Fabrication of a Nb-Based 180-Degree IF Hybrid for Balanced SIS Mixers

180-degree IF hybrids are potentially useful for balanced superconductor-insulator-superconductor (SIS) mixers. We have developed a compact Nb-based 180-degree hybrid for 4-12 GHz which addresses concerns of element size, ohmic loss, and IF bandwidth. The fabrication scheme developed for these elements will be discussed, including the use of a thin overlayer Au process for via contacts, RF diode sputtered SiO_x in lieu of sublimated SiO_x films in order to improve the wafer yield, and diagnostic Nb capacitors to evaluate these SiO_x films. Experimental results will be presented and compared with simulations of these lumped element transmission line "rat-race" hybrids. It should be noted that the hybrids can be used in cryogenic balanced mixers for any RF band.