Oxygen diffusion barriers for epitaxial thin-film heterostructures with highly conducting SrMoO3 electrodes

Abstract

Transition metal perovskite oxide SrMoO 3 with a Mo 4 + 4d 2 electronic configuration exhibits a room-temperature resistivity of 5.1 μ ω cm in a single-crystal form and, therefore, is considered a prominent conducting electrode material for all-oxide microelectronic devices. Stabilization of the unfavorable Mo 4 + valence state in SrMoO 3 thin films necessitates reductive growth conditions that are often incompatible with a highly oxidative environment necessary to grow epitaxial heterostructures with fully oxygenated functional layers (e.g., tunable dielectric Ba xSr 1 - xTiO 3). Interestingly, only a few unit cells of the perovskite titanate capping layers SrTiO 3, BaTiO 3, and Ba 0.5Sr 0.5TiO 3 act as an efficient oxygen barrier and minimize SrMoO 3 oxidation into electrically insulating SrMoO 4 in the broad range of the thin-film growth parameters. The Mo valence state in SrMoO 3, determined by x-ray photoelectron spectroscopy, is used to analyze oxygen diffusion through the capping layers. The lowest level of oxygen diffusion is observed in Ba 0.5Sr 0.5TiO 3. A Ba 0.5Sr 0.5TiO 3 film with a thickness of only 6 unit cells preserves the Mo 4 + oxidation state in the SrMoO 3 underlayer up to the oxygen partial pressure of 8 mTorr at the temperature of 630 °C. Results, therefore, indicate that SrMoO 3 films covered with atomically thin Ba 0.5Sr 0.5TiO 3 remain conducting in an oxygen environment and can be integrated into all-oxide thin-film heterostructures with other functional materials.