Miniaturized Multi-Cantilever MEMS Resonators with Low Motional Impedance

Microelectromechanical system (MEMS) cantilever resonators suffer from high motional impedance (R). This paper investigates the use of mechanically coupled multi-cantilever piezoelectric MEMS resonators in the resolution of this issue. A double-sided actuating design, which utilizes a resonator with a 2.5 μm thick AlN film as the passive layer, is employed to reduce R. The results of experimental and finite element analysis (FEA) show agreement regarding single- to sextuple-cantilever resonators. Compared with a standalone cantilever resonator, the multi-cantilever resonator significantly reduces R; meanwhile, the high quality factor (Q) and effective electromechanical coupling coefficient (Kt²) are maintained. The 30 μm wide quadruple-cantilever resonator achieves a resonance frequency (f) of 55.8 kHz, a Q value of 10,300, and a series impedance (R) as low as 28.6 kΩ at a pressure of 0.02 Pa; meanwhile, the smaller size of this resonator compared to the existing multi-cantilever resonators is preserved. This represents a significant advancement in MEMS resonators for miniaturized ultra-low-power oscillator applications.