USRE37509EExpiredUtility

Smectic liquid crystal devices

Assignee: SECR DEFENCE BRITPriority: Apr 3, 1986Filed: Jan 10, 1995Granted: Jan 15, 2002

Est. expiryApr 3, 2006(expired)· nominal 20-yr term from priority

Inventors:Madeline J. Bradshaw Edward P. Raynes

C09K 19/44G02F 1/1416C09K 19/46C09K 19/126C09K 19/2021G02F 1/141G02F 1/137

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Claims

Abstract

A method, device, and material for providing a fast switching liquid crystal display employs the ferro electric effect of chiral smectic liquid crystal material. To provide a uniform appearance the liquid crystal material is arranged to have a long cholesteric pitch at a temperature close to a smectic/cholesteric phase transistion temperature. This long cholesteric pitch allows liquid crystal molecules to cool from the cholesteric to smectic phase with a uniform alignment. The smectic material is contained in a cell between wells ( 2, 3 ) bearing electrodes ( 5, 6 ) and surface treated to provide homogeneous alignment of liquid crystal material ( 7 ).

Claims

exact text as granted — not AI-modified

We claim:

1. A method of making a liquid crystal display device comprises the steps;
providing two cell walls spaced apart by a spacer to contain a layer of a liquid crystal material, the wall inner surfaces having formed thereon electrode structures and at least one wall surface treated to provide a liquid crystal alignment,
providing a tilted chiral smectic liquid crystal material having a cholesteric phase at an elevated temperature above ambient between the chiral smectic and isotropic phases with a cholesteric pitch p greater than half the layer thickness d at a temperature at least 0.1° C. above a cholesteric to smectic transition temperature and a significant spontaneous polarization Ps in the chiral smectic phase,
heating the material to the cholesteric phase,
introducing and sealing the material into the space between the walls,
cooling the material to the tilted chiral smectic phase.

2. The method of claim 1 A method of making a liquid crystal display device comprising the steps:

providing two cell walls spaced apart by a spacer to contain a layer of a liquid crystal material, the wall inner surfaces having formed thereon electrode structures and at least one wall surface treated to provide a liquid crystal alignment,

providing a tilted chiral smectic liquid crystal material having a cholesteric phase at an elevated temperature above ambient between the chiral smectic and isotropic phases with a cholesteric pitch p greater than half the layer thickness d at a temperature at least 0 . 1 ° C. above a cholesteric to smectic transition temperature and a significant spontaneous polarization Ps n the chiral smectic phase,

heating the material to the cholesteric phase,

introducing and sealing the material into the space between the walls,

cooling the material to the tilted chiral smectic phase,

and comprising the further steps of reheating to above the smectic/cholesteric transition temperature and slowly cooling, whilst a unidirectional voltage pulse is applied.

3. The method of claim 1 wherein the material is cooled at a rate of less than 20° C./minute within +/−5° C. of the cholesteric/smectic phase transition.

4. The method of claim 1 wherein the material is cooled at a rate of less than 2° C./minute within +/−5° C. of the cholesteric/smectic phase transition.

5. The method of claim 1 2 wherein both walls are surface alignment treated and the cell is arranged with the alignment direction parallel in the same direction.

6. The method of claim 1 2 wherein both walls are surface alignment treated and the cell is arranged with the alignment direction parallel in opposite directions.

7. The method of claim 1 wherein the alignment is produced by unidirectional rubbing.

8. The method of claim 1 wherein the alignment is produced by oblique evaporation of silicon oxide.

9. A liquid crystal device comprising a layer of a tilted chiral smectic liquid crystal material contained between two cell walls each carrying electrode structures and at least one wall surface treated to give alignment to the liquid crystal molecules, a first linear polarizer and one of a second polarizer and an amount of dichroic dye in the liquid crystal material, the liquid crystal material having switched states and a tilted chiral smectic phase at normal device operating temperatures and a cholesteric phase at a higher, above ambient, temperature, with a cholesteric pitch greater than half the layer thickness d in the cholesteric phase for at least 0.1° C. above the cholesteric to smectic transition temperature, and a spontaneous polarization.

10. The device of claim 9 wherein the cell walls are surface treated to align liquid crystal molecules in the same direction with a splayed configuration across the layer thickness.

11. The device of claim 9 wherein the electrodes on each wall are formed as strip electrodes with strip electrodes on one wall forming an angle with strip electrodes on another wall thereby forming a matrix format.

12. The device of claim 9 wherein the electrodes are formed as strip electrodes arranged in a segment format.

13. The device of claim 9 wherein the electrodes are formed as sheet electrodes.

14. The device of claim 9 wherein the liquid crystal layer thickness is up to 15 μm.

15. The device of claim 9 wherein the cholesteric pitch p is greater than d/2 at a temperature at least 5° C. above the transition temperature.

16. The device of claim 9 wherein one polarizer is a neutral polarizer and a second polarizer is comprised of two differently coloured polarizers arranged with their optical axis orthogonal with respect to each other.

17. The device of claim 9 wherein said first polarizer is arranged with an optical axis parallel to the liquid crystal molecular alignment in one of said switched states, and another polarizer is arranged with an optical axis crossed with respect to the first polarizer.

18. The device of claim 9 wherein the cholesteric pitch within 0.1° C. of the cholesteric/smectic trasition is greater than four times the liquid crystal layer thickness.

19. The device of claim 9 and further comprising means for applying the two d.c. voltages of opposite polarity to the electrode structures to switch the liquid crystal material into two different states.

20. A liquid crystal material mixture for use in a liquid crystal display device comprising a material having a tilted chiral smectic phase at normal device operating temperatures and a cholesteric phase at an elevated temperature, the mixture having a cholesteric pitch greater than 4 μm in the cholesteric phase at least 0.1° C. above a cholesteric to smectic transition temperature, and a substantial spontaneous polarization coefficient Ps, in the smectic phase.

21. The material of claim 20 wherein the material has the following phases with temperature:
isotropic⇄cholesteric⇄smectic A⇄chiral smectic⇄solid.

22. The material of claim 20 wherein the material has the following phases with temperature:
isotropic⇄cholesteric⇄chiral smectic⇄solid.

23. The material of claim 20 wherein the pitch in the cholesteric phase is greater than 4 μm over a temperature range up to 5° C. above the cholesteric smectic phase transition.

24. The material of claim 20 wherein the smectic pitch is greater than 2 μm.

25. The material of claim 20 wherein the spontaneous polarization is greater than 0.1 nC/cm 2 .

26. The material of claim 20 wherein the cholesteric/smectic phase transition is above 40° C.

27. The material of claim 20 wherein the cholesteric smectic phase transition is above 100° C.

28. The material of claim 20 and further including an amount of a dichroic dye.

29. A method of making a liquid crystal display device comprises the steps:

providing a tilted chiral smectic liquid crystal material having a cholesteric phase at an elevated temperature above ambient between the chiral smectic and isotropic phases with a cholesteric pitch p greater than half the layer thickness d at a temperature for at least 0 . 1 ° C. above a cholesteric to smectic transition temperature and a significant spontaneous polarization Ps in the chiral smectic phase,

heating the material to the cholesteric phase,

introducing and sealing the material into the space between the walls,

cooling the material to the tilted chiral smectic phase, and

realigning the liquid crystal material with respect to said at least one treated wall surface.

30. The method of claim 29 wherein said step of realigning comprises the steps of reheating said liquid crystal material to above the smectic/cholesteric temperature and recooling to below the smectic/cholesteric transition temperature.

31. The method of claim 30 , wherein said recooling step includes the step of recooling whilst a unidirectional voltage pulse is applied.

32. A method of making a liquid crystal display device comprises the steps:

providing a tilted chiral smectic liquid crystal material having a cholesteric phase at an elevated temperature above ambient between the chiral smectic and isotropic phases with a cholesteric pitch p greater than half the layer thickness d at a temperature for at least 0 . 1 ° C. above a cholesteric to smectic transition temperature and a significant spontaneous polarization Ps in the chiral smectic phase,

heating the material to the cholesteric phase,

introducing and sealing the material into the space between the walls,

cooling the material to the tilted chiral smectic phase, wherein both walls are surface alignment treated and the cell is arranged with the alignment direction parallel in the same direction.

33. The method of claim 32 , wherein said step of surface alignment treating of said walls comprises providing surface alignment and surface tilt.

34. A method of making a liquid crystal display device comprises the steps:

providing a tilted chiral smectic liquid crystal material having a cholesteric phase at an elevated temperature above ambient between the chiral smectic and isotropic phases with a cholesteric pitch p greater than half the layer thickness d at a temperature for at least 0 . 1 ° C. above a cholesteric to smectic transition temperature and a significant spontaneous polarization Ps in the chiral smectic phase,

heating the material to the cholesteric phase,

introducing and sealing the material into the space between the walls,

cooling the material to the tilted chiral smectic phase, wherein both walls are surface alignment treated and the cell is arranged with the alignment direction parallel in opposite direction.

35. The method of claim 34 , wherein said step of surface alignment treating of said walls comprises providing surface alignment and surface tilt.

36. A liquid crystal device comprising a layer of a tilted chiral smectic liquid crystal material contained between two cell walls each carrying electrode structures and at least one wall surface treated to give alignment to the liquid crystal molecules, a first linear polarizer and one of a second polarizer and an amount of dichroic dye in the liquid crystal material, the liquid crystal material having switched states and a tilted chiral smectic phase at normal device operating temperatures and a cholesteric phase at a higher, above ambient, temperature, with a cholesteric pitch greater than half the layer thickness d in the cholesteric phase for at least 0 . 1 ° C. above the cholesteric to smectic transition temperature, and a spontaneous polarization, wherein the cell walls are surface treated to align liquid crystal molecules in the same direction with a splayed configuration across the layer thickness.

37. A liquid crystal device comprising a layer of a tilted chiral smectic liquid crystal material contained between two cell walls each carrying electrode structures and both wall surfaces treated to give parallel alignment and surface tilt to the liquid crystal molecules, a first linear polarizer and one of a second polarizer and an amount of dichroic dye in the liquid crystal material, the liquid crystal material having switched states and a tilted chiral smectic phase at normal device operating temperatures and a cholesteric phase at a higher, above ambient, temperature, with a cholesteric pitch greater than half the layer thickness d in the cholesteric phase for at least 0 . 1 ° C. above the cholesteric to smectic transition temperature, and a spontaneous polarization.

38. The device of claim 37 , wherein said surface tilt is about 2 °.

39. The device of claim 37 , wherein said liquid crystal material is comprised of a liquid crystal material having the following phases with temperature:

cholesteric⇄smectic A⇄chiral smectic.

40. The device of claim 38 , wherein said liquid crystal material is comprised of a liquid crystal material having the following phases with temperature:

cholesteric⇄smectic A⇄chiral smectic.

41. The device of claim 37 , wherein said wall surfaces are treated to give parallel alignment in the same direction.

42. The device of claim 37 , wherein said wall surfaces are treated to give parallel alignment in the opposite direction.

43. The device of claim 41 , wherein said wall surfaces are treated to provide a splayed configuration across the layer thickness.

44. A liquid crystal device comprising a layer of a tilted chiral smectic liquid crystal material contained between two cell walls each carrying electrode structures and at least one wall surface treated to give alignment to the liquid crystal molecules, a first linear polarizer and one of a second polarizer and an amount of dichroic dye in the liquid crystal material, the liquid crystal material having switched states and a tilted chiral smectic phase at normal device operating temperatures and a cholesteric phase at a higher, above ambient, temperature, with a cholesteric pitch greater than half the layer thickness d in the cholesteric phase for at least 0 . 1 ° C. above the cholesteric to smectic transition temperature, and a spontaneous polarization, said align liquid crystal material having substantially zero twist above the cholesteric to smectic transition temperature.

45. The device of claim 44 , wherein said zero twist is from the cholesteric to smectic transition temperature to a temperature at least 3 ° C. above the cholesteric to smectic transition temperature.

46. The device of claim 44 , wherein said zero twist is from the cholesteric to smectic transition temperature to a temperature at least 8 ° C. above the cholesteric to smectic transition temperature.

47. A liquid crystal device comprising a layer of a tilted chiral smectic liquid crystal material contained between two cell walls each carrying electrode structures and at least one wall surface treated to give alignment to the liquid crystal molecules, a first linear polarizer and one of a second polarizer and an amount of dichroic dye in the liquid crystal material, the liquid crystal material having switched states and a tilted chiral smectic phase at normal device operating temperatures and a cholesteric phase at a higher, above ambient, temperature, with a cholesteric pitch greater than half the layer thickness d in the cholesteric phase for at least 0 . 1 ° C. above the cholesteric to smectic transition temperature, and a spontaneous polarization, one polarizer is a neutral polarizer and a second polarizer is comprised of two differently colored polarizers arranged with their optical axis orthogonal with respect to each other.

48. The device of 11 , further including driver circuits connected to said electrodes.

49. A liquid crystal material mixture for use in a liquid crystal display device comprising a material having a tilted chiral smectic phase at normal device operating temperatures and a cholesteric phase at an elevated temperature, the mixture having a cholesteric pitch greater than 4 μm in the cholesteric phase at least 0 . 1 ° C. above a cholesteric to smectic transition temperature and a substantial spontaneous polarization coefficient Ps, in the smectic phase, wherein said mixture has substantially zero twist at a temperature above the cholesteric to smectic transition temperature in a liquid crystal cell.

50. The material of claim 49 wherein the material has the following phases with temperature:

isotropic⇄cholesteric⇄smectic A⇄chiral smectic⇄solid.

51. The material of claim 49 wherein the material has the following phases with temperature:

isotropic⇄cholesteric⇄chiral smectic⇄solid.

52. The material of claim 49 wherein the pitch in the cholesteric phase is greater than 4 μm over a temperature range up to 5 ° C. above the cholesteric smectic phase transition.

53. The material of claim 49 wherein the smectic pitch is greater than 2 μm.

54. The material of claim 49 wherein the spontaneous polarization is greater than 0 . 1 nC/cm 2 .

55. The material of claim 49 wherein the cholesteric/smectic phase transition temperature is above 40 ° C.

56. The material of claim 49 wherein the cholesteric/smectic phase transition temperature is above 100 ° C.

57. The material of claim 49 and further including an amount of a dichroic dye.

58. The material of claim 49 wherein said mixture has a zero twist from the cholesteric to smectic transition temperature to a temperature at least 3 ° C. above the cholesteric to smectic transition temperature.

59. The material of claim 49 wherein said mixture has a zero twist from the cholesteric to smectic transition temperature to a temperature at least 8 ° C. above the cholesteric to smectic transition temperature.

60. A method of making a liquid crystal display device in accordance with claim 1 , wherein said liquid crystal material has substantially zero twist at a temperature above the cholesteric to smectic transition temperature.

61. A method of making a liquid crystal display device in accordance with claim 9 , wherein said liquid crystal material has substantially zero twist at a temperature above the cholesteric to smectic transition temperature.

62. A method of making a liquid crystal display device comprises the steps:

providing a tilted chiral smectic liquid crystal material having a cholesteric phase at an elevated temperature above ambient between the chiral smectic and isotropic phases with a substantially zero twist cholesteric pitch p at a temperature for at least 0 . 1 ° C. above a cholesteric to smectic transition temperature and a significant spontaneous polarization Ps in the chiral smectic phase,

heating the material to the cholesteric phase,

introducing and sealing the material into the space between the walls,

cooling the material at a controlled rate from the cholesteric phase to the tilted chiral smectic phase, and

realigning the liquid crystal material with respect to said at least one treated wall surface.

63. The method of claim 62 wherein said step of realigning comprises the steps of reheating said liquid crystal material to above the smectic/cholesteric transition temperature and recooling to below the smectic/cholesteric transition temperature.

64. The method of claim 63 , wherein said recooling step includes the step of recooling whilst a unidirectional voltage pulse is applied.

65. The method of claim 62 wherein the material is cooled at a rate of less than 20 ° C./minute within +/− 5 ° C. of the cholesteric/smectic phase transition.

66. The method of claim 62 wherein the material is cooled at a rate of less than 2 ° C./minute within +/− 5 ° C. of the cholesteric/smectic phase transition.

67. The method of claim 62 wherein both walls are surface alignment treated and the cell is arranged with the alignment direction parallel in the same direction.

68. The method of claim 62 wherein both walls are surface alignment treated and the cell is arranged with the alignment direction parallel in opposite directions.

69. The method of claim 62 wherein the alignment is produced by the unidirectional rubbing.

70. The method of claim 62 wherein the alignment is produced by oblique evaporation of silicon oxide.

71. The method of claim 29 , wherein said step of realigning comprises the step of applying pulses of an alternating voltage to said liquid crystal material while in said smectic phase to give zero twist in said smectic phase.

72. The method of claim 29 , wherein said step of realigning comprises the steps of applying pulses of an alternating voltage to said liquid crystal material while in said smectic phase to give zero twist alignment in said smectic phase, reheating said liquid crystal material to above the smectic/cholesteric transition temperature and recooling to below the smectic/cholesteric transition temperature.

73. The method of claim 29 , wherein said step of realigning comprises the steps of applying pulses of an alternating voltage to said liquid crystal material while in said smectic phase to give zero twist alignment in said smectic phase, reheating said liquid crystal material to above the smectic/cholesteric transition temperature and recooling to below the smectic/cholesteric transition temperature while a unidirectional voltage pulse is applied.

74. The method of claim 2 , wherein said liquid crystal material has a smectic pitch greater than 0 . 1 μm in its smectic phase.

75. The method of claim 29 , wherein said liquid crystal material has a smectic pitch greater than 0 . 1 μm in its smectic phase.

76. The method of claim 2 , wherein said liquid crystal material has a smectic pitch greater than said layer thickness d in its smectic phase.

77. The method of claim 29 , wherein said liquid crystal material has a smectic pitch greater than said layer thickness d in its smectic phase.

78. The device of claim 9 , including means for heating the liquid crystal material to its cholesteric phase and for applying a unidirectional voltage to said material while said material cools to its tilted chiral smectic phase.

79. The device of claim 9 , wherein said liquid crystal material at a normal device operating temperature has a smectic pitch of greater than 0 . 1 μm.

80. The device of claim 9 , wherein said liquid crystal material at a normal device operating temperature has a smectic pitch of greater than said layer thickness d.

81. The method of claim 2 , wherein said material has zero twist at a temperature up to 14 ° C. above the cholesteric to smectic transition temperature.

82. The method of claim 29 , wherein both walls are surface treated to provide similar alignment in the same direction.

83. The method of claim 29 , wherein both walls are surface treated to provide similar alignment in different directions.

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