Microwave characterization of superconducting coplanar resonators made out of granular aluminium

TL;DR

This study investigates microwave resonators made from granular aluminium films, analyzing their properties and potential applications in superconducting devices, with a focus on kinetic inductance, quality factors, and two-level systems.

Contribution

It provides a detailed microwave characterization of granular aluminium resonators, linking their properties to oxygen content and resistivity, and discusses their relevance for superconducting device design.

Findings

Kinetic inductance varies with temperature and oxygen content.

Presence of two-level systems affects quality factors at low temperatures.

Characterization methods aid in designing MKIDs and superinductors.

Abstract

We have designed, fabricated and characterized microwave resonators made out of thin films of granular aluminium (grAl) with different oxygen content. We extract the contribution of the large kinetic-inductance of this disordered superconductor from the frequency shift of the resonators as a function of temperature, and discuss the correlation with the resistivity of the films. At low temperatures, measurements of the internal quality factor as a function of microwave power indicate the presence of two-level systems, which are inherent to the growth process of the granular aluminium. The characterization methods presented here may be useful for the design of MKIDs, high-impedance resonators and superinductors.