Ba0.5Sr0.5TiO3 (BST) thin films doped with W were deposited oil LaNiO3 (LNO) electrode by RF-magnetron sputtering. The microstructure and electrical properties of BST thin films were studied as a function of W content, W-doped BST films show smoother surface and smaller grain size in comparison with the undoped BST film. With increasing W content, the dielectric constant. tunability, dissipation factor. and leakage current decrease while the figure of merit (FOM) and breakdown strength increase. Doping with the optimal content of 1% W. the BST film has a dielectric constant of 239, a tunability of 30%, a dissipation factor of 0.0066, a FOM value of 45.2, a leakage current density of 16 nA/cm(2) and a breakdown strength of 500 kV/cm. (C) 2004 Elsevier B.V. All rights reserved.