Platinum thin film electrodes for high-temperature chemical sensor applications

Metal thin film electrodes that may withstand harsh-environments are crucial in the development of advanced chemical sensor applications, as well as, microelectromechanical (MEMS) devices that operate at elevated temperatures. The objective of this work was to investigate high-temperature platinum (Pt) thin films that are compatible for these applications. Special attention was paid to the development of new Pt-based electrode compositions and microstructures that limit sintering and grain coarsening. This work investigated different multilayer coatings of hafnium (Hf) and zirconium (Zr) as both the adhesion layers and grain boundary pinning-phases within the Pt films. All adhesion layers and Pt layers were deposited to the same ∼35 nm and ∼425 nm thicknesses, respectively. The coating deposition was completed by DC magnetron sputtering on alumina substrates at 200 °C. The multilayer Pt thin films were processed at 800 °C and 1200 °C for 1–48 h, since the anticipated operation temperature is ≥1000 °C. Scanning Electron Microscopy (SEM), Energy-dispersive X-ray Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS) were utilized to characterize the changes in chemistry and microstructure. Electrical resistivities of the as-deposited and thermally processed Pt films were evaluated by four-point probe technique. The work identified a Hf–Zr–Pt multilayer thin film that demonstrated a room temperature resistivity <625 × 10−9 Ω m after being processed to 1200 °C for 48 h. A lift-off technique was finally used to produce an electrode pattern with the optimum film structure for sustained high-temperature operation.