Effects of alignment layer on pretilt angle and electrical characteristics for the photo-aligned twisted nematic cell on polyimide surfaces

The alignment layer effects on the pretilt angle generation and electrical characteristics of photoaligned twisted nematic (TN)-liquid crystal displays (LCDs) for a polyimide (PI) surface with side chains were studied. The generated pretilt angle of nematic liquid crystal (NLC) on the rubbed PI surface with one layer was almost the same as that on the PI surface with two layers. However, the generated pretilt angle of NLC on the photoinduced PI surface with two layers was larger than that on the PI surface with one layer generated by oblique UV exposure on the PI surface. The different mechanisms of pretilt generation in NLC in the rubbing- and photoalignment methods were examined. The pretilt angle of the NLC on the photoinduced PI surface is attributed to surface roughness and side chains due to photodissociation of the polymer with UV exposure on the PI surface. We observed the same characteristics of voltage-transmittance (V-T) and response time for one and two layers on the PI surface. We also observed the same voltage holding ratio (VHR) characteristics for one and two layers on the photoaligned TN-LCD. Finally, we suggest that the VHR of photoaligned TN-LCDs was higher than that of the rubbing-aligned TN-LCDs.