Development of hybrid suspended microchannel resonators for mass sensing in liquid

Suspended microchannel resonators have proved to be the best candidates for a variety of technological applications requiring accurate measurements in liquid. These devices eliminate the viscous damping by placing the solution inside a hollow resonator surrounded by vacuum, thus reaching sub-femtogram resolution. The main fabrication method of suspended microchannel resonators is standard cleanroom fabrication, which allows to create resonators with excellent mass sensitivity. However, fabrication steps are expensive and complex, and inherently planar, thus limiting three-dimensional design. In this scenario, polymeric resonators printed by two-photon polymerization(TPP) emerged as a valid solution to increase the low prototyping speed and accessibility of silicon-based resonators, but low quality factor and mass sensitivity limit their performance. In this work, a novel fabrication technique based on a hybrid structure has been developed. A single mask cleanroom fabrication process has been carried out to create silicon nitride supporting beams. Then, 3D-printing by TPP was used to fabricate microfluidic lids. The final silicon chip can be plugged into a stereolithographic microfluidic interface for handling and connecting to the external world. Fabricated devices were mechanically characterised in vacuum by laser Doppler vibrometry before and after the printing process. Damping analysis was conducted to define the main dissipation sources in hybrid devices. Intrinsic losses in the polymer layer were defined as dominant damping sources. A quality factor of 510 at 341 kHz was reached with a 350 µm x 50 µm hybrid double-clamped beam. The theoretical mass responsivity and minimum mass resolution of this device were estimated to be 1.84 Hz/pg and 14.75 ag, respectively, which still compete with conventional fabricated SMRs.