Non-Contact Liquid Crystal Alignment by Using ZnO Films
Chia-Chun Liu1*, Chieh-Lun Lee1, Fung-Jie Guo2, Shie-Chang Jeng3
1Institute of Lighting and Energy Photonics, National Chiao Tung University, Tainan, Taiwan
2Institute of Photonics System, National Chiao Tung University, Tainan, Taiwan
3Institute of Imaging and Biomedical Photonics, National Chiao Tung University, Tainan, Taiwan
* presenting author:Chia-Chun Liu,
Applications of inorganic ZnO films for aligning liquid crystals (LCs) are very promising for LCD systems operated in severe conditions, where a highly durable material is needed. In this work, the process of dip-coating was applied to form the ZnO films for liquid crystal alignment. A solution of zinc acetate dihydrate (0.2854 g, 1.3 mmol) in 130 mL of isopropanol was stirred vigorously at 120 °C for 10 minutes. 2-(Dimethylamino)ethanol (0.1158 g, 1.3mmol) was slowly added to the above solution and stirred at the same temperature for an additional 2 hours to form a homogeneous precursor solution. The ITO glass substrate was withdraw vertically from the prepared-solution. The as-prepared film was annealed at 200 ℃ in air for 90 minutes to form a ZnO thin film. The antiparallel LC cells were fabricated with a ~5 um mylar spacer and filled with LC molecules. The photographs of the vertically-aligned LCD (VA-LCD) observed by POM with the crossed polarizers are shown in Fig. 1. The uniform dark state images indicate that LC molecules are aligned perpendicularly to the ZnO films. The voltage-dependent optical transmittance of the VA-LCD is shown in Fig. 2. The results show that the threshold voltage is around 2.2 V, which is close to the theoretical value. The comparison of electro-optical properties between polyimide and ZnO alignment films will be conducted in the near future.

Keywords: dip, alignment, ZnO