Experimental Characterization of a Nonlinear Electrostatic-Capacitive MEMS Resonator Featuring 1:2 Internal Resonance

This letter describes the experimental characterization of an electrostatic-capacitive micro electro-mechanical systems (MEMSs) nonlinear resonator exhibiting a 1:2 internal resonance. The proposed MEMS device is based on double-clamped parallel curved beams connected with a vertical link and has been fabricated using the thick epitaxial layer for micro-gyroscopes and accelerometers (ThELMA) process developed by STMicroelectronics. The device geometry combined with the parallel-plate readout mechanism, enhances the nonlinear dynamic behavior, resulting in the coupling of two in-plane vibration modes set by design in a 1:2 frequency ratio. The proposed MEMS resonator has been characterized in the frequency and time domain with and without the electrical activation of the 1:2 internal resonance. A tailored front-end circuit coupled to the resonator has been developed to measure the MEMS transfer function and the free-decay response. Experimental results have demonstrated the possibility to effectively activate the 1:2 internal resonance. The transfer function and the free-decay response highlighted the presence of two distinct harmonic contributions at 416.57 and 837.81 kHz related to the two coupled vibration modes. This behavior is consistent with the presence of nonlinear modal coupling phenomena, in which the energy introduced into the system through the excitation of one mode is partially transferred to the coupled one.