Investigating Millimeter-Wave Thin-film Superconducting Resonators: A Study Using Tunnel Junction Detectors

TL;DR

This study measures the propagation loss and wave velocity of superconducting millimeter-wave resonators using tunnel junction detectors, revealing significant dielectric loss contributions at 4 K.

Contribution

It introduces a novel measurement setup employing tunnel junction detectors for precise characterization of superconducting millimeter-wave resonators.

Findings

Resonance frequencies closely match theoretical predictions

Measured losses exceed quasi-particle loss estimates

Dielectric loss in silicon dioxide is the dominant loss factor

Abstract

Investigations into the propagation characteristics, specifically loss and wave velocity, of superconducting coplanar waveguides and microstrip lines were conducted at a 2 mm wavelength. This was achieved through the measurement of on-chip half-wavelength resonators, employing superconductor-insulator-superconductor tunnel junctions as detectors. A continuous wave millimeter wave probe signal was introduced to the chip via a silicon membrane-based orthomode transducer. This setup not only facilitated the injection of the probe signal but also provided a reference path essential for differential measurements. The observed resonance frequencies aligned closely with theoretical predictions, exhibiting a discrepancy of only several percent. However, the measured losses significantly exceeded those anticipated from quasi-particle loss mechanisms, suggesting the presence of additional loss factors. Notably, the measurement results revealed that the tangential loss attributable to the dielectric layer, specifically silicon dioxide, was approximately $\rm{7\pm 2 \times 10^{-3}}$. This factor emerged as the dominant contributor to overall loss at temperatures around 4 K.