奈米銀線薄膜加熱器之噴印技術與圖樣設計

Pattern Design of Printed Silver Nanowire for Thin Film Heater

王博玄(Po-Hsuan Wang)

指導教授 ： 廖英志

國立臺灣大學/工學院/化學工程學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.00315

摘要

本論文提供一個簡易且迅速的噴墨直寫技術來製作圖樣化的奈米銀線薄膜。透過設計銀線成線後形成的網格狀結構，此元件可以應用於微型加熱器並能同時具備高穿透度以及良好的導熱、導電特性。由於銀線能夠藉由交疊產生具縫隙的導電迴路，利用噴墨技術可以控制銀線於基材上的面密度，並直接影響局部電阻值。這一特性使得奈米銀線可以用作設計加熱陣列、圖樣化加熱器或是梯度式加熱器。

首先，為了避免噴墨時銀線的聚集導致噴頭的堵塞，經由沉降測試探討噴墨製程前墨水的穩定性。待尋找出合適的濃度後，再利用壓電式噴墨印表機將墨水噴印於約45度C的玻璃及聚對苯二甲酸乙二酯(PET)上，能夠迅速沉積出奈米銀線導線並且不需額外的高溫燒結，噴印出的奈米銀線導線寬度最細可達100微米。另外，為了找出適當的噴印層數來達到足夠低的電阻值，我們噴印不同層數的導線於玻璃和PET基材上並量測其電阻，發現至少需噴印20層以上方可形成連續導線，由於面密度的提升，隨著層數增加，電阻成反比關係下降。

接著進行圖樣化的設計：分別為1*1平方公分的網格加熱器以及0.25*5平方公分的梯度加熱器。利用紫外-可見光光譜量測銀線網格的穿透度，可發現其於極低的電阻值之下(~20 歐姆)仍有高於75%之穿透度。透過紅外線熱像儀量測加熱元件的溫度展現，發現在輸入電壓為4伏特時網格加熱器可達到100度C左右。梯度加熱器則是依據噴印層數對電阻的關係圖來進行設計：透過不同層數導線(30~70層)的串並聯，在輸入電壓15伏特時於導線的兩端能達到約50度C的溫差，且輸入功率與平衡溫度成正比關係。

由於玻璃基板過大的熱容，使得加熱器容易產生響應時間(response time)過長的問題，因此將基材替換為PET，同時利用紅外線熱像儀偵測縱向溫度分佈，搭配熱傳理論來探討加熱曲線的變化，發現其響應時間縮短至小於5秒並能反覆彎折超過5000次。最後合併熱致變色元件(Thermochromic device)來進行元件的整合與封裝，展現出此製程應用於印刷電子的發展潛力。

關鍵字

噴墨印刷 ； 奈米銀線 ； 金屬網格 ； 薄膜加熱器 ； 圖樣化

並列摘要

In this study, we introduced a convenient and facile direct printing method to fabricate a patterned silver nanowires (AgNWs) thin film. With a mesh structure, it can be served as a micro heater with both good transparency and high thermal/electrical conductivity. Due to the percolative effect of AgNWs, through inkjet process, the number density of AgNWs per unit area can also be effectively controlled, which can affect the local resistance directly. This creates the possibility to design the desired gradient heater, heater array, and patterned heater. Sedimentation test was carried out to ensure the stability of AgNWs ink and to prevent the clogging at inkjet nozzle. For the ink formulation, the as-prepared AgNWs solution was dispersed in deionized water and inkjet printed under 45°C on glass and PET without annealing post treatment. The width of printed silver single line was about 100 um from scanning electron microscope (SEM). By utilizing IR thermography, the maximum temperature for a thin film mesh heater can rise up above 90oC at an input voltage of 4 volt with a uniform heating. For the design of pattern, a gradient heater was fabricated through simple serial and parallel circuits with different printed layers. The temperature difference can reach 50°C at an input voltage of 15V. When the substrate changed to PET, the heating device showed a very short response time (<5 sec) compared to the glass. Bending test proved that the AgNWs heater on PET substrate can endure more than 5000 times of bending cycles. Also we combined the theory of 1-D heat transfer to discuss the influence of changing substrate. Combined with the thermochromic application, this technique demonstrated a great potential for printed electronics.

並列關鍵字

Inkjet printing, Silver nanowires ； Metal mesh ； Electrode ； Thin film heater ； Pattern.

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