AlN/Pt/LN-Y128 packageless acoustic wave temperature sensor.

Batteryless, wireless and packageless acoustic wave sensors are particularly desirable for harsh high temperature environments. In this paper, an acoustic wave sensor based on a lithium niobate (Y+128° cut, abbreviated LN-Y128) substrate with a buried platinum interdigital transducer (IDT) in an aluminum nitride (AlN) overlayer is investigated. Previously, it was demonstrated theoretically that due to the specific properties of LN-Y128, Rayleigh-type guided waves can propagate at the AlN/IDT(Pt)/LN-Y128 interface. Here, this structure is, for the first time, studied experimentally, including the growth and properties of the AlN layer onto irregular platinum IDTs. Both Shear Horizontal and Rayleigh type waves have been identified after the AlN deposition and the velocities are consistent with the fitted SDA-FEM-SDA simulations. Electrical measurements with a surface perturbation and temperature measurements show that the AlN/IDT(Pt)/LN-Y128 bilayer structure is promising as a packageless high temperature sensor.