False-coloured high-angle annular dark field STEM image centred on the AlO x tunnel barrier of a typical JJ fabricated at KIT, with average thickness d 2 nm as indicated by the white arrow. Individual columns of atoms of the Al grain in the top electrode are visible due to zone axis alignment, which is not the case for the bottom Al electrode (additional STEM images with thickness variations and structural defects such as grain boundaries are shown in Supplementary Fig. 27 ).
