Fabrication of two-point-supported annular-type microresonators with capacitive transducer gaps

Disk microresonators employing in-plane resonant modes are promising candidates as functional elements for high-sensitive mass sensing applications because they provide a high quality factor (Q) in air at atmospheric pressure. The authors have newly designed and fabricated single crystal silicon (SCS) annular micromechanical resonators with an inner to outer radius ratio of 0.17. The beam structures to support the resonator were connected to the two nodal points expected for a specified in-plane resonant mode. The resonator was electrostatically driven and detected with 150-nm-wide vertical transducer gaps that were fabricated by trench etching of the SCS using deep reactive ion etching (D-RIE) with a resist mask patterned by electron beam lithography. The fabricated resonators show a resonant peak at 50.10 MHz with a Q of 3000 in air. The measured peak resonant frequency agreed well with the frequency predicted by finite element simulations.