Title :
Study of the Surface Morphology of Nb Films and the Microstructure of Nb/AlOx-Al/Nb Trilayers
Author :
Du, Jia ; Charles, Andrew D M ; Petersson, Karl D.
Author_Institution :
CSIRO Ind. Phys., Lindfield
fDate :
6/1/2007 12:00:00 AM
Abstract :
To optimize the current-voltage characteristics of Nb/AlOx-Al/Nb Josephson tunnel junctions, a uniform and well defined insulating barrier (AlOx) is required so that no leakage current occurs between the upper and lower Nb electrodes. We investigated the dependence of the surface morphology of dc magnetron-sputtered Nb thin films on deposition parameters using atomic force microscopy (AFM), the cross-sectional microstructure of the Nb/AlOx-Al/Nb trilayers using transmission electron microscopy (TEM), and anodization profiling. The surface roughness of the base Nb layer was found to affect the AlOx-Al layer and thus the quality of Nb/AlOx-Al/Nb trilayer. Diffusion of Al at the Al/Nb interface increases with increasing roughness of the base Nb layer, which increases the minimum Al thickness required to cover base-Nb. The importance of sufficient sample-cooling during the trilayer deposition was also confirmed by the TEM study and anodization profiling.
Keywords :
Josephson effect; aluminium; aluminium compounds; anodisation; atomic force microscopy; crystal microstructure; electrodes; multilayers; niobium; sputter deposition; superconducting materials; surface diffusion; surface morphology; surface roughness; thin films; transmission electron microscopy; AFM; Josephson tunnel junctions; Nb; Nb surface; Nb-AlO-Al-Nb; Nb-AlOx-Al-Nb; TEM; anodization profiling; atomic force microscopy; cross-sectional microstructure; current-voltage characteristics; dc magnetron-sputtered thin films; deposition parameters; diffusion; electrodes; insulating barrier; surface morphology; surface roughness; transmission electron microscopy; trilayers; Atomic force microscopy; Current-voltage characteristics; Insulation; Magnetic force microscopy; Microstructure; Niobium; Rough surfaces; Surface morphology; Surface roughness; Transmission electron microscopy; Cross-sectional microstructure; Josephson junction; Nb/AlOx-Al/Nb trilayer; niobium (Nb) film; surface morphology;
Journal_Title :
Applied Superconductivity, IEEE Transactions on
DOI :
10.1109/TASC.2007.898838