Thin films of(Ba,Sr)TiO3onPt/SiO2/Sisubstrates were deposited using rf magnetron sputtering at various substrate temperatures andO2/(Ar+O2)mixing ratios (OMR). The crystallinity of the films improved significantly as the OMR increased. The dielectric constant increased with increasing OMR and reached a maximum value at 50&percent; OMR. The leakage current density decreased with increasing oxygen flow, but had a minimum value at 40&percent; OMR. The results for the dielectric constant and the leakage current were interpreted in terms of polarization effect and loss theory. The film deposited at 450 °C and 50&percent; OMR exhibited good surface morphology and had a dielectric constant of 375, a tangent loss of 0.074 at 100 kHz, a leakage current density of7.35×10−9 A/cm2at an electric field of 100 kV/cm with a delay time of 30 s, and a charge storage density of49 fC/&mgr;m2at an applied field of 150 kV/cm. The 10 yr lifetime of time-dependent dielectric breakdown studies indicate that a 50&percent; OMR sample has a longer lifetime than the 0&percent; OMR sample. ©1997 American Institute of Physics.