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IEEE Transactions on Microwave Theory and Techniques

Measurements and Modeling of Kinetic Inductance Microstrip Delay Lines

J.M. Pond, J. H. Claassen, William L. Carter

Published Dec 1, 1987• 51 citations
Publisher

Abstract

Superconducting microstrip, with phase velocities of about 0.01c, employing kinetic inductance have been fabricated using niobium nitride and a silicon dielectric. Delay lines using this phenomenon have several advantages for analog signal processing, including low loss and very compact size. Measurements of kinetic inductance microstrip delay lines were made in the frequency domain and the time domain. The results were compared to theoretical predictions and an accurate circuit model was developed. The circuit model was used to determine the frequency- and temperature-dependent losses of the delay line.

DOI
10.1109/tmtt.1987.1133845

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Superconducting microstrip, with phase velocities of about 0.01c, employing kinetic inductance have been fabricated using niobium nitride and a silicon dielectric. Delay lines using this phenomenon have several advantages for analog signal processing, including low loss and very compact size. Measurements of kinetic inductance microstrip delay lines were made in the frequency domain and the time domain. The results were compared to theoretical predictions and an accurate circuit model was developed. The circuit model was used to determine the frequency- and temperature-dependent losses of the delay line.
A simple design for superconducting kinetic inductance delay lines is presented. Delay lines were fabricated with a thin-film process involving only DC magnetron deposition and anodization of Nb. Phase-velocity measurements demonstrated wave slowing to less than 1/150 of the velocity of light in free space with associated impedances in the ohm range. Phase velocity changes on lines which were in physical proximity to long Josephson junctions and normal conducting lines were investigated. Variations larger than 10% of the equilibrium value were observed with junction-coupled lines under bias application. Locally heated lines exhibited changes exceeding a factor of two. Loss and phase velocity were determined as a function of bias conditions in both cases. Measured line loss was within expectations.>
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The nonlinear response associated with the current dependence of the superconducting kinetic inductance was studied in capacitively shunted NbTiN microstrip transmission lines.It was found that the inductance per unit length of one microstrip line could be changed by up to 20% by applying a dc current, corresponding to a single-pass time delay of 0.7 ns.To investigate nonlinear dissipation, Bragg reflectors were placed on either end of a section of this type of transmission line, creating resonances over a range of frequencies.From the change in the resonance linewidth and amplitude with dc current, the ratio of the reactive to the dissipative response of the line was found to be 788.The low dissipation makes these transmission lines suitable for a number of applications that are microwave-and millimeter-wave band analogs of nonlinear optical processes.As an example, by applying a millimeter-wave pump tone, very-wide-band parametric amplification was observed between about 3 and 34 GHz.Use as a current variable delay line for an on-chip millimeter-wave Fourier transform spectrometer is also considered.