Resistance stability of AuIn2 thin-film resistors for Pb-alloy Josephson integrated circuits

The influence of In diffusion on resistance stability of AuIn2 thin-film resistors was studied and the mechanism for resistance change was clarified. When resistors with In concentration below that of AuIn2 were in contact with Pb-In-Au alloy interconnection lines, In diffused from the Pb alloy into the resistors. This diffusion caused grain growth in the In-diffused zone, in addition to a phase change from an AuIn and AuIn2 mixture to AuIn2 single phase. The In-diffusion-induced grain growth decreased film resistivity because resistivity is mainly determined by grain-boundary scattering. When the resistor was preannealed before being connected to interconnection lines to saturate grain growth, excellent resistance stability was obtained even though In concentration shifted by ∼2 wt. % below AuIn2 stoichiometry.