Green´s function analysis of Lamb wave resonators

We have extended the K-model, a Green´s function model previously developed for the precise simulation of surface acoustic wave (SAW) device at radio frequencies (RF), to the computation of Lamb wave resonators (LWR). The effective permittivity for Lamb wave excitation on thin aluminum nitride plates with different electrode configurations is compared. The results of the electromechanical coupling coefficient k² computed from the effective permittivity agree closely with the classical approximation based on the open and shorted velocities v₀ and v_m. Although a backside metallization increases the value of k² the frequency spacing of resonance and anti-resonance is reduced due to capacitive feedthrough through the bottom electrode. Finally, we demonstrate the ability of the model to predict the numerous spurious modes that are excited with low-electrode-count interdigital transducers (IDT).