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Investigating Elastic Anisotropy of 4H-SiC Using Ultra-High Q Bulk Acoustic Wave Resonators | IEEE Journals & Magazine | IEEE Xplore

Investigating Elastic Anisotropy of 4H-SiC Using Ultra-High Q Bulk Acoustic Wave Resonators


Abstract:

Hexagonal 4H-silicon carbide (4H-SiC) is a transversely isotropic substrate garnering interest for precision MEMS devices such as resonant gyroscopes. This paper investig...Show More

Abstract:

Hexagonal 4H-silicon carbide (4H-SiC) is a transversely isotropic substrate garnering interest for precision MEMS devices such as resonant gyroscopes. This paper investigates the elastic anisotropy of 4H-SiC by utilizing capacitive bulk acoustic wave (BAW) resonators with ultra-high mechanical quality factors (Q) enabled by phononic crystals. We directly measure the value of C66 using Lamé mode resonators for the first time and numerically fit the values of C11 and C12 using BAW elliptical modes in center-supported solid disk resonators. We compare (00 01) 4H-SiC to (111) Si, another in-plane isotropic material and validate (0 001) 4H-SiC's superior robustness to fabrication and design variations. Measurement of in-plane BAW elliptical modes in multiple disk resonators with as-born frequency splits as low as 3 ppm reveal (00 01) 4H-SiC's transverse isotropy across process corners. Lamé mode resonators display a temperature coefficient of frequency (TCF) three times lower compared to its Si counterpart. Finally, this paper provides a modified set of elastic constants for 4H-SiC with a view towards monocrystalline SiC MEMS devices.
Published in: Journal of Microelectromechanical Systems ( Volume: 29, Issue: 6, December 2020)
Page(s): 1473 - 1482
Date of Publication: 25 September 2020

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