Liquid-crystal display device

• US 6,963,322 B2
• Filed: 09/23/2002
• Issued: 11/08/2005
• Est. Priority Date: 09/28/2001
• Status: Expired due to Fees

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Sakaigawa, Akira
• Primary Examiner(s): Shankar, Vijay
• Assistant Examiner(s): DHARIA, PRABODH M
• Application Number:
  US10/252,464
• Publication Number:
  US 20030063057A1
• Time in Patent Office: 1,142 Days
• Field of Search: 345 84- 90, 345/149, 345/150, 345/152, 345/63, 345/72, 345/77, 345/147, 345/431, 345/432, 345 94- 97, 345/131, 349/93, 349/94, 349/149, 349/123, 349/156, 349/129, 349/132, 349/133, 349/49, 349/34, 349/61, 349/74, 349/432, 349/33, 349/89, 349/172
• 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 the pixel electrodes, and the other substrate has opposing electrodes formed thereon. The orientation of the liquid crystal is controlled to exhibit bistability in which bistable states having different transmittances are maintained when no voltage is applied as a result of applying a voltage exceeding a threshold value, and to exhibit a continuous response characteristic 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 the 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 comprised of a pair of substrates bonded together with a predetermined spacing therebetween and a nematic 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 a liquid crystal exhibits bistability such that bistable states having different transmittances are provided and both states are capable of existing when no voltage is applied and wherein the state can be switched when a voltage exceeding a predetermined threshold value is applied, and the liquid crystal exhibits a continuous 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 the liquid crystal does not exhibit a memory effect in such a range, and

wherein said driving circuit selectively controls which of two modes each pixel operates in, a two-gradation display mode using the bistability or a multi-gradation display mode using the continuous response characteristic in which no memory effect is present.

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 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 a phase orientation orientation of said nematic liquid crystal 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.