- 學位論文
扭轉型光學補償彎曲模式液晶盒之光電特性研究
Study on the Electro-optical Characteristics of Twisted Optically Compensated Bend Liquid Crystal Cell
摘要
光學補償彎曲模式(OCB)具有廣視角、高對比及快速響應的特性，因此成為下一個世代液晶顯示器裡相當看好的一項技術。然而它卻有兩個嚴重的問題存在，這是因為OCB顯示模式必須操作在彎曲態上，才會具有上述的優點。第一個問題是要達到彎曲態，一開始必須施加一個很大的暖機電壓，而且需要一段暖機時間，第二個問題是操作在彎曲態下其光程差較小，會造成顯示器穿透率下降亮度不足的情況。在我們的研究裡，提供了三種方法並藉由實驗與模擬的方式來解決上述OCB顯示模式的兩大問題。 在沒有添加旋性物質的條件下，我們試著發展一種新型的OCB液晶盒，利用扭曲到展曲之間拓撲形狀的差異所產生的能障，在沒有外加驅動電壓下，便可將OCB液晶盒維持在扭曲態，我們將這種類型的液晶盒稱作扭轉型光學補償彎曲模式液晶盒(TOCB cell)，由於這種TOCB cell 沒有展曲態，因此並不需要任何的暖機電壓或暖機時間。 在第一個研究裡，TOCB cell的形成是利用照光可聚合的高分子單體混入液晶中，並注入同向配向液晶盒(π-cell)內，在照射UV光使高分子聚合的期間，施以適當的curing電壓在液晶盒上。在配向膜表面形成高分子網狀的結構，無施加驅動電壓下，便可將液晶分子傾角控制在20到28度之間，使扭曲與展曲之間的能障變大，使OCB液晶盒有機會穩定在扭曲態而形成TOCB cell。 在第二個研究裡，利用高傾角配向的高分子網狀圖案形成TOCB cell，我們稱它是圖案-扭轉型光學補償彎曲模式液晶盒(Pattern-TOCB cell)。Pattern-TOCB cell的平均傾角仍比傳統的OCB液晶盒要來的高。藉由高傾角配向的高分子網狀圖案可增加扭曲與展曲之間的能障來形成Pattern-TOCB cell，利用照光可聚合的高分子單體混入液晶中並注入π-cell，照射UV光通過一光罩後到達液晶盒，期間並施以適當的curing電壓。在照到光的區域形成高傾角的高分子網狀結構，無施加驅動電壓下，便可使液晶分子產生高傾角配向的結構，這樣的結構能使未照光區域的液晶分子形成扭曲的狀態。TOCB和Pattern-TOCB cell在加上補償膜後的光穿透率比傳統OCB液晶盒來的高，且他們的應答速度比傳統OCB液晶盒有過之而無不及。 在第三個研究裡，在共通電極上設計條狀電極以產生橫向電場，橫向電場能增加扭曲與展曲之間的能障，使傳統OCB液晶盒形成TOCB cell，我們稱它是橫向電場-扭轉型光學補償彎曲模式液晶盒(Lateral-Field-TOCB cell)。Lateral-Field-TOCB cell的傾角與傳統的OCB液晶盒相似，條狀電極的配置是平行於配向方向。我們發現橫向電場能消除TOCB或傳統180°扭轉的OCB液晶盒在低電壓時T-V曲線上的凹陷現象(光學躍動)，因此Lateral-Field-TOCB cell的光效率會比TOCB cell更好，而Lateral-Field-TOCB cell的相關光電特性是藉由模擬軟體LCD Master來分析。
並列摘要
In our studies, we have proposed three methods by experiment or simulation to solve the issues of the optically compensated bend (OCB) mode. We have developed a new liquid crystal cell based on a non-chiral-doped OCB mode. When no applied driving voltage, the twist-to-splay energy barrier induced by topological differences remained in a twist state. We have called this twisted cell a twist optically compensated bend (TOCB) cell. The TOCB cell has no splay state, so it dose not require any warm-up time or warm-up voltage in electrical driving. In the first study, the TOCB cell was manufactured by the irradiation of UV light onto a π-cell, which filled with nematic liquid crystal (NLC) and UV-curable polymer mixture upon a curing voltage being applied to it. While the alignment layer forms a polymer network, the pretilt angle is controlled at 20-28°. Such that the energy barrier between the twist and splay states increases and the π-twist state might be stabilized. In the second study, the TOCB cell was made using a polymer network pattern with high-pretilt-angle alignment, called a patterned-TOCB cell. The average pretilt angle of the patterned-TOCB cell was higher than that of a conventional OCB cell. The high-pretilt-angle alignment pattern can increase the energy barrier between the twist and splay states. The patterned-TOCB cell arose from the irradiation of UV light through a photomask and onto a π-cell, which was filled with NLC and UV-curable polymer mixture upon a curing voltage being applied to it. The UV-light-irradiated regions assume a high-pretilt-angle alignment, which enables the nonirradiated regions to assume the twist state. The light efficiencies of the TOCB and patterned-TOCB cells were higher than—and the response time was comparable to—that of a conventional OCB cell. In the third study, the TOCB cell was produced by the lateral-electric-field, which can increase the energy barrier between the twist and splay states, and that generated by the rectangle-bar-electrodes at the common electrode, called a lateral-field-TOCB cell. The pretilt angle of the lateral-field-TOCB cell was as same as a conventional OCB cell. The rectangle-bar-electrodes are parallel to the rubbing direction. The lateral-electric-field can eliminate the concave (optical bounce) of T-V curve of a TOCB cell or a π-twist cell at low voltage. Thus, the light efficiency of the lateral-field-TOCB cell might be higher than that of a TOCB cell. The electro-optical characteristics of the lateral-field-TOCB cell are demonstrated by LCD Master Software.
參考文獻
延伸閱讀
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