Ultralow Acoustic Loss Micromachined Butterfly Lamb Wave Resonators on AlN Plates.

This study reports the design of a novel Butterfly Lamb wave resonator (LWR) employing the S0 mode in the AlN plate, and for the first time, its ultrahigh parallel-resonance quality factor ( Qp ) of 4,021 is demonstrated, indicating an ultralow acoustic loss. Although the series resonance quality factor ( Qs ) is widely used for various loss comparisons, it is inconclusive since Qs is always dominated by the routing resistance ( Rs ), which is normally huge without the thick metal rewiring. Instead, Qp is a precise representation of the acoustic loss level for its independence of Rs and as it is closer to Qmax of the Bode Q -curve in the IDT-excited devices. A butterfly-shaped resonance cavity, theoretically predicted to reduce the anchor loss and suppress the transverse spurious mode, has been applied to the AlN LWR and experimentally shown to boost the Qp by 2.3 times. In addition, a directly measured Bode- Q curve for the LWR is reported for the first time, showing superior Q profile for the Butterfly-LWR than the conventional-LWR and good agreement with the 3 dB- Qp 's.