Characterization of MKIDs for CMB Observation at 220 GHz With the South Pole Telescope

• Published in: IEEE transactions on applied superconductivity Vol. 33; no. 5; pp. 1 - 5
• Main Authors: Dibert, K. R., Barry, P. S., Anderson, A. J., Benson, B. A., Cecil, T., Chang, C. L., Fichman, K. N., Karkare, K., Li, J., Natoli, T., Pan, Z., Rouble, M., Shirokoff, E., Young, M.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.08.2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Aluminum; CMB; Coplanar waveguides; Detectors; Frequency shift; Inductance; Inductors; MKIDs; Optical detectors; Optical filters; Optical resonators; Pixels; Resonators; South Pole; South Pole Telescope; Spectral sensitivity; Transition temperature
• ISSN: 1051-8223; 1558-2515
• DOI: 10.1109/TASC.2023.3250386

We present an updated design of the 220 GHz microwave kinetic inductance detector (MKID) pixel for SPT-3G+, the next-generation camera for the South Pole Telescope. We show results of the dark testing of a 63-pixel array with mean inductor quality factor <inline-formula><tex-math notation="LaTeX">Q_{i} = 4.8 \times 10^{5}</tex-math></inline-formula>, aluminum inductor transition temperature <inline-formula><tex-math notation="LaTeX">T_{c} = 1.19</tex-math></inline-formula> K, and kinetic inductance fraction <inline-formula><tex-math notation="LaTeX">\alpha _{k} = 0.32</tex-math></inline-formula>. We optically characterize both the microstrip-coupled and CPW-coupled resonators, and find both have a spectral response close to prediction with an optical efficiency of <inline-formula><tex-math notation="LaTeX">\eta \sim 70\%</tex-math></inline-formula>. However, we find slightly lower optical response on the lower edge of the band than predicted, with neighboring dark detectors showing more response in this region, though at level consistent with less than 5% frequency shift relative to the optical detectors. The detectors show polarized response consistent with expectations, with a cross-polar response of <inline-formula><tex-math notation="LaTeX">\sim 10\%</tex-math></inline-formula> for both detector orientations.