Comparative study of shunted bicrystal Josephson junctions

In order to optimize the series array performance of Y Ba₂Cu₃O_7−x (YBCO) grain boundary shunted junctions, a method to determine and control the junction resistance R_s and Au/YBCO contact resistivity ρ _c has been developed. 200 nm thick c-oriented YBCO films were grown by intermittent thermal coevaporation on bicrystal yttria-stabilized zirconia substrates. A gold contact overlayer of thickness d_n was deposited in situ. Normal junction resistances have been measured as a function of d_n and shunt width w. It was shown that, in accordance with theoretical estimates, the junction shunt resistance is essentially controlled by the c-axis Au/YBCO interface specific resistance and scales as . The product ρ _c ρ _n ≃ 3.10⁻¹⁴ Ω² cm ³ was estimated from the experimental data, leading to ρ _c ≈ 10⁻⁸ Ωcm ² for typical values of ρ _n for gold thin films.