In this paper, we first investigated the degradation of the performance of liquid crystals display (LCD) units after driving by a DC bias. Missed segments were found in the test LCD units. By carefully investigating the alignment layer and ITO layer separately, an explanation of the ITO failure is proposed: voltages applied to the liquid crystal cell causes accumulation of charged impurities or ions, resulting in a decomposition reaction of ITO in regions where segment and common planes overlap and there are scratches on the PI layer. Consequent, missing segments in the corresponding regions is generated.
To prevent this kind of degradation, we studied the correlation between the alignment layer and ions adsorption. Both organic alignment layer (PI2555, SE1211, and FPI) and inorganic alignment layer (SiOx, SiO2, and Al203) are analyzed by residual DC and voltage holding ratio measurement. A correlation between ion adsorption and the dielectric constant of the alignment layer is demonstrated. Alignment layer with a smaller dielectric constant is good for reducing ion adsorption in the alignment layer. Alignment layer with a bigger dielectric constant is good for reducing mobile ions in the LC device, and could be used in non-active areas of the liquid crystal device to remove ion from the active area.