Reflection mode liquid crystal display devices having a parallel electric field and .alpha..sub.0 which is .ltoreq. 30.degree.

• US 5,841,499 A
• Filed: 04/04/1996
• Issued: 11/24/1998
• Est. Priority Date: 01/09/1990
• Status: Expired due to Term

• Current Assignee: Merck Patent GmbH (Merck & Co., Inc.)
• Original Assignee: Merck Patent GmbH (Merck & Co., Inc.)
• Inventors: Windscheid, Friedrich, Kiefer, Rudolf, Fehrenbach, Waltraud, Ne Staudacher, Barbara W., Baur, Gunter
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Parker, Kenneth
• Application Number:
  US08/627,388
• Time in Patent Office: 964 Days
• Field of Search: 349/68, 349/67, 349/87, 349/123, 349/19, 349/138, 349/39, 349/42, 349/136, 349/141
• US Class Current: 349/141
• CPC Class Codes: G02F 1/134363 for applying an electric field parallel to the substrate, i.e. in-plane switching [IPS]
• CPC Class Codes: G02F 1/1396 the liquid crystal being selectively controlled between a twisted state and a non-twisted state, e.g. TN-LC cell G02F1/141 takes precedence
• CPC Class Codes: G02F 2201/124 interdigital

Abstract

An electro-optical display device comprising a liquid crystal layer achieves switching using an electric field component which is predominantly parallel to the surface of the liquid crystal layer. Low dependence of image contrast on viewing angle is achieved by selection of parameters including pretilt angle α₀, orientation angle β₀, etc. of the liquid crystal molecules in the layer. Reflection mode devices are described.

Claims

1. An electro-optical display device comprising a plurality of liquid crystal ,switching elements which comprise a liquid crystal layer comprising liquid crystal molecules and having a surface for display of an image which is switched under control of an electric field having a component predominantly parallel to said surface, and, sandwiching said liquid crystal layer, a polarizer/analyzer and a reflector, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o <

30°

, wherein said liquid crystal switching elements further comprise;

(a) said liquid crystal molecules which are twistable;

(b) a substrate; and

(c) an electrode structure which generates said electric field having a component predominantly parallel to the surface of said liquid crystal layer, and

wherein said electrode structure is arranged alternately in at least two different planes in parallel with said substrate.

2. The electro-optical display device of claim 1, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

25°

.

3. The electro-optical display device of claim 1, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

20°

.

4. The electro-optical display device of claim 1, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

10°

.

5. The electro-optical display device of claim 1, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

5°

.

6. An electro-optical display device of claim 1, wherein said liquid crystal molecules have an orientation angle β

_o, 0°

<

β

_o <

90°

.

7. The electro-optical display device of claim 1, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

3°

.

8. The electro-optical display device of claim 1, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

2°

.

9. The electro-optical display device of claim 1, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

1°

.

10. The electro-optical display device of claim 1, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

20°

.

11. The electro-optical display device of claim 1, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

10°

.

12. The electro-optical display device of claim 1, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

5°

.

13. The electro-optical display device of claim 1, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

2°

.

14. The electro-optical display device of claim 1, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

1°

.

15. The electro-optical display device of claim 1, wherein said liquid crystal molecules have a pretilt angle α

_o which is about 5°

.

16. The electro-optical display device of claim 1, wherein said liquid crystal molecules have a pretilt angle α

_o which is about 1°

.

17. The electro-optical display device of claim 1, wherein said liquid crystal molecules have a pretilt angle α

_o which is about 0°

.

18. An electro-optical display device of claim 1, wherein said liquid crystal molecules have an orientation angle β

_o, 0°

<

β

_o <

90°

.

19. An electro-optical display device of claim 18, wherein β

_o is not 45°

.

20. The electro-optical display device of claim 19, wherein β

_o is not about 40° and

not about 50°

.

21. The electro-optical display device of claim 1, further comprising:

(d) a voltage source or a current source connected to said electrode structure.

22. The electro-optical display device of claim 1, further comprising:

(d) a voltage source connected to said electrode structure.

23. The electro-optical display device of claim 22, further comprising:

(e) an orientation layer, in contact with at least one surface of said liquid crystal layer, which aligns the liquid crystal molecules in a direction whereby they have an orientation angle β

_o, 0°

<

β

_o <

90°

.

24. The electro-optical display device of claim 23, comprising an orientation layer, in contact with at least one surface of said liquid crystal layer, which aligns the liquid crystal molecules in a direction whereby they have said pretilt angle α

_o, 0°

≦

α

_o <

30°

.

25. The electro-optical display device of claim 23, wherein the reflector is an electrically insulating mirror.

26. The electro-optical display device of claim 1, wherein said liquid crystal layer is nematic.

27. The electro-optical display device of claim 1, wherein the axes of switching-effective twisting of the liquid crystal molecules are substantially perpendicular to the plane of the substrate.

28. The electro-optical display device of claim 1, wherein, within the image spot of the liquid crystal switching element, said electrode structure is formed between the substrate and the liquid crystal layer and has at least one pair of electrodes with a space therebetween.

29. The electro-optical display device of claim 28, wherein each pair of electrodes comprises strip- or line-type electrodes which extend to make a space between said pair of electrodes.

30. The electro-optical display device of claim 29, wherein the electrodes intermesh in comb fashion.

31. The electro-optical display device of claim 28, wherein the space between the pair of electrodes is 2 μ

m to 50 μ

m.

32. The electro-optical display device of claim 28, wherein the applied voltage between the pair of electrodes is one volt to 80 volts.

33. The electro-optical display device of claim 1, wherein the thickness of the liquid crystal layer is 1 μ

m to 10 μ

m.

34. The electro-optical display device of claim 1, wherein the area of the image spots of the liquid crystal switching elements is 10 μ

m² to 1 mm².

35. The electro-optical display device of claim 1, wherein the plurality of liquid crystal switching elements are arranged in the form of a matrix.

36. The electro-optical display device of claim 35, wherein said matrix is an active matrix.

37. The electro-optical display device of claim 36, wherein the active matrix is a transistor matrix.

38. The electro-optical display device of claim 1, wherein the plurality of liquid crystal switching elements are addressed by the time multiplex method.

39. The electro-optical display device of claim 38, wherein the switching elements are used to alter the brightness and/or color of a pixel of the electro-optical display device.

40. The electro-optical display device of claim 1, wherein the electrode structure is located between one substrate and the liquid crystal layer.

41. The electro-optical display device of claim 40, wherein said at least two planes are located between the liquid-crystal layer and a substrate.

42. The electro-optical display device of claim 41, wherein said two planes of the alternating electrodes are formed by the two opposite surfaces of a thin layer.

43. The electro-optical display device of claim 42, wherein said thin layer is an insulating film.

44. The electro-optical display device of claim 1, wherein the liquid-crystal switching elements constitute an multiplicity of pixels.

45. The electro-optical display device of claim 1, wherein the liquid crystal layer contains a dichroic dye.

46. The electro-optical display device of claim 1 further comprising a current or voltage source.

47. The electro-optical display device of claim 1 further comprising a voltage source.

48. The electro-optical display device of claim 1 which is driven by a matrix of active switching elements.

49. The electro-optical display device of claim 48, wherein the switching elements of the active matrix are thin-film transistors.

50. The electro-optical display device of claim 1 wherein the switching elements are provided with optical compensation.

51. The electro-optical display device of claim 1, wherein the switching elements comprise a birefringent optical compensator in optical correlation with the liquid-crystal layer.

52. The electro-optical display device of claim 1 which is driven by a direct triggering device.

53. The electro-optical display device of claim 1 which is directly driven according to the time multiplex method.

54. An electro-optical display device comprising a plurality of liquid crystal switching elements which comprise a liquid crystal layer comprising liquid crystal molecules and having a surface for display of an image which is switched under control of an electric field having a component predominantly parallel to said surface, and, sandwiching said liquid crystal layer, a polarizer/analyzer and a reflector, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o <

30° and

wherein said liquid crystal switching elements further comprise;

(a) said liquid crystal molecules which are twistable;

(b) a substrate; and

(c) an electrode structure which generates said electric field having a component predominantly parallel to the surface of said liquid crystal layer,

wherein the initial twist angle β

of the liquid crystal molecules is within 15 degrees of 0°

, or within 5 degrees of 60°

.

55. The electro-optical display device of claims 54, wherein Δ

n·

d/λ

of the liquid crystal layer is larger than zero but smaller than two.

56. The electro-optical display device of claim 54, wherein the electrode structure is located in one plane.

57. The electro-optical display device of claim 54, wherein the reflector is an electrically insulating mirror.

58. An electro-optical display device comprising a plurality of liquid crystal switching elements which comprise a liquid crystal layer comprising liquid crystal molecules and having a surface for display of an image which is switched under control of an electric field having a component predominantly parallel to said surface, and sandwiching said liquid crystal layer, a polarizer/analyzer and a reflector wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

30° and

wherein the reflector is an electrically mirror.

59. An electro-optical display device of claim 58, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o <

20°

.

60. An electro-optical display device comprising a plurality of liquid crystal switching elements which comprise a liquid crystal layer comprising liquid crystal molecules and having a surface for display of an image which is switched under control of an electric field having a component predominantly parallel to said surface, and, sandwiching said liquid crystal layer, a polarizer/analyzer and a reflector, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o <

30°

, wherein said liquid crystal layer comprises a polymer.

61. An electro-optical display device comprising a liquid crystal layer comprising liquid crystal molecules and having a surface for display of an image which is switched under control of an electric field having a component predominantly parallel to said surface, and, sandwiching said liquid crystal layer, a polarizer/analyzer and a reflector, wherein said liquid crystal molecules are in homogeneous alignment and have a pretilt angle α

_o and an orientation angle β

_o which prevent domain formation in said image and/or which impart to said image a small viewing angle dependence and a correspondingly improved image contrast.

62. A method of viewing the image of an electro-optical display device from different viewing angles in the range ⊖

=10°

-60° and

observing a small dependence of image contrast on viewing angle in said range, comprising viewing at different angles ⊖

in said range the image of the electro-optical display device of claim 61.

63. An electro-optical display device comprising a liquid crystal layer comprising liquid crystal molecules and having a surface for display of an image which is switched under control of an electric field having a component predominantly parallel to said surface, and, sandwiching said liquid crystal layer, a polarizer/analyzer and a reflector, wherein said liquid crystal molecules are in homogeneous alignment and have a pretilt angle α

_o and an orientation angle β

_o which reduce domain formation in said image and/or which impart to said image a small viewing angle dependence and a correspondingly improved image contrast.

64. An electro-optical display device of claim 63, wherein said α

_o and β

_o values impart to said image a small dependence of transmission on viewing angle which when graphed as a curve according to FIG. 8 at a given observation angle is more symmetric about the graph'"'"'s center point than the corresponding curve of FIG. 8.

65. The electro-optical display device of claim 64, wherein said liquid crystal layer has a negative dielectric anisotropy and 0°

<

β

_o ≦

20°

.

66. The electro-optical display device of claim 64, wherein said liquid crystal layer has a positive dielectric anisotropy and 70°

≦

β

_o <

90°

.

67. A method of viewing the image of an electro-optical display device from different viewing angles in the range ⊖

=10°

-60° and

observing a small dependence of image contrast on viewing angle in said range, comprising viewing at different angles ⊖

in said range the image of the electro-optical display device of claim 64.

68. An electro-optical display device of claim 63, wherein said α

_o and β

_o values impart to said image a small dependence of transmission on viewing angle which when graphed as a curve according to FIG. 7 at a given observation angle has a degree of symmetry about the graph'"'"'s center point closer to that of the corresponding curve of FIG. 7 than of FIG. 8.

69. An electro-optical display device of claim 63, wherein said α

_o and β

_o values impart to said image a small viewing angle dependence wherein the variation of the degree of light transmission (1-fmin/fmax) is, over all φ

values, below about 0.57 when ⊖

is up to 45°

.

70. A method of viewing the image of an electro-optical display device from different viewing angles in the range ⊖

=10°

-60° and

observing a small dependence of image contrast on viewing angle in said range, comprising viewing at different angles ⊖

in said range the image of the electro-optical display device of claim 63.

71. An electro-optical display device comprising a liquid crystal layer comprising liquid crystal molecules and having a surface for display of an image which is switched under control of an electric field having a component predominantly parallel to said surface, and, sandwiching said liquid crystal layer, a polarizer/analyzer and a reflector, wherein said liquid crystal molecules are in homogeneous alignment and said device has an initial state configuration in the absence of electric field which during operation suppresses domain formation in said image and/or which imparts to said image a small viewing angle dependence and a correspondingly improved image contrast.

72. A liquid crystal switching element comprising a liquid crystal layer comprising liquid crystal molecules and having a surface for display of an image which is switched under control of an electric field having a component predominantly parallel to said surface and, sandwiching said liquid crystal layer, a polarizer/analyzer and a reflector, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

<

30°

, wherein said liquid crystal switching element further comprises;

(a) said liquid crystal molecules which are twistable;

(b) a substrate; and

(c) an electrode structure which generates said electric field having a component predominantly parallel to the surface of said liquid crystal layer, and

wherein said electrode structure is arranged alternately in at least two different planes in parallel with said substrate.

73. A method of viewing the image of an electro-optical display device from different viewing angles in the range ⊖

=10-60° and

observing a small dependence of image contrast on viewing angle in said range, comprising viewing at different angles ⊖

in said range the image of an electrooptical display device comprising a plurality of liquid crystal switching elements which comprise a liquid crystal layer comprising liquid crystal molecules and having a surface for display of an image which is switched under control of an electric field having a component predominantly parallel to said surface, and, sandwiching said liquid crystal layer, a polarizer/analyzer and a reflector, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o <

30°

.

74. The method of claim 73, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

25°

.

75. The method of claim 73, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

20°

.

76. The method of claim 73, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

10°

.

77. The method of claim 73, wherein said liquid crystal molecules have a pretilt α

_o, 0°

≦

α

_o ≦

5°

.

78. The method of claim 77, wherein said liquid crystal molecules have an orientation angle β

_o, 0°

<

β

_o <

90°

.

79. The method of claim 73, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

3°

.

80. The method of claim 73, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

2°

.

81. The method of claim 73, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

1°

.

82. The method of claim 73, were said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

20°

.

83. The method of claim 73, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

10°

.

84. The method of claim 73, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

5°

.

85. The method of claim 73, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

2°

.

86. The method of claim 73, wherein said liquid crystal molecules have a pretilt angle α

_o, 0°

≦

α

_o ≦

1°

.

87. The method of claim 73, wherein said liquid crystal molecules have a pretilt angle α

_o which is about 5°

.

88. The method of claim 73, wherein said liquid crystal molecules have a pretilt angle α

_o which is about 1°

.

89. The method of claim 73, wherein said liquid crystal molecules have a pretilt angle α

_o which is about 0°

.

90. The method of claim 73, wherein said liquid crystal molecules have an orientation angle β

_o, 0°

<

β

_o <

90°

.