Liquid crystal display device

• US 20050275780A1
• Filed: 08/18/2004
• Published: 12/15/2005
• Est. Priority Date: 08/20/2003
• Status: Active Grant

• Current Assignee: Japan Display Central Incorporated (Japan Display Incorporated)
• Original Assignee: Toshiba Matsushita Display Technology (Japan Display Incorporated)
• Inventors: Hisatake, Yuzo
• Granted Patent: US 7,423,715 B2
• Time in Patent Office: Days
• US Class Current: 349/120
• CPC Class Codes: G02F 1/133632 with refractive index ellipsoid inclined relative to the LC-layer surface
• CPC Class Codes: G02F 1/136222 Colour filters incorporated in the active matrix substrate
• 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 2413/105 with varying inclination in thickness direction, e.g. hybrid oriented discotic LC

Abstract

A liquid crystal display device includes a liquid crystal panel having a structure in which a liquid crystal layer LQ is held between a pair of electrode substrates AR, CT, a pair of polarizers PL which hold the liquid crystal panel therebetween, and a pair of optical retardation plates RT arranged between the liquid crystal panel and the pair of polarizers PL. Each optical retardation plate RT has a refractive anisotropy in which average refractive indices nx, ny, and nz in an x-axis direction, a y-axis direction, and a z-axis direction being perpendicular to each other satisfy nx>ny>nz in a state when the z-axis direction conforms to the normal direction. The x-axis direction of each optical retardation plate RT is almost parallel to the transmission axis of the polarizer PL adjacent to a corresponding optical retardation plates RT.

Claims

1. A liquid crystal display device comprising:

a liquid crystal cell in which liquid crystal molecules are held between a pair of substrates that produce an electric field corresponding to a voltage applied thereto, set in an alignment substantially vertical to each substrate plane when the voltage is not applied to said substrates, and set in an alignment that directors of said molecules are tilted in a predetermined cross section when the voltage is applied to said substrates; and

an optical retardation plate arranged to face said liquid crystal cell;

wherein said optical retardation plate includes at least first and second regions stacked in a thickness direction to have negative retardation which presents an optical axis set in a direction substantially vertical to each substrate plane, and said first region includes a plurality of negative refraction members having optical axes which are tilted on a same side as that of said liquid crystal molecules in said predetermined cross section and whose tilt angles are set to have slight differences consecutively in the thickness direction.

4. The liquid crystal display device according to claim 1, wherein said optical retardation plate includes a negative biaxial retardation plate.

5. The liquid crystal display device according to claim 4, wherein said biaxial retardation plate has in-plane retardation which compensates for visual angle dependence of a pair of polarizers that hold said retardation plate and liquid crystal cell therebetween.

6. The liquid crystal display device according to claim 5, wherein said liquid crystal cell is divided into domains in which alignment directions of liquid crystal molecules make angles.

7. The liquid crystal display device according to claim 6, wherein said liquid crystal cell is divided into two domains.

8. The liquid crystal display device according to claim 6, wherein said liquid crystal cell is divided into four domains.

2. A liquid crystal display device comprising:

a liquid crystal cell in which liquid crystal molecules are held between a pair of substrates that produce an electric field corresponding to a voltage applied thereto, set in an alignment substantially vertical to each substrate plane when the voltage is not applied to said substrates, and set in an alignment that directors of said molecules are tilted in a predetermined cross section when the voltage is applied to said substrates; and

an optical retardation plate arranged to face said liquid crystal cell;

wherein said optical retardation plate includes first and second regions stacked in a thickness direction, said first region includes a plurality of negative refraction members having optical axes which are tilted on a same side as that of said liquid crystal molecules in said predetermined cross section and whose tilt angles are set to have slight differences consecutively in the thickness direction, and said second region includes a plurality of negative refraction members having optical axes which are tilted on an opposite side to that of said liquid crystal molecules in said predetermined cross section and whose tilt angles are set to have slight differences consecutively in the thickness direction.

10. The liquid crystal display device according to claim 2, wherein said optical retardation plate includes a negative biaxial retardation plate.

11. The liquid crystal display device according to claim 10, wherein said biaxial retardation plate has an in-plane retardation which compensates for visual angle dependence of a pair of polarizers that hold said retardation plate and liquid crystal cell therebetween.

12. The liquid crystal display device according to claim 11, wherein said liquid crystal cell is divided into domains in which alignment directions of the liquid crystal molecules make angles.

13. The liquid crystal display device according to claim 12, wherein said liquid crystal cell is divided into two domains.

14. The liquid crystal display device according to claim 12, wherein said liquid crystal cell is divided into four domains.

3. A liquid crystal display device comprising:

a liquid crystal cell in which liquid crystal molecules are held between a pair of substrates that produce an electric field corresponding to a voltage applied thereto; and

a pair of optical retardation plates arranged to hold said liquid crystal cell therebetween;

wherein each of said optical retardation plates includes first and second regions stacked in a thickness direction, said first region includes a plurality of negative refraction members having optical axes which are tilted on a predetermined side and whose tilt angles are set to have slight differences consecutively in the thickness direction, and said second region includes a plurality of negative refraction members having optical axes which are tilted on an opposite side to said predetermined side and whose tilt angles are set to have slight differences consecutively in the thickness direction.

9. The liquid crystal display device according to claim 3, wherein said pair of optical retardation plates are in a crossed Nicol, and a thickness t of each optical retardation plate satisfies relational expressions given by 30 nm≦

(nx−

ny)t≦

70 nm and 100 nm≦

(nx−

nz)t≦

140 nm, where nx, ny, and nz are average refractive indices in an x-axis direction, a y-axis direction, and a z-axis direction, respectively.

15. The liquid crystal display device according to claim 3, wherein said optical retardation plate includes a negative biaxial retardation plate.

16. The liquid crystal display device according to claim 15, wherein said biaxial retardation plate has in-plane retardation which compensates for visual angle dependence of a pair of polarizers that hold said retardation plate and liquid crystal cell therebetween.

17. The liquid crystal display device according to claim 16, wherein said liquid crystal cell is divided into domains in which alignment directions of the liquid crystal molecules make angles.

18. The liquid crystal display device according to claim 17, wherein said liquid crystal cell is divided into two domains.

19. The liquid crystal display device according to claim 17, wherein said liquid crystal cell is divided into four domains.

20. A liquid crystal display device comprising:

a liquid crystal cell in which liquid crystal molecules are held between a pair of substrates that produce an electric field corresponding to a voltage applied thereto, set in an alignment substantially vertical to each substrate plane when the voltage is not applied to said substrates, and set in an alignment that directors of said molecules are tilted in a predetermined cross section when the voltage is applied to said substrates; and

a pair of optical retardation plates arranged to hold said liquid crystal cell therebetween;

wherein each of said optical retardation plates includes first and second regions stacked in a thickness direction to have negative retardation that presents an optical axis set in a direction substantially vertical to each substrate plane, said first region includes a plurality of negative refraction members having optical axes which are tilted on a same side as that of said liquid crystal molecules in said predetermined cross section and whose tilt angles are set to have slight differences consecutively in the thickness direction, and said second region includes a plurality of negative refraction members having optical axes which are tilted on an opposite side as that of said liquid crystal molecules in said predetermined cross section and whose tilt angles are set to have slight differences consecutively in the thickness direction.