Reflective and transflective liquid crystal displays for low-power mobile applications

Abstract

We describe the main features of current reflective and transflective liquid crystal displays (LCDs) for low-power mobile applications. The reflective LCD is relatively simple but not readable in dark environment, and the transflective LCD involves complicated fabrication processes. We demonstrate two types of transflective liquid crystal displays (LCDs) in a single gap geometry to overcome these problems. One type of our transflective LCD with a single gap has multimodes based on the homogeneous alignment and the hybrid alignment, with a low helical twisting power. This multimode transflective LCD was fabricated by a single-step exposure of the ultraviolet (UV) light through an array of metal reflectors used as an amplitude photomask which gives an alternating homogeneous and homeotropic LC configuration. The single-step UV exposure produces no variations of the cell gap. In such configuration, the electro-optical disparity between the transmissive region and the reflective region was found to be significantly reduced by the low helical twisting power of the chiral dopant. Another type having a single cell gap and a single LC mode was developed using a patterned retardation layer. In this transflective configuration, a single LC mode of the 60-degree twisted nematic LC was used for both transmissive and reflective applications. The patterned retardation layer was fabricated using a reactive mesogen by photo-patterning. The measured electro-optic characteristics of the single mode transflective LCD agree well with numerical simulations.