Test structures and their application in structural testing of digital RSFQ circuits

As the niobium (Nb) LTS RSFQ processes advance being the technology for future ultrahigh-speed systems in the digital domain, the quality of the process should be maintained high for a successful realization of these complex circuits. A defect-oriented testing (DOT) approach is essential so as to increase the yield of the process. Little information is available in this area and the recent increase of Josephson junctions to around 90,000 per chip requires a detailed study on this topic. In this paper we present how DOT can be applied to RSFQ circuits. As a result of a study conducted on an RSFQ process, a list of possible defects has been identified and described in detail. We have also developed test-structures for detection of the top-ranking defects, which will be used for the probability distribution of faults in the process. One of the highly probable defects will be used to elaborate the DOT technique for fault modeling and simulation purposes