ANALYSIS ON THE ELECTRO-OPTICAL CHARACTERISTICS OF FILM-TYPE LOW TWISED NEMATIC LIQUID CRYSTAL DISPLAYS (FLTN-LCDS)

초록

Low Twisted Nematic-Liquid Crystal Displays (LTN-LCDs) are expected to be used widely in the liquid crystal displays because of their low threshold voltage, sufficiently large gray-scale capability for full color displays, and wide viewing angles compared with the conventional TN-LCDs1). However, the LTN-LCDs are known to have some serious problems such as a low contrast ratio and a little colorization at a half tone state. To overcome these problems, film-type LTN-LCDs (FLTN-LCDs) were introduced by using retardation films2,3). In this study, we noticed the fast response time of the FLTN-LCDs and analyzed the effect of various design and material parameters on the response time by using a rigorous simulation method. In calculating the dynamic molecular profiles of liquid crystals, we adopted the Erickson-Leslie theory, neglecting the inertial moment of molecules and applied the Gibbs free energy density. For the calculation of an optical transmission, we used the 4´4 matrix method suggested by Berreman. As the results, it was clarified that the FLTN-LCDs show more than several times faster decay time than the TN-LCDs. The response time becomes fast with decreasing the twisting angle but becomes constant under some range of the twisting angle. Moreover, the response time is markedly reduced to 10 msec or so with decreasing a cell gap according to the optimum condition of Dnd. We also present the optimum design conditions of the FLTN-LCDs to realize high contrast ratio, wide viewing angle, good gray-scale capability and negligible inherent colorization.