High Sensitivity Graphene Temperature Sensor via Liquid Assist

自石墨烯2004年被發現以來，因為在光學、熱傳、電性、機械強度方面許多特殊的性質，一直是備受矚目的研究對象，其中極大的比表面積(2630 m^2⁄g)以及豐富中孔結構的性質，使其在吸附氣體分子時可以具有很高的靈敏度。 本研究根據石墨烯對氣體吸附具有高靈敏度的性質，利用水汽吸附提升石墨烯溫度感測元件之靈敏度，並且藉由多次轉印的方式，減少傳統轉印過程中濕蝕刻步驟對石墨烯造成的破壞而造成接觸電阻過高的問題。實驗之石墨烯由常壓化學氣相沉積法並搭配純度99.8%銅箔和3M銅箔膠帶兩種催化劑製備而成，並用靜電轉印的方式，將石墨烯轉印在矽晶圓上製作成溫度感測試片，量測階段同時記錄溫度變化與電阻變化，最後經由計算得到各實驗條件下之溫度電阻係數(temperature coefficient of resistance, TCR)，並分析其溫度感測的性質，探討催化劑種類、吸附液體種類、轉印次數對石墨烯溫度感測的影響。 研究結果顯示，退火有幫助試片達一致化的效果，且用去離子水作為吸附液體的試片穩定性較佳，而TCR的變異係數依照轉印次數而有所不同。經退火的純質石墨烯在吸附去離子水後，轉印一次石墨烯製成的試片其TCR約為-0.380±0.126，而轉印三次與五次的TCR分別為-0.317±0.056與-0.342±0.055，並可以藉由多次轉印石墨烯，來降低試片本身的接觸電阻，以提升再現性，在相同量測條件下，轉印三次試片的變異係數比轉印一次減少16%，而轉印三次和轉印五次試片的變異係數相差約1.6%，此外，本實驗所使用的兩種銅箔所製作出的石墨烯溫度感測器在相同量測條件下有相近的TCR，兩者均值相差0.95%。Graphene was discovered in 2004 and regarded as a remarkable material cause by a lot of properties, such as optical, thermal, electrical and mechanical. Furthermore, it not only has ultra-high specific surface area (2630 m^2⁄g) but also rich in pore structure, so that may have the high sensitivity in gas adsorption. In this study, improving the temperature coefficient of resistance (TCR) of the graphene temperature sensor on the basis of graphene property which has high sensitivity in gas adsorption. And we reduce the internal contact resistance of graphene by transferring more than once. The few-layer graphene was grown by atmospheric pressure chemical vapor deposition using two kinds of catalysts, and 99.8% purity copper foils and 3M copper tapes. Graphene, then, transferred to the silicon wafer substrate. Finally, we discuss the effect of catalysts, liquids and transferring time. The experimental results indicate that annealing and deionized water adsorption are helpful to improve the consistency. However, the coefficient of variation in TCR will vary with the transferring time, and we find that a way to improve the reproducibility by transferring more than one time. Under the same measurement conditions, the coefficient of variation of samples which compare transferring three times (TCR=-0.317±0.056) with transferring one time (TCR=-0.380±0.126) will be decrease 16%. Moreover, the graphene grown by difference copper catalysts have similar TCR with difference of 0.95%