Highly Sensitive Pt-TiO_2-Pt Sandwich-type Metal Oxide Gas Sensors of Hydrogen: Influence of the electrode design on the gas sensing properties

摘要

In this paper, we present a metal oxide-based hydrogen gas sensor with high sensitivity and short response time, operating at room temperature. Our sensors have a sandwich-like structure with a thin metal oxide layer in between the top and bottom electrode. The electrodes are in a shape of long narrow bridges, perpendicular to each other. It has been shown that narrowing the top electrode down to ～100 nm causes the sensitivity to substantially increase and reduces the response time. The sensor response (ratio R_(Air)/R_(H2)) to 1% H_2 in synthetic air can be as high as ～10~5 at room temperature, with response time of only a few seconds. A theoretical model explaining such a behavior is also proposed. The increased sensitivity of sensors with narrow top electrode is explained by non-trivial abrupt change of the charge carrier transport mechanism from thermoemission to electron drift. This change is caused by the hot electron temperature instability induced by combination of the H_2 diffusion profile under the top electrode and high intensity of electric field between the electrodes.