An Al2O3 sensor for low humidity content: Characterization by impedance spectroscopy

A sensor able to measure very low humidity concentrations and with possible applications for geophysical research has been developed using Al2O3 porous thin films. The sensor is obtained by anodization in sulphuric acid of an Al thin film deposited by d.c. sputtering. The electrical properties are evaluated using impedance spectroscopy for different contents of water vapour in the range 20 to 200 ppmv and for temperatures from -60 to +40 degrees C. The response of the sensor changes according to the frequency of the applied voltage. These results allow us to formulate a hypothesis on the mechanism of water absorption.