Acoustic properties of co-doped AlN thin films at low temperatures studied by picosecond ultrasonics

(Mg0.5Zr0.5)xAl1-xN and (Mg0.5Hf0.5)xAl1-xN thin films are AlN-base piezoelectric materials, and their piezoelectric coefficients are higher than those of pure AlN, being promising materials for acoustic devices. However, their acoustic properties remain unknown because of measurement difficulty for deposited thin films. In this study, we measure their longitudinal-wave elastic constants C33 and their temperature coefficients using picosecond ultrasound spectroscopy for 0 33 = 398.2 ± 0.7GPa for pure AlN, and it largely decreases by doping Mg, Zr, and Hf, leading to a minimum values of 316.8 ± 1.6 GPa for (Mg0.5Zr0.5)0.126Al0.874N.Nagakubo A., Arita M., Yokoyama T., et al. "Acoustic properties of co-doped AlN thin films at low temperatures studied by picosecond ultrasonics", Japanese Journal of Applied Physics, 54(7), 07HD01 (2015) https://doi.org/10.7567/JJAP.54.07HD01