離子電荷對扭轉線狀液晶盒時變電容特性之影響

Abstract

液晶盒中存在很多離子，這些離子不是存在液晶本身即是在液晶盒製作過程中引入的，在外加電場作用下，離子被解離並向相反極性電極方向移動，造成離子電荷效應。在本論文中，我們對各種摻雜離子濃度扭轉線狀液晶盒在不同驅動電壓下之時變電容和光學特性做研究，我們相信液晶盒電容除了由液晶分子誘發極化貢獻外，空間電荷極化貢獻電容亦不可忽視。我們利用模擬程式模擬比對光學量測結果並藉此計算出液晶分子誘發極化貢獻電容值，同時空間電荷極化貢獻電容值亦可藉由實驗和模擬比較而得。除了驗證出空間電荷極化貢獻電容值確實存在外，我們亦發現其隨著驅動電壓的上升而變大的趨勢。因此在離子效應下液晶盒電容量測必須要考慮空間電荷貢獻電容值的影響。

Liquid crystal cells may contain many ions which come either from the raw material itself or from impurities during the cell fabrication. The ions dissociated by an applied electric field move to the electrode with the opposite electric polarity and cause ionic charge effects. We have studied the time response of capacitance and transmittance of TN-LC cells with different doped density of TBAI under different DC driving voltages. We believe that the capacitance characteristic of liquid crystal cells is resulted from induced polarization from liquid crystal molecules and space-charge polarization from fast ions. In this thesis, we utilize the comparison of both simulated and measured transmittance to find the capacitance contributed from LC dipoles and to evaluate the capacitance contributed from space charge polarization. The results show the capacitance contributed from fast ions indeed exists and has an increasing trend with increasing DC driving voltages. Hence, the foregoing capacitance component not included in the previous studies must be considered in the capacitance measurement under the influence of ionic charge effects.