Microstrip superconducting quantum interference device amplifiers with submicron Josephson junctions: enhanced gain at gigahertz frequencies

TL;DR

This paper reports on a superconducting quantum interference device (SQUID) amplifier with submicron Josephson junctions, achieving enhanced gain at gigahertz frequencies due to reduced self-capacitance and improved coupling design.

Contribution

The study introduces a SQUID amplifier with submicron junctions that improves gain and transfer function at microwave frequencies, utilizing a novel device layout for better signal coupling.

Findings

Gain of 32 dB at 1.55 GHz achieved

Enhanced transfer function compared to larger junction SQUIDs

Effective coupling with a microstrip coil at cryogenic temperatures

Abstract

We present measurements of an amplifier based on a dc superconducting quantum interference device (SQUID) with submicron Al-AlOx-Al Josephson junctions. The small junction size reduces their self-capacitance and allows for the use of relatively large resistive shunts while maintaining nonhysteretic operation. This leads to an enhancement of the SQUID transfer function compared to SQUIDs with micron-scale junctions. The device layout is modified from that of a conventional SQUID to allow for coupling signals into the amplifier with a substantial mutual inductance for a relatively short microstrip coil. Measurements at 310 mK exhibit gain of 32 dB at 1.55 GHz.