Annealing effect on the methane sensing performance of Pt–SnO2/ZnO double layer sensor

Low power consumption is a new emerged requirement for methane sensors long-term working in a gas supervisory   control   system. Great challenges remain in development of heat free methane sensors based on metal oxide semiconductors (MOS). In this work, Pt-doped SnO 2 (Pt-SnO 2 ) grow on well aligned ZnO nanorod-array to form an inter-staggered double-layer structure on AZO glass by a two-step hydrothermal method, with the annealing temperature being systematically studied. The optimized processing parameters are 1 at% Pt doping content and 700 °C annealing temperature, offering the best sensing response of 3.36 to 800 ppm CH 4 at room temperature. SnO 2 /ZnO without Pt doping shows linear I-V relationship, while the Pt-SnO 2 /ZnO shows a Schottky-like I-V curve with the Schottky barrier height decreases as increasing the CH 4 concentration. The activation energy (Δ E a ) for CH 4 dissociation decreases with increasing the annealing temperature, and the Δ E a of the optimized Pt-SnO 2 /ZnO sample is only one-third of that in the SnO 2 /ZnO. In addition to the piezoelectric polarization electric field in ZnO, the build up Schottky-like barrier and the reduced activation energy via Pt doping and annealing are demonstrated to be efficient for enhancing the methane sensing performance at low operation temperature.