Recent Advances in Frequency-Multiplexed TES Readout: Vastly Reduced Parasitics and an Increase in Multiplexing Factor with Sub-Kelvin SQUIDs

Abstract

Cosmic microwave background (CMB) measurements are fundamentally limited by photon statistics. Therefore, ground-based CMB observatories have been increasing the number of detectors that are simultaneously observing the sky. Thanks to the advent of monolithically fabricated transition edge sensor (TES) arrays, the number of on-sky detectors has been increasing exponentially for over a decade. The next-generation experiment CMB-S4 will increase this detector count by more than an order of magnitude from the current state-of-the-art to 500,000. The readout of such a huge number of exquisitely precise sub-Kelvin sensors is feasible using an existing technology: frequency-domain multiplexing (fMux). To further optimize this system and reduce complexity and cost, we have recently made significant advances including the elimination of 4 K electronics, a massive decrease of parasitic in-series impedances, and a significant increase in multiplexing factor. MotivationTransition edge sensors (TES) are a mature and extremely successful technology for calorimetric and bolometric measurements. Their low operating temperature (0.01 − 0.5 K), low (0.01 − 2 Ω) impedance, and stringent noise requirement ( 10 pA/ √ Hz) calls for a sophisticated multi-stage readout system. As the per-experiment number of detectors starts to approach O(10 6 ), 1 a highly multiplexed, simple to assemble, and cost-effective solution is required.Digital frequency-domain multiplexing 2,3 uses an LC resonator in series with each TES detector to select a frequency at which a voltage bias is applied. This voltage bias keeps the

A Review of X-ray Microcalorimeters Based on Superconducting Transition Edge Sensors for Astrophysics and Particle Physics

“…If successful, it will open up a new era in observational cosmology. The LiteBIRD detectors core technology will be an array of more than 4000 TES bolometers [193], divided between the low-, mid-and high-frequency bands, and read-out with MHz-FDM [194]. The current baseline foresees TESs with a normal resistance of about 1 Ω, a time constant of 0.1-2.2 ms and saturation power around 0.7-0.9 pW.…”

Low Noise Frequency Domain Multiplexing of TES Bolometers using Sub-kelvin SQUIDs

“…This work was done using a technology demonstrator circuit board called the CIMM, described previously in 8 . In contrast with deployed Dfmux systems, in which the cryogenic readout components are spread across two cryogenic temperature stages 10 , the CIMM holds all cryogenic readout components on a single printed circuite board at 250 mK.…”

“…Here, we present recent work aimed at reducing readout noise and parasitic impedance, and improving readout packaging 8,9 . In section 2, we describe the hardware used for these measurements, including a technology demonstrator circuit board called the Cold Integrated Multiplexing Module (CIMM).…”