AlN/Al0.8Sc0.2N film S mode lamb wave resonator with spurious mode suppression

Abstract

High-performance Lamb wave devices have a vast application prospect in modern wireless communication systems. This paper proposes a method of spurious mode suppression by reducing the overlap length of electrodes according to modal shapes. The AlN/Al0.8Sc0.2N composite film is used to achieve a trade-off between electromechanical coupling coefficient (kt2) and Q factor. The finite-element analysis (FEA) is employed to study the performance of the lowest-order symmetric mode (S0) Lamb wave resonators (LWRs), and the FEA result shows a spurious mode in the impedance response. According to the results of modal shape analysis, the typical LWR, the LWR with the circle-shaped arrangement of electrodes, the LWR with the circle-shaped apodization, and the LWR with the arc-shaped apodization are fabricated to suppress the spurious mode and investigate the performance of the LWRs. The measurement results show that the spurious mode is effectively suppressed over a wide frequency range (1.9–2.2 GHz) by the three designed electrode configurations. The LWR with the circle-shaped apodization working at 2.023 GHz has a Qp factor of 955, a moderate kt2 of 2.97%, a figure-of-merit (Q×kt2) of 28.4, and a large value of f×Q×kt2 (5.773 × 1010). Utilizing modal shapes to design the electrode configuration of LWRs can suppress spurious modes without significant performance deterioration.