Finite element analysis of anchor loss in AlN Lamb wave resonators

Acoustic energy leakage through support tethers into the substrate, known as anchor loss, decreases the quality factors (Q) of micromechanical aluminum nitride (AlN) Lamb wave resonators. In this work, we present a theoretical study on the anchor loss of the AlN Lamb wave resonators by using the perfect matched layer (PML) approach in the finite element analysis (FEA) simulation. The anchor loss Q´s of the resonator with different anchor widths and lengths were theoretically calculated and compared. The tether geometries significantly affect the anchor loss Q when the interdigital transducer (IDT) widths are equal to 5.4 and 4.44 μm and less influence the anchor loss Q while the IDT width equals 2.77 μm. The results indicate that the anchor loss dominates the loss mechanism in the Lamb wave resonator at low frequencies and other damping sources decrease the Q at high frequencies. The PML-based FEA method is also utilized to compute the anchor loss Q´s of the Lamb wave resonators utilizing the flat and convex free edges, showing good agreement with the experimental Q´s in the literature.