MEMS Actuated Piezoelectrically with AlN Films

We analyse the mechanical response of a doubly-clamped microbridge actuated piezoelectrically using sputtered AlN, working first as an actuator and then as a resonator. The quasi-static response of the microbridge under DC electrical excitation is measured. Out-of-plane displacements as high as 0.22 mum/V are obtained, which provides an actuation response suitable for RF switching applications. On the other hand, the resonance frequencies of the microbridges are determined by means of laser interferometry. We compare the response of microbridges with different dimensions and different initial buckling (induced by the residual stress of the layers). We show that it is possible to perform a rough tuning of the resonance frequencies by allowing a determined amount of built-in stress in the microbridge during its fabrication. For a given resonator, a DC bias added to the AC excitation signal allows to fine-tune the resonance frequencies. Our microbridges yield a tuning factor of around 88 Hz/V for a 500 mum-long microbridge.