Hydrogen induced tunnel emission in Pt/(BaxSr1-x)Ti1+yO3+z/Pt thin film capacitors

The leakage current density-applied field (J-E-A) characteristics of (BaxSr 1-x)Ti1+yO3+z (BSTO) thin film capacitors with Pt electrodes that have been annealed in forming gas (95% Ar 5% H-2 or D-2) were investigated over the temperature range from -60 to +60 degreesC. Forming gas annealing significa ntly increased the leakage current density. The J-E-A characteristics exhib ited features that could not be fully explained by either a simple thermion ic emission or tunneling (Fowler-Nordeim) formalism. Using the general char ge transport theory of Murphy and Good, we show that the J-E-A characterist ics can be successfully interpreted in terms of tunneling of electrons thro ugh the interfacial Schottky barrier with the peak in energy distribution o f the incident carriers strongly dependent on applied field. At high applie d fields the energy distribution of incident carriers is peaked near the Fe rmi level in the electron injecting metal electrode at all temperatures con sidered in this study, leading to almost temperature independent J-E-A char acteristics. 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 obs erved. Good agreement between experiment and theory is demonstrated for a r easonable parameter set for BSTO thin films strongly suggesting that the hi gh leakage current density often observed after forming gas annealing resul ts from tunneling of electrons through the interfacial Schottky barrier. (C ) 2001 American Institute of Physics.