Silicon on Nothing Mems Electromechanical Resonator

The very significant growth of the wireless communication industry has spawned tremendous interest in the development of high performances radio frequencies (RF) components. Micro Electro Mechanical Systems (MEMS) are good candidates to allow reconfigurable RF functions such as filters, oscillators or antennas. This paper will focus on the MEMS electromechanical resonators which show interesting performances to replace SAW filters or quartz reference oscillators, allowing smaller integrated functions with lower power consumption. The resonant frequency depends on the material properties, such as Young's modulus and density, and on the movable mechanical structure dimensions (beam length defined by photolithography). Thus, it is possible to obtain multi frequencies resonators on a wafer. The resonator performance (frequency, quality factor) strongly depends on the environment, like moisture or pressure, which imply the need for a vacuum package. This paper will present first resonator mechanisms and mechanical behaviors followed by state of the art descriptions with applications and specifications overview. Then MEMS resonator developments at STMicroelectronics including FEM analysis, technological developments and characterization are detailed.Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/EDA-Publishing

Estimating Mean Bedload Transport Rates and Their Uncertainty

Measuring bedload transport rates usually involves measuring the flux of sediment or collecting sediment during a certain interval of time Δt. Because bedload transport rates exhibit significant non‐Gaussian fluctuations, their time‐averaged rates depend a great deal on Δt. We begin by exploring this issue theoretically within the framework of Markov processes. We define the bedload transport rate either as the particle flux through a control surface or as a quantity related to the number of moving particles and their velocities in a control volume. These quantities are double averaged; that is, we calculate their ensemble and time averages. Both definitions lead to the same expression for the double‐averaged mean rate and to the same scaling for the variance's dependence on the length of the sampling duration Δt. These findings lead us to propose a protocol for measuring double‐averaged transport rates. We apply this protocol to an experiment we ran in a narrow flume using steady‐state conditions (constant water discharge and sediment feed rates), in which the time variations in the particle flux, the number of moving particles, and their velocities were measured using high‐speed cameras. The data agree well with the previously defined theoretical relationships. Lastly, we apply our experimental protocol to other flow conditions (a long laboratory flume and a gravel‐bed river) to show its potential across various contexts

L'acoustique picoseconde colorée (l'outil métrologique qu'attendait la technologie BAW [résonateur acoustique à onde de volume])

Cette thèse a été réalisée pour le labo-commun ST-IEMN, dans le cadre du projet industriel de STMicroelectronics visant à réaliser des résonateurs à ondes acoustiques de volume (BAW : Bulk Acoustic Wave) pour des applications de fitrage RF. A l'instar du quartz, le BAW exploite la résonance du mode d'épaisseur d'une couche piézoélectrique comprise entre deux électrodes. Pour le passage en production de ces composants le contrôle de la fréquence est un défi à relever, et il passe par une connaissance précise des paramètres mécaniques du dispositif. Pour cela, nous exploitons une technique expérimentale permettant de caractériser acoustiquement des empilements de matériaux en couches minces: l'acoustique picoseconde. Nous avons développé la particularité du montage de l'IEMN : l'accordabilité en longueur d'onde. A partir de cette spécificité, des études plus fondamentales ont donné lieu à l'élaboration de protocoles expérimentaux permettant d'augmenter le nombre de caractéristiques mesurables par acoustique picoseconde. L'exploitation de ces protocoles pour la caratérisation des matériaux liés au BAW nous a permis d'enrichir une base de données des paramètres nécessaires à la modélisation et à la conception des dispositifs. D'autre part, nous avons développé des méthodes d'analyse d'empilements complexes, qui ont pu ètre testées sur la version industrielle de la technique d'acoustique picoseconde. Nous avons finalement défini un protocole de suivi de procédé de réalisation des BAW, basé sur une métrologie par acoustique picosecondeThis PhD has been realized for the ST-IEMN Lab, in the frame of an industrial development at STMicroelectronics on Bulk Acoustic Wave (BAW) resonators. The operating principle of a BAW is based on the excitation of the thickness mode of a piezoelectric layer sandwiched between two electrodes. The control of the frequency is a challenging question for the mass production of such components, and requires a precise control of mechanical properties of the device. ln this work, we use an original experimental technique that enables the acoustic characterization of thin films stacks : colored picosecond ultrasonics. We particularly develop the specificity of the IEMN setup : the wavelegth tunability. Through fundamental studies we set up protocols and thus, increase the number of parameters that can be measured with the technique. This work enables us to feed a database ofparameters needed for the design and the modeling of the devices. We also work on complex stacks characterization, a part of the methods has been tested on the industrial version of picosecond ultrasonics. Finally we propose a metrological srategy, based on picosecond ultrasonics, in orde to assist the process of BAW resonators.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

How bar generate sediment transport pulses in gravel-bed channels

We ran flume experiments with constant water dis- charge and sediment feed rate at the inlet. Experi- ments were conducted over long times (typically 600 h). The bars migrated downstream intermittently, producing the most important pulses. When the bar position was stable for a few hours, additional pulses resulted from sediment transfer from pool to pool, in the form of sediment waves (bedload sheets)

Catégorisations politiques et transformations sociales en agriculture

Revue disponible en ligne à l'adresse : https://www.cahiersagricultures.fr/component/toc/?task=topic&id=672International audienc