Microstructure of Josephson junctions in relation to their properties

Abstract

The microstructure of various types of Josephson junctions is investigated with cross-sectional (CS) high-resolution electron microscopy (HREM). Special specimen preparation techniques, to facilitate the CS investigation, are discussed in the first part. Examples are shown of specially produced arrays of junctions and of the focused ion beam thinning technique allowing us to investigate specific measured junctions. Ramp-type junctions with (PrBCGaO) barrier layers are discussed in more detail in the second part. The microstructure of PrBCGaO (0.1 < x < 1.0) thin films, barrier layers and bulk material is studied by HREM. Thin barrier layers with contain a Ga-rich intergrowth, never observed before in YBCO-type structures. Ga-rich inclusions in single thin films exhibit a similar structure. In addition, diffusion of Ga in the ion-etched substrate surface region was observed. The observed segregation of Ga from the PrBCGaO barrier layer explains the observed junction properties.

Low- or high-angle Ar ion-beam etching to create ramp-type Josephson junctions

“…The interfaces E1/B and B/E2, as well as the quality of all layers, were investigated using HREM. More structural and crystallographic details are reported in [12,13]. No amorphous layer is present at the interface between E and B layers and no secondary phases are detected.…”

Ga segregation in DyBa2Cu3O7−δ/PrBa2Cu3−xGaxO7−δ/DyBa2Cu3O7−δ ramp-type Josephson junctions

“…Hence, the structure, interfaces, and microstructural defects of these ramp-type JJs were studied by HREM and ED. 9,10 In this letter we concentrate on the particularities in the PrBCGaO barrier layer. The junction, discussed here have a ramp angle of 20°-28°and a barrier layer thickness of 10-30 nm.…”