High efficiency superconducting filterbanks with impedance-defined resolution for millimeter-wave spectroscopy

Abstract

We present a high efficiency, high resolution on-chip filterbank spectrometer designed for line intensity mapping and broadband wave-like dark matter searches. Existing superconducting filterbank architectures used by the mm-wave community are limited by a 50% inherent efficiency limit and are highly sensitive to resonator thin-film dielectric loss. The design presented in this paper addresses these bottlenecks by eliminating the termination resistor and employing a niobium-on-silicon coplanar waveguide resonant structures for the filterbanks. Sonnet electromagnetic simulations of a 10-channel device around 90 GHz demonstrate a resolving power of $R=1211\pm105$ and a peak efficiency of 82% for the initial channel at a nominal dielectric loss tangent of $10^{-3}$. However, signal propagation along the feedline exhibits an incremental efficiency loss of 0.85% per channel, revealing a scalability bottleneck. These efficiency metrics account for dielectric absorption, imperfect optimization of shunt spacing along the feedline, and spectral overlap from neighboring channels. Additional simulations show that a 300 channel feedline is feasible using a dielectric with loss tangent of $10^{-4}$, meeting the sampling requirements for the 90 GHz atmospheric window in future millimeter-wave surveys. Sensitivity analyses confirm that the design is robust against typical fabrication uncertainties with the exception of dielectric thickness, providing path towards the high resolution, high efficiency, and high channel count on-chip detector technology for next-generation millimeter-wave spectroscopic experiments.