Back lit cholesteric liquid crystal display

• US 7,009,666 B2
• Filed: 09/24/2001
• Issued: 03/07/2006
• Est. Priority Date: 08/23/1999
• Status: Expired due to Term

• Current Assignee: Kent Displays Incorporated
• Original Assignee: Kent Displays Incorporated
• Inventors: Khan, Asad A., Stefanov, Michael E., Catchpole, Clive
• Primary Examiner(s): Pham, Long
• Assistant Examiner(s): Rao, Shrinivas H.
• Application Number:
  US09/961,441
• Publication Number:
  US 20020030776A1
• Time in Patent Office: 1,625 Days
• Field of Search: 349/96, 349/68, 250/225, 438/30
• US Class Current: 349/96
• CPC Class Codes: G02F 1/133528 Polarisers
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/133541 Circular polarisers
• CPC Class Codes: G02F 1/133555 Transflectors
• CPC Class Codes: G02F 1/133723 Polyimide, polyamide-imide
• CPC Class Codes: G02F 1/133738 for homogeneous alignment
• CPC Class Codes: G02F 1/133757 with different alignment orientations
• CPC Class Codes: G02F 1/13718 based on a change of the texture state of a cholesteric liquid crystal

Abstract

A reflective cholesteric display that may be viewed under a wide range of ambient lighting conditions, ranging from complete darkness to bright sunlight. The display includes a chiral nematic liquid crystal material located between first and second substrates, an ambidextrous or bi-directional circular polarizer, a partial mirror, also referred to as a transflector, and a light source. The liquid crystal material includes focal conic and planar textures that are stable in the absence of an electric field. The ambidextrous circular polarizer is located adjacent to one of the substrates that constrain the liquid crystal material. The chiral nematic liquid crystal display may be operated in both a transmissive mode and a reflective mode.

Claims

1. A bistable, backlit cholesteric liquid crystal display, comprising:

a) a layer of cholesteric liquid crystal material located between first and second substrates, said cholesteric liquid crystal material including focal conic and reflective planar textures that are stable in an absence of an electric field, said second substrate being closer to an exterior of the display than said first substrate;

b) drive electronics adapted to electrically address regions of the cholesteric liquid crystal material effective to cause said cholesteric liquid crystal material to exhibit the focal conic and planar textures resulting in an image;

c) a bi-directional circular polarizer having opposing sides, wherein said bi-directional circular polarizer circularly polarizes light incident from either of said opposing sides including passing circularly polarized light to said layer of cholesteric liquid crystal material;

d) a transflector having a light reflective side and a light transmitting side, the light reflective side being adapted to reflect light received from said bi-directional circular polarizer, said bi-directional circular polarizer being located between said transflector and said first substrate; and

e) a light source adapted to be selectively energizable to emit light, said light passing through said transflector from said light transmitting side toward said light reflecting side.

2. The liquid crystal display of claim 1 wherein said planar texture has a circular polarization of a predetermined handedness.

3. The liquid crystal display of claim 1 wherein said bi-directional circular polarizer comprises a first quarter wave retarder and a second quarter wave retarder and a linear polarizer located between said first quarter wave retarder and said second quarter wave retarder.

4. The liquid crystal display of claim 1 further comprising an alignment material on at least one of said first and second substrates.

5. The liquid crystal display of claim 4 wherein said alignment material provides a liquid crystal director of said cholesteric liquid crystal material with a pretilt angle of about 21°

from the substrate.

6. The liquid crystal display of claim 4 wherein said alignment material is adapted to orient molecules of said cholesteric liquid crystal material effective to enable light reflected from said display to have an S3 stokes parameter greater than 0.75.

7. The liquid crystal display of claim 4 wherein said alignment material is adapted to orient molecules of said cholesteric liquid crystal material effective to enable light reflected from said display to have an S3 stokes parameter greater than 0.90.

8. The liquid crystal display of claim 1 further comprising a rubbed alignment material on both of said first and second substrates.

9. The liquid crystal display of claim 1 further comprising a rubbed alignment material on said first substrate.

10. The liquid crystal display of claim 1 wherein said light source has a spectral distribution that matches a reflection spectrum of the display.

11. A bistable, backlit cholesteric liquid crystal display, comprising:

a) a cholesteric liquid crystal material located between first and second substrates, said cholesteric liquid crystal material including a planar texture having a circular polarization of a predetermined handedness and a focal conic texture that are stable in an absence of an electric field, said second substrate being closer to an exterior of the display than said first substrate;

b) drive electronics adapted to electrically address regions of the cholesteric liquid crystal material effective to cause said cholesteric liquid crystal material to exhibit the focal conic and planar textures resulting in an image;

c) a first quarter wave retarder;

d) a second quarter wave retarder;

e) a linear polarizer located between said first quarter waver retarder and said second quarter wave retarder;

f) a transflector having a light reflective side and a light transmitting side, the light reflective side being adapted to reflect light received from said second quarter wave retarder, wherein said first quarter wave retarder, said linear polarizer and said second quarter wave retarder are located between said transflector and said first substrate; and

g) a light source adapted to be selectively energizable to emit light, said light passing through said transflector from said light transmitting side toward said light reflecting side.

12. The liquid crystal display of claim 11 wherein said light source is adapted to have a spectral distribution that matches a reflection spectrum of the display.

13. The liquid crystal display of claim 11 further comprising an alignment material on at least one of said first and second substrates.

14. The liquid crystal display of claim 13 wherein said alignment material provides a liquid crystal director of said cholesteric liquid crystal material with a pretilt angle of about 21°

from the substrate.

15. The liquid crystal display of claim 13 wherein said alignment material is adapted to orient molecules of said cholesteric liquid crystal material effective to enable light reflected from said display to have an S3 stokes parameter greater than 0.75.

16. The liquid crystal display of claim 13 wherein said alignment material is adapted to orient molecules of said cholesteric liquid crystal material effective to enable light reflected from said display to have an S3 stokes parameter greater than 0.90.

17. The liquid crystal display of claim 11 further comprising a rubbed alignment material on both of said first and second substrates.

18. A bistable, backlit cholesteric liquid crystal display, comprising:

a) a cholesteric liquid crystal material located between first and second substrates, said cholesteric liquid crystal material including focal conic and reflective planar textures that are stable in an absence of an electric field, an alignment material on at least one of said first and second substrates, said alignment material being adapted to orient molecules of said cholesteric liquid crystal material effective to enable light reflected from said display to have an S3 stokes parameter greater than 0.75, said second substrate being closer to an exterior of the display than said first substrate;

b) drive electronics adapted to electrically address regions of the cholesteric liquid crystal material effective to cause said cholesteric liquid crystal material to exhibit the focal conic and planar textures resulting in an image;

c) a bi-directional circular polarizer having opposing sides, wherein said bi-directional circular polarizer is adapted to circularly polarize light incident from either of said opposing sides including passing circularly polarized light to said layer of cholesteric liquid crystal material;

d) a transflector having a light reflective side and a light transmitting side, the light reflective side being adapted to reflect light received from said bi-directional circular polarizer, said bi-directional circular polarizer being located between said transflector and said first substrate; and

e) a light source adapted to be selectively energizable to emit light, said light passing through said transflector from said light transmitting side toward said light reflecting side.

19. A bistable, backlit cholesteric liquid crystal display device, comprising:

a layer of cholesteric liquid crystal material including focal conic and reflective planar textures that are stable in an absence of an electric field, said layer having a first side and a second side, the second side being closer to an exterior of the display device than said first side;

means for selectively addressing regions of the cholesteric liquid crystal material effective to cause said cholesteric liquid crystal material to exhibit the focal conic and reflective planar textures resulting in an image;

a bi-directional circular polarizer comprising a first quarter wave retarder, a second quarter wave retarder and a linear polarizer located between said first quarter wave retarder and said second quarter wave retarder;

a transflector having a light reflective side and a light transmitting side, said bi-directional circular polarizer being located between said transflector and said first side of said cholesteric liquid crystal material, the light reflective side being adapted to reflect light received from said bi-directional circular polarizer; and

a light source adapted to be selectively energizeable to emit light, said light passing through said transflector from said light transmitting side toward said light reflecting side.

20. The liquid crystal display device of claim 19 further comprising an alignment layer in contact with at least one of said sides of said cholesteric liquid crystal layer, said alignment layer being adapted to orient adjacent molecules of said cholesteric liquid crystal material in a particular direction.

21. The liquid crystal display device of claim 20 wherein said molecules of said cholesteric liquid crystal material are oriented effective to enable light reflected from said display to have an S3 stokes parameter greater than 0.75.

22. The liquid crystal display device of claim 20 wherein said molecules of said cholesteric liquid crystal material are oriented effective to enable light reflected from said display to have an S3 stokes parameter greater than 0.90.

23. The liquid crystal display device of claim 19 further comprising stacked layers of said cholesteric liquid crystal material.

24. The liquid crystal display device of claim 23 wherein one of said stacked layers of said cholesteric liquid crystal material is adapted to have a pitch length effective to reflect visible light of one color and another of said stacked layers of said cholesteric liquid crystal material is adapted to have a pitch length effective to reflect visible light of a different color.

25. The liquid crystal display device of claim 23 comprising a triple stack of said liquid crystal layers, wherein one of said layers is adapted to reflect red light, one of said layers is adapted to reflect green light and one of said layers is adapted to reflect blue light.

26. The liquid crystal display device of claim 23 wherein one of said stacked layers is adapted to have a pitch length effective to reflect visible light of one color and another of said stacked layers is adapted to have a pitch length effective to reflect infrared electromagnetic radiation.

27. The liquid crystal display device of claim 19 wherein said means for selectively addressing regions of the cholesteric liquid crystal material comprises drive electronics that electrically address regions of the cholesteric liquid crystal material effective to cause said cholesteric liquid crystal material to exhibit the focal conic and planar textures resulting in an image.

28. A bistable, backlit cholesteric liquid crystal display comprising:

a layer of cholesteric liquid crystal material including focal conic and reflective planar textures that are stable in an absence of an electric field, said layer having a first side and a second side, the second side being closer to an exterior of the display than the first side;

drive electronics adapted to electrically address regions of the cholesteric liquid crystal material effective to cause said cholesteric liquid crystal material to exhibit the focal conic and planar textures resulting in an image;

polarizing means for circularly polarizing light in two opposite directions and for passing circularly polarized light to said layer of cholesteric liquid crystal material;

a transflector having a light reflective side and a light transmitting side, said bi-directional circular polarizer being located between said transflector and said first side of said layer of cholesteric liquid crystal material, the light reflective side being adapted to reflect light received from said polarizing means; and

a light source adapted to be selectively energizable to emit light, said light passing through said transflector from said light transmitting side toward said light reflecting side.

29. A bistable, backlit cholesteric liquid crystal display comprising:

a layer of cholesteric liquid crystal material including focal conic and reflective planar textures that are stable in an absence of an electric field, said layer having a first side and a second side, the second side being closer to an exterior of the display than the first side, an alignment material on at least one of said first and second substrates, said alignment material being adapted to orient molecules of said cholesteric liquid crystal material effective to enable light reflected from said display to have an S3 stokes parameter greater than 0.75;

drive electronics adapted to electrically address regions of the cholesteric liquid crystal material effective to cause said cholesteric liquid crystal material to exhibit the focal conic and planar textures resulting in an image;

a bi-directional circular polarizer;

a transflector having a light reflective side and a light transmitting side, said bi-directional circular polarizer being located between said transflector and said first side of said layer of cholesteric liquid crystal material, the light reflective side being adapted to reflect light received from said bi-directional circular polarizer; and

a light source selectively energizeable to emit light, said light passing through said transflector from said light transmitting side toward said light reflecting side.

30. A bistable, backlit cholesteric liquid crystal display comprising:

a layer of cholesteric liquid crystal material including focal conic and reflective planar textures that are stable in an absence of an electric field, said layer having a first side and a second side, the second side being closer to an exterior of the display than the first side, a substrate having one side in contact with said second side of said layer of cholesteric liquid crystal display material and another side forming an external surface of said display;

drive electronics adapted to electrically address regions of the cholesteric liquid crystal material effective to cause said cholesteric liquid crystal material to exhibit the focal conic and planar textures resulting in an image;

a bi-directional circular polarizer;

a transflector having a light reflective side and a light transmitting side, said bi-directional circular polarizer being located between said transflector and said cholesteric liquid crystal material, the light reflective side being adapted to reflect light received from said bi-directional circular polarizer; and

a light source adapted to be selectively energizable to emit light, said light passing through said transflector from said light transmitting side toward said light reflecting side.

31. A bistable, backlit cholesteric liquid crystal display comprising:

a layer of cholesteric liquid crystal material including focal conic and reflective planar textures that are stable in an absence of an electric field, said layer having a first side and a second side, the second side being closer to an exterior of the display than the first side;

electrical addressing means for electrically addressing regions of the cholesteric liquid crystal material effective to cause said cholesteric liquid crystal material to exhibit the focal conic and planar textures resulting in an image;

polarizing means for circularly polarizing light in two opposite directions including passing circularly polarized light to said layer of cholesteric liquid crystal material;

transflector means for reflecting light incident on one side of the transflector and transmitting light incident on the other side of the transflector, said polarizing means being located between said transflector and said first side of said layer of cholesteric liquid crystal material; and

means for emitting light from said light transmitting side of said transflector toward said light reflecting side of said transflector.

32. A bistable, backlit cholesteric liquid crystal display comprising:

a layer of cholesteric liquid crystal material including focal conic and reflective planar textures that are stable in an absence of an electric field, said layer having a first side and a second side, the second side being closer to an exterior of the display than the first side;

drive electronics adapted to electrically address regions of the cholesteric liquid crystal material effective to cause said cholesteric liquid crystal material to exhibit the focal conic and planar textures resulting in an image;

a bi-directional circular polarizer;

a transflector having a light reflective side proximal to said bi-directional circular polarizer and a light transmitting side distal from said bi-directional circular polarizer, said bi-directional circular polarizer being located between said transflector and said first side of said layer of chiral nematic liquid crystal material; and

a light source located behind said transflector proximal to said light transmitting side and distal to said light reflecting side.