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

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.

Large active-area superconducting microwire detector array with single-photon sensitivity in the near-infrared

“…As the active areas are scaled in these devices, it will also be important to implement higher fill-factor designs that avoid performance degradation by current crowding effects in the bends. Known approaches to this include increasing the thickness of bends 50,51 and placing bends outside of a high fill-factor active area 52 . At 25% fill-factor and without an optical stack, the arrays characterized in this work have a system detection efficiency of approximately 4.2% (see supplemental information for details).…”

Characterization of a superconducting microstrip single-photon detector shunted with an external resistor

“…The triggering of the pulse response in the SNSPD is mainly through the formation of the hotspot across the nanowire, which has a good tolerance to the ratio of I b /I sw because of a narrow strip width. Thus, when the ratio of I b /I sw reaches a certain level (generally >80% I sw ) [37], the SNSPD can generate a high probability of photon detection (e.g. IDE ∼100% for NbN SNSPD).…”

Niobium Nitride Preparation for Superconducting Single-Photon Detectors

“…The nanowires, which were curved in a circular shape, eliminated the current crowding effect while significantly reducing dark counts. Xiong et al [89] also avoided this effect by reducing the proportion of serpentine structures while thickening the curved parts while maintaining a high filling factor. As it stands, some researchers have abandoned meandering structures and instead design spiral structures.…”