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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Optimization of cold resonant filters for frequency domain multiplexed readout of POLARBEAR-2

K. Hattori, Y. Akiba, Kam Arnold, Darcy R. Barron, A. N. Bender, M. Dobbs, T. de Haan, Nicholas L. Harrington, M. Hasegawa, M. Hazumi, W. L. Holzapfel, Yasuto Hori, BRIAN G. KEATING, Adrian Tae-Jin Lee, J. Montgomery, Hideki Morii, Michael J. Myers, Kaja M. Rotermund, Ian Shirley, Graeme M. Smecher, N. Stebor, Aritoki Suzuki, T. Tomaru

Published Aug 19, 2014• 9 citations
Publisher

Abstract

For the next generation of Cosmic Microwave Background (CMB) experiments, kilopixel arrays of Transition Edge Sensor (TES) bolometers are necessary to achieve the required sensitivity and their science goals. We are developing read-out electronics for POLARBEAR-2 CMB experiment, which multiplexes 32-TES bolometers through a single superconducting quantum interface device (SQUID). To increase both the bandwidth of the SQUID electronics and the multiplexing factor, we are modifying cold wiring and developing LC filters, and a low-inductance superconducting cable. Using these components, we will show frequency domain multiplexing up to 3 MHz.

DOI
10.1117/12.2057045

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Abstract Digital Frequency-Domain Multiplexing (DfMux) is a technique that uses MHz superconducting resonators and Superconducting Quantum Interference Device (SQUID) arrays to read out sets of transition edge sensors. DfMux has been used by several Cosmic Microwave Background experiments, including most recently POLARBEAR-2 and SPT-3 G with multiplexing factors as high as 68, and is the baseline readout technology for the planned satellite mission LiteBIRD. Here, we present recent work focused on improving DfMux readout noise, reducing parasitic impedance, and improving sensor operation. We have achieved a substantial reduction in stray impedance by integrating the sensors, resonators, and SQUID array onto a single-carrier board operated at 250 mK. This also drastically simplifies the packaging of the cryogenic components and leads to better-controlled crosstalk. We demonstrate a low readout noise level of 8.6 $$\mathrm{pA/Hz}1^{1/2}$$ pA / Hz 1 1 / 2 , which was made possible by operating the SQUID array at a reduced temperature and with a low dynamic impedance. This is a factor of two improvement compared to the achieved readout noise level in currently operating Cosmic Microwave Background experiments using DfMux and represents a critical step toward maturation of the technology for the next generation of instruments.

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Readout demonstration of 512 TES bolometers using a single microwave SQUID multiplexer (Conference Presentation)

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To enable the next-generation of bolometric cameras, we are developing the microwave SQUID multiplexer (μMUX). Upcoming receivers such as Simons Observatory, CCAT-prime, BICEP array, Ali-CPT, and CMB-S4 plan to instrument focal planes with 50,000-500,000 sensors. Sensor count is achieved by tiling many 150 mm-diameter densely packed detector arrays into these focal planes. The fabrication and quality of large-format bolometer arrays has been demonstrated and is now mature. In contrast, the readout technology required for next-generation receivers needs development. The sensitivity, low cross-talk, high multiplexing density, and small component size make the μMUX well-suited for this goal. In this approach, the TES signal modulates the inductance of an rf-SQUID that loads a high-Q microwave resonator. The coupled signal therefore modulates the microwave resonance frequency, which may be read out using homodyne techniques. By coupling each resonator to the same microwave feedline, many detectors can be read out on a single coaxial cable pair. The multiplexing density is in practice limited by signal bandwidth, allowable cross-talk, and the digitization bandwidth of room-temperature readout electronics. We present the design and performance of a scalable 64-channel multiplexer chip optimized for bolometric applications. We utilize a new quarter wave resonator design that increases the physical linear density by a factor of two, therefore achieving a smaller footprint for simplified detector packaging. Measurements of this design show 100 kHz resonator bandwidth, uniform 1.8 MHz frequency spacing, and an input referred current noise of 35 pA/√Hz that is well below the level of an optimized, background-limited TES bolometer. Using 8 daisy-chained and frequency scaled chips, we create a 512-channel multiplexer and use it to readout a 512 TES-bolometer array. We present the results of this large-scale μMUX demonstration including system yield, signal cross-talk, and an analysis of noise in various TES bias configurations. The result demonstrates the multiplexing density required to read out 2,000 sensors between 4-8 GHz.

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Abstract A microwave SQUID multiplexer ( μ MUX) with a high multiplexing factor is a promising readout approach for large-scale superconducting transition-edge sensor (TES) bolometer arrays. This paper reports on the characteristics of 16-channel μ MUX prototype chips and a 60-channel readout module developed to read out TES bolometers for the Ali cosmic microwave background polarization telescope (AliCPT). We designed two different coupling structures between the resonator and the radio-frequency superconducting interference device: design A with a mutual inductance ( M T ) of 2.3 pH and design B with an M T of 6.5 pH. For design A, the mean resonator bandwidth ( Δ f BW ) and peak-to-peak frequency shift ( Δ f pp ) are approximately 610 kHz and 290 kHz, respectively. The measured mean open-loop current noise is less than 40 pA / Hz . Preliminary results indicate that crosstalk between adjacent channels is below 1% in our design A μ MUX chip. A measured channel with design B shows a Δ f BW of 586 kHz and a current noise of 33 pA / Hz , similar to the design A channels. In comparison, the Δ f pp of 803 kHz is much larger than the design A channels due to a larger M T . The readout module, consisting of two design A chips and two design B chips, shows 60 resonances, corresponding to a yield of 94%. In the future, we will place 32 design A channels within the same chip dimension to increase the channel density and build a larger readout module suitable for AliCPT TES arrays.

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Characterization of Electrical Crosstalk in FDM Readout for a CMB Experiment

E. Di Giorgi, Vishal Anvekar, M. P. Bruijn +9 more

The new generation of Cosmic Microwave Background (CMB) experiments exploits the properties of low-temperature detectors, particularly superconducting Transition Edge Sensor (TES) bolometers, whose characteristics make them ideal for present and future CMB measurements. Frequency Domain Multiplexing (FDM) configuration is performed by connecting an LC filter in series with each TES. The presence of the LC filters and the SQUID input coil and wiring in series with all the LC channels cause systematic electrical crosstalk.In this work we present the tests and characterization performed on an LC chip produced by SRON (Space Research Organization Netherlands) for the experiment SWIPE. These LC chips are composed of lithographically fabricated inductors and by parallel plate capacitors. The measurements were focused on retrieving the resonance frequencies to be compared to the expected design values, the quality factor and the parasitic resistance. The results were consistent with previous measurements performed on similar setups, showing Q-factors above$\mathbf {10^{4}}$and parasitic resistance on the order of$\mathbf {10^{-2}\;\Omega }$. The dependence of the properties of the LC filters and the SQUID on the temperature and the bias settings was studied. Measurements to define the level and the major contributors to electrical crosstalk were performed. Both modeling and experimental results indicated an electrical crosstalk level on the order of 10-4.

IEEE Transactions on Applied Superconductivity•Apr 20, 2026•0 citations
For the next generation of Cosmic Microwave Background (CMB) experiments, kilopixel arrays of Transition Edge Sensor (TES) bolometers are necessary to achieve the required sensitivity and their science goals. We are developing read-out electronics for POLARBEAR-2 CMB experiment, which multiplexes 32-TES bolometers through a single superconducting quantum interface device (SQUID). To increase both the bandwidth of the SQUID electronics and the multiplexing factor, we are modifying cold wiring and developing LC filters, and a low-inductance superconducting cable. Using these components, we will show frequency domain multiplexing up to 3 MHz.
Abstract Digital Frequency-Domain Multiplexing (DfMux) is a technique that uses MHz superconducting resonators and Superconducting Quantum Interference Device (SQUID) arrays to read out sets of transition edge sensors. DfMux has been used by several Cosmic Microwave Background experiments, including most recently POLARBEAR-2 and SPT-3 G with multiplexing factors as high as 68, and is the baseline readout technology for the planned satellite mission LiteBIRD. Here, we present recent work focused on improving DfMux readout noise, reducing parasitic impedance, and improving sensor operation. We have achieved a substantial reduction in stray impedance by integrating the sensors, resonators, and SQUID array onto a single-carrier board operated at 250 mK. This also drastically simplifies the packaging of the cryogenic components and leads to better-controlled crosstalk. We demonstrate a low readout noise level of 8.6 pA/Hz11/2\mathrm{pA/Hz}1^{1/2}pA/Hz11/2 pA / Hz 1 1 / 2 , which was made possible by operating the SQUID array at a reduced temperature and with a low dynamic impedance. This is a factor of two improvement compared to the achieved readout noise level in currently operating Cosmic Microwave Background experiments using DfMux and represents a critical step toward maturation of the technology for the next generation of instruments.
To enable the next-generation of bolometric cameras, we are developing the microwave SQUID multiplexer (μMUX). Upcoming receivers such as Simons Observatory, CCAT-prime, BICEP array, Ali-CPT, and CMB-S4 plan to instrument focal planes with 50,000-500,000 sensors. Sensor count is achieved by tiling many 150 mm-diameter densely packed detector arrays into these focal planes. The fabrication and quality of large-format bolometer arrays has been demonstrated and is now mature. In contrast, the readout technology required for next-generation receivers needs development. The sensitivity, low cross-talk, high multiplexing density, and small component size make the μMUX well-suited for this goal. In this approach, the TES signal modulates the inductance of an rf-SQUID that loads a high-Q microwave resonator. The coupled signal therefore modulates the microwave resonance frequency, which may be read out using homodyne techniques. By coupling each resonator to the same microwave feedline, many detectors can be read out on a single coaxial cable pair. The multiplexing density is in practice limited by signal bandwidth, allowable cross-talk, and the digitization bandwidth of room-temperature readout electronics. We present the design and performance of a scalable 64-channel multiplexer chip optimized for bolometric applications. We utilize a new quarter wave resonator design that increases the physical linear density by a factor of two, therefore achieving a smaller footprint for simplified detector packaging. Measurements of this design show 100 kHz resonator bandwidth, uniform 1.8 MHz frequency spacing, and an input referred current noise of 35 pA/√Hz that is well below the level of an optimized, background-limited TES bolometer. Using 8 daisy-chained and frequency scaled chips, we create a 512-channel multiplexer and use it to readout a 512 TES-bolometer array. We present the results of this large-scale μMUX demonstration including system yield, signal cross-talk, and an analysis of noise in various TES bias configurations. The result demonstrates the multiplexing density required to read out 2,000 sensors between 4-8 GHz.
LiteBIRD is a satellite mission designed to map the polarization of the Cosmic Microwave Background (CMB) at degree and larger scales from 40 to 402 GHz. LiteBIRD will use 4,600 Transition-Edge Sensor (TES) bolometers biased and read out using Digital Frequency Domain Multiplexing (DfMux). The DfMux implementation for LiteBIRD uses sub-kelvin Superconducting Quantum Interference Device (SQUID) at the same 0.1 K thermal stage as the detectors, this allows for reduced parasitic impedances within the mK circuit and improved SQUID performance. Additionally it must work in the integrated system with the spacecraft’s wiring harnesses, which will be longer than is typical on similar ground based experiments, and therefore have more significant parasitic impedances which will impact readout performance. The properties of SQUID candidates at millikelvin temperatures and effects of the spacecraft-like meter scale wiring harness are investigated. Additionally, the possibility of inductively rather than resistively biasing our bolometers at the 0.1K stage, to reduce power dissipation in the bias element, is investigated. We will report progress on validating the cryogenic components of this readout system.
We describe the development of a frequency-domain multiplexer (MUX) to read out arrays of superconducting transition-edge sensors (TES). Fabrication of large-format arrays of these sensors is becoming practical; however, reading out each sensor in the array is a major instrumental challenge. Frequency-domain multiplexing can greatly simplify the instrumentation of large arrays by reducing the number of SQUID's (superconducting quantum interference devices) and wires to the low temperature stages. Each sensor is AC biased at a different frequency, ranging from 380 kHz to 1 MHz. Each sensor signal amplitude-modulates its respective AC bias frequency. An LC filter associated with each sensor suppresses Johnson noise from the other sensors. The signals are combined at a current summing node and measured by a single SQUID. The individual signals from each sensor are then lock-in detected by room temperature electronics. Test chips with fully lithographed LC filters for up to 32 channels have been designed and fabricated. The capacitance and inductance values have been measured and are close to the design goals. We discuss the basic principles of frequency-domain multiplexing, the design and testing of the test chips, and the implementation of a practical system.
Abstract A microwave SQUID multiplexer ( μ MUX) with a high multiplexing factor is a promising readout approach for large-scale superconducting transition-edge sensor (TES) bolometer arrays. This paper reports on the characteristics of 16-channel μ MUX prototype chips and a 60-channel readout module developed to read out TES bolometers for the Ali cosmic microwave background polarization telescope (AliCPT). We designed two different coupling structures between the resonator and the radio-frequency superconducting interference device: design A with a mutual inductance ( M T ) of 2.3 pH and design B with an M T of 6.5 pH. For design A, the mean resonator bandwidth ( Δ f BW ) and peak-to-peak frequency shift ( Δ f pp ) are approximately 610 kHz and 290 kHz, respectively. The measured mean open-loop current noise is less than 40 pA / Hz . Preliminary results indicate that crosstalk between adjacent channels is below 1% in our design A μ MUX chip. A measured channel with design B shows a Δ f BW of 586 kHz and a current noise of 33 pA / Hz , similar to the design A channels. In comparison, the Δ f pp of 803 kHz is much larger than the design A channels due to a larger M T . The readout module, consisting of two design A chips and two design B chips, shows 60 resonances, corresponding to a yield of 94%. In the future, we will place 32 design A channels within the same chip dimension to increase the channel density and build a larger readout module suitable for AliCPT TES arrays.
The new generation of Cosmic Microwave Background (CMB) experiments exploits the properties of low-temperature detectors, particularly superconducting Transition Edge Sensor (TES) bolometers, whose characteristics make them ideal for present and future CMB measurements. Frequency Domain Multiplexing (FDM) configuration is performed by connecting an LC filter in series with each TES. The presence of the LC filters and the SQUID input coil and wiring in series with all the LC channels cause systematic electrical crosstalk.In this work we present the tests and characterization performed on an LC chip produced by SRON (Space Research Organization Netherlands) for the experiment SWIPE. These LC chips are composed of lithographically fabricated inductors and by parallel plate capacitors. The measurements were focused on retrieving the resonance frequencies to be compared to the expected design values, the quality factor and the parasitic resistance. The results were consistent with previous measurements performed on similar setups, showing Q-factors above104\mathbf {10^{4}}104and parasitic resistance on the order of10−2  Ω\mathbf {10^{-2}\;\Omega }10−2Ω. The dependence of the properties of the LC filters and the SQUID on the temperature and the bias settings was studied. Measurements to define the level and the major contributors to electrical crosstalk were performed. Both modeling and experimental results indicated an electrical crosstalk level on the order of 10-4.