Superconductor Electronics Fabrication Process with MoNx Kinetic Inductors and Self-Shunted Josephson Junctions

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/AlOx-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 MoNx kinetic inductors instead of geometrical inductors. We present fabrication details and properties of MoNx films with a wide range of T-c, including residual stress, electrical resistivity, critical current, and magnetic field penetration depth lambda(0). As kinetic inductors, we implemented Mo-2 N films with Tc about 8 K,lambda(0) about 0.51 mu m, 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 AlOx tunnel barriers and J(c) = 0.6 mA/mu m(2), and with 10-nm thick Si1-xNbx 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 Si1-xNbx 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 AlOx tunnel barriers.