外差干涉儀相位差之量測 研究扭轉向列型液晶盒雜質離子效應

Abstract

本論文的重要性為首次以外差干涉儀量測相位差的方法，來研究摩擦配向扭轉向列型液晶受該液晶盒中雜質離子所影響的光電效應。本論文結果証明，某些TFT-LCD所用液晶層主要離子是由低解離率離子所主導，與最近發表的文獻一致。而本論文也首次證實了雜質離子存在於某些摩擦PI配向層中，在該配向層裡，同時存在著高、低解離率的雜質離子主導影響中間液晶層的光電效應。本論文也是第一次，用理論所推導的雜質離子的解離和運動方程式，來分析實驗結果的數據，從而獲得不同雜質離子種類於不同溫度下的離子濃度、遷移率及其所對應的解離與遷移率的活化能。 目前我們並不清楚這些存在於摩擦PI配向層中的高、低解離率的雜質的來源，但我們認為利用本論文所揭示的實驗和解析方法，結合材料的不同成份的調配以及製程參數的改變，在進一步探討之下，有可能認證這些高、低解離率的雜質離子的來源及其化學成份和結構，有助於研發無高、低解離率雜質離子的高品質摩擦PI配向膜，以達成無影像殘留的高顯示品質的TFT-LCDs。 我們認為，用過去文獻中所發表量測穿透率的方法，來觀測離子效應是否取決於液晶層或配向層的雜質離子，也是可行的，但相位差量測方法更顯得穩定和準確。本論文所揭示的量測方法與嶄新的理論分析，也可以應用到未來探討，用非接觸式配向膜所製作的液晶盒的離子光電效應。

For the first time, we report the usage of heterodyne-interferometric phase measurements to study electro-optical effects of a rubbed-polyimide-aligned twisted nematic (TN) liquid crystal (LC) cell caused by ionic impurities within the cell. Our experimental results have confirmed that, in some cases, the dominant ionic species in LC mixtures used for TFT-TNs came from impurities of low-ionization-rate(LIR) in agreement with recent publications. However, for the first time, we have observed, in some cases, ions from both high-ionization-rate (HIR) and LIR impurities have existed in the rubbed PI alignment layers of TN cells. Also, for the first time, we have carried out numerical calculations using our ion generation and transport equations to analyze and fit the measured phase data. We have obtained ion concentration and ion mobility for LIR ions within LC mixture and both HIR and LIR ions in the PI alignment layers at different temperatures. From the measured temperature-dependent phase data, we have derived the activation energies of ion-dissociation and ionic mobility of the LC mixture, and activation energies of ion-dissociation of PI alignment layers, within the TN cell. At present, we don’t know the origin and chemical compositions and structures of these HIR and LIR impurities in the LC mixture and rubbed PI films. However, we believe that, by using the experimental and analytical methods reported in this thesis to do further studies on samples of various chemical compositions and process parameters, we can find out the origins as well as chemical and structural properties of these HIR and LIR impurities and their associated ions. We hope that further researches will lead us to realize high-quality and impurity-ion-free rubbed PI alignment layers for TFT-LCDs with high-display qualities without image sticking. Although both phase and intensity measurements can be used to study electro-optical phenomena caused by field-driven net mobile ions accumulated at the interfaces between the LC mixture and the PI alignment layers of the TN cell, we believe that the phase measurement reported in this thesis is more stable and effective. The analytical and experimental methods reported in this thesis can also be applied to study the ionic effects of LC cells made from non-contact LC alignments.