Very High-Frequency Silicon Carbide Microdisk Resonators With Multimode Responses in Water for Particle Sensing.

We report on the first experimental demonstration of silicon carbide (SiC) microdisk resonators operating in water, featuring robust multimode resonances in the high and very high frequency (HF/VHF) bands. Thanks to its excellent mechanical, optical, thermal properties and biocompatibility, SiC is particularly attractive for physical, chemical, and biological applications in liquid. Compared with the prevailing device structures in beams and cantilevers, disk resonators offer larger capturing surfaces at the same length scale and greater flexibility in accessing their richer multimode responses, which can be harnessed for enhancing the mass sensing performance in liquid. In this paper, we design and fabricate SiC microdisks and experimentally characterize their multimode resonances in both air and water. We observe up to 28 flexural modes within ~ 5–200 MHz and quality ($Q$) factors as high as ~ 1050 in air, as well as 12 modes within ~3–190 MHz and $Q\text{s}$ up to ~ 30 in water. These metrics are the highest among the reported flexural-mode micromechanical resonators operating in liquid. We further demonstrate the detection of single microparticle in water using the SiC microdisks and investigate the position-dependent multimode responses by combining laser interferometry and optical tweezering techniques. We observe multimode frequency shifts in response to single silica microbead loading, with mass responsivity up to ~ 120 Hz/fg. This SiC multimode resonator platform may help advance in-liquid particle sensing and biological measurement applications. [2018-0259] [ABSTRACT FROM AUTHOR]