新型廣視角、高亮度、高對比之扭轉-垂直配向液晶顯示元件

Novel Wide-Viewing-Angle, High-Brightness and High-Contrast-Ratio Twisted-Vertical Aligned Liquid Crystal Display Devices

彭政忠(Cheng-Chung Peng)

指導教授 ： 徐桂珠

國立中央大學/理學院/光電科學研究所/博士(2011年)

摘要

由於扭轉-垂直配向(twisted-vertical aligned, TVA)液晶顯示模式具有扭轉向列(twisted nematic, TN)及垂直配向(vertical alignment, VA)兩種模式的優點，因此這篇論文選定此TVA模式作為開發新型液晶顯示器之基本架構。TVA液晶元件，主要是在VA液晶盒內摻入對掌性化合物(Chiral compound)，該化合物濃度可決定液晶盒厚度d與對掌性液晶分子間螺距 p (Chiral pitch)的比率d/p值，並調整液晶分子扭轉的角度，而且由該d/p比率與光程差(Δnd)值決定TVA液晶盒的最大穿透率，其中∆n為液晶分子雙折射率。
在本篇論文中我們提出三種利用簡單製程所完成的定向結構，它可使液晶分子形變成一連續扭轉之形態，稱為連續區域之扭轉-垂直配向(continuum domain twisted-vertical aligned, CDTVA)液晶元件。第一種定向結構為畫素(pixel)周圍形成一突出物(protrusion)結構，第二、三種定向結構分別為單純上下兩層之銦錫氧化物(Indium-Tin-Oxide, ITO)透明電極(無蝕刻圖案)及上下兩層之ITO透明電極，蝕刻成特定圖案。我們利用單一配向之TVA液晶盒，模擬最佳參數條件d/p與Δnd，發現當符合Mauguin參數(u)近似於√3時，液晶盒最大穿透率與液晶分子排列方向無相關性，此結果與TN液晶模式特性吻合，並在我們提出的CDTVA液晶結構中，利用模擬及實驗獲得驗證。
我們針對不同的定向結構，設計不同畫素尺寸及電極圖案，研究該TVA液晶盒光學特性及液晶分子定向之穩定性。第一、二種定向結構，發現每一次電壓開關過程中，在畫素內的光學紋影，無法獲得穩定的定向結果。第三種定向結構，其液晶分子定向之穩定性可獲得改善。針對第三種定向結構，我們進一步利用半色調灰階(halftone-grayscale)的概念，設計一新型的電極圖案，以改善斜視角方向之灰階反轉的問題。最後，我們與現有廣視角液晶顯示元件作比較，本論文提出的各種TVA液晶顯示元件，其最大穿透率遠高於傳統PVA (patterned vertical alignment)液晶盒，其對比度及斜視角之顯示品質，較其它液晶顯示模式佳，而且不需要複雜製程即可實現。

關鍵字

液晶顯示元件 ； 高對比 ； 高亮度 ； 廣視角

並列摘要

The aim of this work is to create a novel liquid crystal display (LCD) based on the twisted-vertical aligned (TVA) mode, which combines the merits of the twisted nemtatic (TN) and vertical alignment (VA) modes. The TVA cell is doped with a chiral compound in the VA cell. The concentration of the chiral dopant is suitably adjusted to produce an optimal cell thickness-to-natural pitch ratio (d/p). The maximum transmittance of the TVA cell is determined by the d/p value and optical path difference ∆nd, where ∆n presents the LC birefringence.
In this dissertation, we propose three orienting structures without complex manufacture to make the LC alignment be deformed to a continuous twisted configuration, called the “continuum domain TVA (CDTVA)” cell. The first orienting structure is used to surround the protrusion in a pixel. The second and third orienting structures are both common and pixel ITO electrodes with and without the designated patterns, respectively. We used the mono-domain TVA cells to simulate the optimum conditions of d/p and ∆nd in the structure. When the Mauguin parameter (u) is approximately √3, the maximum transmission of the TVA cell is independent of the direction of orientation of the LC molecules. This result corresponds to that of a TN cell and agrees well with the simulated and experimental results in the CDTVA cell.
We designed various orienting structures with different pixel sizes and ITO patterns in order to study the stability of LC orientation and the optical performance in the novel TVA cells. The previous orienting structures 1 and 2 of the CDTVA cells had unstable schlieren patterns after each switching on/off cycle, because the LC orientation was unstable. The stability of the LC orientation can be improved in structure 3 of the CDTVA cell. Based on structure 3, we designed a new ITO pattern to improve the problem of grayscale inversion at an oblique viewing angle by using the concept of halftone-grayscale method. Finally, we compared various LCD modes with wide viewing angle and found that the maximum transmittance of our proposed TVA LCD cells in this dissertation is higher than that of conventional patterned vertical alignment (PVA) cells. The contrast ratio and the off-axis image quality are higher than that of other LCD modes. Moreover, it can be simply modified to produce a multidomain TVA cell because its fabrication processes is not complex.

並列關鍵字

LCD ； High Contrast Ratio ； High Brightness ； Wide Viewing Angle

參考文獻

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