Gas-sensing properties of sprayed films of (CdO)/sub x/(ZnO)/sub 1-x/ mixed oxide

A novel NO/sub 2/ sensor based on (CdO)/sub x/(ZnO)/sub 1-x/ mixed-oxide thin films deposited by the spray pyrolysis technique is developed. The sensor response to 3-ppm NO/sub 2/ is studied in the range 50/spl deg/C-350/spl deg/C for three different film compositions. The device is also tested for other harmful gases, such as CO (300 ppm) and CH/sub 4/ (3000 ppm). The sensor response to these reducing gases is different at different temperatures varying from the response typical for the p-type semiconductor to that typical for the n-type semiconductor. Satisfactory response to NO/sub 2/ and dynamic behavior at 230/spl deg/C, as well as low resistivity, are observed for the mixed-oxide film with 30% Cd. The response to interfering gas is poor at working temperature (230/spl deg/C). On the basis of this study, a possible sensing mechanism is proposed.