Micromechanical resonators are devices that vibrate at specified resonance frequencies and are used for timing, sensing, and signal processing. The most important performance metric for micromechanical resonators is the quality factor, which determines how quickly energy is dissipated in the resonator, or how quickly it stops vibrating after excited. We have developed a design for micromechanical resonators that significantly increases the quality factor. We use phononic crystals as tethers (i.e., supporting structures that hold the resonator to the substrate). The tethers act like acoustic mirrors and confine acoustic energy in the resonator. Our results show at least a three-fold improvement in quality factor and our resonators appear to not be limited by energy dissipation through the tethers.
The invention is described in detail in the following paper:
V.J. Gokhale and J.J. Gorman, Approaching the intrinsic quality factor limit for micromechanical bulk acoustic resonators using phononic crystal tethers, Appl. Phys. Lett., 111, 013501, 2017. Published 7/5/17.
Micromechanical resonators are currently commercially used as oscillators for time-keeping and as filters for signal processing in mobile communications. The current practice for supporting a resonator is to use simple narrow beams. This results in significant acoustic energy loss through these beams, which results in a low quality factor. The presented design is superior in that it stop acoustic energy from leaving the resonator, yielding higher quality factor. Our design is fully compatible with existing fabrication techniques and can be applied to commercial designs with minimal effort.