Optically isotropic liquid crystals for next-generation displays

Abstract

LCDs have become indispensable in our daily lives. They are used everywhere, such as in cell phones, computers, television sets, and data projectors. Based on continuous innovation, their overall display quality has reached a satisfactory level. Viewingangle restrictions are no longer an issue following implementation of multidomain structures and phase-compensation films, their contrast ratio has exceeded onemillion to one through local LED-backlight dimming, and sunlight washout has been overcome by employing transflective displays. LCD technology is, thus, relatively mature. However, some challenges still remain, including their relatively slow response time. This causes image blur for fast-moving objects and holds back adoption of colorsequential displays, which promise to triple light efficiency and resolution density. Much effort has been devoted to improving LCD response times. With continuously improving low-viscosity liquid-crystal (LC) properties, device configuration, and driving methods, the response time has been reduced to 2–5ms.1 However, it is still not fast enough to eliminate the color breakup observed in colorsequential displays. Suppressing this phenomenon requires LC response times of less than 1ms. To achieve this goal, optically isotropic LC is emerging as a potential next-generation display technology. A conventional, nematic LC turns isotropic when the temperature exceeds the clearing point. Within a few degrees above the nematic-isotropic transition temperature, LCs can still be controlled by an electric field and exhibit 100ns response time.2 However, the remaining phase is too small and the required operating voltage too high for display applications. By introducing a certain amount of chiral dopant and polymers into a LC host, polymer-stabilized LC composites can be made optically isotropic over a reasonably wide temperature range.3 Compared to conventional, nematic LCDs, this new optically isotropic LC exhibits several advantages. First, the system can be Figure 1. Optically isotropic liquid crystals (LCs) in an in-planeswitching electrode cell. Left/right: Voltage-off/on. P: Polarizer. A: Analyzer. E: Electric field.