Higher-order mode internal electrostatic transduction of a bulk-mode ring resonator on a quartz substrate

This paper reports the use of internal electrostatic transduction to excite and detect the fifth bulk lateral mode of a 54 mum outer-diameter, 12 mum-wide, and 2.5 mum-thick poly-silicon ring resonator at 1.95 GHz, with a quality factor Q~8000 in room air. The resonator is fabricated on a quartz substrate to reduce electrical feedthrough. The transducer is a sandwich of 500 nm of electrically floating polysilicon between layers of 50 nm of Si₃N₄, formed by refill of a trench etched in the structural polysilicon layer. This scalable double-gap internal electrostatic transducer is compatible with conventional optical lithography, since its critical dimensions are defined by deposition.