Anchor loss suppression using butterfly-shaped plates for AlN Lamb wave resonators

The use of butterfly-shaped thin plates, formed by reducing the tether-to-plate angle, can raised the quality factor (Q) of aluminum nitride (AlN) Lamb wave resonators (LWRs) by eliminating the anchor loss. The finite element analysis (FEA) simulation results show that the butterfly-shaped plate can efficiently keep the vibration far from the edges at the tether-to-plate plane, so that the acoustic wave leaky through the supporting tethers is reduced. Specifically, the rounded butterfly-shaped resonators show more efficient suppression in the anchor loss compared to the beveled butterfly-shaped resonators. The measured frequency response for a 863-MHz AlN LWR with 45° beveled tether-to-plate transition yields a Q of 1,979 which upwards 30% over a conventional rectangular resonator; another AlN LWR on the butterfly-shaped plate with rounded tether-to-plate transition yields a Q of 2,531, representing a 67% improvement.