掺高分子聚合物twisted π-cell液晶顯示元件之研究

Electro-Optical Characteristics of a Twisted π-cell Liquid Crystal Device Stabilized by Aligned Polymer

陳敬生(Ching-Sheng Chen)

指導教授 ： 吳俊傑 ； 陳殿榮

國立臺北科技大學/機電學院/光電工程系所/碩士(2005年)

摘要

OCB（Optically Compensated Bend）Mode，又稱π-cell，即光學補償彎曲模式。液晶分子沿著液晶層厚度方向以上下對稱的方式呈現彎曲排列，同時有著廣視角及電光學應答速度快的優點，被視為可用於液晶電視及監視器等次世代的液晶顯示模式。可是這種模式目前尚有待須克服的技術問題，就是當初期狀態為擴散配向（Splay Alignment）轉移到彎曲配向（Bend Alignment）時，需要施加較大的臨界電壓來克服自由能障礙，才能使彎曲狀態的配向趨於穩定，此時便需要花上一段暖機時間（Warm-up time）才能達成轉換的動作，對於顯示器的應用上是一項待欲解決的問題。
本研究使用了向列型液晶材料及具有對掌手徵性(chiral)的旋性活化物，在特定重量濃度百分比範圍內混入液晶，設計出一個具有快速光學響應且狀態穩定的twisted π-cell液晶分子架構，有效的消除了warm-up time。此外我們於twisted π-cell架構下混入高分子單體（Monomer），其目的是想了解高分子網狀架構（Polymer network）對於twisted π-cell會有什麼樣的光電特性上的影響。我們將已製作好的樣本於照射UV的同時加入交流方波電壓（Vuv），可使單體分子於液晶層表面聚合成高分子網狀結構，經過實驗量測後發現polymer network的確會影響液晶分子的配向狀態與預傾角角度，有效地降低了twist state轉換至bend state的轉換過渡區域電壓。

關鍵字

Twisted π-cell ； Optical bounce ； OCB ； Chiral dopant ； Polymer network

並列摘要

OCB（Optically Compensated Bend）mode or pi-cell is promising as the next generation display mode, due to its fast response and wide viewing angle. However this mode has some intrinsical problems. Firstly, it has long warm up time. It takes long time to shift from splay alignment to bend alignment because it stays on splay alignment at initial state. Secondly, it has high critical voltage; high energy barrier must be overcome, to shift from splay alignment to bend alignment. Thirdly, bend configuration at low driving field is unstable.

This study employed the mixture of nematic liquid crystal and chiral dopant to pre- pare sample cells. We designed a twisted pi-cell with fast optical response but without the unstable problem, and removed the warm up time successfully. Besides, we employ- ed monomer to mix with the chiral-doped liquid crystal. High voltage was applied on cells as being irradiated by UV light. After UV curing, the liquid crystal molecules were aligned with polymer network. The experimental results showed the reduced transform voltage at witch twist alignment transfered to bend alignment.

並列關鍵字

Twisted π-cell ； Optical bounce ； OCB ； Chiral dopant ； Polymer network

參考文獻

[4] K.R. Sarma, H. Franklin, M. Johnson, K. Frost, and A. Bernot, “Active-matrix LCDs using gray-scale in halftone methods,” SID Symp. pp.48-150, 1989.

[5] K.H. Yang, “Two-domain twisted nematic and tilted homeotropic liquid crystal display for active matrix applications,” IDRC’91 Digest, pp.66-72, 1991.

[6] T. Sunata, T. lnada, T. Nakagawa, T. Matsushita, “A wide-viewing-angle 10 inch diagonal full-color active-matrix LCD using a halftone grayscale method,” 1991 IDRC Conference Record, pp.255-257, 1991.

[8] K. Takatori, K. Sumiyoshi, Y. Hirai, and S. Kaneko, “A complementary TN LCD with wide-viewing-angle gray-scale,” Japan Display’92, pp591-594, 1992

[9] Y. Toko, T. Sugiyama, K. Katoh, Y. Iimura, and S. Kobayashi, “TN-LCDs fabricated by non-rubbing showing wide and homogenous viewing sagular characteristics and excellent voltage holding ratio,” Society for Information Dis-