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No description available.

Achieving the utmost reliability of power semiconductors is an ongoing challenge for the scientists and engineers in the packaging community of the industry and research institutions. Still the semiconductor and therefore the function of the power module could live longer, when only the bonding and joining technologies would be more stable against power and temperature cycling wearout. In particular, the conventional electrical connection to the top and bottom surface of the semiconductor is limiting the lifetime due to degradation. For both, the solder layer under the backside and the Al-wire on the topside of the die, it is necessary to develop new contact technologies, as the substitution of just one connection does not perform the required reliability of the module. In this work, different new technologies for power modules were evaluated and an own development is presented. Especially the new development is characterized by an outstanding reliability while keeping the design flexibility of the currently applied methods. To achieve that, the solder joints were replaced by Ag-sintered connections and Cu-wires were bonded as a substitute of Al-wires. This new approach is called DBB-Technology („Danfoss BondBuffer“) and is demonstrated in the example of a 1700V DBB power module. With the help of this technology sintering creates two joints: One between the bottom of die and the substrate and between the die and a thin Cu-foil, which is located on top. This Cu foil (BondBuffer) enables the Cu-bond process as top contact technology without damaging the semiconductor. The DBB Cu foil acts as an absorber for the high bond-forces. The detailed characterization of a DBB-covered semiconductor module reveals an extraordinary high reliability improvement, enhanced thermal impedance and upgraded electrical properties. / Leistungsmodule unterliegen in der Anwendung vielfältigen, kombinierten Beanspruchungen, die je nach Anwendung eine Herausforderung an unterschiedliche Verbindungsstellen im Modul darstellen. Die Betriebsdauer eines Leistungsmoduls wird im Wesentlichen von den halbleiternahen Aufbau- und Verbindungstechniken limitiert. Das geht z.B. aus umfangreichen Lastwechseluntersuchungen hervor, in denen als Fehlermechanismen die Zerrüttung des Lots unter dem Chip oder das Abheben des Aluminium-Bonddrahts vom Halbleiter identifiziert wurden. Die einzelnen Verbindungsschichten im Leistungsmodul bilden eine Funktionskette, die beim Ausfall nur eines Gliedes die gesamte Funktionalität verliert. Maßnahmen zur Optimierung einzelner Schichten, z. B. der Halbleiter-Substrat-Verbindung oder nur der oberseitigen Chipkontaktierung, bringen alleinstehend also nicht den gewünschten Erfolg. In dieser Arbeit werden unterschiedliche Aufbaukonzepte leistungselektronischer Module aus Fachveröffentlichungen verglichen, bevor das eigene Konzept beschrieben wird. Die Lösung basiert dabei auf innovativen und sehr robusten Fügetechnologien, die gezielt herkömmliche Verbindungen im Aufbau ersetzen. Das Ergebnis ist ein Leistungsmodul mit verbesserten thermischen, elektrischen und thermo-mechanischen Eigenschaften. Eine wesentliche Rolle spielt dabei das Silbersintern als Alternative zum Löten. Dank der Sintertechnik geht der Halbleiter eine hochfeste Verbindung mit dem Substrat ein. Darüber hinaus ermöglicht die Sintertechnologie das stoffschlüssige Verbinden einer dünnen Kupferfolie mit der oberen Halbleitermetallisierung. Diese Kupferfolie ist erforderlich, um das Cu-Drahtbonden für die oberseitige Kontaktierung der Halbleiter anzuwenden, ohne diesen aufgrund hoher Bondkräfte zu zerstören. Dank der vorteilhaften Materialeigenschaften ist die Cu-Bondverbindung deutlich leistungsfähiger als eine Al-Bondverbindung. Diese Kombination aus robusten Fügestellen trägt den Namen DBB-Technologie („Danfoss BondBuffer“) und soll zukünftig dank der Verfügbarkeit sinterbarer Halbleiter in hochzuverlässigen Leistungsmodulen angewendet werden.

Gold-based catalysts can be replaced with platinum group catalysts in catalytic automotive exhaust aftertreatment if their thermal stability and durability issues can be resolved. Hence, one of the potential markets for gold catalysis is the automotive after treatment market, our interest is to synthesize a gold-based catalyst which has practical applications in automotive industry specifically for diesel-methane dual fuel low-temperature combustion strategy where the exhaust temperature is varying from ~ 200 to400° C. Our research focused on synthesizing a bimetallic gold-copper catalyst which is not only highly active for CO oxidation reaction but also sinter-resistant at temperatures normally observed at LTC engine exhaust. The Au-Cu@SiO2 catalyst exhibited excellent efficacy for CO oxidation with >95% conversion to CO2 achieved at 300 °C. While the presence of Cu enhanced CO conversion at low to intermediate temperatures (50-300 °C), silica encapsulation of the Au-Cu nanocomposites facilitated for remarkable stability of the catalyst. Moreover, the catalyst exhibited remarkable stability at high reaction temperatures which could be attributed to the SiO2 encapsulation of nanoparticles. The activity and stability of Au-Cu@SiO2 catalyst are suitable for its application in automotive after treatment devices, especially in low-temperature combustion engine exhaust.

A thermo-mechanical finite element model is developed to determine the temperature history and residual stresses in a Cu-H13 thin-walled plate deposited by the Laser Engineered Net Shaping (LENSTM) process. The same model is also applied to a H13-H13 sample to compare the results. The input laser power is adjusted to maintain a steady molten pool size and depth. For a constant scanning speed the laser power decreases with the addition of more layers, and with the increase of scanning speed the laser power needs to be increased. The Z-component of residual stresses is greater than the other components, and is compressive near the center of the wall and tensile at the free edges. The residual stress levels near the free edges are higher in the H13-H13 sample than in the Cu-H13 sample. In these regions, the use of unidirectional scanning results in a higher stress accumulation than the alternating scanning.

The increasing production of natural gas liquids attracts both academia and industry to develop on-purpose techniques converting those light alkanes to value-added chemicals. Dehydroaromatization is an alternative path for light alkane conversion to produce aromatics but still lacks active and stable catalysts. This work aims at the development of efficient dehydroaromatization catalysts by tuning the metal/acid bifunctionality of the Pt/HZSM-5 catalyst. Additionally, through co-processing light alkane with ammonia during the dehydroaromatization process, this study also proposes a new reaction system that could directly link the C-N bond for nitrile synthesis. The results suggested that the activity, selectivity, and stability of the monometallic Pt/HZSM-5 catalyst are highly dependent upon the Pt loading, the limit loading of 100 ppm is required to maintain sufficient metal functionality. To further minimize the Pt loading, the chemical properties of the Pt species were tuned by a second metal such as Zn or Cu. Consequently, the activity and stability of the catalyst are enhanced by orders of magnitude and the maximized metal functionality was achieved at Pt loading of 10 ppm. Characterizations show that Pt can be atomically dispersed as a hybrid [Pt1-Zn6] cluster in the Pt-Zn@HZSM-5 or forming single atom alloy type [Pt1-Cu4] ensembles in the Pt-Cu@HZSM-5. Specifically, the initial turnover frequencies of propane and ethane to BTX are up to 178.8 and 128.7 s-1 over the Pt-Cu@HZSM-5, up to 3-4 orders of magnitude higher than the state-of-the-art Pt-based catalyst. Furthermore, the deactivated catalyst can be continuously regenerated, demonstrating excellent stability of such a catalyst under hash oxidation conditions for coke burn-off. A new catalytic system named ammodehydrogenation (ADeH) for ethane selective conversion to acetonitrile, ethylene, and hydrogen over a bifunctional catalyst is proposed. Ethane ADeH over the Pt/HZSM-5 catalyst is active at low temperatures and atmospheric pressure for CH3CN production. The Pt/HZSM-5 shows high coke-resistibility during the ethane ADeH due to the strong interaction of NH3 with the acid sites of the catalyst. The catalyst can be further optimized by adding Co, the Pt-Co/HZSM-5 catalyst on ethane ADeH indicating that an appropriate balance between the metal and acid functionalities is critical for ethane ADeH.

No description available.

No description available.

No description available.

Surface and grain boundary electron scattering contribute significantly to resistivity as the dimensions of polycrystalline metallic conductors are reduced to, and below, the electron mean free path. A quantitative measurement of the relative contributions of surface and grain boundary scattering to resistivity is very challenging, requiring not only the preparation of suitably small conductors having independent variation of the two relevant length scales, namely, the sample critical dimension and the grain size, but also independent experimental quantification of these two length scales. In most work to date the sample grain size has been either assumed equal to conductor dimension or measured for only a small number of grains. Thus, the quantification of the classical size effect still suffers from an uncertainty in the relative contributions of surface and grain boundary scattering. In this work, a quantitative analysis of both surface and grain boundary scattering in Cu thin films with independent variation of film thickness (27 nm to 158 nm) and grain size (35 nm to 425 nm) in samples prepared by sub-ambient temperature film deposition followed by annealing is reported. Film resistivities of carefully characterized samples were measured at both room temperature and at 4.2 K and were compared with several scattering models that include the effects of surface and grain boundary scattering. Grain boundary scattering is found to provide the strongest contribution to the resistivity increase. However, a weaker, but significant, role is also observed for surface scattering. Several of the published models for grain boundary and surface scattering are explored and the Matthiessen's rule combination of the Mayadas and Shatzkes' model of grain boundary scattering and Fuchs and Sondheimer's model of surface scattering resistivity contributions is found to be most appropriate. It is found that the experimental data are best described by a grain boundary reflection coefficient of 0.43 and a surface specularity coefficient of 0.52. This analysis finds a significantly lower contribution from surface scattering than has been reported in previous works, which is in part due to the careful quantitative microstructural characterization of samples performed. The data does suggest that there is a roughness dependence to the surface scattering, but this was not conclusively demonstrated. Voids and impurities were found to have negligible impact on the measured resistivities of the carefully prepared films.