Aluminium nitride–niobium multilayers and free-standing structures for MEMS

In this article we investigate aluminium nitride–niobium thin films sputtered on Si wafers and free-standing structures made of these layers. The quality of the films is characterized by Rutherford backscattering (RBS), X-ray diffraction and time-of-flight secondary ion mass spectroscopy (TOF SIMS). The thickness and composition of the intermediate layers between the silicon and AlN was found to be crucial for the uniformity and orientation of the AlN. Optimization of growth conditions and layer thicknesses was performed in order to achieve a high quality of the films. Parameters of sputtered AlN layers of different thicknesses sufficient for use in piezoelectric and thermal switches were attained. Subsequently, a sacrificial layer technology was developed to manufacture multilayer free-standing bridges of different lengths and widths from Nb–AlN structures. Bridges down to 20 μm in size were controllably produced and investigated by e-beam microscopy. The technology proved to be reliable and robust at all ranges of investigated thicknesses and lateral sizes of microstructures.