AlN/Sapphire: Promising Structure for High Temperature and High Frequency SAW Devices

In this paper, the performance of AlN/sapphire structure in high frequencies is investigated. Several SAW devices are fabricated with various designs (free-space delay, wavelength, metallization ratio, etc.) to study simultaneously different parameters (acoustic velocity, electromechanical coupling (K-2), acoustic propagation loss (alpha), and temperature coefficient of frequency) versus frequency and temperature. Experimental results show that, as expected, alpha increases with temperature while K-2 is enhanced at high temperatures. Because of the antagonistic evolution of these two parameters, insertion loss decreases or increases as function of the free-space delay. We also demonstrate that this structure allows fabrication of devices operating up to 1.5 GHz and that the frequency varies linearly with temperature.