共面電場切換模態薄膜電晶體液晶顯示器在不同電極結構下之串音特性研究

Abstract

近年來，薄膜電晶體液晶顯示器產業在基礎和應用方面急速擴展，其成長比預期中還快，尤其是在液晶電視取代映像管電視的可能性方面。因此，若想真正取代傳統映像管電視的市場，大面板尺寸和高解析度的要求則是必然的趨勢。然而，這兩種趨勢將伴隨著兩個嚴重的問題產生：面板尺寸加大會造成視角的問題，而解析度的提高將要求電極間的距離更為接近，使電性耦合的串音問題更容易發生，造成影像品質的降低。近來，由於雙疇共面電場切換模態的液晶顯示器具有超廣視角、色差小和均勻的灰階轉換反應時間的超優動畫品質，因而在液晶電視的應用上是一個非常重要的技術。然而，假如共面電場切換模態的電極結構沒有適當的設計，將會造成低開口率和可見的串音現象，故兩者都需加以優化，以避免亮度下降和影像品質的降低。 在本論文中，我們首先研究共面電場切換模態薄膜電晶體液晶顯示器的電容耦合效應，以進一步量化其串音的特性。我們推導共面電場切換模態液晶盒的電容耦合率(CCRp)，並研究耦合電壓對光電特性影響的效應，以進一步驗證電容耦合率的分析方法。此外，我們藉由分析三個傳統共面電場切換模態的陣列結構之串音特性，再進一步來驗證我們的理論。我們的結果顯示當共通電極置放於資料線旁時，可以屏蔽資料線和畫素電極間的電容耦合效應，使CCRp從13% (S-IPS-2) 降到2.4% (S-IPS-1)，CIR(串音強度率)從21.2% (S-IPS-2) 降到3.9% (S-IPS-1)。此外，我們也提出共通電極重疊畫素電極的結構，它不僅可使開口率相較於傳統結構提高1.28倍，而且可使CCRp從13% (S-IPS-2) 降到9.1% (S-IPS-3)。 雖然共面電場切換模態具有廣視角的超優技術，然而它卻有低開口率的缺點，此缺點可藉由AS-IPS的新結構來改善。然而，驅動電極和資料線間的雜散電容耦合所造成的串音效應，會進一步降低影像品質。改善的方法為在AS-IPS結構的資料線和共通電極間沉積一層厚的有機絕緣層來降低串音。在本論文中，我們的研究著重在共面電場切換模態的兩個設計重點，即提高開口率並降低串音。以AS-IPS技術為基礎，我們也提出一新的電極結構，即AS'-IPS，它不僅可使CCRp從1.2% (AS-IPS) 降到0.05% (AS'-IPS)，同時可使開口率相較於優化的AS-IPS結構提高1.25倍。 具有有機絕緣層的AS-IPS結構雖然可提高開口率，但也伴隨著製造成本的增加，因此，同時就成本和品質而言，有機絕緣層的優化厚度將是重要議題；本論文更提出一個簡單方法來分析AS-IPS結構的有機絕緣層最佳厚度，若要得到一個高開口率及低串音的共面電場切換模態面板，從製造的觀點切入，將是最具成本效益的方法。我們推導AS-IPS液晶盒電容耦合率 (CCRp and CCRc)，並分析兩個面板的RC延遲，以進一步量化其串音特性。其中，兩個面板包括AS-IPS和我們提出的新結構AS'-IPS。結果顯示在相同的優化有機絕緣層厚度下，AS'-IPS的CCRp相較於AS-IPS為非常的小。因此，在成本效益的前提下，AS'-IPS對於有機絕緣層厚度和成本的降低將具有相當的潛力。最後，我們藉由適當的取捨、權衡輕重，來決定有機絕緣層的優化厚度，並設計出一個廣視角、高穿透率、低串音和具成本效益的優化電極結構。

Growth rate of TFT-LCD industries has been faster than predicted due to rapid expansion of infrastructure and applications, particularly the possible replacement of cathode ray tube (CRT) by thin-film-transistor liquid-crystal display (TFT-LCD) in TV applications. For TFT-LCDs to replace CRT-TVs, large panel size and high resolution are necessary. However, with increasing display size and resolution, the narrow viewing angle characteristics and image degradation due to the electrical coupling between the data-bus line and the display electrodes, called “crosstalk”, become serious problems. Recently, TFT-LCD using an in-plane switching (IPS) mode with dual domains presents an important technology for LCD-TV applications because of its super wide viewing angles, small color shift, and uniformity of response times between gray-scale levels, thus exhibiting excellent motion-picture qualities. However, the electrode configuration of IPS mode, if it is not properly designed, will result in a small aperture ratio and visible crosstalk. Both require optimization so as not to cause poor brightness and crosstalk-induced image degradation. In this dissertation, we firstly investigate the capacitive coupling effect of the TFT-IPS mode to quantify the crosstalk properties. We derive the capacitive coupling ratio (CCRp) of the IPS cell and investigate the effect of coupling voltage on electro-optics characteristics to verify the analyzing method of CCR. In addition, we analyze the crosstalk properties of three conventional TFT-IPS array structures to further verify our theory. Our results show that a common electrode placed adjacent to the data line could shield capacitive coupling between the data-bus line and the pixel electrodes, and reduce CCRp from 13% (S-IPS-2) to 2.4% (S-IPS-1) and crosstalk intensity ratio (CIR) from 21.2% (S-IPS-2) to 3.9% (S-IPS-1). We also report the common-overlapping-pixel structure that not only increases the aperture ratio by 1.28 times but also reduces CCRp from 13% (S-IPS-2) to 9.1% (S-IPS-3). Although the in-plane switching (IPS) mode has been known as an excellent technology for realizing wide viewing angles, it has a low aperture ratio that has been improved by Advanced Super-IPS (AS-IPS). However, it is well known that crosstalk caused by parasitic capacitive coupling between driving electrodes and data-bus lines could result in image degradation. The reduction of crosstalk is realized by placing a thick organic layer between the data-bus line and the common electrode of AS-IPS. In this study, we investigate two design issues on IPS mode to obtain high aperture ratio and reduction in crosstalk. On the basis of AS-IPS technologies, we also propose the design of a novel TFT-IPS electrode structure, which is named “AS'-IPS”. It not only reduces the crosstalk in terms of a capacitive coupling ratio (CCRp) from 1.2% (AS-IPS) to 0.05% (AS'-IPS) but also increases substantially the aperture ratio by 1.25 times over that of the optimized AS-IPS. Advanced Super-IPS (AS-IPS) structure with organic insulator layer was invented to achieve a higher aperture ratio, causing the manufacturing cost to increase. Consequently, the optimum thickness of the organic insulator layer is very important for both the cost and performance. In this dissertation, we propose a simple method to analyze the optimum thickness of organic insulator layer for AS-IPS structure. From the manufacturing standpoint, this is the most cost-effective method at increasing aperture ratio as well as reducing crosstalk. We derive the capacitive coupling ratio (CCRp and CCRc) of the AS-IPS cell and analyze the delay time of two panels to quantify their crosstalk properties. These panels include the advance structure (AS-IPS) and our modified structure (AS'-IPS). As a result, the CCRp of AS'-IPS is very small compared with that of AS-IPS using same optimized thickness of the organic insulator layer, and the AS'-IPS has the potential for further reduction in the thickness of the organic insulator for lower manufacturing cost. Finally, we determine the optimum thickness of the organic insulator layer by a proper trade-off and design a well electrode configuration which exhibits wide viewing angle, high transmittance, low crosstalk and lower manufacturing cost.