Enhancement of superconductivity in NbN nanowires by negative electron-beam lithography with positive resist

TL;DR

This study demonstrates that negative electron-beam lithography with positive resist improves the superconducting properties of NbN nanowires, leading to higher critical temperatures and currents, which benefits superconducting nanowire single-photon detectors.

Contribution

It provides experimental evidence that negative lithography reduces edge damage, enhancing superconducting performance of NbN nanowires compared to positive lithography.

Findings

Higher critical temperature at 4.2 K for negative lithography nanowires

Increased ratio of critical current to depairing current with negative lithography

Enhanced superconducting properties due to reduced edge damage

Abstract

We performed comparative experimental investigation of superconducting NbN nanowires which were prepared by means of positive-and negative electron-beam lithography with the same positive tone Poly-methyl-methacrylate (PMMA) resist. We show that nanowires with a thickness 4.9 nm and widths less than 100 nm demonstrate at 4.2 K higher critical temperature and higher density of critical and retrapping currents when they are prepared by negative lithography. Also the ratio of the experimental critical-current to the depairing critical current is larger for nanowires prepared by negative lithography. We associate the observed enhancement of superconducting properties with the difference in the degree of damage that nanowire edges sustain in the lithographic process. A whole range of advantages which is offered by the negative lithography with positive PMMA resist ensures high potential of this technology for improving performance metrics of superconducting nanowire singe-photon detectors.