Atomic Layer Deposition Niobium Nitride Films for High-Q Resonators

TL;DR

This paper introduces atomic layer deposition (ALD) for niobium nitride films, enabling precise control of film properties and high-quality microwave resonators for detector applications, improving uniformity and performance.

Contribution

It demonstrates ALD as a viable method for fabricating uniform, high-quality NbN films with tunable properties for high-Q resonators, advancing detector technology.

Findings

ALD NbN films achieve wafer-scale uniformity for 4-30 nm thickness.

Resonators exhibit high quality factors suitable for detector multiplexing.

Critical temperature and quality factor depend on ALD process parameters.

Abstract

Niobium nitride (NbN) is a useful material for fabricating detectors because of its high critical temperature and relatively high kinetic inductance. In particular, NbN can be used to fabricate nanowire detectors and mm-wave transmission lines. When deposited, NbN is usually sputtered, leaving room for concern about uniformity at small thicknesses. We present atomic layer deposition niobium nitride (ALD NbN) as an alternative technique that allows for precision control of deposition parameters such as film thickness, stage temperature, and nitrogen flow. Atomic-scale control over film thickness admits wafer-scale uniformity for films 4-30 nm thick; control over deposition temperature gives rise to growth rate changes, which can be used to optimize film thickness and critical temperature. In order to characterize ALD NbN in the radio-frequency regime, we construct single-layer microwave resonators and test their performance as a function of stage temperature and input power. ALD processes can admit high resonator quality factors, which in turn increase detector multiplexing capabilities. We present measurements of the critical temperature and internal quality factor of ALD NbN resonators under the variation of ALD parameters.