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

Abstract

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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), acoustic propagation loss (α), and temperature coefficient of frequency) versus frequency and temperature. Experimental results show that, as expected, α increases with temperature while K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> 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.