高分子穩定型強誘電性液晶配向與光電特性探討

Development of Uniform Alignment and V-Shaped Switching in a Polymer Stabilized Ferroelectric Liquid Crystal Cell

陳文旭(Wen-Hsu Chen)

指導教授 ： 吳俊傑 ； 陳殿榮

國立臺北科技大學/電資學院/光電工程系研究所/碩士(2009年)

摘要

本研究探討高分子穩定型強誘電性液晶的配向與光電特性，實驗上主要分為二部份：(1) 高分子對強誘電性液晶配向的影響；(2)無PI垂直配向液晶盒結構，來加以探討。
首先，不具有SmA相的FLC材料，在N*-SmC*相轉移過程中，由於表面電傾效應的影響，液晶分子排列上會與rubbing方向產生一個夾角，因此層會朝著相反方向作傾斜，造成缺陷的產生。實驗中，我們將高分子FLC穩定在N*相，並外加交流電場，使液晶分子達到解旋狀態，作規則性排列，且因電場的牽制作用，降低熱擾動的現象，同時照射UV光。當FLC從N*相轉移至SmC*時，液晶分子由於受到高分子網的束縛，故表面電傾角度減小，且domain分佈縮小，因此巨觀上，呈現均勻配向的效果。另外，在無PI的液晶盒中，我們將具有SmA相的FLC材料加熱至N*相，同時外加20V交流電場，使液晶呈現垂直排列。再將其降溫穩定於SmA相，同時照射UV光。當FLC相轉移至SmC*時，由於高分子網穩定住液晶層的結構，因此液晶層不會產生崩塌現象，達到無PI垂直配向的效果。
整體上，我們利用高分子網穩定液晶分子的特性，達到均勻配向的效果，並呈現V shaped 的光電特性，具灰階顯示能力。此外，亦成功製造無PI垂直配向的液晶盒，由於省略高溫烘烤PI的步驟，因此可降低對塑膠基板產生的破壞，運用到可撓式面板上。

關鍵字

強誘電性液晶 ； 表面電傾效應 ； 配向 ； 無PI垂直配向

並列摘要

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.

並列關鍵字

Ferroelectric Liquid Crystal ； Surface Electroclinic Effect ； Alignment ； Polyimide Free Cell

參考文獻

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[8] Chenhui Wang, Control of Layer Defects in Smectic C* Ferroelectric Liquid Crystal Devices, Ph.D. Thesis, Kent State University, U.S.A, 2003.