Fabrication of high quality Nb/AlOx-Al/NbJosephson junctions. III. Annealing stability ofAlOx tunneling barriers

For pt.II see ibid., vol.2, p.84 (1992). Changes in current-voltage characteristics of Nb/AlO_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 _x barrier junctions, compared to that of AlO_x barrier junctions, was measured, and it was concluded that the decrease at initial annealing is due to changes in the AlO_x barrier itself