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IEEE Transactions on Applied Superconductivity

Modeling Strategies for Superconducting Microstrip Transmission Line Structures

Kongpop U-yen, Karwan Rostem, Edward J. Wollack

Published Apr 17, 2018• 12 citations
Publisher

Abstract

Strategies are explored to reduce the electromagnetic simulation time of electrically large superconducting transmission line structures while retaining model accuracy. The complex surface reactance of an infinite thin-film superconducting sheet is evaluated with the BCS (Bardeen-Cooper-Schrieffer) theory and used as an input to model the phase velocity and characteristic impedance of finite width transmission line structures. Commercially available electromagnetic simulation software are employed for the calculations and the results are compared with limiting analytic forms from the literature. The influences of line width, metallization thickness, and substrate height on microstrip transmission line propagation are considered in detail and a scaling approach is presented to compensate for the leading order effect in numerical simulations. These findings are particularly important near the energy gap of the superconductor due to the influence of the kinetic inductance on the transmission line dispersion.

DOI
10.1109/tasc.2018.2827987

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Strategies are explored to reduce the electromagnetic simulation time of electrically large superconducting transmission line structures while retaining model accuracy. The complex surface reactance of an infinite thin-film superconducting sheet is evaluated with the BCS (Bardeen-Cooper-Schrieffer) theory and used as an input to model the phase velocity and characteristic impedance of finite width transmission line structures. Commercially available electromagnetic simulation software are employed for the calculations and the results are compared with limiting analytic forms from the literature. The influences of line width, metallization thickness, and substrate height on microstrip transmission line propagation are considered in detail and a scaling approach is presented to compensate for the leading order effect in numerical simulations. These findings are particularly important near the energy gap of the superconductor due to the influence of the kinetic inductance on the transmission line dispersion.
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This paper investigates linear and nonlinear microwave propagation in a periodic superconductor-normal conductor microstrip transmission line (S-N muTL). We derive closed-form equations for complex propagation constant, input impedance and complex resonant frequencies for linear infinite and finite periodic S-N muTL. Jumps on the curves of attenuation constants, input impedances and eigenfrequencies occur exactly at the Bragg frequencies. We demonstrate that the finite S-N muTL shows the same behavior as infinite periodic SmuTL, when there is enough number of unit cells. Furthermore, nonlinear microwave signal propagation analyses are carried out based on the self-consistent method, when the kinetic inductance of the superconducting segments is in the nonlinear regime.
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The simplest model of nonlinear response of a superconducting thin film is used for modeling the nonlinear phenomena in a superconducting transmission line and a microstrip resonator. The specified characteristic power of the transmission line is suggested to use as a fitting parameter for numerical description of the microstrip line nonlinearity at microwaves. Quantitative agreement of simulated and experimental data has been obtained for the incident power dependent transmission coefficient of a microstrip line section and a high quality microstrip resonator. Numerical results have also been obtained for the power of the third harmonic radiated from the nonlinear resonator.
Abstract Interconnects are a major discriminator for superconducting digital technology, enabling energy-efficient data transfer and high-bandwidth heterogeneous integration. We report a method to simulate propagation of picosecond pulses in superconducting passive transmission lines (PTLs). A frequency-domain propagator model obtained from the Ansys high-frequency structure simulator (HFSS) field solver is incorporated in a Cadence Spectre circuit model, so that the particular PTL geometry can be simulated in the time-domain. The Mattis Bardeen complex conductivity of the superconductor is encoded in the HFSS field solver as a complex-conductivity insulator. Experimental and simulation results show that Nb 20 Ω microstrip PTLs with 200 nm interlayer dielectric thickness can support propagation of a single-flux-quantum pulse up to 7 mm and a double-flux-quantum pulse up to 28 mm.