Reflection liquid crystal display device

• US 6,567,149 B1
• Filed: 10/13/2000
• Issued: 05/20/2003
• Est. Priority Date: 04/17/1998
• Status: Expired due to Fees

• Current Assignee: Toshiba Matsushita Display Technology (Japan Display Incorporated)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Ogawa, Tetsu, Sekime, Tomaoki, Yamaguchi, Hisanori, Iwai, Yoshio
• Primary Examiner(s): Kim, Robert H.
• Assistant Examiner(s): DI GRAZIO, JEANNE A
• Application Number:
  US09/673,310
• Time in Patent Office: 949 Days
• Field of Search: 349/180, 349/181
• US Class Current: 349/181
• CPC Class Codes: G02F 1/133531 characterised by the arrangement of polariser or analyser axes
• CPC Class Codes: G02F 1/13363 Birefringent elements, e.g. for optical compensation
• 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 1/1398 the twist being below 90°
• CPC Class Codes: G02F 2203/02 reflective

Abstract

A reflection liquid crystal display device comprising only one polarization film, wherein the twist angle of a nematic liquid crystal ranges from 0° to 90°, the relationship between the difference between the indices of birefringence Δn_LC, the thickness of the liquid crystal layer d_LC, and the retardation of the phase plate R_F is expressed by Δn_LC.d_LC=0.20 to 0.30 μm, R_F-Δn_LC.d_LC=−0.20 to −0.05 μm; Defining the direction in which a nematic liquid crystal is twisted toward a lower substrate when viewed from above an upper substrate as positive and letting the direction of the major axis of the liquid crystal molecule the nearest to one of the upper and lower substrates be represented by Φ_LC, the direction of the phase lagging axis of the phase plate be represented Φ_F, and the direction of the absorbing or transmitting axis of the polarization film be represented by Φ_P, the relationship between the directions is expressed by Φ_F-Φ_LC=−40° to −25°, Φ_P-Φ_F=+50° to +80° or Φ_F-Φ_LC=+65° to 105°, Φ_P-Φ_F=−60° to −90°. Therefore, bright white can be displayed and a nonchromatic high-contrast image can be also displayed.

Claims

1. A reflective liquid crystal display device comprising:

a liquid crystal cell wherein nematic liquid crystal is sealed in between a pair of substrates;

a polarization film located on one of the substrates of said liquid crystal cell;

a phase plate located between said polarization film and said liquid crystal cell; and

optical reflection means located on the side of the other substrate;

wherein

the twist angle of the nematic liquid crystal between said pair of substrates is in the range of 0°

to 90°

;

the product Δ

n_LC d_LC of the index of birefringence Δ

n_LC of said nematic liquid crystal and the thickness d_LC of the liquid crystal layer is in the range of 0.20 to 0.30 micrometers;

the relations of the direction of the major axis Φ

_LC of the liquid crystal molecule closest to said one of the substrates, the direction Φ

_F of the phase lagging axis of said phase plate, and the direction Φ

_P of the absorption axis or transmission axis of said polarization film are such that Φ

_F-Φ

_LC is in the range of −

40°

to −

25°

, Φ

_P-Φ

_F is in the range of −

50°

to +80°

, or Φ

_F-Φ

_LC is in the range of +65°

to +105°

, Φ

_P-Φ

_F is in the range of −

60°

to −

90°

; and

the difference of indices of birefringence Δ

R as defined by R_F-Δ

n_LC d_LC using said product Δ

n_LC d_LC and retardation R_F of said phase plate is in the range of −

0.20 micrometers to −

0.05 micrometers.

2. The reflective liquid crystal display device of claim 1, wherein said twist angle of said nematic liquid crystal is in the range of 30°

to 65°

.

3. The reflective liquid crystal display device of claim 1, wherein said R_F is in the range of 0.10 micrometers to 0.30 micrometers.

4. The reflective liquid crystal display device of claim 1, wherein said phase plate is made of at least one selected from the group consisting of polycarbonate, polyarylate, and polysulfone.

5. The reflective liquid crystal display device of claim 1, wherein Z-coefficient Qz of said phase plate is in the range 1.0 to 3.0, said Qz being a coefficient defined by Qz=(nx−

nz)/(nx−

ny) where nx (refractive index in the direction of slow axis), ny (refractive index in the direction of fast axis) and nz are refractive indices in the respective axial directions in a spatial coordinate system (x, y, z) with the normal to the plane of the plate being defined as z-axis.

6. The reflective liquid crystal display device of claim 5, wherein said Qz is in the range of 1.0 to 2.0.

7. The reflective liquid crystal display device of claim 1, wherein a scattering film is located on said one of the substrates.

8. The reflective liquid crystal display device of claim 7, wherein said scattering film is located between said phase plate and said one of the substrates.

9. The reflective liquid crystal display device of claim 7, wherein said scattering film is a front scattering film.

10. The reflective liquid crystal display device of claim 1, wherein said optical reflection means is a metal electrode including at least one metal selected from the group consisting of aluminum and silver as a component.

11. The reflective liquid crystal display device of claim 10, wherein a surface of said metal electrode is specular.

12. The reflective liquid crystal display device of claim 10, wherein a scattering film is located on said metal electrode.

13. The reflective liquid crystal display device of claim 10, wherein a surface of said metal electrode has projections and depressions with an average angle of inclination in the range of 3°

to 12° and

causes diffuse reflection of incident light.

14. The reflective liquid crystal display device of claim 1, wherein said the other of the substrates is a transparent substrate on the outer side of which optical reflection means is located.

15. The reflective liquid crystal display device of claim 14, wherein a layer of air intervenes between said transparent substrate and said optical reflection means.

16. The reflective liquid crystal display device of claim 1, wherein a color filter is located on the side of said one of the substrates.

17. The reflective liquid crystal display device of claim 1, wherein a nonlinear switching device is located on the side of said the other of the substrates.

18. The reflective liquid crystal display device of claim 17, wherein an insulating flattening film is formed on top of said nonlinear switching device, and said nonlinear switching device and an electrode on said the other of the substrates are electrically continuous through a contact hole formed on the flattening film.