Characterization of dual high transition temperature superconducting quantum interference device first-order planar gradiometers on a chip

The dual first-order planar gradiometers of high transition temperature (high- T_c) superconducting quantum interference devices (SQUIDs) were designed and fabricated on a 10×10 mm² SrTiO₃ bicrystal substrate. Each gradiometer consists of four bare SQUIDs which are connected to two symmetric pickup loops. Any two of the SQUIDs can be connected in series to obtain better performance. In this study, by selecting the coupling direction of SQUID, a balance resolution of 0.08% was achieved. And, a second-order electronic planar gradiometer was composed of these two first-order gradiometers. Experimental data showed that the noise performance of the second-order electronic planar gradiometer composed of two planar first-order gradiometers can reach 15 μ ₀ / Hz^1/2 at 1 kHz in an unshielded environment, which is comparable to the noise level of a magnetometer in a shielded environment.