Niobium-Silicide Junction Technology for Superconducting Digital Electronics

We present a technology based on Nb/NbxSi1−x/Nb junctions, with barriers near the metal-insulator transition, for applications in superconducting electronics (SCE) as an alternative to Nb/AlOx/Nb tunnel junctions. Josephson junctions with co-sputtered amorphous Nb-Si barriers can be made with a wide variety of electrical properties: critical current density (Jc), capacitance (C), and normal resistance (Rn) can be reliably selected within wide ranges by choosing both the barrier thickness and Nb concentration. Nonhysteretic Nb/NbxSi1−x/Nb junctions with IcRn products greater than 1 mV, where Ic is the critical current, and Jc values near 100 kA/cm2 have been fabricated and are promising for superconductive digital electronics. These barriers have thicknesses of several nanometers; this improves fabrication reproducibility and junction uniformity, both of which are necessary for complex digital circuits. Recent improvements to our deposition system have allowed us to obtain better uniformity across the wafer. key words: amorphous alloy, Josephson device fabrication, Josephson junctions, superconducting devices