膽固醇液晶材料特性與穩定灰階之研究

Abstract

本研究中針對液晶的介電異向性及黏滯係數的差異做光電特性上的探討，並以有配向條件的下達成穩定灰階。實驗中，驅動電壓主要受介電異向性影響，而黏滯係數主要影響反應時間。此外，降低液晶盒間隙可有效改善驅動電壓，但也因此液晶受到邊界效應的影響更為明顯。實驗量測最佳結果Vth= 5.5V，Vsat= 9V，Vreset= 28V，但反應時間從50 ms增加至300 ms。 灰階驅動方面，以有配向條件下， Planar 與Focal conic state反射率差異甚距，為達到灰階必須維持兩狀態的區塊共存。此外，表面配向給予膽固醇液晶排列作用，但在驅動至Focal conic state後除去電壓，穩態仍會受到影響，導致反射率隨時間不斷改變。實驗中我們以三種方式達到穩定灰階，其中以主動式的驅動方式可以達到最快（500ms）且最穩定的灰階。

In this thesis, the influence of liquid crystals dielectric anisotropy and viscosity on electro-optical properties are discussed. The stable gray scale can be achieved in the case with surface rubbing. The driving voltage and response time are mainly affected by dielectric anisotropy and viscosity respectively. High dielectric anisotropy and small cell gap will cause low driving voltage, Vth=5.5V, Vsat=9V, Vreset=28V. Decreasing cell gap, however, increases response time from 50 ms to 300 ms due to the strong boundary condition. In order to achieve gray scale in the case with rubbing, the reflective planar and scattering focal conic state have to be maintained at the same time. Besides, the stability of focal conic state will be affected by surface alignment after removing the driving voltage. 3 multi-level gray scale methods can be achieved via either active or passive driving. The active driving method has the fastest driving time (500 ms) and the most stable gray scale.