Precision Deep Reactive Ion Etching of Monocrystalline 4H-SiCOI for Bulk Acoustic Wave Resonators with Ultra-Low Dissipation

Abstract

Integrated mechanical resonators with high quality factors (Q) made in high acoustic velocity materials are essential for a wide range of applications, including chemical sensors, timing resonators, and high-performance inertial sensors for navigation in GPS-occluded environments. While silicon is the most popular substrate for the implementation of microelectromechanical systems (MEMS) resonators, SiC exhibits an exceptionally small intrinsic phononic dissipation due to its low Akhiezer damping limit. This paper reports on the latest developments of precision deep reactive ion etching (DRIE) of monocrystalline 4H SiC-on-Insulator (SiCOI) substrates with the aim to fully take advantage of the exquisite mechanical properties of crystalline SiC. To wit, capacitive Lamé mode micromechanical resonators exhibit ƒ·Q products beyond 1 × 1014 Hz independent of crystalline orientation. The contribution of surface roughness to dissipation and practical considerations to etch mirror-polished trenches in SiCOI substrates are discussed, paving the way towards micromechanical monocrystalline SiC resonators with Qs beyond 100 Million.