The different Al contents effects of Ba0.5Sr0.5Ti0.95Mg0.05O3 (BSTM) thin films grown on Pt/TiN/SiO2/Si substrates in the crystallographic structure, surface morphology, dielectric constant, loss tangent, leakage current, and figure of merit were investigated. The BSTM films properties are studied as a function of Al content and have remarkable improvements including dielectric loss, leakage current, and figure of merit (FOM) as well as films grain sizes. With increasing Al content, the dielectric constant (k), tunability (T), loss tangent (tan delta), and leakage current density (J(L)) decrease while the FOM, defined as T/tan delta, and breakdown strength increases. The maximum dielectric constant at zero bias, tunability, dielectric loss, FOM, and leakage current density of 1 mol% Al-doped BSTM films at 280 kV cm(-1) are 248, 40%, 0.0093, 43, and 3.76 x 10(-7) A cm(-2), however, the same measured conditions of undoped BSTM films are 341, 54%, 0.0265, 20, and 1.19 x 10(-6) A cm(-2), respectively. The dc resistivity increases from 2.33 x 10(11) Omega cm of the BSTM film to 6.08 x 10(12) Omega cm of the 5 mol% Al-doped BSTM film at 280 kV cm(-1). In addition, the tolerance factor (t) of Al-doped BSTM perovskite thin films is 0.97 as compared to 0.87 of the undoped BSTM thin films. The increasing of tolerance factor value indicates that the specimens with Al-doped BSTM films are more stable than undoped specimens. (C) 2007 Elsevier B. V. All rights reserved.