Liquid crystal display device

• US 20050264735A1
• Filed: 05/25/2005
• Published: 12/01/2005
• Est. Priority Date: 05/27/2004
• Status: Active Grant

• Current Assignee: Japan Display Central Incorporated (Japan Display Incorporated)
• Original Assignee: Toshiba Matsushita Display Technology (Japan Display Incorporated)
• Inventors: Hisatake, Yuzo, Murayama, Akio, Tago, Chigusa
• Granted Patent: US 7,397,525 B2
• Time in Patent Office: Days
• US Class Current: 349/119
• CPC Class Codes: G02F 1/133531 characterised by the arrangement of polariser or analyser axes
• CPC Class Codes: G02F 1/133541 Circular polarisers
• 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 1/133638 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 2413/04 Number of plates greater than or equal to 4
• CPC Class Codes: G02F 2413/08 with a particular optical axis orientation
• CPC Class Codes: G02F 2413/12 Biaxial compensators
• CPC Class Codes: G02F 2413/13 Positive birefingence

Abstract

A first phase plate and a third phase plate, which constitute a polarizer structure, cooperate to impart a phase difference of a ¼ wavelength to linearly polarized light that emerges from a first polarizer plate. A second phase plate and a fourth phase plate cooperate to impart a phase difference of a ¼ wavelength to linearly polarized light that emerges from a second polarizer plate. Slow axes in planes of the first phase plate and the second phase plate are substantially parallel. A crossed-axes angle between slow axes in planes of the first phase plate and the third phase plate is 60°, a crossed-axes angle between slow axes in planes of the second phase plate and the fourth phase plate is 60°, and a crossed-axes angle between slow axes in planes of the third phase plate and fourth phase plate is 60°.

Claims

1. A liquid crystal display device comprising:

a first polarizer plate that is disposed on one side of a liquid crystal cell in which a liquid crystal layer is sandwiched between two electrode-equipped substrates;

a second polarizer plate that is disposed on the other side of the liquid crystal cell;

a first phase plate that is disposed between the first polarizer plate and the liquid crystal cell;

a second phase plate that is disposed between the second polarizer plate and the liquid crystal cell;

a third phase plate that is disposed between the first polarizer plate and the first phase plate; and

a fourth phase plate that is disposed between the second polarizer plate and the second phase plate,

wherein the first phase plate and the third phase plate cooperate to impart a phase difference of a ¼

wavelength to linearly polarized light that emerges from the first polarizer plate, and the second phase plate and the fourth phase plate cooperate to impart a phase difference of a ¼

wavelength to linearly polarized light that emerges from the second polarizer plate,

slow axes in planes of the first phase plate and the second phase plate are substantially parallel, and

a slow axis of the first phase plate and the second phase plate, a slow axis of the third phase plate and a slow axis of the fourth phase plate are disposed in such directions as to cancel in-plane anisotropies.

2. The liquid crystal display device according to claim 1, wherein a crossed-axes angle between slow axes in planes of the first phase plate and the third phase plate is 60°

, a crossed-axes angle between slow axes in planes of the second phase plate and the fourth phase plate is 60°

, and a crossed-axes angle between slow axes in planes of the third phase plate and fourth phase plate is 60°

.

3. The liquid crystal display device according to claim 1, wherein crossed-axes angles of slow axes in planes of the first, second, third and fourth phase plates are set such that a characteristic value corresponding to contrast/viewing-angle characteristics is a reference value or more.

4. The liquid crystal display device according to claim 1, further comprising:

a variable retarder structure that includes the liquid crystal cell;

a polarizer structure that includes the first polarizer plate, the first phase plate and the third phase plate; and

an analyzer structure that includes the second polarizer plate, the second phase plate and the fourth phase plate,

wherein the polarizer structure and the analyzer structure are configured such that black display is effected in a state in which an in-plane phase difference of the variable retarder structure is substantially zero.

5. The liquid crystal display device according to claim 4, wherein the liquid crystal display device is a vertical-electric-field type electrically controlled birefringence mode liquid crystal display device that is provided with means for applying a voltage between the two electrode-equipped substrates.

6. The liquid crystal display device according to claim 5, wherein the liquid crystal layer is formed of a nematic liquid crystal composition, and liquid crystal molecules in the liquid crystal layer are aligned substantially vertical to a major surface of the substrate in a state in which no voltage is applied to the liquid crystal layer.

7. The liquid crystal display device according to claim 5, wherein the liquid crystal display device has a multi-domain structure in which liquid crystal molecules within a pixel are oriented at least in two directions, regardless of a state in which a predetermined voltage is applied or irrespective of an applied voltage.

8. The liquid crystal display device according to claim 7, wherein a protrusion for multi-domain control is provided within the pixel.

9. The liquid crystal display device according to claim 7, wherein a slit for multi-domain control is provided in the electrode.

10. The liquid crystal display device according to claim 7, wherein orientation films, which are subjected to an orientation process for multi-domain control, are provided on those surface of the two substrates, which sandwich the liquid crystal layer.

11. The liquid crystal display device according to claim 1, wherein the first phase plate and the third phase plate have the same characteristics of wavelength dispersion of phase difference, and the second phase plate and the fourth phase plate have the same characteristics of wavelength dispersion of phase difference.

12. The liquid crystal display device according to claim 11, wherein when an angle θ

p1 is formed between a transmission axis of the first polarizer plate and a reference axis, an angle θ

1 is formed between the slow axis of the first phase plate and the reference axis, and an angle θ

3 is formed between the slow axis of the third phase plate R3 and the reference axis, a relationship,

θ

1=θ

p1+2·

(θ

3−

θ

p1)±

π

/4, 0≦

θ

1≦

π

is established between θ

p1, θ

1 and θ

3, and

when an angle θ

p2 is formed between a transmission axis of the second polarizer plate and the reference axis, an angle θ

2 is formed between the slow axis of the second phase plate and the reference axis, and an angle θ

4 is formed between the slow axis of the fourth phase plate and the reference axis, a relationship,

θ

2=θ

p2+2·

(θ

4−

θ

p2)±

π

/4, 0≦

θ

2≦

π

is established between θ

p2, θ

2 and θ

4.