Superconductor Electronics Fabrication Process with MoN${}_x$ Kinetic Inductors and Self-Shunted Josephson Junctions

Abstract

Recent progress in superconductor electronics fabrication has enabled single-flux-quantum (SFQ) digital circuits with close to one million Josephson junctions (JJs) on 1-cm${}^2$ chips. Increasing the integration scale further is challenging because of the large area of SFQ logic cells, mainly determined by the area of resistively shunted Nb/AlO${}_x$-Al/Nb JJs and geometrical inductors utilizing multiple layers of Nb. To overcome these challenges, we are developing a fabrication process with self-shunted high-J${}_c$ JJs and compact thin-film MoN${}_x$ kinetic inductors instead of geometrical inductors. We present fabrication details and properties of MoN${}_x$ films with a wide range of T${}_c$, including residual stress, electrical resistivity, critical current, and magnetic field penetration depth λ${}_0$. As kinetic inductors, we implemented Mo${}_2$N films with T${}_c$ about 8 K, λ${}_0$ about 0.51 μm, and inductance adjustable in the range from 2 to 8 pH/sq. We also present data on fabrication and electrical characterization of Nb-based self-shunted JJs with AlO${}_x$ tunnel barriers and J${}_c$ = 0.6 mA/μm${}^2$, and with 10-nm thick Si${}_{1-x}$Nb${}_x$ barriers, with x from 0.03 to 0.15, fabricated on 200-mm wafers by co-sputtering. We demonstrate that the electron transport mechanism in Si${}_{1-x}$Nb${}_x$ barriers at x < 0.08 is inelastic resonant tunneling via chains of multiple localized states. At larger x, their Josephson characteristics are strongly dependent on x and residual stress in Nb electrodes, and in general are inferior to AlO${}_x$ tunnel barriers.

12 pages, 14 figures, 1 table, 51 references. Presented at the 13th European Conference on Applied Superconductivity, EUCAS 2017, 17-21 September 2017, Geneva, Switzerland

References in corpus (9)

• Advanced Fabrication Processes for Superconducting Very Large Scale Integrated Circuits
• Superconductor Digital Electronics: Scalability and Energy Efficiency Issues
• Properties of Unshunted and Resistively Shunted Nb/AlOx-Al/Nb Josephson Junctions With Critical Current Densities from 0.1 mA/μm^2 to 1 mA/μm^2
• Inductance of Circuit Structures for MIT LL Superconductor Electronics Fabrication Process with 8 Niobium Layers
• AC-Biased Shift Registers as Fabrication Process Benchmark Circuits and Flux Trapping Diagnostic Tool
• New AC-Powered SFQ Digital Circuits
• Intrinsically shunted Josephson junctions for electronics applications
• Superconducting Energy Scales and Anomalous Dissipative Conductivity in Thin Films of Molybdenum Nitride
• Developments Toward a 250-nm, Fully Planarized Fabrication Process With Ten Superconducting Layers And Self-Shunted Josephson Junctions

Cited by in corpus (12)

• Adiabatic Superconducting Artificial Neural Network: Basic Cells
• Very Large Scale Integration of Josephson-Junction-Based Superconductor Random Access Memories
• Inductance and mutual inductance of superconductor integrated circuit features with sizes down to 120 nm. Part I
• Superconducting circuits without inductors based on bistable Josephson junctions
• Planarized Fabrication Process With Two Layers of SIS Josephson Junctions and Integration of SIS and SFS π-Junctions
• Progress toward superconductor electronics fabrication process with planarized NbN and NbN/Nb layers
• SMART: A Heterogeneous Scratchpad Memory Architecture for Superconductor SFQ-based Systolic CNN Accelerators
• Self- and Mutual Inductance of NbN and Bilayer NbN/Nb Inductors in Planarized Fabrication Process With Nb Ground Planes
• Scalability of Superconductor Electronics: Limitations Imposed by AC Clock and Flux Bias Transformers
• Contemporary implementations of spiking bio-inspired neural networks
• Low-Cost Superconducting Fan-Out with Cell I${}_{\text{C}}$ Ranking
• Stacked Josephson junctions for quantum circuit applications