Electronic technique and system for non-contact reading of temperature sensors based on piezoelectric MEMS resonators

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This work investigates an electronic technique and system for non-contact reading of the temperature-dependent resonant frequency of piezoelectric MEMS resonators. The proposed approach exploits magnetic coupling between an interrogation unit and a sensor unit to achieve non-contact operation. A dedicated electronic circuit in the interrogation unit alternatively switches the system between the excitation and detection phases, thus implementing a time-gated technique. The MEMS resonator in the sensor unit is driven into resonance during the excitation phase, while its damped response is sensed in the detection phase. An electronic circuit down-mixes the damped response of the resonator and the frequency of the resulting signal is measured through a post-processing technique based on autocorrelation. The system has been applied to the reading of a temperature sensor based on a MEMS aluminum-nitride thin-film piezoelectric-on-silicon disk resonator vibrating in radial contour mode. The experimental characterization of the non-contact system determined the temperature coefficient of frequency of the MEMS resonator to be −47.4 ppm/°C, in good agreement with the measurements taken by directly probing the resonator.