Fabrication issues in optimizing YBa2Cu0O( 7-x) flux transformers for low l/f noise.

摘要

We describe an improved interconnect technology for the fabrication of multiturn flux transformers from YBa(sub 2)Cu(sub 3)O(sub 7-x)-SrTiO(sub 3)-YBa(sub 2)Cu(sub 3)O(sub 7-x) multilayers. The essential improvements are reductions in the thicknesses of the trilayer films, typically to 100 nm 250 nm and 250 mn respectively, and in the deposition rate, to 0.07 nm/laser pulse. This process yields crossovers in which the critical current density in the upper YBa(sub 2)Cu(sub 3)O(sub 7-x) film at 77K is (2-3) (times) 10(sup 6) A cm(sup (minus)2). In situ trilayers exhibited 1/f flux noise levels at lHz below the measurement sensitivity of 15(mu)(Phi)(sub 0) Hz(sup (minus)1/2), where (Phi)(sub 0) is the flux quantum. However, the flux noise of trilayers in which each layer had been patterned was significantly higher. The best flip-chip magnetometer had a white noise of 40 fT Hz(sup (minus)1/2) increasing to 340 fT Hz(sup (minus)1/2) at lHz; the corresponding flux noise levels were 9 (mu)(Phi)(sub 0) Hz(sup (minus)l/2) and 75 (mu)(Phi)(sub 0) Hz(sup (minus)l/2), respectively.