The effects of thickness and operation temperature on ZnO:Al thin film CO gas sensor

Al-doped ZnO films were deposited onto SiO2/Si substrates by rf magnetron sputtering system as a CO gas sensor. The dependence of the thin film thickness on CO gas sensing properties was investigated, where the film thickness was varied by controlling the deposition time. The structure of the deposited ZnO:Al films was determined by X-ray diffraction, scanning electron microscopy and atomic force microscopy. The CO gas sensing properties were determined by in situ measurement for surface resistance of the thin film as a function of film thickness, different atmosphere, and operation temperature. It was shown that the films were flat and smooth with (0 0 0 1) preferred orientation. The grain size was increased as the film thickness was increased during deposition. Here, the CO gas sensing properties were relative to the structural characteristics where the maximum sensitivity of 61.6% was obtained at 65 nm film thickness for the operation temperature of 400 °C.