Characteristics of vertically-stacked planar tunnel junction structures

Whole-wafer multilayer tunnel structures consisting of vertically stacked Al/sub 2/O/sub 3/ tunnel barriers separated by thin Nb layers have been deposited under UHV (ultrahigh vacuum) conditions, with repeat distances ranging from 10-50 nm. Using a modification of the conventional SNEP process, these structures have been fabricated into vertical series arrays. Using this technique it is possible to select different numbers of junctions on the same substrate and so determine the properties of each barrier. Information gained from such structures provides a considerable insight into the factors determining junction characteristics such as critical current density and quality as well as serving as the basis for the study of novel types of structures and devices.>