Field-Induced Alignment of Ferroelectric Liquid Crystal with the Phase Sequence of N*-SmC* in an Uniform External Electric Field

Abstract

We proposed a new field-induced alignment method for a ferroelectric liquid crystal (FLC) which exhibited chiral nematic (N*) to smectic C* (SmC*) phase transition. Homogeneous alignment for the FLC with the phase sequence of N*-SmC* can be obtained by applying an electric field to the cell at the temperature 2-3°C higher than the N*-SmC* phase transition temperature. Conventionally, the electric field is applied through indium-tin-oxide (ITO) electrodes, which is located inside of the cell, during alignment process. However, it is difficult to apply this alignment process to mass production of thin film transistor liquid crystal display (TFT-LCD) panels, where these electrodes are shielded by drive ICs after module process. In addition, the alignment of TFT-LCD panel would be destroyed by an external shock, which could not be restored afterwards. We examined the field-induced alignment states of FLC in test cells and TFT-LCD panels by putting those into an uniform electric field. We found that each test cell had a different characteristic electric field for alignment which was dependent on the spontaneous polarization. From the comparison between the TFT-LCD panel and test cell, these two exhibit different electric fields for alignment. These results were analyzed by the equivalent circuit modeling, which revealed that the alignment voltage to supply the same electric field on LC was higher in LCD panels than in test cells, even though the same liquid crystals were used for the two.