Liquid crystal display device having wide viewing angle and improved contrast ratio

• US 20020149733A1
• Filed: 04/01/2002
• Published: 10/17/2002
• Est. Priority Date: 05/29/1997
• Status: Active Grant

• Current Assignee: Samsung Display Company Limited (Samsung Electronics Co. Ltd.)
• Original Assignee: Hea-Ri Lee, Jae-Jin Lyu, Jian-Min Chen, Kyeong-Hyeon Kim
• Inventors: Lyu, Jae-Jin, Kim, Kyeong-Hyeon, Lee, Hea-Ri, Chen, Jian-Min
• Granted Patent: US 6,646,701 B2
• Time in Patent Office: Days
• US Class Current: 349/155
• CPC Class Codes: G02F 1/13363 Birefringent elements, e.g. for optical compensation
• CPC Class Codes: G02F 1/133634 the refractive index Nz perpendicular to the element surface being different from in-plane refractive indices Nx and Ny, e.g. biaxial or with normal optical axis
• CPC Class Codes: G02F 1/1337 Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
• CPC Class Codes: G02F 1/133742 for homeotropic alignment
• CPC Class Codes: G02F 1/13712 the liquid crystal having negative dielectric anisotropy
• CPC Class Codes: G02F 1/1393 the birefringence of the liquid crystal being electrically controlled, e.g. ECB-, DAP-, HAN-, PI-LC cells G02F1/1396, G02F1/141 take precedence
• 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

Abstract

A liquid crystal display comprises two parallel spaced substrates and a liquid crystal layer with negative dielectric anisotropy interposed between the substrates. The ratio d/p, the cell gap d between the substrates to the pitch p of the liquid crystal layer, is equal to or less than 0.3, and the retardation value Δn*d may be in the range of 0.25-0.4. In absence of electric field, the liquid crystal molecules are arranged vertically to the substrates, and when the sufficient electric field is applied, the liquid crystal molecules are parallel to the substrates and twisted by 90° from one substrate to the other.

To the outer surface of a liquid crystal cell having a liquid crystal material with a negative dielectric anisotropy, a combination of a-plate, c-plate or biaxial compensation films is attached. The direction having the largest refractive index of the a-plate or the biaxial film is parallel or perpendicular to the polarizing direction of adjacent polarizer. The difference between the summation of the retardation (n_x-n_z)*d of the a-plate, the c-plate and the biaxial films and the polarizers, and the retardation due to birefringence of the liquid crystal cell is equal to or less than 15% of the retardation due to birefringence of the liquid crystal cell. The retardation (n_x-n_z)*d of the a-plate or the biaxial film is 0-100 nm. n_x, n_y and n_z are the refractive indies of the x, y and z axes respectively when the z axis is perpendicular to the surface of the liquid crystal cell, the x axis is in the surface of the liquid crystal cell and having the largest refractive index of the a-plate or the biaxial film and the y axis is in same plane as the x axis and perpendicular to the x axis, and d is the thickness of the film.

Claims

1. A liquid crystal display comprising:

two spaced apart substrates, each substrate having an electrode; and

a liquid crystal layer with negative dielectric anisotropy which is interposed between the two substrates and homeotropically aligned;

wherein cell gap between the substrates divided by pitch of the liquid crystal layer is equal to or less than 0.3.

2. The liquid crystal display of claim 1, wherein the liquid crystal layer comprises a chiral nematic liquid crystal material.

3. The liquid crystal display of claim 1, wherein the liquid crystal layer comprises a nematic liquid crystal material including chiral dopant of 0.01-1.0 wt %.

4. The liquid crystal display of claim 1, further comprising two alignment layers which are formed on inner surfaces of the substrates respectively and align the liquid crystal layer homeotropically.

5. The liquid crystal display of claim 4, wherein the alignment layers are not rubbed.

6. The liquid crystal display of claim 4, wherein one of the alignment layers is rubbed.

7. The liquid crystal display of claim 4, wherein both the alignment layers are rubbed.

8. The liquid crystal display of claim 1, wherein the refractive anisotropy of the liquid crystal layer is in the range of 0.065-0.123.

9. The liquid crystal display of claim 8, wherein the cell gap between the substrates is in the range of 3.0-6.0 μ

m.

10. The liquid crystal display of claim 9, wherein the dielectric anisotropy multiplied by the cell gap is equal to or less than 0.4.

11. The liquid crystal display of claim 1, further comprising two polarizers which are attached to the outer surfaces of the substrates respectively and have polarizing directions perpendicular to each other.

13. The liquid crystal display of claim 12, wherein the difference between the summation of the retardation (n_xa1-n_za1)*d_a1 of the first a-plate compensation film, the retardation (n_xc1-n_zc1)*d_c1 of the first c-plate compensation film and the retardation of the first and the second polarizers, and the retardation due to birefringence of the liquid crystal cell is equal to or less than 15% of the retardation value due to birefringence of the liquid crystal cell,

where a z-axis is perpendicular to the first surface of the liquid crystal cell, an x-axis is the same direction as the direction having a largest refractive index in the first a-plate compensation film, n_xa1, n_za1, n_xc1 and n_zc1 are respectively the refractive indices along the x-axis and the z-axis of the first a-plate and of the first c-plate compensation films, and d_a1 and d_c1 are the thickness of the first a-plate and the first c-plate compensation films respectively.

14. The liquid crystal display of claim 13, wherein the retardation value (n_xa1-n_ya1)*d_a1 of the first a-plate compensation film is in the range of 0-100 nm,

where a y-axis is in the first surface of the liquid crystal cell and perpendicular to the x-axis, and n_ya1 is the refractive index of the first a-plate compensation film along the y-axis.

15. The liquid crystal display of claim 14, wherein the liquid crystal cell comprises:

a pair of transparent substrates;

homeotropic alignment layers which are formed on the substrates and divided into two regions whose buffing directions are different; and

a liquid crystal material with negative dielectric anisotropy interposed between the alignment layers.

16. The liquid crystal display of claim 15, wherein the buffing direction of the alignment layer adjacent to the first a-plate compensation film matches with the direction having the largest refractive index of the first a-plate compensation film.

17. The liquid crystal display of claim 12, further comprising a second c-plate compensation film attached to the second surface of the liquid crystal cell.

18. The liquid crystal display of claim 17, wherein the difference between the summation of the retardation (n_xa1-n_za1)*d_a1 of the first a-plate compensation film, the retardation (n_xc1-n_zc1)*d_c1 of the first c-plate compensation film, the retardation (n_xc2-n_zc2)*d_c2 of the second c-plate compensation film and the retardation of the first and the second polarizers, and the retardation due to birefringence of the liquid crystal cell is equal to or less than 15% of the retardation value due to birefringence of the liquid crystal cell,

where a z-axis is perpendicular to the first plane of the liquid crystal cell, a x-axis is the direction having a largest refractive index in the first a-plate compensation film, n_xa1, n_za1, n_xc1, n_zc1, n_xc2 and n_zc2 are respectively the refractive indices along the x-axis and the z-axis of the first a-plate, the first c-plate and the second c-plate compensation film, and d_a1, d_c1 and d_c1 are the thickness of the first a-plate, the first c-plate and the second c-plate compensation films respectively.

19. The liquid crystal display of claim 18, wherein the retardation value (n_xa1-n_ya1)*d_a1 of the first a-plate compensation film is in the range of 0-100 nm,

where a y-axis is in the first plane and perpendicular to the x-axis, n_ya1 is the refractive index of the first a-plate compensation film along the y-axis.

20. The liquid crystal display of claim 19, wherein the liquid crystal cell comprises:

a pair of transparent substrates;

homeotropic alignment layers which are formed on the substrates and divided into two regions whose buffing directions are different; and

a liquid crystal material with negative dielectric anisotropy interposed between the alignment layers.

21. The liquid crystal display of claim 20, wherein the buffing direction of the alignment layer adjacent to the first a-plate compensation film matches with the direction having the largest refractive index of the first a-plate compensation film.

22. The liquid crystal display of claim 17, further comprising a second c-plate compensation film attached to the second c-plate compensation film.

23. The liquid crystal display of claim 22, wherein the direction having a largest refractive index in the second a-plate compensation film is parallel or perpendicular to the polarizing direction of the second polarizer.

24. The liquid crystal display of claim 23, wherein the difference between the summation of the retardation (n_xa1-n_za1)*d_a1 of the first a-plate compensation film, the retardation (n_xa2-n_za2)*d_a2 of the second a-plate compensation film, the retardation (n_xc1-n_zc1)*d_c1 of the first c-plate compensation film, the retardation (n_xc2-n_zc2)*d_c2 of the second c-plate compensation film and the retardation of the first and second polarizers, and the retardation due to birefringence of the liquid crystal cell is equal to or less than 15% of the retardation value due to birefringence of the liquid crystal cell,

where a z-axis is perpendicular to the first plane of the liquid crystal cell, a x-axis is the direction having a largest refractive index in the first or the second a-plate compensation film, n_xa1, n_za1, n_xa2, n_za2, n_xc1, n_zc1, n_xc2 and n_zc2 are respectively the refractive indices along the x-axis and the z-axis of the first a-plate, the second a-plate, the first c-plate and the second c-plate compensation film, and d_a1, d_a2, d_c1 and d_c1 are the thickness of the first a-plate, the second a-plate, the first c-plate and the second c-plate compensation films respectively.

25. The liquid crystal display of claim 24, wherein the summation of the retardation value (n_xa1-n_ya1)*d_a1 of the first a-plate compensation film and the retardation value (n_xa2-n_ya2)*d_a2 of the second a-plate compensation film is in the range of 0-100 nm,

where a y-axis is in the first plane and perpendicular to the x-axis, n_ya1 and n_ya2 are the refractive indices of the first and the second a-plate compensation film along the y-axis.

26. The liquid crystal display of claim 25, wherein the liquid crystal cell comprises:

a pair of transparent substrates;

homeotropic alignment layers which are formed on the substrates and divided into two regions whose buffing directions are different; and

a liquid crystal material with negative dielectric anisotropy interposed between the alignment layers.

27. The liquid crystal display of claim 26, wherein the buffing directions of the alignment layers adjacent to the first and the second a-plate compensation films match with the directions having the largest refractive index of the first and the second a-plate compensation films.

29. The liquid crystal display of claim 28, wherein the difference between the summation of the retardation (n_xb1-n_zb1)*d_b1 of the first biaxial compensation film, the retardation (n_xc1-n_zc1)*d_c1 of the first c-plate compensation film and the retardation of the first and the second polarizers, and the retardation due to birefringence of the liquid crystal cell is equal to or less than 15% of the retardation value due to birefringence of the liquid crystal cell,

where a z-axis is perpendicular to the first plane of the liquid crystal cell, a x-axis is the same direction as the direction having a largest refractive index in the first biaxial compensation film, n_xb1, n_zb1, n_xc1 and n_zc1 are respectively the refractive indices along the x-axis and the z-axis of the first biaxial and the first c-plate compensation film, and d_b1 and d_c1 are the thickness of the first biaxial and the first c-plate compensation films respectively.

30. The liquid crystal display of claim 29, wherein the retardation value (n_xb1-n_yb1)*d_b1 of the first biaxial compensation film is in the range of 0-100 nm,

where a y-axis is in the first plane and perpendicular to the x-axis, n_yb1 is the refractive index of the first biaxial compensation film along the y-axis.

31. The liquid crystal display of claim 30, wherein the liquid crystal cell comprises:

a pair of transparent substrates;

homeotropic alignment layers which are formed on the substrates and divided into two regions whose buffing directions are different; and

a liquid crystal material with negative dielectric anisotropy interposed between the alignment layers.

32. The liquid crystal display of claim 31, wherein the buffing direction of the alignment layer adjacent to the first biaxial compensation film matches with the direction having the largest refractive index of the first biaxial compensation film.

33. The liquid crystal display of claim 28, further comprising a second c-plate compensation film attached to the second surface of the liquid crystal cell.

34. The liquid crystal display of claim 33, wherein the difference between the summation of the retardation (n_xb1-n_zb1)*d_b1 of the first biaxial compensation film, the retardation (n_xc1-n_zc1)*d_c1 of the first c-plate compensation film, the retardation (n_xc2-n_zc2)*d_c2 of the second c-plate compensation film and the retardation of the first and the second polarizers, and the retardation due to birefringence of the liquid crystal cell is equal to or less than 15% of the retardation value due to birefringence of the liquid crystal cell,

where a z-axis is perpendicular to the first plane of the liquid crystal cell, a x-axis is the direction having a largest refractive index in the first biaxial compensation film, n_xb1, n_zb1, n_xc1, n_zc1, n_xc2 and n_zc2 are respectively the refractive indices along the x-axis and the z-axis of the first biaxial, the first c-plate and the second c-plate compensation film, and d_b1, d_c1 and d_c1 are the thickness of the first biaxial, the first c-plate and the second c-plate compensation films respectively.

35. The liquid crystal display of claim 34, wherein the retardation value (n_xb1-n_yb1)*d_b1 of the first biaxial compensation film is in the range of 0-100 nm,

where a y-axis is in the first plane and perpendicular to the x-axis, n_yb1 is the refractive index of the first biaxial compensation film along the y-axis.

36. The liquid crystal display of claim 35, wherein the liquid crystal cell comprises:

a pair of transparent substrates;

homeotropic alignment layers formed on the substrates and divided into two regions whose buffing directions are different; and

a liquid crystal material with negative dielectric anisotropy interposed between the alignment layers.

37. The liquid crystal display of claim 36, wherein the buffing direction of the alignment layer adjacent to the first biaxial compensation film matches with the direction having the largest refractive index of the first biaxial compensation film.

38. The liquid crystal display of claim 28, further comprising a second biaxial compensation film attached to the second c-plate compensation film.

39. The liquid crystal display of claim 38, wherein the direction having a largest refractive index in the second biaxial compensation film is parallel or perpendicular to the polarizing direction of the second polarizer.

40. The liquid crystal display of claim 39, wherein the difference between the summation of the retardation (n_xb1-n_zb1)*d_b1 of the first biaxial compensation film, the retardation (n_xb2-n_zb2)*d_b2 of the second biaxial compensation film, the retardation (n_xc1-n_zc1)*d_c1 of the first c-plate compensation film, the retardation (n_xc2-n_zc2)*d_c2 of the second c-plate compensation film and the retardation of the first and the second polarizers, and the retardation due to birefringence of the liquid crystal cell is equal to or less than 15% of the retardation value due to birefringence of the liquid crystal cell,

where a z-axis is perpendicular to the first plane of the liquid crystal cell, a x-axis is the direction having a largest refractive index in the first or the second biaxial compensation film, n_xb1, n_zb1, n_xb2, n_zb2, n_xc1, n_zc1, n_xc2 and n_zc2 are respectively the refractive indices along the x-axis and the z-axis of the first biaxial, the second biaxial, the first c-plate and the second c-plate compensation film, and d_b1, d_b2, d_c1 and d_c1 are the thickness of the first biaxial, the second biaxial, the first c-plate and the second plate compensation films respectively.

41. The liquid crystal display of claim 40, wherein the summation of the retardation value (n_xb1-n_yb1)*d_b1 of the first biaxial compensation film and the retardation value (n_xb2-n_yb2)*d_b2 of the second biaxial compensation film is in the range of 0-100 nm,

where a y-axis is in the first plane and perpendicular to the x-axis, n_yb1, n_ybz are the refractive indices of the first biaxial and the second biaxial compensation films along the y-axis.

42. The liquid crystal display of claim 41, wherein the liquid crystal cell comprises:

a pair of transparent substrates;

homeotropic alignment layers formed on the substrates and divided into two regions whose buffing directions are different; and

a liquid crystal material with negative dielectric anisotropy interposed between the alignment layers.

43. The liquid crystal display of claim 42, wherein the buffing directions of the alignment layers adjacent to the first and the second biaxial compensation films match with the directions having the largest refractive index of the first and the second biaxial compensation films.

12. A liquid crystal display comprising:

a vertically aligned liquid crystal cell having a first and a second surfaces opposite each other and having a liquid crystal material with negative dielectric anisotropy;

a first and a second polarizers attached to the first and the second surfaces of the liquid crystal cell respectively; and

a first a-plate compensation film and a first c-plate compensation film disposed between the first surface of the liquid crystal cell and the first polarizer,

wherein a direction having a largest refractive index in the first a-plate compensation film is parallel or perpendicular to the polarizing direction of the first polarizer.

28. A liquid crystal display comprising:

a vertically aligned liquid crystal cell having a first surface and a second surface opposite each other and having a liquid crystal material with negative dielectric anisotropy;

a first and a second polarizers attached to the first and the second surfaces of the liquid crystal cell respectively; and

a first biaxial compensation film and a first c-plate compensation film disposed between the first surface of the liquid crystal cell and the first polarizer,

wherein a direction having a largest refractive index in the first biaxial compensation film is parallel or perpendicular to the polarizing direction of the first polarizer.

44. A liquid crystal display comprising:

a vertically aligned liquid crystal cell having a first and a second surfaces opposite each other and having a liquid crystal material with negative dielectric anisotropy;

a first and a second polarizers attached to the first and the second surfaces of the liquid crystal cell respectively;

a first biaxial compensation film disposed between the first surface of the liquid crystal cell and the first polarizer; and

wherein a direction having a largest refractive index in the first biaxial compensation film is parallel or perpendicular to the polarizing direction axis of the first polarizer.

45. The liquid crystal display of claim 44, wherein the difference between the summation of the retardation value of the first biaxial compensation film, (n_xb1-n_zb1)*d_b1 and the first and the second polarizers, and the retardation value due to birefringence of the liquid crystal cell is equal to or less than 15% of the retardation value due to birefringence of the liquid crystal cell,

where a z-axis is perpendicular to the first plane of the liquid crystal cell, a x-axis is the same direction as the direction having a largest refractive index in the first biaxial compensation film, n_xb1 and n_zb1 are respectively the refractive indices along the x-axis and the z-axis of the first biaxial compensation film, and d_b1 is the thickness of the first biaxial compensation film.

46. The liquid crystal display of claim 45, wherein the retardation value (n_xb1-n_yb1)*d_b1 of the first biaxial compensation film is in the range of 0-100 nm,

where a y-axis is in the first plane of the liquid crystal cell and perpendicular to the x-axis, n_yb1 is the refractive index of the first biaxial compensation film along the y-axis.

47. The liquid crystal display of claim 46, wherein the liquid crystal cell comprises:

a pair of transparent substrates;

homeotropic alignment layers which are formed on the substrates and divided into two regions whose buffing directions are different; and

a liquid crystal material with negative dielectric anisotropy interposed between the alignment layers.

48. The liquid crystal display of claim 47, wherein the buffing direction of the alignment layer adjacent to the first biaxial compensation film matches with the direction having the largest refractive index of the first biaxial compensation film.

49. The liquid crystal display of claim 44, further comprising a second biaxial compensation film attached to the second surface of the liquid crystal cell.

50. The liquid crystal display of claim 49, wherein the direction having a largest refractive index in the second biaxial compensation film is parallel or perpendicular to the polarizing direction of the second polarizer.

51. The liquid crystal display of claim 50, wherein the difference between the summation of the retardation value of the first biaxial compensation film, (n_xb1-n_zb1)*d_b1, the retardation value of the second biaxial compensation film, (n_xb2-n_zb2)*d_b2 and the first and the second polarizers, and the retardation value due to birefringence of the liquid crystal cell is equal to or less than 15% of the retardation value due to birefringence of the liquid crystal cell,

where a z-axis is perpendicular to the first plane of the liquid crystal cell, a x-axis is the direction having a largest refractive index in the first biaxial or the second biaxial compensation film, n_xb1, n_zb1, n_xb2 and n_zb2 are respectively the refractive indices along the x-axis and the z-axis of the first and the second biaxial compensation films, and d_b1 and d₂ are the thickness of the first and the second biaxial compensation films respectively.

52. The liquid crystal display of claim 51, wherein the summation of the retardation value (n_xb1-n_yb1)*d_b1 of the first biaxial compensation film and the retardation value (n_xb2-n_yb2)*d_b2 of the second biaxial compensation film is in the range of 0-100 nm ,

where a y-axis is in the first plane of the liquid crystal cell and perpendicular to the x-axis, n_yb1 and n_yb2 are the refractive indices of the first and the second biaxial compensation films along the y-axis.

53. The liquid crystal display of claim 52, wherein the liquid crystal cell comprises:

a pair of transparent substrates;

homeotropic alignment layers formed on the substrates and divided into two regions whose buffing directions are different; and

a liquid crystal material with negative dielectric anisotropy interposed between the alignment layers.

54. The liquid crystal display of claim 53, wherein the buffing directions of the alignment layers adjacent to the first and the second biaxial compensation films match with the directions having the largest refractive index of the first and the second biaxial compensation films.