High voltage dielectric properties of spin coated BaTiO3 on Ni foils

The voltage dependence of the electrical leakage current density of chemical solution deposited BaTiO3 films on high purity Ni foils was investigated as function of the underlying Ni microstructure. Depending on the Ni heat-treatment prior to BaTiO3 deposition, it was found that pores in the dielectric followed the profiles of the underlying Ni grain boundary grooved microstructure. The electrical properties were then characterized on capacitors with and without the presence of Ni grain boundaries. When a Ni grain boundary from the substrate is present, it is found that the loss tangent of the capacitor rises rapidly when the dc bias exceeds ~30kV/cm. The critical bias increases to ~100kV/cm when no substrate grain boundaries are included in the capacitor. In addition, the C-V curves are much more symmetric when grain boundaries are absent. This disparity in the electrical behavior was analyzed in terms of the mechanisms of charge conduction across the Ni-dielectric interface. While a reversed biased Schottky emission mechanism dominates the currents in areas free of Ni grain boundaries, the barrier at the cathode is ineffective when Ni grain boundaries are present in the substrate leading to considerable leakage current dominated by the forward biased Schottky barrier at the anode. The results are important to both embedded and surface mount capacitors.