Fabrication of high quality Nb/AlO/sub /x-Al/Nb Josephson junctions. III. Annealing stability of AlO/sub /x tunneling barriers

For pt.II see ibid., vol.2, p.84 (1992). Changes in current-voltage characteristics of Nb/AlO/sub /x-Al/Nb Josephson junctions due to annealing are studied. The surface of the Nb counterelectrode was plasma-nitrided to clarify the effects of oxygen diffusing from it. From anodization profiles, it was confirmed that surface nitridation protects the tunneling barrier from oxygen diffusion. Surface nitridation improved the junction stability for long annealing. The decrease in critical current at initial annealing was found to be independent of nitridation. The annealing stability of AlN/sub /x barrier junctions, compared to that of AlO/sub /x barrier junctions, was measured, and it was concluded that the decrease at initial annealing is due to changes in the AlO/sub /x barrier itself.<
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