Fabrication of AlN/Si SAW delay lines with very low RF signal noise

In this work we investigate the influence of the substrate resistivity and of different buffer layers on the out-of-band insertion losses in AlN SAW devices fabricated on (1 0 0) silicon substrates. The measurements have shown that the out-of-band insertion loss is improved by increasing the substrate resistivity but also by the introduction of an insulating buffer layer material. An out-of-band insertion loss as low as -75 dB has been achieved by the device realized on a silicon nitride buffer layer. This can be explained in terms of inhibition of the diffusion of silicon atoms in the AlN film. Our results show that silicon nitride represents a good solution in terms of low out-of-band insertion loss and cost effectiveness for the realization of nitride-based piezoelectric MEMS devices on silicon substrates.