測試與分析垂直配向液晶盒內之雜質離子

Abstract

本論文的重要性在於首次以光學相位差量測液晶盒中液晶層的光電效應，證明實驗樣品的雜質離子主要來自配向層，再用VHR的量測方法，來研究分析垂直配向液晶盒中的配向膜內雜質離子。本論文引用楊界雄教授所發表，鐵電性液晶層中高、低解離率離子的概念，加上雜質離子的解離和傳輸方程式，推導出雜質離子對輸入電壓造成的壓降，以此模型與實驗數據來做分析，結果證明，配向層中同時存在著高、低解離率雜質離子。 利用上述物理模型，能夠清楚的解釋本論文中，高、低解離率雜質離子，在不同溫度下的離子濃度、遷移率，進而推算出所對應的解離活化能。 配向層材料在液晶顯示器中，扮演很重要的角色，雖然目前我們並不清楚這些存在於配向層中，雜質離子的來源，但未來若能將本論文提出的方法，結合不同材料、不同製程方式，有可能得知哪種化學成分、結構，會產生出高、低解離率雜質離子，研發無雜質離子的高品質配向膜，並降低配向層材料的價格，得到更理想化的液晶顯示器。

For the first time, we study ionic phenomena of vertical aligned (VA) liquid crystal (LC) cells using polyimide (PI) alignment films by Voltage Holding Ratio (VHR) measurement. First, we measured heterodyne-interferometric phase versus applied voltages on the VA cells to confirm that the dominant ions were from the PI alignment layers (called EMR phenomenon) within the VA cells. We have derived our analytic equations based on published ionic generation and transport theory, and used these equations to fit the VHR data of the EMR samples measured at two different temperatures. As a surprise, there existed both ions from high-ionization–rate (HIR) and low-ionization–rate (LIR) impurities in PI alignment layers within the VA cells. Using the stated physical models, we have obtained HIR and LIR ion concentration and their corresponding mobility within PI alignment layers. However, the ion concentration of HIR impurities was almost independent of temperature as expected. Furthermore, we have also derived the corresponding activation energies of ion concentration for LIR impurities within PI layers from the data measured at two temperatures. The materials of alignment layer play an important role on the performances of TFT-LCDs. We do not clearly understand the origin of those ionic impurities within the alignment layer. With further investigations by changing LC and PI materials and by varying the cell process parameters, it might be possible to find out chemical compositions and structures of LIR and HIR ion within the PI alignment layers leading to reduce or eliminate them for the realization of high-quality and ion-free PI alignment layers for TFT-LCDs without image sticking. Our work has opened a new chapter to study ionic phenomena in PI alignment layers for VA cells.