HIGH-T-C JOSEPHSON-JUNCTIONS FABRICATED USING A FOCUSED ION-BEAM TECHNIQUE

The narrow-focused Ga-ion beam (FIB) technique has the two functions o f etching and deposition. Using each of the functions (etching or depo sition) of FIB independently, we have fabricated high-T-c Josephson ju nctions with structures of two types both on MgO and SrTiO3 substrates . We studied the current-voltage characteristics of these junctions an d the interfaces of these junctions were observed by cross-sectional t ransmission electron microscopy. Both FIB junctions have been confirme d to be grain boundary junctions. The formation of the gain boundary i n these junctions strongly depends on the crystal structures of NdBaCu O (perovskite-like), MgO (face centered cubic); SrTiO3 (perovskite-lik e) and tungstein (body centered cubic) deposited by a focused ion beam chemical vapor deposition, and the degree of the lattice mismatch bet ween them.