Bistable liquid crystal display device
First Claim
1. A method of driving a liquid crystal display device including a liquid crystal cell comprising the steps of:
- providing the liquid crystal cell with a first voltage pulse to initiate Freedricksz transition of said layer of said liquid crystal material, and a second voltage used to select either said first or second metastable state of said liquid crystal material, and a third voltage used to maintain the selected metastable state;
sensing a temperature at the liquid crystal display device; and
adjusting at least either an amplitude or width of said first voltage pulse used to initiate the Freedricksz transition based on the sensed temperature, to change a d/p value, wherein d and p represent cell spacing of the liquid crystal cell and unstrained pitch of the liquid crystal material, respectively.
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Accused Products
Abstract
A bistable liquid crystal display device having a plurality of display cells which include a pair of substrates arranged substantially in parallel, each substrate having a confronting surface bearing transparent electrodes, and a layer of chiral-nematic liquid crystal materials contained between the substrates. The display device is switched between first and second metastable states caused by relaxation from a state previously formed by the Freedricksz transition, the first and second metastable states corresponding to arrangements of liquid crystal molecules gradually twisted between the substrates by 360° for the first (or T) metastable state, or by 0° for the second (or U) metastable state, respectively, and of maintaining the selected metastable state by applied third voltages. At least either the amplitude or width of the first voltage used to initiate the Freedricksz transition may preferably be adjusted, to thereby provide a liquid crystal display device of high display quality, capable of achieving a high speed drive over a wide range of temperatures.
31 Citations
29 Claims
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1. A method of driving a liquid crystal display device including a liquid crystal cell comprising the steps of:
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providing the liquid crystal cell with a first voltage pulse to initiate Freedricksz transition of said layer of said liquid crystal material, and a second voltage used to select either said first or second metastable state of said liquid crystal material, and a third voltage used to maintain the selected metastable state;
sensing a temperature at the liquid crystal display device; and
adjusting at least either an amplitude or width of said first voltage pulse used to initiate the Freedricksz transition based on the sensed temperature, to change a d/p value, wherein d and p represent cell spacing of the liquid crystal cell and unstrained pitch of the liquid crystal material, respectively.
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2. A method of driving a liquid crystal display device including a liquid crystal cell including two substrates arranged in parallel, each substrate having a confronting surface bearing at least one transparent electrode, an alignment film disposed over said transparent electrode, a layer of liquid crystal material contained between said substrates, said liquid crystal material being chiral-nematic liquid crystal with a positive dielectric anisotropy, a surface of said alignment film being alignment treated with an anti-parallel alignment direction and pre-tilt angles formed on respective alignment film surfaces by the electrodes, said method comprising the steps of:
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providing the liquid crystal cell with a first voltage pulse to initiate Freedricksz transition of said layer of said liquid crystal material, and a second voltage used to select either said first or second metastable state of said liquid crystal material, and a third voltage used to maintain the selected metastable state;
sensing a temperature at the liquid crystal display device; and
adjusting at least either an amplitude or width of said first voltage pulse used to initiate the Freedricksz transition based on the sensed temperature, to change a d/p value, wherein d and p represent cell spacing of the liquid crystal cell and unstrained pitch of the liquid crystal material, respectively. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9)
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10. A method of driving a liquid crystal display device including a liquid crystal cell including two substrates arranged in parallel, each substrate having a confronting surface bearing at least one transparent electrode, an alignment film disposed over said transparent electrode, a layer of liquid crystal material contained between said substrates, said liquid crystal material being chiral-nematic liquid crystal with a positive dielectric anisotropy, a surface of said alignment film being alignment treated with an anti-parallel alignment direction and pre-tilt angles formed on respective alignment film surfaces by the electrodes, said method comprising the steps of:
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providing the liquid crystal cell with a first voltage to initiate Freedricksz transition of said layer of said liquid crystal material, and a second voltage used to select either said first or second metastable state of said liquid crystal material, and a third voltage used to maintain the selected metastable state, adjusting at least either an amplitude or width of said first voltage used to initiate the Freedricksz transition, wherein said liquid crystal material contained between said substrates has a kinetic viscosity equal to or smaller than 17 (mm2/sec) at 20°
C.- View Dependent Claims (11, 12)
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13. A liquid crystal display device comprising:
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a liquid crystal cell including two substrates arranged in parallel, each substrate having a confronting surface bearing at least one transparent electrode, an alignment film disposed over said at least one transparent electrode, a layer of liquid crystal material contained between said substrates, said liquid crystal material being chiral-nematic liquid crystal with a positive dielectric anisotropy, a surface of said alignment film being alignment treated with an anti-parallel alignment direction and pre-tilt angles formed on respective alignment film surfaces by a molecular axis of said liquid crystal material at an initial state being substantially equal to each other, a ratio of an unstrained pitch to a thickness of the layer of liquid crystal material being approximately from 1 to 3, said liquid crystal cell being switched between first and second metastable states caused by relaxation from a state previously formed by Freedricksz transition, the first and second metastable states corresponding to arrangements of said liquid crystal material gradually twisted between the substrates by 360°
or 0°
, respectively;
means for applying first, second, and third voltages between the electrodes, said first voltage being a pulse voltage used to initiate the Freedricksz transition of said layer of said liquid crystal material, said second voltage being used to select either said first or second metastable state of said liquid crystal material, and said third voltage being used to maintain the selected metastable state; and
means for sensing a temperature at the liquid crystal display device;
wherein at least either an amplitude or width of said first voltage pulse used to initiate the Freedricksz transition is adjusted based on the sensed temperature, to change a d/p value, wherein d and p represent cell spacing of the liquid crystal cell and unstrained pitch of the liquid crystal material, respectively. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20)
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21. A liquid crystal display device comprising:
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a liquid crystal cell including two substrates arranged in parallel, each substrate having a confronting surface bearing at least one transparent electrode, an alignment film disposed over said at least one transparent electrode, a layer of liquid crystal material contained between said substrates, said liquid crystal material being chiral-nematic liquid crystal with a positive dielectric anisotropy, a surface of said alignment film being alignment treated with an anti-parallel alignment direction and pre-tilt angles formed on respective alignment film surfaces by a molecular axis of said liquid crystal material at an initial state being substantially equal to each other, a ratio of an unstrained pitch to a thickness of the layer of liquid crystal material being approximately from 1 to 3, said liquid crystal cell being switched between first and second metastable states caused by relaxation from a state previously formed by Freedricksz transition, the first and second metastable states corresponding to arrangements of said liquid crystal material gradually twisted between the substrates by 360°
or 0°
, respectively; and
means for applying first, second, and third voltages between the electrodes, said first voltage being used to initiate the Freedricksz transition of said layer of said liquid crystal material, said second voltage being used to select either said first or second metastable state of said liquid crystal material, and said third voltage being used to maintain the selected metastable state, wherein at least either an amplitude or width of said first voltage potential used to initiate the Freedricksz transition is adjusted, and wherein said liquid crystal material contained between said substrates has a kinetic viscosity equal to or smaller than 17 (mm2/sec) at 20°
C.- View Dependent Claims (22, 23)
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24. A liquid crystal display device comprising:
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a liquid crystal cell including two substrates arranged in parallel, each substrate having a confronting surface bearing at least one transparent electrode, an alignment film disposed over said transparent electrode, a layer of liquid crystal material contained between said substrates, said liquid crystal material being chiral-nematic liquid crystal with a positive dielectric anisotropy, a surface of said alignment film being alignment treated with an anti-parallel alignment direction and pre-tilt angles formed on respective alignment film surfaces by a molecular axis of said liquid crystal material at an initial state being substantially equal to each other, a ratio of an unstrained pitch to a thickness of the layer of said liquid crystal material being approximately from 1 to 3, said liquid crystal cell being switched between first and second metastable states caused by relaxation from a state previously formed by Freedricksz transition, the first and second metastable states corresponding to arrangements of said liquid crystal molecules gradually twisted between the substrates by 360°
or 0°
, respectively;
means for applying first, second, and third voltages between the electrodes, said first voltage being a pulse voltage used to initiate the Freedricksz transition of said layer of said liquid crystal material, said second voltage being used to select either said first or second metastable state of said liquid crystal material, and said third voltage being used to maintain the selected mestable state; and
means for sensing a temperature at the liquid crystal display device;
wherein at least either an amplitude or width of said first voltage pulse used to initiate the Freedricksz transition is adjusted based on the sensed temperature, to change a d/p value, wherein d and p represent cell spacing of the liquid crystal cell and unstrained pitch of the liquid crystal material, respectively. - View Dependent Claims (26)
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25. A liquid crystal display device comprising:
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a liquid crystal cell including two substrates arranged in parallel, each substrate having a confronting surface bearing at least one transparent electrode, an alignment film disposed over said transparent electrode, a layer of liquid crystal material contained between said substrates, said liquid crystal material being chiral-nematic liquid crystal with a positive dielectric anisotropy, a surface of said alignment film being alignment treated with an anti-parallel alignment direction and pre-tilt angles formed on respective alignment film surfaces by a molecular axis of said liquid crystal material at an initial state being substantially equal to each other, a ratio of an unstrained pitch to a thickness of the layer of said liquid crystal material being approximately from 1 to 3, said liquid crystal cell being switched between first and second metastable states caused by relaxation from a state previously formed by Freedricksz transition, the first and second metastable states corresponding to arrangements of said liquid crystal molecules gradually twisted between the substrates by 360°
or 0°
, respectively; and
means for applying first, second, and third voltages between the electrodes, said first voltage being used to initiate the Freedricksz transition of said layer of said liquid crystal material, said second voltage being used to select either said first or second metastable state of said liquid crystal material, and said third voltage being used to maintain the selected metastable state;
wherein at least either an amplitude or width of said first voltage potential used to initiate the Freedricksz transition is adjusted, and wherein said liquid crystal material contained between said insulating substrates has a kinetic viscosity equal to or smaller than 17 (mm2/sec) at 20°
C.- View Dependent Claims (27, 28, 29)
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Specification