Influences of platinum doping concentrations and operation temperatures on oxygen sensitivity of Pt/SnO2/Pt resistive gas sensors

Abstract

Influences of surface platinum (Pt) doping concentrations and operation temperatures on oxygen sensing properties of Pt/SnO2/Pt metal–semiconductor–metal (MSM) resistive gas sensors were investigated incorporating structural and chemical variations. Although tetragonal phase dominated crystallographic structure of the virgin film, it was observed that the triclinic phase with minor peak intensities was also present. With increasing the doped Pt concentration, the triclinic phase of the SnO2 cannot be detected due to diffusion of the Pt into the SnO2 lattices. Surface particle sizes increased up to 200 nm and relative porosity of the film surface almost enhanced with increasing the Pt concentrations. Oxygen deficient and chemically metastable phase of the SnxOy was transformed to SnO2 with the Pt addition due to catalytic effects of the Pt. Different vibrational modes became active depending on the Pt content which was due to the stretching of the SnO2 bonds. In addition, the resistivity of the Pt-doped SnO2 films increased with the Pt additions. The oxygen sensitivity of the sensor increased with increasing both the Pt concentrations and operation temperatures. The optimum operation temperature was found to be 335 °C. Interestingly, as operation temperature exceeds to 225 °C, high Pt concentration decreased the sensor sensitivity. In addition, selectivity of the MSM sensor changes with the Pt additions. The obtained results have depicted that the parameters used in the sensor fabrication and operation should be carefully selected to increase sensing properties of the MSM resistive gas sensors.