Improved multi-loop DC SQUID

We report on an improved version of a multiloop thin film dc-SQUID. The new design features thirty-two parallel loops, a loop area of 400 × 400 μm, a total inductance of 20pH, and a coupling constant of 0.5 between the SQUID and the thin film input coil. Particular care was taken to decrease the capacitance shunting the main inductance. A novel "chessboard" design was used for this purpose. Preliminary results in a flux locked loop configuration give a coupled energy sensitivity of 900h at 1KHz with very low l/f noise.