Piezoelectric actuation of microbridges using AlN

We demonstrate the piezoelectric actuation of a microbridge based on a sputtered aluminium nitride (AlN) thin film. The suspended microbridge consists of a silicon nitride structural layer supporting a Mo/AlN/Mo actuator. A complete technology for the fabrication of the microactuators, fully compatible with standard silicon ICs technologies, has been developed. It includes: (1) the selection of the substrate and the structural layer, (2) the selection of molybdenum as metal for the bottom electrode, (3) the optimization of the sputtering of AlN on molybdenum in order to achieve (002) oriented films with good crystal quality, low residual stress and good piezoelectric response and (4) the fine tuning of the surface micromachining techniques necessary to release the whole structure. Preliminary results on the characteristics of the microactuators are reported. An actuation voltage of 16 V applied to a 350 μm-long bridge produces a deflection of 3.5 μm with negligible current consumption.