Ion Beam Nitridation of Al for Tunnel Barrier Applications

We have formed AlNx tunnel barriers in Nb Josephson junctions using a nitrogen ion beam operated at low energy (<150 eV). Independent control of ion energy and dose allowed for the exploration of a wide parameter space in which devices were fabricated with good quality and reproducibility with J_c < 10 kA/cm². The junctions were stable up to temperatures of at least 200degC, implying that the nitrogen atoms are strongly bound and do not desorb as gaseous molecular N₂. Large-area uniformity was also investigated where the spatial variation in ion current density was correlated with J_c. This technique could be applied to form other metal nitrides at room temperature for device applications where a high degree of control is desired.