INTERFACIAL STUDY OF NB JOSEPHSON-JUNCTIONS WITH OVERLAYER STRUCTURE

We compare interfaces of Nb/AlO(x)-Al/Nb and Nb/ZrO(x)-Zr/Nb junctions using secondary ion mass spectroscopy and cross-sectional transmissio n electron microscopy. We have clarified that an interface of the Nb/A lO(x)-Al/Nb junction is drastically different from that of the Nb/ZrO( x)-Zr/Nb junction. An adsorbed water vapor layer plays an important ro le in suppressing grain boundary diffusion between Nb and Al at the in terface of the Nb/AlO(x)-Al/Nb junction. In depositing Nb and Al at lo w power and cooling the substrate, it is important to control the form ation of the adsorbed water vapor layer for fabricating Nb/AlO(x)-Al/N b junctions exhibiting excellent current-voltage characteristics.