Enhanced voltage swing of rapid-single-flux-quantum distributed output amplifier equipped with double-stack superconducting quantum interference devices

抄録

We report the enhanced voltage swing of a rapid-single-flux-quantum (RSFQ) distributed amplifier by replacing a single superconducting quantum interference device (SQUID) with a double-stack-SQUID (DSS). A DSS is composed of two stacked 2-junction SQUIDs sharing one sensing inductor. Thanks to its stack structure, a DSS is expected to generate twofold output voltage. We have designed a 12-stage RSFQ distributed amplifier equipped with DSSs. The maximum output voltage swing reached 10.2 mV in simulation. Test chips were fabricated using a 25-µA/µm² Nb integration process. In measurements, a test chip was cooled in a liquid helium bath. The experimental output voltage swing was up to 8.34 mV.