Barium strontium titanate (Ba0.5Sr0.5TiO3, BST) thin films were prepared on Pt/Ti/SiO2/Si and Pt/Cr/SiO2/Si substrates by sol-gel method. The effects of Pt/Ti and Pt/Cr bottom electrodes on the microstructure and dielectric properties of BST thin films were studied. The X-ray diffraction patterns show that both these films crystallize into a perovskite structure. The atomic force micrographs indicate that the films using Pt/Ti and Pt/Cr as bottom electrodes have different grain distributions and grain sizes. The dielectric constant of the films using Pt/Cr as bottom electrodes decreases significantly and the loss tangent and tunability decrease slightly. However, the figure of merit of the films using Pt/Cr as bottom electrodes still increases from 24.3 to 27.6. (c) 2005 Elsevier B.V. All rights reserved.