Mitsuru Ikezaki

Threshold Voltage Biased E-Mode TN LCD—Optimum Optical Design for Grayscale Application

Abstract In a normally white (NW) twisted nematic (TN) liquid crystal displays (LCDs), there are two optical eigenmodes, an extraordinary-ray mode (e-mode) and an ordinary-ray mode (o-mode). With zero or a low-bias voltage as the brightest state of the display, both eigenmodes have insufficient display performance for the analog grayscale application. The former has a large color change as a function of viewing zone. The latter has quite a narrow horizontal viewing zone. By applying a threshold voltage as a bias to represent the brightest level of the e-mode NW, the optical performance in the vertical viewing zone was much improved. Further optimization of the d*delta-n for this mode of operation resulted in a small color change and a wide viewing zone by choosing d*delta-n = 0.47 micrometers. We conclude that the threshold-voltage biased e-mode NW of the first-minimum thin-film-transistor (TFT) driven TN can achieve a wide viewing angle for analog-grayscale applications.