Multifunctional humidity-gas sensor fabricated on silicon substrate

This paper describes a multifunctional humidity-gas sensor developed with thin-film technology, which is compatible with IC fabrication processes. The sensor is small and inexpensive, being fabricated on a silicon substrate using photolithography. The sensing material is a semiconducting Fe₂O₃-based thin film which is deposited by rf sputtering on a porous Al₂O₃ film. The impedance is measured between the top electrode (Pt) and the bottom electrode (Al). This sensor is sensitive to humidity, especially in middle and high humidity ranges at room temperature, while it is also sensitive to combustible gases such as hydrogen at 400°C. The response time is short enough from a practical point of view