Effect of barrier layers on BaTiO₃ thin film capacitors on Si substrates

The choice of the bottom electrode or barrier layer plays an important role in determining the electrical and structural properties of metal/ferroelectric/metal thin film capacitors. A substantial improvement of the electrical and structural properties of the capacitors was found by using RuO₂ as a bottom electrode. Electrical measurement on a capacitor with a structure of BaTiO₃(246 nm)/RuO₂ (200 nm)/SiO₂/Si, where the BaTiO₃ thin film was deposited at room temperature, showed a dielectric constant of around 15, leakage current density of 1.6 × 10^-7A/cm² at 4 V, a dc conductivity of 9.8 × 10¹⁴S/cm, and a capacitance per unit area of 5.6 × 10⁴pF/cm². A similar structure but with polycrystalline BaTiO³ (273 nm) as the dielectric deposited at 680°C showed a dielectric constant of 290, leakage current density of 1.7 × 10^-3A/cm² at 4 V, a dc conductivity of 1.2 × 10^-8 S/cm, and a capacitance per unit area of 9.4 × 10⁵ pF/cm². Scanning electron microscopy analysis on the films showed differences in the microstructure due to the use of different bottom electrode materials, such as RuO₂ or Pd.