A Novel Piezoelectric Microtransformer for Autonmous Sensors Applications

This work relates to a novel piezoelectric transformer to be used in an autonomous sensor unit, possibly in conjunction with a RF-MEMS retro-modulator.Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/handle/2042/16838

Electrostatically-Driven Resonator on Soi with Improved Temperature Stability

This paper deals with a single-crystal-silicon (SCS) MEMS resonator with improved temperature stability. While simulations have shown that the temperature coefficient of resonant frequency can be down to 1 ppm/degrees C, preliminary measurements on non-optimised structures gave evidence of a temperature coefficient of 29 ppm/degrees C. Design, optimisation, experimental results with post process simulation and prospective work are presented.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

Surface Conditioning Effect on Vacuum Microelectronics Components Fabricated by Deep Reactive Ion Etching

Advances in material processing such as silicon micromachining are opening the way to vacuum microelectronics. Two-dimensional vacuum components can be fabricated using the microsystems processes. We developed such devices using a single metal layer and silicon micromachining by DRIE. The latter technological step has significant impact on the characteristics of the vacuum components. This paper presents a brief summary of electron emission possibilities and the design leading to the fabrication of a lateral field emission diode. First measurement results and the aging of the devices are also discussed.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

Wideband Mid Infrared Absorber using surface Doped Black Silicon

Black silicon (BSi) is a synthetic nanomaterial with high aspect ratio nano protrusions inducing several interesting properties such as a very large absorptivity of incident radiation. We have recently shown that heavily doping the BSi in volume enables to significantly enhance its mid infrared absorptivity and tune its spectral range of interest up to 20 micrometer. In the present letter, we explore the effect of surface doping on BSi radiative properties and it absorptance, in particular since surface doping enables reaching even larger dopant concentrations than volume doping but at more limited penetration depths. We considered 12 different wafers of BSi, fabricated with cryogenic plasma etching on n and p-type silicon wafers and doped using ion-implantation with different dopant types, dosages and ion beam energies leading to different dopant concentrations and profiles. The different wafers radiative properties, reflectance, transmittance and absorptance, are measured using Fourier transform infrared spectroscopy. We show that doping an n-type BSi wafer with Phosphorous with a dose of 10^17 atm/cm2 and an energy of 100 keV increases its absorptivity up to of 98% in the spectral range of 1-5 micrometer. We propose a simple phenomenological explanation of the observed results based on the dopant concentration profiles and the corresponding incident radiation penetration depth. Obtained results provide simple design rules and pave the way for using ion-implanted BSi for various applications such as solar energy harvesting, thermo-photovoltaics and infrared radiation sensing where both high absorptance and variable dopant concentration profiles are required

Étude et caractérisation des propriétés d'absorption électromagnétique du silicium micro/nano-structuré

Cette thèse porte sur une étude expérimentale et théorique de surfaces micro-structurées de silicium, obtenues par traitement dans un plasma SF6/02 à des températures cryogéniques. La texturation qui résulte de ce traitement confère à ces surfaces des propriétés remarquables. L'une d'entre elles est la capacité de piéger et absorber la lumière, qui se traduit par une couleur noire de ces surfaces, d'où l'appellation Black Silicon. Cette propriété qu'on retrouve dans la gamme spectrale du visible et du proche infra-rouge, présente un intérêt particulier pour la conversion d'énergie solaire, aussi bien par voie photovoltaïque que par voie photo-thermique. L'étude que nous avons menée a toutefois porté sur une gamme spectrale plus large, s'étendant jusqu'aux Térahertz. A cet effet, différentes techniques de caractérisation spectrales ont été mises en œuvre. L'analyse des résultats a été effectuée également au moyen de simulations électromagnétiques. Des corrélations ont été mises en évidence entre les propriétés optiques et les caractéristiques morphologiques des surfaces micro-structurées. L'analyse d'images prises au microscope électronique a permis d'esquisser une théorie pour tenter d'expliquer le mécanisme de formation des microstructures de Black Silicon. Enfin, un microcomposant a été réalisé en vue de mettre en œuvre le premier volet applicatif de ce travail. Il s'agit d'un dispositif de conversion photo-thermique qui incorpore des thermo-résistances en platine sur une surface de Black Silicon réalisée sur une membrane thermiquement isoléeThis thesis deals with an experimental and theoretical study of micro-structured silicon surfaces, obtained by processing in SF6/02 plasma at cryogenic temperatures. Texturing which results from this treatment gives remarkable properties to these surfaces. One of them is the ability to trap and absorb light, resulting in a black color of the surface, hence the name of Black Silicon. This property that we find in the visible and near infrared spectral ranges, is of particular interest for solar energy conversion, both through photovoltaic and photo-thermal means. The study that we conducted, however, covered a much wider spectral range, extending to the Terahertz. For this purpose, different spectral characterization techniques have been implemented. Analysis of the results was also done using electromagnetic simulations. Correlations were found between the optical and morphological characteristics of micro-structured surfaces. The analysis of images taken by electron microscopy allowed sketching a theory attempting to explain the mechanism of formation of the microstructures of Black Silicon. Finally, a micro-component has been fabricated towards implementing the first part of this application work. It is a photo-thermal conversion device that incorporates platinum thermo-resistance on a surface of Black Silicon, realized on a thermally insulated Silicon membranePARIS-EST-Université (770839901) / SudocSudocFranceF

Sensitivity optimization of micro-machined thermo-resistive flow-rate sensors on silicon substrates

We report on an optimized micro-machined thermal flow-rate sensor as part of an autonomous multi-parameter sensing device for water network monitoring. The sensor has been optimized under the following constraints: low power consumption and high sensitivity, while employing a large thermal conductivity substrate, namely silicon. The resulting device consists of a platinum resistive heater deposited on a thin silicon pillar ~ 100 $\mu$m high and 5 $\mu$m wide in the middle of a nearly 100 $\mu$m wide cavity. Operated under the anemometric scheme, the reported sensor shows a larger sensitivity in the velocity range up to 1 m/s compared to different sensors based on similar high conductivity substrates such as bulk silicon or silicon membrane with a power consumption of 44 mW. Obtained performances are assessed with both CFD simulation and experimental characterization

Wall Slip of Soft-Jammed Systems: A Generic Simple Shear Process

International audienceFrom well-controlled long creep tests we show that the residual apparent yield stress observed with soft-jammed systems along smooth surfaces is an artefact due to edge effects. By removing these effects we can determine the stress solely associated with steady state wall slip below the material yield stress. This stress is found to vary linearly with the slip velocity for a wide range of materials whatever the structure, the interaction types between the elements and with the wall, and the concentration. Thus wall slip results from the laminar flow of some given free liquid volume remaining between the (rough) jammed structure formed by the elements, and the smooth wall. This phenomenon may be described by the simple shear flow in a Newtonian liquid layer of uniform thickness. For various systems this equivalent thickness varies in a narrow range (35 ± 15 nm)