Is AlN/Sapphire bilayer structure an alternative to langasite for ultra-high-temperature SAW applications?

This paper explores the potentiality to use AlN/sapphire structure as alternative piezoelectric material to langasite (LGS) for high-temperature SAW applications. In situ SAW measurements performed in vacuum up to 1050°C attest that AlN/Sapphire is more stable than LGS in such conditions. While in the case of LGS, the signal is completely lost after 8 hours at 1050°C, the device based on AlN/sapphire stays alive for 60 hours at this extreme temperature. Moreover, the degradation is attributed not to AlN but to the agglomeration phenomena undergone by the Iridium IDTs. The AlN/Sapphire structure shows also, between room temperature and at least 1050°C, a great sensitivity to temperature as well as a good linearity, which is very suitable for temperature sensor applications.