ELECTRON-BEAM DAMAGED HIGH-TEMPERATURE SUPERCONDUCTOR JOSEPHSON-JUNCTIONS

Results are presented on the fabrication and characterization of high critical temperature Josephson junctions in thin films of YBa2Cu3O7-de lta produced by the process of focused electron-beam irradiation using 350 keV electrons. The junctions so produced have uniform spatial cur rent densities, can be described in terms of the resistive shunted jun ction model, and their current densities can be tailored for a given o perating temperature. The physical properties of the damaged barrier c an be described as a superconducting material of either reduced or zer o critical temperature (T-c), which has a length of similar to 15 nm. The T-c reduction is caused primarily by oxygen Frenkel defects in the Cu-O planes. The large beam currents used in the fabrication of the j unctions mean that the extent of the barrier is limited by the inciden t electron-beam diameter, rather than by scattering within the film. T he properties of the barrier can be calculated using a superconductor/ normal/superconductor (SNS) junction model with no boundary resistanc e. From the SNS model, we can predict the scaling of the critical curr ent-resistance (IcRn) product and gain insight into the factors contro lling the junction properties, T-c, and reproducibility. From the meas ured IcRn scaling data, we can predict the IcRn product of a junction at a given operating temperature with a given current density. IcRn pr oducts of similar to 2 mV can be achieved at 4.2 K. The reproducibilit y of several junctions in a number of samples can be characterized by the ratio of the maximum-to-minimum critical currents on the same subs trate of less than 1.4. Stability over several months has been demonst rated at room and refrigerator temperatures (297 and 281 K) for juncti ons that have been initially over damaged and then annealed at tempera tures similar to 380 K. Junctions manufactured using conventional lith ography (0.5 mu m wide) and which are suitable for digital electronics (I-c = 500 mu A at 40 K) can achieve IcRn products of 650 mu V at 40 K. The production of 100 of these stabilized junctions could be accomp lished in similar to 4h of irradiation time. The IcRn scaling also ind icates that junctions suitable for high sensitivity superconducting qu antum interference devices (I-c similar to 100 mu A) can be made with IcRn products of similar to 120 mu V at 77 K. (C) 1997 American Instit ute of Physics.