High-Tc Josephson Junctions Fabricated Using a Focused Ion Beam Technique

The narrow-focused Ga-ion beam (FIB) technique has the two functions of etching and deposition. Using each of the functions (etching or deposition) of FIB independently, we have fabricated high-T c Josephson junctions with structures of two types both on MgO and SrTiO3 substrates. We studied the current-voltage characteristics of these junctions and the interfaces of these junctions were observed by cross-sectional transmission electron microscopy. Both FIB junctions have been confirmed to be grain boundary junctions. The formation of the grain boundary in these junctions strongly depends on the crystal structures of NdBaCuO (perovskite-like), MgO (face centered cubic), SrTiO3 (perovskite-like) and tungstein (body centered cubic) deposited by a focused ion beam chemical vapor deposition, and the degree of the lattice mismatch between them.