三階電極對垂直配向邊緣場效驅動之負型液晶的設計

Abstract

延續我們先前在3D結構VA-FFS方面的深入研究，我們發現負型液晶相較於正型液晶在VA-FFS中具有更大的亮度穿透率優勢。此外，透過頂部共用電極的應用，我們進一步提高了穿透率，使其達到80%，同時也顯著降低了操作電壓至10伏特以下。本論文的目的在於將頂部像素電極納入原有的3D結構VA-FFS中。除了原有的頂部共用電極、像素電極和底部共用電極外，引入三階電極並透過它的頂部像素電極對液晶盒內部局部電場進行調控，期望改善因電場強度不足而導致的低亮度問題。然而，值得注意的是，過去的實驗都是在液晶層厚度僅有2.6μm的條件下進行的。而液晶層厚度的減少將增加封裝的難度。此外，過厚的液晶層將導致液晶過度扭轉，引起相位過度延遲的現象，進而降低穿透率，這也是本次實驗的另一個重點，將頂部像素電極放在較厚的液晶層上，期望通過局部地改善區域電場，進一步提高液晶的性能表現。 本論文將透過多種不同的W(electrode width)以及G(electrode gap)搭配不同尺寸的頂部像素電極，從V-T圖中找出最佳運作電壓，觀察其液晶盒內部的電場分布，並與先前未進行改善的結構做出比較。 除了延續先前實驗的井字型結構，本論文另外衍生出相較於井字型的新排列模式—六邊型排列，對比於井字型如同四邊型般地排列間格區域，該排列模式以六邊形的方式進行排列，並導入三階電極結構來更進一步觀察其改善效果。

In this research, we continue our previous research on 3D structure Vertically-Aligned Fringing-Field Switching (VA-FFS) Liquid Crystal (LC). From our previous research, we found that negative liquid crystals (i.e. LC with negative dielectric anisotropy) have a significant brightness transmittance advantage over positive liquid crystals (i.e. LC with positive dielectric anisotropy) in VA-FFS LC. Additionally, by applying a top common electrode to the design, we could further increase the transmittance to 80% while significantly reducing the operating voltage to below 10 volts. The purpose of this research is to incorporate another top pixel electrode into the original 3D structure VA-FFS LC so that we can now form a new 3-level electrode design. In this new design, the new top pixel electrode can be used to vary the local electric field within the liquid crystal cell. Our aim was to improve the low brightness issue caused by insufficient electric field strength. However, we also realized that some of previous experiments and simulations were conducted with a liquid crystal layer thickness (cell gap) of only 2.6μm. In general, a very thin cell gap of the liquid crystal layer can cause difficulty in LC cell fabrication. On the other hand, an overly thick liquid crystal layer may cause excessive rotation of the liquid crystal molecules, leading to excessive phase retardation and hence reduces its overall transmittance. Therefore, another aim of our experiment was to place the top pixel electrode on a thicker liquid crystal layer, hoping to improve the local electric field regionally and further enhance the performance of the device.

In this research, we will determine the optimal operating voltage from V-T curves by using various combinations of W (electrode width) and G (electrode gap) with different sizes of top pixel electrodes. We will observe the electric field distribution within the liquid crystal cell and compare it with the previously unimproved structure. Besides continuing the previous experiment's grid structure, this research also introduces a new arrangement pattern derived from the grid structure—a hexagonal arrangement. Compared to the grid structure's square-like interval regions, this hexagonal arrangement pattern uses a hexagonal arrangement and incorporates a new three-electrode design structure to further observe its effects and improvements.