Noise Properties of Directly-coupled Single-layer High-Tc 2nd-order SQUID Gradiometer

We have fabricated planar-type single-layer second-order high-Tc SQUID gradiometers. The devices consisted of symmetrically designed three parallel-connected square pickup loops that were directly coupled to the SQUID. $YBa_2$$Cu_3$$O_{7}$ film was deposited on $SrTiO_3$ substrate by a PLD system and patterned into a device by the photolithography with ion milling technique. Junctions of the SQUID were either step-edge or bicrystal type. All the structures were formed on a 10 mm $\times$ 5 mm substrate. Balancing of the gradiometer was achieved by adjusting the width of the central pickup loop. The gradiometer noise was measured both inside and outside a magnetically shielded room. Details of the results will be discussed.