An 8.8 GHz Aluminum Nitride S1 Lamb Mode Resonator

This paper presents an 8.8 GHz aluminum nitride (AlN) microelectromechanical system (MEMS) resonator. The high frequency resonance is attained by exploiting the high phase velocity S1 Lamb mode in a 400 nm AlN thin film. Finite element analyzes (FEA) are employed to show a high phase velocity greater than 20000 m/s and a significant electromechanical coupling (K²) of 3.8% for S1 when h = 0.2λ. Compared with the S0 mode, the S1 mode shows a theoretical K² that is enhanced by a factor of 1.58, while its phase velocity and resonance frequency 2.45 times those of the S0 mode. As predicted by the simulation, the fabricated resonator demonstrates a high frequency resonance at 8.8 GHz and a large electromechanical coupling $\left({k_t^2}\right)$ of 3.1%. Among the demonstrated S1 mode devices, this work has achieved a high product of merit, $f \cdot k_t^2 \cdot Q$, of 44.8. This result highlights the potential of S1 mode resonators for integration into RF front-end modules. This work paves the way for the development of high-performance acoustic devices for 6G and beyond.