High-Tc superconducting detector for highly-sensitive microwave magnetometry

We have fabricated arrays of High-T${}_c$ Superconducting Quantum Interference Devices (SQUIDs) with randomly distributed loop sizes as sensitive antennas for Radio-Frequency (RF) waves. These sub-wavelength size devices known as Superconducting Quantum Interference Filters (SQIFs) detect the magnetic component of the electromagnetic field. We use a scalable ion irradiation technique to pattern the circuits and engineer the Josephson junctions needed to make SQUIDs. Here we report on a 300 SQUIDs series array with loops area ranging from $6$ to $60\mu m^2$, folded in a meander line covering a $3.5
mm\times 8\ mm$substratearea,madeoutofa$150$-nm-thick$$\mathrm{Y}\mathrm{B}\mathrm{a}$_2$\mathrm{C}\mathrm{u}$_3$\mathrm{O}$_7$film\mathrm{.}Operatingatatemperature$T=66\ K$ in a un-shielded magnetic environment, under low DC bias current ($I=60\mu A$) and DC magnetic field ($B=3\mu T$), this SQIF can detect a magnetic field of a few $pT$ at a frequency of $1.125GHz$, which corresponds to a sensitivity of a few hundreds of $fT\mathrm{/}\sqrt{Hz}$, and shows linear response over 7 decades in RF power. This work is a promising approach for the realization of low dissipative sub-wavelength GHz magnetometers.