Superconductive thin-film devices for microwave applications

At IEN, two types of superconductive microwave sensors have been developed. Nb microbridge bolometers, working in the frequency range between 26 and 40 GHz, have been fabricated on polyimide substrates. For these devices we have measured a responsivity of 7 x 103 V/W. With a careful choice of device parameters, it is possible to achieve a noise equivalent power (NEP) of about 10 -12 W/VHZ, 3 orders of magnitude lower than that obtained with conventional bolometers. SIS mixers for radioastronomical observations at 94 GHz based on Nb/Al-AlOj./Nb Josephson tunnel junctions have been also realized. Josephson junctions, both single and two junctions stacks, have been fabricated using a SNAP process where liquid anodization is used not only for insulation and area patterning, but also for trimming the junction dimensions at a micrometer level. In order to use these junctions as SIS mixers for astrophysical observations at 94 GHz and possibly at higher frequencies, we have fabricated junctions with an area of a few square micrometer and current densities up to 10' A/cm2. The junctions are integrated with a low-pass filter made with a stripline technique, designed by means of a 3D electromagnetic simulator. The reflection coefficient of the filter has been evaluated to be 0.2 in the best case. © Società Italiana di Fisica.