Line width narrowing of superconducting nanowire single photon detectors using atomic layer etching

Superconducting nanowire single photon detectors (SNSPDs) have shown remarkable photon detection characteristics, and scalable architectures allow for the fabrication of SNSPD cameras with over a hundred thousand pixels. Producing such large format devices requires the use of a high throughput lithography process such as stepper photolithography. This restricts nanowire widths to the resolution limit of the photolithography system, which limits performance, particularly for mid-infrared wavelengths. In this paper, we develop an SNSPD fabrication process that uses bidirectional atomic layer etching to reduce nanowire widths by > 100 nm, achieving performance that has only previously been attained using low throughput electron beam lithography. This fabrication process will allow for high-pixel count SNSPD cameras with improved performance due to reduced nanowire widths.