A first-order (S1
) Lamb Wave Resonator (LWR) with trapezoid grooves configuration on the top surface of Aluminum Nitride (AlN) membrane between interdigital electrodes (IDTs) is proposed in this paper. Both the simulation and experiment results demonstrate that the K
2
eff
can be enhanced with the depth of the trapezoid grooves increasing. Meanwhile, the spurious modes can be suppressed by the trapezoid grooves. 75% improvement on the K
2
eff
has been achieved in a 2.45 GHz S1
mode LWR with trapezoid grooves with spurious modes free. The K
2
eff
reaches up to 5.47% without quality factor degradation.
Knowledge of the effective elastic, piezoelectric and dielectric properties facilitates the design of radio frequency devices, for example film bulk acoustic resonators (FBARs). Based on the Reuss model and Eshelby-Mori-Tanaka (EMT) micromechanics theory, this paper predicts the effective properties of bilayer composite piezoelectric film consisting of AlN film and vertical compound ScAlN film. The evaluated material coefficients and original material parameters are substituted into the FEM simulation to investigate the performance of FBARs, respectively. The consistent resonant frequencies of FBARs demonstrate the accuracy of Reuss model in calculating the effective parameters of bilayer composite piezoelectric film.
The effective electromechanical coupling coefficient (Keff^2) is one of the crucial parameters to evaluate the performance of resonators. However, the low effective electromechanical coupling coefficient Keff^2 limits the application of lamb wave resonators (LWRs) in filters. This work presents the impact of metallization rate on the Keff^2 of AlN Checker-mode resonators (CKMRs) by using the finite element analysis approach for the first time. Four types of piezoelectric effect excitation configurations are proposed with different electrode designs based on AlN CKMRs. The results show that CKMRs have the largest Keff^2 with the metallization rate of 0.25-0.31 for top electrode. Meanwhile, when the metallization rate of top electrode varies from 0.2 to 0.7, the Keff^2 of open CKMRs possess the most remarkable enhancement about 235% of CKMRs. By properly optimizing the electrode design, CKMRs exhibit potential in the commercial applications.
This paper reports on a design journey for laterally-excited bulk acoustic wave resonator (XBAR) with adjustable piezoelectric coupling coefficient (K2). The vibration principle and resonant characteristics of XBAR are investigated by theoretical and simulation analysis, and the way to adjust K2 by introducing two grooves in the area between interdigital electrodes (IDEs) is proved to be effective by using finite element method (FEM) simulation and the Modified Butterworth-Van Dyke model with series capacitor Cr (MBVD-Cr) first, and then the impact of groove depth (Hg) and groove width (Wg) on K2 of XBAR is theoretically analyzed. Specifically, the K2 can be effectively adjusted by setting different values of Hg and Wg. After optimization, the maximum regulation range of K2 is from 2.02% to 45.05%. The fluted XBAR has a remarkable potential in building XBAR bandpass filter for specific frequency band, which greatly optimizes the XBAR filter design.
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