Fabrication of WO 3 nanodot-based microsensors highly sensitive to hydrogen

Abstract

A novel approach that involves electrochemical anodising for fabricating WO 3 nanodot-based microsensors is presented. The formation of gas sensing film is assisted by a nanoporous anodic alumina layer grown from a thin layer of aluminium sputtering-deposited over a thin layer of tungsten (Al/W bilayer). The anodic film annealed at 500 °C consists of a self-ordered array of WO 3 nanodots (∼50 nm), each composed of few nanocrystallites (∼9 nm) having thermostable tetragonal structure. The processes for forming the WO 3 nanodot active films are fully compatible with standard technology for fabrication of sensor chips on a micromachined silicon wafer. Characterization of the WO 3 nanodot film was performed by field-emission scanning electron microscopy, atomic force microscopy and X-ray diffraction analysis. A study of the ability of the WO 3 nanodot-based microsensors to detect H 2, CO, ethanol and relative humidity was presented for the first time. High sensitivity to hydrogen, with linear response characteristic was obtained in the range of low H 2 concentrations (5–20 ppm). The gas sensing mechanism of the WO 3 nanodot-based sensors was discussed.