Porous Hot-Wire Metal Oxides Thin Films in Hydrogen Sensing

In this work, the gas sensing properties of porous hot-wire WO3 (hwWO3) thin films have been investigated. These films were deposited on oxidized silicon substrates by heating a tungsten filament in a vacuum chamber. The resistance variations of these configurations caused by changes in their environment were monitored. Reversible changes of resistance, of the order of several MOhms, were observed in hwWO3 films caused by the presence or upon removal of H2 and without superficial doping of samples with noble metals. The magnitude of these changes, related to the sensitivity, was found to depend on hydrogen concentration and temperature of measurement. The time needed (response time) for the resistance to drop after H2 exposure was found comparable to that needed to recover to its initial value after H2 removal. Response times of the order of a few seconds were measured on hwWO3 films much shorter than those measured on WO3 samples deposited by chemical vapor deposition.