Fabrication of 3-nm-thick Si₃N₄ membranes for solid-state nanopores using the poly-Si sacrificial layer process

摘要

To improve the spatial resolution of solid-state nanopores, thinning the membrane is a very important issue. The most commonly used membrane material for solid-state nanopores is silicon nitride (Si₃N₄). However, until now, stable wafer-scale fabrication of Si₃N₄ membranes with a thickness of less than 5?nm has not been reported, although a further reduction in thickness is desired to improve spatial resolution. In the present study, to fabricate thinner Si₃N₄ membranes with a thickness of less than 5?nm in a wafer, a new fabrication process that employs a polycrystalline-Si (poly-Si) sacrificial layer was developed. This process enables the stable fabrication of Si₃N₄ membranes with thicknesses of 3?nm. Nanopores were fabricated in the membrane using a transmission electron microscope (TEM) beam. Based on the relationship between the ionic current through the nanopores and their diameter, the effective thickness of the nanopores was estimated to range from 0.6 to 2.2?nm. Moreover, DNA translocation through the nanopores was observed.