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تسجيل مستخدم جديدDevelopments Toward a 250-nm, Fully Planarized Fabrication Process With Ten Superconducting Layers And Self-Shunted Josephson Junctions
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We are developing a superconductor electronics fabrication process with up to nine planarized superconducting layers, stackable stud vias, self-shunted Nb/AlOx-Al/Nb Josephson junctions, and one layer of MoNx kinetic inductors. The minimum feature size of resistors and inductors in the process is 250 nm. We present data on the mutual inductance of Nb stripline and microstrip inductors with linewidth and spacing from 250 nm to 1 {mu}m made on the same or adjacent Nb layers, as well as the data on the linewidth and resistance uniformity.
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We present our new fabrication Process for Superconductor Electronics (PSE2) that integrates two (2) layers of Josephson junctions in a fully planarized multilayer process on 200-mm wafers. The two junction layers can be, e.g., conventional Supercond
uctor-Insulator-Superconductor (SIS) Nb/Al/AlO_x/Nb junctions with the same or different Josephson critical current densities, J_c. The process also allows integration of high-J_c Superconductor-Ferromagnet-Superconductor (SFS) or SFSS JJs on the first junction layer with Nb/Al/AlO_x/Nb trilayer junctions on the second junction layer, or vice versa. In the present node, the SFS trilayer, Nb/Ni/Nb is placed below the standard SIS trilayer and separated by one niobium wiring layer. The main purpose of integrating the SFS and SIS junction layers is to provide compact {pi}-phase shifters in logic cells of superconductor digital circuits and random access memories, and thereby increase the integration scale and functional density of superconductor electronics. The current node of the two-junction-layer process has six planarized niobium layers, two layers of resistors, and 350-nm minimum feature size. The target Josephson critical current densities for the SIS junctions are 100 {mu}A/{mu}m^2 and 200 {mu}A/{mu}m^2. We present the salient features of the new process, fabrication details, and characterization results on two layers of Josephson junctions integrated into one process, both for the conventional and {pi}-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/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 {lambda}$_0$. As kinetic inductors, we implemented Mo$_2$N films with T$_c$ 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 AlO$_x$ tunnel barriers and J$_c$ = 0.6 mA/{mu}m$^2$, 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.
In this letter, we present the study of the high-frequency mixing properties of ion irradiated YBa2Cu3O7 Josephson nano-junctions. The frequency range, spanning above and below the characteristic frequencies fc of the junctions, permits clear observa
tion of the transition between two mixing regimes. The experimental conversion gain was found to be in good agreement with the prediction of the three ports model. Finally, we discuss the potential of the junctions to build a Josephson mixer operating in the terahertz frequency range.
We present a cluster algorithm for resistively shunted Josephson junctions and similar physical systems, which dramatically improves sampling efficiency. The algorithm combines local updates in Fourier space with rejection-free cluster updates which
exploit the symmetries of the Josephson coupling energy. As an application, we consider the localization transition of a single junction at intermediate Josephson coupling and determine the temperature dependence of the zero bias resistance as a function of dissipation strength.
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