由於現今社會快速工業化與都市化所帶來的影響，人們的生活環境正面臨重大的空氣汙染問題，其排放的有毒氣體正對人體健康、生態環境與全球氣候構成嚴重的威脅[1-3]。其中，最具危害性的氣體包括二氧化氮（NO2）、二氧化硫（SO2）、一氧化碳（CO）和硫化氫（H2S），而且這些危害性的氣體也與國人的呼吸系統和心血管疾病密切相關[4]。近年來，透過分析人體呼出的氣體來檢測哮喘、肺癌、腎臟疾病和糖尿病等多種疾病的研究日益受到關注[8]。舉例來說，人體呼出氣體中含有氮氣、氧氣、二氧化碳、一氧化碳、一氧化氮、水蒸氣，以及烴類、醇類、萜烯、醛類等揮發性有機化合物（VOC）與非揮發性分子的混合物[9]。因此，針對大氣環境中的有害氣體進行定性或定量分析，對於保障健康安全及創造經濟效益至關重要。隨著微機電製程技術的革新，其為氣體感測器提供了多種創新的解決方案，並且達到小尺寸、高精確度、低成本和低功耗等優勢[12,13]，使之能夠應用於環境監測[14]、食品安全[15]、醫療儀器[16]及加工生產[17]等領域。迄今已開發出許多不同種類的氣體感測機制，包括：電化學式[22-24]、光纖[25,26]、金屬氧化物半導體（MOS）[27-29]、電容式[30]、場效電晶體（FET）[31]，以及石英晶體微天平（QCM）[32]。目前，互補式金屬氧化物半導體（CMOS）的製造技術已相當成熟，是各大商業晶圓代工廠的標準製程，該技術提供多層的介電層、金屬層以及多晶矽（Poly-Si）的堆疊，同時若再結合CMOS的後製程，即能將各種感測元件與積體電路做單晶整合，完成CMOS-MEMS氣體感測器 [36-40]。據此，本研究基於台灣積體電路製造股份有限公司（TSMC）所提供的標準商用CMOS製造平台，並利用後製程加工技術，實現可在室溫下操作的氣體感測器，包含安培式與蕭特基型兩種。
本研究的第一個設計係微型CMOS-MEMS安培式氣體感測器，其包含一個懸浮式微孔結構之工作電極、一個固定式具有相似微孔結構之輔助電極，以及電解液儲存槽的微型腔體，其中該懸浮式工作電極的優勢在於提升感測靈敏度並降低感測器的反應時間。此外，本研究也在工作電極的表面鍍上一層鎳金屬（Ni）薄膜，以便在常溫環境下進行乙醇感測。根據量測結果顯示，在20 ppm至1000 ppm乙醇氣體濃度範圍內，具有高靈敏度、快速反應時間與極佳的選擇性。
本研究的第二個設計為CMOS-MEMS蕭特基氣體感測器，該設計的核心特色為利用一個微型腔體來做為感測區域，並透過開放式交錯指叉狀電極（opened IDEs）來進行訊號感測。其中，參考設計與本研究提出之設計皆使用相同的電極形狀，主要差別係在於感測電極的金屬種類，藉此來驗證蕭特基效應的機制與作用。根據量測結果顯示，相較於對稱金屬材料之參考設計，本研究所提出的非對稱金屬材料設計對於NO₂氣體的感測靈敏度(sensitivity)提升了兩倍，並具有更佳的線性度表現。此外，非對稱金屬材料之設計在常溫下，展現出該感測器在量測NO₂中具有良好的辨識區別性(selectivity)。
簡言之，本研究基於台積電（TSMC）標準CMOS製程開發出高性能的室溫氣體感測器。該技術有望應用於環境監測、醫療保健等多個領域，提供更準確且可靠的量測結果。不僅如此，本研究的成果也顯示創新氣體感測技術的未來與發展潛力。

The environment is presently under considerable issues due to air pollution caused by rapid industrialization and urbanization. The emission of toxic gases causes severe risks to human health, ecosystems, and climate [1-3]. The most harmful gases are nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO), and hydrogen sulfide (H2S), which are linked to respiratory and cardiovascular issues [4]. Recently, there has been growing interest in analyzing exhaled human breath to detect various diseases, including asthma, lung cancer, kidney disease, and diabetes [8]. Exhaled breath contains nitrogen, oxygen, carbon dioxide, carbon monoxide, nitric oxide, water vapor, and a mixture of Volatile Organic Compounds (VOC) such as hydrocarbons, alcohols, terpenes, aldehydes, and other nonvolatile molecules [9]. Therefore, it is essential to conduct qualitative or quantitative analyses of these atmosphere gases to ensure health safety and provide economic benefits. Micro-electromechanical systems (MEMS) gas sensors exhibits the excellent features including reduced physical size, improved accuracy, lower costs, and decreased power consumption [12, 13], that can apply across various fields, such as environmental monitoring [14], food quality assessment [15], medical instrumentation [16], and process control [17]. To date, several sensing techniques have been introduced, including electrochemical sensors [22-24], optical fiber sensors [25, 26], metal oxide semiconductors (MOS) [27-29], capacitance sensing electrodes [30], field-effect transistors (FET) [31], and quartz crystal microbalances (QCM) [32].Complementary Metal Oxide Semiconductor (CMOS) process is well-established fabrication technology provided by various commercial foundry. The standard CMOS platform offers multiple layers of dielectric, metal, and poly-silicon (Poly-Si). Combining with the post-CMOS micromachining processes, this capability allows for the fabrication and monolithic integration of various sensing units, auxiliary structures, and electrical routings to create CMOS-based gas sensors [36-40]. This thesis leverages the benefits of the standard commercially available CMOS fabrication platform together with the post-CMOS micromachining processes provided by TSMC (Taiwan Semiconductor Manufacturing Company) to propose two designs, Amperometric type and Schottky contact-based type, both operating at room temperature.
The first design features a micro CMOS-MEMS amperometric gas sensor that includes a suspended plate with a micro-hole structure as the working electrode, a fully-anchored plate with a similar micro-hole structure as the counter electrode, and a micro cavity serving as the electrolyte reservoir. The suspended working electrode is specifically designed to enhance sensitivity and reduce the sensor’s response time. A nickel (Ni) film is deposited on the working electrode to facilitate ethanol sensing under ambient conditions. This sensor demonstrates the high sensitivity, fast response time, and excellent selectivity within the range of 20 to 1000 ppm of ethanol gas.
The second design involves a CMOS-MEMS Schottky contact-based gas sensor that features an opened interdigitated electrode (opened IDEs) for signal acquisition, along with a micro cavity that serves as the sensing area. Both the reference and proposed designs utilize opened IDEs with symmetric and asymmetric metal contacts to illustrate the related-Schottky effects in the sensor. The proposed design, which incorporates asymmetric metal contacts, demonstrates a two-fold improvement in sensitivity and the improved linearity characteristics for NO2 gas in comparison to the reference design with symmetric metal contacts. In addition, the proposed sensor shows its selectivity for NO2 gas at room temperature.
Overall, this thesis establishes a foundation for developing high-performance room-temperature gas sensors using the standard TSMC CMOS process. The findings and advancements from this study could transform in various fields such as environmental monitoring and healthcare sector by providing more accurate and reliable measurements. The progress achieved in this research is promising for further innovation and exploration in gas sensor technology.