NBN TUNNEL JUNCTIONS WITH THERMALLY OXIDIZED SPUTTER

THERE HAS BEEN CONSIDERABLE INTEREST IN RECENT YEARS IN FABRICATION OF ALL NIOBIUM NITRIDE SUPERCONDUCTING CIRCUITS. THE HIGH TRANSITION TEMPERATURE OF NBN IS TECHNOLOGICALLY IMPORTANT BECAUSE IT ALLOWS NBN-BASED CIRCUITS TO BE COOLED WITH SMALL AND RELIABLE CLOSED CYCLE REFRIGERATORS (CCR). WE HAVE DEMONSTRATED THE FEASIBILITY OF OPERATING NBN-BASED JOSEPHSON CIRCUITRY IN A CCR ENVIRONMENT. THE FABRICATION OF SUCH CIRCUITS RELIES ON THE DEVELOPMENT OF A PROCESS THAT RELIABLY PRODUCES JOSEPHSON TUNNEL JUNCTIONS. WE HAVE DEVELOPED A PROCESS CAPABLE OF PRODUCING HIGH QUALITY NBN/MGO/NBN DEVICES. OUR PROCESS EXPLOITS THERMALLY OXIDIZED SPUTTER-DEPOSITED MAGNESIUM AS A TUNNEL BARRIER AND PROVIDED A RELATIVELY REPRODUCIBLE MEANS FOR TUNNEL BARRIER FORMATION. HOWEVER, A MAJOR PROBLEM WITH SPUTTER-DEPOSITED MG IS THE PRESENCE OF EXCESSIVE UNOXIDIZED MAGNESIUM. THIS EXCESS MG REACTS WITH NIOBIUM NITRIDE ELECTRODES AND FORMS POOR INTERFACES. USE OF A DIFFUSSION BARRIER BETWEEN NIOBIUM NITRIDE AND MAGNESIUM SHOULD ALLEVIATE THIS PROBLEM. THE GOAL OF THIS RESEARCH IS TO IDENTIFY A SUITABLE DIFFUSION BARRIER.