Quantensysteme

We present a detailed study of the microstructure of submicron Al/Al−O/Al Josephson junctions fabricated by the conventional shadow evaporation technique. The morphology of the dielectric Al−O layer, which plays the key role for junction transport properties, has been investigated by making use of high resolution electron microscopy. We demonstrate, that the flatness and thickness of the aluminum oxide layer strongly depends on its grain structure. The most pronounced thickness deviations are observed in the vicinity of so-called “triple points,” where the grain boundary crosses the interlayer, forming a two-grain contact. Additionally we show that even for the single-grain contact, the Al/Al−O interface is not atomically flat, which can cause additional flicker noise at subkelvin temperatures.