Surface micromachining requires the use of easily-removable sacrificial layers fully compatible with all the materials
and technological processes involved. Silicon dioxide films, thermally grown on silicon substrates or deposited by CVD,
are commonly used as sacrificial layers in surface micromachining technologies, despite their low lateral etch rate in
conventional fluorinate solutions. The development of silicon oxide layers with high etch rates poses a great
technological challenge. In this work we have investigated the possibility of obtaining easily removable silicon oxide
layers by pulsed-DC magnetron reactive sputtering. We have carried out a comprehensive study of the influence of the
deposition parameters (total pressure and gas composition) on the composition, residual stress and lateral etch rate in
fluorine wet solutions of the films. This study has allowed to determine the sputtering conditions to deposit, at very high
rates (up to 0.1 μm/min), silicon oxide films with excellent characteristics for their use as sacrificial layers. Films with
roughness around 5 nm rms, residual stress below 100 MPa and very high etch rate (up to 5 μm/min in the lateral
directions), around 70 times greater than for thermal silicon oxide, have been achieved. The structural characteristics of
these easily removable silicon oxide layers have been assessed by infrared spectroscopy and atomic force microscopy,
which have revealed that the films exhibit some kind of porous structure, related to very specific sputter conditions.
Finally, the viability of these films has been demonstrated by using them as sacrificial layer in the fabrication process of
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 built-in 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.