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

SrTi_0.6Fe_0.4O_3-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.