Design and Performance of the Antenna-Coupled Lumped-Element Kinetic Inductance Detector

P S Barry,S Doyle,A L Hornsby,E Mayer,Q Y Tang,J Vieira,A Kofman,E Shirokoff,A Nadolski

doi:10.1007/s10909-018-1943-y

Abstract

Focal plane arrays consisting of low-noise, polarisation-sensitive detectors have made possible the pioneering advances in the study of the cosmic microwave background (CMB). To make further progress, the next generation of CMB experiments (e.g. CMB-S4) will require a substantial increase in the number of detectors compared to current instruments. Arrays of kinetic inductance detectors (KIDs) provide a possible path to realising such large-format arrays owing to their intrinsic multiplexing advantage and relative cryogenic simplicity. In this paper, we report on the design of a variant of the traditional KID design: the antenna-coupled lumped-element KID. A polarisation-sensitive twin-slot antenna placed behind an optimised hemispherical lens couples power onto a thin-film superconducting microstrip line. The power is then guided into the inductive section of an aluminium KID, where it is absorbed and modifies both the resonant frequency and quality factor of the KID. We present the various aspects of the design and preliminary results from the first set of seven-element prototype arrays and compare to the expected modelled performance.

Highlights

Kinetic inductance detectors (KIDs) [1] are considered a compelling alternative technology for large-format focal plane arrays
A number of projects operating at millimetre (NIKA-2 [2], TolTEC [5], SuperSpec [3,4]) and submillimetre (SpaceKIDs [6], BLAST-TNG [7]) wavelengths will help to deliver the first large-scale on-sky demonstration of KID arrays, whose promise of high multiplexing factors and simple fabrication provides a path to reduced cost and complexity of future large-format focal plane instruments
The resonant frequency and quality factor are extracted from fits to VNA sweeps, and a standard single-tone homodyne configuration is used to characterise the noise performance [1]

Summary

Introduction

Kinetic inductance detectors (KIDs) [1] are considered a compelling alternative technology for large-format focal plane arrays. State-of-the-art CMB experiments are at ‘stage 3’, with focal planes containing 5000–15,000 TESs [13–15] operating close to the background-limit In this case, further improvements in sensitivity can only be achieved by increasing total focal plane area and number of detectors. Estimates indicate that CMB-S4 will require a minimum of 500,000 background-limited detectors across ∼ 10 ground-based telescopes [17] It is here where the advantages of KIDs could play an important role in realising the generation of CMB experiments. The constant current density across the inductor gives a spatially uniform responsivity, and the design of the inductor can be arranged to form an efficient free-space absorber This additional degree of freedom is a major advantage of the leKID and is compatible with various radiation coupling schemes [7,8]. 1 mm mm-wave input mm-wave input from antenna SiNx + Nb ground plane mm-wave absorbing length

Millimetre-Wave Coupling

RF Design

Preliminary Results

Conclusions and Future Work