Superconducting NbN Resonator Parametric Amplifiers for Millimetre Wavelengths

Area of Science:

• Materials Science
• Superconductivity
• Microwave Engineering

Background:

• High critical temperature (Tc) superconducting films are crucial for sensitive detectors and amplifiers.
• Niobium Nitride (NbN) is a promising material for superconducting devices due to its high Tc and critical magnetic field.
• Kinetic inductance parametric amplifiers require specific film properties, including high normal-state resistivity, for optimal performance.

Purpose of the Study:

• To develop a reactive sputtering process for fabricating high Tc NbN thin films with tailored high normal-state resistivity.
• To optimize the sputtering conditions for achieving full nitridation of the NbN target.
• To evaluate the performance of NbN films in resonator parametric amplifiers.

Main Methods:

• Reactive sputtering deposition with precise control over target nitridation.
• Characterization of NbN thin films, including critical temperature (Tc) and normal-state resistivity measurements.
• Fabrication and testing of coplanar waveguide resonator parametric amplifiers using the developed NbN films.

Main Results:

• Achieved NbN thin films with a critical temperature (Tc) of 10.5 K and resistivity of ~1000 μΩ cm.
• Demonstrated the potential for application across the millimetre-wave frequency range (24-300 GHz).
• Fabricated parametric amplifiers exhibiting high gain (>20 dB) at 25 GHz with reproducible amplification profiles.

Conclusions:

• The developed reactive sputtering process enables the fabrication of high-quality NbN films suitable for kinetic inductance parametric amplifiers.
• The high Tc and resistivity of the NbN films facilitate efficient operation of parametric amplifiers with reduced pump tone power.
• The fabricated devices show excellent performance, validating the potential of these NbN films for advanced microwave applications.