外部元件對VFLC線性灰階調變研究

Linear gray level adjustment for a ferroelectric liquid crystal cell

黃仁宏(Ren-Hung Huang)

指導教授 ： 吳俊傑 ； 蔡淑雲

國立臺北科技大學/機電學院/光電工程系所/碩士(2005年)

https://doi.org/10.6841/NTUT.2005.00200

摘要

強誘電性液晶盒(ferroelectric liquid crystal cell；FLC cell)可以等效為電阻與電容的並聯組合而成，其反轉頻率(inversion frequency)強烈相依於液晶層的等效電阻及配向層的等效電容。我們在液晶盒外加電阻與電容，來提高反轉頻率，藉由此關係，可以達到零起始電壓(thresholdless)、無遲滯現象(hysteresis-free)的V型FLC cell，並且利用電路分壓的觀念來解釋觀察到的光學現象。一般室溫下的強誘電性液晶發生V-shape現象都在極低的電壓頻率(0.01~1Hz)，經由改變外部電阻、電容值可提高反轉頻率到數百Hz。進一步改變外部電容，調變V-Shape的斜率，更可達到在很寬的頻率區間中進行線性灰階的切割及調變。
此外，本論文也嘗試把FLC做垂直配向，討論其靜態與動態光學現象，並觀測其光學圖樣與模擬結果作一比較；FLC在垂直配向不同於水平配向會有缺陷的產生，所以會有很好的暗態表現，其暗態好壞與否與FLC材料的螺旋距(pitch)和液晶盒的間隙(cell gap)有相當大的相依性。

關鍵字

強誘電性液晶 ； 灰階 ； 垂直配向

並列摘要

A ferroelectric liquid crystal (FLC) cell can be modeled as a combination of capacitors and resistors. In accordance with the properties of the FLC cell, external electric elements, such as capacitors and resistors, are usually connected to achieve a V-shaped performance at a driving inversion frequency . However, the inversion frequency is strongly dependent on the external electric elements and the applied voltage.
The relation between an external capacitor and the profile of the V-shape is discussed through a voltage divider across the ferroelectric liquid crystal cell. An optimized circuit is demonstrated to alter the profile of the V-shaped electro-optical transmittance and raise the characteristic frequency so that the linear gray levels can be modulated in a wide range of applied voltage.
On the other hand, we study the vertical alignment for a ferroelectric liquid crystal that has fast response, high contrast, and analog gray scale capability. In contrast to the conventional rubbing alignment in a planar geometry, smectic layers arrange themselves parallel to the substrates, and thus extremely uniform alignment of molecules in large area is naturally achieved.

並列關鍵字

ferroelectric liquid crystal ； V-shape ； gray level ； vertical alignment

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