Effect of temperature on microwave resonances induced by bias wires and shunted Josephson junctions
Résumé
SFQ-based digital superconducting integrated circuits are realized as a combination of shunted Josephson junctions generally biased with superconducting wires routed over a ground plane [1], [2]. These bias wires form microstrip lines that potentially lead to unwanted resonances if not considered during the design. This work presents a study of the effect of temperature on the resonances of a shunted Josephson junction connected with its bias wires and bondpads, fabricated with the 1 kA/cm² RSFQ niobium process of the FLUXONICS Foundry [1]. A lumped element method based on a compact lossless LCL T-model is used to simulate the behavior of the resonant shunted Josephson junction from 2.9 K to 7 K. The time domain simulations used to extract the I-V characteristics of the shunted junction are performed with JSIM [3]. The temperature-depending inductances and critical currents of the Josephson junctions are fitted to the experimental data, and the limits of the RCSJ model and simulation tools are discussed. [1] J. Kunert et al., “Recent developments in superconductor digital electronics technology at FLUXONICS foundry,” IEEE Trans. Appl. Supercond., vol. 23, no. 5, 2013. [2] S. Nagasawa et al., “Nb 9-Layer Fabrication Process for Superconducting Large-Scale SFQ Circuits and Its Process Evaluation,” IEICE Trans. Electron., vol. E97.C, no. 3, pp. 132–140, 2014. [3] E. S. Fang and T. Van Duzer, “A Josephson integrated circuit simulator (JSIM) for superconductive electronics application,” Extended Abstracts of 1989 Intl. Superconductivity Electronics Conf. (ISEC 1989). Tokyo, Japan, pp. 407–410, 1989.
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