Highly hydrogen-sensitive SnO2 nanoscale-particle films with platinum electrodes

We report a novel hydrogen-sensitive Schottky-diode device based on an SnO2 film consisting of nanoscale particles and with platinum electrodes on top, which has a very high response. SnO2 films were prepared through thermal oxidation of metallic Sn films, which were deposited using electron-beam evaporation with thicknesses ranging from 5 nm to 100 nm. The average size of the nano-particles shrinks as the thickness of the original Sn films decreases. Interdigital platinum (Pt) electrodes were fabricated on the SnO2 films for hydrogen sensing studies. Very high relative response (current change of 168 times) to low concentration H2 (100 ppm) was found for the device based on SnO2 film converted from 20 nm-thick as-deposited Sn film. Its response speed is also very fast, which is less than 10 s to reach half of the maximum response. It has excellent selectivity with low response to CO and null response to CH4. We propose that the sensing mechanism is the reduction of the Schottky barrier height (SBH) at the Pt/SnO2 interface. A pinch-off model and a circuit model are presented to reveal the relationship between the relative response and the film thickness or particle size.