Ultra fast response, multistable reflective cholesteric liquid crystal displays

• US 5,661,533 A
• Filed: 05/19/1995
• Issued: 08/26/1997
• Est. Priority Date: 05/19/1995
• Status: Expired due to Fees

• Current Assignee: Kent Display Systems Incorporated
• Original Assignee: Advanced Display Systems Incorporated
• Inventors: Ma, Yao-Dong, Wu, Bao-Gang, Zhou, Hongxi
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): MILLER, CHARLES LELAND
• Application Number:
  US08/445,181
• Time in Patent Office: 830 Days
• Field of Search: 359/90, 359/91, 359/102, 359/101, 359/75, 349/88, 349/115, 349/169, 349/176
• US Class Current: 349/169
• CPC Class Codes: G02F 1/133711 by organic films, e.g. polymeric films
• CPC Class Codes: G02F 1/133765 without a surface treatment
• CPC Class Codes: G02F 1/13718 based on a change of the texture state of a cholesteric liquid crystal
• CPC Class Codes: G02F 2203/30 Gray scale
• CPC Class Codes: G09G 2300/0486 Cholesteric liquid crystals, including chiral-nematic liquid crystals, with transitions between focal conic, planar, and homeotropic states

Abstract

Surfactant-containing multistable cholesteric liquid crystal displays exhibit ultra fast response times with both video speed and gray scale capability.

Claims

1. A liquid crystal cell structure comprising:

a first solid substrate having a first inner surface coated with a first conductive layer;

a second solid substrate having a second inner surface coated with a second conductive layer; and

a substantially indefinite zero field multistable cholesteric liquid crystal mix located in a space between the first inner surface of the first solid substrate and the second inner surface of the second solid substrate, the liquid crystal mix comprising a surface active agent;

a plurality of liquid crystals; and

at least one twist agent forming multiple cholesteric domains;

wherein each of the multiple cholesteric domains is a visible or near-visible reflective unit;

wherein an orientation of each of the multiple cholesteric domains can be changed by application of a voltage pulse;

liquid crystal mix is below about 150 milliseconds.

2. The liquid crystal cell structure of claim 1, wherein the first conductive layer is coated with a first amorphous boundary layer.

3. The liquid crystal cell structure of claim 2, wherein the first amorphous boundary layer comprises a polyimide.

4. The liquid crystal cell structure of claim 2, wherein the first amorphous boundary layer comprises a silane.

5. The liquid crystal cell structure of claim 2, wherein helical axes of multiple cholesteric domains are oriented in random directions at the interface with the respective boundary layers.

6. The liquid crystal cell structure of claim 1, wherein the second conductive layer is coated with a second amorphous boundary layer.

7. The liquid crystal cell structure of claim 6, wherein the second amorphous boundary layer comprises a polyimide.

8. The liquid crystal cell structure of claim 6, wherein the second amorphous boundary layer comprises a silane.

9. The liquid crystal cell structure of claim 6, wherein helical axes of multiple cholesteric domains are oriented in random directions at the interface with the respective boundary layers.

10. The liquid crystal cell structure of claim 1, wherein the liquid crystal mix is substantially free of polymer additive.

11. The liquid crystal cell structure of claim 1, wherein the surface active agent is a non-ionic surface active agent in an amount from about 0.1% to about 10% by weight, based on the total weight of the liquid crystal mix.

12. The liquid crystal cell structure of claim 1, wherein the surface active agent is a non-ionic surface active agent in an amount from about 1% to about 3% by weight, based on the total weight of the liquid crystal mix.

13. The liquid crystal cell structure of claim 1, wherein the relaxation time is below about 150 microseconds.

14. The liquid crystal cell structure of claim 1, further comprising up to about 5% by weight of water, based on the total weight of the liquid crystal mix.

15. A liquid crystal cell structure comprising:

a first solid substrate having a first inner surface coated with a first conductive layer;

a second solid substrate having a second inner surface coated with a second conductive layer; and

a substantially indefinite zero field multistable cholesteric liquid crystal mix located in a space between the first inner surface of the first solid substrate and the second inner surface of the second solid substrate, the liquid mix being substantially free of polymer additive, and the liquid crystal mix comprising a non-ionic surface active agent;

plurality of liquid crystals; and

at least one twist agent forming multiple cholesteric domains;

wherein each of the multiple cholesteric domains is a visible or near-visible reflective unit; and

wherein relaxation time of the liquid crystal mix is below about 150 milliseconds.

16. The liquid crystal cell structure of claim 15, wherein the first conductive layer is coated with a first amorphous boundary layer.

17. The liquid crystal cell structure of claim 16, wherein the first amorphous boundary layer comprises a polyimide.

18. The liquid crystal cell structure of claim 16, wherein the first amorphous boundary layer comprises a silane.

19. The liquid crystal cell structure of claim 16, wherein helical axes of multiple cholesteric domains are oriented in random directions at the interface with the respective boundary layers.

20. The liquid crystal cell structure of claim 15, wherein the second conductive layer is coated with a second amorphous boundary layer.

21. The liquid crystal cell structure of claim 20, wherein the second amorphous boundary layer comprises a polyimide.

22. The liquid crystal cell structure of claim 20, wherein the second amorphous boundary layer comprises a silane.

23. The liquid crystal cell structure of claim 20, wherein helical axes of multiple cholesteric domains are oriented in random directions at the interface with the respective boundary layers.

24. The liquid crystal cell structure of claim 15, wherein the non-ionic surface active agent is in an amount from about 0.1% to about 10% by weight, based on the total weight of the liquid crystal mix.

25. The liquid crystal cell structure of claim 15, wherein the non-ionic surface active agent is in an amount from about 1% to about 3% by weight, based on the total weight of the liquid crystal mix.

26. The liquid crystal cell structure of claim 15, wherein the relaxation time is below about 150 microseconds.

27. The liquid crystal cell structure of claim 15, further comprising up to about 5% by weight of water, based on the total weight of the liquid crystal mix.

28. A liquid crystal cell structure comprising:

a first solid substrate having a first inner surface coated with a first coating comprising a first conductive layer;

a second solid substrate having a second inner surface coated with a second coating comprising a second conductive layer; and

a substantially indefinite zero field multistable cholesteric liquid crystal mix located in a space between the first inner surface of the first solid substrate and the second inner surface of the second solid substrate, the liquid mix being substantially free of polymer additive, and the liquid crystal mix comprising a non-ionic surface active agent in a range of from about 0.1% to about 10% by weight, based on the total weight of the liquid crystal mix;

a plurality of liquid crystals; and

at least one twist agent forming multiple cholesteric domains;

wherein each of the multiple cholesteric domains is a visible or near-visible reflective unit;

wherein an orientation of each of the multiple cholesteric domains can be changed by application of a voltage pulse;

wherein the orientation of each of the multiple cholesteric domains is substantially free of interactions among the multiple cholesteric domains and also substantially free of interaction among the multiple cholesteric domains and the first and second solid substrates to yield zero field multistability; and

wherein relaxation time of the liquid crystal mix is below about 150 microseconds.

29. The liquid crystal cell structure of claim 28, wherein the non-ionic surface active agent is in an amount from about 1% to about 3% by weight, based on the total weight of the liquid crystal mix.

30. The liquid crystal cell structure of claim 28, further comprising up to about 5% by weight of water, based on the total weight of the liquid crystal mix.

31. A method of forming a display in a light modulation device comprising:

providing a cholesteric liquid crystal cell structure having a liquid crystal mix substantially free of polymer additive, having a surface active agent, reflecting light in a visible or near visible region, having a relaxation time of less than about 150 milliseconds, and capable of exhibiting substantially indefinite zero field multistable behavior; and

applying a driving voltage across the liquid crystal material to change a domain orientation of the liquid crystal material at a speed, wherein the driving voltage is a function of the width of a voltage pulse.

32. The method of claim 31 further comprising:

removing the driving voltage across the liquid crystal material whereby the domain orientation is transformed from one state to a different state.

33. The method of claim 31, wherein the driving voltage is a single voltage pulse.

34. The method of claim 33, wherein the single voltage pulse allows achievement of an unlimited gray scale capability.

35. The method of claim 31, wherein the driving voltage is a succession of pulses.

36. The method of claim 35, wherein the succession of pulses allows an unlimited gray scale capability.

37. The method of claim 31, wherein the driving voltage is applied by means of a matrix drive method wherein:

space="preserve" listing-type="equation">V.sub.N =(V.sub.R -V.sub.S)/2; and

wherein V_N is the minimum cross-talk voltage, V_R is the voltage pulse required to achieve the maximum zero field stable reflective state, and V_S is the driving voltage employed to establish domain structures intermediate between the planar and focal-conic extremes.

38. The method of claim 37, wherein V_N is smaller than V_T, and wherein V_T is the threshold voltage.

39. The method of claim 31, wherein the speed of changing the domain orientation of the liquid crystal material is dependent on both the driving voltage and the width of the voltage pulse.

40. The method of claim 31, wherein the relaxation time is less than about 150 microseconds.