Gas-sensitivity of SnO2 layers treated by rapid thermal annealing process

A rapid thermal annealing (RTA) treatment was used to improve the performance of ammonia sensors based on a MOSFET structure with a thin SnO2 layer used as a gate. RTA processes in vacuum with duration of 15–60 s and temperatures 600–800°C were applied. After thermal treatment samples are subjected to a cycle of successive steps with different environmental conditions in order to reveal the sensitivity, selectivity and reversibility of the response. It is found that the RTA process at 800°C, with duration of 60 s, rise time of 2 s and fall time of 4 s results in enhanced sensitivity to the active agent (NH3), reduced cross-sensitivity to water vapours (relative humidity) and improved reversibility of the deviceʹs response. This overall improvement of the performance is explained by surface changes of the SnO2 layer, provoked by the RTA process. Such changes are revealed by reflection high-energy electron diffraction (RHEED) and scanning electron microscopy (SEM).