Fabrication and properties of HTS diffusion type weak links

This paper reports on intentionally weakened links produced by diffusing Al or Cu into the grain boundaries of microbridges of high Tc superconductors. Thin and narrow (70--130 nm) strips of Al or Cu were deposited across previously patterned microbridges and diffused into them for a short time at 300--450 degrees C. Dc and rf Josephson properties were registered IcRn products of up to 3 mV were measured at 4.2 K for a laser ablated Bi--Pb--Ca--Sr--Cu--O film (Tc = 64 K) and 0.9 mV at 77 K for an Y--Ba--Cu--O film (Tc = 87 K). Problems with electron resist residues could be circumvented by depositing a thin layer of Ag on the high Tc superconductor before further processing