Influence of the morphology of platinum combined with β-Ga2O3 on the VOC response of work function type sensors

Polycrystalline β-Ga2O3/platinum thick films can be used as a novel sensing layer for the detection of VOC (volatile organic compounds) in sensors based on the readout of the work function (Kelvin probe, Floating Gate FET). An intermittent short thermal activation at 175 °C enables a subsequent room temperature operation. The supposed mechanism is based on the formation of oxygen species during this thermal activation. After cooling down to room temperature those species remain on the surface for some hours to days. The sensing mechanism at room temperature is assumed to be based on a reaction of reducing gases with this oxygen species resulting in a change of the work function due to the change of the surface properties. The addition of platinum as catalyst is necessary to obtain a response to various VOC. Pt clusters with varying size are investigated which are responsible for improving the VOC sensitivity. Therefore platinum on micro- and nanoscale was used. The best variants are capable to detect small concentrations (ppb–ppm) of different VOC (aldehydes, alcohols, esters, ketones, and hydrocarbons) as well as toxic CO well below their odor or toxicity threshold. Meaningful responses are still present some days after the thermal activation.