A single-chip SQUID magnetometer

A superconducting quantum interference device (SQUID) magnetometer in which all components are integrated on a single chip is discussed. The chip includes a feedback circuit, a pickup coil, and a SQUID sensor. The feedback circuit consists of a superconducting storage loop and a WRITE gate. The chip, fabricated with Nb/AlO/sub x//Nb Josephson junctions, Mo resistors and SiO/sub 2/ insulation. The sensitivity is 7*10/sup -5/ Phi /sub 0// square root Hz for the flux in the SQUID sensor and 4.5*10/sup -9/ T/m square root Hz for the magnetic field gradient at the pickup coil. This sensitivity is limited by environmental noise and can be increased with shielding. The device is useful for the construction of a magnetometer array for biomagnetic image sensing.<>