Shear mode bulk acoustic wave resonator based on c-axis oriented AlN thin film

Abstract

A shear mode resonator based on bulk waves trapped in c-axis oriented AlN thin films was fabricated, simulated, and tested. The active 1.55 μm thick AlN layer was deposited on top of an acoustic Bragg reflector composed of SiO2/AlN λ/4 layer pairs. The resonance was excited by means of interdigitated electrodes consisting of 150 nm thick Al lines. Analytical and simulation calculations show that the in-plane electric field excites bulk acoustic wave shear modes that are trapped in such an AlN film slab. The experimental frequency corresponds well to the theoretical one. The evaluated resonance of the fundamental shear mode at 1.86 GHz revealed a coupling of 0.15% and Q-factor of 870 in air and 260 in silicon oil.