Patent ID: 7224417

Claim:
A nematic bistable display device comprising: a nematic liquid-crystal layer ( 10 ) placed between two plates( 20 , 30 ) provided with electrodes ( 22 , 32 ) and with anchoring means ( 24 , 34 ) which ensure monostable surface anchoring states of the liquid crystal ( 10 ) defining two stable textures without electrical field, one texture having the liquid crystal molecules mainly parallel and the other texture having a twist about +/−180° from one plate to the other, along a direction normal to the plates, the symmetry and the force of at least one of the anchoring states allowing the anchoring to be broken in an electric field perpendicular to the plates( 20 , 30 ); means ( 40 ) for applying an electric field to the liquid crystal, between the two plates ( 20 , 30 ), and for breaking the anchoring to at least one of the surfaces, with a transient passage of the surface director parallel to the field and relaxation after the field has been cut off towards one or other of said two stable textures, which differ from each other by a 180° twist from one plate to the other, along a direction normal to the plates, and are both compatible with monostable anchoring states; wherein it furthermore includes: control means ( 40 ) for producing, after the anchoring has been broken, hybrid textures in which the said two stable textures coexist in a controlled proportion in a pixel, one texture corresponding to a bright state, the other corresponding to a dark state, a grey state value being proportional to the density in each bright and dark states, the said textures being separated by 180° disclination lines in the volume or by 180° reorientation walls on one of the surfaces; and means ( 40 ) for then applying on the liciuid-crystal layer electric pulses to stick all the 180° disclination lines to the surface by transforming the 180° disclination lines into 180° reorientation walls, for long-term stabilization of the hybrid textures by immobilization of these 180° reorientation walls on the surface.