Epitaxial thin-film YBa2Cu3O7 flux transformers with multiturn input c
oils have been constructed on 1 cm 2MgO substrates using PrBa2Cu3O7 as
an insulator. By coupling these to high-temperature superconducting q
uantum interference devices (SQUIDs) using a flip-chip technology, sev
eral low-noise magnetometers and a gradiometer have been constructed.
The yield of fully working flux transformers on 1 cm 2 substrates exce
eds 80%, and field sensitivities at 77 K of (520 +/- 30)fT/square-root
Hz at 1 Hz and (165 +/- 8)fT/square-root Hz above 10 Hz have been ach
ieved. No evidence for excess low-frequency noise above that of the un
coupled SQUID has been found in the flip-chip magnetometers.