Pixel Design Optimization of Fringe-Field Switching Mode for Applying Negative Liquid Crystals in High-Resolution Mobile Displays

We demonstrate an optimized fringe-field switching pixel structure to apply negative liquid crystals (nLCs) for high-resolution mobile displays. Pixel transmittance can be improved by applying nLCs, but the driving voltage increases because Δε of the nLC is lower than that of the positive LC (pLC). In spite of applying an nLC, a similar driving voltage can be achieved by changing the pixel structure. It is easy to obtain a low driving voltage in a strong electric field by applying a thinner passivation layer using photo acryl (PAC). In addition, while the edge electrodes of the conventional Vcom-on-top (VOT) structure are operated with in-plane switching, all electrodes of the pixel-on-top (POT) structure are operated with fringe-field switching. Therefore, the driving voltage can be reduced by applying a POT structure with PAC. Furthermore, crosstalk can be improved because the capacitance (Cdp) between data lines and pixel electrodes is reduced by applying a POT structure. As a result, applying the proposed structure with nLC has two advantages. First, transmittance increases by more than 20% based on 4.5-in-high definition pixels. Second, crosstalk in the POT structure is more stable than that in the VOT structure, despite variations in low gate voltage (VGL). Consequently, because of higher transmittance and stable crosstalk, the proposed POT structure with nLC can be used for mobile displays.