Advanced RuO₂ Thin Films for pH Sensing Application

• Main Authors: Xinyue Yao, Mikko Vepsäläinen, Fabio Isa, Phil Martin, Paul Munroe, Avi Bendavid
• Format: Article
• Language: English
• Published: MDPI AG 2020-11-01
• Series: Sensors
• Subjects: ruthenium dioxide; magnetron sputtering conditions; thin film characterisation; pH performance
• Online Access: https://www.mdpi.com/1424-8220/20/22/6432

RuO₂ thin films were prepared using magnetron sputtering under different deposition conditions, including direct current (DC) and radio frequency (RF) discharges, metallic/oxide cathodes, different substrate temperatures, pressures, and deposition times. The surface morphology, residual stress, composition, crystal structure, mechanical properties, and pH performances of these RuO₂ thin films were investigated. The RuO₂ thin films RF sputtered from a metallic cathode at 250 °C exhibited good pH sensitivity of 56.35 mV/pH. However, these films were rougher, less dense, and relatively softer. However, the DC sputtered RuO₂ thin film prepared from an oxide cathode at 250 °C exhibited a pH sensitivity of 57.37 mV/pH with a smoother surface, denser microstructure and higher hardness. The thin film RF sputtered from the metallic cathode exhibited better pH response than those RF sputtered from the oxide cathode due to the higher percentage of the RuO₃ phase present in this film.