  This paper details the development of high-quality, c-axis oriented AlN thin
films up to 2 {\mu}m thick, using sputtering on platinum-coated SOI substrates
for use in piezoelectric MEMS. Our comprehensive studies illustrate how
important growth parameters such as the base Pt electrode quality, deposition
temperature, power, and pressure, can influence film quality. With careful
adjustment of these parameters, we managed to manipulate residual stresses
(from compressive -1.2 GPa to tensile 230 MPa), and attain a high level of
orientation in the AlN thin films, evidenced by < 5deg FWHM X-Ray diffraction
peak widths. We also report on film surface quality regarding roughness, as
assessed by atomic force microscopy, and grain size, as determined through
scanning electron microscopy. Having attained the desired film quality, we
proceeded to a fabrication process to create piezoelectric micromachined
ultrasound transducers (PMUTs) with the AlN on SOI material stack, using deep
reactive ion etching (DRIE). Initial evaluations of the vibrational behavior of
the created devices, as observed through Laser Doppler Vibrometry, hint at the
potential of these optimized AlN thin films for MEMS transducer development.

Applied Physics