Liquid-crystal display device

• US 20030063057A1
• Filed: 09/23/2002
• Published: 04/03/2003
• Est. Priority Date: 09/28/2001
• Status: Active Grant

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Sakaigawa, Akira
• Granted Patent: US 6,963,322 B2
• Time in Patent Office: Days
• US Class Current: 345/87
• CPC Class Codes: G09G 2300/0482 Use of memory effects in nematic liquid crystals
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/3651 using multistable liquid crystals, e.g. ferroelectric liquid crystals

Abstract

In a liquid-crystal display device, one of substrates has pixel electrodes and TFTs for driving these pixel electrodes formed thereon, and the other substrate has opposing electrodes facing the corresponding pixel electrodes formed thereon. The orientation of a liquid crystal is controlled to exhibit bistability in which bistable states having different transmittances are maintained when no voltage is applied and the bistable state can be switched as a result of applying a voltage exceeding a threshold value, and to exhibit response characteristic such that the transmittance varies continuously in response to an applied voltage in a predetermined range which does not exceed the threshold value. The voltage applied to the liquid crystal can be selectively controlled between a voltage equal to or higher than a threshold value and a voltage lower than the threshold value, and a two-gradation display using the bistability and a multi-gradation display using the response characteristic are made.

Claims

1. A liquid-crystal display device comprising:

a panel having a flat construction and formed of a pair of substrates bonded together with a predetermined spacing therebetween and a liquid crystal held in the spacing, one of the substrates having pixel electrodes arranged in a matrix and switching elements for driving the pixel electrodes formed thereon, and the other substrate having opposing electrodes facing the corresponding pixel electrodes formed thereon; and

a driving circuit for driving each switching element in order to write a signal to each pixel electrode, and for applying a voltage corresponding to the signal between the opposing electrode and the pixel electrode to control the transmittance of the liquid crystal,

wherein the orientation of said liquid crystal is controlled by the pair of substrates in such a manner that the liquid crystal exhibits bistability such that bistable states having different transmittances are maintained when no voltage is applied and the bistable states can be switched when a voltage exceeding a predetermined threshold value is applied, and exhibits a response characteristic in which the transmittance changes continuously, in response to an applied voltage, in a range which does not exceed the threshold value, and

wherein said driving circuit can selectively control the voltage applied to the liquid crystal between a voltage equal to or higher than a threshold value and a voltage lower than the threshold value, and a two-gradation display using the bistability and a multi-gradation display using the response characteristic are made.

2. A liquid-crystal display device according to claim 1, wherein the orientation control of the liquid crystal is performed by said pair of substrates by making the anchoring strengths thereof with respect to the liquid crystal differ from each other, thus imparting bistability to the liquid crystal.

3. A liquid-crystal display device according to claim 1, wherein the orientation control of the liquid crystal is performed by said pair of substrates by processing the states of the surfaces thereof in contact with the liquid crystal so as to be different from each other, thus imparting bistability to the liquid crystal.

4. A liquid-crystal display device according to claim 1, wherein the orientation control of the liquid crystal is performed by said pair of substrates by forming different orientation films on the surfaces thereof in contact with the liquid crystal, thus imparting bistability to the liquid crystal.

5. A liquid-crystal display device according to claim 1, wherein said driving circuit switches the electrical potential of the opposing electrode in order to selectively control a voltage to be applied to the liquid crystal between a voltage equal to or higher than a threshold value and a voltage lower than the threshold value.

6. A liquid-crystal display device according to claim 1, wherein said driving circuit switches the amplitude of a signal to be written into the pixel electrode in order to selectively control the voltage to be applied to the pixel electrode between a voltage equal to or higher than a threshold value and a voltage lower than the threshold value.

7. A liquid-crystal display device according to claim 1, wherein said liquid crystal shows a nematic phase whose orientation is controlled in the horizontal direction by said pair of substrates.

8. A liquid-crystal display device according to claim 7, wherein said liquid crystal shows a twisted nematic phase in which the orientation is twisted between said pair of substrates.