Quality-factor amplification in piezoelectric MEMS resonators applying an all-electrical feedback loop

Abstract

An all-electrical velocity feedback control to enhance the quality factor of piezoelectric aluminium nitride (AlN)-based microcantilevers and microbridges was implemented. Two alternatives to obtain a velocity-proportional signal were demonstrated depending on the top electrode configuration. For a straightforward electrode design in one-port configuration (i.e. self-actuation and self-sensing), a velocity signal, proportional to the piezoelectric current, was used in the feedback loop by cancelling out the dielectric current electronically. For top electrodes allowing a two-port configuration (i.e. one for actuation and one for sensing), the piezoelectric current is directly extracted and its relationship with velocity is analysed taking the symmetry of the modal shape into account. Standard operational amplifier-based configurations for the feedback circuits were implemented on a printed circuit board. Quality factors were determined from the transient electrical response of the devices. Comparable results were obtained from the displacement spectrum applying a laser Doppler vibrometer. Quality factors as high as 2 × 105, corresponding to an enhancement factor of about 200, were achieved in air for the lowest gain margin achievable before the circuit becomes unstable, making this kind of device more competitive for mass sensor applications due to enhanced spectral resolution.

Efficient parametric amplification in micro-resonators with integrated piezoelectric actuation and sensing capabilities

“…4 When operated in air or in liquid, the quality factors dramatically decrease, thus leading to loss of performance. Several strategies have been proposed to overcome those difficulties, such as active closed loop enhancement 4,5 or parametric amplification, introduced by the pioneering work of Rugar and Gr€ utter 6 and used for torsional microresonators. 7 More recently, this principle has been applied to micro and nano-beams driven by Lorentz forces 8 or by piezoelectric action, 9,10 to an array of microcantilevers 11 and to carbon nanotubes.…”

Lock-in driven quality factor enhancement with parasitic effect compensation of a self-actuated piezoelectric MEMS cantilever

“…Most recently, an all-electrical feedback loop was presented in [6] which uses an I-V conversion of the piezoelectric current directly as feedback by adding it to the stimulus. This present study presents an alternative approach, shown in Fig.…”

“…4 applying a lock-in amplifier connected to the I-V converter. The lock-in working in X-Y mode extracts the real part, representing the conductance G of the piezoelectric aluminum nitride (AlN) actuated MEMS resonator replacing the original, low level, highly amplified and thus noisy feedback signal [6] and modulates the voltage amplitude applied to the MEMS resonator.…”

“…The quality factor (Q-factor) of a resonating microstructure is a key parameter having a strong impact on the sensitivity and the resolution of the measured quantities [2], [4], [6]. When operating the microstructures in fluidic…”

“…One method is to detect a resonance mode shaped deflection of the cantilever optically and use this information for realizing the feedback [9]. A different approach is the use of the piezoelectric current provided by a thin film such as aluminum nitride (AlN) to realize a feedback loop [2], [6]. It is objective of this study to evaluate the parasitic effect compensation to extract a resonance from a feedback signal in combination with a Q-control circuit.…”