Superconducting quantum interference devices made with normal metal and insulator barrier Josephson junctions in Y-Ba-Cu-O directly written with a focused helium beam

We will present electrical transport data for Y-Ba-Cu-O superconducting quantum interference devices (SQUIDs) with focused helium ion damage Josephson junctions. The junctions were directly written with a 30~keV focused helium ion beam, which locally creates disorder in Y-Ba-Cu-O that induces a superconducting-insulator transition. SQUIDs with Josephson junctions written with a dose of 4$\times10^{16}$~He$^+$/cm$^2$ have metallic barriers and show a current-voltage characteristic (I-V) well-described by the resistively shunted junction model. The spectral density of the flux noise is 10~$\mu\Phi_0/\surd$Hz at 10~Hz and the white noise at higher frequencies is 2~$\mu\Phi_0/\surd$Hz. SQUIDs with junctions written with higher ion doses ($\sim9\times10^{16}$~He$^+$/cm$^2$) have insulating Josephson barriers with a critical current of 22~$\mu$A and a resistance of 12~$\Omega$ at 4~K. The I-V for all of these devices is not hysteretic due to the small capacitance and the resistance. At higher voltage the junction I-V curve shows tunnel-junction behavior and a superconducting energy gap edge at 20~mV. We will discuss how these results are a promising step forward for sensitive magnetic sensors made from high temperature superconductors at various temperatures.