Kinetic Inductance Detector Arrays Research Articles

Nonlinear characteristics of Ti, Nb, and NbN superconducting resonators for parametric amplifiers

Superconducting resonators and parametric amplifiers are important components in scientific systems such as kinetic inductance detector arrays, frequency-domain multiplexers for other superconducting bolometers, spin-ensemble based memories, and circuit quantum electrodynamics demonstrators. In this paper, we report microwave measurements of superconducting Ti, Nb, and NbN resonators and their use as parametric amplifiers. These half-wave resonators were fabricated under near identical sputtering and lithographic conditions to ensure a like-for-like comparison of material properties. We report a wide range of properties and behaviours in terms of transition temperatures, resistivities, rate-limiting nonlinear response times, nonlinear dissipation, signs of the nonlinear inductances and their dependences on temperature and resonance harmonic. We have successfully operated Nb and NbN resonators as high gain parametric amplifiers, achieving greater than 20 dB of power amplification. We have shown that for a half-wave resonator, amplification can be realised not only in the fundamental resonance but also in the higher harmonic resonances. Further, for materials with high transition temperatures, e.g. Nb and NbN, amplification can be achieved at K, i.e. a temperature maintained by a pulse tube cooler. Finally, in materials systems that have very fast response times, e.g. NbN, we have found that a cross-harmonic type of amplification can be achieved by placing pump tone in a different resonant mode as the signal and the idler. This wide range of observations will have important implications on the design and application of superconducting parametric amplifiers.

Resolving Power of Visible-To-Near-Infrared Hybrid β−Ta/Nb−Ti−N Kinetic Inductance Detectors

Kinetic inductance detectors (KIDs) are superconducting energy-resolving detectors, sensitive to single photons from the near-infrared to ultraviolet. We study a hybrid KID design consisting of a $\ensuremath{\beta}$-phase tantalum ($\ensuremath{\beta}$-$\mathrm{Ta}$) inductor and a $\mathrm{Nb}\text{\ensuremath{-}}\mathrm{Ti}\text{\ensuremath{-}}\mathrm{N}$ interdigitated capacitor. The devices show an average intrinsic quality factor ${Q}_{i}$ of $4.3\ifmmode\times\else\texttimes\fi{}{10}^{5}\ifmmode\pm\else\textpm\fi{}1.3\ifmmode\times\else\texttimes\fi{}{10}^{5}$. To increase the power captured by the light-sensitive inductor, we 3D print an array of $150\ifmmode\times\else\texttimes\fi{}150\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\mathrm{m}$ resin microlenses on the backside of the sapphire substrate. The shape deviation between design and printed lenses is smaller than $1\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\mathrm{m}$, and the alignment accuracy of this process is ${\ensuremath{\delta}}_{x}=+5.8\ifmmode\pm\else\textpm\fi{}0.5\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\mathrm{m}$ and ${\ensuremath{\delta}}_{y}=+8.3\ifmmode\pm\else\textpm\fi{}3.3\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\mathrm{m}$. We measure a resolving power for 1545--402 nm that is limited to 4.9 by saturation in the KID's phase response. We can model the saturation in the phase response with the evolution of the number of quasiparticles generated by a photon event. An alternative coordinate system that has a linear response raises the resolving power to 5.9 at 402 nm. We verify the measured resolving power with a two-line measurement using a laser source and a monochromator. We discuss several improvements that can be made to the devices on a route towards KID arrays with high resolving powers.

A scalable cryogenic LED module for selectively illuminating kinetic inductance detector arrays.

We present the design and measured performance of a light emitting diode (LED) module for spatially mapping kinetic inductance detector (KID) arrays in the laboratory. Our novel approach uses a multiplexing scheme that only requires seven wires to control 480 red LEDs, and the number of LEDs can be scaled up without adding any additional wires. This multiplexing approach relies on active surface mount components that can operate at cryogenic temperatures down to 10K. Cryogenic tests in liquid nitrogen and inside our cryostat demonstrate that the multiplexer circuit works at 77 and 10K, respectively. The LED module presented here is tailored for our millimeter-wave detector modules, but the approach could be adapted for use with other KID-based detector systems.

Frequency Domain Multiplexing for Microwave Kinetic Inductance Detectors: Comparing the Xilinx ZCU111 RFSoC with the New 2x2 RFSoC Board

The Xilinx ZCU111 Radio Frequency System on Chip (RFSoC) is a promising solution for reading out large arrays of microwave kinetic inductance detectors (MKIDs). The board boasts eight on-chip 12-bit / 4.096 GSPS analogue-to-digital converters (ADCs) and eight 14-bit / 6.554 GSPS digital-to-analogue converters (DACs), as well as field programmable gate array (FPGA) resources of 930,000 logic cells and 4,272 digital signal processing (DSP) slices. While this is sufficient data converter bandwidth for the readout of 8,000 MKIDs, with a 2 MHz channel-spacing, and a 1 MHz sampling rate (per channel), additional FPGA resources are needed to perform the DSP needed to process this large number of MKIDs. A solution to this problem is the new Xilinx RFSoC 2x2 board. This board costs only one fifth of the ZCU111 while still providing the same logic resources as the ZCU111, albeit with only a quarter of the data converter resources. Thus, using multiple RFSoC 2x2 boards would provide a better balance between FPGA resources and data converters, allowing the full utilization of the RF bandwidth provided by the data converters, while also lowering the cost per pixel value of the readout system, from approximately EUR2.50 per pixel with the ZCU111, to EUR1 per pixel.

Design of the Kinetic Inductance Detector Based Focal Plane Assembly for the Terahertz Intensity Mapper

We report on the kinetic inductance detector (KID) array focal plane assembly design for the Terahertz Intensity Mapper (TIM). Each of the 2 arrays consists of 4 wafer-sized dies (quadrants), and the overall assembly must satisfy thermal and mechanical requirements, while maintaining high optical efficiency and a suitable electromagnetic environment for the KIDs. In particular, our design manages to strictly maintain a 50 \(\mu \mathrm {m}\) air gap between the array and the horn block. We have prototyped and are now testing a sub-scale assembly which houses a single quadrant for characterization before integration into the full array. The initial test result shows a >95% yield, indicating a good performance of our TIM detector packaging design.

A Kinetic Inductance Detectors Array Design for High Background Conditions at 150 GHz

We present a design for an array of kinetic inductance detectors (KIDs) integrated with phased array antennas for imaging at 150 GHz under high background conditions. The microstrip geometry KID detectors are projected to achieve photon noise limited sensitivity with larger than 100 pW absorbed optical power. Both the microstrip KIDs and the antenna feed network make use of a low-loss amorphous silicon dielectric. A new aspect of the antenna implementation is the use of a NbTiN microstrip feed network to facilitate impedance matching to the 50 Ohm antenna. The array has 256 pixels on a 6-inch wafer and each pixel has two polarizations with two Al KIDs. The KIDs are designed with a half wavelength microstrip transmission line with parallel plate capacitors at the two ends. The resonance frequency range is 400–800 MHz. The readout feedline is also implemented in microstrip and has an impedance transformer from 50 to 9 Ohm at its input and output.

Observations with KIDs Interferometer Spectrum Survey (KISS)

We describe the preliminary on-sky results of the KIDs Interferometer Spectrum Survey (KISS), a spectral imager with a 1 deg field of view (FoV). The instrument operates in the range 120–180 GHz from the 2.25m Q-U-I JOint TEnerife telescope in Teide Observatory (Tenerife, Canary Islands), at 2 395m altitude above sea level. Spectra at low resolution, up to 1.45 GHz, are obtained using a fast (3.72 Hz mechanical frequency) Fourier transform spectrometer, coupled to a continuous dilution cryostat with a stabilized temperature of 170mK that hosts two 316-pixel arrays of lumped-element kinetic inductance detectors. KISS generates more than 3 000 spectra per second during observations and represents a pathfinder to demonstrate the potential for spectral mapping with large FoV.We give an overall description of the spectral mapping paradigm and we present recent results from observations, in this paper.

Accurate sky signal reconstruction for ground-based spectroscopy with kinetic inductance detectors

Context.Wide-field spectrometers are needed to deal with current astrophysical challenges that require multiband observations at millimeter wavelengths. An example of these is the KIDs Interferometer Spectrum Survey (KISS), which uses two arrays of kinetic inductance detectors (KIDs) coupled to a Martin-Puplett interferometer (MPI). KISS has a wide instantaneous field of view (1 deg in diameter) and a spectral resolution of up to 1.45 GHz in the 120–180 GHz electromagnetic band. The instrument is installed on the 2.25 m Q-U-I JOint TEnerife telescope at the Teide Observatory (Tenerife, Canary Islands), at an altitude of 2395 m above sea level.Aims.This work presents an original readout modulation method developed to improve the sky signal reconstruction accuracy for types of instruments for which a fast sampling frequency is required, both to remove atmospheric fluctuations and to perform full spectroscopic measurements on each sampled sky position.Methods.We first demonstrate the feasibility of this technique using simulations. We then apply such a scheme to on-sky calibration.Results.We show that the sky signal can be reconstructed to better than 0.5% for astrophysical sources, and to better than 2% for large background variations such as in “skydip”, in an ideal noiseless scenario. The readout modulation method is validated by observations on-sky during the KISS commissioning campaign.Conclusions.We conclude that accurate photometry can be obtained for future KID-based interferometry using the MPI.

Design evaluation of microwave transmission properties of YBa2Cu3O7-based kinetic inductance detectors

We designed, fabricated, and characterized microwave transmission properties with rewound strip structures for YBa2Cu3O7 (YBCO)-based kinetic inductance detectors (KIDs). The superconducting rewound strip serves as a microwave resonator and as a broadband terahertz-wave antenna. To predict the microwave resonance characteristics before fabrication, the line-width (w) and space (s) dependence of the spiral resonators were analyzed using an electromagnetic simulator; the resonance frequency increased, and the quality factor decreased with increasing w and s from 10 to 40 μm. YBCO-based KID arrays with different w (10 and 40 μm) were fabricated on 10 mm-square MgO substrates, cooled to 3 K using a 4He refrigerator, and evaluated using a vector network analyzer to verify the result of the simulation experimentally. The measured resonance frequency ratio of 1.11 times (5.04 → 5.59 GHz) agreed with the simulated ones of 1.10 times (4.84 → 5.33 GHz) between w = 10 and 40 μm. The other resonance characteristics, such as transmission coefficient and quality factor, have a similar w dependence with the simulation.

Understanding and minimizing resonance frequency deviations on a 4-in. kilo-pixel kinetic inductance detector array

One of the advantages of kinetic inductance detectors is their intrinsic frequency domain multiplexing capability. However, fabrication imperfections usually give rise to resonance frequency deviations, which create frequency collision and limit the array yield. Here, we study the resonance frequency deviation of a 4-in. kilo-pixel lumped-element kinetic inductance detector (LEKID) array using optical mapping. Using the measured resonator dimensions and film thickness, the fractional deviation can be explained within ±25×10−3, whereas the residual deviation is due to variation of electric film properties. Using the capacitor trimming technique, the fractional deviation is decreased by a factor of 14. The yield of the trimming process is found to be 97%. The mapping yield, measured under a 110 K background, is improved from 69% to 76%, which can be further improved to 81% after updating our readout system. With the improvement in yield, the capacitor trimming technique may benefit future large-format LEKID arrays.

Galaxy Evolution Probe

The Galaxy Evolution Probe (GEP) is a concept for a mid- and far-infrared space observatory to measure key properties of large samples of galaxies with large and unbiased surveys. GEP will attempt to achieve zodiacal light and Galactic dust emission photon background-limited observations by utilizing a 6 Kelvin, 2.0 meter primary mirror and sensitive arrays of kinetic inductance detectors. It will have two instrument modules: a 10 - 400 micron hyperspectral imager with spectral resolution R = 8 (GEP-I) and a 24 - 193 micron, R = 200 grating spectrometer (GEP-S). GEP-I surveys will identify star-forming galaxies via their thermal dust emission and simultaneously measure redshifts using polycyclic aromatic hydrocarbon emission lines. Galaxy luminosities derived from star formation and nuclear supermassive black hole accretion will be measured for each source, enabling the cosmic star formation history to be measured to much greater precision than previously possible. Using optically thin far-infrared fine-structure lines, surveys with GEP-S will measure the growth of metallicity in the hearts of galaxies over cosmic time and extraplanar gas will be mapped in spiral galaxies in the local universe to investigate feedback processes. The science case and mission architecture designed to meet the science requirements are described, and the kinetic inductance detector and readout electronics state of the art and needed developments are described. This paper supersedes the GEP concept study report cited in it by providing new content, including: a summary of recent mid-infrared KID development, a discussion of microlens array fabrication for mid-infrared KIDs, and additional context for galaxy surveys. The reader interested in more technical details may want to consult the concept study report.

End-to-end deep learning pipeline for microwave kinetic inductance detector resonator identification and tuning

We present the development of a machine learning-based pipeline to fully automate the calibration of the frequency comb used to read out optical/IR microwave kinetic inductance detector (MKID) arrays. This process involves determining the resonant frequency and optimal drive power of every pixel (i.e., resonator) in the array, which is typically done manually. Modern optical/IR MKID arrays, such as the DARK-Speckle Near-Infrared Energy-Resolving Superconducting Spectrophotometer and the MKID exoplanet camera, contain 10 to 20,000 pixels, making the calibration process extremely time-consuming; each 2000-pixel feedline requires 4 to 6 h of manual tuning. We present a pipeline that uses a single convolutional neural network to perform both resonator identification and tuning simultaneously. We find that our pipeline has performance equal to that of the manual tuning process and requires just 12 min of computational time per feedline.

Subgap Kinetic Inductance Detector Sensitive to 85-GHz Radiation

We have fabricated an array of subgap kinetic inductance detectors (SKIDs) made of granular aluminum (${T}_{c}\ensuremath{\sim}2$ K) sensitive in the 80--90 GHz frequency band and operating at 300 mK. We measure a noise equivalent power of $1.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}\phantom{\rule{0.2em}{0ex}}{\mathrm{W}/\mathrm{Hz}}^{0.5}$ on average and $2.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}\phantom{\rule{0.2em}{0ex}}{\mathrm{W}/\mathrm{Hz}}^{0.5}$ at best, for an illuminating power of 50 fW per pixel. Even though the circuit design of SKIDs is identical to that of the kinetic inductance detectors, the SKIDs operating principle is based on their sensitivity to subgap excitations. This detection scheme is advantageous because it avoids having to lower the operating temperature proportionally to the lowest detectable frequency. The SKIDs presented here are intrinsically selecting the 80--90 GHz frequency band, well below the superconducting spectral gap of the film, at approximately 180 GHz.

A chemically etched corrugated feedhorn array for D-band CMB observations

We present the design, manufacturing, and testing of a 37-element array of corrugated feedhorns for Cosmic Microwave Background CMB) measurements between 140 and 170 GHz. The array was designed to be coupled to Kinetic Inductance Detector arrays, either directly (for total power measurements) or through an orthomode transducer (for polarization measurements). We manufactured the array in platelets by chemically etching aluminum plates of 0.3 mm and 0.4 mm thickness. The process is fast, low-cost, scalable, and yields high-performance antennas compared to other techniques in the same frequency range. Room temperature electromagnetic measurements show excellent repeatability with an average cross polarization level about − 20 dB, return loss about − 25 dB, first sidelobes below − 25 dB and far sidelobes below − 35 dB. Our results qualify this process as a valid candidate for state-of-the-art CMB experiments, where large detector arrays with high sensitivity and polarization purity are of paramount importance in the quest for the discovery of CMB polarization B-modes.

Three-Wave Mixing Kinetic Inductance Traveling-Wave Amplifier with Near-Quantum-Limited Noise Performance

We present a theoretical model and experimental characterization of a microwave kinetic inductance traveling-wave amplifier (KIT), whose noise performance, measured by a shot-noise tunnel junction (SNTJ), approaches the quantum limit. Biased with a dc current, the KIT operates in a three-wave mixing fashion, thereby reducing by several orders of magnitude the power of the microwave pump tone and associated parasitic heating compared to conventional four-wave mixing KIT devices. It consists of a 50 Ohms artificial transmission line whose dispersion allows for a controlled amplification bandwidth. We measure $16.5^{+1}_{-1.3}$ dB of gain across a 2 GHz bandwidth with an input 1 dB compression power of -63 dBm, in qualitative agreement with theory. Using a theoretical framework that accounts for the SNTJ-generated noise entering both the signal and idler ports of the KIT, we measure the system-added noise of an amplification chain that integrates the KIT as the first amplifier. This system-added noise, $3.1\pm0.6$ quanta (equivalent to $0.66\pm0.15$ K) between 3.5 and 5.5 GHz, is the one that a device replacing the SNTJ in that chain would see. This KIT is therefore suitable to read large arrays of microwave kinetic inductance detectors and promising for multiplexed superconducting qubit readout.

Second generation readout for large format photon counting microwave kinetic inductance detectors.

We present the development of a second generation digital readout system for photon counting microwave kinetic inductance detector (MKID) arrays operating in the optical and near-infrared wavelength bands. Our system retains much of the core signal processing architecture from the first generation system but with a significantly higher bandwidth, enabling the readout of kilopixel MKID arrays. Each set of readout boards is capable of reading out 1024 MKID pixels multiplexed over 2 GHz of bandwidth; two such units can be placed in parallel to read out a full 2048 pixel microwave feedline over a 4 GHz-8 GHz band. As in the first generation readout, our system is capable of identifying, analyzing, and recording photon detection events in real time with a time resolution of order a few microseconds. Here, we describe the hardware and firmware, and present an analysis of the noise properties of the system. We also present a novel algorithm for efficiently suppressing IQ mixer sidebands to below -30 dBc.

Reducing the Susceptibility of Lumped-Element KIDs to Two-Level System Effects

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 lumped-element 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.

The long duration cryogenic system of the OLIMPO balloon–borne experiment: Design and in–flight performance

We describe the design and in–flight performance of the cryostat and the self–contained 3He refrigerator for the OLIMPO balloon–borne experiment, a spectrophotometer to measure the Sunyaev–Zel’dovich effect in clusters of galaxies.The 3He refrigerator provides the 0.3 K operation temperature for the four arrays of kinetic inductance detectors working in 4 bands centered at 150, 250, 350 and 460 GHz. The cryostat provides the 1.65 K base temperature for the 3He refrigerator, and cools down the reimaging optics and the filters chain at about 2 K.The integrated system was designed for a hold time of about 15 days, to achieve the sensitivity required by the planned OLIMPO observations, and successfully operated during the first long–duration stratospheric flight of OLIMPO in July 2018.The cryostat features two tanks, one for liquid nitrogen and the other one for liquid helium. The long hold time has been achieved by means of custom stiff G10 fiberglass tubes support, which ensures low thermal conductivity and remarkable structural stiffness; multi–layer superinsulation, and a vapour cooled shield, all reducing the heat load on the liquid helium tank.The system was tested in the lab, with more than 15 days of unmanned operations, and then in the long duration balloon flight in the stratosphere. In both cases, the detector temperature was below 300 mK, with thermal stability better than ±0.5 mK.The system also operated successfully in the long duration stratospheric balloon flight.

The first flight of the OLIMPO experiment: instrument performance

OLIMPO is a balloon-borne experiment aiming at spectroscopic measurements of the Sunyaev-Zel’dovich effect in clusters of galaxies. The instrument operates from the stratosphere, so that it can cover a wide frequency range (from ∼ 130 to ∼ 520 GHz in 4 bands), including frequencies which are not observable with ground-based instruments. OLIMPO is composed of a 2.6-m aperture telescope, a differential Fourier transform spectrometer and four arrays of lumped element kinetic inductance detectors operating at the temperature of 0.3 K. The payload was launched from the Longyearbyen airport (Svalbard Islands) on July 14th, 2018, and operated for 5 days, at an altitude of 38 km around the North Pole. We report the in-flight performance of the first lumped element kinetic inductance detector arrays ever flown onboard a stratospheric balloon.

Development of Large Array of Kinetic Inductance Detectors Using Commercial-Class External Foundries

This study focuses on kinetic inductance detectors (KIDs) fabricated in external foundries using 6 and 8-inch processes. These processes allow us to fabricate large arrays of KIDs in a scalable manner. The support of such a wide variety of astronomical and particle-physics applications requires large numbers of superconducting detectors. For example, the sensitivity of the cosmic microwave background measurements has exponentially improved over the past few decades. The most significant advantage of KIDs is scalability to a large array due to the intrinsic frequency multiplexing scheme. The first step of fabricating a large array of KIDs is designing test chips to check the performance of the 6 and 8-inch micro-electro-mechanical system processes. The KIDs are made of a single pure aluminum film and consist of coplanar waveguide quarter wavelength resonators with a feedline. Each wafer is filled with 32 chips, where the chip size is 20 × 20 mm2, with 48 resonators on each chip. The chips are evaluated using a dilution refrigerator at temperatures ranging from 100 to 500 mK. The quality factor of the resonators, temperature dependency of the resonance frequency, and yields are comparable with those of the KIDs fabricated in a dedicated clean room for superconducting detectors.