Low microwave loss in deposited Si and Ge thin-film dielectrics at single-photon power and low temperatures

TL;DR

This study demonstrates that thin-film Ge and Si dielectrics can achieve extremely low microwave losses at near single-photon powers and millikelvin temperatures, suitable for quantum and microwave devices.

Contribution

It provides detailed measurements of microwave loss tangents in deposited Ge and Si thin-films at cryogenic temperatures and low powers, highlighting their potential for quantum device applications.

Findings

Germanium films have a loss tangent of 1-2×10⁻⁶ at single-photon power.

Silicon films have a loss tangent of 0.6-2×10⁻⁵ at single-photon power.

Interface contamination affects the loss in these dielectric films.

Abstract

Our study shows that deposited Ge and Si dielectric thin-films can exhibit low microwave losses at near single-photon powers and sub-Kelvin temperatures ($\approx$40 mK). This low loss enables their use in a wide range of devices, including low-loss coplanar, microstrip, and stripline resonators, as well as layers for device isolation, inter-wiring dielectrics, and passivation in microwave and Josephson junction circuit fabrication. We use coplanar microwave resonator structures with narrow trace widths of 2-16 $\mu \textrm{m}$ to maximize the sensitivity of loss tangent measurements to the interface and properties of the deposited dielectrics, rather than to optimize the quality factor. In this configuration, thermally-evaporated $\approx 1 \mu \textrm{m}$ thick amorphous germanium (a-Ge) films deposited on Si (100) have a single photon loss tangent of $1-2\times10^{-6}$ and, $9 \mu \textrm{m}$-thick chemical vapor deposited (CVD) homoepitaxial Si has a single photon loss tangent of $0.6-2\times 10^{-5}$. Interface contamination limits the loss in these devices.