Bi-stable RF-MEMS Switched Capacitor Based on Metal-to-Metal Stiction

International audienceThis paper presents a new concept for the realization of a bi-stable RF-MEMS switched capacitor using a resistive contact. The main idea is to maintain the device in a given position using metal-to-metal stiction. The metal-to-metal contact is used only for mechanical purposes and has no electrical function. 20 Volts, 10 μsec pulses are used to switch the device from one stable position to the other. After disconnection, the device maintains its position with extremely little change over long periods. 0.06% on-state capacitance relative shift has been measured over 4 days with daily control, and lab environment closet storage. 5 minutes periodic cycling shows very little drift in both states of the RF-MEMS capacitor. Moreover, the device is fabricated using MEMS conventional processing steps permits to obtain capacitive contrast of 3

Microwave and millimeter-wave high- Q micromachined resonators

Alternative techniques for integrating high-quality factor resonators using micromachining techniques have been investigated. Two methods are presented which include suspending microstrip lines on thin dielectric membranes, resulting in an effective dielectric constant of near unity, and integrating three-dimensional micromachined waveguide cavity resonators with planar feedlines. These resonators show large improvements in quality factor over conventional techniques, and more importantly, allow for planar integration in complex systems. Resonators were fabricated in suspended microstrip at 29, 37, and 62 GHz with quality factors of over 450 with very close agreement between simulated and measured results. An integrated micromachined cavity resonator was also fabricated with a TE 011 resonance quality factor of 1117 at 24 GHz and a TE 021 resonance quality factor of 1163 at 38 GHz. To the authors' knowledge, these are the highest quality factor planar resonators without the use of superconductive materials, and can be used in microwave and millimeter-wave low-loss filters and low-phase-noise oscillators. ©1999 John Wiley & Sons, Inc. Int J RF and Microwave CAE 9: 326–337, 1999.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/35227/1/4_ftp.pd

Fibre Bragg grating photowriting in microstructured optical fibres for refractive index measurement

International audienceWe report results relating to fibre Bragg grating photowriting in two kinds of Ge-doped core microstructured optical fibre devoted to sensing applications. A cross-comparison between theoretical and experimental modal field patterns is carried out. We present the first values of the spectral sensitivity of a Bragg grating in relation to the refractive index of calibrated oils inserted into the holes

A study on controllable aluminium doped zinc oxide patterning by chemical etching for MEMS application

This present work reports on the study of controllable aluminium doped zinc oxide (AZO) patterning by chemical etching for MEMS application. The AZO thin film was prepared by RF magnetron sputtering as it is capable of producing uniform thin film at high deposition rates. X-Ray diffraction (XRD) and atomic force microscopy (AFM) characterization were done to characterize AZO thin film. The sputtered AZO thin film shows c-axis (002) orientation, low surface roughness and high crystalline quality. To pattern AZO thin film for MEMS application, wet etching was chosen due to its ease of processing with few controlling parameters. Four etching solutions were used namely: 10 % Nitric acid, 10 % Phosphoric acid, 10 % Acetic acid and Molybdenum etch solutions. For the first time, chemical etching using Molybdenum etch that consist of a mixture of CH3COOH, HNO3 and H3PO4 was characterized and reported. The effect of these acidic solutions on the undercut etching, vertical and lateral etch rate were studied. The etched AZO were characterized by scanning electron microscopy (SEM) and stylus profilometer. The investigations showed that the Molybdenum etch has the lowest undercut etching of 7.11 µm, and is highly effective in terms of lateral and vertical etching with an etch ratio of 1.30. Successful fine patterning of AZO thin films was demonstrated at device level on a surface acoustic wave resonator fabricated in 0.35 μm CMOS technology. The AZO thin film acts as the piezoelectric thin film for acoustic wave generation. Patterning of the AZO thin film is necessary for access to measurement probe pads. The working acoustic resonator showed resonance peak at 1.044 GHz at 45.28 dB insertion loss indicating that the proposed Molybdenum etch method does not adversely affect the device’s operating characteristic

Finished Genome of the Fungal Wheat Pathogen Mycosphaerella graminicola Reveals Dispensome Structure, Chromosome Plasticity, and Stealth Pathogenesis.

The plant-pathogenic fungus Mycosphaerella graminicola (asexual stage: Septoria tritici) causes septoria tritici blotch, a disease that greatly reduces the yield and quality of wheat. This disease is economically important in most wheat-growing areas worldwide and threatens global food production. Control of the disease has been hampered by a limited understanding of the genetic and biochemical bases of pathogenicity, including mechanisms of infection and of resistance in the host. Unlike most other plant pathogens, M. graminicola has a long latent period during which it evades host defenses. Although this type of stealth pathogenicity occurs commonly in Mycosphaerella and other Dothideomycetes, the largest class of plant-pathogenic fungi, its genetic basis is not known. To address this problem, the genome of M. graminicolawas sequenced completely. The finished genome contains 21 chromosomes, eight of which could be lost with no visible effect on the fungus and thus are dispensable. This eight-chromosome dispensome is dynamic in field and progeny isolates, is different from the core genome in gene and repeat content, and appears to have originated by ancient horizontal transfer from an unknown donor. Synteny plots of the M. graminicola chromosomes versus those of the only other sequenced Dothideomycete, Stagonospora nodorum, revealed conservation of gene content but not order or orientation, suggesting a high rate of intra-chromosomal rearrangement in one or both species. This observed “mesosynteny” is very different from synteny seen between other organisms. A surprising feature of the M. graminicolagenome compared to other sequenced plant pathogens was that it contained very few genes for enzymes that break down plant cell walls, which was more similar to endophytes than to pathogens. The stealth pathogenesis of M. graminicola probably involves degradation of proteins rather than carbohydrates to evade host defenses during the biotrophic stage of infection and may have evolved from endophytic ancestors

Surgimiento del capitalismo en El Salvador

De 1864 a 1896, se operó un cambio en las relaciones de producción. La case totalidad del intercambio mercantil externo se efectuó a través de intermediarios españoles, Inglaterra, Holanda y Francia, pugnaban por alcanzar un trato directo con las Indias y lo consiguieron cuando el poder político-militar se debilitó después del tratado de Utrecht. Los esfuerzos del gobierno de El Salvador se encaminaron a fomentar la producción de gran variedad de plantas, con valor potencial como productos de exportación. Se les permitió a los productores recibir un tratamiento preferencial. Aumentó la producción exportable del café, que desplazó al añil. Antes, en la primera mitad del s. XIX los ingleses habían logrado el monopolio del comercio del añil salvadoreño

Systèmes lasers intégrant des micro-miroirs déformables a base de MEMS optiques

This work deals with the integration of MEMS (Micro- Electro- Mechanical- System) in fibre laser systems in order to generate short pulses. Q-switching short laser cavities associated with these components produces pulses in the nanosecond regime. These deformable micro-mirrors reached modulation frequencies upper than one megahertz, giving access to mode-locking in fibre laser sources. This new fibre laser system showed MOEMS capability to replace more famous modulators, as acousto-optic or electro-optic ones. They offer a good potential in miniaturization and cost reduction of pulsed fibre laser sources.LIMOGES-BU Sciences (870852109) / SudocSudocFranceF