Properties of AuIn2 Resistors for Josephson Integrated Circuits

摘要

The influences of film thickness and composition on the resistivity and microstructure of AuIn2 films, which are used as resistors in Josephson integrated circuits, have been investigated. The films were prepared by evaporating Au and In layers onto SiO-coated Si wafers held at 348 K. The resistivity at 4.2 K was found to be ≈5 µΩ-cm for 40-nm-thick films and to vary as ≈d−0.76 over the thickness range 30–250 nm. Corresponding sheet resistances ranged from 0.05 to 2 Ω/□. Resistivity changes were also observed as the composition was altered. A decrease of ≈10% in the In/Au thickness ratio from that of AuIn2 produced an increase of ≈50% in resistivity. A similar increase in In/Au ratio produced ≤10% decrease in resistivity. Electron microscopy analysis revealed that the grain size of AuIn2 films increases with film thickness, and is approximately two times smaller for the low In/Au ratio films than for those of nominal or larger In/Au ratios. The factors governing the resistivity of AuIn2 films were analyzed using the Fuchs surface scattering and Mayadas-Shatzkes (M-S) grain boundary scattering theories. It was found that the M-S theory can be used to explain the resistivity data for a range of choices of r and p, the grain-boundary-reflection and surface-reflection coefficients, respectively. Reasonable agreement was obtained for parameter values between r = 0.31, p = 0, ρl = 3 × 10−11 Ω-cm2 and r = 0.74, p = 1, ρl = 0.8 × 10−11 Ω-cm2. The available evidence is interpreted as favoring grain boundary scattering as the dominant scattering mechanism.