Reducing the Susceptibility of Lumped-Element KIDs to Two-Level System Effects
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Reducing the Susceptibility of Lumped‑Element KIDs to Two‑Level System Effects A. L. Hornsby1 · P. S. Barry2,3 · S. M. Doyle1 · Q. Y. Tang2 · E. Shirokoff2 Received: 20 August 2019 / Accepted: 3 July 2020 © The Author(s) 2020
Abstract Arrays of lumped-element kinetic inductance detectors (LEKIDs) optically coupled through an antenna-coupled transmission line are a promising candidate for future cosmic microwave background experiments. However, the dielectric materials used for the microstrip architecture are known to degrade the performance of superconducting resonators. In this paper, we investigate the feasibility of microstrip coupling to a LEKID, focusing on a systematic study of the effect of depositing amorphous silicon nitride on a LEKID. The discrete and spatially separated inductive and capacitive regions of the LEKID allow us to vary the degree of dielectric coverage and determine the limitations of the microstrip coupling architecture. We show that by careful removal of dielectric from regions of high electric field in the capacitor, there is minimal degradation in dielectric loss tangent of a partially covered lumpedelement resonator. We present the effects on the resonant frequency and noise power spectral density and, using the dark responsivity, provide an estimate for the resulting detector sensitivity. Keywords CMB · Instrumentation · Kinetic inductance detectors
1 Introduction The temperature and polarization anisotropies contained in the cosmic microwave background (CMB) offer a unique window into how our Universe began. Detection of primordial B-modes is one of the main objectives for future CMB experiments and are critical to testing models of inflation[1, 2]. Current experiments,
* A. L. Hornsby [email protected] 1
School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA, UK
2
Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
3
Argonne National Laboratory, 9700 South Cass Avenue, Lemont, IL 60439, USA
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Vol.:(0123456789)
Journal of Low Temperature Physics
with focal planes based on arrays of superconducting transition-edge sensors (TESs), now routinely operate with sensitivity close to the backgroundlimit[3–5]. To further increase sensitivity, more detectors are required. It is now well known that observations at multiple frequencies are necessary in order to constrain and remove foreground contamination[3]. To maximize focal plane efficiency, each on-sky pixel includes dual-band, dual-polarization sensitivity, with each pixel requiring four detectors. The number of detectors required by the next generation of CMB experiments presents a significant technical challenge. Kinetic inductance detectors (KIDs) are superconducting resonators whose resonant frequency and quality factor are modified with absorbed optical power[6]. Large arrays of KIDs can be constructed without the need for ancillary multiplexing components, significantly reducing the cryogenic complexity of an experiment
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