Nb/a-Si/Nb Josephson junctions for high-density superconducting circuits

We present electrical characterization data of sputtered Nb/a-Si/Nb Josephson junctions (JJs) for high-speed and high-density superconducting circuits. Junctions were studied with critical current densities (J(c)) ranging from 0.01 to 3 mA/mu m(2) at 4K. For junctions deposited at room temperature and processed to a maximum temperature of 150 C-circle, the dependence of J(c) on barrier thickness d is exponential, J(c) alpha exp (-d/d(0)), with d0 constant over the entire range of Jc values studied. Junctions were annealed at temperatures up to 300 C-circle to study changes in their electrical properties and possible compatibility with high temperature fabrication processes. Current-voltage characteristics, critical current uniformity, critical current modulation with in-plane magnetic field, and sub-gap resistance behavior of these junctions were measured at 4K and demonstrate that the junction properties do not degrade with annealing. These data indicate that Nb/a-Si/Nb JJs are a potential candidate for higher speed and higher density superconducting circuits.