High slew rate large bandwidth integrated dc SQUID magnetometer for NMR applications

We have developed an integrated dc SQUID magnetometer, with additional positive feedback (APF) unmodulated SQUID electronics system for low frequency true NMR applications. We constructed our SQUID circuit using an 11-layer Nb/Al/AlO/sub x//Nb process. Our design modifies previous APF approaches by incorporating selectable, high resolution on-chip feedback resistance. The on-chip resistance selection allows us to maximize the SQUID gain, dV/d/spl Phi/, at the operating point. With the use of APF we have achieved a slew rate greater than 10/sup 6/ /spl Phi//sub 0//s, and a bandwidth of approximately 300 kHz, which is suitable for sensitive NMR measurements.<>