Anchor loss reduction in ALN Lamb wave resonators using phononic crystal strip tethers

Formation of allowed and stopped frequency bands of elastic wave propagation in the periodic media, also known as phononic crystal (PnC), recently has attracted great attention in enabling high quality factor (Q) electroacoustic devices. To eliminate the anchor loss, the acoustic band gap structures are employed in the support tethers of the aluminum nitride (AlN) Lamb wave resonators. The PnC strip tethers which are made of periodic cross-shape beams based on the 4-μm-thick AlN slab are well designed to reduce the anchor loss and then significantly increase the Q's of the AlN Lamb wave devices in resonance. The experimental results show that the PnC strips are introduced to stop the Lamb wave propagation through the support tethers, and the Q of the AlN Lamb wave resonator increases from 1849 to 2773 when the resonance frequency falls in the acoustic band gap. Intriguingly, the Q improves from 2396 to 3296 while the resonance frequency falls in the in-plane motion forbidden band.