where A is a constant, e is the electronic charge, is the corresponding tunneling barrier height, is the effective electron mass, E is the electric field magnitude and h is the Planck constant. Based on this model, linear fitting was performed on the SFO thin films by plotting ln(J) vs. 1/E. A good linear fit was obtained for no anneal and O2 annealed SFO samples, suggesting a trap-assisted tunneling conduction mechanism, as seen by the fitting data in the insets of Fig. 2b and d, respectively. The fitting shows that is 132 meV and 136 meV for the SFO samples without annealing and annealed in O2, respectively. However, the trap-assisted tunneling model did not yield a good linear trend for the SFO film annealed in vacuum. On the other hand, the Schottky emission model is used to explain temperature-dependent leakage mechanisms that are dominated by injection of charge carriers at the metal-insulator interface, and is given by the following: