Stable electrodes and ultrathin passivation coatings for high temperature sensors in harsh environments

Sensor operation in harsh environments up to 1000degC requires robust packages including stable electrodes and protective coatings. We have developed nanostructured ultra-thin (< 100 nm) Pt-10%Rh / ZrO₂ electrode structures grown by e-beam co-evaporation that operate at temperatures approaching 1000degC. X-ray diffraction (XRD), resistivity, and electron microscopy (EM) studies indicate incorporation of ZrO₂ within the film delays recrystallization, maintaining a stable morphology. We have also developed ultra-thin (< 50 nm) SiAlON passivation coatings that mechanically protect the sensor surfaces, yet allow interaction with the environment. Different SiAlON stoichiometeries were produced by rf magnetron sputtering of Al and Si targets in O₂/N₂/Ar mixtures. The SiAlON films are amorphous and extremely smooth (< 1 nm rms) and remain so even after extended annealing at 1000degC. Our results are applicable to a wide range of high temperature sensor configurations.