Study of selectivity of NO2 sensors composed of WO3 and MnO2 thin films grown by radio frequency sputtering

Thin-film WO3 sensors with MnO2 filters were prepared to reduce interference of O3 for ppb-range NO2 sensors. A trilayer structure, MnO2 filter, MnO2 + WO3 insulting layer and WO3 film, was deposited by radio frequency sputtering. The microstructure, crystalline phase and chemical composition of the films were characterized by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The sensors were tested for 25–200 ppb O3 and 50–400 ppb NO2 in moist air at working temperatures ranging from 150 to 250 °C. The results show that the sensors with thin MnO2 filters are capable to reduce the O3 interference while keeping a good response to NO2.