Microwave Kinetic Inductance Detector Arrays Research Articles

Investigation of reflection-based measurements of microwave kinetic inductance detectors in the optical bands

In this paper, we investigate the single photon response from the reflection of the microwave kinetic inductance detector (MKID) array. Reflection measurements are carried out using two configurations: one is measured simultaneously with the transmission, and the other is obtained with a single-ended MKID array terminated with an open load. Compared with the transmission, reflection measurements significantly reduce the readout noise of the single-ended MKID array. This is also reflected in the improvement of the median energy resolving power by around 20%–30% under pulsed photon illumination at λ = 405 nm, mainly due to an increase in the size of the resonance circle on the IQ plane. This method has the potential to be used to read out large MKID arrays.

CCAT-Prime: Characterization of the First 280 GHz MKID Array for Prime-Cam

The Prime-Cam receiver on the Fred Young Submillimeter Telescope for the CCAT-prime project aims to address important astrophysical and cosmological questions with sensitive broadband, polarimetric, and spectroscopic measurements. The primary frequency bands in development include 280, 350, and 850 GHz for the polarization-sensitive broadband channels and 210--420 GHz for the spectrometers. Microwave kinetic inductance detectors (MKIDs) are a natural choice of detector technology for the simplicity in multiplexed readout needed for large format arrays at these high frequencies. We present here the initial lab characterization of the feedhorn-coupled 280 GHz polarimetric MKID array, and outline the plans for the subsequent MKID arrays and the development of the testbed to characterize them.

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.

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.

GroundBIRD: A CMB Polarization Experiment with MKID Arrays

GroundBIRD is a ground-based experiment for the precise observation of the polarization of the cosmic microwave background (CMB). To achieve high sensitivity at large angular scale, we adopt three features in this experiment: fast rotation scanning, microwave kinetic inductance detector (MKID) and cold optics. The rotation scanning strategy has the advantage to suppress $1/f$ noise. It also provides a large sky coverage of 40\%, which corresponds to the large angular scales of $l \sim 6$. This allows us to constrain the tensor-to-scalar ratio by using low $l$ B-mode spectrum. The focal plane consists of 7 MKID arrays for two target frequencies, 145 GHz and 220 GHz band. There are 161 pixels in total, of which 138 are for 144 GHz and 23 are for 220 GHz. This array is currently under development and the prototype will soon be evaluated in telescope. The GroundBIRD telescope will observe the CMB at the Teide observatory. The telescope was moved from Japan to Tenerife and is now under test. We present the status and plan of the GroundBIRD experiment.

Design optimization of a 10 kilopixel optical band Microwave Kinetic Inductance Detector

In order to make improved spectral imaging measurements in the ultraviolet, visible and near infrared bands, we investigated the design of a 10 kilopixel Microwave Kinetic Inductance Detector (MKID) sensitive in these bands. We evaluate design parameters for MKIDs arrays with equally spaced resonant frequencies and high intrinsic and coupling quality factors. Resonance frequencies were chosen in the range of 2.8–4.8 GHz with an average of 2 MHz intervals. We describe the optimization of our design, including reduced cross-coupling. Through simulations, we find the average intrinsic and coupling quality factors to be on the order of 107 and 3 × 104 respectively, which are good enough for our purposes.

Linewidth dependence of NbN-based microwave kinetic inductance detectors

We analysed, fabricated, and characterised niobium nitride (NbN)-based microwave kinetic inductance detectors (MKIDs) with a rewound strip structure (spiral-MKIDs). To control resonance characteristics precisely, the linewidth (w) dependence of rewound spiral resonators varying between w = 10, 20, and 40 μm was analysed using an electromagnetic field simulator; the resonance frequencies (f0’s) were obtained as 4.42, 4.58, and 5.15 GHz respectively, proving that the inductance decreases as the w increases. To verify the simulation results experimentally, NbN-based MKID arrays with different linewidths were fabricated on 10×10 mm2 sapphire substrates, and cooled down to 3 K. The microwave characteristics with a vector network analyser, and f0’s were found to be 4.11, 4.23, and 4.85 GHz for the MKIDs with w = 10, 20, and 40 μm, respectively. These values are in agreement with the simulation results within 7.6% accuracy. The other resonance characteristics such as the scattering-matrix element (S21) and loaded quality factor (QL) showed the similar w dependence with the simulation. Spiral-MKIDs with narrower w is expected to have better detector performance owing to shallower S21 and higher QL.

Mitigation of cosmic ray effect on microwave kinetic inductance detector arrays

For space observatories, the glitches caused by high energy phonons created by the interaction of cosmic ray particles with a detector substrate lead to dead time during observation. Mitigating the impact of cosmic rays is therefore an important requirement for detectors to be used in future space missions. In order to investigate possible solutions, we carry out a systematic study by testing four large arrays of Microwave Kinetic Inductance Detectors (MKIDs), each consisting of ∼960 pixels and fabricated on monolithic 55 mm × 55 mm × 0.35 mm Si substrates. We compare the response to cosmic ray interactions in our laboratory for different detector arrays: A standard array with only the MKID array as reference, an array with a low Tc superconducting film as a phonon absorber on the opposite side of the substrate, and arrays with MKIDs on membranes. The idea is that the low Tc layer down converts the phonon energy to values below the pair breaking threshold of the MKIDs, and the membranes isolate the sensitive part of the MKIDs from phonons created in the substrate. We find that the dead time can be reduced up to a factor of 40 when compared to the reference array. Simulations show that the dead time can be reduced to below 1% for the tested detector arrays when operated in a spacecraft in an L2 or a similar far-Earth orbit. The technique described here is also applicable and important for large superconducting qubit arrays for future quantum computers.

Development of Multi-chroic MKIDs for Next-Generation CMB Polarization Studies

We report on the status of an ongoing effort to develop arrays of horn-coupled, polarization-sensitive microwave kinetic inductance detectors (MKIDs) that are each sensitive to two spectral bands between 125 and 280 GHz. These multi-chroic MKID arrays are tailored for next-generation, large-detector-count experiments that are being designed to simultaneously characterize the polarization properties of both the cosmic microwave background (CMB) and Galactic dust emission. We present our device design and describe laboratory-based measurement results from two 23-element prototype arrays. From dark measurements of our first engineering array we demonstrated a multiplexing factor of 92, showed the resonators respond to bath temperature changes as expected, and found that the fabrication yield was 100%. From our first optically loaded array we found the MKIDs respond to millimeter-wave pulses, additional optical characterization measurements are ongoing. We end by discussing our plans for scaling up this technology to kilo-pixel arrays over the next two years.

Millimeter-Wave Polarimeters Using Kinetic Inductance Detectors for TolTEC and Beyond.

Microwave Kinetic Inductance Detectors (MKIDs) provide a compelling path forward to the large-format polarimeter, imaging, and spectrometer arrays needed for next-generation experiments in millimeter-wave cosmology and astronomy. We describe the development of feedhorn-coupled MKID detectors for the TolTEC millimeter-wave imaging polarimeter being constructed for the 50-meter Large Millimeter Telescope (LMT). Observations with TolTEC are planned to begin in early 2019. TolTEC will comprise ∼7,000 polarization sensitive MKIDs and will represent the first MKID arrays fabricated and deployed on monolithic 150 mm diameter silicon wafers - a critical step towards future large-scale experiments with over 105 detectors. TolTEC will operate in observational bands at 1.1, 1.4, and 2.0 mm and will use dichroic filters to define a physically independent focal plane for each passband, thus allowing the polarimeters to use simple, direct-absorption inductive structures that are impedance matched to incident radiation. This work is part of a larger program at NIST-Boulder to develop MKID-based detector technologies for use over a wide range of photon energies spanning millimeter-waves to X-rays. We present the detailed pixel layout and describe the methods, tools, and flexible design parameters that allow this solution to be optimized for use anywhere in the millimeter and sub-millimeter bands. We also present measurements of prototype devices operating in the 1.1 mm band and compare the observed optical performance to that predicted from models and simulations.

MKID digital readout tuning with deep learning

Microwave Kinetic Inductance Detector (MKID) devices offer inherent spectral resolution, simultaneous read out of thousands of pixels, and photon-limited sensitivity at optical wavelengths. Before taking observations the readout power and frequency of each pixel must be individually tuned, and if the equilibrium state of the pixels change, then the readout must be retuned. This process has previously been performed through manual inspection, and typically takes one hour per 500 resonators (20 h for a ten-kilo-pixel array). We present an algorithm based on a deep convolution neural network (CNN) architecture to determine the optimal bias power for each resonator. The bias point classifications from this CNN model, and those from alternative automated methods, are compared to those from human decisions, and the accuracy of each method is assessed. On a test feed-line dataset, the CNN achieves an accuracy of 90% within 1 dB of the designated optimal value, which is equivalent accuracy to a randomly selected human operator, and superior to the highest scoring alternative automated method by 10%. On a full ten-kilopixel array, the CNN performs the characterization in a matter of minutes — paving the way for future mega-pixel MKID arrays.

Large-format platinum silicide microwave kinetic inductance detectors for optical to near-IR astronomy.

We have fabricated and characterized 10,000 and 20,440 pixel Microwave Kinetic Inductance Detector (MKID) arrays for the Dark-speckle Near-IR Energy-resolved Superconducting Spectrophotometer (DARKNESS) and the MKID Exoplanet Camera (MEC). These instruments are designed to sit behind adaptive optics systems with the goal of directly imaging exoplanets in a 800-1400 nm band. Previous large optical and near-IR MKID arrays were fabricated using substoichiometric titanium nitride (TiN) on a silicon substrate. These arrays, however, suffered from severe non-uniformities in the TiN critical temperature, causing resonances to shift away from their designed values and lowering usable detector yield. We have begun fabricating DARKNESS and MEC arrays using platinum silicide (PtSi) on sapphire instead of TiN. Not only do these arrays have much higher uniformity than the TiN arrays, resulting in higher pixel yields, they have demonstrated better spectral resolution than TiN MKIDs of similar design. PtSi MKIDs also do not display the hot pixel effects seen when illuminating TiN on silicon MKIDs with photons with wavelengths shorter than 1 µm.

Cryogenic LED pixel-to-frequency mapper for kinetic inductance detector arrays

We present a cryogenic wafer mapper based on light emitting diodes (LEDs) for spatial mapping of a large microwave kinetic inductance detector (MKID) array. In this scheme, an array of LEDs, addressed by DC wires and collimated through horns onto the detectors, is mounted in front of the detector wafer. By illuminating each LED individually and sweeping the frequency response of all the resonators, we can unambiguously correspond a detector pixel to its measured resonance frequency. We have demonstrated mapping a 76.2 mm 90-pixel MKID array using a mapper containing 126 LEDs with 16 DC bias wires. With the frequency to pixel-position correspondence data obtained by the LED mapper, we have found a radially position-dependent frequency non-uniformity of ≲1.6% over the 76.2 mm wafer. Our LED wafer mapper has no moving parts and is easy to implement. It may find broad applications in superconducting detectors and quantum computing/information experiments.

Multiplexed Readout for 1000-Pixel Arrays of Microwave Kinetic Inductance Detectors

Microwave Kinetic Inductance Detectors (MKIDs) are the most attractive radiation detectors for far-infrared and sub-mm astronomy: They combine ultimate sensitivity with the possibility to create very large detector arrays, in excess of 10 000 pixels. This is possible by reading-out the arrays using RF frequency division multiplexing, which allows multiplexing ratios in excess of 1000 pixels per readout line. We describe a novel readout system for large arrays of MKIDs, operating in a 2 GHz band in the 4-8 GHz range. The readout, which is a combination of a digital front- and back-end and an analog up- and down-converter system, can read out up to 4000 detectors simultaneously with 1 kHz datarate. The system achieves a readout noise power spectral density of -98 dBc/Hz while reading 1000 carriers simultaneously, which scales linear with the number of carriers. We demonstrate that 4000 state-of-the-art Aluminium-NbTiN MKIDs can be read out without deteriorating their intrinsic performance.

Development of an $$8\times 8$$ 8 × 8 CPW Microwave Kinetic Inductance Detector (MKID) Array at 0.35 THz

Microwave kinetic inductance detectors (MKIDs) are promising for THz direct detector arrays of large size, particularly with simple frequency-division multiplexing. Purple Mountain Observatory is developing a terahertz superconducting imaging array (TeSIA) for the DATE5 telescope to be constructed at Dome A, Antarctica. Here we report on the development of a prototype array for the TeSIA, namely an $$8\times 8$$ CPW MKID array at 0.35 THz. The resonance frequencies of the MKIDs span the 4–5.575 GHz band with an interval of 25 MHz. Each detector is integrated with a twin-slot antenna centered at 0.5 THz and with a relative bandwidth of 10 %, while the whole MKID array with a micro-lens array. Detailed design and measurement results will be presented.

THE ARCONS PIPELINE: DATA REDUCTION FOR MKID ARRAYS

The Array Camera for Optical to Near-IR Spectrophotometry, or ARCONS, is a camera based on Microwave Kinetic Inductance Detectors (MKIDs), a new technology that has the potential for broad application in astronomy. Using an array of MKIDs, the instrument is able to produce time-resolved imaging and low-resolution spectroscopy constructed from detections of individual photons. The arrival time and energy of each photon are recorded in a manner similar to X-ray calorimetry, but at higher photon fluxes. The technique works over a very large wavelength range, is free from fundamental read noise and dark-current limitations, and provides microsecond-level timing resolution. Since the instrument reads out all pixels continuously while exposing, there is no loss of active exposure time to readout. The technology requires a different approach to data reduction compared to conventional CCDs. We outline here the prototype data reduction pipeline developed for ARCONS, though many of the principles are also more broadly applicable to energy-resolved photon counting arrays (e.g., transition edge sensors, superconducting tunnel junctions). We describe the pipeline's current status, and the algorithms and techniques employed in taking data from the arrival of photons at the MKID array to the production of images, spectra, and time-resolved light curves.

Highly multiplexible thermal kinetic inductance detectors for x-ray imaging spectroscopy

For X-ray imaging spectroscopy, high spatial resolution over a large field of view is often as important as high energy resolution, but current X-ray detectors do not provide both in the same device. Thermal Kinetic Inductance Detectors (TKIDs) are being developed as they offer a feasible way to combine the energy resolution of transition edge sensors with pixel counts approaching CCDs and thus promise significant improvements for many X-ray spectroscopy applications. TKIDs are a variation of Microwave Kinetic Inductance Detectors (MKIDs) and share their multiplexibility: working MKID arrays with 2024 pixels have recently been demonstrated and much bigger arrays are under development. In this work, we present a TKID prototype, which is able to achieve an energy resolution of 75 eV at 5.9 keV, even though its general design still has to be optimized. We further describe TKID fabrication, characterization, multiplexing, and working principle and demonstrate the necessity of a data fitting algorithm in order to extract photon energies. With further design optimizations, we expect to be able to improve our TKID energy resolution to less than 10 eV at 5.9 keV.

ARCONS: A 2024 Pixel Optical through Near-IR Cryogenic Imaging Spectrophotometer

We present the design, construction, and commissioning results of ARCONS, the Array Camera for Optical to Near-IR Spectrophotometry. ARCONS is the first ground-based instrument in the optical through near-IR wavelength range based on microwave kinetic inductance detectors (MKIDs). MKIDs are revolutionary cryogenic detectors, capable of detecting single photons and measuring their energy without filters or gratings, similar to an X-ray microcalorimeter. MKIDs are nearly ideal, noiseless photon detectors, as they do not suffer from read noise or dark current and have nearly perfect cosmic ray rejection. ARCONS is an integral field spectrograph (IFS) containing a lens-coupled 2024 pixel MKID array yielding a 20″ × 20″ field of view and has been deployed on the Palomar 200 inch and Lick 120 inch telescopes for 24 nights of observing. We present initial results showing that ARCONS and its MKID arrays are now a fully operational and powerful tool for astronomical observations.

Crosstalk Reduction for Superconducting Microwave Resonator Arrays

Large-scale arrays of Microwave Kinetic Inductance Detectors (MKIDs) are attractive candidates for use in imaging instruments for next generation submillimeter-wave telescopes such as CCAT. We have designed and fabricated tightly packed ~250-pixel MKID arrays using lumped-element resonators etched from a thin layer of superconducting TiNx deposited on a silicon substrate. The high pixel packing density in our initial design resulted in large microwave crosstalk due to electromagnetic coupling between the resonators. Our second design eliminates this problem by adding a grounding shield and using a double-wound geometry for the meander inductor to allow conductors with opposite polarity to be in close proximity. In addition, the resonator frequencies are distributed in a checkerboard pattern across the array. We present details for the two resonator and array designs and describe a circuit model for the full array that predicts the distribution of resonator frequencies and the crosstalk level. We also show results from a new experimental technique that conveniently measures crosstalk without the need for an optical setup. Our results reveal an improvement in crosstalk from 57% in the initial design down to \leq 2% in the second design. The general procedure and design guidelines in this work are applicable to future large arrays employing microwave resonators.

Superconducting Films for Absorber-Coupled MKID Detectors for Sub-Millimeter and Far-Infrared Astronomy

We describe measurements of the properties, at dc, gigahertz, and terahertz frequencies, of thin (10 nm) aluminum films with 10 Omega/square normal state sheet resistance. Such films can be applied to construct microwave kinetic inductance detector arrays for submillimeter and far-infrared astronomical applications in which incident power excites quasiparticles directly in a superconducting resonator that is configured to present a matched-impedance to the high frequency radiation being detected. For films 10 nm thick, we report normal state sheet resistance, resistance-temperature curves for the superconducting transition, quality factor and kinetic inductance fraction for microwave resonators made from patterned films, and terahertz measurements of sheet impedance measured with a Fourier Transform Spectrometer. We compare properties with similar resonators made from niobium 600 nm thick.