THERMAL STABILITY OF EPITAXIAL SrRuO3 BOTTOM ELECTRODES AND THEIR CONTRIBUTION TO THE CHARACTERISTICS OF (Ba0.5Sr0.5)TiO3 FILMS GROWN ON THEM

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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 (Ba0.5Sr0.5)TiO3 films were grown on these pre-heat-treated SrRuO3 bottom electrodes by RF magnetron sputter deposition. (Ba0.5Sr0.5)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 (Ba0.5Sr0.5)TiO3 film inducing the concentration of electric field and/or the diffusion of Ru into (Ba0.5Sr0.5)TiO3 film. This result suggests that the characteristics of capacitors are significantly affected by the heat treatment conditions of SrRuO3 bottom electrodes.

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