Performance of thin AlxOy, SixNy and AlN passivation layers for high temperature SAW device applications

This paper investigates the potential of passivation coatings for surface acoustic wave devices (SAW) based on aluminum nitride as a piezoelectric layer to operate at temperatures up to 1000 °C and in pure oxygen atmosphere. To increase the durability of SAW devices, a thin passivation layer was deposited on top of the structure, consisting of either aluminum nitride, alumina or silicon nitride. To investigate the effectivity of the passivation layer as oxygen diffusion barrier, time resolved X-ray diffraction (XRD) measurements were performed at 1000 °C in pure oxygen atmosphere for up to 24 h. Furthermore, the influence of an additional layer on top of the structure on the SAW performance were examined. Therefore, samples were measured before and after the deposition process. Afterwards, the samples were placed in a furnace in pure oxygen atmosphere to test the robustness of the different layers.