具奈米粒子塗佈配向層之液晶元件雙穩態特性研究

Abstract

本論文於混合排列向列型液晶盒元件(Hybrid Alignment Nematic Liquid Crystal Device, HAN-LCD )的水平配向基板表面塗佈二氧化矽奈米粒子(SiO_2 nanoparticle)，研究其雙穩態(Bistable)的特性，藉由施加相反極性的脈衝電壓(Pulse Voltage)於雙穩態HAN-LCD，將可切換元件的亮態及暗態兩種穩態。 論文中已證實，SiO_2奈米粒子於水平配向基板表面的塗佈濃度以及元件內離子雜質的存在，都對元件的雙穩態特性產生影響。另根據元件內的自由能密度的計算，由帶負電的SiO_2奈米粒子及離子雜質所造成的內建電場，可穩定元件的暗態。 此外，本元件除了用於雙穩態顯示之外，同時具有動態顯示的特性。與一般HAN-LCD作比較，發現雙穩態液晶元件除了上升時間較長之外，其餘動態特性與一般HAN-LCD無明顯差別，故此元件可依產品使用的需求操作於動態顯示或雙穩態顯示，因此為此類型雙穩態元件最大特點。

The bistable hybrid-aligned nematic liquid crystal device (HAN-LCD) was fabricated with silica nanoparticle-coated polyimide (PI) alignment films. The triboelectrically-charged silica nanoparticles and the existence of impurity ions in the LC can cause an internal electric field to stabilize the device in the homeotropic state (dark state) after turning off the driving voltage. For switching back to the HAN state (bright state) from the homeotropic state, a voltage pulse with proper polarity was applied for changing the ion distribution in the device. The capability of controlling bistability was achieved through modification of the ion density in the LC layer and the surface properties of the homogeneous PI alignment layer. In addition, the electro-optical characteristics of the bistable HAN-LCD operated in the dynamic mode were studied and compared with the normal HAN-LCD. Our proposed device is not only being able to operate in bistable display mode, but also in dynamic display mode when appling an AC voltage.