Very low noise all-niobium DC SQUIDs

All-niobium thin film planar DC SQUIDs have been fabricated, containing submicron tunnel junctions. The fabrication method using photoresist techniques is briefly described. The IcR product of the SQUIDs is 0.3 mV, the inductance 1 nH. They show no changes after repeated thermal cycling or storage over extended periods. The best intrinsic energy resolution obtained so far in a flux-locked loop configuration is 4 . 10^-32J/Hz. The noise power is an order of magnitude higher than predicted from the simple RSJ model calculation.