- 學位論文
以液晶指向矢模擬垂直電場驅動之藍相液晶光電特性及其背光系統設計
Using the Director Model and Backlight Design for a Vertical-Field-Switching Blue Phase Liquid Crystal
摘要
通常液晶的藍相(Blue phase)介於各向同性相(Isotropic phase)及膽固醇相(Cholesteric phase)之間，存在溫度範圍狹窄(1~2℃)，所以應用上比較困難。但是近年BPLC (Blue phase liquid crystal)摻雜高分子之後，其穩定存在的溫度範圍可以被擴展至超過60℃，使得PS-BPLC(Polymer-stabilized blue phase liquid crystal) 成為顯示器應用中潛力強大的競爭者，特別是在場序式驅動的LCD。PS-BPLC 材料本身具有快速響應的特性，在LCD 的應用上不但可解決快速影像切換下所造成的影像模糊問題，亦適用於場序驅動搭配發光二極體(Light emitting diode, LED)背光的方式，達到降低成本、簡化製程並呈現高畫質、高色彩飽和度的效果。所以，最近無論學術界或產業界都十分注目於PS-BPLC 的研究與技術的發展。 基本上PS-BPLC 是一個擁有晶格結構的高旋性液晶分子系統，其光電機制是由電場所誘發的雙折射，通常叫作克爾效應(Kerr effect)。在Kerr effect 中，誘發雙折射與電場強度的平方成正比。然而，這種線性關係只在低電場下符合。當電場逐漸增大時，所誘發的雙折射不可能無限制增加，因而逐漸飽和。顯然Kerr effect 無法描述這種飽和的行為。因此，在本論文中，我們提出利用液晶指向矢模型來模擬和解釋PS-BPLC的光電特性，並探討本質的克爾效應。另外，由Kerr effect 要得到BPLC 液晶盒的反應時間也相當困難。利用液晶指向矢模型，還能夠計算BPLC盒的反應時間，其模擬結果與實驗結果亦相當符合。我們也對垂直電場驅動之BPLC顯示器的背光光源嘗試進行設計。利用模擬設計的方式，可以減少量測上的許多程序，對於BPLC顯示器來說是一大的幫助。
並列摘要
Blue phase of liquid crystal usually exists in a very narrow temperature range (1~2℃) between the chiral-nematic and the isotropic phases, and was difficult for practical applications. However, after polymer stabilized, the stable temperature range has been extended to over 60℃, which makes the PS-BPLC a strong candidate for display applications, especially for color sequential displays. PS-BPLC material is a good solution to overcome the image blurring caused by the fast motion pictures because PS-BPLC has superior feature of micro-second (μs) order response time. For this reason, a promising new technology involving PS-BPLC is emerging recently. In this dissertation, we propose a director model to simulate and explain the observed electro-optical properties and backlight design of polymer-stabilized blue phase liquid crystal (PS-BPLC) with vertical-field-switching cell. Basically, PS-BPLC is a highly chiral liquid crystal system with a crystal-like structure. The electro-optical mechanism of PS-BPLC is the electric-field-induced birefringence known as the Kerr effect. According to the Kerr effect, the induced birefringence is proportional to E^2, where E is the magnitude of the electric field. However, this linear relationship is valid only in low field region. As E increases, the induced birefringence cannot increase unlimitedly, i.e., it will gradually saturate. Apparently, the Kerr effect model cannot describe this behavior. Furthermore, the Kerr model has difficulty to obtain the response time of a PS-BPLC cell. Using the liquid crystal director model, we can calculated the response time of the IPS-BPLC cell, and the simulated results match the experimental results well. Backlight design applications driven by vertical field switching cell can be reduced to the measurement of many programs, it is a great help for PS-BPLC.