Cross-sectional TEM observation of Nb/AlO/sub x/-Al/Nb junction structures

Abstract

A study of the microstructure of Nb/AlO/sub x/-Al/Nb Josephson junctions by cross-sectional transmission electron microscopy (TEM) yielded information regarded the junction barrier region. Both thick Nb and several-nanometer Al form polycrystalline films with columnar structures. Nb is oriented to the [110] plane, and Al to the [111] plane. The 200-nm lower Nb has a wavy surface with -5-nm smoothness, but its surface is planarized by several-nanometer Al deposited on it. Thus, AlO/sub x/ with a smoothness under 1 nm can be formed on Al. The upper Nb has a good crystalline structure, even just above the AlO/sub x/ barrier.