INNOVATIVE HUMIDITY SENSITIVE ELECTRICAL-PROPERTIES OF SOL-GEL PROCESSED CERAMIC THIN-FILMS

Thin films based on K-doped TiO2 and on magnetite with very large humi dity sensitivity were prepared using a sol-gel technique. Metal alkoxi de solutions were deposited onto Al2O3 Substrates with comb-type Au el ectrodes with dip-coating and heated in air, for preparing prototype h umidity sensors. The humidity sensing electrical properties of the fil ms were evaluated using a.c. measurements. Resistance vs relative humi dity (RH) values showed variations as high as 8 and 7 orders of magnit ude in the RH range tested (4-85%), for the iron oxide and titania-bas ed films heated to 300 degrees C, respectively. These resistance chang es, although the films were dense, are even larger than those reported for porous ceramics. These novel results are interpreted in terms of conduction mechanisms, which are different from the mechanism usually accepted for porous ceramics.