色彩偏移最小化膽固醇液晶顯示器之製作

Abstract

近年來，液晶顯示器因為其輕薄便利之優勢，已逐漸取代傳統映像管顯示器。膽固醇液晶由於省電不需背光模組、偏正片、彩色濾光片及反射式特性，只需依賴環境光即可使人眼觀察到色彩並閱讀。非常適合於發展可撓式面板的產業應用，像電子報紙、室外看板、標籤等。對於膽固醇液晶，當外加電場時，可改變膽固醇液晶的反射強度，但也跟著出現色彩偏移(blue shift)現象，這現象嚴重的妨礙顯示器的應用。在本篇論文中，我們使用色差(岛E*ab)對色彩偏移進行分析和討論，這是因為岛E*ab能比一般傳統的反射頻譜得到更精確的數值來描述色彩偏移。為了解決色彩偏移的問題，我們藉著參雜負型液晶來改變膽固醇液晶的介電參數(岛ε)和折射參數(岛n)。藉由上述方法，岛ε=7.8的材料，當提供電場範圍(岛V)為7.3V時，岛E*ab增加量(blue shift)為14，而當材料之岛ε降至1.3時，所需外加電場範圍變為25V，才能使岛E*ab增加量相同。此實驗證實縮小膽固醇液晶混合物的岛ε能有效地壓制色彩偏移現象，並同時保有灰階的效果。另外，縮小膽固醇液晶混合物的岛n亦可成功地降低最大色差。

Liquid crystal displays (LCDs) have played an important role in flat panel display (FPD) industry and have already achieved a significant market impact, in recent years. Cholesteric Liquid Crystals (CLCs) have great advantages for reflective mode displays due to their lower power consumption, backlight-free, polarizer-free, color filter-free structure and good readability. This let they are suitable for the flexible display applications such as electronic paper, signboard, bill-board, label, etc. The reflectance of CLC can be changed by applying voltage. The blue shift, however, accompany the process. This phenomenon is a hindrance to display applications. In this thesis, the blue shift were analyzed by color difference (岛E*ab), because the 岛E*ab could get an exact value for color change than the reflection spectrum. To solve the blue shift phenomenon, the various host dielectric anisotropic (岛ε) and birefringence (岛n) were prepared by mixing negative and positive nematic LCs. The experiment results showed the values of 岛E*ab was increased to 14 for the 岛ε of LCs was 7.8, while the applying incremental voltage (岛V) was 7.3V. The same 岛E*ab=14 was obtained when the applied voltage increased to 25V in the 岛ε=1.3 material. The result indicated the low 岛ε CLC mixtures could effectively suppress blue shift phenomenon and produce smooth gray scale. In addition, the lower 岛n CLC mixtures were found to have the smaller 岛E*ab.