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

摘要

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驴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 ${rm SiO}_{rm x}$ in lieu of sublimated SiO films in order to improve the wafer yield, and diagnostic Nb capacitors to evaluate these ${rm SiO}_{rm x}$ films. Experimental results will be presented and compared with simulations of these lumped element transmission line 驴rat-race驴 hybrids. It should be noted that the hybrids can be used in cryogenic balanced mixers for any RF band.