Structural and dielectric properties of Ba0.5Sr0.5TiO3 thin films grown on Si by off-axis sputtering

Polycrystalline and epitaxial Ba0.5Sr0.5TiO3 thin films were grown on Si by 90° off-axis sputtering for potential charge storage applications. Polycrystalline BST films deposited on Pt/Ta coated Si have demonstrated a dielectric constant as high as 600, and a loss tangent as low as 0.01 under optimized growth conditions. Epitaxial Ba0.5Sr0.5TiO3 (110) was achieved by depositions on metallic SrRuO3 (110) electrode, which was epitaxially grown on YSZ (100) buffered Si. The epitaxial heterostructure showed a high degree of crystallinity with little interdiffusion near the interfaces. The measured dielectric constant is about 360, and the leakage current density is lower than 4x10−7 A/cm2 at 1 V. A strong frequency dependence on dielectric constant and loss tangent is observed in 1–10 MHz frequency range for both types of film. This is attributed to the effect of a series resistance in the measurement loop. We show that roll-off frequency depends on both the magnitude of the capacitance and the resistivity of the bottom electrode.