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A systematic comparison between several pairs of contact materials based on an innovative methodology early developed at NOVA MEMS is hereby presented. The technique exploits a commercial nanoindenter coupled with electrical measurements, and test vehicles specially designed in order to investigate the underlying physics driving the surface-related failure modes. The study provides a comprehensive understanding of micro-contact behavior with respect to the impact of low-to medium levels of electrical current. The decrease of the contact resistance, when the contact force increases, is measured for contact pairs of soft material (Au/Au contact), harder materials (Ru/Ru and Rh/Rh contacts) and mixed configuration (Au/Ru and Au/Ni contacts). The contact temperatures have been calculated and compared to the theoretical values of softening temperature for each couple of contact materials. This threshold temperature is reached for gold, ruthenium and rhodium material, with different levels of current intensity. In spite of that, no softening behavior has been observed for mixed contact at the theoretical softening temperature of both materials. Hence, considering the sensitivity to power handling and the related failure mechanisms, namely the contact adhesion, the enhanced resilience of the bimetallic contacts Au/Ru and Au/Ni was demonstrated. Finally focusing on the temperature distribution around the hottest levels on the surface contact interface, these results have been theoretically investigated.

Micro-scale solid oxide fuel cells (µ-SOFCs) constitute a promising power generation technology for portable devices such as aerospace exploration, medical devices and consumer electronics. Fuel cell systems include several functional units providing gas reforming, electrochemical power generation, and post-combustion of unused fuel. All such units require operation at controlled temperature with appropriate gases. Although various µ-SOFC components have been demonstrated, the evaluation of the thermal balance is cumbersome, as there is no micro platform providing thermal insulation, controlled heating, temperature control, and gas exchange. Our testing platform is designed for this purpose. It consists of two sealed glass substrates with integrated platinum thermistors for heating and temperature control, and channels to supply and evacuate gases. Its fabrication is compatible with silicon chip bonding. The heating elements are thick-film platinum thermistors allowing to heat up to 700°C. Efficient thermal decoupling along the carrier allows convenient lowtemperature electrical and fluidic connections. A fluidic MEMS module -a prototype gas reformer -was bonded onto the carrier to demonstrate tight gas connections at elevated temperature. Laboratoire de Production Microtechnique (LPM) AbstractMicro-scale solid oxide fuel cells (µ-SOFCs) constitute a promising power generation technology for portable devices such as aerospace exploration, medical devices and consumer electronics. Fuel cell systems include several functional units providing gas reforming, electrochemical power generation, and post-combustion of unused fuel. All such units require operation at controlled temperature with appropriate gases. Although various µ-SOFC components have been demonstrated, the evaluation of the thermal balance is cumbersome, as there is no micro platform providing thermal insulation, controlled heating, temperature control, and gas exchange. Our testing platform is designed for this purpose. It consists of two sealed glass substrates with integrated platinum thermistors for heating and temperature control, and channels to supply and evacuate gases. Its fabrication is compatible with silicon chip bonding. The heating elements are thick-film platinum thermistors allowing to heat up to 700°C. Efficient thermal decoupling along the carrier allows convenient low-temperature electrical and fluidic connections. A fluidic MEMS module -a prototype gas reformer -was bonded onto the carrier to demonstrate tight gas connections at elevated temperature.

Low temperature micro-solid oxide fuel cell (micro-SOFC) systems are an attractive alternative power source for small-size portable electronic devices due to their high energy efficiency and density. Here, we report on a thermally self-sustainable reformer -micro-SOFC assembly. The device consists of a micro-reformer bonded to a silicon chip containing 30 micro-SOFC membranes and a functional glass carrier with gas channels and screenprinted heaters for start-up. Thermal independence of the device from the externally powered heater is achieved by exothermic reforming reactions above 470 °C. The reforming reaction and the fuel gas flow rate of the n-butane/air gas mixture controls the operation temperature and gas composition on the micro-SOFC membrane. In the temperature range between 505 °C and 570 °C, the gas composition after the micro-reformer consists of 12 vol.% to 28 vol.% H 2 .An open-circuit voltage of 1.0 V and maximum power density of 47 mW cm -2 at 565 °C is achieved with the on-chip produced hydrogen at the micro-SOFC membranes.

An integrated system of a microreformer and a carrier allowing for syngas generation from liquefied petroleum gas (LPG) for micro-SOFC application is discussed. The microreformer with an overall size of 12.7 mm 6 12.7 mm 6 1.9 mm is fabricated with micro-electro-mechanical system (MEMS) technologies. As a catalyst, a special foam-like material made from ceria-zirconia nanoparticles doped with rhodium is used to fill the reformer cavity of 58.5 mm 3 . The microreformer is fixed onto a microfabricated structure with built-in fluidic channels and integrated heaters, the so-called functional carrier. It allows for thermal decoupling of the cold inlet gas and the hot fuel processing zone. Two methods for heating the microreformer are compared in this study: a) heating in an external furnace and b) heating with the two built-in heaters on the functional carrier. With both methods, high butane conversion rates of 74%-85% are obtained at around 550 uC. In addition, high hydrogen and carbon monoxide yields and selectivities are achieved. The results confirm those from classical lab reformers built without MEMS technology (N. Hotz et al., Chem. Eng. Sci., 2008, 63, 5193; N. Hotz et al., Appl. Catal., B, 2007, 73, 336). The material combinations and processing techniques enable syngas production with the present MEMS based microreformer with high performance for temperatures up to 700 uC. The functional carrier is the basis for a new platform, which can integrate the micro-SOFC membranes and the gas processing unit as subsystem of an entire micro-SOFC system.