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

Sensor operation in harsh environments up to 1000°C requires robust packages including stable electrodes and protective coatings. We have developed nanostructured ultra-thin (≪ 100 nm) Pt-10%Rh / ZrO
2
electrode structures grown by e-beam co-evaporation that operate at temperatures approaching 1000°C. X-ray diffraction (XRD), resistivity, and electron microscopy (EM) studies indicate incorporation of ZrO
2
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 O
2
/N
2
/Ar mixtures. The SiAlON films are amorphous and extremely smooth (≪ 1 nm rms) and remain so even after extended annealing at 1000°C. Our results are applicable to a wide range of high temperature sensor configurations.