負型非等向液晶在快速響應之水平配向邊緣場效驅動液晶顯示器之模擬研究

Fast Response Parallel-Aligned Fringe Field Switching Liquid Crystal Display with Negative Dielectric Anisotropy

顏景德(Ching-Te Yen)

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/NTU202102078

摘要

液晶顯示器在現今社會上已經被廣泛使用，液晶顯示技術有TN、VA、PA、IPS、FFS等等，而在科技日新月異的時代，液晶顯示器逐漸追求高穿透率以及快速響應的特性。本文主要接續研究蔡永傑博士與陳世睿學長的正型液晶結構設計，探討的顯示器類型為負型液晶PA-FFS水平配向邊緣場效驅動顯示器，透過改變基本上液晶分子其配向，達成快速響應的特性。
本論文利用特殊的光配向設計，在電極上設計不同方向的配向，使得部分的液晶分子受到外加電場時偏轉，部分的液晶分子保持不動，產生虛擬牆，加速整體液晶分子的響應時間。論文中對於結構的部分探討不同電極寬度、不同電極間距以及不同虛擬牆寬度，了解到虛擬牆間距的大小對於整體的穿透率以及響應時間有關。
接著討論結構以外的液晶配向部分，在本論文中發現配向部份的設計，不論是改變配向區域的比例、配向區域的寬度、配向區域的角度，對於整體的穿透率以及響應時間並無大幅度的變化。反倒是配向區域的角度越大，所造成的漏光情況會更加嚴重，所以設計上偏向使用小角度以及小寬度的配向，而不同方向的配向會造成虛擬牆位置改變，導致穿透率以及響應時間有變化。再來將傳統的配向結構與本論文設計的結構比較穿透率以及響應時間差異，得知本論文的結構的確能夠改善響應時間。最後利用雙層電極的結構來增加整體的穿透率以及將負型液晶配向的結構設計與正型液晶配向的結構設計比較，能夠使得原本只能使用的正型液晶水平配向邊緣場效驅動顯示器推廣至負型液晶使用，使得負型液晶也能夠應用在PA-FFS水平配向邊緣場效驅動顯示器。

關鍵字

快速響應 ； 水平配向邊緣場效驅動 ； 負型液晶 ； 多重配向 ； 虛擬牆

並列摘要

Liquid crystal display has been widely used today, with liquid crystal technologies such as TN (Twist Nematic)、VA (Vertical Alignment)、PA (Parallel Alignment)、IPS (In-Plane Switching) and FFS (Fringe-Field Switching). As the performances of displays are growing rapidly in recent years, liquid crystal displays are also continuously improving with e.g. higher transmission and faster response time. In this thesis, we will continue to study the design of PA-FFS (Parallel Alignment Fringe-Field Switching) liquid crystal display with different rubbing angles, which was previously proposed in our laboratory. Instead of using liquid crystals with positive dielectric anisotropy as in previous design, in this thesis we will investigate the results by using liquid crystals with negative dielectric anisotropy. Our goal is to achieve fast liquid crystal response time characteristics by e.g. changing the alignment directions of PA-FFS liquid crystal molecules.
In this thesis, our proposed structure requires the use of photo-alignment technology in order to achieve different alignment directions of liquid crystal molecules. In this structure, some of the liquid crystal molecules can rotate when subjected to an external electric field whereas some of the liquid crystal molecules remain stationary and thus help create the so-called virtual wall. Virtual wall can help accelerate the response time of liquid crystal molecules. In this thesis, we analyzed the results by changing different electrode widths, electrode gap and virtual wall widths. It is shown that that the size of the virtual wall spacing can have great influence on the overall transmittance and response time.
Then, we discuss the alignment of liquid crystals. It is found no matter if we change the ratio of the alignment area, the width of the alignment area or the rubbing angle of the alignment area, it has no much effect on the overall transmittance and response time. However, we know that the larger the rubbing angle of the alignment area, the more the light leakage there will be and hence lower the contrast ratio. Therefore, we prefer the designs with smaller rubbing angle and smaller width of alignment area. Different alignment directions will cause a change in the position of virtual wall and hence result in changes in transmittance and response time.
Then we compared our new PA-FFS designs with the traditional PA-FFS alignment in order to examine the differences in transmittance and response time that exist between them. It is found that the new designs in this thesis can indeed help improve the response time a lot compared to the traditional PA-FFS design. Similar to our previous design with positive dielectric anisotropy, we also showed in this thesis that the double-layer electrode structure can be used to increase the overall transmittance. Finally, we also compared the results of our new designs of PA-FFS with negative dielectric anisotropy in this thesis with the results obtained using positive dielectric anisotropy. We showed that our new designs of PA-FFS with different (or multi) rubbing directions, which were originally proposed for liquid crystals with positive dielectric anisotropy in our laboratory, can indeed be also extended to liquid crystals with negative dielectric anisotropy.

並列關鍵字

Fast response ； parallel-aligned fringe field switching ； negative dielectric liquid crystal ； multi-rubbing ； virtual wall

參考文獻

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