Multistep atomic layer deposition process for ultrathin superconducting NbN films with high critical current density on amorphous substrate

Abstract

This study presents a multistep process of plasma-enhanced atomic layer deposition of ultrathin superconductive films of niobium nitride from metal organic precursor tris(diethylamido)(tert-butylimido)niobium(V). While using NH3/Ar and H2/Ar gas mixtures as reactants, a comprehensive analysis was performed pertaining to the influence of operating parameters, such as the duration of plasma exposure to the H2/Ar reactant, gas-flow ratio, plasma exposure duration and power of inductively coupled plasma source for the NH3/Ar reactant, on the obtained films’ parameters, such as resistivity, superconducting transition temperature and critical current density. Amorphous silicon oxide was used as the substrate. It was shown by experiments, that films’ resistivity affects the value of critical current density. As a result, the all-time record resistivity of 147 µΩ·cm was achieved for films with a thickness of 8 nm. When cooling in the Gifford McMahon closed-cycle cryostat, the values of superconducting transition temperature and critical current density were equal to 12.3 К and 9 МА/cm2 at a liquid helium temperature, respectively.