Higher-order dielectrically transduced bulk-mode ring resonator with low motional resistance

This paper reports internal dielectric transduction of the 41^st radial bulk-mode of a ring resonator at 2.79 GHz with a quality factor exceeding 11,500 in air. The transducer electrodes are integrated within the vibrating structure in a dense serpentine pattern, with the dielectric-filled gaps strategically placed on the nodal lines to excite the 41^st order bulk radial mode. The serpentine dielectric transduction results in a low motional resistance of less than 500 Ω, which can be detected by direct two-port transmission measurements. The “notched” ring design allows for anchoring this resonator at the center nodal line of the ring, resulting in higher Q and lower motional resistance. This resonator is fabricated by a double nanogap process, where 30 nm silicon nitride sidewall layers are formed using a combination of optically defined trenches and deposition of a high-κ dielectric followed by a doped polysilicon layer.