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

Abstract

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 $\Delta \varepsilon$ 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 ${\rm V}_{\rm com}$ -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 $(C_{\rm dp})$ 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 $({\rm V}_{\rm GL})$ . Consequently, because of higher transmittance and stable crosstalk, the proposed POT structure with nLC can be used for mobile displays.