T. Lamminmäki

Large-displacement modelling and simulation of micromechanical electrostatically driven resonators using the harmonic balance method

Nonlinearities in electrostatically driven micromechanical resonators are studied with circuit simulations. Models for the resonators are built of elementary electrical equivalent-circuit blocks constructed of nonlinear voltage-controlled current and charge sources. They are simulated with the harmonic balance method in the RF-simulation program APLAC. Spring softening effects due to the capacitive transducer and spring hardening effects due to the resonators third order spring coefficient are demonstrated by simulations. For verification, a model for a micromachined high-Q beam resonator structure has been constructed, and its measured large-displacement frequency-domain transfer characteristics are successfully reproduced by model simulations.

Reducing the Effect of Parasitic Capacitance on MEMS Measurements

The use of micromechanical resonant structures in RF electronics possesses often a problem caused by a very low signal amplitude. In order to alleviate the influence of parasitic capacitance we propose here the use of the differential amplifier and demonstrate its use here on the processed electrostatically driven resonators. The component used in verifying the use of differential amplifier is a clamped-clamped beam resonator with Q=8000 and resonant frequency of f 0 = 12.3 MHz. A low-noise high input-impedance amplifier was used as a reference.