InxOyNz films with a Ta2O5 promoter for the detection of CO, H2, and CH4

Abstract

A new combination of gas sensitive materials based on InxOyNz and Ta2O5 capable of detecting traces of combustible gases (CO, H2, and CH4) is presented. Compared to pure InxOyNz films (∼120nm), InxOyNz films using a thin (∼3nm) oxidized tantalum overlayer (δ-Ta2O5) show a significantly enhanced sensitivity to CO, H2, and CH4 at 350–450°C, while the cross-sensitivity to NO2 is reduced by one order of magnitude. The CO sensitivity at 400–450°C is increased by a factor of 2.0–4.0 and the H2 sensitivity is increased by a factor of 1.5–2.0. The relative change of the dc-resistance is 0.42–1.02 for 60ppm CO and 10–12 for 1000ppm H2. With respect to the gas concentration applied, the highest sensitivity is observed for CO among the tested combustible gases. The optimum operating temperatures for the detection of H2 and CO are 400 and 450°C, respectively. Remarkably, a low concentration of 200ppm CH4 can be detected with pure InxOyNz at 450°C, but the same concentration of CH4 can be detected at temperatures as low as 350°C using InxOyNz with the thin δ-Ta2O5 modification. The new film system shows optimum sensitivity to 200ppm CH4 at 450°C, demonstrating a relative change of the dc-resistance of 0.66 with a response time τ50 of about 30s. This sensitivity is found to be three times of that given by pure InxOyNz.