Investigation Into the Quality Factor of Piezoelectric-on-Silica Micromachined Resonators

In this paper, we investigate loss mechanisms in piezoelectric-on-silica bulk acoustic wave resonators, including those resulting from thermoelastic damping (TED), surface roughness, and supporting tethers. Alternate resonator designs, piezoelectric materials, and fabrication processes are demonstrated to empirically test these loss mechanisms. Quality factors (Qs) in the order of ~16000 at a center frequency of 5 MHz have been consistently measured for aluminum nitride (AlN)-on-silica coupled-ring resonators. It is shown that neither TED nor surface losses are the dominant sources of loss for AlN-on-silica resonators in the megahertz regime. Instead, it is suggested that charge redistribution loss resulting from nonuniform strain across the piezoelectric layer is the dominant loss mechanism, with a charge redistribution Q of ~38000 at 5 MHz for AlN-on-silica devices. When all loss mechanisms are considered, the total Q is estimated to be 25000, a value comparable to the measured results of the piezoelectric-on-silica resonators of this paper.