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The Simons Observatory (SO) is a cosmic microwave background instrumentation suite in the Atacama Desert of Chile. More than 65,000 polarization-sensitive transition-edge sensor (TES) bolometers will be fielded in the frequency range spanning 27 to 280 GHz, with three separate dichroic designs. The mid-frequency 90/150 GHz and ultra-high-frequency 220/280 GHz detector arrays, fabricated at NIST, account for 39 of 49 total detector modules and implement the feedhorn-fed orthomode transducer-coupled TES bolometer architecture. A robust production-level fabrication framework for these detector arrays and the monolithic DC/RF routing wafers has been developed, which includes single device prototyping, process monitoring techniques, in-process metrology, and cryogenic measurements of critical film properties. Application of this framework has resulted in timely delivery of nearly 100 total superconducting focal plane components to SO with 88 % of detector wafers meeting nominal criteria for integration into a detector module: a channel yield > 95 % and T c in the targeted range. [ABSTRACT FROM AUTHOR]

The Simons Observatory is a cosmic microwave background experiment stationed atop Cerro Toco, at an elevation of 5200 ms in Chile's Atacama Desert. The receivers of the Observatory will contain more than 60,000 transition edge sensor bolometers. In order to read out this large detector count in a scalable manner, we utilize a microwave superconducting quantum interference device (SQUID) multiplexing scheme where each detector is inductively coupled to an rf SQUID, which in turn is inductively coupled to a GHz resonator. More than 2000 SQUIDs and resonators are fabricated on a single 76.2-mm-diameter silicon wafer. To qualify wafers before integration, we cryogenically screen ∼ 10% of the devices on each wafer by use of a standard set of measurements. From these data, we report parameter value trends in 47 wafers that were fabricated in the past two years. We show good control in key parameters such as frequency placement, internal quality factor, and response to applied flux. We demonstrate a wafer acceptance yield of 86%. [ABSTRACT FROM AUTHOR]

The Astrophysics 2020 Decadal Report recommended a line of Probe missions with far-infrared imaging or spectroscopy capabilities. The achievable sensitivity of these FIR missions will be enabled by cooled telescopes and advanced cryogenic detector technologies, potentially resulting in up to three orders of magnitude improvement in sensitivity and mapping speeds up to more than a million times of those achieved so far with past missions. We have obtained NASA funding to build and demonstrate transition edge sensor (TES)-based kilopixel arrays with the properties that match the requirements for cryogenic far-infrared space missions: The arrays are very closely tileable in one direction and with a moderate gap in the other direction. This array architecture can meet the sampling and pixel number requirement of a few 104 pixels. Many details of the architecture have already been demonstrated individually, and the detector board will be optimized for the use of the latest cryogenic NIST 2D time-domain SQUID readout multiplexers with a high-density fanout scheme. Additionally, we will use flex lines that are very similar to those developed at Princeton University for the ACT project. This method allows virtually unlimited tileability of the detector arrays and thus a compact detector/readout design for future FIR instrumentation requiring large pixel counts. We already have a pixel design which, if implemented with TES operating at less than 100 mK, will meet the continuum sensitivity requirements for background-limited cryogenic space missions of NEP < 10–18 W/√Hz). Furthermore, our array design will be compatible with lower noise TES designs for spectroscopy that we are currently demonstrating in our laboratory. [ABSTRACT FROM AUTHOR]

The Simons Observatory (SO) is a cosmic microwave background instrumentation suite being deployed in the Atacama Desert in northern Chile. The telescopes within SO use three types of dichroic transition-edge sensor (TES) detector arrays, with the 90 and 150 GHz Mid-Frequency (MF) arrays containing 65% of the approximately 68,000 detectors in the first phase of SO. All of the 26 required MF detector arrays have now been fabricated, packaged into detector modules, and tested in laboratory cryostats. Across all modules, we find an average operable detector yield of 84% and median saturation powers of (2.8, 8.0) pW with interquartile ranges of (1, 2) pW at (90, 150) GHz, respectively, falling within their targeted ranges. We measure TES normal resistances and superconducting transition temperatures on each detector wafer to be uniform within 3%, with overall central values of 7.5 m Ω and 165 mK, respectively. Results on time constants, optical efficiency, and noise performance are also presented and are consistent with achieving instrument sensitivity forecasts. [ABSTRACT FROM AUTHOR]

The Simons Observatory (SO) will detect and map the temperature and polarization of the millimeter-wavelength sky from Cerro Toco, Chile, across a range of angular scales, providing rich data sets for cosmological and astrophysical analysis. The SO focal planes will be tiled with compact hexagonal packages, called universal focal-plane modules (UFMs), in which the transition-edge sensor (TES) detectors are coupled to 100 mK microwave-multiplexing electronics. Three different types of dichroic TES detector arrays with bands centered at 30/40, 90/150, and 220/280 GHz will be implemented across the 49 planned UFMs. The 90/150 GHz and 220/280 GHz arrays each contain 1764 TESes, which are read out with two 910x multiplexer circuits. The modules contain a series of routed silicon chips, which are packaged together in a controlled electromagnetic environment and operated at 100 mK. Following an overview of the module design, we report on early results from the first 220/280 GHz UFM, including detector yield, as well as readout and detector noise levels. [ABSTRACT FROM AUTHOR]

The Advanced ACTPol (AdvACT) upgrade to the Atacama Cosmology Telescope (ACT) features arrays of aluminum manganese transition-edge sensors (TESes) optimized for ground-based observations of the cosmic microwave background (CMB). Array testing shows highly responsive detectors with anticipated in-band noise performance under optical loading. We report on TES parameters measured with impedance data taken on a subset of TESes. We then compare modeled noise spectral densities to measurements. We find excess noise at frequencies around 100 Hz, nearly outside of the signal band of CMB measurements. In addition, we describe full-array noise measurements in the laboratory and in the field for two new AdvACT mid-frequency arrays, sensitive at bands centered on 90 and 150 GHz, and data for the high-frequency array (150/230 GHz) as deployed. [ABSTRACT FROM AUTHOR]

Advanced ACTPol (AdvACT) will use an array of multichroic polarization-sensitive AlMn transition edge sensor (TES) bolometers read out through time-division multiplexing. Aluminum doped with a low concentration of manganese can be deposited to a bulk film thickness for a more reliable superconducting critical temperature uniformity compared to thin bilayers. To build the TES, the AlMn alloy is deposited, over Nb wiring, to a specific thickness to set the TES normal resistance. The doping concentration of manganese coarsely defines the TES critical temperature, while a fine tuning is achieved by heating the deposited film to a specific temperature. The TES island is connected to the thermal bath via four silicon-nitride membranes, where their geometry defines the thermal conductance to the temperature of the bath. Lastly, the TES heat capacity is increased by addition of PdAu electrically connected to the AlMn film. Designs and performance characteristics of these AlMn TESs are presented for use in AdvACT. [ABSTRACT FROM AUTHOR]