Bulk disc resonators radial and wineglass mode resonance characterization for mass sensing applications

Abstract

This paper reports the design and fabrication of bulk mode micromechanical disc resonators operating in radial and wine-glass modes of excitation. The reported structures are fabricated utilizing a single crystal SOI wafer through micromachining processes. Both resonators are fabricated on a device layer with a thickness of 20 µm and a gap size of 1.75 µm between the resonant beam and surrounding electrodes. Four anchors support the resonant disc using a T-shaped connection stem. The designed structures resonate at 2.87 and 3.99 MHz, in wine glass and radial modes respectively, and are electrostatically actuated by a DC voltage of 110 V between the disc and electrodes. The designed resonators show high quality factors while operating in air, 1,1876.2 for wine-glass and 7380 for radial. In addition, the resonators are used for distributed and point mass measurements of a sputtered gold metal layer. The wine glass resonator shows a frequency down shift of 1 kHz for a 44 ngr gold point mass, and a frequency shift of 22 kHz for a distributed mass of 83 µgr. Same test is performed on radial mode resonator and a resonance frequency shift of 1.24 and 25.54 kHz was observed for point and distributed mass, respectively in air and at room temperature.