A piezoelectric circular crested lamb wave disk resonator with spurious mode suppression and quality factor enhancement

Abstract

Nowadays, nearly all the reported Lamb wave resonators (LWRs) are straight crested LWRs, which suffer from inherent spurious modes and low quality factors (Q). Circular crested LWRs are promising replacements for straight crested LWRs. To date, only one short conference paper reported utilizing circular crested Lamb waves for LWRs, yet it did not demonstrate effective boundary conditions to harness the circular crested Lamb waves and had resonant mode limitations. For the first time, this work demonstrates a circular crested Lamb wave disk resonator (LWDR), which utilizes a piezoelectric disk for energy concentration. Utilizing circular crested Lamb waves, the proposed resonator avoids only utilizing waves propagating in the lateral direction in the straight crested LWRs, thus eliminating the transverse spurious modes as no transverse direction exists. Besides, different from straight crested Lamb waves maintaining the same displacement amplitude along the propagation direction, circular crested Lamb waves exhibit displacement attenuation toward the piezoelectric disk edges, which effectively concentrates energy in the device center and improves Q. Based on 20 at. % scandium-doped aluminum nitride (Al0.8Sc0.2N) thin films, the circular crested LWDR can excite various symmetric and asymmetric modes. The microfabricated circular crested LWDR effectively suppresses transverse spurious modes and achieves a 40.7% Q improvement in experiments with no degradation in effective electromechanical coupling coefficients (keff2) compared with the straight crested LWR when working in the S0 mode. With the advantages of spurious mode suppression, Q enhancement, and fabrication robustness, the circular crested LWDR is a promising candidate for next-generation filters and oscillators.