Fabrication of antenna-coupled KID array for Cosmic Microwave Background detection

TL;DR

This paper reports the fabrication and testing of a 150GHz antenna-coupled MKID array optimized for Cosmic Microwave Background detection, highlighting its potential for large-scale CMB experiments.

Contribution

It introduces a novel antenna-coupled MKID design with a specific fabrication process suitable for large-scale CMB detection.

Findings

Successful fabrication of 150GHz MKID array

Microstrip resonators measured with expected performance

Potential for scaling to 500,000 detectors in CMB-S4

Abstract

Kinetic Inductance Detectors (KIDs) have become an attractive alternative to traditional bolometers in the sub-mm and mm observing community due to their innate frequency multiplexing capabilities and simple lithographic processes. These advantages make KIDs a viable option for the $O(500,000)$ detectors needed for the upcoming Cosmic Microwave Background - Stage 4 (CMB-S4) experiment. We have fabricated antenna-coupled MKID array in the 150GHz band optimized for CMB detection. Our design uses a twin slot antenna coupled to inverted microstrip made from a superconducting Nb/Al bilayer and SiN$_x$, which is then coupled to an Al KID grown on high resistivity Si. We present the fabrication process and measurements of SiN$_x$ microstrip resonators.