Thin films of the aluminum oxide (Al2O3)-titanium oxide (TiO2) system including Al2O3, TiO2, and Al2O3/TiO2 were prepared by radio-frequency (r.f.) magnetron sputtering using ceramic targets of Al2O3, TiO2, and Al2O3/TiO2 composites with different Al2O3/TiO2 ratio. These films were studied at different substrate temperatures, r.f. powers, and annealing temperatures. Composition, microstructure, thermomechanical property of internal stress, and mechanical property of scratch adhesion, were evaluated. A thin film with a dielectric constant of 62 and a loss tangent of 0.012 was obtained at 500 degreesC from a 10/90 target. This thin film remained the high dielectric constant of TiO2, but had an improvement in the dielectric loss tangent. Al2O3-containing films had a higher resistivity and breakdown field, which was improved further by annealing. Optical properties, such as refractive index and optical transmittance, were also investigated. (C) 2004 Elsevier B.V. All rights reserved.