高靈敏光激發奈米結構與常壓噴射式電漿處理之氧化鋅常溫氣體感測器

High Sensitivity Photo-activated Nanostructure and Atmospheric Pressure Plasma Jet Treated Zinc Oxide Gas Sensor at Room Temperature

駱玠錞(Jie-Chun Luo)

指導教授 ： 田維誠

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2015年)

https://doi.org/10.6342/NTU.2015.02409

摘要

揮發性有機化合物(Volatile organic compounds, VOCs)在環境檢測一直是十分重要的角色，過量的VOCs可能對人體造成如抑制中樞神經系統、致癌等危害，在特定的濃度內，更可能發生氣爆等不可忽視的問題。也因此，世界各國對VOCs都有嚴格的規範，其中由於甲苯被廣泛存在於顏料、汽油等，量測甲苯又是另一項重要的議題。
傳統的以金屬氧化物為感測材料的氣體感測器在應用上，通常會再另外設計一層加熱器，藉由加熱至極高溫來增加氣體感測器的靈敏度。雖然可增加VOCs的吸附、脫附效率，但在製程上不僅需要另外設計一道光罩，且由於長時間加溫的影響，與目前主流的CMOS-based電路整合上會更為困難且增加製程成本，也不利於應用在可能氣爆的環境中。綜上所述，本研究致力於開發一移除加熱器並同時具備高靈敏度的常溫型量測氣體感測器。
本研究主題有二，一為開發一高靈敏之氣體感測器。我們使用微機電(Microelectromechanical Systems, MEMs)製程開發一平面指叉狀電極，以濺鍍的方式鍍上氧化鋅薄膜，並以水熱法製備特殊的氧化鋅奈米結構。二為以常壓噴射式電漿(Atmospheric Pressure Plasma Jet, APPJ)處理我們濺鍍的氧化鋅薄膜，並和傳統的爐管退火處理過的氧化鋅薄膜氣體感測器做退火時間之等效比較。
在水熱法製備之氧化鋅奈米結構氣體感測器方面，我們得到了水熱法製備的最佳時間為5分鐘，形狀為珊瑚狀結構，靈敏度相較於薄膜感測器提升了將近10倍，對於100-5000 ppm的甲苯有良好的線性度，量測極限為50 ppm，線性範圍內的靈敏度為26.04 ppm/ppm，上升時間約10.17秒，回復時間約5.17秒。相較於無照光環境上，以2 μw/cm2強度的紫外光光源照射可提升靈敏度約17%。

在常壓噴射式電漿處理過後的氣體感測器上，我們固定甲苯在500-5000 ppm的範圍內，討論其退火時間跟溫度和傳統爐管退火時間和溫度之等效化，我們找出傳統爐管退火對100 nm厚的氧化鋅薄膜氣體感測器量測甲苯的最佳參數為退火200℃/3小時，靈敏度可達2.80 ppm/ppm，上升時間約3秒，回復時間約3.5秒，靈敏度相較於氧化鋅薄膜感測器提升了9.03%；常壓噴射式電漿退火對100 nm厚的氧化鋅薄膜氣體感測器量測甲苯的最佳參數為退火1分鐘，靈敏度可達2.71 ppm/ppm，上升時間約10秒，回復時間約5.75秒，靈敏度相較於氧化鋅薄膜感測器提升了5.68%。氣體感測器在200℃溫度下的傳統爐管退火3小時的結果和常壓噴射式電漿處理1分鐘的結果相當接近。

關鍵字

氣體感測器 ； 紫外光 ； 常溫 ； 氧化鋅 ； 奈米結構 ； 常壓噴射式電漿

並列摘要

Volatile organic compounds (VOCs) monitoring is one of key indices for environmental monitoring. Long exposure of VOCs at a specific concentration could lead to nervous system suppressing, cancers, and potentially an explosion disaster. It is important nowadays that governance was used to regulate the VOCs emission.
Traditional gas sensors utilizing metal oxide as the sensing material were typically equipped with a heater. Although the sensitivity was increased by incorporating a heater, one more photo-mask and additional processing were required to define the heater. With the high temperature heating, it’s not desirable to integrate with CMOS-based circuits and use in explosive environment. In this work, we developed a semiconductor-based gas senor which can detect toluene with high sensitivity at room temperature.
Two main topics were conducted in this research work. The first topic is to develop a high sensitivity gas sensor using micro-electromechanical systems (MEMs) technologies. The seed sensing film was deposited by a sputter and nanostructures were fabricated by a hydrothermal method with a special Zinc-nitrate/HMTA ratio. The second topic is to develop an atmospheric pressure plasma Jet (APPJ) treated ZnO sensing film for thin film gas sensor at room temperature.
In our ZnO gas sensor using a hydrothermal method to form nanostructures, we found an optimized fabricating time of 5 minutes to provide the maximum sensitivity of the sensor, the nanostructures are coral-like shape. Comparing to a thin film gas sensor with 100nm thickness ZnO without surface treatment, the sensitivity increased approximately 10 times when using a nanostructured ZnO gas sensor. The linearity of our gas sensor for toluene is in the range of 100-5000 ppm, the detection limit is 50 ppm, the rising time is ~10.17 seconds and recovery time is ~5.17 seconds. Comparison with the sensor operated at dark condition, we found the photo-activated sensor with 2 μw/cm2 UV exposure can increase the sensitivity approximately 17%.
In APPJ treated gas sensors, we fixed the gas concentration in the range of 500-5000 ppm to compare the heating time and the heating temperature between APPJ and calcination approach. The best parameter for calcination is 200℃ for 3 hours, the resulted sensor rising time is ~3 seconds and recovery time is ~3.5 seconds. Comparison with gas sensors without annealing, gas sensors with annealing provided a better sensitivity of 2.80 ppm/ppm (~9.03% increase than ZnO thin film sensors). The best parameter for APPJ is 1 minute, the resulted sensor rising time is ~10 seconds and recovery time is ~5.75 seconds. Comparison with gas sensors without annealing, gas sensors using APPJ treatment provided a better sensitivity of 2.71 ppm/ppm ( ~5.68% increase than ZnO thin film sensors ). The sensor performance using calcining for 3hr at 200℃ is similar to the sensor performance with APPJ treatment for 1min.

並列關鍵字

gas sensor ； UV ； room temperature ； ZnO ； nanostructure ； atmospheric pressure plasma jet treatment

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