Surface Acoustic Wave sensor based on AlN/Sapphire structure for high temperature and high frequency applications

In this work, the performance of AlN/Sapphire structure in high frequencies is investigated. Several SAW devices were performed with various designs (gap, wavelength, metallization ratio, ... ) to study simultaneously different parameters (acoustic velocity, electromechanical coupling (K-2), acoustic propagation loss (alpha), TCF) versus frequency and temperature. Experimental results showed that as expected, alpha increases with temperature while K-2 is enhanced at high temperatures. Due to the antagonistic evolution of these two parameters, insertion loss decreases or increases as function of the gap. We also evidenced that this structure allows fabrication of devices operating up to 1.5 GHz and that the frequency varies linearly with temperature.