Evaluation technique of cell thickness, pretilt angle, and twist angle for guest-host liquid crystal displays

In this study, we demonstrated the evaluation of the device parameters, such as the cell thickness d, pretilt angles at the top and bottom substrates θ0 and θd, and twist angle φt for the guest-host (GH)-type electrically controlled birefringence (ECB) and twisted nematic (TN) modes, using the renormalized transmission ellipsometry (RTE). In the proposed technique, the extended Cauchy equation and the extinction coefficients for the ordinary and extraordinary rays based on the three Gaussian functions were employed as a description of the dielectric function. As a result, the numerically calculated phase difference Δ and angle of amplitude ratio Ψ determined using the proposed technique provided good agreement with the measured Δ and Ψ by introducing the extinction coefficient to the RTE. Furthermore, the device parameters for the GH-ECB and the GH-TN cells were obtained. It was confirmed that the extinction coefficient should be taken into consideration in an analysis of GH liquid crystal displays.