本研究為製作快速切換雙穩態之膽固醇液晶顯示元件,其利用攙雜手性分子(ZLI-3786)於負型向列型液晶(95-465)混和製作膽固醇液晶。此種膽固醇液晶具有螺旋結構,並有布拉格反射的特性,螺距與膽固醇液晶平均折射率將會影響布拉格反射。透過三電極驅動方式來切換水平及垂直電場於試片上,驅使膽固醇液晶分子螺旋軸進行排列,借以達到控制螺旋軸分別排列為Standing螺旋及Lying螺旋與改善響應時間的效果。根據本實驗結果,比較使用傳統的垂直電場、三電極水平電場與垂直電場此三種的驅動方式對於響應時間關係,可以發現使用三電極的水平電場與垂直電場可加快液晶的總響應時間,改善傳統垂直電場上升時間與下降時間。此外,本實驗觀察到手性分子濃度影響螺距及門檻電壓,並由於反射強度取決於螺距層數量,而電壓會影響螺距層數。 綜上所論,為了獲得一個最佳化結果,手性分子濃度、電極、溫度以及電壓的掌握等,都是相當重要的環節,因此,本論文製作出具有快速切換雙穩態的膽固醇液晶元件,完成優化液晶盒光電特性之目的。
In this thesis, the electro-optical properties of a cholesteric liquid crystal cell, composed of chiral dopant and nematic liquid crystal with negative dielectric anisotropy, are investigated. The chiral dopant gives rise to a helical structure of the nematic LC. The cell has Bragg reflection as a result of the helical pitch of the liquid crystals molecules. We drive the chiral nematic liquid crystal cell using three-terminal electrodes. Bragg reflection and threshold voltage of the cell are significantly related with the chiral dopant concentration. Wavelength shifts are observed by in-plane electric field drving and temperature change. Bistable switching between the standing-helix and lying-helix states is achieved by in-plane and vertical electrical field. Compared to conventional cholesteric cells switching between the focal conic and homeotropic states, the proposed cell has fast bistable switching. We realize a fast-swtiching memory mode in a cholesteric cell utilizing three-terminal electrodes.