Superconducting Pickup Coils Fabricated On A Glass Epoxy Polyimide Resin Substrate For Squid Magnetometers

We developed a new fabrication technique of superconducting pickup coils on a glass epoxy polyimide resin (GEPR) substrate, which is robust against mechanical shock compared to those fabricated on a silicon substrate. Niobium pickup coils were fabricated on a 3-inch-shape GEPR wafer using thin-film process. The wafer has copper terminals embedded on the surface in advance. Therefore, an additional substrate is not needed to assemble a magnetometer/gradiometer with a SQUID chip. Connecting these pickup coils with a SQUID chip, a magnetometer and a gradiometer were fabricated and were characterized. Both the magnetometer and the gradiometer have no damage against 50 thermal cycles between room temperature and 77 K. The field resolution of these magnetometer and gradiometer with the detection area of 10 mm x 10 mm are 2.7 fT/root Hz and 4.1 fT/root Hz at 1 kHz respectively, which are good enough for biomagnetic measurements.