Liquid crystal cells – elements and systems – With specified nonchemical characteristic of liquid crystal... – Within nematic phase
Reexamination Certificate
1998-09-14
2001-12-04
Malinowski, Walter J. (Department: 2164)
Liquid crystal cells, elements and systems
With specified nonchemical characteristic of liquid crystal...
Within nematic phase
Reexamination Certificate
active
06327017
ABSTRACT:
BACKGROUND
The present invention relates to the field of liquid-crystal-based display devices.
More precisely, the present invention relates to the field of display devices having a bistable effect.
Liquid-crystal-based display devices have already given rise to a vast literature.
Mention may be made for example, in a non-limiting manner, of the following documents:
(1) Europhysics Letters (25) (7), p 527-531 “Critical Behaviour of a Nematic-Liquid-Crystal Anchoring at a Monostable-Bistable Surface Transition” by M. Nobili et al.;
(2) J. Phys. II France 5 (1995), p 531-560 “Surface Walls on a Bistable Anchoring of Nematic Liquid Crystals” by M. Nobil et al.;
(3) Liquid Crystals 1992, vol. 12, No. 3, p 515-520 “Dynamics of surface anchoring breaking in a nematic liquid crystal” by A. Gharbi et al.;
(4) Liquid Crystals 1991, vol. 10, No. 2, p 289-293 “Flow induced bistable anchoring switching in nematic liquid crystals” by R. Barberi et al., which describes bistable-anchoring devices;
(5) Appl. Phys. Letters 55 (24) “Electrically Controlled surface bistability in nematic liquid crystals” by R. Barberi et al., which describes bistable-anchoring devices;
(6) Appl. Phys. Letters 60 (9) “Flexoelectrically controlled surface bistable switching in nematic liquid crystals” by R. Barberi et al.;
(7) Appl. Phys. Letters (62) (25) “Intrinsic multiplexability of surface bistable nematic displays” by R. Barberi et al.,
(8) Appl. Phys. Letters 40 (11) “A Multiplexible bistable nematic liquid crystal display using thermal erasure” by G. D. Boyd et al.;
(9) Appl. Phys. Letters 37 (12) “Threshold and switching characteristics of a bistable nematic liquid-crystal storage display” by Julian Cheng et al.;
(10) Appl. Phys. Letters 36 (7) “Liquid-crystal orientational bistabillity and nematic storage effects” by G. D. Boyd et al.;
(11) J. Appl. Phys. 52 (4) “Boundary-layer model of field effects in a bistable liquid-crystal geometry” by J. Cheng et al.;
(12) J. Appl. Phys. 52 (4) “The propagation of disclinations in bistable switching” by J. Cheng et al.;
(13) J. Appl. Phys. 52 (2) “Surface pinning of disclinations and the stability of bistable nematic storage displays” by J. Cheng et al.;
(14) Appl. Phys. Letters 40 (12) “A nematic liquid crystal storage display based on bistable boundary layer configurations” by J. Cheng et al.;
(15) App. Phys. Letters 43 (4) “Discovery of DC switching of a bistable boundary layer liquid crystal display” by R. B. Meyer et al.;
(16) J. Appl. Phys. 56 (2) “Physical mechanisms of DC switching in a liquid-crystal bistable boundary layer display” by R. N. Thurston et al.;
(17) J. Appl. Phys. 53 (6) “Optical properties of a new bistable twisted nematic liquid crystal boundary layer display” by R. N. Thurston et al.;
(18) J. Appl. Phys. 52 (4) “New bistable liquid-crystal twist cell” by D. W. Berreman et al.;
(19) Appl. Phys. Letter 37 (1) “New bistable cholesteric liquid-crystal display” by D. W. Berreman et al.;
(20) Asia Display 95 “A bistable Twisted Nematic (BTN) LCD Driven by a Passive-Matrix Addressing” by T. Tanaka et al.;
(21) J. Appl. Phys. (59) (9) “Fast switching in a bistable 270° twist display” by H. A. Van Sprang.
SUMMARY
The abovementioned documents essentially concern studies relating to the breaking of bistable anchorings, to anchoring energies and to changes of state induced by the propagation of defects.
The object of the present invention is to improve liquid-crystal display devices in order to make it possible to obtain a novel bistable effect.
This object is achieved according to the present invention by virtue of a display device comprising two parallel transparent plates provided with transparent electrodes on their internal surfaces and containing a liquid-crystal material, characterized in that the device comprises:
means defining a monostable anchoring on each plate;
means capable of breaking, on command, at least one of these anchorings; and
means capable of inducing, after this breaking, a bistable volume effect in the absence of an electric field.
These two volume textures, which maintain a stable state in the absence of an external electric field, must be compatible with the monostable anchorings on the plates.
According to one particular embodiment;
the plates define different anchoring thresholds (these anchorings may be, for example, planar or homeotropic);
the thickness of the device between the two plates is sufficiently small to allow hydrodynamic coupling between the internal surfaces of these plates; and
means are provided which are capable of applying, between the electrodes of the two plates, alternately a write electric field pulse above a threshold capable of breaking the anchorings on the two plates in order to define, after interruption of this electric field, a twisted first stable state resulting from hydrodynamic coupling between the two plates, and a second electric field below the said threshold capable of breaking a single anchoring or having a falling edge which varies slowly in order to decouple the tilts on the two plates, so as to define a homogeneous second stable state.
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Liquid Crystals, Aug. 1991, U.K. vol. 10, No. 2, pp. 289-293 “Flow Induced Bistable Anchoring Switching In Nematic Liquid Crystals”.
Journal of Applied Physics, Apr. 1981, vol. 52, No. 4.
Applied Physics Letters, Dec. 11, 1989 vol. 55, No. 24.
Applied Physics Letters, Mar. 2, 1992, vol. 60, No. 9.
Barberi Ricardo
Dozov Ivan
Durand Georges
Giocondo Michele
Lelidis Ioannis
Blakely Kokoloff Taylor & Zafman
Malinowski Walter J.
Nemoptic S.A.
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