液晶指向矢擾動對VA和IPS液晶盒造成暗態漏光之研究

Abstract

在液晶顯示器的應用上，對比度的高低將決定其在市場上的接受度。對比度為顯示器亮態程度與暗態程度的比值，一般而言，暗態不夠暗是影響液晶顯示器對比度不夠好的主因。本論文的目的在於研究VA和IPS液晶盒的光散射效應對於暗態不夠暗之影響[14]。在排除正交偏光片本身元件漏光的情況下，藉由實驗數值我們可計算出液晶光散射效應造成的本質漏光。不管是e-mode架構或是o-mode架構，IPS液晶盒之本質漏光隨溫度的升高而劇烈地上升直至液晶相與液態相的相變溫度；相較於IPS液晶盒，VA液晶盒之本質漏光對溫度的改變並不敏感。我們以向列型液晶指向矢擾動理論為基礎，導出公式來解釋實驗結果。此外，我們亦提出一個可用於任何範圍的穿透式非扭轉型液晶盒之預傾角量測方法[13]，以簡單的光學系統測量出光經過液晶盒所產生的相位差，經由計算後便可求出預傾角。

The contrast ratio of a LCD is one of the most important parameters in evaluating the front-of-screen qualities of a display. The contrast ratio is defined as the ratio of the amplitude of the bright state to that of the dark state. Generally speaking, the main point is that the amplitude of the dark state is not dark enough so that the contrast ratio is not good enough. The purpose of this thesis is the study on dark-state light leakage induced by director fluctuation in VA and IPS liquid crystal cells[14]. We have measured intrinsic light leakage of VA and IPS LC cells between “ideal” crossed polarizers as a function of temperature. The measured intrinsic light leakage of VA LC cell were independent of temperature up to the nematic-to-isotropic transition temperature in comparison to a increasing light leakage as temperature increases in IPS LC cells arranged in either o-mode or e-mode configuration. We have derived equations based on light scattering caused by fluctuations of nematic LC director to explain our experimental results. Besides, we have demonstrated a method[13] to measure the pretilt angle of a transmissive non-twisted nematic liquid crystal cell, which can be used in all range by measuring the phase retardation of the LC cell using a simple optical system.