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Journal of Applied Physics

Geometric dependence of Josephson junction normal-state resistance for superconducting qubit design

Dae-Yun Kim, Seon-Myeong Choi, Dae Seok Han, June-Young M. Lee, Kiho Kim, Hyeokshin Kwon, Jaeho Shin

Published Mar 20, 2026• 0 citations
Publisher

Abstract

Josephson junctions (JJs) are critical components in superconducting quantum circuits, where their electrical properties directly determine qubit transition frequencies. While advances in fabrication have enabled precise control over junction area and oxide thickness, the influence of junction geometry beyond area has remained largely unexplored. Here, we report clear and reproducible evidence that the normal-state resistance (Rn) of JJs depends strongly on geometric parameters, demonstrating that (Rn) exhibits a systematic and reproducible dependence on junction geometry beyond simple area scaling. To account for this behavior, we introduce an edge-resistance model that incorporates perimeter-related contributions to (Rn). Our findings highlight the crucial role of geometric design in JJ electrical characteristics and provide a practical framework for improving frequency precision and uniformity in large-scale superconducting quantum processors.

DOI
10.1063/5.0317288

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Josephson junctions (JJs) are critical components in superconducting quantum circuits, where their electrical properties directly determine qubit transition frequencies. While advances in fabrication have enabled precise control over junction area and oxide thickness, the influence of junction geometry beyond area has remained largely unexplored. Here, we report clear and reproducible evidence that the normal-state resistance (Rn) of JJs depends strongly on geometric parameters, demonstrating that (Rn) exhibits a systematic and reproducible dependence on junction geometry beyond simple area scaling. To account for this behavior, we introduce an edge-resistance model that incorporates perimeter-related contributions to (Rn). Our findings highlight the crucial role of geometric design in JJ electrical characteristics and provide a practical framework for improving frequency precision and uniformity in large-scale superconducting quantum processors.
Reproducible Josephson junction (JJ) characteristics are essential for frequency-deterministic and scalable superconducting quantum processors. We show that the normal-state resistance and its reproducibility in Al/AlOx/Al JJs are governed not by oxide thickness, but by fabrication-history–induced disorder in the tunneling barrier. By comparing junctions fabricated on bare wafers, lift-off–processed base layers, and dry-etched base layers under identical oxidation conditions, we observe large differences in resistance and wafer-to-wafer variability. Atomic force microscopy reveals distinct surface disorder imprinted by prior fabrication steps, while cross-sectional transmission electron microscopy show that the average AlOx barrier thickness is comparable across the three fabrication histories within experimental uncertainty. The enhanced resistance on rough, plasma-damaged surfaces therefore originates from nanoscale barrier disorder rather than thickness variations. These results establish fabrication history as a key determinant of JJ barrier quality and highlight the need for holistic process control to achieve deterministic qubit frequency targeting.
Abstract Josephson superconducting qubits and parametric amplifiers are prominent examples of superconducting quantum circuits that have shown rapid progress in recent years. As such devices become more complex, the requirements for reproducibility of their electrical properties across a chip are being tightened. Critical current of the Josephson junction Ic is the essential electrical parameter in a chip. So, its variation is to be minimized. According to the Ambegaokar–Baratoff formula, critical current is related to normal-state resistance, which can be measured at room temperature. In this study, we focused on the dominant source of non-uniformity for the Josephson junction critical current–junction area variation. We optimized Josephson junction fabrication process and demonstrated resistance variation of 9.8–4.4% and 4.8–2.3% across 22 × 22 mm2 and 5 × 10 mm2 chip areas, respectively. For a wide range of junction areas from 0.008 to 0.12 μm2, we ensure a small linewidth standard deviation of 4 nm measured over 4500 junctions with linear dimensions from 80 to 680 nm. We found that the dominate source of junction area variation limiting Ic{\mathrm{I}}_{\mathrm{c}}Ic​ I c reproducibility is the imperfection of the evaporation system. The developed fabrication process was tested on superconducting highly coherent transmon qubits (T1 > 100 μs) and a nonlinear asymmetric inductive element parametric amplifier.
Geometric dependence of critical-current variation in Al/AlOx{\rm _x}x​/Al Josephson junctions: a model-based analysis
Achieving uniform critical current across Josephson junctions is essential for the large-scale integration of superconducting quantum circuits. In this work, we statistically analyzed the variation of the critical current of Al/AlOx{\rm _x}x​/Al junctions using room-temperature tunnel resistance statistics, and identified the dominant contribution among the modeled sources of the variation based on their dependence on geometry and deposition conditions of junctions. Our model-based analysis reveals that fluctuations in the Al film thickness play the dominant role among the modeled contributing factors. Based on this analysis, we found that, in Dolan-bridge double-angle deposition, adopting a deposition angle of 30-degree for bilayer junctions significantly improves uniformity, yielding a relative standard deviation of 1.2% (0.5%) across a 9.75 mm (1.5 mm) square region.
Achieving uniform critical current across Josephson junctions is essential for the large-scale integration of superconducting quantum circuits. In this work, we statistically analyzed the variation of the critical current of Al/AlOx/Al junctions using room-temperature tunnel resistance statistics and identified the dominant contribution among the modeled sources of the variation based on their dependence on geometry and deposition conditions of junctions. Our model-based analysis reveals that fluctuations in the Al film thickness play the dominant role among the modeled contributing factors. Based on this analysis, we found that, in Dolan-bridge double-angle deposition, adopting a deposition angle of 30° for bilayer junctions significantly improves uniformity, yielding a relative standard deviation of 1.2% (0.5%) across a 9.75 mm (1.5 mm) square region.
Alternating-bias assisted annealing (ABAA) has been effectively utilized to tune the normal-state resistance of sub-micrometer Josephson junctions (JJs). However, how the annealing efficiency is affected by pre-annealing thermal history, oxidation exposure, and junction geometry remains unexplored for micrometer-scale devices. Here, we systematically investigate the ABAA behavior in micrometer-scale JJs to address the growing demands of modern superconducting devices. The dependence of resistance tuning on the pre-annealing heating time, annealing temperature, bias voltage, oxidation exposure, junction linewidth, and aspect ratio is thoroughly characterized. Our results will contribute a predictive framework for the precise resistance control of micrometer-scale JJs, thereby guiding the deterministic fabrication of high-performance superconducting quantum hardware.
In superconducting quantum circuits, Josephson junctions are a key component to provide nonlinearity and enable superconducting qubits. Fabricating junctions with precise critical currents is crucial to defining qubit frequency. Here we suppress the critical current variation of Josephson junctions by varying the critical current density Jc and junction areas. The relative standard deviation of the critical current Ic is controlled to be below 0.8%. This uniform fabrication is promising for realizing scalable superconducting quantum computation.