Properties of AuIn₂ Resistors for Josephson Integrated Circuits

The influences of film thickness and composition on the resistivity and microstructure of AuIn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> 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 AuIn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> 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 AuIn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> 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 AuIn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> 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-cm 2 and r = 0.74, p = 1, ρl = 0.8 × 10 −11 Ω-cm 2 . The available evidence is interpreted as favoring grain boundary scattering as the dominant scattering mechanism.