INTEGRATED HIGH T-C SUPERCONDUCTING MAGNETOMETER WITH MULTITURN INPUTCOIL AND GRAIN-BOUNDARY JUNCTIONS

We have fabricated and tested integrated magnetometers based on the su perconducting quantum interference device (SQUID). The magnetometer co nsists of two patterned films of YBa2Cu3O7, separated by an insulating layer of SrTiO3. A multiturn input coil was integrated on top of the SQUID, where the misorientation angle in a SrTiO3 bicrystal substrate was used to form the grain boundary junctions. The noise spectrum was characterized at 77 K and showed that above 10 Hz the magnetometer sen sitivity is limited by a white noise level of around 4 x 10(-5) Phi(0) /Hz(1/2). In the 4 mm x 4 mm detection area of the input coil, this tr anslates into a magnetic field sensitivity of 320 fT/Hz(1/2) at 100 Hz . Compared to the theoretical value of an optimized SQUID the white no ise level of the magnetometer is two times higher. Below 10 Hz the noi se is dominated by 1/f noise mainly due to the critical current fluctu ations. (C) 1995 American Institute of Physics.