Thin film micro carbon dioxide sensor using MEMS process

• Published in: Sensors and actuators. B, Chemical Vol. 102; no. 1; pp. 20 - 26
• Main Authors: Bang, Yeung-Il, Song, Kap-Duk, Joo, Byung-Su, Huh, Jeung-Soo, Choi, Soon-Don, Lee, Duk-Dong
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2004
• Subjects: Carbon dioxide sensor; MEMS technology; NASICON; Carbon dioxide sensor; NASICON; MEMS technology
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/j.snb.2003.11.039

Pt/Na + ion conductive ceramic thin film/Pt/carbonate (Na 2CO 3:BaCO 3=1:1.7 mol) system CO 2 micro gas sensor was fabricated and the sensing properties were investigated. The Na + ion conductive thin film was prepared by RF magnetron sputtering method. The thin film micro carbon dioxide sensor was prepared by using silicon process combined with MEMS technology. A NASICON thin film (2000–2500 Å) as main layer of the device was formed on N/O/N film using magnetron sputtering system. In order to simplify the device process, both the heater and lower electrode were formed on the same plane. And carbonate thin film as a sensing layer was formed on the upper electrode by sputtering sodium–barium carbonate target (Na 2CO 3:BaCO 3=1:1.7 molar ratio). The area of the sensing layer was 0.55 mm×0.4 mm and that of total device was 3.2 mm×4.5 mm. The study of NASICON thin film conductivity was carried out using AC impedance spectroscopy. The properties of NASICON thin film for various temperatures were investigated. The NASICON thin film showed a higher ionic conductivity (0.43 S/cm) compared to that of bulk NASICON material. The Nernst’s slope of 57 mV per decade for CO 2 concentrations from 1000 to 10,000 ppm was obtained at operating temperature of 400 °C. The power consumption of the fabricated sensor was about 52 mW at 400 °C. As results, it is supposed that the fabricated sensor could be applied for monitoring CO 2 gas in environment.