Patent ID: 8085370
Filing Date: 2011-12-27
Classification: G02F

Abstract:
1. A bistable twisted nematic (πBTN) liquid crystal display device comprising a liquid crystal layer ( 150 ) of thickness d, birefringence Δ n and retardation Δnd, said liquid crystal layer being situated between two substrates ( 120 , 180 ) and between a polarizer ( 100 ) and a reflector ( 200 ), said liquid crystal layer ( 150 ) in the absence of an applied electric field having two stable uniformly twisted textures, the twists of the two stable textures differing by an angle being equal mainly to 180°, and at least one compensation layer ( 110 ) positioned between said polarizer ( 100 ) and said reflector ( 200 ), said compensation layer ( 110 ) being composed of at least one birefringent film, said birefringent film having an optical anisotropy defined by three characteristic refractive indices nx, ny, nz, along three corresponding axis x, y, z of index ellipsoid, x and y being situated inside the substrates plane, nx and ny being called in plane indices, with nx≧ny, x being called slow axis, and z being perpendicular to the substrates plane ( 120 , 180 ) with biaxiality parameter Nz equal to (nx−nz)/(nx−ny), characterized in that Nz lies between −∞ and ½ so that under oblique viewing the retardation of the stable texture corresponding to the dark state is compensated to improve the contrast ratio and simultaneously the retardation of the stable texture corresponding to the bright state is modified to decrease the color shift.