High quality factor silicon nitride nanomechanical resonators fabricated by maskless femtosecond laser micromachining

Abstract

Freestanding silicon nitride (SiN) devices are central to the field of nanomechanical resonators and other technology applications such as transmission electron imaging and nanopore bioassays. Nanofabrication techniques used for fabricating these devices often lack flexibility. While photolithography requires printing of an expensive photomask for each new design iteration, electron beam lithography is slow and commands high equipment cost. Here, we demonstrate maskless rapid prototyping of freestanding SiN nanomechanical resonators fabricated by femtosecond laser ablation of a plain SiN membrane in ambient air. We fabricate microbeams with different widths from 7 to 100  μm, and we characterize their resonance frequency and mechanical quality (Q) factors. We find that membrane cracking can be avoided during fabrication by carefully engineering the etch pattern, and that laser etching has a negligible effect on built-in tensile stress. For each beam, Q-factors are measured for several eigenmodes and are found to remain high after laser etching. All beams show quality factors greater than 105, while unetched plain membranes have Q > 106. Possible causes for Q-factor reduction are identified, along with future process improvement directions.