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Open AccessArticle

Low-Concentration Ammonia Gas Sensors Manufactured Using the CMOS–MEMS Technique

1
Department of Mechanical Engineering, National Chung Hsing University, Taichung 402, Taiwan
2
Department of Biomedical Engineering, National Taiwan University, Taipei 106, Taiwan
3
Department of Bio-Industrial Mechatronics Engineering, National Chung Hsing University, Taichung 402, Taiwan
4
Department of Electro-Optical Engineering, National United University, Miaoli 360, Taiwan
*
Author to whom correspondence should be addressed.
Micromachines 2020, 11(1), 92; https://doi.org/10.3390/mi11010092
Received: 10 December 2019 / Revised: 11 January 2020 / Accepted: 12 January 2020 / Published: 15 January 2020
(This article belongs to the Special Issue 10th Anniversary of Micromachines)
This study describes the fabrication of an ammonia gas sensor (AGS) using a complementary metal oxide semiconductor (CMOS)–microelectromechanical system (MEMS) technique. The structure of the AGS features interdigitated electrodes (IDEs) and a sensing material on a silicon substrate. The IDEs are the stacked aluminum layers that are made using the CMOS process. The sensing material; polypyrrole/reduced graphene oxide (PPy/RGO), is synthesized using the oxidation–reduction method; and the material is characterized using an electron spectroscope for chemical analysis (ESCA), a scanning electron microscope (SEM), and high-resolution X-ray diffraction (XRD). After the CMOS process; the AGS needs post-processing to etch an oxide layer and to deposit the sensing material. The resistance of the AGS changes when it is exposed to ammonia. A non-inverting amplifier circuit converts the resistance of the AGS into a voltage signal. The AGS operates at room temperature. Experiments show that the AGS response is 4.5% at a concentration of 1 ppm NH3; and it exhibits good repeatability. The lowest concentration that the AGS can detect is 0.1 ppm NH3 View Full-Text
Keywords: ammonia; gas sensor; low concentration; CMOS process; MEMS ammonia; gas sensor; low concentration; CMOS process; MEMS
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Shen, W.-C.; Shih, P.-J.; Tsai, Y.-C.; Hsu, C.-C.; Dai, C.-L. Low-Concentration Ammonia Gas Sensors Manufactured Using the CMOS–MEMS Technique. Micromachines 2020, 11, 92.

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