Influence of multi-layer TiO₂/SnO₂ heterojunctions on fast and sensitive ethanol detection

The fabrication of MEMS gas sensors based on SMO sensing materials has become popular in commercials. However, due to the dense surface, the MEMS gas sensor based on sputtered sensing film always shows low sensitivity and slow response. Herein, we report multi-layer TiO₂/SnO₂ heterojunctions sensing film deposited by sputtering techniques. SnO₂ and TiO₂ thin film have an approximate thickness of 265.34 nm and 66.28 nm, respectively. The effects of different-layer TiO₂/SnO₂ heterojunctions and annealing temperatures to sensing film on gas sensing properties were investigated. The different samples with the same surface and annealed temperature exhibit different gas sensing properties, which indicates that more layer heterojunctions may decrease the positive effects of heterojunctions and oxygen adsorptions on the gas sensing properties. The two-layer TiO₂/SnO₂ heterojunctions sensing film with an annealed temperature of 400 °C in air obtain the best gas sensing properties, which has a response value of 7.54 and response/recovery time of 33/298 s to 50 ppm ethanol at 260 °C. Furthermore, the MEMS gas sensor based on two-layer TiO₂/SnO₂ heterojunctions sensing film can detect ethanol ranging from 1 ppm to 1000 ppm with excellent linearity.