PECVD SiO/sub 2/ dielectric for niobium Josephson IC process

The authors have produced high-quality SiO/sub 2/ dielectric films by plasma-enhanced chemical vapor deposition (PECVD) applicable to a Nb-based, all-refractory Josephson integrated circuit process. PECVD SiO/sub 2/ was used for two insulating layers, ground plane isolation, and resistor isolation. Evaporated SiO was retained as the last insulating layer because the relatively high temperature needed for PECVD can degrade the already fabricated Josephson junctions. A thin SiO barrier layer had to be used in order to prevent the deterioration of the critical temperature of the ground plane. A successful application has been demonstrated by the fabrication and testing of a Josephson sampler circuit which shows acceptable Josephson junction current-voltage characteristic and a time resolution of 4.9 ps measured in liquid helium.