全新式精密圖案塗佈技術之開發與研究-「太極塗佈法」

Abstract

精密圖案產生技術之應用範圍越來越廣泛，除了過去廣為應用在書籍印刷等知識傳播領域外，近年來配合現代科技的發展，也被大量運用於半導體、平面顯示器及生物醫學產業。而因應全球綠色環保節能之大趨勢，各式圖案塗佈技術(pattern coating)正如雨後春筍般的被開發並應用，此類技術利用流體控制及機械動作，直接將圖案定義於塗佈基材上，以免去傳統批式(batch)製程中高耗時、耗能、高廢料、且高污染之微影蝕刻製程，並以捲對捲(roll-to-roll)方式快速且連續生產。 圖案塗佈技術中，可依圖案塗佈母模需求大分為需母模與無需母模之技術。後者相較於前者有較高之圖案可變動性，且無重製母模所衍生額外工與料之成本。無需母模之圖案塗佈技術透過機械動作或是流體控制，將擬塗佈流體截斷成不連續之流體區段，再藉由控制塗佈頭與塗佈基板的相對運動直接產生各式各樣圖案；此技術高效率地產生微型圖案。其包括了噴印、筆寫式塗佈、機械阻斷式塗佈、以及本論文所開發的氣泡截斷式塗佈技術。其中噴印塗佈技術有最大的圖案可變動性，但其受限於工作流體的黏度與塗膜的均勻度；而筆寫式塗佈技術，其圖案可變動性高，但速度與精度會相互限制；機械阻斷式塗佈具傳統面塗佈技術之優點，然此技術因機台慣性而無法提升流體阻斷頻率、且受限複雜機電系統之精度、及機台操作與維護等問題；故針對此，本論文在塗佈頭中加入氣-液雙相流體產生器，產生非連續流體源，利用流體慣性小之本質優勢，以大幅改善機械流體阻斷技術低頻率與精度之缺點。 本研究之目的在開發一濕式塗佈領域全新概念的精密捲對捲圖案塗佈(簡稱「太極塗佈法」)之設計技術及其雛形設備。此技術利用提供不連續之雙相流體產生源，並配合基板之連續移動來產生斷續圖案，為結合傳統的「狹縫式塗佈技術」與微機電(MEMS)新領域的「微雙相流產生技術」之創新塗佈技術。因此其承襲了狹縫式塗佈技術之高黏度容忍性與大塗佈速度調變範圍等之優點；同時含有微流體控制(microfluidic)技術的高解析度及高反應性之特質。 本論文內容分為三大部分，循此時間序以達成此一全新技術之開發及其相關理論之建立： (1)以單一毛細管作成塗佈頭，進行雙相流塗佈機制之初步探討： 雙相流充填技術研究目的在瞭解雙相流體充填參數與雙相流體尺寸及其穩定性之關係。此研究利用實驗配合理論發現雙相流充填系統之氣體腔室、及液體前延之塗佈行為皆會嚴重影響雙相流產生。 毛細管雙相流塗佈結果除成功了證明”太極塗佈法”概念之可行性；文中並建立U-V塗佈視窗，討論參數(如塗佈間距(G)、液體段長度(la)、及氣泡段長度(lb))對太極塗佈法塗佈視窗之影響。 (2)以單管T型微流塗佈頭證實太極塗佈法連續生產之可行性： 雙相流產生研究之目的在找出穩定之雙相流產生方式、及雙相流塗佈技術可用之段塞流操作區域。本研究中證明文獻中最常使用之針筒式幫浦雙相流驅動方式並非最佳選擇，利用雙壓力驅動之流體源產生之氣-液雙相流之穩定度會好出許多，因而本研究利用高壓空氣作為流體輸送源。而在以驅動壓力(Pc及Pd)作為操作變數的過程中，吾人提出有效壓力之概念及解釋其物理意義，並利用實驗及理論方式探討T型流道上下游長度比例(G*)、流體特性(黏度及表面張力)及操作壓力比值與所產生之雙相流體特性(長度、頻率、流動速度)及流量關係；而由本文所提出的等效黏度理論模型，並經實驗驗證，發現複雜的雙相流行為可在工程上簡單的被精準預測，並作為未來塗佈設計之準則(guide line)。此模型同時預測段塞流之操作區域大小主要受到G*影響，而且當T型流道上下游長度幾乎相等時，存在有最大之操作區域。 在單管雙相流塗佈研究中，除證實可成功連續且穩定地塗佈微型圖案區塊外，並以實驗定義其塗佈速度(V)-塗佈間距(G)之塗佈視窗，而塗佈視窗被兩相互交叉之液膜邊界及氣泡邊界隔開；當氣體壓力(Pd)增加時，氣泡長度增長且雙相流體流量增大，可擴大塗佈視窗。 (3)利用雙管T型微流道塗佈頭配合氣泡同步控制技術，進一步推進太極塗佈法平行生產之可能性： 研究中分別設計雙管流道被動式及主動式氣泡同步產生器；被動式是利用一對被動閥門，限制雙流道中流體界面，使氣泡同步成長，以持續產生同相位之氣泡；而主動式則是利用兩組獨立微型加熱器，在氣液界面附近產生局部熱點，可分別調整驅動雙流道之氣泡產生，以穩定產生同步氣泡；而後配合塗佈動作，成功於基板上塗佈出平行對齊之液體微區塊。

Various applications for micro-patterning have been proposed. In recent years, micro-patterning technology has been applied in many new fields, such as semiconductor, flat panel display, biomedical, and so on. In response to the global environmental issue, varieties of pattern coating technology are being developed and applied. The methods combine fluid control and mechanical motion with a roll-to-roll process to define micro pattern directly, and avoids the drawbacks of lithography method, such as time and power consuming, low material utilization, and high pollution in the traditional batch type process. Pattern coating technology can be classified into two groups as template-needed methods and template-less methods. The latter has higher pattern flexibility because it does not need to fabricate new templates when pattern changes. The template-less methods include ink-jet printing, pen printing, stopper coating and air-bubble coating, in which the last one is the subject being investigated in this study. Amount the templat-less methods, ink-jet printing has the best patterning flexibility, but is limited by low viscosity fluids and has the drawback of poor film uniformity. The pen printing method has also the advantage of pattern flexibility, but the coating speed is restricted by the pattern accuracy. The stopper coating method has the benefit of traditional coating methods; however, the operation frequency is restricted by the machine inertia and the maintenance of the complex electro-mechanical systems can be a challenge. Therefore, in this study, low inertia micro two-phase flow is introduced as the discontinuous working fluid to improve the precision and extend the workable frequency range. The purpose of this study is to develop the conceptual roll-to-roll precision pattern coating technology, coined Air-Bubble Coating, and to build up the prototype equipment for it. This method can be considered as an advanced-die-coating method, which combines the well-know die coating with the microfluidic technology. Micro two-phase flow is utilized to be the upstream discontinuous coating source and micro-patches can be generated in the coating process. Therefore, the method has the advantages of wide range of fluid viscosity and high coating speed, as with die coating methods, and high precision and response, as with microfluidic system. The dissertation work is divided into three parts to develop the new concept technology and build up the corresponding theories, step by step: (1)Using capillary tube as coating head to investigate the coating mechanism: The process of micro two-phase segments feeding in capillary tube is used to investigate the effects of operation parameters on the two-phase segment size and uniformity. From the experiment, it has been found that the installed air chamber and the lubrication of leading liquid segment affect the segment size uniformity significantly. Theoretical models are proposed to explain the phenomenon. The feasibility of Air-Bubble coating method with capillary tube is conceptually proven. Moreover, the U(fluid speed)- V(coating speed) coating windows with different coating gaps, length of liquid segments and bubbles have also been discussed. (2)To coat micro patches sequentially with single T-junction channel The purpose is to find out the most stable micro two-phase flow generation method and the workable range for Air-Bubble coating. In the study, it has been found that micro two-phase flow has much better stability by using a dual constant pressure source than a commonly used dual constant flow rate source, which is usually a dual syringe pump system. With a dual pressure driven source, the pressures Pc and Pd are chosen as the operation variables, and the concept and physical explanation of effect pressure (Pe) are proposed. The experimental and theoretical methods are further used to investigate the effects of channel geometry (length ratio of upstream and downstream channel, G*), fluid properties (viscosity and surface tension) and pressure ratio (Pe/Pc) on the characteristics (bubble length, frequency and velocity) and flow rate ratio(