DEVICE-STRUCTURE DEPENDENCE OF SHIFT IN SQUID CHARACTERISTICS BY FLUXTRAPPING

Shifts in voltage-flux characteristics of a SQUID by flux trapping hav e been measured to study effectiveness of guard ring structure on shie lding of magnetic field. The measurements are made under controlled ma gnetic field. Magnitude of the shift depends on the device structure. It is found that there exists a threshold field for the flux trapping, and the field is reduced by introducing the guard-ring in the SQUID. Comparing to the SQUID without the structure, the SQUID with it needs higher-grade shielding to prevent the flux trapping during cooling dow n.