The Multi-Mode Resonance in AlN Lamb Wave Resonators

• Published in: Journal of microelectromechanical systems Vol. 27; no. 6; pp. 973 - 984
• Main Authors: Zou, Jie, Lin, Chih-Ming, Gao, Anming, Pisano, Albert P.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.12.2018; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acoustic resonance; Aluminum nitride; Configuration management; coupling coefficient; Coupling coefficients; Design parameters; Dispersion; Electrodes; Finite element analysis; Finite element method; Group velocity; III-V semiconductor materials; Lamb wave modes; Lamb wave resonators; Lamb waves; Mathematical models; MEMS resonators; Phase velocity; piezoMEMS; Resonant frequency; Resonators
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2018.2867813

The characteristics of the multi-mode resonance behavior of AlN Lamb wave resonators (LWRs) are theoretically and experimentally investigated for the first time in this paper. Adler's approach and finite element method (FEM) are used to calculate the dispersive characteristics of the phase velocity (<inline-formula> <tex-math notation="LaTeX">v_{p} </tex-math></inline-formula>), group velocity (<inline-formula> <tex-math notation="LaTeX">v_{g} </tex-math></inline-formula>), effective coupling coefficient (<inline-formula> <tex-math notation="LaTeX">k^{2}_{\text {eff}} </tex-math></inline-formula>), and temperature coefficient of frequency for the first eight Lamb wave modes with different transducer configurations. The FEM is performed to take an insight into the mode shapes of the S 0 mode and S 1 mode specifically: the S 0 mode is more contour-like and exhibits the largest <inline-formula> <tex-math notation="LaTeX">k^{2}_{\text {eff}} </tex-math></inline-formula> when <inline-formula> <tex-math notation="LaTeX">h_{\text {AlN}}/\lambda </tex-math></inline-formula> is close to 0.5; the S 1 mode is strong in vertical direction and can enable high resonance frequency (<inline-formula> <tex-math notation="LaTeX">f_{s} </tex-math></inline-formula>) and large <inline-formula> <tex-math notation="LaTeX">k^{2} </tex-math></inline-formula> simultaneously when AlN thickness is very thin. Experimentally, AlN LWRs with different AlN thicknesses are designed and fabricated. The measured results are fitted into the multi-resonance BVD model so that the device performance parameters, as well as the equivalent, lumped element values are extracted and compared. By choosing different normalized AlN thicknesses, the performance of different Lamb wave modes varies largely due to the dispersive characteristics and agrees well with theoretically predicted acoustic characteristics. This paper lays the foundation for characterizing the multi-resonance behaviors of AlN LWRs and gives guidance on choosing the optimal design parameters and Lamb wave modes for different applications. [2018-0040]