Fabrication of integrated HTS-SQUID magnetometers having multiturn input coils with different sizes

► Integrated HTS-SQUID magnetometers with a 20-turn input coil were fabricated. ► Two types of magnetometers with different washer sizes and different coil widths were fabricated. ► Type-I had a 2-μm-wide coil on a 200×200-μm2 washer, and Type-II had a 4-μm-wide coil on a 300×300-μm2 washer. ► Both the magnetometers exhibited rather low white noise level around 25 fT/Hz1/2 (@77K, 1kHz). ► The wider coil in the Type-II allowed a larger superconducting current in the loop consisting of the coil and a pickup one. We have studied the fabrication process for high-Tc superconducting quantum interference devices (HTS-SQUIDs) containing ramp-edge-type Josephson junctions and multilayer superconducting wiring. Integrated HTS-SQUID magnetometers with a 20-turn input coil were fabricated. SmBCO and La-doped ErBCO were used for base- and counter-electrodes having Tc’s around 90K, respectively. MgO (100) substrates with a size of 15×15mm2 were used. Two types of magnetometers with different washer sizes and different coil widths were fabricated: Type-I had a 2-μm-wide coil on a 200×200-μm2 washer, and Type-II had a 4-μm-wide coil on a 300×300-μm2 washer. Both the magnetometers exhibited rather low white noise level around 25fT/Hz1/2 (@77K, 1kHz). Peak-to-peak modulation voltage around 16–20mV was obtained for both the magnetometers. When the external magnetic field increased, the modulation curve was abruptly distorted. Modulation corresponding to 51 flux quanta appeared in the V–Φ curve of a Type-I magnetometer. On the other hand, modulation up to 121 flux quanta could be seen for a Type-II magnetometer. It was likely that the critical current of the superconducting loop consisting of a pickup and an input coil restricted the number of the observed flux quanta. It seems that the wider coil in the Type-II allowed a larger superconducting current in the loop. We succeeded in improving dynamic range of the V–Φ characteristics.