Ultrathin, High-Lifetime Silicon Nitride Membranes for Nanopore Sensing

Thin membranes are highly sought-after for nano-pore-based single-molecule sensing, and fabrication of such membranes becomes challenging in the less than or similar to 10 nm thickness regime where a plethora of useful molecule information can be acquired by nanopore sensing. In this work, we present a scalable and controllable method to fabricate silicon nitride (SixNy) membranes with effective thickness down to similar to 1.5 nm using standard silicon processing and chemical etching using hydrofluoric acid (HF). Nanopores were fabricated using the controlled breakdown method with estimated pore diameters down to similar to 1.8 nm yielding events >500,000 and >1,800,000 from dsDNA and bovine serum albumin (BSA) protein, respectively, demonstrating the high-performance and extended lifetime of the pores fabricated through our membranes. We used two different compositions of SixNy for membrane fabrication (near-stoichiometric and silicon-rich SixNy) and compared them against commercial membranes. The final thicknesses of the membranes were measured using ellipsometry and were in good agreement with the values calculated from the bulk etch rates and DNA translocation characteristics. The stoichiometry and the density of the membrane layers were characterized with Rutherford backscattering spectrometry while the nanopores were characterized using pH-conductance, conductivity-conductance, and power spectral density (PSD) graphs.

Automated summary

In this work, a scalable and controllable method to fabricate thin silicon nitride (SixNy) membranes with effective thickness down to 1.5 nm was presented. Nanopores with estimated pore diameters down to 1.8 nm were also fabricated through a controlled breakdown method. These membranes demonstrated high-performance and extended lifetime in single-molecule sensing of dsDNA and BSA protein. Different compositions of SixNy membranes were compared with commercial membranes, and their properties were characterized using various methods.