Ba0.6Sr0.4TiO3 (BST) dielectric thin films doped by Cr were prepared using an alkoxide-based sol-gel method on the Pt/Ti/SiO2/Si substrate. Atomic force microscopy and X-ray diffraction analysis showed that increasing the Cr-doping ratio causes increased grain size while the surface remains smooth and crack-free. It was also found that compared with undoped films the increase of Cr content in BST improves the dielectric constant and the leakage-current characteristics. The figure of merit reached the maximum value of 72.3 at the 5 mol% of Cr doping. This composition showed the dielectric constant of 426, the loss factor of 0.0065, tenability of 47.7%, and leakage-current density (at the electric field of 100 kV/cm) of 5.31 x 10(-8) A/cm(2). The results show that the Cr-doped BST thin films are prospective candidates for applications in tunable devices, (C) 2004 Elsevier B.V. All rights reserved.