52 GHz 35% Scandium Doped Aluminum Nitride Overmoded Bulk Acoustic Resonator

Scandium doped Aluminum Nitride (ScAlN) has become a piezoelectric material of interest for Bulk Acoustic Wave (BAW) resonators as it offers an intrinsically high electromechanical coupling (k2t). However, little is known about ScAlN at mm-wave frequencies. In this work, we demonstrate an innovative Overmoded Bulk Acoustic Resonator (OBAR) design that incorporates 35% Scandium doped Aluminum Nitride (Sc0.35Al0.65N) piezoelectric layer. The ScAlN OBAR presented herein is a BAW device that is excited in the 2nd overtone by means of the ScAlN layer and a stack of metal electrodes that act simultaneously as acoustic cavity and as acoustic Bragg mirrors. The fabricated device demonstrates k2t of 6.1% and Quality factor (Q) of 114 at 52 GHz - a substantial improvement in the k2t. Q figure of merit of ScAlN acoustic resonators at mm-wave frequencies.