Achieving the Intrinsic Limit of Quality Factor in VHF Extensional-Mode Block Resonators

In this work we demonstrate that it is possible to push the most dominant sources of extrinsic loss (i.e. anchor and air loss) in high-frequency thin-film piezoelectric-on-substrate (TPoS) MEMS resonator to levels that they no longer limit the overall $Q$. This is achieved through altering the substrate regions around the resonators, etching notch and reflector structures, so that the resulted acoustic cavity is virtually not leaking acoustic energy once the resonator is operated in vacuum. We experimentally prove our technique by presenting an 1100% improvement in $Q$ for a TPoS resonator operating at ~82 MHz and achieving an $f\times Q$ of $2.6\times 10^{12}$.