Improving the electro-optical properties of bistable reflective cholesteric liquid crystal displays

We have improved the electro-optical properties of a bistable cholesteric liquid crystal display (Ch-LCD) that is driven by a 3+2 dynamic driving scheme (3+2 DDS). The best contrast ratio is achieved at the selection period of 1.2-1.5 ms/line and the temperature range 26-30°C. The suitable preparation period and evolution period for contrast ratio are 40 times and 20 times the selection time, respectively. In the 3+2 DDS, rubbing the homeotropic alignment layer increases reflectivity of the ON state and keeps the reflectivity of the OFF state at the same level, so reflectivity and contrast ratio alike increase as a result. However, in a delayed homeotropic reset driving method, when the homeotropic alignment layer is rubbed, the reflectivity of both the ON and OFF states increases, thus the contrast ratio decreases. The combination of driving method and aligned surface morphology influences the relaxation mechanism in the cholesteric texture. By optimizing panel condition, we have demonstrated an 8.4' foldable VGA Ch-LCD that exhibits high reflectivity and contrast ratio with an addressing speed of around 1.2 ms/line.