A NEW TECHNIQUE FOR THE PREPARATION OF HIGHLY SENSITIVE HYDROGEN SENSORS BASED ON SNO2 (BI2O3) THIN-FILMS

H-2 in air can be detected with sensors based on semiconductor oxides. A new technique for growing a hydrogen sensor based on SnO2(Bi2O3) thin films is presented here. The thin films have a thickness of 200-250 nm and the metals are in the atomic ratio Bi/Sn = (3-5) at.%/(97-95) at.%. The two metals are deposited by means of evaporation in a high vacuum; the metal-semiconductor phase transformation consists of a thermal cycle in air. The initial step involves a fast transition from room temperature up to 350-degrees-C over a few minutes, and causes a local partial melting of the metallic alloy. The surface of these thin films is made up of spongy agglomerates, having a surface area about 1000 times larger than a flat surface and covering about 60-70% of the total area. Sensors grown with this method also seem to be able to detect a few ppm of H-2 in air at 450-degrees-C with a response time of about 10-20 s.