Thin film micro carbon dioxide sensor using MEMS process

Pt/Na+ ion conductive ceramic thin film/Pt/carbonate (Na2CO3:BaCO3 = 1:1.7mol) system CO2 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 (2000-2500Angstrom) 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 (Na2CO3:BaCO3 = 1:1.7 molar ratio). The area of the sensing layer was 0.55 mm x 0.4 mm and that of total device was 3.2 mm x 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 CO2 concentrations from 1000 to 10,000 ppm was obtained at operating temperature of 400degreesC. The power consumption of the fabricated sensor was about 52 mW at 400degreesC. As results, it is supposed that the fabricated sensor could be applied for monitoring CO2 gas in environment. (C) 2004 Elsevier B.V. All rights reserved.