Ultrathin SiNx nanopore membranes fabricated using the SiO₂ sacrificial layer process

SiN membranes with thicknesses of 3-7 nm were fabricated using the SiO₂ sacrificial layer process. Then, nanopores were fabricated in the membranes via dielectric breakdown. The current noise of the nanopore membranes was approximately 3/5 that of membranes fabricated using the conventional poly-Si sacrificial layer process. In addition, ionic current blockades were measured when poly(dT)₆₀ passed through the nanopores, and the effective thickness of the nanopores was estimated based on those current-blockade values. The effective thickness was approximately 4.8 nm when the deposited thickness of the SiN membrane was 6.03 nm. On the other hand, the effective thickness and the actual thickness were almost the same when the deposited thickness was 3.07 nm. This suggests the difficulty of forming the shape in which the membrane was thinner only near the nanopore than in the other area as the actual thickness decreased.