Reduction of residual DC voltage via RC matching in LCD

Abstract

To reduce the residual direct-current (DC) voltage in liquid-crystal display (LCD) using the polymer-stabilized vertical-alignment (PS-VA) mode, the electrical time constant of two or more serially connected dielectric materials, such as liquid crystals (LCs) and silicon nitride (SiNx), is investigated. PSpice simulation of the alternating-current (AC) voltage changes in the two dielectric materials shows mismatch of the time constant, and a resistance cross capacitance (RC) between the two layers is found to be the source of the residual DC voltage. The optimization of the stoichiometry of SiNx is effective for matching the time constant of LCs because it is easy to control the time constant by changing the gas ratio, e.g., SiH4, N2, and NH3, when SiNx is deposited. We suggest that image sticking in the LCD panel can be minimized via RC optimization between the SiNx and LCs by adjusting the stoichiometry of SiNx, which means that the chronic problem of off-axis gamma distortion in the VA mode for large sized, high-resolution TV up to Quad Ultra High Definition (QUHD, 15360 x 8640) can be solved.