本論文探討新穎3D奈米柱狀結構金屬氧化物堆疊式異質接面二氧化碳氣體感測器之研製。吾人先利用硝酸銀及氫氟酸之蝕刻溶液於P型(100)矽基板形成奈米柱狀結構，利用射頻濺鍍系統(Sputtering system)成長氧化銅(CuO)薄膜，再濺鍍成長本質絕緣層三氧化二鋁(Al2O3)薄膜於其上，然後濺鍍上二氧化錫(SnO2)完成SnO2/Al2O3/CuO (PIN)異質接面感測組合。接著以金屬(Cu或Ag)做為連接層及重複上述步驟做成SnO2/Al2O3/CuO (PIN) 堆疊式異質接面。最後再蒸鍍金屬鈀(Pd)及鋁(Al)分別於矽基板最上層及背面作為催化層及金屬接觸層完成Pd/SnO2/Al2O3/CuO/Metal/SnO2/Al2O3/CuO/P-Si/Al 3D奈米結構金屬氧化物堆疊式異質接面二氧化碳氣體感測器元件。
吾人利用EDX、AFM及SEM分別量測各別薄膜的結晶及觀察他們的表面結構和厚度來探討這些材料的基本特性及做最佳選擇。此外，本研究共製作四種不同結構元件來比較其感測特性:(1)使用不同本質絕緣層材料(Al2O3、HfO2)，(2)使用不同金屬(Ag、Cu)做為連接層，(3)比較結構為平面堆疊式結構及單層3D奈米柱狀結構，(4)同時使用3D奈米柱狀及堆疊式結構。
實驗結果顯示，本質絕緣層為氧化鋁(~8.9eV)較二氧化鉿(~5.7eV)有較大的能隙，可更有效地降低元件之漏電流；又以Ag為連接層的堆疊式結構比以銅為連接層的堆疊是有較佳的感測特性。這是因為添加適量的銀會提高感測層的化學活性，增強對二氧化碳的吸附反應，在吸附過程中金屬銀(Ag)在材料中得以重新分佈，提高了其自身活性並增強對二氧化碳吸附反應，使得感測器對氣體的靈敏度提升。相較於平面式結構，以銀為連接層的堆疊式結構，在二氧化碳濃度3000ppm時，靈敏度可由554%提升至796%。此外，3D奈米柱狀結構者，因可有效增加氣體接觸之面積/體積比，及增加氣體分子的吸附能力，故相較於平面薄膜式者，靈敏度也由554%提升至812%。如同時使用3D奈米柱狀及堆疊結構，則靈敏度更由554%提升至2187%。
最後，值得一提的是本研究發展出之3D奈米柱狀PIN 堆疊式二氧化碳感測器不但選擇性好，對O2及酒精氣體無明顯反應。且其特性也較以往文獻發表者為佳。如在150℃，濃度3000ppm下，其靈敏度為2187%，反應時間為20秒及回復時間為40秒; 但在相同條件下，已發表的Ti/BaTiO3-CuO-Ag(1%)/P-Si/Pt 的感測器，靈敏度、反應時間及回復時間才分別為70%，1.5min及2min。很明顯吾人發展者特性有明顯的提升。

In this thesis, we developed the tandem heterojunctions with 3D nano structures for CO2 gas sensing applications. The tandem type sensing element effectively increases the sensing ability. For example, in a planar type sensor, under the condition of 150 oC, -3V, and 3000 ppm CO2 ambient, the sensor sensitivity can be promoted from 554% to 796% and 812% , respectively for the 2D structure , Ag connected tandem heterojunction sensing element, and 3D nano rod device but with single heterojunction sensing element. Furthermore, if both of the tandem sensing element and 3D nano-structures are employed, the sensitivity improvement can even increase up to 2187%. Besides, the improvement in the sensitivity also leads the reduction of response time from few minutes of the conventional resistive type to tenths seconds.

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