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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 Jc < 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 Jc. This technique could be applied to form other metal nitrides at room temperature for device applications where a high degree of control is desired.