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

<?Pub Dtl?>Recent progress in superconductor electronics fabrication has enabled single-flux-quantum (SFQ) digital circuits with close to one million Josephson junctions (JJs) on <inline-formula><tex-math notation="LaTeX"> ${\text{1}}\hbox{-}{\text{cm}}^{2}$</tex-math></inline-formula> 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<italic>_x</italic>–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-<inline-formula> <tex-math notation="LaTeX">$J_{{\rm{c}}}$</tex-math></inline-formula> JJs and compact thin-film MoN<italic>_x </italic> kinetic inductors instead of geometrical inductors. We present fabrication details and properties of <inline-formula><tex-math notation="LaTeX">${\text{MoN}}_{x}$</tex-math></inline-formula> films with a wide range of <inline-formula><tex-math notation="LaTeX">$T_{{\rm{c}}}$</tex-math></inline-formula>, including residual stress, electrical resistivity, critical current, and magnetic field penetration depth <inline-formula> <tex-math notation="LaTeX">$\lambda _{0}$</tex-math></inline-formula>. As kinetic inductors, we implemented Mo₂N films with <inline-formula><tex-math notation="LaTeX">$T_{{\rm{c}}}$</tex-math></inline-formula> about 8 K, <inline-formula><tex-math notation="LaTeX">$\lambda _{0}$</tex-math></inline-formula> 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<italic>_x</italic> tunnel barriers and <inline-formula><tex-math notation="LaTeX">$J_{{\rm{c}}}= {\text{0.6}}\,{\text{mA}}{/}\mu{\text{m}}^{2}$</tex-math> </inline-formula>, and with 10-nm thick Si₁₋<italic>_x</italic>Nb<italic>_x </italic> barriers, with <italic>x</italic> from 0.03 to 0.15, fabricated on 200-mm wafers by co-sputtering. We demonstrate that the electron transport mechanism in Si₁₋<italic>_x</italic>Nb<italic>_x</italic> barriers at <inline-formula><tex-math notation="LaTeX">$x< {{0.08}}$</tex-math></inline-formula> is inelastic resonant tunneling via chains of multiple localized states. At larger <italic>x</italic>, their Josephson characteristics are strongly dependent on <italic>x</italic> and residual stress in Nb electrodes, and in general are inferior to AlO<italic>_x</italic> tunnel barriers.