Fabrication of suspended microchannel resonators with integrated piezoelectric transduction

Suspended microchannel resonators (SMRs) are resonant mass sensors that contain liquid within the mechanical structure, therefore minimizing damping associated with the fluidic viscous drag. In this paper, we present a novel fabrication process for transparent SMRs with integrated piezoelectric (PZE) transduction, based on thin film depositions and trench filling. Our method allows to finely tune the geometry and the dimensions of the embedded channels, through a short and well-controlled wet etching in KOH. After channel definition, the wafer has a flat surface that enables further microfabrication processing. Piezoelectric (PZE) electrodes are placed on top of each resonator, enabling independent transduction of the devices. Devices are fabricated with a yield higher than 95%, and characterized with and without fluids (water and IPA). PZE-transduced SMRs show a mass responsivity up to 1125 ± 0.06 mHz/pg and a non-monotonic dependence of the quality factor on fluidic viscosity. Besides PZE actuation and readout, our fabrication process is compatible with the integration of other types of transducers in close proximity to the fluid, broadening the spectrum of potential applications.