DEVELOPMENT OF A PRACTICAL HIGH TRANSITION TEMPERATURE SQUID

THE RECENT DISCOVERY A HIGH TRANSITION TEMPERATURE SUPERCONDUCTORS (TC > OR - 95K) AND THEIR SUBSEQUENT PREPARATION IN THIN-FILM OPENS THE POSSIBILITY OF FABRICATING A PRACTICAL SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE (SQUID) FROM THESE MATERIALS. SINCE THE SQUID IS THE MOST SENSITIVE DETECTOR OF MAGNETIC FLUX KNOWN, THERE ARE INNUMERABLE APPLICATIONS RANGING FROM MAGENTOENCEPHALOGRAPHY (MEG) TO MAGNETIC ANOMALY DETECTION. PRESENTLY, SQUIDS MUST BE COOLED TO 4 K IN ORDER TO OPERATE. USE OF THE NEW HIGH-TC SUPERCONDUCTORS WOULD ALLOW OPERATION AT A WIDE VARIETY OF TEMPERATURES RANGING FROM ABOVE 77 K TO BELOW 10 K; THE TEMPERATURE OF OPERATION CAN BE SELECTED FOR OPTIMAL PERFORMANCE AND COOLING COST. THE KEY COMPONENT IN CONVENTIONAL SQUIDS IS A JOSEPHSON TUNNEL JUNCTION, WHICH WILL NOT BE EASY TO FABRICATE IN THE NEW PEROVSKITE SUPERCONDUCTORS DUE TO THEIR VERY SHORT SUPERCONDUCTING COHERENCE LENGTH AND THEIR PRESENT NEED FOR HIGH TEMPERATURE HEAT TREATMENT. WE PROPOSE TO OVERCOME THESE OBSTACLES BY DEVELOPING A DIFFERENT TYPE OF JOSEPHSON JUNCTION, NAMELY A SUPERCONDUCTOR-NORMAL METAL-SUPERCONDUCTOR (SNS) MICROBRIDGE. THE GOAL OF PHASE I IS TO DETERMINE THE FEASIBILITY OF MAKING A PRACTICAL HIGH-TC SQUID USING SNS MICROBRIDGES, AND TO DETAIL A FABRICATION PROCESS TO BE IMPLEMENTED IN PHASE II.