Optimization of tungsten oxide films electro-deposited on macroporous silicon for gas sensing applications: Effect of annealing temperature

Polycrystalline WO3 films grown on macroporous silicon via electrochemical deposition, have been studied as a function of annealing temperature. The hybrid structure was characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The microstructure and grain-size of the metal oxide film were found to have significant influence on its electrical and sensing properties. DC conductivity measurements reveal the rectifying behavior of the junction, which is found to increase with annealing temperature. The increased sensitivity of the samples annealed at 700 °C has been attributed to a lower grain size, which contributes to an increase in the depletion region per unit length. An extrapolation of the variation of the resistance ΔR/R0=1.5% predicts possible ethanol sensing up to 1 ppm.