Effect of small liquid crystal molecules on the driving voltage of cholesteric liquid crystal displays

Abstract

In order to achieve a lower driving voltage of a cholesteric liquid crystal display (Ch-LCD) we formulated new nematic liquid crystal mixtures with dopants. The interesting thing is that the driving voltage is decreased more by adding the low molecular weight of liquid crystal materials in the cholesteric mixtures without decreasing its reflectivity. The cholesteric mixture is optimized by adding 20 wt% of CN-007 enough to drive the display, necessary for using a commercial STN driver. Homogeneous alignment layers provide a higher reflective panel because of stabilizing the planar texture of cholesteric liquid crystal, while homeotropic alignment layers provide a higher contrast ratio because of stabilizing focal-conic structure. The rubbing condition depending on the driving scheme also affects the panel properties. The combination of the panel structure and the process condition of cholesteric mixtures make the Ch-LCD high reflectivity and contrast ratio. Two 5.7 in. VGA monochromic cholesteric reflective liquid crystal displays with a high resolution like this folding type are demonstrated using a STN driver.