The 90 and 150 GHz universal focal-plane modules for the Simons Observatory

Abstract

The Simons Observatory (SO) is a suite of telescopes located in the Atacama Desert in Chile that will make sensitive measurements of the cosmic microwave background. There are a host of cosmological and astrophysical questions that SO is forecasted to address. The universal focal-plane modules (UFMs) populate the four SO telescope receiver focal planes. There are three varieties of UFMs, each of which contains transitionedge-sensor bolometers observing in two spectral bands between 30 and 290 GHz. We describe the novel mid-frequency UFMs, which target two of the six spectral bands at 90 and 150 GHz and are central to the cosmological goals of SO.

The Simons Observatory: Differentiating Thermal and Optical Effects in Superconducting Transition-Edge Sensing Bolometers

“…Due to the signal's tiny amplitude [2], SO must fabricate, characterize and deploy tens of thousands of optically-coupled, densely-packed Transition-Edge Sensors (TESes) in their telescopes to meet the science goals. SO will deploy ∼70,000 detectors packaged within 49 detector-readout focal plane modules distributed among four telescopes [3]. This paper describes a new method for simultaneously characterizing the detector's thermal parameters and optical efficiencies without requiring more than one time-consuming cooldown of the This work was supported in part by a grant from the Simons Foundation (Award 457687, B.K.).…”

“…Estimates of both η opt and ξ therm for all the detectors in a module can be used to disambiguate signal fluctuations due to atmospheric fluctuations in the field from those caused by bath temperature fluctuations. Additionally, it is useful for predicting on-sky simultaneous biasability of detectors associated with each of the 12 module bias lines [3], [12] because it allows incorporation of the impact of η opt variations among the detectors.…”

SPT-3G+: Mapping the High-Frequency Cosmic Microwave Background Using Kinetic Inductance Detectors

“…The alignment of the feedhorns to the pixels on the silicon wafer is defined by pin and slot alignment features removed from the silicon wafers using a deep reactive ion etch (DRIE), similar to the scheme used by the Simons Observatory. 56 The backside of the silicon detector wafer beneath each pixel is partially removed with a DRIE and then metallized with Nb in order to form λ/4 backshort for the waveguide cavity. The distance between the device layer and the backshort is controlled by using the insulator layer of a silicon-on-insulator wafer to stop the DRIE process at a well defined distance from the device layer.…”

The Simons Observatory: Large-Scale Characterization of 90/150 GHz TES Detector Modules

“…Prior to installation on the telescopes, the detector modules are evaluated in laboratory cryostats to ensure their performance is sufficient to achieve the sensitivity projections in [1]. The first MF detector modules were produced in early 2021, and their initial testing results are reported in [8,9]. Here we present the testing results of the full set of 26 SO MF detector modules.…”