垂直配向邊緣場效驅動液晶技術應用於顯示器元件之研究

Abstract

響應時間快速對液晶顯示器非常重要，因為可以避免動態影像模糊。垂直配像邊緣場效驅動(VA-FFS)就具有快速響應時間的特性，以這項技術為基礎，我們繼續研究其他可能影響反應時間的因素。本篇論文討論了轉動機制和響應時間的關聯。結果顯示負型液晶的響應時間比正型液晶慢，這是因為液晶分子在垂直電場中的特殊行為與較低的虛擬牆密度所致。我們稱此負型液晶之特殊行為「兩階段過程」，以其轉動會先從一些區域開始，之後才帶動其他區域轉動的特性得名。根本原因是沒有明確轉動方向的「猶豫液晶」會等待其他有明確方向的液晶引導它們。負型液晶在VA-FFS中優勢，即是更高的穿透度，但也意謂更少的虛擬牆可以被用來加快回復時間。 本篇研究也探討二維與三維電極間的比較。我們發現三維電極可以限制液晶分子的轉動方向，進而縮短上升(啟動)時間。換句話說，三維電極有更少的「猶豫液晶」。這在負型液晶上尤其明顯。另一個使用負型液晶的三維電極比較快的原因是:在二維電極中，所有負型液晶皆可以完全轉動，也就延長了整體的上升時間。但在三維電極中，部分負型液晶不能完全轉動，因為均勻的電場限制它們的轉動。 最終，我們發現使用正型液晶的三維電極在快速反應時間上極具潛力，但它的穿透度遠低於使用負型液晶的同型元件。因此，我們採用三種方法改善它的穿透度: 雙面FFS、FFS、突起物。最終，我們將其穿透度提升10-15%。

Fast response time is significant for LCD because it can avoid unwanted motion blur. Based on VA-FFS (vertically-aligned fringe field switching ) mode, which features fast response time, we continue to study other factors that can affect response time. The relation of switching mechanism and response time in VA-FFS mode has been studied in this thesis. The result shows that negative LC is slower than positive LC in VA-FFS mode, due to its special molecule behavior in vertical fields and the lower density of virtual walls in the LC cell. We name this molecule behavior of negative LC as the “two-step process”, owing to the feature that negative LC will begin the rotation in some regions, and then the others. The root cause is that “hesitant LC molecules” without clear falling direction would be waiting for those with determined directions to guide them. Negative LC still has an advantage in VA-FFS mode, which is higher transmittance, although it means less disclinations that can be used as virtual wall for faster fall time. The comparison between 2D and 3D electrodes has also been discussed. We find that 3D electrode can restrict the rotating directions of LC molecules to achieve faster rise time. In other words, there are less “hesitant LC”. This is especially obvious for negative LC. Another reason why 3D electrode using negative LC is faster is that in 2D pattern, all negative LC molecules are allowed to fully rotate, which extends the overall rise time. However, in 3D pattern, parts of the negative LC molecules could not fully rotate due to equal distribution of electric fields in all directions. Finally, we find that positive LC in 3D electrode is most competitive for fast response time device, but it has much lower transmittance than negative LC does. Therefore, we use three methods to improve its transmittance: DFFS, DFFS with 3-level electrode design, and protrusion. Eventually, we can improve transmittance by 10-15%.