Micromachined metal oxide gas sensors: opportunities to improve sensor performance

This review deals with gas sensors combining a metal oxide based sensing la yer and a substrate realized by using micromachining. It starts by giving a n overview of the design principles and technology involved in the fabricat ion of micromachined substrates examining thermal and mechanical aspects. B oth kinds of micromachined substrates, closed-membrane-type and the suspend ed-membrane-type, are discussed. The deposition of the sensing layer is com plicated by the mechanical fragility of the micromachined substrates. Diffe rent approaches used for the formation of the sensing layer such as thin fi lm and thick film deposition techniques are reviewed. Finally, the gas sens ing function of the sensitive layer is analyzed and various ways for extrac ting the information are: presented with respect to the improvement of sens or performance brought by this new approach. (C) 2001 Elsevier Science B.V. All rights reserved.