CAPACITIVE HUMIDITY SENSOR WITH CONTROLLED PERFORMANCES, BASED ON POROUS AL2O3 THIN-FILM GROWN ON SIO2-SI SUBSTRATE

The electrical properties of a capacitive humidity sensor, based on an aluminium sputtered film anodized in sulfuric acid, are investigated. A silicon substrate, covered with SiO2, was used because of the exten sive use of this material in microelectronics. Al2O3 layers with contr olled thickness were deposited by sputtering onto the porous Al2O3 fil m and their influence on the sensor performances was studied. Dependin g on the thickness of the sputtered alumina layer, the sensors show a linear response in different ranges of r.h. The response and recovery times are 0.5 and 15 s, respectively, for all humidity ranges; a low h ysteresis effect was observed. The sensor performances are interpreted in terms of variation of the pore dimensions on the sensor surface.