By scanning with a $30$-$\mathrm{keV}$ focused $\mathrm{He}$ ion beam ($\mathrm{He}$-FIB) across ${\mathrm{Y}\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ (YBCO) thin-film microbridges, we create Josephson barriers with critical current density $j_c$ adjustable by irradiation dose $D$. The dependence $j_c(D)$ yields an exponential decay. At $4.2\mathrm{K}$, a transition from flux-flow to Josephson behavior occurs when $j_c$ decreases below approximately $2\mathrm{MA}/\mathrm{c}{\mathrm{m}}^2$. The Josephson junctions exhibit current-voltage characteristics (IVCs) that are well described by the resistively and capacitively shunted junction model, without excess current for characteristic voltages $V_c\lesssim 1\mathrm{mV}$. Devices on $\mathrm{Mg}\mathrm{O}$ and LSAT substrates show nonhysteretic IVCs, while devices on ${\mathrm{Sr}\mathrm{Ti}\mathrm{O}}_3$ show a small hysteresis. For all junctions, an approximate scaling $V_c\propto j_c^{1/2}$ is found. $\mathrm{He}$-FIB irradiation with a high dose produces barriers with $j_c=0$ and high resistances of $10\mathrm{k}\mathrm{\Omega }$ to $1\mathrm{G}\mathrm{\Omega }$. This provides the possibility to write highly resistive walls or areas into YBCO using a He-FIB. Transmission electron microscopy reveals an amorphous phase within the walls, whereas for lower doses the YBCO stays crystalline. We have also “drawn” superconducting quantum-interference devices (SQUIDs) by using a $\mathrm{He}$-FIB for the definition of the SQUID hole and the junctions. The SQUIDs show high performance, with flux noise $<500\mathrm{n}{\mathrm{\Phi }}_0/\mathrm{H}{\mathrm{z}}^{1/2}$ in the thermal white-noise limit for a device with $19\mathrm{pH}$ inductance.

• Received 25 January 2019

DOI:https://doi.org/10.1103/PhysRevApplied.11.044082