Nanostructured gas sensors and electrical characterization of deposited SnO2 nanoparticles in ambient gas atmosphere

SnO2 nanoparticles with small particle size distribution (σ < 1.2), and diameters of 10, 15 and 20 nm are deposited on platinum interdigital transducers with 2 μm finger width and 2 μm spacing. Impedance spectroscopy measurements in synthetic air, taken in the temperature range between 100 and 250 °C show a clear dependence of the measured impedance on the particle size. Three different contributions to the overall impedance have been resolved for 10 nm particles and assigned to the contribution of bulk, intergranular contact and electrode contact. Particles of larger diameters do not allow such a clear distinction. The experimental observations have been analyzed by fitting the measured data with equivalent circuit functions, where typical serial connections of simple R and parallel RCs are used for fitting. As expected for a semiconducting material, the resistance decreases with increasing temperature. Activation energies of the different charge carrier transport processes were determined from Arrhenius plots.