SnO2 sol–gel derived thin films for integrated gas sensors

In this paper, we present for the first time the compatibility of sol–gel method for SnO2 thin film preparation with the silicon technology for integrated gas sensor microfabrication. An integrated circuit (IC) compatible test structure of medium power consumption equipped with boron-doped silicon heater and Au/W metallization is developed. The acid composition of the (liquid) sol phase, the thermal budget of sensing layer structuring, selective wet etching of SnO2 sensing film, thickness uniformity and step coverage of SnO2 sol–gel films are fitted with the requirement of above test structure where metal layer is deposited before SnO2 film. Nanometric grain sizes of undoped and antimony doped polycrystalline SnO2 films are obtained, as revealed by XRD investigations. The AFM measurements of SnO2 thin films deposited on existing Au/W metallization shown the excellent step coverage and morphology of SnO2 films used for gas sensing applications. Low temperature gas sensing properties of our SnO2 sol–gel derived thin films in reducing (CH4, CH3COOH) and oxidizing (NO2) are preliminary reported by using our integrated test structure.