Long-term stability of SnO2 gas sensors: The role of impurities

The target of this research was the minimization of the long-term drift of thick film SnO₂ semiconductor gas sensors. Sensing nanoparticle material was precipitated from the solution using original method, which excludes the penetration of impurities into crystalline lattice. It was shown that the rate constant of crystallite growth of this material at 700degC is lower than the rate constant measured for commercial Sigma-Aldrich nanomaterial by a factor of 10. This difference was attributed to higher concentration of Na⁺ and Cl^- ions promoting the crystal growth of the commercial material. Both materials doped with Pd and Pt were used for the fabrication of thick film sensors. Their stability was estimated as a drift of sensor signal to propane (0.2% in air) after 330, 460, and 590 hours of operation. Total signal drift was of 25% for the commercial SnO₂ and only ~1% for the home-made one. This indicates the drastic influence of impurities in the initial material on the signal long-term stability of semiconductor gas sensors.