With improvements in quality and performance, the liquid crystal display (LCD) has spread into a wide variety of applications, including PCs, PDAs and TVs.   A crucial element in the design of high-performance LCDs is the precise control of the distribution of liquid crystal alignment.    Given the fact that the surface alignment of a liquid crystal is generally determined by the anchoring strength, it has become increasingly important to achieve a high-precision measurement and an evaluation method of the anchoring strength.   In particular, with an increase of popularity of VA-mode LCDs, evaluation of the polar anchoring strength has become important.   The surface polar anchoring strength is one of the most crucial elements which govern the response property of VA-mode LCDs, therefore, a quantitative evaluation of the relation between the anchoring strength and the response property of the liquid crystal is an extremely important problem.

We devised a new measurement method: the Psi Delta HAN cell (PDH) method, for the surface polar anchoring strength using a hybrid alignment nematic liquid crystal (HAN) cell.    In the PDH method, the alignment distribution of a liquid crystal is determined from the numerical fitting of experimental values of the angular dependence of the amplitude ratios and the phase differences that is measured in the perpendicular direction to the alignment plane and that of theoretical values.   The measurement results of cell gap dependences of the polar anchoring strengths B0 and Bd at the interfaces of a parallel alignment layer and a perpendicular alignment layer are respectively shown in Fig.1.   The polar anchoring strengths are constant to the cell gap, therefore, we conformed the validity of PDH method.   We also discussed the relation between the polar anchoring strength at the vertical interface and the response property of the VA mode liquid crystal cell.

Fig.1 Cell gap dependences of the polar anchoring strength B0 and Bd.