銀金屬強化奈米結構於軟性導電薄膜與電極直寫之應用

近來電子產業的蓬勃發展中，可撓性印刷電子元件受到廣泛的矚目，主要利用平版、凹版、網版，甚至噴墨等印刷技術來印製如無線射頻辨識系統 (RFID)、有機發光二極體 (O/PLED)、有機太陽能電池 (OPVs)，電子紙(E-paper)等電子產品的應用。因為印刷具有製程減縮迅速、減少製程材料使用、低廢棄物產生等優點，使得可撓性印刷電子元件相關研究備受期待而發展迅速。為了因應未來更廣泛的應用，近期的發展趨勢更是衍伸出像電子皮膚等如此具可拉伸性之導電薄膜的感測元件應用，有別於以往的可彎曲特性，發展具有可拉伸的特性，則必須承受更大的應力破壞，最直接的就是接點問題，故此論文便提出合併低溫製程墨水增進奈米銀線拉伸導體內強化接點焊接之觀點來達到提高導電材料拉伸強度的需求。電子元件內部之導線結構為不可或缺之要件，有別於傳統高溫製程、複雜程序、無法彎曲以及高成本等缺點，進而發展出可撓性印刷電子元件，但因其基材使用塑膠類或高分子薄膜等軟性基材，而非傳統耐高溫的硬式基材，故研究如何將導電材料以製圖程序方便簡單以及低溫不破壞基板來製備導線，並朝向能兼具透明和廣泛拉伸應用作為目標及展望，而本論文研究即利用熱化學反應加速銀粒子生成導線，與使用奈米銀線製作高拉伸導電薄膜以及噴墨奈米銀線來直接印刷圖樣技術等方法，提供有效低溫製作高貼附性與高透明直寫圖樣化銀導線的方式來印刷導電薄膜。廣義來說，傳統與可撓性印刷的電子元件之間並無太大的差異，皆具有以金屬導線為主體的元件設計，但實際上可以將其開發策略中的重大轉變分類為3 大部分：基板種類、導電材料、製程過程。故論文第一章部分即總括介紹可撓性印刷電子元件的發展過程、導電墨水的開發與種類、印刷方式介紹以及相關理論。製程過程方面：在研究可撓性印刷電子元件時，對於常見的奈米金屬導線製程，以傳統合成金屬奈米粒子導電墨水的方式，要得到高導電率的金屬導線都必須經由高溫至少150℃以上與長時間1 小時以上的燒結，確保金屬奈米粒子邊界的燒熔連結才能達到高導電率的需求，然而，通常可撓式基板是不耐高溫的，避免對基材的破壞，許多研究皆尋求低製程溫度(100℃)亦能達到高導電率的方法作為目標。而本論文第二章部分則是提出利用銀氨水溶液與二乙醇胺水溶液相互混合後，在加熱的過程中，二乙醇胺水溶液在鹼性環境下會自發氧化反應生成出醛類，進而與具有銀離子錯合物的銀氨溶液行快速的銀鏡反應來幫助大量生成奈米銀粒子，並透過印刷的製程來得到想要的金屬銀導線圖樣或塗佈，發展出一種熱反應性的導電銀墨水。只要在75℃ 低溫時間不到20 分鐘的加熱過程中利用產生的銀鏡反應來快速還原金屬，加速生成導電銀粒子並降低加熱過程中對基材的破壞，並達到純銀導電度的26% (銀的電阻率約為1.59 μΩ*cm)。基板種類方面：以趨勢發展拉伸性電子元件而言，如何有效的保護材料在拉伸的過程中不受到破壞，亦是關鍵的研究課題。近來有研究顯示翻模轉印、導線設計架橋方式或是將拉伸薄膜先做預拉的動作後沉積導電物質等等，甚至合併一維的導電材料到可拉伸的材質基材上，但一維結構之間的連結網絡也成為關鍵所在，故論文第三章部分則是探討利用反應性的墨水生成導電銀粒子於奈米銀線接點間增強其連結的作用，進而使其嵌入於聚氨酯拉伸薄膜中，金屬粒子與線體結構的相輔相成，使其在拉伸過程中導電更穩定，不以元件先預拉的方式來說，通常拉伸導電薄膜在50%的應變變化下就會變得不穩定，而利用此反應法增強奈米銀線接點方式的拉伸導電薄膜可以高達100%的變化量下，電阻並無太大的變化，而高達130%左右才有明顯的電阻上升變化。導電材料方面：在可撓性印刷電子元件的發展與應用中，有別傳統金屬粒子導線的不透光與現今常用的透明ITO 導電薄膜在未來材料短缺的問題下，為能保有金屬高導電的特性又能兼具如ITO 玻璃一樣的高透明特性，蘊育出奈米銀線這種能達到兼具透明性與可撓性的取代性導電材料出現，但目前銀線最大的問題在於其貼附程度非常差，故鮮少看到奈米銀線的薄膜或導線在無任何加強貼附性的狀況下，可以像ITO 玻璃一樣能夠做如黃光微影蝕刻等後製程方式來做需要的圖樣。故論文第四章部分即將一般奈米銀線原本懸浮在異丙醇溶劑之中，因極易揮發的溶劑不利於直寫式印刷的應用，利用溶液置換法，製作穩定懸浮於水相並能用於噴墨製程的奈米銀線導電墨水與奈米二氧化鈦線墨水。進而用其全噴墨製程噴塗所要之透明圖樣化電極與光感測材料奈米二氧化鈦線來製作紫外光光感測器，噴印出來的光感元件可視穿透度可達80%以上，於驅動電壓2V 之下可以有提升時間0.4 秒與復原時間0.1 秒的高反應效果，元件偵測電流開關比更高達2000 左右之展現，證明噴墨印刷應用於元件上的可行性。最後，在末章節部分即總結可撓性印刷電子發展研究上的成果，此論文將提供印刷技術應用於可撓性印刷電子元件發展產業上問題解決的貢獻，提升未來商業化發展的可能性。

關鍵字

奈米銀線；奈米銀粒子；反應性導電墨水；高拉伸導電薄膜；全噴墨印刷光感測元件

並列摘要

In the development of recent electrical industry, flexible printing electronic devices have become more attractive things for the future. It mainly utilized the printing technology such as off-set printing, screen printing, even like inkjet printing technology of these methods to fabricate the RFID system, O/PLED, OPVs, E-Paper and so on. Because of these printing technologies have many advantages like simple rapid process, material costs and wastes reduction, the lower waste pollution…etc. It makes the flexible printing electronic related researches with high anticipation and rapid development. For the further widespread applications, stretchable conductive thin films were developed for some related application along the innovation requirements such as E-skin sensor. Stretchable electronics differentiate with traditional flexible electronics and have become more popular in the future. These extended issues are still the aims of effort for related researchers. Here we applied a novel concept about low temperature chemically sintering nanowires for the reinforcement of network connection between each nanowires material. Recently, the related researches of flexible printing electronics are still under developing. Here we supply the thermal accelerative reaction to create the conductive lines of silver nanoparticles. Also used the silver nanowires to fabricate highly stretchable conductive films or compose the electronic devices with patterned nanowires films in direct printing method, that all needed to resolve in urgency. Therefore, the aim of this dissertation is resolving the encountered problems in the flexible printing electronics, to enhance the performance and find ways to make a breakthrough in flexible printing electronic researches. In general, there are no much difference between flexible printed electronics and conventional electronics. Both of these are designed to have a metallic conductor element or conductive tracks inside as a main component. But in practical details, it can be classified with a significant change of the development strategy or direction into three parts: substrate type, various conductive materials, processing improvement. In Chapter 1, we will give a description of flexible printing electronics, and further introduce the overall development process about pre-, in-, post-process categories, contents include of development of various conductive inks, commonly utilized printing technology, related theories in printing quality and post-treatment or test in flexible printing electronics. About the processing improvement section, whereas metallic nanoparticle inks often require high annealing temperatures (>150°C) to decompose stabilizing agents and other polymeric additives that inhibit electrical conductivity. Recent exploration into silver precursor inks has yielded promising results. Unfortunately, even these temperatures render the ink incompatible with many plastic and paper substrates used in flexible electronic and biomedical devices. In Chapter 2, we use a simple and effective silver ink formulation was developed to generate silver tracks with high electrical conductivity on flexible substrates at low sintering temperatures. Diethanolamine (DEA), a self-oxidizing compound at moderate temperatures, was mixed with a silver ammonia solution to form a clear and stable solution. After inkjet-printed or pen-written on plastic sheets, DEA in the silver ink decomposes at temperatures higher than 50 °C and generates formaldehyde, which reacts spontaneously with silver ammonia ions to form silver thin films. The electrical conductivity of the inkjet-printed silver films can be 26% of the bulk silver after heating at 75 °C for 20 min and show great adhesion on plastic sheets. About the substrate selection section, in stretching or elastic deformation processes with large strains, it is difficult for traditional conductors, such as metal tracks or indium tin oxide (ITO) thin films, to maintain electrical conductivity simultaneously with mechanical stability. Typical examples are using the film transfer methods, or buckled serpentine metal structures on stretchable substrates, or metal thin films on pre-strained substrates to preserve structural integrity of the laminated metal thin films at large strains, or using the percolating networks of m-NW thin films can more effectively accommodate strains and show good tolerance in the stretching process. One of the challenges to implement m-NWs as thin film conductors is that the insulating ligands used in the synthesis or solution dispersion must be removed after film deposition to ensure effective electrical contacts between m-NWs. Therefore, in Chapter 3, we demonstrate a new chemical soldering method to enhance silver nanowire (AgNW) network connections by a simple and fast solution-based process.Upon applying a reactive ink over AgNW thin films, silver nanoparticles are preferentially generated over the nanowire junctions and solder the nanomesh structures. The soldered nanostructure reinforces the conducting network and exhibits no obvious change in electrical conductivity in the stretching or rolling process with elongation strains up to 130%. About the various conductive materials section, one-dimensional nanostructure materials show more attractive advantages such as electrical conductivity, mechanical flexibility, excellent transparency and have received substantial attentions in the last few years. Like conductive silver nanowires, as a well promising candidate to replace the ITO conductor, but the use of silver nanowire networks still involves poor substrate adhesion issue. So there are rare papers have mentioned the patterning of silver nanowire thin films after materials deposition, such as lithography process post-treatment. In Chapter 4, we will demonstrate the controlled deposition of networks of various nanowires in well-defined patterns by inkjet printing for UV detection. Inks containing silver or titanium dioxide (TiO2) nanowires were first formulated adequately to form stable suspension for inkjet printing applications. The printed photodetector showed a high transparency and a fairly low dark current of 10-12–10-14 A with a high on/off ratio of 2000 to UV radiation. Under a bias voltage of 2 V, the detector showed fast responses to UV illumination with a rise time of 0.4 s and a recovery time of 0.1 s. This method shows the feasibility of applying inkjet printing technology to create nanowire thin films with specific patterns in printing electronics. Finally, in Chapter 5, we conclude and summarize the achievements of this thesis research. This study shows the related researches of printing applications that have opened up a whole new direction, and can be applied to business development of flexible printed electronics in the future.

並列關鍵字

Silver nanowires ； Silver nanoparticles ； Conductive reaction inks ； Highly stretchable conductive thin films ； All-printed UV photodetector

參考文獻

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銀金屬強化奈米結構於軟性導電薄膜與電極直寫之應用

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