Fabrication of NO x gas sensors using In 2O 3–ZnO composite films

Abstract

In 2O 3–ZnO composite films were fabricated and their NO x sensing characteristics were investigated in this study. The content of ZnO in In 2O 3–ZnO film was controlled by adjusting the Zn 2+/In 3+ molar ratio ( r) during the film preparation. With suitable amount of ZnO incorporated into the In 2O 3 films, the responses of the composite films to NO x at operation temperatures below 200 °C were greatly improved. However, as the ZnO content was further increased, the grain of the composite film started to merge into big ones, thus decreasing the surface area and resulting in lower sensor responses. The detection limit ( S/ N = 3) of In 2O 3–ZnO composite film ( r = 0.67) reached 12 ppb at 150 °C. Both pure In 2O 3 ( r = 0) and In 2O 3–ZnO composite films ( r = 0.67) showed no response to CO gas.