Regensburg 2010 – wissenschaftliches Programm
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DF: Fachverband Dielektrische Festkörper
DF 10: Dielectric surfaces and interfaces
DF 10.6: Vortrag
Mittwoch, 24. März 2010, 16:10–16:30, H11
(Ba,Sr)TiO3 tunable capacitors with Al2O3 barrier layer — •Shunyi Li1, Yuliang Zheng2, Andre Wachau1, Robert Schafranek1, Rolf Jakoby2, and Andreas Klein1 — 1Institut für Materialwissenschaft, Technische Universität Darmstadt, Darmstadt, Germany — 2Mikrowellentechnik, Technische Universität Darmstadt, Darmstadt, Germany
(Ba,Sr)TiO3, due to its high non-linearity of dielectric constants under electric field, is considered as a promising material for tunable integrated components for microwave applications. However, the high dielectric loss and high leakage current still remain a main impediment, where the interface between electrodes and dielectrics plays an important role. BST varactors with Al2O3 barrier layers at the interfaces are prepared via RF magnetron sputtering. The interface formation has been studied by using x-ray photoelectron spectroscopy with in situ sample preparation. A high energy barrier for electrons is formed at the BST/Al2O3 contact. Leakage current measurements show that the injection of charge carriers into dielectrics can be effectively reduced by the barrier layer. Significant changes of dielectric properties are observed during dielectric characterizations. The capacitance and the tunability are reduced due to the insertion of Al2O3, and the overall capacitance can be well simulated by serial capacitor model. The quality factor of the varactor is improved due to the better insulating interfaces. By introducing the Al2O3 layer, charged interfaces are observed in the dielectric measurements, which is considered as the result of accumulation of charge carriers at the BST/Al2O3 interfaces.