Effect of Thermal Cycling on the Electrical Characteristics of HTS SQIFs and SQUIDs

In order to investigate the stability of HTS SQUIDs and SQIFs (arrays of SQUIDs with different loop size) based on YBCO bicrystal Josephson junctions we thermally cycled them in a controlled way 1000 times between 300 K and 77 K. The samples, which were partly covered with a Teflon protection layer, were electrically characterized after predetermined numbers of cycles. From these measurements the electrical parameters like critical current, normal resistance, maximum voltage modulation, width of the SQIF-peak and of the SQUID modulation, coupling inductance of the SQUID, and the maximum magnetic-field-to-voltage transfer factor were determined. Additionally, the critical current density of the YBCO-layers was determined.