Interfacial Study of Nb Josephson Junctions with Overlayer Structure

Shin'ichi MOROHASHI  

IEICE TRANSACTIONS on Electronics   Vol.E77-C   No.8   pp.1150-1156
Publication Date: 1994/08/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: INVITED PAPER (Special Section on Superconducting Devices)
Category: LTS
Josephson junctions,  tunneling barrier,  secondary ion mass spectroscopy,  cross-sectional transmission electron microscopy,  interface,  adsorbed water vapor layer,  

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We compare interfaces of Nb/AlOx-Al/Nb and Nb/ZrOx-Zr/Nb junctions using secondary ion mass spectroscopy and cross-sectional transmission electron microscopy. We have clarified that an interface of the Nb/AlOx-Al/Nb junction is drastically different from that of the Nb/ZrOxZr/Nb junction. An adsorbed water vapor layer plays an important role in suppressing grain boundary diffusion between Nb and Al at the interface of the Nb/AlOxAl/Nb junction. In depositing Nb and Al at low power and cooling the substrate, it is important to control the formation of the adsorbed water vapor layer for fabricating Nb/AlOx-Al/Nb junctions exhibiting excellent current-voltage characteristics.