METHODS FOR THE PREPARATION OF NO, NO2 AND H-2 SENSORS BASED ON TIN OXIDE THIN-FILMS, GROWN BY MEANS OF THE RF MAGNETRON SPUTTERING TECHNIQUE

Thin films based on SnO2 (SnO2, SnO2-Pd, SnO2(Bi2O3), SnO2(In) and ITO (90% In2O3, 10% SnO2)) have been grown by means of the r.f. magnetron sputtering technique in order to be used as gas sensors. Sensors based on SnO2 with additives show a high sensitivity to nitrogen oxides at temperatures close to 573 K, while they show a great sensitivity to the H2 present in dry air in the range 623-723 K, except for the ITO thin films. The sensor with the highest response to nitrogen oxides is the SnO2(In) thin film, which presents a sensitivity of 20 in 20 ppm of NO at an operating temperature of 573 K. The sensors with the highest sensitivity to H2 is the SnO2-Pd thin film grown by the RGTO (rheotaxial growth and thermal oxidation) technique; it has a sensitivity equal to 50 in 50 ppm of H2 at an operating temperature of 623 K. Each kind of gas sensor is characterized by XRD and SEM analysis and by its response curves to various gases; the height of the eV(s) barrier is also obtained for SnO2 thin films. The mechanisms of interaction between the thin-film surface and the various gases have also been investigated.