Electrooptical Properties of Vertically Aligned Twisted Nematic Cells with Negative Dielectric Anisotropy

Two types of vertically aligned twisted nematic (VATN) liquid crystal (LC) cells in which a chiral nematic LC with negative dielectric anisotropy is used are proposed. In one type of the VATN cells, both substrate surfaces are treated by rubbing to obtain a slight tilt angle from the normal of each substrate, and in another one, only one substrate surface is treated by rubbing. In this study, some electrooptical properties are investigated experimentally and by simulations. Similar T–V characteristics were obtained for both types of cell in which d/P 0≈0.5 (ratio of the cell thickness to the equilibrium value of the chiral pitch). It is shown that these cells exhibit a good colorless black–white display image. The threshold voltage of VATN cells is expressed by π√{1-4(K 22/K 33)2(d/P 0)2}K 33/(ε 0 ∣Δε∣).