A 60-GHz NbN single-flux quantum counter circuit

A Josephson binary counter using single-flux quanta transitions of DC SQUIDs (superconducting quantum interference devices) has been fabricated using an eight-level NbN-based process. High-speed binary division has been demonstrated at 4.2 K, with single-cell counting observed at 60 GHz using the Josephson voltage-to-frequency relationship. Count rate was primarily limited by conservative process and design rules. The counter was designed for operation at 4.2 K. At 8-10 K, the beta /sub L/ of the SQUIDs would not allow operation, though the junction characteristics were good.<
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