Chris Colpaert

Adequate measuring techniques for ions in liquid crystal layers

Abstract The ion contamination in twisted nematic liquid crystals should be limited to assure good electro-optical performance of AM-LCDs. Today, pure liquid crystal mixtures are produced, though little information is available on long term stability, and on the kind of ions that contaminate the liquid crystal. The first step in the determination of the ion source is the development of an appropriate measuring technique that characterizes the ions in the liquid crystal. In this article such a new method is proposed. A comparison with former techniques is made.

Transient leakage current in nematic LCDs

Abstract In this paper we present the transient leakage current measurement method for nematic liquid crystal displays as a technique to obtain information on the mobility and concentration of ionic impurities. The mobility depends on the temperature according to an Arrhenius-type relation, with an activation energy of about 0·3 eV. This dependence can be explained through the variation of the LC viscosity with temperature. The transported charge has also an Arrhenius relation, with an activation energy around 0·2 eV. Additionally, the influence of both a heat treatment and UV illumination on these parameters was investigated.

Influence of ionic contaminations on SSFLCD addressing

Abstract In this paper a theoretical SSFLCD switching model is presented which focuses on the calculation of the internal electric field. Using this model we can investigate the joint dynamics of the FLC reorientation and charge carrier transport inside the LC-layer with or without applied voltage. We give some results on charge separation and addressing problems.

A Simple Numerical Transmission Model for General LCD-Configurations

Abstract The transmission of a LCD for normal incident light can be simply calculated by a clever use of the Jones calculus. Several cases are treated in different ways. The results for a few examples are compared with the more general simulations according to the 4 × 4 Berreman method, which also takes internal reflections into account. Our fast optical calculations are useful when predicted molecular distributions should be confronted with experimental optical spectra.