Two-Dimensional Cryogenic Readout for Far IR Bolometers

SeeQC is developing cryogenic multiplexing readout circuitry for superconducting sensor arrays. Our design and advanced multi-layer Niobium fabrication process enable us to make a compact SQUID based readout for large scale superconducting bolometer arrays. Arrays of superconducting transition edge sensors (TES) are frequently deployed in instruments for far infrared (IR) astronomy, particularly for cosmic microwave background (CMB) measurements. In order to reduce thermal loading due to wiring between the detectors and readout, as well as to reduce the cost of readout electronics, multiplexing (in either time or frequency domains) of multiple detectors on a single readout channel has become a key technology for enabling detector arrays at the kilo-pixel level and beyond. Current NASA missions employing time domain multiplexing (TDM) include HAWC+ and PIPER. These experiments feature a SQUID based TDM readout circuit that is interfaced to the TES array through an Indium bump bonding process. Next generation missions such as PIPER Dual Polarization Upgrade and PICO require and increase in sensor density. As part of the 2019 SBIR subtopic S1.04, NASA put out a call for kilo-pixel scale cryogenic, multiplexed readout capable of reading out two TES per 1 mm2 pixel. In Phase I, SeeQC designed, fabricated and performed preliminary tests on single pixel and small array TDM readout circuits that meet the area/pixel goal set by NASA. SeeQC also fabricated flux tunable superconducting resonators as a first step towards developing microwave SQUID multiplexing (µmux) as an alternative readout technology with a higher multiplexing factor. In Phase II we will continue to test and iterate our designs, with a particular aim at demonstrating scalability to larger arrays. In addition, we will develop a process based on our existing superconducting bump technology to enable hybridization of our readout arrays to NASA's TES arrays.

Transition edge sensors are used in both x-ray and far IR astronomy, including polarization sensitive cosmic microwave background measurements. Large format TES arrays, such as used by current NASA missions PIP and HAWC+ require two-dimensional, cryogenic multiplexed readout. The multiplexer designs developed in this work will be compatible with these missions, as well as enabling future NASA missions such as PICO and the dual polarization upgrade to PIPER>

Cryogenic multiplexers enable superconducting sensor arrays. TES bolometer arrays are used in a a variety of far IR astronomy experiments. TES calorimeter arrays are used for high resolution, time-resolved x-ray spectroscopy for applications such as nuclear physics and materials analysis. Multiplexing based on microwave resonators (mu-mux) is closely related to readout of superconducting qubits.

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