YBCO Bicrystal Junctions on Sapphire: d-Wave Impact and Possible Applications

The current transport and Josephson effect have been investigated in YBCO junctions, fabricated on the sapphire bicrystal substrates. The YBCO film with thickness t150 nm was deposited by dc sputtering on the epitaxial CeO₂buffer layer made by rf magnetron sputtering. The junctions were characterized at dc and at mm waves. 5 m wide junctions have moderately high normal state resistance R_N= 5÷30 with critical currents I_c=50÷200 A which give I_cR_Nproduct of order of 0.5÷2 mV. The tolerance of characteristic interface resistance (R_NS) was around 30% for the junctions on a chip. Experimental data, discussed in terms of d-wave symmetry, demonstrate possibility of design of small scale integrated Josephson microwave circuits.