标题: 新型高对比、高亮度、无转态之Pi-cell液晶显示元件
Novel High Contrast, High Brightness and Transition-Free Pi-cell Liquid Crystal Display Device
作者: 陈司芬
Chen, Szu-Fen F。
谢汉萍
Shieh, Han-Ping D.
光电工程学系
关键字: 光学补偿弯曲模态;反应型单体;奈米结构;成核;OCB;Reactive Monomer;Nanostructure;Nucleation
公开日期: 2009
摘要: 薄膜电晶体液晶显示器(TFT-LCD)技术已取代传统CRT电视应用的主流。为了使TFT-LCD显示技术能够稳占庞大的TV应用市场商机,TFT-LCD开发、制造…等相关业者无不致力于持续改善TFT-LCD的影像品质。由于TFT-LCD先天上驱动原理的限制,因此TFT-LCD动画显示模糊效应(Motion blur effect)的问题一再地被广泛讨论并寻求解决的方法。在目前所有被应用的LCD技术中,光学补偿弯曲模态(Optically Compensated Bend, OCB;另称为Pi-cell)是目前反应速度最快的向列型液晶模态,由于液晶盒(LC-cell)特殊的结构设计使它不仅具有快速响应,同时也是具备广视角显示品质的液晶模态,因此在解决TFT-LCD TV动画模糊效应上也是最强而有力的显示模态。
由于Pi-cell快速响应的优点,使得高解析度色序法驱动的液晶显示技术(Field Sequential Color Liquid Crystal Display)得以有实现的可能性。然而,Pi-cell有不同液晶形变态之间的转换与回复(State transition and Recovery)问题,造成在实际应用上的困难,甚至有在显示品质最佳化上的可能性存在。本论文中,针对此问题提出了二种新的解决方式:
一、以奈米结构将液晶配向层之表面进行改质,以便形成”成核点” (nucleus),使得Pi-cell在由分散(Splay)模态转换成弯曲(Bend)模态前必经的成核现象(Nucleation)及完成转态所需时间由现在的2分钟(cell gap~5μm,0→6V驱动)缩减至少于1秒。使得Pi-cell即便是需要经过转态过程,亦能在几乎无法察觉的时间内均匀地转态完毕,且无需于瞬间外加约18 V高脉冲电压。
二、在前一项研究中,并不能消除Pi-cell的转态特性,在显示器的电压操作区间仍必须维持一个约2V的临界电压以保持弯曲(Bend)模态的稳定存在。基于液晶光学特性具有不同入射光波长的分散特性 (dispersion),红 (R)、绿(G)、蓝(B) 三波长的电压-透过率特性曲线(V-T curve)并不一致,因此RGB的临界电压并不相同 (VR< VG<VB)。为确保显示器运作能维持在弯曲模态,必须将临界电压维持在VB,使得Pi-cell的透过率和对比相当程度被牺牲。因此,我们另外提出新颖的反应型单体(reactive monomer)应用及cell结构设计,使得Pi-cell中的液晶分子稳定在弯曲模态—驱动模态下,如此一来便克服了Pi-cell的转态问题;同时,由于新结构的cell边界残留位相差值较小,亦使得新型RMM-Pi-cell在不加补偿膜的情况下,其静态对比度从传统Pi-cell的26提升到288 (实验室测试样品), 提升度达11倍。
本论文在显示应用技术领域上的贡献在于提出以奈米结构对Pi-cell的液晶配向层进行改质,以改善其转态时间及利用反应型单体层来消除现有Pi-cell本质的转态特性,使得其所造成之光学品质缺点得以被解决或改善。而其实现方式仅需在现有的TFT-LCD的Cell制程架构中,增加1~2道简单的制程,即可以完全相容于现有的制造方式,倘若将现有的显示器技术结合本论文研究成果将可以创造出一种具有高影像品质的新型Pi-cell液晶显示元件,使得此液晶模态的优势不只有应用在一般TFT-LCD,更能实现色序法驱动的液晶显示技术。
TFT-LCD Technology has become the mainstream in replacing CRTs in TV and other applications. In order for thin-film-transistor liquid-crystal display (TFT-LCD) technology to claim an even larger share of the TV market, manufacturers must continue to improve image quality. The issue of motion blur effect in TFT-LCD TVs has been widely discussed lately. Among the reported LC modes the Pi-cell, also known as Optically Compensated Bend (OCB) mode, has been found to be a strong candidate to reduce the motion blur effect. Due to the LC-cell structure and the driving scheme, Pi-cell is not only a wide viewing angle display technology, but also the fastest-response LCD mode among the commercialized LCD modes.
Because of the fast response of the Pi-cell, the field sequential color LCD (FSC-LCD) which displays R, G and B colors in sequence in a pixel is promising for the high-resolution display. However, Pi-cell possesses intrinsic transition and recovery issues which lead to compromised optical properties, thus, limited in its applications. In this dissertation, we proposed two modified Pi-cells to resolve these issues.
1.Proposed Nanostructure Enhanced Pi-cell (NE-Pi-cell) modified the surface of alignment layer (PI) to create nuclei for speeding up the transition rate. The transition time of a NE-Pi-cell was reduced from 2 minutes to less than 1 sec compared with the conventional one. Moreover, the transition process was uniformly completed without applying high voltage pulse (~18V).
2.Even if the previous topic could speed up the transition rate to almost zero, the critical voltage also needed to be kept over 2V for maintaining the bend state of a Pi-cell. Based on the light dispersion property of liquid crystals, the critical voltage of R, G and B were different; i.e. VR< VG< VB. In order to confirm that the Pi-cell could operate in bend state, a critical voltage larger than VB needed to be chosen, which led to compromised optical qualities. Therefore, we suggested reactive monomer modified Pi-cell (RMM-Pi-cell) to eliminate the splay-to bend state transition. Besides, because of smaller residual retardation at the dark state, the static contrast ratio of a RMM-Pi-cell, compared with conventional Pi-cell, was improved from 26 to 288 (the test samples fabricated in laboratory), up to a factor of 11 without using compensation films.
We have demonstrated a novel alignment layer modified method of a Pi-cell for uniform and fast transition without high voltage pulses. Moreover, a transition-free and high optical performance Pi-cell has also proposed in this dissertation. The proposed novel Pi-cells only need one or two simple extra processes in conventional manufacturing of TFT-LCD. Combining the research results with current high image quality LCD technology, the novel high image quality Pi-cell will be realized. The results can not only improve the image qualities for general TFT-LCD applications, but also realize the FSC-LCDs.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT009324820
http://hdl.handle.net/11536/79216
显示于类别:Thesis


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