BISTABLE CHOLESTERIC REFLECTIVE DISPLAYS: Materials and Drive Schemes

Cholesteric liquid crystals possess a helical structure and exhibit two stable states at zero field: the planar texture and the focal conic texture. In the planar texture, they reflect circularly polarized light, whereas in the focal conic texture, they scatter light in forward directions. They can be switched from the planar texture to the focal conic texture by a low-voltage pulse and switched from the focal conic texture to the planar texture by a high-voltage pulse. The wavelength of the reflected light is easily adjusted by varying the pitch of cholesteric liquid crystals. They can be used to make reflective displays that do not need a back light and have a good readability under room-light conditions. We first review the optical properties of bistable cholesteric reflective displays and discuss the techniques used to achieve high contrast and large viewing angle. We then discuss the transitions among the cholesteric textures and the drive schemes used to address bistable cholesteric reflective displays.