Abstract
Future cosmic microwave background (CMB) experiments, including the large scale ground-based Stage Four CMB Experiment (CMB-S4), satellites, and balloons, aim to map the CMB to an unprecedented precision in order to answer several key questions in cosmology. However, to reach the target noise sensitivity, more than 100,000 detectors will be needed. Arrays of kinetic inductance detectors (KIDs) are a promising alternative for experiments that require large number of detectors due to the intrinsic multiplexing capabilities. We present the fabrication procedure for a prototype planar orthomode transducer (OMT)-coupled multi-color KID array optimized for 220/270 GHz frequency bands. These devices are made from silicon-on-insulator wafers to provide a low-loss substrate for the KIDs. The OMT couples the two polarizations of light from a wide-band feedhorn to separate Nb/SiN/Nb microstrip lines, which are then coupled to Al/Nb lumped-element KIDs (LEKIDs). The silicon on the backside of the OMT is etched away using deep reactive ion etch to release the OMT membrane to enable operation over a wide bandwidth. Finally, the buried oxide is removed underneath the KID capacitors in order to minimize two-level system noise and loss mitigation. We achieved a good yield (> 80%) on our prototype devices.
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Heidelberg MLA150: https://himt.de/index.php/maskless-write-lasers.html
YES CV200 RFS Plasma Strip/Descum System: http://www.yieldengineering.com/products/plasma-strip-descum-systems/cv200rf-series
AJA ATC 2200 UHV Sputtering System: http://www.ajaint.com/atc-series-sputtering-systems.html
PlasmaTherm ICP Fluorine Etcher: http://www.plasma-therm.com/apex_SLR.html
Plasma-Therm Apex SLR: http://www.plasma-therm.com/versaline.html
Plasma-Therm Versaline DSE: http://www.plasma-therm.com/etch-dse.html
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Acknowledgements
This work is partially supported by NSF award #1554565 and the Kavli NSF-PFC3 Detector Development Grant. This work was supported in part by the Kavli Institute for Cosmological Physics at the University of Chicago through Grant NSF PHY-1125897 and an endowment from the Kavli Foundation and its founder Fred Kavli. This work made use of the Pritzker Nanofabrication Facility of the Institute for Molecular Engineering at the University of Chicago, which receives support from SHyNE, a node of the National Science Foundations National Nanotechnology Coordinated Infrastructure (NSF NNCI-1542205).
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Tang, Q.Y., Barry, P.S., Cecil, T.W. et al. Fabrication of OMT-Coupled Kinetic Inductance Detector for CMB Detection. J Low Temp Phys 199, 362–368 (2020). https://doi.org/10.1007/s10909-020-02341-5
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DOI: https://doi.org/10.1007/s10909-020-02341-5