Influence of Ionic Charges on the Time Dependent Capacitance Characteristic of TN-LC Cells

• Main Authors: Tzu-Chieh Lai, 賴梓傑
• Other Authors: Shu-Hsia Chen
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/28449889404943874222

碩士 === 國立交通大學 === 光電工程所 === 89 === 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.