Performance of Bi-Sr-Ca-Cu-O thick film rf SQUIDs at liquid nitrogen temperatures

Abstract
Periodic oscillations in the V‐Φ characteristics have been observed up to 97 K in radio frequency SQUIDs fabricated from screen printed Bi‐Sr‐Ca‐Cu‐O thick films. The SQUID has been operated successfully in the flux‐locked‐loop mode at 77 K. Stability of the SQUID output and its noise performance have been found to improve considerably when the SQUID is operated in the flux‐locked‐loop mode as compared to that in the open‐loop mode. The spectral noise density, in the white noise region, is 5×10−4 Φ0/√Hz at 77 K for the flux‐locked‐loop mode.