Morphological investigation of aluminium nitride films on various substrates for MEMS applications

TLDR: In this paper, a C-axis oriented AlN films were observed on most of the substrates, where the surface morphologies of the films grown on the 1·5 μm thick SiO2 layer and GaAs substrate were found to be non-uniform.

Abstract: Piezoelectric films, such as aluminium nitride (AlN), are of great interest for the fabrication of thin film bulk/surface acoustic resonators, where the growth parameters and the substrate material influence the morphological properties. Herein, AlN films were deposited using RF reactive sputtering on Si, SiO2, metal (Al, Cu, Cr and Au) coated silicon, GaAs and InP substrates. C-axis (002) oriented AlN films were observed on most of the substrates, where the surface morphologies of the films grown on the 1·5 μm thick SiO2 layer and GaAs substrate were found to be non-uniform. Moreover, AlN films deposited on the Cr electrode exhibit well textured film with fairly uniform grains, while the films deposited on other metal electrodes exhibit a granular type of structure with mixed small and large grains. After optimisation of growth parameters, silicon micromachining was performed by the wet chemical etching method. Suspended Cr–AlN–Cr–SiO2 cantilevers of 20 μm in width were fabricated for futuristic...