Epitaxial Aluminum Scandium Nitride Super High Frequency Acoustic Resonators

• Published in: Journal of microelectromechanical systems Vol. 29; no. 4; pp. 490 - 498
• Main Authors: Park, Mingyo, Hao, Zhijian, Dargis, Rytis, Clark, Andrew, Ansari, Azadeh
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.08.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Acoustic properties; Acoustic resonators/filters; Acoustics; Aluminum; Coupling (molecular); Coupling coefficients; Crystal structure; Crystallinity; epitaxial aluminum nitride; Epitaxial growth; Film thickness; Frequency response; High frequencies; lamb wave resonators; Molecular beam epitaxy; molecular beam epitaxy (MBE); Nitrides; Piezoelectricity; Q factors; Resonators; Scandium; Silicon; Silicon substrates; Single crystals; Superhigh frequencies; Surface acoustic wave devices; surface acoustic wave resonators; Surface acoustic waves; Thick films; Thin films; Wireless communications
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2020.3001233

This paper demonstrates super high frequency (SHF) Lamb and surface acoustic wave resonators based on single-crystal orientation Aluminum Scandium Nitride (AlScN) thin films grown on silicon substrates by molecular beam epitaxy (MBE). We report on the experimental frequency response and electromechanical properties of 400 nm-thick crystalline AlScN acoustic resonators with up to 12% Sc/(Sc+Al) ratio. The film thickness is optimized for operation at the SHF range, targeting emerging wireless communication standards, such as 4G LTE/5G. We report on high-performance acoustic devices that take advantage of the crystallinity, and high piezoelectric properties of 400 nm-thick epitaxial AlScN films. Our work presents enhanced effective electromechanical coupling coefficients (<inline-formula> <tex-math notation="LaTeX">k_{eff}^{2} </tex-math></inline-formula>) up to 5.3% and unloaded quality factors (<inline-formula> <tex-math notation="LaTeX">Q_{m} </tex-math></inline-formula>) of ~192 at 3-10 GHz. However, fabrication challenges due to the high-stress levels of sub-micron AlScN epi-layers grown on Si substrates remain challenging and will be discussed in this paper. [2019-0231]