GHz AlN lateral overmoded bulk acoustic wave resonators with a f · Q of 1.17 × 1013

This work presents a new class of devices, AlN-based lateral overmoded bulk acoustic wave resonators (LO-BAR), to investigate the Q limit imposed by the intrinsic loss of thin film AlN. The LOBAR devices utilize a rectangular AlN thin film plate with a small percentage (0.57%) inter-digitated transducer (IDT) fingers coverage to minimize the piezoelectric-metal interface loss. This design experimentally pushes the f · Q product value (1.17×10¹³) for thin-film AlN to magnitude level close to the theoretical limit predicted by the Akhizer effect (AKE) for AlN (2.5-5 × 10¹³). To study the performance of the LOBAR design, the IDT to rectangular plate coverage ratio was varied. The results have shown that the Q of the LOBAR device scales nonlinearly and inversely with coverage ratio. Measurement of the highest Q LOBAR device for temperatures varying between 300 and 400 K have indicated that the AlN LOBAR has a temperature coefficient of frequency (TCF) of -16.25 ppm/K, and phonon-phonon dissipation (AKE) is not yet the dominant loss mechanism.