X-RAY DETECTORS USING SUPERCONDUCTING TRANSITION METAL TUNNEL JUNCTIONS

THIS PROJECT'S OBJECTIVES ARE (1) TO ADVANCE THE STATE OF THE ART OF X-RAY DETECTION BY DEVELOPING SUPERCONDUCTOR-INSULATOR-SUPERCONDUCTOR TUNNEL JUNCTION X-RAY DETECTORS FROM NIOBIUM AND ALUMINUM JUNCTION TECHNOLOGY AND (2) TO DESIGN SUCH DETECTORS USING MULTILAYERELECTRODES THAT FORM QUASIPARTICLE TRAPS. TO DATE, THE MOSTPROMISING EXPERIMENTAL X-RAY DETECTORS BASED ON SUPERCONDUCTORS HAVE BEEN FABRICATED FROM TIN-BASED TUNNEL JUNCTIONS, WHICH DEGRADE WITH TIME AND THERMAL CYCLING. HOWEVER, NIOBIUM JUNCTION TECHNOLOGY, DEVELOPED OVER THE PAST EIGHT YEARS FOR DIGITAL LOGIC, HAS PROVED TO BE VERY STABLE. THIS PROJECT EXPLOITS CURRENT DEPOSITION TECHNIQUES, ALLOWING COMPLEX MULTILAYER ELECTRODES TO BE MADE USING TRANSITION METAL FILMS. SUCH MULTILAYER ELECTRODES ARE DESIGNED TO OPTIMIZE THE ANTICIPATED PERFORMANCE OF THE DETECTORS. PHASE INCLUDES VERY LOW TEMPERATURE MEASUREMENTS OF LEAKAGE CURRENTS IN JUNCTIONS MADE IN THIS PROJECT, DETERMINATIONS OF THE PERFORMANCE OF THE MOST PROMISING OF THESE JUNCTIONS (USING EQUIPMENT AT THE LAWRENCE LIVERMORE NATIONAL LABORATORY), AND DESIGN OF AN OPTIMUM X-RAY DETECTOR (IN COLLABORATION WITH THE UNIVERSITY OF CALIFORNIA AT SAN DIEGO).