Transport Properties of NbN Thin Films Patterned With a Focused Helium Ion Beam

Niobium nitride (NbN) is an important material for superconducting electronics because of its relatively high transition temperature in comparison to other conventional superconductors. Recent advances in the use of gas field focused ion beams for material modification motivate directly written NbN electronics. In this work, we study the electrical transport properties of ultra-thin film NbN microbridges irradiated with a focused helium ion beam. Twenty 4-
$\mu$
m wide strips were structured into an NbN thin film and irradiated with a helium ion microscope with ion fluences ranging from
$1 \times 10^{18}$
He
$^+/$
cm
$^{2}$
to
$3 \times 10^{18}$
He
$^+/$
cm
$^{2}$
. We report the temperature and magnetic field dependence of the transport properties. At a higher dose of
$1 \times 10^{20}$
He
$^+$
, the irradiation reduces the critical temperature of a narrow region resulting in a planar superconductor-reduced
$T_{c}$
superconductor-superconductor (SS'S) Josephson junctions. This establishes that NbN can be modified in this manner for nanoelectronics, opening up possibilities for superconducting logic circuits and other higher-speed and high-temperature applications.