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arXiv:1009.2657

YBa2Cu3O7 grain boundary junctions and low-noise superconducting quantum interference devices patterned by a focused ion beam down to 80 nm linewidth

Joachim Nagel, K. B. Konovalenko, M. Kemmler, M. Turad, R. Werner, E. Kleisz, S. Menzel, R. Klingeler, Bernd Büchner, R. Kleiner, D. Koelle

Published Sep 14, 2010• 1 citation
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Abstract

YBa$_2$Cu$_3$O$_7$ 24$^\circ$ (30$^\circ$) bicrystal grain boundary junctions (GBJs), shunted with 60\,nm (20\,nm) thick Au, were fabricated by focused ion beam milling with widths $80\,{\rm nm} \le w \le 7.8\,μ$m. At 4.2\,K we find critical current densities $j_c$ in the $10^5\,{\rm A/cm^2}$ range %\dkc{\#1} (without a clear dependence on $w$) and an increase in resistance times junction area $ρ$ with an approximate scaling $ρ\propto w^{1/2}$. For the narrowest GBJs $j_cρ\approx 100\,μ$V, which is promising for the realization of sensitive nanoSQUIDs for the detection of small spin systems. We demonstrate that our fabrication process allows the realization of sensitive nanoscale dc SQUIDs; for a SQUID with $w\approx 100$\,nm wide GBJs we find an rms magnetic flux noise spectral density of $S_Φ^{1/2}\approx 4\,μΦ_0/{\rm Hz}^{1/2}$ in the white noise limit. We also derive an expression for the spin sensitivity $S_μ^{1/2}$, which depends on $S_Φ^{1/2}$, on the location and orientation of the magnetic moment of a magnetic particle to be detected by the SQUID, and on the SQUID geometry. For the not optimized SQUIDs presented here, we estimate $S_μ^{1/2}=390\,μ_B/\sqrt{\rm{Hz}}$, which could be further improved by at least an order of magnitude.

DOI
10.48550/arxiv.1009.2657

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