This paper, originally published on 31 August 2022, was replaced with a corrected/revised version on 6 August 2024. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.
Cryogenic characterization of transition-edge sensor (TES) bolometers is a time- and labor-intensive process. As new experiments deploy larger and larger arrays of TES bolometers, the testing process will become more of a bottleneck. Thus it is desirable to develop a method for evaluating detector performance at room temperature. One possibility is using machine learning to correlate detectors’ visual appearance with their cryogenic properties. Here, we use three engineering-grade TES bolometer wafers from the production cycle for SPT-3G, the current receiver on the South Pole Telescope, to train and test such an algorithm. High-resolution images of these TES bolometers were captured and relevant features were calculated from the images. Cryogenic performance metrics, including a detector’s ability to tune and superconducting parameters such as normal resistance, critical temperature, and transition width, were also measured. A random forest algorithm was trained to predict these performance metrics from the visual features. Analysis of the images proved highly successful. While the ability of the random forest algorithm to predict cryogenic features was limited with the chosen set of input image features, it is possible that an increase in data volume or the addition of more image features will solve this problem.
The third-generation South Pole Telescope camera (SPT-3G) improves upon its predecessor (SPTpol) by an order of magnitude increase in detectors on the focal plane. The technology used to read out and control these detectors, digital frequency-domain multiplexing (DfMUX), is conceptually the same as used for SPTpol, but extended to accommodate more detectors. A nearly 5× expansion in the readout operating bandwidth has enabled the use of this large focal plane, and SPT-3G performance meets the forecasting targets relevant to its science objectives. However, the electrical dynamics of the higher-bandwidth readout differ from predictions based on models of the SPTpol system due to the higher frequencies used and parasitic impedances associated with new cryogenic electronic architecture. To address this, we present an updated derivation for electrical crosstalk in higher-bandwidth DfMUX systems and identify two previously uncharacterized contributions to readout noise, which become dominant at high bias frequency. The updated crosstalk and noise models successfully describe the measured crosstalk and readout noise performance of SPT-3G. These results also suggest specific changes to warm electronics component values, wire-harness properties, and SQUID parameters, to improve the readout system for future experiments using DfMUX, such as the LiteBIRD space telescope.
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