Electrical properties and microstructures of Pt/Ba0.5Sr0.5TiO3/SrRuO3 capacitors

Thin film polycrystalline Ba0.5Sr0.5TiO3 capacitors employing conductive perovskite oxide SrRuO3 as 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 nm Ba0.5Sr0.5TiO3 (BSTO) thicknesses, respectively. The lowest SiO2 equivalent thickness of 0.54 nm was obtained for 20-nm-thick BSTO capacitors; their leakage current density was less than 1×10−7 A/cm2 for ±1.8 V bias. The cross-sectional transmission electron microscope observation revealed that BSTO and SrRuO3 (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.”