Thin film polycrystallineBa0.5Sr0.5TiO3capacitors employing conductive perovskite oxideSrRuO3as a bottom electrode were fabricated on Si substrates by rf-magnetron sputtering. Dielectric constants of these capacitors were observed to be 206, 214, and 146 for 60, 40, and 20 nmBa0.5Sr0.5TiO3(BSTO) thicknesses, respectively. The lowestSiO2equivalent thickness of 0.54 nm was obtained for 20-nm-thick BSTO capacitors; their leakage current density was less than1×10−7 A/cm2for ±1.8 V bias. The cross-sectional transmission electron microscope observation revealed that BSTO andSrRuO3(SRO) formed continuous columnar grains and showed epitaxial growth at the interface of BSTO/SRO within each column; this microstructure of the capacitors was tentatively designated “local epitaxial film.” ©1997 American Institute of Physics.