Liquid crystal display device

• US 20050146659A1
• Filed: 01/05/2005
• Published: 07/07/2005
• Est. Priority Date: 01/05/2004
• Status: Active Grant

• Current Assignee: HannStar Display Corporation
• Original Assignee: NEC LCD Technologies Limited (NEC Corporation)
• Inventors: Sakamoto, Michiaki, Ishii, Toshiya
• Granted Patent: US 7,180,561 B2
• Time in Patent Office: Days
• US Class Current: 349/117
• CPC Class Codes: G02F 1/133638 Waveplates, i.e. plates with a retardation value of lambda/n
• 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 2413/14 Negative birefingence

Abstract

A liquid crystal display device includes a liquid crystal cell, first and second polarizers disposed outside the liquid crystal cell, first and second retardation plates arranged between the first and second polarizers, and the liquid crystal cell, and optical layers arranged between the first and second retardation plates and the liquid crystal cell. The first and second retardation plates have lagging axes perpendicular with each other. The first polarizer has an absorption axis inclining by about 45 degrees relative to the lagging axis of the first retardation plate, and inclining by about 90 degrees relative to an absorption axis of the second polarizer. The absorption axes of the first and second polarizers are angularly deviated such that characteristic of a viewing angle in the liquid crystal display device is rendered symmetric, relative to a symmetry axis about which liquid crystal is aligned in different directions.

Claims

1. A liquid crystal display device including:

(a) a liquid crystal cell comprised of a pair of substrates each having at least one electrode formed thereon, and a liquid crystal layer sandwiched between said substrates;

(b) a first polarizer arranged to face said liquid crystal cell;

(c) a second polarizer arranged to face said liquid crystal cell at the opposite side of said first polarizer;

(d) a first retardation plate arranged between said first polarizer and said liquid crystal cell;

(e) a second retardation plate arranged between said second polarizer and said liquid crystal cell; and

(f) an optical layer having negative uniaxial retardation and arranged at least one of between said first retardation plate and said liquid crystal cell, between said second retardation plate and said liquid crystal cell, between said first retardation plate and said first polarizer, and between said second retardation plate and said second polarizer,

wherein each of said first and second retardation plates has a lagging axis in a plane disposed in parallel with said substrates, and has retardation of almost λ

/4, lagging axes of said first and second retardation plates being perpendicular with each other,

said first polarizer has an absorption axis inclining by about 45 degrees relative to said lagging axis of said first retardation plate, and inclining by about 90 degrees relative to an absorption axis of said second polarizer,

said liquid crystal layer is composed of liquid crystal which has negative dielectric anisotropy and which is aligned vertically when no voltage is applied thereto, and aligned in four directions when a voltage is applied thereto, and

said absorption axes of said first and second polarizers are angularly deviated such that characteristic of a viewing angle in said liquid crystal display device is rendered symmetric, relative to a symmetry axis about which said liquid crystal in said liquid crystal layer is aligned in different directions.

2. The liquid crystal display device as set forth in claim 1, wherein an angle at which said absorption axes of said first and second polarizers are angularly deviated relative to said symmetry axis is determined to be an angle at which symmetry in said characteristic of a viewing angle in said liquid crystal display device is accomplished.

3. The liquid crystal display device as set forth in claim 1, wherein said liquid crystal cell has a first area in which a light passes therethrough and a second area in which a light is reflected, and said liquid crystal is aligned in four directions in each of said first and second areas.

4. The liquid crystal display device as set forth in claim 3, wherein said liquid crystal layer has retardation of 333±

20 nanometers in said first area, and 150±

20 nanometers in said second area.

5. The liquid crystal display device as set forth in claim 1, wherein said optical layer is arranged between said first retardation plate and said liquid crystal cell, between said first retardation plate and said first polarizer, and between said second retardation plate and said second polarizer.

6. The liquid crystal display device as set forth in claim 1, wherein said optical layer is arranged between said first retardation plate and said liquid crystal cell, between said second retardation plate and said liquid crystal cell, between said first retardation plate and said first polarizer, and between said second retardation plate and said second polarizer.

7. The liquid crystal display device as set forth in claim 6, wherein an optical layer arranged between said first retardation plate and said first polarizer has retardation of 25 nanometers in a thickness-wise direction thereof, an optical layer arranged between said second retardation plate and said second polarizer has retardation of 25 nanometers in a thickness-wise direction thereof, an optical layer arranged between said first retardation plate and said liquid crystal cell has retardation of 75 nanometers in a thickness-wise direction thereof, and an optical layer arranged between said second retardation plate and said liquid crystal cell has retardation of 75 nanometers in a thickness-wise direction thereof, and

an angle at which said absorption axes of said first and second polarizers are angularly deviated relative to said symmetry axis is determined to be 20 degrees.

8. The liquid crystal display device as set forth in claim 6, wherein an optical layer arranged between said first retardation plate and said first polarizer has retardation of 25 nanometers in a thickness-wise direction thereof, an optical layer arranged between said second retardation plate and said second polarizer has retardation of 25 nanometers in a thickness-wise direction thereof, an optical layer arranged between said first retardation plate and said liquid crystal cell has retardation of 100 nanometers in a thickness-wise direction thereof, and an optical layer arranged between said second retardation plate and said liquid crystal cell has retardation of 100 nanometers in a thickness-wise direction thereof, and

an angle at which said absorption axes of said first and second polarizers are angularly deviated relative to said symmetry axis is determined to be 5 degrees.

9. The liquid crystal display device as set forth in claim 5, wherein an optical layer arranged between said first retardation plate and said first polarizer is comprised of a support for supporting said first polarizer, and an optical layer arranged between said second retardation plate and said second polarizer is comprised of a support for supporting said second polarizer.

10. The liquid crystal display device as set forth in claim 6, wherein an optical layer arranged between said first retardation plate and said first polarizer is comprised of a support for supporting said first polarizer, and an optical layer arranged between said second retardation plate and said second polarizer is comprised of a support for supporting said second polarizer.

11. The liquid crystal display device as set forth in claim 1, wherein said electrode in at least one of said substrates is formed with a slit.

12. The liquid crystal display device as set forth in claim 11, wherein said slit defines a boundary about which said liquid crystal in said liquid crystal layer is aligned in different directions.

13. The liquid crystal display device as set forth in claim 1, wherein said electrode in at least one of said substrates is formed at a surface facing said liquid crystal layer with an electrically insulating projection defining a boundary about which said liquid crystal in said liquid crystal layer is aligned in different directions.

14. The liquid crystal display device as set forth in claim 1, wherein said electrode in at least one of said substrates is formed at a surface facing said liquid crystal layer with a slit, and an electrically insulating projection defining a boundary about which said liquid crystal in said liquid crystal layer is aligned in different directions is formed in said slit.