# 18th International Workshop on Low Temperature Detectors (LTD-18)

22-26 July 2019
Milano
Europe/Rome timezone

## Measuring Transmission Line Losses at sub-mm wavelengths with an on-chip Fabry-Perot resonator

23 Jul 2019, 17:45
1h 15m
Piazza Città di Lombardia (Milano)

### Piazza Città di Lombardia

#### Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
Poster Low Temperature Detector fabrication techniques and materials

### Speaker

Sebastian Hähnle (SRON, Netherlands Institute for Space Research)

### Description

Transmission line losses at sub-mm wavelengths present a significant challenge for highly integrated superconducting circuits, such as on-chip spectrometers, multi-color/dual polarization detectors for measurements of the CMB or phased array antennas. In the case of on-chip spectrometers like DESHIMA or SuperSpec, an internal loss better than $\tan^{-1}\delta = Qi \sim 10^4$ is required to eliminate power loss at both the individual filters and on the path between the antenna feed and the filterbank. While ohmic losses are negligible at frequencies significantly below the gap frequency of the superconductor ($2\Delta \approx1.1\$THz for NbTiN), other loss mechanisms become significant, such as radiation loss in the case of co-planar waveguides (CPW) and dielectric loss in microstrips (MS). At very high frequencies, above $500\$GHz for NbTiN, also the superconducting losses can increase.

We present the design and measurement results for a novel lab on-chip experiment capable of characterizing the internal losses of arbitrary transmission line geometries at frequencies up to 1 THz allowing accurate loss tangent estimates down to $\tan\delta =10^{-4}$. We use a Fabry-Perot resonator operated at mode numbers $n > 50$ that is coupled to a frequency-tunable THz source via a lens-antenna. The power transmitted through the Fabry-Perot is read out using an Al-NbTiN hybrid CPW microwave kinetic inductance detector(mKID). Multiple chips with both CPW and MS transmission lines have been designed, fabricated and measured using NbTiN as a lossless superconductor and a-Si as dielectric in case of the microstrips. Measurements were carried out in a $^3$He/$^4$He sorption cooler at $250\$mK at frequencies from 320 to 370 GHz.
We find $Q_i> 1.5\times10^4$ for CPW resonators and $Q_i = 1\times10^4$ for PECVD deposited a-SI, reaching the performance required for the implementation of microstrip filters in on-chip spectrometers.

Student (Ph.D., M.Sc. or B.Sc.) Y N

### Primary authors

Sebastian Hähnle (SRON, Netherlands Institute for Space Research) Kevin Kouwenhoven (Delft University of Technology) Nuri van Marrewijk (Delft University of Technology) Akira Endo (Delft University of Technology) David Thoen (Delft University of Technology) Mr Vignesh Murugesan (SRON, Netherlands Institute for Space Research) Prof. Jochem Baselmans (SRON)