THERMAL STABILITY OF EPITAXIAL SrRuO₃ BOTTOM ELECTRODES AND THEIR CONTRIBUTION TO THE CHARACTERISTICS OF (Ba_0.5Sr_0.5)TiO₃ FILMS GROWN ON THEM

ABSTRACT

Thermal stability of epitaxial SrRuO₃ films grown on (100)SrTiO₃ substrates by RF magnetron sputter deposition as a function of the oxygen partial pressure (pO₂) was investigated in view of the crystal structure, surface roughness and electrical resistivity. The surface normal lattice parameter and diffraction peak intensity of SrRuO₃ films heat-treated at 700°C decreased with the decrease of pO₂ below 1.7 Pa, and finally SrRuO₃ peak completely disappeared at pO₂ below 1.7 × 10⁻⁴ Pa. Surface roughness also became high with decreasing the pO₂. X-ray diffraction and Non-Rutherford Elastic Resonance Scattering measurements suggest that SrRuO₃film most probably decomposes to metal Ru and amorphous SrO after the heat treatment at pO₂ below 1.7 × 10⁻⁴ Pa. Epitaxial (Ba_0.5Sr_0.5)TiO₃ films were grown on these pre-heat-treated SrRuO₃ bottom electrodes by RF magnetron sputter deposition. (Ba_0.5Sr_0.5)TiO₃ film with low crystallinity deposited on SrRuO₃ bottom electrode heat-treated under pO₂ below 1.7 × 10⁻⁴ Pa showed much higher leakage current than the others. This is considered to be due to the high surface roughness of (Ba_0.5Sr_0.5)TiO₃ film inducing the concentration of electric field and/or the diffusion of Ru into (Ba_0.5Sr_0.5)TiO₃ film. This result suggests that the characteristics of capacitors are significantly affected by the heat treatment conditions of SrRuO₃ bottom electrodes.

Keywords:

• SrRuO₃
• oxide electrode
• epitaxial
• thermal stability
• Sputtering
• (Ba,Sr)TiO₃
• thin film
• capacitor

ACKNOWLEDGMENTS

The authors are thankful to Prof. Seiichiro Koda and Dr. Hiroshi Uchida of Sophia University for preparing standard samples of XRF measurement.