High-Q low impedance UHF-band ALN-ON-SI mems resonators using quasi-symmetrical Lamb wave modes

This paper describes the phase velocity dispersion characteristics of Lamb waves propagating in AlN-on-Si plates, which achieves high quality factor (Q > 10000) and low motional resistance (R<sub>m</sub> <; 50 Ω) at 260 MHz in air by using the fundamental quasi-symmetrical (QS<sub>0</sub>) mode. We have found that the ratio of the Si layer thickness (h<sub>Si</sub>) over the acoustic wavelength (λ) sets a limit for the QS<sub>0</sub> mode resonance at higher frequencies as increasing the ratio of h<sub>Sl</sub>/λ reduces the electromechanical coupling for the QS<sub>0</sub> mode while enhancing the spurious quasi-antisymmetrical (QA<sub>0</sub>) mode. Lastly, we also experimentally demonstrate that using multiple tethers helps suppress spurious modes.

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