Vibrational modes as the origin of dielectric loss at 0.27$\unicode{x2013}$100 THz in a-SiC:H

TL;DR

This study investigates the origin of dielectric loss in hydrogenated amorphous SiC films across a broad THz spectrum, revealing vibrational modes above 10 THz as the primary loss mechanism.

Contribution

It provides the first comprehensive measurement of dielectric loss in a-SiC:H from 0.27 to 100 THz and links loss to vibrational modes above 10 THz.

Findings

Loss dominated by vibrational modes above 10 THz.

Good agreement with Maxwell-Helmholtz-Drude dispersion model.

Loss increases with frequency in the THz range.

Abstract

Low-loss deposited dielectrics are beneficial for the advancement of superconducting integrated circuits for astronomy. In the microwave band ($\mathrm{\sim}$1$\unicode{x2013}$10 GHz) the cryogenic and low-power dielectric loss is dominated by two-level systems. However, the origin of the loss in the millimeter-submillimeter band ($\mathrm{\sim}$0.1$\unicode{x2013}$1 THz) is not understood. We measured the loss of hydrogenated amorphous SiC (a-SiC:H) films in the 0.27$\unicode{x2013}$100 THz range using superconducting microstrip resonators and Fourier-transform spectroscopy. The agreement between the loss data and a Maxwell-Helmholtz-Drude dispersion model suggests that vibrational modes above 10 THz dominate the loss in the a-SiC:H above 200 GHz.