Phase-controlled molybdenum dioxide electrodes by RF reactive magnetron sputtering for achieving high-k rutile TiO₂ dielectric

Molybdenum dioxide (MoO₂) has recently garnered attention as a promising oxide electrode for next-generation dynamic random-access memory capacitors owing to its high work function, low resistivity, and good thermal stability. The formation of pure, reliable MoO₂ films is a significant challenge because of their higher formation energy than that of non-conductive orthorhombic molybdenum trioxide (MoO₃). Herein, we investigated the controlled growth of MoO₂ films by manipulating the process pressure and oxygen-to-argon (O₂/Ar) ratio using radio frequency reactive magnetron sputtering. By increasing the O₂/Ar ratio at a fixed process pressure (pp), sputtered MoO_x films were fabricated as metallic Mo, monoclinic MoO₂, and orthorhombic MoO₃. The MoO₂ film with Mo/O atomic ratio of 0.5 was achieved in the narrow process window of O₂/Ar ratio of 0.22 and pp = 3 mtorr. The MoO₂ films exhibited a smooth surface morphology with a root mean square roughness of 0.34–0.68 nm. The resistivity of MoO₂ film was 972 μΩ cm, which was decreased to 374–524 μΩ cm by rapid thermal annealing in N₂ at 600 °C-800 °C. The phase-controlled MoO₂ electrode led to the in-situ crystallization of high-k rutile TiO₂ with a dielectric constant of 93 via local epitaxial growth. This might be attributed to the excellent coherence in the atomic arrangement and low lattice mismatch between the distorted rutile MoO₂ (011) and rutile TiO₂ (110) planes.