F. Ludwig et al., FABRICATION ISSUES IN OPTIMIZING YBA2CU3O7-X FLUX TRANSFORMERS FOR LOW 1 F NOISE/, Superconductor science and technology, 7(5), 1994, pp. 273-276
We describe an improved interconnect technology for the fabrication of
multiturn flux transformers from YBa2Cu3O7-x-SrTiO3-YBa2Cu3O7-x multi
layers. The essential improvements are reductions in the thicknesses o
f the trilayer films, typically to 100 nm, 250 nm and 250 nm respectiv
ely, and in the deposition rate, to 0.07 nm/laser pulse. This process
yields crossovers in which the critical current density in the upper Y
Ba2Cu3O7-x film at 77 K is (2-3) X 10(6) cm-2. In situ trilayers exhib
ited 1/f flux noise levels at 1 Hz below the measurement sensitivity o
f 15 muPHI0 Hz-1/2, where PHI0 is the flux quantum. However the flux n
oise of trilayers in which each layer had been patterned was significa
ntly higher. The best flip-chip magnetometer had a white noise of 40 f
T Hz-1/2, increasing to 340 fT Hz-1/2 at 1 Hz; the corresponding flux
noise levels were 9 muPHI0 Hz-1/2 and 75 muPHI0 Hz-1/2.