Nanoporous tungsten trioxide grown by electrochemical anodization of tungsten for gas sensing applications

A gas sensitive nanoporous tungsten trioxide sensor produce by an anodization process is presented. The anodization of metallic tungsten layer to tungsten trioxide allows the on-wafer fabrication of the gas sensitive layer. The variation of the electrochemical potential enables the adjustability of the surface morphology and stoichiometry of the material. Nanoporous WO3-x with pore diameters between 5 and 600nm has been fabricated. XRD-measurements reveal that after the anodization process the material is amorphous. The annealing at 500 degrees C leads to a monoclinic/orthorhombic lattice. The developed sensor is highly sensitive to NO2 traces in the ppb range.