Effect of Precursor Sol Ageing on Sol-Gel Derived Ruthenium Oxide Thin Films

Abstract

In the present work we have optimized the process parameters to yield homogeneous, smooth ruthenium oxide (RuO₂) thin films on silicon substrates by a solution deposition technique using RuCl₃.×.H₂O as the precursor material. Films were annealed in a temperature range of 300°C to 700°C, and it was found that RuO₂ crystallizes at a temperature as low as 400°C. The crystallinity of the films improves with increased annealing temperature and the resistivity decreases from 4.86µΩ-m (films annealed at 400°C) to 2.94pµΩ (films annealed at 700°C). Ageing of the precursor solution has a pronounced effect on the measured resistivities of RuO₂ thin films. It was found that the measured room temperature resistivities increases from 2.94µΩ-m to 45.7µΩ-m when the precursor sol is aged for aged 60 days. AFM analysis on the aged films shows that the grain size and the surface roughness of the annealed films increase with the ageing of the precursor solution. From XPS analysis we have detected the presence of non-transformed RuCl₃ in case of films prepared from aged solution. We propose, that solution ageing inhibits the transformation of RuCl₃ to RuO₂ during the annealing of the films. The deterioration of the conductivity with solution ageing is thought to be related with the chloride contamination in the annealed films.