David B. Tuckerman

Flexible superconducting Nb transmission lines on thin film polyimide for quantum computing applications

We describe progress and initial results achieved towards the goal of developing integrated multi-conductor arrays of shielded controlled-impedance flexible superconducting transmission lines with ultra-miniature cross sections and wide bandwidths (dc to >10 GHz) over meter-scale lengths. Intended primarily for use in future scaled-up quantum computing systems, such flexible thin-film Nb/polyimide ribbon cables provide a physically compact and ultra-low thermal conductance alternative to the rapidly increasing number of discrete coaxial cables that are currently used by quantum computing experimentalists to transmit signals between the low-temperature stages (from ~ 4 K down to ~ 20 mK) of a dilution refrigerator. S-parameters are presented for 2-metal layer Nb microstrip structures with lengths ranging up to 550 mm. Weakly coupled open-circuit microstrip resonators provided a sensitive measure of the overall transmission line loss as a function of frequency, temperature, and power. Two common polyimide dielectrics, one conventional and the other photo-definable (PI-2611 and HD-4100, respectively) were compared. Our most striking result, not previously reported to our knowledge, was that the dielectric loss tangents of both polyimides are remarkably low at deep cryogenic temperatures, typically 100

Cryogenic microwave characterization of Kapton polyimide using superconducting resonators

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Influence of fatigue and bending strain on critical currents of niobium superconducting flexible cables containing Ti and Cu interfacial layers

smaller than corresponding room temperature values. This enables fairly long-distance transmission of microwave signals without excessive attenuation and permits usefully high rf power levels to be transmitted without creating excessive dielectric heating. We observed loss tangents as low as 2.2

Preserving Nb Superconducvity in Thin Film Flexible Structures

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High-Quality Factor Superconducting Flexible Resonators Embedded in Thin-Film Polyimide HD-4110

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Microwave Loss Measurements of Copper-Clad Superconducting Niobium Microstrip Resonators on Flexible Polyimide Substrates

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Microwave Performance of Niobium/Kapton Superconducting Flexible Cables

at 20 mK. Our fabrication techniques could be extended to more complex structures such as multiconductor, multi-layer stripline or rectangular coax, and integrated attenuators and thermalization structures.

Heat Transfer For Superconducting Integrated Circuits At Millikelvin Temperatures

Half-wavelength, capacitively-coupled superconducting microstrip resonators have been constructed on 50.8 μm (2 mil) thick flexible Kapton polyimide substrates. The metal stack-up on each side was a 50 nm Ti adhesion layer followed by a 250 nm Nb layer. These resonators yield high quality factors (loaded Q as high as 4110) at 1.2 K in the 2-10 GHz frequency range, implying a loss tangent of less than 0.000275 at 2 GHz. This work provides complex dielectric permittivity information for Kapton materials that have not previously been reported for this temperature (1-6 K) and frequency range. Furthermore it provides confidence that commercially available flexible Kapton is potentially useful as a substrate material for flexible superconducting interconnects or cables, which are of great interest for use in cryogenic electronics systems.

Embedded Niobium Using PI-2611 for Superconducting Flexible Cables

Niobium is a viable material for thin-film superconducting flexible microwave cables. To aid in the design of superconducting flexible cables using Nb, it is important to evaluate not only the superconductor electrical performance, but also mechanical reliability performance since these cables should be reasonably robust when flexed. In this paper, we performed fatigue and bending tests on Nb-only and Ti/Nb/Cu multilayer signal lines on flexible Kapton substrates and measured the change in critical current (<inline-formula><tex-math notation=LaTeX>

Minimizing Film Stress and Degradation in Thin-Film Niobium Superconducting Cables

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