扭轉向列型液晶盒的殘留電壓以及其內部離子之特性

液晶顯示器中雜質離子的存在是一滋擾，其影響液晶顯示器之顯示品質，例如：閥值電壓、電壓保持率、影像閃爍和影像殘留。本論文係描述在兩具有相同液晶混合物，不同配向材料之摩擦配向扭轉向列型液晶盒(TN cells)，進行離子效應對電光(electro-optics)和殘留直流電壓(VrDCs)的影響。我們也進行嶄新的實驗，發現一TN液晶盒的殘留電壓值是源自液晶介質處的離子所造成，而另一TN液晶盒則是源自配向層處的離子所造成。我們測量的殘留電壓值指出：「前者有兩種不同的指數衰減率(相似於M. Mizusaki等人的發表結果)，但後者僅有一個指數衰減率。」本論文中，我們也提出新的實驗方法和適切的方程式，來探討兩具有相同液晶混合物，不同配向材料之摩擦配向TN液晶樣品盒內部的離子特性。我們在實驗上使用一LCR、一外差干涉儀和一電流計，去測量1 kHz至100 kHz之不同電壓對應的電容值、在1 kHz頻率下之不同電壓值對應的相位延遲，並在兩個TN樣品盒上施加0.1 Hz 中等灰度電壓1.3 V，來量測不同時間對應的相位延遲和不同時間對應的電流值。與上述有關之數據，我們提出方程式，使在相同TN樣品盒的配向膜內與液晶介質內之自由電荷的場驅動傳輸互為獨立，以獲得分別源於液晶側或配向側的累積電荷，在液晶-配向鄰近區域上所引起與時間相依之離子電壓。我們的實驗方法提出可行性，用於進一步研究在同液晶樣品盒內的薄配向膜以及液晶混合物，來找出雜質離子的結構和來源，以及活化能、遷移率、離子濃度等等…除此之外，我們相信本論文之方法，可以選擇和優化液晶混合物和配向材料，用於低刷新率之薄膜晶體驅動的液晶顯示器來實現低功耗之息屏顯示。

關鍵字

扭轉向列型液晶盒；扭轉向列型液晶的電光；配向層中的離子；向列液晶中的離子；低刷新率薄膜電晶體液晶顯示器

並列摘要

The presence of impurity ions in liquid-crystal displays (LCDs) is one of the nuisances that affect the display qualities such as threshold voltage, voltage holding ratio, flicker and image sticking. In this thesis, we report the ionic effects on electro-optics and residual direct current voltages (VrDCs) of two PI-aligned TN cells with same LC mixture but different PI-alignment materials. We have also carried out new experimental methods to find out that the observed VrDCs are caused by LC-PI-interfacial (IF) trapped ions generated and transported from the LC medium for one of TN cells, and from the PI layers for the other TN cell. Our measured VrDCs indicate that the former has two different exponential-decay rates similar to the published results by M. Mizusaki et al. [chap.3 ref. 3], but the latter has only a single exponential-decay rate. In this thesis, we also report our investigation of intra-cell ionic properties of two TN LC cells made of same LC mixture but different PI-alignment materials. By using an LCR meter, a heterodyne interferometry, and a current meter, we have measured the data of capacitance versus voltage from 1 kHz to 100 kHz, the phase retardation versus voltage at 1 kHz, and the phase retardation versus time and the current versus time by applying a mid-grayscale voltage of 1.3 V at 0.1 Hz on the two TN cells. Related to the above measured data, we have developed equations to characterize the field-driven transports of mobile charge carriers within the PI films independently from that within the LC medium of same TN cell to obtain the time-dependent ionic-charge voltages caused by accumulated charges on the proximities of LC-PI interfaces originated either from LC side or from PI sides, respectively. Our experimental methods provide promising possibilities by further investigations to find out the origins and the chemical structures of impurity ions, as well as mobile-charge-carrier activation energy, mobility, ion concentration…etc. within thin in-cell PI-alignment films independently from within the LC mixture of the same LC cell. Furthermore, we believe that the methods presented in this thesis can be applied to select and optimize LC mixtures and PI materials to accomplish low-refresh-rate thin-film-transistor-driven LCDs leading to the realization of always-on displays.