PROXIMITY EFFECTS IN SUPERCONDUCTING WIRE BONDING

To investigate the superconducting characteristics of a superconducting wire bonding connection, a series of Nb electrodes consisting of an Au pad formed on a Si chip are made, and the pads are connected in series with a superconducting wire (Pb76In20Au4). The I-V characteristics of the superconducting connection reflect the typical characteristics of an S-N-S sandwich structure, with normal resistance on the order of mu Omega when a critical current(I-C) level is exceeded. The dependence of I-C on the thickness of Au is an exponential decrement, and I-C is over a hundred mA when Au thickness is between 20 nm and 230 nm. Auger analysis is applied to obtain the depth profile of the bonded part, revealing mutual Au and In atomic diffusion at the interface between the Au intermediate layer and the PbInAu wire.