Surface stabilized ferroelectric liquid crystal devices

• US 4,813,767 A
• Filed: 08/19/1987
• Issued: 03/21/1989
• Est. Priority Date: 01/08/1980
• Status: Expired due to Term

• Current Assignee: Clark, Noel A., Sven T. Lagerwall
• Original Assignee: Clark, Noel A., Sven T. Lagerwall
• Inventors: Clark, Noel A., Lagerwall, Sven T.
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): Lewis, David
• Application Number:
  US07/088,482
• Time in Patent Office: 580 Days
• Field of Search: 350/350 S, 350/341
• US Class Current: 349/133
• CPC Class Codes: C09K 19/02 characterised by optical, electrical or physical properties of the components, in general
• CPC Class Codes: C09K 19/0225 Ferroelectric
• CPC Class Codes: G02F 1/141 using ferroelectric liquid crystals

Abstract

A liquid crystal device including a ferroelectric liquid crystal disposed between plates treated to enforce a particular ferroelectric molecular orientation to the plates. The devices employ alone or in combination non-planar boundary conditions, polar boundary conditions, boundaries with multiple physical states, intrinsic spontaneous splay distortion of the polarization orientation field, combined ferroelectric and dielectric torques, layers tilted with respect to the plates. The plates are spaced by a distance sufficiently small to ensure unwinding of the helix typical in a bulk of the material to form either monostable, bistable or multistable states which exhibit novel electro-optic properties. The liquid crystal is responsive to an externally applied electric field, temperature or the like to make a light valve or other electro-optical device.

Claims

1. A liquid crystal device comprising:

a quantity of ferroeletric liquid crystal having a plurality of adjacently disposed layers each comprised of a plurality of molecules, each molecule having a long axis, said molecules of said layers in a bulk of said liquid crystal, forming helices having axes perpendicular to said layers;

first means, transverse to and contiguous with at least a portion of as surface of said layers, for aligning the long axes of said molecules adjacent to said first means at a first angle Ω

₁ (α

) from the normal to said first means, said angle Ω

₁ (α

) being a predetermined function of an angle α

, said angle α

being an angle between a reference vector in a first plane parallel to said first means and a projection of said long axes of said molecules onto said first plane; and

second means, transverse to and contiguous with at least a portion of an opposite surface of said layers, for aligning the long axes of said molecules adjacent to said second means at a second angle Ω

₂ (α

) from the normal to said second means, said angle Ω

₂ (α

) being a predetermined function of α

which is different from said function of said angle Ω

₁ (α

), the distances between said first and second means being less than the distance at which said helices form in the absence of a electric field, said first and second means causing said long axes to assume one of a plurality of stable orientations.

2. A device as in claim 1 wherein said angle Ω

₁ (α

) is a constant over all said angles α and

said angle Ω

₂ (α

) is a constant over all said angles α

.

3. A device as in claim 1 wherein said first and second means are parallel.

4. A device as in claim 1 wherein at least one of said angles Ω

₁ (α

) and Ω

₂ (α

) is symmetric with respect to a plane perpendicular to said plane within which said angle α

lies.

5. A device as in claim 1 wherein at least one of said angles Ω

₁ (α

) and Ω

₂ (α

) is undefined for certain values of α

.

6. A device as in claim 1 wherein said layers are not normal to said first and second means.

7. A device as in claim 1 wherein said first and second means are also for inducing splay in the polarization field of said liquid crystal homogeneously over at least a substantial portion of said first and second means.

8. A device as in claim 1 wherein said first means aligns said long axes more strongly than said second means by a predetermined degree homogeneously over at least a substantial portion of said first and second means.

9. A device as in claim 1 wherein said first and second means are both for inducing unsymmetric anisotropic conical conditions on said long axes but have different directions of anisotropy homogeneously over at least a substantial portion of said first and second means.

10. A device as in claim 1 wherein the distance between said first and second means varies over the area of said first and second means.

11. A device in as in claim 10 wherein said distance varies in discrete steps over the area of said second and second means.

12. A device as in claim 1 wherein a selected substantial portion of said first means aligns said long axes more strongly in a predetermined manner than the remainder of said first means, and said device further comprises electro-optical means for exploiting said selected portion aligning said long axes than said remainder to produce optical effects.

13. A device as in claim 1 further comprising means for heating a portion of said liquid crystal to a sufficient extend to create states different from states in unheated portions of said liquid crystal.

14. A device as in claim 1 further comprising means for applying an electric field to at least a portion of said layers in a direction having a significant component perpendicular to said layers, the strength of said electric field being sufficient to shift said long axes in said portion from one of said stable orientations to another of said stable orientations.

15. A device as in claim 1 wherein said angles Ω

₁ (α

) and Ω

₂ (α

) are different from 90 degrees.

16. A device as in claim 1 wherein ferroelectric coupling occurs between a polarization vector of said molecules and at least one of said first and second means, said coupling being sufficiently weak to enable switching between a plurality of stable while favoring certain of said stable states.

17. A device as in claim 1 wherein:

said first and second means extend over a portion of said liquid crystal; and

said device further comprises means, contioguous with said liquid crystal portion over which said first and second means do not extend, for aligning said layers at a predetermined angle δ

relative to said layer aligning means, wherein δ

is the angle between the layer aligning means and said layers of said liquid crystal.

18. A device as in claim 17 wherein said layer aligning means includes silicon monoxide obliquely deposited on a surface from a predetermined direction.

19. A liquid crystal electro-optical device comprising:

a quantity of ferroelectric liquid crystals having a plurality of adjacently disposed layers each comprised of a plurality of molecules, each molecule having a long axis, said molecules of said layers in a bulk of said liquid crystal forming helices having axes perpendicular to said layers;

first means, transverse to and continguous with a surface of said layers for aligning the long axes of said molecules adjacent to said first means at a first angle Ω

₁ (α

) from the normal to said first means, said angle Ω

₁ (α

) being predetermined function of an angle α

, said angle (α

) being an angle between a reference vector in a first plane parallel to said frist means and a projection of said long axes of said molecules onto said first plane;

second means, transverse to and contiguous with an opposite surface of said layers, for aligning the long axes of said molecules adjacent to said second means at a second angle Ω

₂ (α

) from the normal to said second means, said angle Ω

₂ (α

) being a predetermined function of α

which is different from said function of said angle Ω

₁ (α

) the distance between said first and second means being less than the distance at which said helices form in the absence of an electric field, said first and second means causing said long axes to assume one of a plurality of stable orientations;

means for applying an electric field to at least a portion of said layers, said electric field having a significant component parallel to said layers, and for reversing the direction of said electric field, the strength of said electric field being sufficient to shift the long axes of molecules in said portion of said layers from one of said stable orientations to another of said stable orientations; and

means for processing light passing through said liquid crystal so that light passing through a portion of said liquid crystal having one of said stable orientations can be distinguished from light passing through said same portion of said liquid crystal having other of said stable orientations.

20. A device as in claim 19 wherein said first angle Ω

₁ (α

) is a constant over all of said angles α and

said second angle Ω

₂ (α

) is a constant over all of said angles α

₂.

21. A device as in claim 19 wherein said first and second means are parallel.

22. A device as in claim 21 wherein said processing means employs birefringence of said liquid crystal.

23. A device as in claim 21 wherein said processing means employs the anisotropic absorption of light by said liquid crystal.

24. A device as in claim 23 further comprising dye molecules mixed with said liquid crystal.

25. A device as in claim 19 wherein the orientation of said long axes varies linearly with said electric field.

26. A device as in claim 20 wherein said processing means includes first ends second polarizers, on opposite sides of said liquid crystal, having polarization directions perpendicularly arranged, one of said polarization directions being parallel to said long axes in one of said stable orientations.

27. A device as in claim 19 wherein said processing means includes a polarizer and a reflector, both disposed parallel to a surface of said liquid crystal.

28. A device as in claim 27 wherein said polarizer and said reflector are on opposite sides of said liquid crystal.

29. A device as in claim 27 wherein said polarizer and reflector are on the same side of said liquid crystal.

30. A device as in claim 27 wherein said processing means includes a second polarizer parallel to said reflector.

31. A device as in claim 19 further comprising third means and another ferroelectric liquid crsytal disposed between said second means and said third means, said third means for aligning the long axes of molecules of said another liquid crystal adjacent to said third means at an angle Ω

₃ (α

) from the normal to said third means, said angle Ω

₃ (α

) being a predetermined function of said angle α

, the distance between said second means and said third means being less than the distance at which said helices form in the absence of an electric field.

32. A device as in claim 19 wherein:

different areas of said liquid crystal can assume different orientations; and

said processing means includes optical means for combining light passing through different areas of said liquid crystal.

33. A device as in claim 32 wherein said optical means includes a cylindrical lens.

34. A device as in claim 19 wherein each of said first means and said second means are displaced from portions of said surfaces of said liquid crystal on which said applying means is disposed.

35. A device as in claim 19 wherein:

said first and second means extend over a portion of said liquid crystal; and

said device further comprises means, contiguous with said liquid crystal portion over which said first and second means do not extend, for aligning said layers.

36. A device as in claim 35 wherein said layer aligning means includes silicon monoxide obliquely deposited on a surface from a predetermined direction.

37. A device as in claim 19 wherein said liquid crystal is such that torques induced by said field from dielectric effects dominate over torques induced by ferroelectric effects.

38. A liquid crystal electro-optical device comprising:

a quantity of ferroelectric liquid crystals having a plurality of adjacently disposed layers each comprised of a plurality of molecules, each molecule having a long axis, said molecules of said layers in a bulk of said liquid crystal forming helices having axes perpendicular to said layers;

first means, transverse to and contiguous with a surface of said layers and capable of assuming any of a plurality of structural states, for aligning the long axes of said molecules adjacent to said first means at a first angle Ω

₁ (α

) from the normal to said first means, said angle Ω

_1`(α

) being a predetermined function of both an angle α and

the structural state of said first means, said angle α

being an angle between a reference vector in a first plane parallel to said first plane;

second means, transverse to and contiguous with an opposite surface of said layers, for aligning the long axes of said molecules adjacent to said second means at a second angle Ω

₂ (α

) from the normal to said second means, said angle Ω

₂ (α

) being a function of said angle α

, the distance between said first and second means being less than the distance at which said helices form in the absence of an electric field, said first and second means causing said long axes to assume one of as plurality of stable orientations;

means for applying an electric field to at least a portion of said layers, said electric field having a significant component parallel to said layers, and for reversing the direction of said electric field, the strength of said electric field being sufficient to shift the long axes of molecules in said portion and to alter said structural state of said first means to produce a shift in the long axes in said portion from one of said stable orientations to another of said stable orientations; and

means for processing light passing through said liquid crystal so that light passing through a portion of said liquid crystal having one of said stable orientations can be distinguished from light passing through said same portion of said liquid crystal having other of said stable orientations.

39. A liquid crystal electro-optical device comprising:

a quantity of ferroelectric liquid crystal having a plurality of adjacently disposed layers each comprised of a plurality of adjacently disposed layers each comprised of a plurality of molecules, each molecule having a long axis and a ferroelectric polarization vector parallel to said layers, said moles forming helices having axes perpendicular to said layers;

first and second means, transverse to and contiguous with said layers, for containing said liquid crystal, at least one of said first and second means for ferroelectrical coupling with and aligning said polarization vectors of said molecules adjacent to said at least one of said first and second means at a predetemrined angle with respect to said first and second means, the distance between said first and second means being less than the distance at which said helices form in the asbsence of an electric field, said first and second means causing said long axes to assume a stable orientation;

means for applying an electric field to at least a portion of said layers, said field being perpendicular to said first and second means, the strength of said field being sufficient to shift said long axes of said molecules from said stable orientation to a different orientation; and

means for processing light passing through said liquid crystal so that light passing through portions of said liquid crystal having said stable orientation can be distinguished from light passing through portions of said liquid crystal having said different orientation.

40. A device as in claim 39 wherein said liquid crystal is any one of the group consisting of S-4-(6-methyl)octylresorcyidene-4'"'"'-octylaniline and bis (S,S-4'"'"'-(6-methyl)-2-chloro-1,4-phenylenediamine and at least one of said first and second means includes an indium-tin oxide coated glass surface.

41. A device as in claim 39 wherein said electric field having a first polarity causes a first different orientation and said electric field having a second polarity causes a second different orientation from said stable orientation.

42. A liquid crystal device comprising:

a quantity of ferroelectric liquid crystal having a plurality of adjacently disposed layers each comprised of a plurality of molecules, each molecules having a long axis, said molecules of said layers in a bulk of said liquid crystal forming helices having axes perpendicular to said layers; and

first and second means each transverse to and contiguous with said layers, for containing said liquid crystal, at least said first means aligning the long axes of said molecules adjacent thereto at an angle Ω

(α

) from the normal to said first means, said angle Ω

(α

) being a predetermined function of an angle and undefined for certain values of α

, said angle α

being an angle between a reference vector in a plane parallel to said first means and a projection of said long axes of said molecules onto said plane, the distance between said first and second means being less than the distance at which said helices form in the absence of an electric field, said first and second means causing said long axes to assume one of a plurality of stable orientations.

43. A liquid crystal device comprising:

a quantity of ferroelectric liquid crystal having a plurality of adjacently disposed layers each comprised of a plurality of molecules, each molecule having a long axis, said moles of said layers in a bulk of said liquid crystal forming helices having axes perpendicular to said layers; and

first and second means, each transverse to and contiguous with said layers, for containing said liquid crystal, at least said first means aligning the long axes of said moles adjacent thereto at an angle Ω

(α

) from the normal for said first means, said angle Ω

(α

) being a predetermined function of an angle α

, said angle α

being an angle between a reference vector in a plane parallel to said first means and a projection of said long axes of said molecules onto said plane, the distance between said first and second means being less than the distance at which said helices form in the absence of an electric field, said first and second means causing said long axes to assume one of a plurality of stable orientations, said first and second means also for inducing splay in the polarization field of said liquid crystal homogeneously over at least a substantial portion of said first and second means.

44. A liquid crystal device comprising:

a quantity of ferroelectric liquid crystal having a plurality of adjacently disposed layers each comprised of a plurality of molecules, each molecule having a long axis, said molecules of said layers in a bulk of said liquid crystal forming helices having axes perpendicular to said layers; and

first and second means, each transverse to and continuous with said layers, for containing said liquid crystal, at least said first means aligning the long axes of said molecules adjacent thereto at an angle α

(α

) from the normal to said first means, said angle Ω

(α

) being a predetermined function of an angle α

, said angle α

being an angle between a reference vector in a plane parallel to said first means and a projection of said long axes of said molecules onto said plane, the distance between said first and second means being less than the distance at which said helices form in the absence of an electric field, said first and second means causing said long axes to assume one of a plurality of stable orientations, said second means also for aligning the long axes of said molecules adjacent thereto but not as strongly as said first means align said molecules adjacent thereto homogeneously over at least a substantial portion of said first and second means.

45. A liquid crystal device comprising:

a quantity of ferroelectric liquid crystal having a plurality of adjacently disposed layers each comprised of a plurality of molecules, each molecule having a long axis, said molecules of said layers in a bulk of said liquid crystal forming helices having axes perpendicular to said layers; and

first and second means, each transverse to and contiguous with said layers, for containing said liquid crystal, at least said first means aligning the long axes of said moles adjacent thereto at an angle 5/8(α

) from the normal to said first means, and angle Ω

(α

) being a predetermined function of an angle α

, said angle α

being angle between a reference vector in a plane parallel to said first means and a projection of said long axes of said molecules onto said plane, the distance between said first and second means being less than the distance at which said helices form in the absence of an electric field, said first and second causing said long axes to assume one of a plurality of stable orientations, said first and second means both also for inducing unsymmetric anisotropic conical conditions on said long axes but having different directions of anisotropy homogeneously over at least a substantial portion of said first and second means.

46. A liquid crystal device comprising:

a quantity of ferroelectric liquid crystal having a plurality of adjacently disposed layers each comprised of a plurality of molecules, each molecule having a long axis, said molecules of said layers in a bulk of said liquid crystal forming helices having axes perpendicular to said layers; and

first and second means, each transverse to and contiguous with said layers, for containing said liquid crystal, at least said first means aligning the long axes of said moles adjacent thereto at an angle Ω

(α

) from the normal to said first means, said angle Ω

(α

) being a predetermined function of an angle α

, said angle α

being an angle between a reference vector in a plane parallel to said first means and a projection of said long axes of said molecules onto said plane, a selected substantial portion of said first means aligning said long axes more strongly than the remainder of said first means in a predetermined manner, the distance between said first and second means being less than the distance at which said helices form in the absence of an electric field, said first and second means causing said long axes to assume one of a plurality of stable orientations.

47. A liquid crystal device comprising:

a quantity of ferroelectric liquid crystal having a plurality of adjacently disposed layers each comprised of a plurality of molecules, each molecule having a long axis said molecules of said layers in a bulk of said liquid crystals forming helices having axes perpendicular to said layers; and

first and second means, each transverse to and contiguous with said layers, for containing said liquid crystal, at least said first means aligning the long axes of said molecules adjacent thereto at an angle Ω

(α

) from the normal to said first means, said angle Ω

(α

) being a predetermined function of an angle α

, said angle α

being an angle between a reference vector in a plane parallel to said first means and a projection of said long axes of said molecules onto said plane, the distance between said first and second means being less than the distance at which said helices form in the absence of an electric field, said first and second means causing said long axes to assume one of a plurality of stable orientations, said molecules and at least said second means each having polarization vectors, coupling between said polarization vectors being sufficiently weak to enable switching between a plurality of stable states while favoring certain of said stable states.