Monocrystalline Silicon Carbide Disk Resonators on Phononic Crystals with Ultra-Low Dissipation Bulk Acoustic Wave Modes

Abstract

Micromechanical resonators with ultra-low energy dissipation are essential for a wide range of applications, such as navigation in GPS-denied environments. Routinely implemented in silicon (Si), their energy dissipation often reaches the quantum limits of Si, which can be surpassed by using materials with lower intrinsic loss. This paper explores dissipation limits in 4H monocrystalline silicon carbide-on-insulator (4H-SiCOI) mechanical resonators fabricated at wafer-level, and reports on ultra-high quality-factors (Q) in gyroscopic-mode disk resonators. The SiC disk resonators are anchored upon an acoustically-engineered Si substrate containing a phononic crystal which suppresses anchor loss and promises QANCHOR near 1 Billion by design. Operating deep in the adiabatic regime, the bulk acoustic wave (BAW) modes of solid SiC disks are mostly free of bulk thermoelastic damping. Capacitively-transduced SiC BAW disk resonators consistently display gyroscopic m = 3 modes with Q-factors above 2 Million (M) at 6.29 MHz, limited by surface TED due to microscale roughness along the disk sidewalls. The surface TED limit is revealed by optical measurements on a SiC disk, with nanoscale smooth sidewalls, exhibiting Q = 18 M at 5.3 MHz, corresponding to f · Q = 9 · 1013 Hz, a 5-fold improvement over the Akhiezer limit of Si. Our results pave the path for integrated SiC resonators and resonant gyroscopes with Q-factors beyond the reach of Si.

Nanomechanical Dissipation and Strain Engineering

“…To examine whether alternative materials could allow for better performing resonators in the future, we consider silicon carbide, [ 48,120,121 ] graphene, [ 15,104,122 ] and diamond, [ 123–125 ] comparing their upper‐bounds of performance relative to silicon nitride. The upper‐bounds are calculated by assuming the material's intrinsic quality factor is the highest experimentally demonstrated to our knowledge at room temperature, [ 121,123,126 ] and their dissipation dilution limit is set by the material yield stress, [ 48,117,127 ] as described in ref. [46].…”

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

“…However, there was a consistent discrepancy between our measurement and theoryparticularly in elliptical wineglass modes; this motivated investigation into a new set of elastic constants that better reflect the mechanical properties of 4H-SiC within the framework of the SiCOI platform. As described earlier, achieving high Q is non-trivial often due to anchor losses which rely on a thorough understanding of 4H-SiC's stiffness to conform to various decoupling schemes' stringent frequency requirements [18], [20].…”

“…The recent development of bond and etch-back thick monocrystalline 4H silicon carbide-on-insulator (4H-SiCOI) substrates [17] and their deep reactive ion etching with high aspect ratio [18], [19] facilitate wafer-level fabrication of capacitive in-plane resonators with ultra-high mechanical Q-factors. Their frequency spectrum measurements have revealed that the elasticity of hexagonal 4H-SiC is not well-understood, evidenced by consistent discrepancy with numerical simulations from wafer to wafer [20].…”

Study of the Influence of Phase Noise on the MEMS Disk Resonator Gyroscope Interface Circuit

“…As a new generation gyroscope, the micro-electro-mechanical system disk resonator gyroscope (MEMS DRG) is an attractive candidate for high-performance MEMS gyroscopes due to its near navigational grade precision and small volume [ 1 , 2 , 3 , 4 , 5 ]. As a solid wave gyroscope (SWG), MEMS DRG inherently possesses a high Q factor and mode match mechanism, which maintain its low mechanical-thermal noise and high mechanical sensitivity [ 6 , 7 , 8 , 9 ].…”