Sputtered SnO2:NiO thin films on self-assembled Au nanoparticle arrays for MEMS compatible NO2 gas sensors

Here, heterostructured Au/SnO2:NiO thin films are fabricated by sputtering SnO2:NiO target onto the self-assembled Au nanoparticle (NPs, diameter ∼ 9.5 nm) arrays and then activated by H2 annealing. Compared with the SnO2 and SnO2:NiO thin film counterparts, the 20 nm thick Au/SnO2:NiO film shows the highest NO2 sensing performance after activated at optimized temperature of 500 °C, with high response of ∼185 to 5 ppm NO2, low detection limit of ∼50 ppb, high selectivity, good stability and also low sensor-to-sensor variation of <15%. The gas sensing property enhancement could not only be attributed to catalytic role of the AuNPs, but also to the effective Schottky barrier and p-n junction formation between Au, SnO2 and NiO, which is verified by the relatively higher Fermi level of ∼4.56 eV compared with those of 4.1-4.3 eV as measured by the ultraviolet photoelectron spectroscopy. Furthermore, this method is of generality to effectively enhance the electron transfer in other sensing materials like pure SnO2 and WO3, showing the promising potency of this Micro-Electrical-Mechanical System (MEMS) compatible heterostucture fabrication method in wafer-scale gas sensor production with high sensitivity, selectivity and good consistency towards low concentration gas detection such as ppb-level NO2.