Fabrication and characteristics of multi-terminal SINIS devices

We fabricated and measured multi-terminal SINIS devices (where S, I, and N denote a superconductor, an insulator, and a normal metal, respectively) with the Nb/Al/AlO_x/Al/AlO_x/Al/Nb structure. The multilayered SINIS structure was fabricated in-situ using sputter deposition of Nb and Al, and thermal oxidation of the Al layers to grow the tunnel barriers. Devices with a characteristic size of about 10 μm were formed via an optical-lithography process that included making an electrical contact to the middle Al layer (16-19 nm thick). Current-voltage characteristics of the devices were measured in different modes (i. e., by feeding the current across the whole device, through each of the junctions, and through the middle Al film) at low temperatures (1.4-4.2 K). Specifically, the devices were tested in a transistor-like configuration to explore the influence of current injection through a SIN junction and the N film on the Josephson critical current and quasiparticle characteristic of the SINIS junction as a whole, and on the characteristics of the second junction.