Current–Voltage Characteristics of SiN Membranes in Solution

Recently, the dielectric breakdown of insulating membranes in aqueous solution has been utilized to fabricate nanopore sensors for various molecular detection applications. Generally, the breakdown phenomenon of an insulator is thought to be strongly related to the behavior of the current through it. However, until now, the current through an insulating membrane in aqueous solution has rarely been measured. In this study, by using thin SiN membranes with large and precisely defined areas, we achieved accurate and reproducible measurements of the current–voltage (I–V) characteristics of SiN membranes in aqueous solution. From the shape of the I–V curves and their temperature dependence, the carrier conduction process in the membrane was found to be mainly governed by the Poole–Frenkel emission and tunnel conduction of the electrons which are transferred by the ions in aqueous solution to the membrane. In addition, we investigated how the I–V characteristics and breakdown voltage changed in accordance with the changes in the solution pH, solute type, solute concentration, and solvent type. The results were categorized into two cases. In one case, both the I–V characteristics and breakdown voltage changed in accordance with the change in each experimental parameter. In the other case, only the breakdown voltage changed without changes in the I–V characteristics. The most drastic changes in both the I–V characteristics and breakdown voltage were observed when the solvent was changed from water to dimethyl sulfoxide (DMSO), whereas the solute was LiCl. This observation was attributed to the differences in ion species that transfer electrons to and from the membrane. H⁺, OH^–, and Cl^– were thought to exchange electrons with the membrane when the solvent was H₂O. On the other hand, Li⁺ and Cl^– may have played a role in the electron exchange reaction when the solvent was DMSO.