Microstructural study of ramp type multilayer Josephson junctions with different ramp slopes

Abstract

The microstructures of YBa 2Cu 3O 7− δ /PrBa 2Cu 3O 7− δ /YBa 2Cu 3O 7− δ ramp type Josephson junctions with different ramp slopes fabricated on (100) SrTiO 3 substrates were studied by means of transmission electron microscopy. The results show that for the ramp slope angles of 15°–40°, the epitaxy was still remained through all layers at the ramp region without the formation of big grain boundaries. No amorphous layers and secondary phases were observed at the barrier interfaces. For a gentle ramp junction, small misoriented grains appeared in some portions of the barrier. The substrate ramp formed during the ion etching process had little influence on the growth of the upper layers. For a steep ramp junction, a dimple was created in the substrate, which caused the bending in the film and the nucleation of misoriented grains, although the epitaxy of the barrier was of good quality. The results demonstrate that the slope angle of the junction ramp is an important factor that influences the performance of the Josephson junctions.