High kinetic inductance NbTiN films for quantum limited travelling wave parametric amplifiers

TL;DR

This paper reports the development of high kinetic inductance NbTiN films optimized via sputtering for use in quantum-limited travelling wave parametric amplifiers, demonstrating promising amplification performance.

Contribution

It introduces an optimized sputtering process for NbTiN films with high kinetic inductance suitable for KI-TWPAs, advancing fabrication techniques for quantum amplifiers.

Findings

Achieved NbTiN film with 8.5 pH/sq kinetic inductance.

Optimized sputtering parameters for precise film control.

Prototype devices show promising amplification performance.

Abstract

A wide-bandwidth and low-noise amplification chain in the microwave regime is crucial for the efficient read-out of quantum systems based on superconducting detectors, such as Microwave Kinetic Inductance Detectors (MKIDs), Transition Edge Sensors (TESs), Magnetic Microcalorimeters (MMCs), and RF cavities, as well as qubits. Kinetic Inductance Travelling Wave Parametric Amplifiers (KI-TWPAs) operated in a three-wave mixing fashion have demonstrated exceptional dynamic range and low-noise performance, approaching the quantum limit. These amplifiers can be fabricated using a single layer of a high kinetic inductance film as weakly dispersive artificial transmission lines, with the ability to control the phase-matched bandwidth through dispersion engineering. In this study, we present the optimisation of the rf sputter-deposition process of NbTiN films using a Nb80%T20 target, with the goal of achieving precise control over film characteristics, resulting in high kinetic inductance while maintaining a high transition temperature. The parameter landscape related to the different sputtering conditions, such as pressure, power, and nitrogen flow, has been explored and the film thickness has been used as a fine-tuning parameter to adjust the properties of the final NbTiN films used for the fabrication of KI-TWPAs. As a final result, we have obtained a NbTiN film with a kinetic inductance of 8.5 pH/sq which we have exploited to fabricate KI-TWPA prototype devices, showing promising amplification performance.