Improving ZnO Thin Film with CuO Nanorods to Enhance the Application in Lower-Work-Temperature Carbon Monoxide Gas Sensing

Abstract

In this study, radio frequency (RF) magnetron sputtering was used to deposit ZnO nanofilms and CuO nanorods. Firstly, the sputtering power was adjusted to study the structural porosity changes of ZnO. The oxygen flux and etching power were then adjusted to roughen the surface of the films to induce the optimal distribution of the CuO nanorods on the surface to increase its surface area for gas reaction. The ZnO film packaging process for gas sensing was also completed, mainly by a self-designed gas sensing circuit, at a lower work temperature of 100°C, to conduct sensitivity and response value analysis of CO gas sensing. In addition, X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) were used to analyze the crystallinity and morphology of ZnO, and high-resolution transmission electron microscopy (HRTEM) was used to analyze the interface microstructure of the ZnO/CuO nanorods. The absorbance of ZnO was measured by UV–Vis spectroscopy to indirectly verify the porosity. The results show that after depositing the ZnO film at 200 W, followed by roughening the surface with oxygen flux of 15 sccm and 100 W etching power for 10 min and then depositing the CuO nanorods for 10 s, the completed thin film structure had better CO sensing characteristics, and the highest response value was enhanced about 5% from 0.983 to 1.031. By optimizing the process parameters and incorporating the CuO nanorods, the sensing characteristics of the ZnO thin film were improved and a lower work temperature of 100°C for CO gas reaction was possible.