Energy level alignment and electrical properties of (Ba, Sr)TiO3/Al2O3 interfaces for tunable capacitors

The interface formation between Ba0.6Sr0.4TiO3 and Al2O3 has been studied using photoelectron spectroscopy with in situ sample preparation. A negligible valence band discontinuity, corresponding to a similar to 5.6 eV barrier for electron transport at the BST/Al2O3 interface is determined. Current-voltage measurements show that the leakage current can be significantly reduced by inserting the Al2O3 barrier layer between barium strontium titanate (BST) and Pt electrode. Different charge injection behavior depending on Al2O3 thickness is observed, which correspond well with the experimentally determined energy band diagrams. Direct tunneling from the metal electrode into the BST conduction band through the Al2O3 barrier layer is observed. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3459899]