A New BTN LCD with High Contrast Ratio and Large Cell Gap

The optical properties of a (0, 2π) transmissive BTN LC cell is optimized by parameter space method. Experimentally the high contrast ratios above 80 within -80° to 80° viewing angle ranges were first obtained. The highest contrast ratio is 250. The large d∆n makes this new BTN large cell gap and low operating voltage possibility. Introduction Bistable twisted nematic (BTN) liquid crystal displays (LCD) that could be switched between two metastable twist states using an electrical pulse was discovered by Berreman et al in 1981. A 0 to 2π bistability was demonstrated in that paper. Recently, Tanaka et al developed a driving method for passivematrix addressing of such BTN displays. This high performance LCD rekindled much interest in BTN LCD. Because of its bistability, the BTN LCD can be driven with the behaviour of an active matrix display, without any cross talk problems associated with passive multiplexing. Another advantage of BTN is that since both bistable twist states of BTN have in plane alignment, the viewing angle of a BTN is much better than TN and STN displays. In some sense, the BTN is actually similar to the wide viewing angle in-planeswitching mode LCD. For (0, 2π) BTN LCD developed by Tanaka et al have lots of advantages, such as high contrast, vide viewing angle and fast response time. But due to d∆n= λ/2, the cell gap must be selected about 2 μm, and such thin cell gap is very difficult to performance industry fabrication. On the other hand, the low ∆n is responding to low ∆ε which results in high driving voltage and increasing cost. In this paper, the optical properties of a (0, 2π) transmissive BTN LC cell is optimized by parameter space method. The new optimized BTN cell experimentally obtained higher contrast ratio within wide viewing ranges than the BTN cell reported by Tanaka. The lager d∆n makes the new BTN cell larger cell gap and lower operating voltage.