Superconducting Coplanar Waveguide Filters for Submillimeter Wave On-Chip Filterbank Spectrometers.

A Endo,J Bueno,A M Baryshev,P P Van Der Werf,V Murugesan,S J C Yates,D J Thoen,T M Klapwijk,J J A Baselmans

doi:10.1007/s10909-016-1579-8

Abstract

We show the first experimental results which prove that superconducting NbTiN coplanar–waveguide resonators can achieve a loaded Q factor in excess of 800 in the 350 GHz band. These resonators can be used as narrow band pass filters for on-chip filter bank spectrometers for astronomy. Moreover, the low-loss coplanar waveguide technology provides an interesting alternative to microstrip lines for constructing large scale submillimeter wave electronics in general.

Highlights

On-chip filterbank spectrometers that use superconducting resonators as narrow band pass filters are becoming more popular as the design for realizing nextgeneration low-resolution millimeter–submillimeter wave (100–1000 GHz) spectrometers for astronomy [1–3]
The concept relies on the availability of superconducting microresonators with sufficiently high Q factors to achieve the required frequency resolution, and a transmission line with low enough losses to carry the signal from the antenna to the far end of the filterbank
Where α is the attenuation constant and λ is the wavelength in the resonator. (Note that Eq 1 holds only if Qi is limited by the nominal transmission loss of the line, and not if losses at the ends of the resonator dominate.) For example, the DESHIMA spectrometer [1,2] in development requires filters with a loaded Ql = 500, equal to the designed frequency resolution of F/ F = 500, at 326–905 GHz

Summary

Introduction

On-chip filterbank spectrometers that use superconducting resonators as narrow band pass filters are becoming more popular as the design for realizing nextgeneration low-resolution millimeter–submillimeter (mm-submm) wave (100–1000 GHz) spectrometers for astronomy [1–3]. The intended evenmode of the CPW is less radiative, the radiation loss per unit length increases rapidly as a function of frequency F; in the case of a perfect conductor with no losses and no kinetic inductance, the attenuation constant is approximately proportional [11] to F3. This has been the main reason that previous attempts to develop an on-chip direct detection spectrometer have adopted microstrip lines and not CPWs [2,3,8] for their resonant filters, though microstrips have their own challenge to minimize material losses, especially in the higher-frequency submillimeter band [8]. We experimentally prove that it is possible to achieve a loaded Ql in excess of 500 required for the 350 GHz band of DESHIMA, indicating that the intrinsic (unloaded) Qi is even higher

Device Design and Fabrication

Measurement of the Filter Q Factor

Conclusion