Oxygen-sensing property of sol-gel-derived SrTi1-x Fe x O3- delta thin films with different iron concentrations (x =0.2-0.8)

In this contribution, SrTi1-x Fe x O3- delta thin film gas sensors with different iron concentrations (x =0.2 to 0.8) were fabricated using a modified sol-gel spin-coating method and annealed at 650 degree C for 1h under synthetic air ambient. X-ray diffraction revealed the single phase polycrystalline structure of the thin films and their crystallinity decreased with iron concentrations. The films with high iron concentrations were not well crystallized and had large amount of amorphous-like structures, as indicated by transmission electron microscopy observation. The oxygen-sensing properties of the sensors were examined at different operating temperatures. The SrTi1-x Fe x O3- delta thin film sensors with x less than or equal to 0.4 showed a normal p-type-sensing response whereas sensors with x greater than or equal to 0.5 exhibited anomalous n-type-sensing response. This abnormal-sensing behavior can be explained by amorphous-like structures in the films with higher iron concentrations, which was caused by incomplete formation of cubic perovskite phase.