Transport properties of ions in ferroelectric liquid crystal cells

Abstract

The transient ionic current in a ferroelectric liquid crystal (FLC) cell was measured as a function of applied voltage at different temperatures. The measured current shows a delay peak which decays rapidly to a steady-state value. The steady-state current exhibits a thermal activated behavior with an activation energy of 0.94 eV, and depends exponentially on the square root of the field strength similar to the Schottky effect. To describe the transport behaviors of the ions, a model with ionization-recombination equations which include a field-dependent ionization coefficient, and a continuity equation for the accumulated surface charges has been introduced. According to the model, the current decay time and the peak position of the delay peak current can be used to determine the ion mobility. Two ionized species have been identified in the FLC medium: a weakly ionized species with a relatively constant mobility of 2.0×10-7 cm2/V·s, and a highly ionized species with a room temperature mobility of 4.1×10-7 cm2/V·s and a thermal activation energy of about 0.71 eV. Detailed calculation of the ionic current and comparison with experimental results are given. © 1989 The Japan Society of Applied Physics.