Tunable mechanical resonator with aluminium nitride piezoelectric actuation

Abstract

The electromechanical response of piezoelectrically-actuated AlN micromachined bridge resonators has been characterized using laser interferometry and electrical admittance measurements. We compare the response of microbridges with different dimensions and buckling (induced by the initial residual stress of the layers). The resonance frequencies are in good agreement with numerical simulations of the electromechanical behavior of the structures. We show that it is possible to perform a rough tuning of the resonance frequencies by allowing a determined amount of builtin stress in the microbridge during its fabrication. Once the resonator is made, a DC bias added to the AC excitation signal allows to fine-tune the frequency. Our microbridges yield a tuning factor of around 88 Hz/V for a 500 µm-long microbridge.

Feedback loops with electrically driven microcantilevers

“…Although a change in m eff could be invoked, it would not lead to a simultaneous increase both in ω 0D and Q FBD due to the opposed effects of m eff in Eqs. (4) and (5). PDF, obtained for β real and negative in Fig.…”

“…Although several methods exist for this monitoring, they can be replaced by a simple frequency meter if an electronic oscillator is built around the vibrating cantilever acting as its frequency determining element. A low cost oscillator obtained in this way is thus highly desirable, and to build one of these oscillating loops, the electrical signal of the time-varying position of the cantilever was obtained by laser interferometry 4 . A driving by a magnetic torque 5 proportional to the current of a solenoid was planned to close the oscillator loop, but studying the transfer function of this driving we found an unintentional electrostatic driving (ED) of the cantilevers in our setup 6 .…”

Bent-beam sensing with triple-beam tuning forks

“…Similar results have previously been reported for buckled silicon nitride/AlN microbridges, whose resonance frequencies were shown to be strongly affected by the amount of initial buckling due to residual stresses. 14,15 In Fig. 5, the resonance frequencies of the three modes M 1 , M 2 , and M 3 are shown as predicted by the bent-beam FEM simulation and as measured in the tilting experiment.…”

Simultaneous magnetic and electrostatic driving of microcantilevers

“…But to have a self-oscillating loop exactly at f 0 , the phase of the loop gain must be exactly n(2π) at f 0 and this requires an exact knowledge of each transfer function within the loop. To build one of these loops we used the laser interferometric setup described in [4] to extract the electrical signal of the time-varying position of the cantilever and to close the loop we adopt a driving by a magnetic torque proportional to the current of a solenoid as it was done in [5]. Although this approach requires cantilevers with a magnetic coating previously magnetized, it is well worth due to the clean driving obtained as compared with other methods as piezoelectric driving.…”