Fabrication of two-point-supported annular microresonators with vertical transducer gaps

Disc 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 for the reduced air-damping effect. Furthermore, it has been reported that a disc resonator supported at fewer nodal points exhibited a higher Q. The authors have designed and fabricated two-point-supported annular micromechanical resonators employing the in-plane resonant modes, which shows two nodal points on the outer circumference, with an inner-to-outer radius ratio of 0.17. The beam structures to support the resonator were newly designed and connected to the two nodal points expected for a specified in-plane resonant mode to decrease the energy loss of the vibration through the supporting structures. The resonator was electrostatically driven and detected with 150nm-wide vertical transducer gaps that were fabricated by trench etching of the single-crystal silicon using deep reactive ion etching with a resist mask patterned by electron beam lithography. The fabricated resonators show a resonant peak at 50.1MHz with a Q of 3000 in air. The measured peak resonant frequency agreed well with the frequency predicted by finite-element simulations.