Gas sensing studies of an n-n heterojunction metal oxide semiconductor sensor array based on WO3 and ZnO composites

An array of composite metal oxide semiconductor (MOS) sensors based on WO₃ and ZnO, has been fabricated and evaluated against various concentrations of ethanol and NO₂ at operating temperatures between 300-500 °C. The composites were prepared by simple manual mechanical mixing and screen printed as porous thick-film gas sensors, and characterized by Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). The composites showed a marked enhancement in response under certain conditions, particularly towards 100 ppm ethanol at 350 °C with a 1.5-fold better response compared to pure WO₃ and 6.5-fold with respect to pure ZnO and towards 800 ppb NO₂ at 300 °C, with a 3.5-fold better response compared to pure WO₃ and 7-fold with respect to pure ZnO. The enhanced behavior was thought to be very complex, with influencing factors being the packing structure, junction effects, composition, microstructure and experimental conditions.