Technique and Circuit for Contactless Readout of Piezoelectric MEMS Resonator Sensors.

Marco Baù,Abid Ali,Vittorio Ferrari,Marco Ferrari,Habiba Begum,Joshua E.-Y Lee

doi:10.3390/s20123483

Abstract

A technique and electronic circuit for contactless electromagnetic interrogation of piezoelectric micro-electromechanical system (MEMS) resonator sensors are proposed. The adopted resonator is an aluminum-nitride (AlN) thin-film piezoelectric-on-silicon (TPoS) disk vibrating in radial contour mode at about 6.3 MHz. The MEMS resonator is operated in one-port configuration and it is connected to a spiral coil, forming the sensor unit. A proximate electronic interrogation unit is electromagnetically coupled through a readout coil to the sensor unit. The proposed technique exploits interleaved excitation and detection phases of the MEMS resonator. A tailored electronic circuit manages the periodic switching between the excitation phase, where it generates the excitation signal driving the readout coil, and the detection phase, where it senses the transient decaying response of the resonator by measuring through a high-impedance amplifier the voltage induced back across the readout coil. This approach advantageously ensures that the readout frequency of the MEMS resonator is first order independent of the interrogation distance between the readout and sensor coils. The reported experimental results show successful contactless readout of the MEMS resonator independently from the interrogation distance over a range of 12 mm, and the application as a resonant sensor for ambient temperature and as a resonant acoustic-load sensor to detect and track the deposition and evaporation processes of water microdroplets on the MEMS resonator surface.

Highlights

Micro-electromechanical system (MEMS) resonators have been intensively investigated in recent years for an increasing number of applications, ranging from timing [1], filtering [2], and actuating to sensing [3]
The measured spectra of G and B around the frequency of the first vibration mode are reported in Figure 5, where, consistently with the Butterworth–van Dyke (BVD) model, the resonant first vibration mode are reported in Figure 5, where, consistently with the BVD model, the resonant first vibration reported in Figure 5, where, BVD
The reportedwork work investigated the application novel application of the contactless time-gatedinterrogation contactless technique to a piezoelectric resonant sensor based on an resonator operating in the interrogation technique to a piezoelectric MEMS resonant sensor based on an aluminum nitride (AlN) thin-film piezoelectric-on-silicon (TPoS) resonator contour-mode and one-port configuration at around

Summary

Introduction

Micro-electromechanical system (MEMS) resonators have been intensively investigated in recent years for an increasing number of applications, ranging from timing [1], filtering [2], and actuating to sensing [3]. One additional advantage of piezoelectric resonators, especially when operated as sensors, is their suitability for contactless interrogation, i.e., excitation and detection of mechanical resonances without required wired connections [16]. Effective contactless interrogation in real applications demands for the readout of the resonant frequency of the resonator to be independent from the stand-off distance between the interrogation and sensor units For this purpose, techniques both in the frequency [17] and time [18] domains have been investigated. Referred to as time-gated, excite the sensor for a finite time duration, and detect the decaying resonant response, from which the resonant frequency and possibly the quality factor are extracted Both techniques, besides being applicable to capacitive sensors [17], have been demonstrated to be to first order independent from the interrogation distance.

Technology and Fabrication Processes

Operating

Discussion parts of theand admittance

Measured

Conclusions