Experimental Study of Energy Dissipation in High Quality Factor Hollow Square Plate MEMS Resonators for Liquid Mass Sensing

We report on a capacitively transduced, Lamé-mode resonator for real-time mass sensing in liquid. The resonators are fabricated in silicon, presenting a square plate geometry, and incorporate an integrated fluidic channel diagonally crossing the 50 μm wide plate. Varying shapes of the buried fluidic channels (rectangular and ellipsoidal) are studied, resulting in mechanical resonance frequencies between 70 and 78 MHz. Volumes of those nanochannels range between 223 and 833 fL. For fluid-filled rectangular channels, quality factors demonstrate increasing values up to 4300 (compared with 3200 in air), when the resonance frequency × quality factor product exceeds 300 GHz. An extensive study has been carried out with the rectangular channels, showing downward frequency shifts proportional to the liquid mass, as compared with dry devices. Experimental mass responsivities for all tested devices approached 1 kHz.pg^-1. We examined different sources of dissipation, taking place in our structures, through qualitative analysis to explain the quality factor variations between dry and wet devices. We particularly focused on flow conditions, the vibration amplitude, the channel design and position relative to the resonator anchor, as well as the variation of acoustic energy dissipation within the embedded-channel cavities.