Hybrid DC SQUIDs containing all refractory thin film Josephson junctions

During the past five years Sperry designed, fabricated, and tested DC SQUIDs and feedback transformer assemblies (FTA) for sensor applications. The SQUID design included a silicon chip with deposited, all refractory, thin-film Josephson junctions contained in a bulk niobium toroidal cavity housing. Features include (1) minimum SQUID loop inductance provided by a cone-shaped structure extending from the chip containing the two Josephson junctions to the toroidal cavity where the input coil and concentric modulation coil are housed, and (2) a removable cap that allows easy access to the chip for repair or replacement. This paper presents (1) the design details of the junction chip, niobium housing, and FTA and (2) the flux noise results in the 0.01 to 1,000 Hz frequency range.