Superconducting boron doped nanocrystalline diamond microwave coplanar resonator

TL;DR

This paper introduces a superconducting boron doped nanocrystalline diamond coplanar waveguide resonator for microwave measurements, revealing high kinetic inductance and low surface resistance at cryogenic temperatures, suitable for sensitive detectors.

Contribution

It demonstrates the use of a simplified effective medium approach to characterize B-NCD films and their potential for high-Q superconducting microwave resonators.

Findings

Large penetration depth (~4.3-4.4 μm) in B-NCD films.

High kinetic inductance (~670-690 pH/□) due to granularity.

Low surface resistance (~2-4 μΩ) at temperatures below 2 K.

Abstract

A superconducting boron doped nanocrystalline diamond (B-NCD) coplanar waveguide resonator (CPR) is presented for kinetic inductance ($L_k$) and penetration depth ($\lambda_{\rm{L}}$) measurements at microwave frequencies of 0.4 to 1.2 GHz and at temperatures below 3 K. Using a simplified effective medium CPR approach, this work demonstrates that thin granular B-NCD films ($t\approx $ 500 nm) on Si have a large penetration depth ($\lambda_{\rm{L}}\approx 4.3$ to 4.4 $\mu$m), and therefore an associated high kinetic inductance ($L_{k,\square} \approx $ 670 to 690 pH/$\square$). These values are much larger than those typically obtained for films on single crystal diamond which is likely due to the significant granularity of the nanocrystalline films. Based on the measured Q factors of the structure, the calculated surface resistance in this frequency range is found to be as low as $\approx$ 2 to 4 $\mu\Omega$ at $T<2$ K, demonstrating the potential for granular B-NCD for high quality factor superconducting microwave resonators and highly sensitive kinetic inductance detectors.