Laser Ultrasound Investigations of AlScN(0001) and AlScN(11-20) Thin Films Prepared by Magnetron Sputter Epitaxy on Sapphire Substrates

Abstract

The laser ultrasound (LU) technique has been used to determine dispersion curves for surface acoustic waves (SAW) propagating in AlScN/Al2O3 systems. Polar and non-polar Al0.77Sc0.23N thin films were prepared by magnetron sputter epitaxy on Al2O3 substrates and coated with a metal layer. SAW dispersion curves have been measured for various propagation directions on the surface. This is easily achieved in LU measurements since no additional surface structures need to be fabricated, which would be required if elastic properties are determined with the help of SAW resonators. Variation of the propagation direction allows for efficient use of the system’s anisotropy when extracting information on elastic properties. This helps to overcome the complexity caused by a large number of elastic constants in the film material. An analysis of the sensitivity of the SAW phase velocities (with respect to the elastic moduli and their dependence on SAW propagation direction) reveals that the non-polar AlScN films are particularly well suited for the extraction of elastic film properties. Good agreement is found between experiment and theoretical predictions, validating LU as a non-destructive and fast technique for the determination of elastic constants of piezoelectric thin films.

Single crystal ferroelectric AlScN nanowires

“…AlScN ferroelectrics show significant promise for use in wideranging device applications, including random-access memory [1][2][3] and acoustic resonators. [4][5][6] Epitaxial growth of AlScN thin films on a wide range of substrates and buffer layers, including Si(111), 7 Al 2 O 3 (0001), 8,9 Al 2 O 3 (0001)/ Mo(110), 10 SiC, 4,11 and GaN(0001) [12][13][14] have been reported. More commonly, columnar polycrystalline AlScN thin films are grown on a variety of textured metallic bottom electrodes deposited onto Si wafers.…”

Editorial for Special Issue “Piezoelectric Aluminium Scandium Nitride (AlScN) Thin Films: Material Development and Applications in Microdevices”

“…In the second section of the Special Issue, four papers [ 8 , 9 , 10 , 11 ] focus on investigating the fundamental properties of AlScN, such as the effects of temperature and Sc concentration, and the extraction of device-relevant acoustic parameters. In the in-depth Raman spectroscopy study by Solonenko et al [ 8 ], peak broadening and various mechanisms that contribute to it are investigated.…”

“…Fatigue testing indicated degraded performance above 200 • C; however, at lower temperatures, >10 5 cycles could be achieved before failure, indicating a high potential for AlScN-based memory applications where ~10 3 cycles are expected. Next, the capabilities of the non-destructive laser ultrasonics technique are demonstrated by Meyer et al [11] for the extraction of elastic constants of AlScN required for accurate device design. A special rotating stage was used to investigate the anisotropy of epitaxial c-plane and a-plane AlScN thin films.…”