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Abstract
Like other fields that rpidly change from academic to commercial interest, therest, there is a need for standardization of nomenclature in liquid crystal technology. A case in point involves the interpretative features of the transmittance vs. voltage curves for 90[ddot] twisted field effect LCDs. It will be shown that a semi-logarithmic plot is far superior to the linear plot. Considerations must be given to the pronounced interferences that are introduced by internal reflection at the electrodeliquid crystal interfaces when using monochromatic light. Measurements should be made with polars both crossed and parallel.
The features of these plots that have offered varying definitions and measurement details are: (1) zero field transmittance, (2) threshold or critical voltage, (3) interference fringes, (4) 90% turn-on voltage, and (5) saturation voltage. The usual practice of attributing threshold voltage solely to elastic constants and dielectric anisotropy overlooks the dominating factor of surface director tilt. Logarithmic plots quickly reveal the fallacy of the saturation voltage parameter. Transmittance can be shown to continuously change at vltage greater than 4 times the 90% turn-on voltage.