Reducing current crowding in meander superconducting strip single-photon detectors by thickening bends

TL;DR

This paper introduces a method to improve superconducting single-photon detectors by thickening bends to reduce current crowding, leading to better efficiency, lower dark counts, and improved timing.

Contribution

It proposes and experimentally verifies a novel technique of thickening bends in superconducting detectors to mitigate current crowding effects, enhancing performance.

Findings

Increased switching current (Isw) with thickened bends.

Enhanced detection efficiency and reduced dark counts.

Improved time jitter performance.

Abstract

To facilitate high optical coupling efficiency and absorptance, the active area of a superconducting nano/microstrip single-photon detector (SNSPD/SMSPD) is often designed as a meander configuration with a high filling factor (e.g., >=0.5). However, the switching current (Isw) of SNSPD/SMSPD, at which the detector switches into the normal state, is significantly suppressed by a geometry-induced "current crowding effect", where there are sharp bends in the strip. Here we propose and experimentally verify an alternative method to reduce current crowding both in SNSPD and SMSPD by directly increasing the thickness of the bends through the deposition and lift-off of a secondary superconducting film. We measure and compare the performance of SNSPDs and SMSPDs with different filling factors and bend configurations, with or without thickened bends. Improvements for detectors were observed in detection efficiency, intrinsic dark count rate, and time jitter, owing to the enhanced Isw. Our method provides a promising way of optimizing SNSPD/SMSPD detection performance.