a large-capacity device due to the optical response characteristics. For example, in the case of using the TN mode, 1 /
If the duty is about 1/400 even in the STN / SBE mode of 200 duty and higher performance, there is a problem that the display quality deteriorates and it cannot be practically used.

Therefore, a method has been considered in which a memory is provided by controlling the liquid crystal and its orientation (for example, those utilizing bistability by an applied voltage, such as J. Appl. Phys. 59, 3087, '86). This utilizes the fact that the applied voltage and transmittance may cause a hysteresis phenomenon in a high twist state exceeding 90 degrees, and the selectively written information is held by a holding voltage that is in a hysteresis loop. Is what you do. Hereinafter, in this specification, this system is abbreviated as HTN system. FIG. 2 shows the concept of the drive waveform in the conventional HTN method.

[0005]

However, the conventional HTN
The method has a drawback that writing can be speeded up by applying a high voltage, but erasing is slow due to natural relaxation. This is peculiar to an electro-optical element using a nematic liquid crystal phase without performing dual frequency driving. For example, H
While the application of the TN write voltage can be performed in a maximum of 0.1 millisecond or less, erasure takes several tens of milliseconds, which is more than 100 times slower than that. For this reason, the erased state is visually recognized and flickers violently, the time required for one frame becomes long, and the frame frequency cannot be increased. This is a practical problem.

Accordingly, an object of the present invention is to provide a driving method capable of providing a highly practical electro-optical element by shortening the erasing time.

[0007]

According to the present invention, there is provided an electro-optical device comprising:
The driving method has a hysteresis characteristic between a pair of substrates.
Driving an electro-optic device sandwiching bistable liquid crystal
Method, select the ON or OFF state of the display.
Write period for applying the selection pulse
Retention period for maintaining the ON or OFF state
And an erasing period for erasing the display state.
In the erasing period, the voltage of the selection pulse is higher than the voltage of the selection pulse.
It is characterized by applying an erase pulse having a high voltage value . FIG. 1 is a diagram showing the concept of the driving method of the present invention.

[0008]

The inventors of the present invention conduct an ordinary HTN drive of a cell having hysteresis in a high twist state exceeding 90 degrees and perform an experiment with a normal HTN. You may have found that. It was also confirmed at the same time that the voltage and pulse width do not necessarily have to be the same as the write pulse.

Although the operation of the present invention is based on the facts described above, it is not a stage where the mechanism can be determined at present. The above fact contradicts the conventional idea that "the liquid crystal returns from the ON state to the initial alignment state because of relaxation, and the liquid crystal can return to the initial alignment state faster without giving any energy".

However, if the ON state at the holding voltage is considered to be a metastable state, it can be considered that the OFF state can be achieved more quickly by applying energy in some form and moving away from the state.

[0011] Although the above-mentioned action cannot be speculated,
In any case, according to the present invention, the erasing time can be shortened.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As an electro-optical element, 400 × 6
A prototype of an HTN type panel of 40 pixels was manufactured. As the alignment treatment, the tilt angle of the liquid crystal is set to 25 degrees by oblique evaporation of silicon oxide, and the twist angle of the liquid crystal is set to 270.
The cell thickness was 6 μm. When this panel is filled with a liquid crystal composition ZLI-1132 manufactured by Merck and a chiral dopant added thereto, and the polarizer is inclined at 45 degrees from the initial alignment direction of the liquid crystal in each substrate,
An electro-optical element having the electro-optical characteristics shown in FIG. 3 is obtained.

When this panel is driven by the conventional HTN method shown in FIG. 2, an erasing time te at room temperature requires about 50 milliseconds. The driving conditions are as follows: the holding voltage VH is 1.5 volts, the selection voltage Vs is 12 volts, the driving pulse width Pw is 1 millisecond, and no voltage is applied within the erasing time te.

However, in the same panel, the same erasing pulse voltage V as in writing is applied by the driving method according to the present invention within the erasing period.
When e is ± 13 volts and the erase pulse width Pe is 1 millisecond, the erase time te is reduced, and the panel can be driven even with an erase time of 25 milliseconds.

Further, in a panel in which a chiral dopant is added to a liquid crystal in a small amount, a panel which is not completely erased for several minutes or more even if an electric field is removed after writing can be manufactured. This cannot be driven by a normal HTN driving method, but if a pulse voltage is applied during the erasing period, erasing can be performed within 50 milliseconds.

Although the embodiment has been described above, the present invention is not limited to the above-described embodiment, but can be applied to any apparatus that applies an electric field other than zero volt during the erasing period.
It goes without saying that there is no limitation on conditions such as the pulse width.

[0017]

As described above, according to the present invention, in a method of driving a bistable electro-optical element driven by a method of holding a written content by applying a bias voltage, an erasing time is shortened. It has the effect of being able to.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a driving method of an electro-optical element according to the present invention.

FIG. 2 is a diagram showing a conventional method for driving an electro-optical element.

FIG. 3 is a diagram illustrating an example of electro-optical characteristics of a liquid crystal electro-optical element.

[Explanation of symbols]

 1.1 Common signal 1.2 Common signal 2.1 Data voltage (Vd) 2.2 Data voltage (Vd) 3.1 Segment signal 3.2 ..Segment signal 4.1 ... Erase voltage (Ve) 5.1 ... Select voltage (Vs) 5.2 ... Select voltage (Vs) 6.1 ... Erase time te 6.2 ... Erase time te 7.1 Drive pulse width Pw 7.2 Drive pulse width Pw 8.1 Write period 8.2 Write period 9.1 Hold period 9 ... 2... Holding period 9.3... Holding period 10.1... 1 frame length 10.2. 1 frame length 10.3. 4: length of one frame 11: voltage-transmittance curve when voltage increases 12: voltage-transmission curve when voltage drops Curve

Claims (1)

(57) [Claims] 1. A semiconductor device having a hysteresis characteristic between a pair of substrates.
Driving an electro-optic device sandwiching bistable liquid crystal
Method to select ON or OFF state of display
Write period for applying a pulse, and holding for holding the ON state or OFF state.
And a erasing period for erasing the display state, wherein the erasing period is higher than the voltage value of the selection pulse.
A method for driving an electro-optical element, comprising applying an erase pulse having a voltage value .