YBa2Cu3O7−x based monolithic integrated dc SQUID magnetometers, consisting of a dc SQUID integrated with a flux transformer on a single bicrystalline substrate, have been fabricated and characterized. The devices consist of four layers, including two superconducting layers, and first realizations operate up to 73 K. A maximum voltage modulation of 32 μV is observed at 40 K. A field sensitivity of 0.17 pT/√Hz is obtained above 200 Hz at 45 K and 0.49 pT/√Hz at 1 Hz and 65 K.
Hilgenkamp, J. W. M., Brons, G. C. S., Soldevilla, J. G., IJsselsteijn, R. P. J., Flokstra, J., & Rogalla, H. (1994). Four layer monolithic integrated high Tc dc SQUID magnetometer. Applied physics letters, 64(25), 3497-3499. https://doi.org/10.1063/1.111252