Characterization of porous Al2O3#SiO2/Si sensor for low and medium humidity ranges

We present the preliminary a.c. electrical characterization of a humidity sensor based on a thin Al2O3 porous layer grown on an SiO2/Si substrate. The sensor is prepared by sputter deposition of a thin film of Al, followed by its anodic oxidation in a sulphuric acid solution. A gold electrode is deposited on the substrate tilted at a grazing angle with respect to the substrate plane. The electrical a.c. measurements are made in the range 100 Hz-15 MHz and in a small chamber where either the relative humidity or the temperature could be easily changed. The sensor response is not influenced by interfering gases like CO, CO2, NO2, CH4, C2H6 and H2. The experimental results of the impedance spectroscopy are compared with the frequency responses of different equivalent circuits of the sensor.