Flexible Coaxial Ribbon Cable for High-Density Superconducting Microwave Device Arrays

TL;DR

This paper introduces a novel flexible superconducting coaxial ribbon cable designed for high-density microwave interconnects in superconducting electronics, demonstrating low loss, minimal cross talk, and reduced heat conduction.

Contribution

The paper presents the design, fabrication, and performance evaluation of a new NbTi-based flexible coaxial cable with superior microwave and thermal properties compared to existing solutions.

Findings

1 dB loss at 8 GHz over 30 cm

-60 dB cross talk between neighboring traces

Heat load of 20 nW per trace from 1 K to 90 mK

Abstract

Superconducting electronics often require high-density microwave interconnects capable of transporting signals between temperature stages with minimal loss, cross talk, and heat conduction. We report the design and fabrication of superconducting 53 wt% Nb-47 wt% Ti (Nb47Ti) FLexible coAXial ribbon cables (FLAX). The ten traces each consist of a 0.076 mm O.D. NbTi inner conductor insulated with PFA (0.28 mm O.D.) and sheathed in a shared 0.025 mm thick Nb47Ti outer conductor. The cable is terminated with G3PO coaxial push-on connectors via stainless steel capillary tubing (1.6 mm O.D., 0.13 mm thick) soldered to a coplanar wave guide transition board. The 30 cm long cable has 1 dB of loss at 8 GHz with -60 dB nearest-neighbor forward cross talk. The loss is 0.5 dB more than commercially available superconducting coax likely due to impedance mismatches caused by manufacturing imperfections in the cable. The reported cross talk is 30 dB lower than previously developed laminated NbTi-onKapton microstrip cables. We estimate the heat load from 1 K to 90 mK to be 20 nW per trace, approximately half the computed load from the smallest commercially available superconducting coax from CryoCoax