Quantitative Analysis of Cell Gap Margin for Uniform Optical Properties Using In-Plane Switching of Liquid Crystals

The allowable range of marginal variation of the cell gap to ensure uniform optical properties when using in-plane switching (IPS) of liquid crystals was evaluated quantitatively. The analysis yielded relationships of transmittance into the cell gap in bright, selected bright and selected intermediate states. The selected state was defined as the state in which a particular constant voltage was applied to the liquid crystals to obtain the desired state in a series of evaluations for different cell gaps. The relationships were used to evaluate normalized variations of transmittance (|ΔT/T|) corresponding to the difference in the cell gap from the optimal value (Δd), and the variations were compared with those in the twisted and supertwisted nematic modes. As a result, the marginal variation for a uniform display using the IPS of liquid crystals was quantitatively confirmed to be much narrower than that in the twisted nematic mode. In the selected bright state, the variation was between those of the twisted and supertwisted nematic modes, while it was comparable to the cell gap margin of the supertwisted nematic mode in the intermediate state; i.e., the variation of ±0.1 µ m in the twisted nematic mode corresponded to that in a range of ±0.02 to ±0.04 µ m in the IPS mode.