Methods for the preparation of NO, NO 2 and H 2 sensors based on tin oxide thin films, grown by means of the r.f. magnetron sputtering technique

Abstract

Thin films based on SnO 2 (SnO 2, SnO 2Pd, SnO 2(Bi 2O 3), SnO 2(In) and ITO (90% In 2O 3, 10% SnO 2)) have been grown by means of the r.f. magnetron sputtering technique in order to be used as gas sensors. Sensors based on SnO 2 with additives show a high sensitivity to nitrogen oxides at temperatures close to 573 K, while they show a great sensitivity to the H 2 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 SnO 2(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 H 2 is the SnO 2Pd thin film grown by the RGTO (rheotaxial growth and thermal oxidation) technique; it has a sensitivity equal to 50 in 50 ppm of H 2 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 SnO 2 thin films. The mechanisms of interaction between the thin-film surface and the various gases have also been investigated.