Effect of Phononic Crystal Orientation on AlNon-Silicon Lamb Wave Micromechanical Resonators

Phononic crystals (PnCs) have been used to boost the quality factor (Q) of AlN-on-Silicon Lamb Wave Resonators (LWRs). But most reports on applying PnCs to resonators have focused on the common <110> orientation within (100) silicon. Little is known on the applicability of other crystal orientations. In this work, we explore the effect of orientation on the acoustic band gap (ABG) of two PnC designs and their effect on boosting Q: a disk PnC and a ring PnC. From Finite Element simulation, we show that the disk PnC’s ABG is insensitive to orientation while adding a hole into the disk to form a ring changes its ABG to be much more sensitive to orientation. Leveraging the PnCs as anchoring boundary of LWRs, the disk PnC exhibits comparable effectiveness to boost Q > 11,000 in the <110> and <100> directions while the ring PnC is effective only in the <110> direction. We further corroborate these trends by incorporating the disk PnC into delay lines in either crystal axis.