Hydrogen induced tunnel emission in Pt/(BaxSr_1-x)Ti_1+yO_3+z/Pt thin film capacitors

Abstract

The leakage current density-applied field (J-EA) characteristics of (BaxSr1-x)Ti1+yO3+z, (BSTO) thin film capacitors with Pt electrodes that have been annealed in forming gas (95% Ar 5% H2 or D2) were investigated over the temperature range from -60 to +60°C. Forming gas annealing significantly increased the leakage current density. The J-EA characteristics exhibited features that could not be fully explained by either a simple thermionic emission or tunneling (Fowler-Nordeim) formalism. Using the general charge transport theory of Murphy and Good, we show that the J-EA characteristics can be successfully interpreted in terms of tunneling of electrons through the interfacial Schottky barrier with the peak in energy distribution of the incident carriers strongly dependent on applied field. At high applied fields the energy distribution of incident carriers is peaked near the Fermi level in the electron injecting metal electrode at all temperatures considered in this study, leading to almost temperature independent J-EA characteristics. At lower applied fields the peak in energy distribution shifts towards the conduction band edge where thermally assisted tunneling occurs and a more pronounced temperature dependence of the current density is observed. Good agreement between experiment and theory is demonstrated for a reasonable parameter set for BSTO thin films strongly suggesting that the high leakage current density often observed after forming gas annealing results from tunneling of electrons through the interfacial Schottky barrier. © 2007 American Institute of Physics.