•Michael Lorenz¹, Holger Hochmuth¹, Martin Schallner², Roland Heidinger³, Daniel Spemann¹ und Marius Grundmann^1
1Universität Leipzig, Fakultät für Physik und Geowissenschaften, Institut für Experimentelle Physik II, D-04103 Leipzig, Germany
²Marconi Communications GmbH, D-71522 Backnang, Germany
³Forschungszentrum Karlsruhe, Institut für Materialforschung I, D-76021 Karlsruhe, Germany

Large-area Ba _x Sr _1-x TiO₃ (BSTO-x) thin films, doped with Fe, Mg, and Y, have been grown by pulsed laser deposition (PLD) on polycrystalline alumina based ceramics. The capacity and Q-factor of planar Pt / BTO:Fe / Pt capacitors were investigated within a temperature range from -35 to +85^° C for applied DC-bias voltages up to 10V at 1kHz. A homogeneous tunability of the capacity of about 60 % was achieved for applied electrical field strengths between 0 and 5V/ mm. Furthermore, by Fe-doping of BTO films and post-deposition annealing of the Pt / BTO / Pt structure the Q-factors could be increased by a factor of four up to 200 compared to the undoped films. However, at a microwave frequency of 30 GHz, higher values of the Q-factor of more than 300 at room temperature were measured for bare BSTO-0.45 films.

These results show the considerable influence of the interface, doping material and post-deposition treatment on the dielectric thin film properties. The physical reasons for this behavior are not completely understood up to now. Supported by the BMBF under FKZ 13N8158.