  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.
