Fabrication and measurement of tall stacked arrays of SNS Josephson junctions

The authors have made tall, uniform stacked Josephson junction arrays by developing an etch process using an inductively coupled plasma etcher. This process produces vertical profiles in thin-film multilayers of alternating superconducting and normal metals. Such a vertical etch is necessary to obtain uniform properties in high-density arrays in order to achieve operating margins for voltage-standard applications. The authors use dry-etchable MoSi₂ for the normal metal barrier of our niobium Josephson junctions and obtain working series arrays with stacks up to 10 junctions tall. The authors present dc and microwave electrical characteristics of distributed and lumped arrays and discuss the technological improvements needed to fabricate lumped arrays for voltage-standard applications.