Low-T_c SQUIDs with a built-in heater module to remove flux trapping

We have fabricated low-T_c SQUIDs (superconducting quantum interference devices) that have a built-in heater module next to the Josephson junctions to remove trapped flux by using only a low heating power. To suppress the generation of magnetic fields, the heater module comprises a double-layer consisting of a heater, which is a narrow Nb film, and an Al electrode. The module can be fabricated together with the SQUID without complicating the process. The Nb heater is transformed to normal metal with sufficient resistance when a current above the critical current flows through it. We demonstrated that the heater module could reliably remove trapped flux with 24 mW without increasing any noise of the SQUID or causing re-trapping.