Dual frequency cholesteric display and drive scheme

• US 6,320,563 B1
• Filed: 01/21/1999
• Issued: 11/20/2001
• Est. Priority Date: 01/21/1999
• Status: Expired due to Term

• Current Assignee: Kent State University
• Original Assignee: Kent State University
• Inventors: Xu, Ming, Yang, Deng-Ke
• Primary Examiner(s): Hjerpe, Richard
• Assistant Examiner(s): Zamani, Ali A.
• Application Number:
  US09/235,082
• Time in Patent Office: 1,034 Days
• Field of Search: 345/87, 345/89, 345/98, 345/94, 345/90, 345/208, 349/94, 349/36, 349/96, 349/86, 349/92, 349/93, 350/160
• US Class Current: 345/87
• CPC Class Codes: G09G 2300/0486 Cholesteric liquid crystals, including chiral-nematic liquid crystals, with transitions between focal conic, planar, and homeotropic states
• CPC Class Codes: G09G 3/3629 using liquid crystals having memory effects, e.g. ferroelectric liquid crystals

Abstract

A dual frequency cholesteric display includes a pair of opposed substrates, wherein one of the substrates has a first plurality of electrodes facing a second plurality of electrodes on the other substrate. A dual frequency bistable cholesteric liquid crystal material is disposed between the substrates, wherein the material and the intersection of the first and second plurality of electrodes forms a plurality of pixels. By selectively applying high and low frequency voltages to the plurality of pixels, the high frequency voltage causes the material to exhibit one texture and the low frequency voltage causes the material to exhibit another texture. By adjusting a voltage amplitude value for each high and low frequency causes each pixel to exhibit a desired reflectance.

Claims

1. A method of addressing a dual frequency bistable cholesteric liquid crystal material having liquid crystal domains disposed between opposed substrates, wherein one of the substrates has a first plurality of electrodes facing a second plurality of electrodes on the other substrate, and wherein the intersection of the first and the second plurality of electrodes forms a plurality of pixels, the method comprising the steps of:

selectively applying high and low frequency voltages to said plurality of pixels, wherein the high frequency voltage drives the material to exhibit one texture so that the liquid crystal domains have a reflectance at one extreme and the low frequency voltage drives the material to exhibit another texture so that the liquid crystal domains have a reflectance at another extreme, wherein the liquid crystal domains are stable after removal of the voltages;

adjusting a voltage amplitude value for each said high and low frequency to obtain a desired reflectance which can be at either extreme or somewhere between the two extremes, wherein said desired reflectance is made up of pixels, each said pixel having a first portion of liquid crystal domains at one extreme and another portion of liquid crystal domains at the other extreme; and

cumulatively adjusting the desired reflectance by simultaneously applying said high and low frequency voltages in multiple pulses such that switching of the liquid crystal domains is accomplished cumulatively so that the amplitude or the duration of the pulses, or both can be reduced.

2. The method according to claim 1 wherein the step of selectively applying further comprises the step of simultaneously applying said high and low frequency voltages.

3. The method according to claim 2 wherein the high frequency is about 10 Kilohertz.

4. The method according to claim 2 wherein the low frequency voltage is about 200 Hertz.

5. The method according to claim 2, further comprising the steps of:

applying both a high and low frequency voltage to said first plurality of electrodes and a high and low frequency voltage to said second plurality of electrodes; and

adjusting the polarity of said high and low frequency voltages applied to drive the material to the one or the other texture.

6. The method according to claim 5, further comprising the step of:

canceling the high frequency voltages applied to a pixel so that only low frequency voltages remain to drive the material to exhibit the other texture.

7. The method according to claim 5, further comprising the step of:

canceling the low frequency voltages applied to a pixel so that only the high frequency voltages remain to drive the material to exhibit the one texture.

8. The method according to claim 2 further comprising the step of:

applying a high and low frequency voltage to one of said plurality of electrodes and a minimal voltage to said other plurality of electrodes, wherein said high and low frequency voltage values nullify each other and said corresponding pixel maintains its texture.

9. The method according to claim 2, wherein application of a higher frequency voltage value to said pixel increases the reflectance of said pixel.

10. The method according to claim 2, wherein application of a lower frequency voltage value to said pixel decreases the reflectance of said pixel.

11. A dual frequency cholesteric display, comprising:

a pair of opposed substrates, wherein one of said substrates has a first plurality of electrodes facing a second plurality of electrodes on the other substrate;

a reflective dual frequency bistable cholesteric liquid crystal material disposed between said substrates, wherein the material and the intersection of the first and second plurality of electrodes forms a plurality of pixels, said material having liquid crystal domains, wherein a plurality of said liquid crystal domains are contained in each of said pixels such that all the liquid crystal domains in a pixel can be either in a focal conic or a planar texture, or the liquid crystal domains in a pixel can have any combination of focal conic and planar textures;

means for selectively applying high and low frequency voltages to said plurality of pixels, wherein the high frequency voltage drives the material to exhibit predominantly one texture and the low frequency voltage drives the material to exhibit predominantly another texture;

means for adjusting a voltage amplitude value for each said high and low frequency to obtain a desired reflectance for each pixel, wherein adjusting the voltage amplitude drives the liquid crystal domains in a corresponding manner so as to change the proportion of liquid crystal domains in each texture; and

means for cumulatively adjusting the reflectance by simultaneously applying high and low frequency voltage pulses to both said plurality of electrodes, wherein cumulatively switching of the liquid crystal domains between textures is accomplished by multiple pulses so that the amplitude or the duration of the pulses, or both can be reduced.

12. The display according to claim 11, wherein said means for selectively applying further comprises means for simultaneously applying said high and low frequency voltages.

13. The display according to claim 12, wherein the high frequency is about 10 kilohertz.

14. The display according to claim 12, wherein the low frequency is about 200 hertz.

15. The display according to claim 12, wherein said means for selectively applying further comprises:

means for applying both a high and low frequency voltage to said first plurality of electrodes and a high and low frequency voltage to said second plurality of electrodes; and

means for adjusting the polarity of said high and low frequency voltages applied to drive the material to the one or the other texture.

16. The display according to claim 15, wherein said means for selectively applying further comprises:

means for canceling the high frequency voltages applied to a pixel so that only low frequency voltages remain to drive the material to exhibit the other texture.

17. The display according to claim 15, wherein said means for selectively applying further comprises:

means for canceling the low frequency voltages applied to a pixel so that only the high frequency voltages remain to drive the material to exhibit the one texture.

18. The display according to claim 12, wherein said means for selectively applying further comprises:

means for applying a high and low frequency voltage to one of said plurality of electrodes and a minimal voltage to said other plurality of electrodes, wherein said high and low frequency voltage values nullify each other and said corresponding pixel maintains its texture.

19. The display according to claim 12, wherein application of a higher frequency voltage value to said pixel increases reflectance of said pixel.

20. The display according to claim 12, wherein application of a lower frequency voltage value to said pixel decreases the reflectance of said pixel.

21. A method of addressing a dual frequency bistable cholesteric liquid crystal material having liquid crystal domains disposed between opposed substrates, wherein one of the substrates has a first plurality of electrodes facing a second plurality of electrodes on the other substrate, and wherein the intersection of the first and the second plurality of electrodes forms a plurality of pixels, the method comprising the steps of:

selectively applying high and low frequency voltages to said plurality of pixels, wherein the high frequency voltage drives the material to exhibit one texture so that the liquid crystal domains have a reflectance at one extreme and the low frequency voltage drives the material to exhibit another texture so that the liquid crystal domains have a reflectance at another extreme, wherein the liquid crystal domains are stable after removal of the voltages; and

adjusting a voltage amplitude value for each said high and low frequency to obtain a desired reflectance which can be at either extreme or somewhere between the two extremes, wherein said desired reflectance is made up of pixels, each said pixel having a first portion of liquid crystal domains at one extreme and another portion of liquid crystal domains at the other extreme.

22. A dual frequency cholesteric display, comprising:

a pair of opposed substrates, wherein one of said substrates has a first plurality of electrodes facing a second plurality of electrodes on the other substrate;

a reflective dual frequency bistable cholesteric liquid crystal material disposed between said substrates, wherein the material and the intersection of the first and second plurality of electrodes forms a plurality of pixels, said material having liquid crystal domains, wherein a plurality of said liquid crystal domains are contained in each of said pixels such that all the liquid crystal domains in a pixel can be either in a focal conic or a planar texture, or the liquid crystal domains in a pixel can have any combination of focal conic and planar textures;

means for selectively applying high and low frequency voltages to said plurality of pixels, wherein the high frequency voltage drives the material to exhibit predominantly one texture and the low frequency voltage drives the material to exhibit predominantly another texture; and

means for adjusting a voltage amplitude value for each said high and low frequency to obtain a desired reflectance for each pixel, wherein adjusting the voltage amplitude drives the liquid crystal domains in a corresponding manner so as to change the proportion of liquid crystal domains in each texture.