Effect of annealing temperature on the crystallization and oxygen sensing property of strontium titanate ferrite sol–gel thin films

SrTi0.6Fe0.4O3−δ (STF40) gas sensors were deposited using a novel modified sol–gel route. The influences of thermal annealing (400–750°C) on the crystallization and oxygen sensing performance were investigated. As revealed by XRD, TEM and XPS studies, the deposited sol–gel thin films had amorphous structure and the formation of cubic perovskite phase started at 450°C. The crystallization of the films improved with annealing temperature and completed at around 650°C. The oxygen sensing characterization of the film sensors were carried out using a custom-designed gas sensing characterization system. Abnormal n-type oxygen sensing response was observed for the sensors annealed at 400 and 450°C, which was found attributed by the n-type amorphous phases that remained in the sol–gel films. On the other hand, good and repeatable p-type oxygen sensing response was obtained for sensors annealed at 500°C and above.