Reactive-sputter deposition and structure of RuO₂ films on sapphire and strontium titanate

Metallic films of RuO₂ were deposited by reactive-sputtering deposition on single crystal substrates of Al₂O₃ (0001) and SrTiO₃ (100) at room temperature and 450 °C. Measurement of the characteristic hysteresis loop revealed that the target's transition from a metal to a metal oxide surface occurred at a very high O₂/Ar ratio (88%) under our experimental conditions. The hysteretical behavior of the transition was evaluated experimentally and was modeled. Resonance-enhanced Rutherford backscattering spectrometry established that the films deposited at 450 °C had an oxygen to ruthenium ratio of 1.97, while a slightly higher value of 2.08 was observed for the films grown at room temperature. The latter films were amorphous, whereas those grown at 450 °C exhibited a highly oriented polycrystalline microstructure. On SrTiO₃ (100), the RuO₂ (100) plane is parallel to the substrate surface, but no in-plane orientation was found. The same face, RuO₂ (100), was also parallel to the surface of Al₂O₃ (0001), and the [001] direction of individual grains of RuO₂ aligned with the three <1010> directions of the substrate to produce a threefold mosaic microstructure.