The Detection of Defects in a Niobium Tri-layer Process

Niobium (Nb) LTS processes are emerging as the technology for future ultra high-speed systems especially in the digital domain. As the number of Josephson Junctions (JJ) per chip has recently increased to around 90000, the quality of the process has to be assured so as to realize these complex circuits. Until now, very little or no information is available in the literature on how to achieve this. In this paper we present an approach and results of a study conducted on an RSFQ process. Measurements and SEM inspection were carried out on sample chips and 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 yield analysis and the determination of the probability distribution of faults in the process. A test chip has been designed, based on the results of this study, and certain types of defects were introduced in the design to study the behavior of faulty junctions and interconnections

Testable Design and Testing of High-Speed Superconductor Microelectronics

True software-defined radio cellular base stations require extremely fast data converters, which can not currently be implemented in semiconductor technology. Superconductor niobium-based delta ADCs have shown to be able to perform this task. The problem of testing these devices is a severe task, as very little is known about possible defects in this technology. This paper shows an approach for gaining information on these defects and illustrates how BIST can be a solution of detecting defects in ADCs under extreme conditions

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

Defect Based Testing of Superconductor Electronics

Recent advances in computing and telecommunication technologies require ultra-highspeed and high-precision devices in the digital domain for their realization. The clock frequencies of semiconductor devices have increased beyond expectations, but will not be able to solve the above-mentioned problems in the near future. At this point, superconductor electronics (SCE) technology is a promising candidate as the theoretical limits are around one Terahertz. The fastest digital device built in this technology, a 770 GHz Toggle flip-flop, proves that SCE is capable of overcoming the challenges

Loss of teeth and enamel in tetrapods: fossil record, genetic data and morphological adaptations

Since their recruitment in the oral cavity, approximately 450 million years ago, teeth have been subjected to strong selective constraints due to the crucial role that they play in species survival. It is therefore quite surprising that the ability to develop functional teeth has subsequently been lost several times, independently, in various lineages. In this review, we concentrate our attention on tetrapods, the only vertebrate lineage in which several clades lack functional teeth from birth to adulthood. Indeed, in other lineages, teeth can be absent in adults but be functionally present in larvae and juveniles, can be absent in the oral cavity but exist in the pharyngeal region, or can develop on the upper jaw but be absent on the lower jaw. Here, we analyse the current data on toothless (edentate) tetrapod taxa, including information available on enamel-less species. Firstly, we provide an analysis of the dispersed and fragmentary morphological data published on the various living taxa concerned (and their extinct relatives) with the aim of tracing the origin of tooth or enamel loss, i.e. toads in Lissamphibia, turtles and birds in Sauropsida, and baleen whales, pangolins, anteaters, sloths, armadillos and aardvark in Mammalia. Secondly, we present current hypotheses on the genetic basis of tooth loss in the chicken and thirdly, we try to answer the question of how these taxa have survived tooth loss given the crucial importance of this tool. The loss of teeth (or only enamel) in all of these taxa was not lethal because it was always preceded in evolution by the pre-adaptation of a secondary tool (beak, baleens, elongated adhesive tongues or hypselodonty) useful for improving efficiency in food uptake. The positive selection of such secondary tools would have led to relaxed functional constraints on teeth and would have later compensated for the loss of teeth. These hypotheses raise numerous questions that will hopefully be answered in the near future