本論文探討整體(3D)奈米柱狀結構之PIN二極體式甲烷(CH4)感測器研製。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)成長多晶二氧化鉿( HfO2)薄膜，再濺鍍上各種不同負型之金屬氧化物(WO3、SnO2、ZnO)作為感測層。並利用XRD、AFM及SEM分別量測薄膜結晶及觀察表面結構和厚度來探討這些材料的基本特性及做最佳選。
最後利用熱蒸鍍系統(Thermal evaporation)成長金屬鈀作為催化電極及接觸電極，並在背面成長金屬鋁作為歐姆電極，如此完成整個Pd/n-MOX/i-HfO2/p-Si/Al PIN二極體之製作。共製作四種不同結構元件來研究比較其感測特性:(1)使用不同本質絕緣層材料(P/N、HfO2、SiO2及TiO2)，(2)使用不同製程通入氬/氧氣體比例之二氧化鉿薄膜為本質絕緣層，(3)結構為傳統平面薄膜式(2D)及3D奈米柱狀，(4)使用不同材料（ZnO、SnO2、WO3）為感測層。
實驗結果顯示，本質絕緣層為氧化鉿薄膜且製程氬/氧比例為5:1時，可最有效地降低元件之漏電流；且3D奈米柱狀結構者，因可有效增加氣體接觸之面積/體積比，故相較於平面薄膜式者，靈敏度也由498.5%提升至1652%。另外，三種不同金屬氧化物感測層的奈米柱狀結構中也以WO3對甲烷氣體感測能力最佳。在溫度200℃，逆偏壓-3V及甲烷氣體濃度100ppm條件下，其靈敏度為152.9%，大大於SnO2及ZnO之85.5%和21.9%。在反應時間及氣體選擇比方面，WO3奈米柱狀結構者也有較快速的反應時間及對氫氣及二氧化碳的選擇比。
本論文之3D奈米柱狀結構PIN甲烷感測器在溫度200℃、濃度100ppm下，其靈敏度為152.9%、反應時間為20s，相較於已發表文獻Pt/ZnO/Zn之MSM Schottky之靈敏度(18%)及反應時間(52.2s)為佳。

The Pd/MOX/HfO2 p-i-n diodes on Si substrate were developed for methane gas (CH4) sensing applications. Firstly, the p(100) Si substrates were etched by AgNO3 mixed HF solution to form nanorod structure. Then the intrinsic layer HfO2 film was deposited on the Si nanorods with radio frequency sputtering system, and followed by deposition of various metal oxide such as WO3、SnO2、ZnO as sensing elements. The sensing element was examined using XRD、AFM and SEM, respectively for crystallinity, surface roughness and morphology. Finally, Pd metal was deposited thermally on the top as the catalyst and electrode contact to complete the device.
We optimized the CH4 gas sensor performances through the following studies :(1) using different intrinsic layer materials such as p/n、HfO2、SiO2、TiO2 , (2) to deposit HfO2 film with varying O2/Ar flow ratio, (3) comparing the 3D nanorod structure to the conventional 2D thin film p/n diode one , and(4) use of different metal oxides such as WO3、SnO2、ZnO as sensing element.
Experimental results show the intrinsic layer of hafnium oxide with oxygen atomic ratio of 5/1 is best dielectric for reduction of off leakage current. Besides, the 3D p-i-n nanostructure enhances the sensitivity of the sensor, from 498.5% of the conventional 2D thin film type to 1652%. In addition, under 200 oC, 3V reverse bias and 100ppm methane ambient, the WO3 sensing element can attain the highest sensitivity of 152.9%, which is more than 85.5% and 21.9% for SnO2 and ZnO, respectively. Furthermore, the WO3 has the fast response time of 20 sec and the highest selectivity compared with hydrogen and carbon dioxide gases.
In this work, under 200 oC and 100ppm ambient, the developed 3D nanorod p-i-n CH4 sensor has the best performance of 152.9% and 20 sec, respectively for sensitivity and response time. The performances are better than that of 18% and 52.2 sec for the reported Pt/ZnO/Zn MSM Schottky diode under same conditions.

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