改善垂直配向邊緣場效驅動液晶顯示器的虛擬牆穩定性之研究

Improving the stability of virtual wall in vertically-aligned fringe field switching mode liquid crystal display

朱崴豪(Wei-Hao Chu)

指導教授 ： 蔡永傑

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202102260

摘要

過去的研究中發現，在2D VAFFS(two-dimensional vertically-aligned fringe field switching)的結構下，使用正型液晶可以得到較快的反應速度，使用負型液晶可以得到較高的穿透率。負型液晶緩慢的反應速度是來自於負型液晶在2D VAFFS中特有的 “兩步驟轉動” (two-step process)。除了反應速度外，“兩步驟轉動” 還會造成虛擬牆消失，因此，3D VAFFS的結構被提出，利用多一個維度的畫素電極(pixel electrode)增加不同方向電場，來藉此穩固住虛擬牆。
然而，在我們過去的研究中發現，3D VAFFS對虛擬牆的穩固有結構大小上的限制，當畫素電極間隔(electrode gap)小於10um時，維持電壓一段時間後還是會發生虛擬牆移動的情況。此外，3D VAFFS中虛擬牆的移動似乎也與“兩步驟轉動”有關，但並未找出明確的機制。
本論文解釋與分析了3D VAFFS 虛擬牆的移動，其原因主要來自於電極間隔四周類似2D VAFFS的結構。此外，本論文也提出了2種電極結構來阻止虛擬牆的移動：菱形電極(Diamond shape)和孔洞圖案電極(Hole pattern)。我們對這兩種方法如何穩固虛擬牆的機制作出解釋。使用這兩種方法，可以把畫素電極寬度(electrode width)與畫素電極間隔縮小到3um甚至以下，同時保有較高的穿透率與高反應速度特性。最後，我們也個別討論2種電極結構在微縮到更小尺寸時遇到的問題，並作出解釋。

關鍵字

快速響應時間 ； 三維電極結構 ； 垂直配向邊緣場效驅動 ； 轉動機制 ； 虛擬牆 ； 菱形電極 ； 孔洞圖案電極

並列摘要

In 2D VAFFS (two-dimensional vertically-aligned fringe field switching) liquid crystal mode, positive liquid crystals (with positive dielectric anisotropy) tend to have faster response time whereas negative liquid crystals (with negative dielectric anisotropy) tend to have higher transmittance. The result of the slower response time in negative liquid crystals is believed to be partly due to the two-step process that occurs. Besides the slower response time, the two-step process can also cause the vanishing of virtual walls. Therefore, 3D VAFFS mode has been proposed in recent years. VAFFS mode uses perpendicular pixel electrode arrangement to provide different electric field directions which can help stabilize virtual walls.
However, from our past research, we have found that the stabilization of 3D VAFFS may be affected and limited by the electrode size. Virtual walls can still move after voltage is being turned on for a while when electrode gap is smaller than 10m. In addition, the movement of virtual walls in 3D VAFFS seemed to be related to the two-step process, but the mechanism was not very clear.
In this thesis, we will attempt to explain the mechanisms involved in the movement of these virtual walls. It is found that they are mainly due to the 2D VAFFS-like electrode structure around the electrode gap. In this thesis, we will also propose two new electrode designs which can help prevent the virtual walls from moving. These two new electrode designs are called “Diamond shape” and “Hole pattern”. We will explain the mechanisms involved in these two electrode designs. We found that we could reduce the electrode width and gap to about 3m (or less) by using these two new electrode designs and still can obtain high transmittance and fast response time in 3D VAFFS. Finally, we will also discuss the problems and mechanisms involved when we reduce these electrode width and gap.

並列關鍵字

Fast response time ； three-dimensional electrode ； vertically aligned fringe field switching ； switching mechanism ； virtual walls ； diamond shape ； hole pattern

參考文獻

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