近年來，專家學者已經開發和研究出各種不同類型的氣體感測器。而自從金屬氧化物半導體與電阻式氣體感測器發表後，由於成熟的半導體製程技術，使得體積小、靈敏度高、可大量生產的半導體式氣體感測器逐漸成為發展之主流。
本論文中所提出的感測元件是以氧化鋅為基材，利用水熱法成長氧化鋅奈米柱，並製作成電阻式氣體感測器，再分別針對不同的氣體，如氫氣、氨氣以及二氧化氮，去研究其感測與響應特性。
首先，探討氧化鋅材料在不同生長條件下的所成長氧化鋅奈米柱的特性。在不同的水溶液濃度、種晶層厚度、水溶液pH值、和成長溫度下所成長的氧化鋅奈米柱也會有顯著的差異。再進一步探討各個條件下所成長氧化鋅奈米柱之表面型態特性，如：長度、直徑、長寬比和結晶面向之差異。
其次，利用黃光微影及熱蒸鍍技術沉積指叉狀電極於藍寶石基板上並結合水熱法成長氧化鋅奈米柱，以製備電阻式氣體感測器。氧化鋅材料除了對氫氣擁有感測特性外，也具備檢測氨氣的能力。尤其在高溫時，元件呈現更短的響應時間與更高的感測靈敏度。
接著研究氧化鋅奈米柱電阻式感測器在不同溫度及濃度下的二氧化氮感測特性，由於二氧化氮為氧化性氣體，吸附後會使得感測器之阻值上升。有鑑於此，我們改變氧化鋅奈米柱之成長條件以降低感測器之電阻，以利提升感測訊號之變化範圍。此外，較大的電流變化量也可使感測器較不易受到雜訊之干擾。
最後，由實驗結果可知，藉由氧化鋅材料本身對氣體的有效的感測特性，加上奈米柱的高表面積和體積比，我們可以製備一高靈敏度之氣體感測器，未來也希望將此感測元件與微機電系統整合以製作多功能之智慧型感測器。

Over the past decades, different types of gas sensors were developed. With the progress of the semiconductor fabrication technologies, semiconductor-based gas sensors with small size and high sensitivity have become the mainstream in the gas sensor community.
The studied resistance-type gas sensors consisted of the zinc oxide (ZnO) material. ZnO material was employed for the gas sensors due to its advantages including wide direct band gap of 3.37 eV at room temperature, high mechanical and thermal stabilities and much larger free exciton binding energy of 60 meV. The studied devices are capable of monitoring different gases such as hydrogen, ammonia, and nitrogen dioxide.
First, different growth conditions of zinc oxide material, such as precursor concentration, thickness of ZnO seed layer, pH value, and the growth temperature, were performed. The features of synthesized ZnO nanorods were investigated in terms of length, diameter, aspect ratio and crystallographic orientation.
Second, the conventional photolithography and thermal evaporation were employed to produce the interdigitated electrodes on the substrate. ZnO nanorods can be selectively grown on the patterned substrate to form the ZnO nanorods-based gas sensors. It is known that ZnO material shows selectivity not only to hydrogen molecules but also to ammonia molecules. The studied device exhibited short response time and high sensitivity, especially at high temperatures.
Finally, the nitrogen dioxide sensing characteristics of the ZnO nanorods-based gas sensors were studied and demonstrated. Based on the sensing mechanism of metal-oxide, the oxidizing gas can lead to the decrease of ZnO conductance. Therefore, in this research, the ZnO nanorods-based gas sensor was fabricated toward relatively low resistivity in order to increase the variation range of the sensing signal. In addition, sensors with large current variation exhibit larger margins to noise interference. Consequently, the ZnO nanorods-based gas sensor shows the potential for the integration of micro-electro-mechanical system (MEMS) application to develop and realize multifunctional smart sensors.

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