Liquid crystal device comprising anchoring means on at least one confinement plate providing a degenerated orientation

• US 6,452,573 B1
• Filed: 04/16/1999
• Issued: 09/17/2002
• Est. Priority Date: 05/07/1997
• Status: Expired due to Fees

• Current Assignee: FIST SA
• Original Assignee: Nemoptic SA
• Inventors: Auroy, Philippe, Raspaud, Eric, Polossat, Eric, Ou Ramdane, Olivier, Forget, Sandrine, Durand, Georges, Martinot-Lagarde, Philippe, Dozov, Ivan
• Primary Examiner(s): Zimmerman, Mark
• Assistant Examiner(s): Monestime, Mackly
• Application Number:
  US09/214,432
• Time in Patent Office: 1,250 Days
• Field of Search: 345/90, 345/84, 345/7, 345/8, 345/9, 345/427, 345/157, 345/158, 349/155, 349/123, 349/128
• US Class Current: 345/8
• CPC Class Codes: G02F 1/1337 Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
• CPC Class Codes: G02F 1/133753 with different alignment orientations or pretilt angles on a same surface, e.g. for grey scale or improved viewing angle
• CPC Class Codes: G02F 1/1391 Bistable or multi-stable liquid crystal cells G02F1/141 takes precedence
• 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 3/3637 with intermediate tones displayed by domain size control domain size control in flat matrix panels other than liquid crystal displays having memory effects G09G3/207

Abstract

The present invention relates to a liquid crystal display device comprising a liquid crystal material sandwiched between two confinement plates (1, 2), the device being characterized by the fact that at least one of the plates (2) is provided with treatment which defines degenerate or nearly degenerate azimuth anchoring without azimuth orientation memory.

Claims

1. A liquid crystal display device comprising a liquid crystal material sandwiched between two confinements (1,2), the device being characterized by the fact that at least one of the plates (2) is provided with treatment which defines degenerate azimuth anchoring so that no azimuth direction is imposed by anchoring to the liquid crystal material and furthermore the liquid crystal molecules are free to turn around a normal to the plates, without azimuth orientation memory so that an external electric or magnetic field does not generate any azimuth orientation memory.

2. A device according to claim 1, characterized by the fact that the treatment comprises passivating a surface of at least one of the plates (1,2) by inhibiting adsorption sites on said surface.

3. A device according to claim 1 or 2, characterized by the fact that the treatment is obtained by selecting a material constituting the confinement plates or by selecting a covering thereon.

4. A device according to claim 3, characterized by the fact that the material comprises a polymer having chains that are fluid or highly mobile or that do not include any adsorption sites for the liquid crystal.

5. A device according to claim 1, characterized by the fact that the treatment includes grafting a coating.

6. A device according to claim 1 characterized by the fact that the treatment operates by saturating adsorption sites.

7. A device according to claim 1 characterized by the fact that the treatment is adapted to avoid strongly interacting with the liquid crystal, in particular to avoid being easily orientated by anisotropic interactions with the mesogenic molecules of the liquid crystal.

8. A device according to claim 1 characterized by the fact that the treatment comprises a compound selected from organofunctional silanes.

9. A device according to claim 1 characterized by the fact that the treatment comprises a compound selected from the family of organofunctional silanes including chlorosilane groups (Si—

Cl), silanol (Si—

OH), or alkoxysilane (Si—

C_nH_2nOH).

10. A device according to claim 1 characterized by the fact that the treatment comprises chromium complexes.

11. A device according to claim 1 characterized by the fact that the treatment is constituted by 3-glyceryloxypropyl trimethoxysilane (GLYMO).

12. A device according to claim 4, characterized by the fact that the material comprises polymers in liquid phase throughout a thermal stability range of a mesogenic phase used, and by the fact that said polymers are grafted onto a surface of at least a plate.

13. a device according to claim 4, characterized by the fact that the material comprises polymers that are insoluble in the liquid crystal, in their vitreous state.

14. A device according to claim 4 characterized by the fact that the material comprises siloxane polymers that are liquid or polymers that are vitreous at ambient temperature.

15. A device according to claim 14, characterized by the fact that the material comprises polyisoprene, polybutadiene, or polystyrene.

16. A device according to claim 1 characterized by the fact that the treatment is adapted to define degenerate planar anchoring.

17. A device according to claim 1 characterized by the fact that the treatment is adapted to define degenerate conical anchoring.

18. A device according to claim 1 characterized by the fact that it comprises means suitable for controlling a change of state by a surface hydrodynamic effect.

19. A device according to claim 1 characterized by the fact that it comprises means suitable for controlling a change of state by a bulk hydrodynamic effect.

20. A device according to claim 1 characterized by the fact that it comprises control means applying a pulse to the liquid crystal that is lower than a breaking threshold on the plate provided with the treatment.

21. A device according to claim 20, characterized by the fact that it comprises control means creating a bulk or surface hydrodynamic effect inducing azimuth rotation of anchoring that is degenerate or nearly degenerate without breaking the zenith anchoring.

22. A device according to claim 1 characterized by the fact that it comprises control means applying a pulse to the liquid crystal that is greater than the breaking threshold on the plate provided with the treatment.

23. A device according to claim 1 characterized by the fact that the treatment is deposited on an isotropic substrate to define anchoring that is degenerate, conical or plane without orientation hysteresis.

24. A device according to claim 1 characterized by the fact that the treatment is deposited on an anisotropic substrate.

25. A device according to claim 24, characterized by the fact that the treatment is deposited on a layer of SiO placed on a confinement plate.

26. A device according to claim 1 characterized by the fact that it comprises means superposing anisotropy on conical or planar degenerate anchoring to produce anchoring that is nearly degenerate having non-zero azimuth energy but no memory or hysteresis.

27. A device according to claim 26, characterized by the fact that the means suitable for superposing anisotropy on conical or planar degenerate anchoring are selected from the group comprising:

rubbing the confinement plate (2) before or after depositing the coating;

depositing the coating on an anisotropic surface;

or inducing anisotropy by irradiating a passivation coating using a beam of polarized light in ultraviolet or in visible range.

28. A device according to claim 1 characterized by the fact that the display device is bistable and that in the absence of a field at least two textures among the three possible textures are stable:

plane/tilted (FIGS. 6a, 7a), plane/bent (FIGS. 6d, 7d), and twisted texture (FIG. 6f).

29. A device according to claim 28, characterized by the fact that the tilts (θ

) of the molecules at rest relative to a normal to the confinement plates are small enough to stabilize the plane/bent texture.

30. A device according to claim 28 characterized by the fact that it includes a chiral doping agent to stabilize the twisted texture.

31. A device according to claim 1 characterized by the fact that the display device is monostable, that the state induced by the control means is unstable, and that the device returns spontaneously to its initial stable state by a continuous path.

32. A device according to claim 31, characterized by the fact that the tilts (θ

) of the molecules at rest relative to a normal to the confinement plates are large.

33. A device according to claim 20, characterized by the fact that the control means are adapted to apply selectively to the liquid crystal a pulse selected from a plurality of control pulses close to the breaking threshold to define selected gray levels.

34. A device according to claim 33, characterized by the fact that the control pulses are of fixed duration and of amplitude that is variable close to the breaking threshold.

35. A device according to claim 33, characterized by the fact that the control pulses are of fixed amplitude and of duration that is variable close to the breaking threshold.

36. A device according to claim 33 characterized by the fact that it is organized as a matrix and that the control means are adapted to apply a voltage Urow=(U_c+U_s) /S to the active row and (U_c−

U_s) /2<

Ucol<

(U_s−

U_c) /2to the columns, U_c and U_s representing respectively the thresholds at which a change of state in the device appears and saturates.

37. A device according to claim 28, characterized by the fact that to erase a written texture, the control means apply a pulse which favors elastic interaction between the two surfaces relative to their hydrodynamic interaction.

38. A device according to claim 33 characterized by the fact that the repetition period of the control pulses which refresh the image is less than the erase time of the device, and that gray level selection is thus given by the root means square value of the voltage applied to the pixel.

39. A device according to claim 1 and 38, characterized by the fact that control means are provided suitable for breaking anchoring on both plates.

40. A device according to claim 39, characterized by the fact that complementary control means are provided suitable for creating an orientation horizontal flow or field.

41. A device according to claim 1 characterized by the fact that the zenith breaking threshold of the degenerate anchoring provided on one plate is higher than the zenith breaking threshold of conventional anchoring provided on the other plate, and means are provided that are suitable for applying a field lying between the two anchoring thresholds defined in this way.

42. A device according to claim 1 characterized by the fact that both plates (1,2) are treated to define degenerate azimuth anchoring without azimuth orientation memory.

43. A device according to claim 1 characterized by the fact that one of the plates induces strong azimuth anchoring and the other induces planar or conical degenerate azimuth anchoring.

44. A device according to claim 43, characterized by the fact that it comprises means suitable for applying an electric field perpendicular to the plates and that the liquid crystal is cholesterized to form a regular helical texture in the cell at a pitch which changes under the action of the field because of the degenerate azimuth anchoring of one of the plates.

45. A device according to claim 44, characterized by the fact that the liquid crystal is of positive anisotropy and that under the field the regular helical texture is conserved, but its pitch varies.

46. A device according to claim 44, characterized by the fact that the liquid crystal has negative anisotropy and that at least one of the anchoring on the plates is tilted;

such that the applied field increases the zenith angle and changes the helical pitch.

47. A device according to claim 43, characterized by the fact that it comprises means suitable for applying an electric parallel to the plates to control twisting of the molecules in the vicinity of the plate having degenerate azimuth anchoring.

48. A device according to claim 47, characterized by the fact that the liquid crystal is nematic with positive dielectric anisotropy and that the field E is applied perpendicularly to the uniform texture of the nematic when there is no field.

49. A device according to claim 47, characterized by the fact that the liquid crystal is nematic with negative anisotropy and that the field E is applied parallel to the uniform texture of the nematic when there is no field.

50. A device according to claim 47, characterized by the fact that the liquid crystal is nematic and that the field is applied in a direction other than zero and 90°

relative to the uniform texture.

51. A device according to claim 47, characterized by the fact that the liquid crystal is cholesterized to obtain a texture that is helical in the absence of the field.