研究具有N*-SmC*相順序之強誘電性液晶形成雙穩態且均勻配向之機制

Development of Defect-Free and Bistability in a Ferroelectric Liquid Crystal Cell with N*-SmC* Phase Sequence

黃舒鈺(Su-Yu Huang)

指導教授 ： 陳殿榮 ； 吳俊傑

國立臺北科技大學/電資學院/光電工程系研究所/碩士(2008年)

摘要

具有SmA-SmC*相轉移的FLC材料，可利用特定表面配向層及控制液晶的預傾角及自由能，在表面穩定的條件下，液晶分子形成UC1及UC2的排列，達到無缺陷且雙穩態的強誘電性液晶顯示器。另一方面，針對具有N*-SmC*相轉移順序的FLC而言，由於表面電傾效應的影響，液晶分子會偏離rubbing方向做排列且由於其自發極化指向有兩個選擇性，因此層傾斜方向相反造成缺陷的產生。在驅動方面，液晶分子初始的排列皆接近rubbing方向使得分子只有一個穩定態。所以即使在表面穩定的條件下，仍然是單穩態的驅動。
本實驗利用強誘電性液晶在N*-SmC*相轉移的過程中，施加一交流電場，經由改變電場振幅與頻率控制液晶分子偏離rubbing軸的角度，製作一均勻配向且具有雙穩態特性的強誘電性液晶盒。實驗中，經由偏光顯微鏡的觀察與電壓-穿透率曲線的量測，探討液晶盒配向的均勻性與光電特性對於偏向角度的大小的依存性。於N*-SmC*相轉移施加交流電場，其正負極性的電場會使得液晶分子相對於rubbing軸而言具有相反方向的偏向角。因此，層結構的方向不一致，造成缺陷的產生。當偏向角度等於圓錐角的一半時，相反方向的層結構重合並垂直rubbing方向，此時缺陷消失並呈現均勻配向的效果。而且，在此情況下驅動液晶盒時，會呈現雙穩態之特性。

關鍵字

強誘電性液晶 ； 雙穩態 ； 偏向角 ； 配向

並列摘要

In the ferroelectric liquid crystal material(FLC) with N*-SmC* phase transition, two types of domain with opposite polarization direction randomly formed in the SmC* phase. The director of molecules in each domain deviate a fixed angle in opposite side from the rubbing direction due to the surface electro-clinic effect. Therefore, horizontal chevron defects form and then, the alignment in this kind of material is not uniform. In this paper, we investigated the relationship between the alignment and the deviation angle in the ferroelectric liquid crystal cell by applying an electric field during N*-SmC* phase transition. The deviation angle is denoted as angle is denoted as the angle between the molecular axis and rubbing direction.
According to the theory of getting bistability in SSFLC, the initial state FLC molecules are limited in two stable states by using the cell with very thin cell gap. In our proposed method, we will first choose the FLC material which have N*-SmC* phase sequence to reduce the influence of temperature dependence of the characteristics of FLC molecules and layer structure on the alignment. Then, applying the electric field aligned method to control the initial state of the FLC molecules to achieve the property of bistabiltiy. We predict that this method can overcome the problems of the cell gap dependence and fragile alignment in SSFLC.

並列關鍵字

surface electroclinic effect ； N*-SmC* ； ferroelectric liquid crystal ； alignment ； Bistability

參考文獻

an Overdriven Liquid Crystal Display”International

Taiwan’06 (2006)

A. Pikin, S. P. Palto, A. Sinha, A. Yasuda, S.

[17] Aira Hotta, Ray Hasegawa and Kohki Takatoh,” Effect

Ferroelectric and Antiferroelectric Liquid Crystals