Planar-type MgB2 SQUIDs utilizing a multilayer process

We report planar-type MgB2 DC SQUIDs fabricated using a multilayer process. The SQUIDs employed sandwich-type MgB2/MgO/MgB2 Josephson junctions and a MgB2 wiring layer. The SQUIDs showed large voltage modulation above 500 mu V at 15K and operated in a broad temperature range from 15 to 37K with a transfer function as high as 2.3 mV/Phi(0). The minimum SQUID noise was measured at 26K in a cryocooler, yielding a white noise around 10 mu Phi(0)/Hz(1/2) and 1/f corner frequency near 10 Hz. The result demonstrates great promise of MgB2 SQUIDs for practical applications. (C) 2013 AIP Publishing LLC.