Reaching the Ionic Current Detection Limit in Silicon-Based Nanopores

Solid-state nanopores act as single-molecule sensors whereby passage of an individual molecule in aqueous electrolyte through a nanopore is registered as a change in ionic conductance ($\Delta $G). Future nanopore applications such as DNA sequencing at high bandwidth require high $\Delta $G for optimal signal-to-noise ratio. Reducing the nanopore diameter and thickness increase $\Delta $G. Molecule size limits the diameter, thus efforts concentrate on minimizing the thickness by thinning oxide/nitride films or using 2D materials. Weighted by electrolyte conductivity the highest $\Delta $G reported to date for DNA translocations were obtained with nanopores made in oxide/nitride films. We present a controlled electron irradiation technique to thin such films to the limit of their stability, producing nanopores tailored to molecule size in amorphous Si with thicknesses less than 2 nm. We compare $\Delta $G values with results found in the literature for DNA translocation through these nanopores, where access resistance becomes comparable to the resistance through the nanopore itself.