Development of Uniform Alignment and V-Shaped Switching in a Polymer Stabilized Ferroelectric Liquid Crystal Cell
| Autor: | Wen-Hsu Chen, 陳文旭 |
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| Rok vydání: | 2009 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 97 Ferroelectric liquid crystal (FLC) device has some primary problems such as the formation of zigzag defects and lack of grayscale capability that limit its applications to display. In this thesis, we developed two types of FLC device, planar aligned (PA) cell for the material with N*-SmC* phase sequence and polyimide free homeotropic aligned FLC cell, showing defect free uniform alignment and V shaped electro-optical switching by using polymer stabilization (PS) method. The effect of photo-polymerization conditions on the uniformity of alignment and electro-optical characteristics in these two FLC modes are discussed. In the pure PA-FLC cell with N*-SmC* phase sequence, two types of domain are formed in random shapes and sizes that result in the formation of horizontal defects. In addition, because of the interaction between polar surface and FLC molecules, the molecules of each domain deviates an angle in opposite side with respect to the rubbing direction, making the defects more obviously. In this experiment, the photo-polymerization process of this kind of cell is carried out in the N* phase under the application of an ac electric field. Experiment results shows that the defect free uniform alignment is obtained in our proposed PS-FLC cell. It is suggested that both the deviation angle and domain size can be reduced by the formation of polymer networks. In our pervious research, we have proposed a method of forming homeotropic alignment in the FLC cell without using polyimide (PI) film. This method is suitable for flexible display application because of the unnecessary of high temperature process on baking polyimide film. When this FLC cell is driven and/or placed for a certain time, however, the stability on keeping both the molecular and layer structures are not so good that reduce its application. To solve this problem, the polymer stabilization method which is considered to have the ability in improving mechanical stability is used. In this experiment, the homeotropic alignment are formed in the SmA phase of the PI-free cell by applying ac electric field through N*-SmA phase transition. Thereafter, the photo-polymerization process with/without applying ac electric field is carried out in the SmA phase to keep the homeotropic alignment more stable. Experiment results show that both the alignment and the stability on layer structure are improved. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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