Highly Conductive RuO$_2$ Thin Films from Novel Facile Aqueous Chemical Solution Deposition

Ruthenium dioxide (RuO$_2$) thin films were synthesized by Chemical Solution Deposition (CSD) on silicon substrates using only water and acetic acid as solvents. The microstructure, phase-purity, electrical and optical properties as well as the thermal stability of the thin films have been characterized. The microstructure of the thin films strongly depends on the annealing temperature: A smooth thin film was achieved at an annealing temperature of 600$^\circ$C. Higher annealing temperatures (800$^\circ$C) led to radial grain growth and an inhomogeneous thin film. A very low resistivity of 0.89 {\Omega}m was measured for a 220 nm-thick thin film prepared at 600$^\circ$. The resistivity of the thin films increases with temperature, which indicates metallic behavior. Phase-purity of the thin films was confirmed with X-ray Diffraction (XRD) measurements, X-ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy. Transmission and reflectivity measurements indicate that RuO$_2$ efficiently blocks the UV-VIS and IR wavelengths. The optical constants determined via spectroscopic ellipsometry show high absorption in the near-IR region as well as a lower one in the UV-VIS region. The thermal stability was investigated by post-annealing, confirming that the thin films are stable up to 750$^\circ$C in synthetic air.