Making AlNx Tunnel Barriers Using a Low-Energy Nitrogen-Ion Beam

A technique based on accelerating positive nitrogen ions onto an aluminum layer has been demonstrated to be effective in forming thin (<2 nm thick) layers of aluminum nitride (AlNx) for use as tunnel barriers in Nb/Al-AlNx/Nb superconductor/ insulator/ superconductor (SIS) Josephson junctions. AlNx is the present material of choice for tunnel barriers because, to a degree greater than that of any other suitable material, it offers the required combination of low leakage current at high current density and greater thermal stability.