1,720,975 research outputs found
Influence of beam geometry on the dielectric charging of RF MEMS switches
No full textThis paper reports on the evolution of electromechanical properties of dielectric-less RF MEMS switches under long-term stress conditions. Two different designs, one based on a clamped-clamped air bridge and the other on a cantilever beam, are characterized and compared by monitoring pull-in and pull-out voltages after a long-time application of different bias voltages. Results show that the beam shape assumed after the snap-down may affect the lifetime of the switch
Influence of temperature on the actuation voltage of RF-MEMS switches
No full textMost of the actual applications for RF-MEMS switch require high reliability, but consolidated qualification procedures are still lacking. This paper focuses, in particular, on the role of temperature on the switch reliability from a mechanical point of view, showing how this depends on the switch architecture and membrane material. Double clamped switches are sensitive to buckling, and this is the factor limiting their operational temperature, even though the range exploitable can be wide enough for many applications. Residual stress and thermal expansion coefficient of the mobile membrane are the most important parameters to understand and control this phenomenon. Cantilever switches are less influenced by the temperature in their performances, and have a much wider operational range. Other temperature-related factors are affecting the switch reliability in this case, such as elastic modulus variation, dielectric charging effects and creep
Modeling of gold microbeams as strain and pressure sensors for characterizing MEMS packages
No full textThis work presents the modeling of gold microbeams for characterizing Micro-electro-mechanical systems (MEMS) packages in terms of both strains induced to the MEMS devices and hermetic sealing capability. The proposed test structures are based on arrays of rectangular shaped clamped-free and clamped–clamped beams, to be realized with a film of electroplated gold by surface micromachining technology. The resonant frequency of the microbeams is modeled by FEM simulations as a function of substrate deformations, which could be induced by the package. Clamped–clamped bridges show a linear change of the square of the resonant frequency in case of in-plane deformations, in fairly good agreement with an approximate analytical model. Cantilever beams are modeled as variable capacitors to detect out-of-plane deformations. Finally, an analytical model to study cantilever beams as resonators for detecting pressure changes is discussed and compared with preliminary experimental results, showing an impact on the quality factor in a range from 0.01 mbar to 1 bar
A Wide Tuning Range MEMS Varactor Based on a Toggle Push-Pull Mechanism
No full textThis paper presents a novel wide tuning range MEMS varactor based on a toggle push – pull mechanism for high RF power applications and improved reliability. The device anchoring utilizes a torsion spring mechanism which virtually allows for a full capacitance tuning range. Improved mechanical stability is also provided by the actively controlled pull-out implementation that is realized without increasing the MEMS manufacturing complexity. As a proof of concept, a toggle MEMS varactor has been modeled, designed and manufactured in shunt configuration on a 50 coplanar transmission line. Analytical and full wave electromechanical models are provided as well as electromagnetic characterization. The device has been manufactured on HR Silicon substrate by using the standard FBK-irst RF MEMS process. Optical profile, DC and RF measurements are presented in the 0-40 GHz frequency band. Excellent RF performance as well as a capacitance tuning ratio of 2.5 has been obtained
RF-MEMS switch design optimization for long-term reliability
No full textThis contribution presents an optimization strategy for the mechanical and geometrical characteristics of clamped-clamped RF-MEMS switches in order to enhance their reliability performances both in terms of switch properties control and long-term stress actuation tests. Experimental measurements demonstrated that the optimized version of the capacitive switch investigated shows an improved resistance to high bias voltage, while the optimized ohmic switch shows a lower and more reproducible contact resistance
Una procedura per la stima degli effetti dell`incertezza di processo sulle prestazioni di dispositivi RF-MEMS
No full textL’utilizzo di dispositivi Micro-Elettro-Meccanici (MEMS) in sistemi a Radio Frequenza (RF) è da tempo oggetto di studio da parte della comunità scientifica internazionale al fine di progettare ricetrasmettitori radio riconfigurabili, ossia adattabili dinamicamente ai requisiti di diversi standard di comunicazione [1]. L’idea di realizzare componenti circuitali a parametri concentrati di tipo RFMEMS è motivato dall’alto fattore di merito, dalle basse perdite e dalla buone prestazioni in termini di linearità di condensatori variabili, induttori e micro-interruttori (switch) implementati in tali tecnologie. Tuttavia, la scarsa maturità delle tecniche per la realizzazione di dispositivi RF-MEMS fa sì che variazioni anche minime di alcuni passi del processo di fabbricazione portino ad alterazioni significative delle caratteristiche dei componenti, con un conseguente deterioramento delle loro prestazioni. Questi problemi sono ulteriormente aggravati dalla dimensione multifisica dei sistemi RF-MEMS, la cui ottimizzazione elettromeccanica ed elettromagnetica spesso richiede modelli assai sofisticati capaci di descrivere non solo il comportamento di una data classe di dispositivi, ma anche le non idealità dovute allo specifico processo tecnologico adottato per realizzarli. Ad esempio, è ben noto che piccole variazioni delle proprietà elastiche di uno strato di metallo sottile possono influenzare notevolmente le caratteristiche RF di condensatori variabili [2]. In questo contesto, i ricercatori dell’Unità di Trento, in stretta collaborazione con quelli del gruppo MemSRaD della Fondazione Bruno Kessler (FBK) di Trento e con il supporto del Dipartimento di Elettrofisica della Technische Universität München (TUM), hanno messo a punto una procedura sperimentale per stimare il valore efficace di alcuni dei parametri che maggiormente influenzano le prestazioni elettromeccaniche ed elettromagnetiche di strutture RF-MEMS. In particolare, l’attenzione dei ricercatori si è concentrata soprattutto sulla stima di quei parametri di progetto che sono particolarmente sensibili alle incertezze del processo tecnologico impiegato. La procedura proposta è stata validata sperimentalmente su un campione omogeneo di dispositivi RF-MEMS e pone le basi per estrarre i parametri efficaci legati alle proprietà dei materiali e non alla specifica geometria dei componenti considerati. Lo scopo ultimo è quello di fornire ai progettisti di dispositivi e reti RF-MEMS un insieme di valori che, una volta scelta la tecnologia da utilizzare, consenta loro di ottimizzare un certo layout ottenendo caratteristiche sperimentali il più possibile simili a quelle simulate in fase di progettazione
35 GHz Analog Phase shifter based on push-pull Toggle MEMS Varactor
No full textThis paper presents the design of two 35 GHz analog MEMS phase shifters to be integrated in reconfigurable reflectarrays. The proposed devices consist of distributed MEMS transmission lines (DMTL) periodically loaded by shunt highly – tunable MEMS varactors. The MEMS varactor exploits a torsion spring anchoring to provide a toggle push – pull mechanism, which allows the
device to have a virtually full travel range. A toggle varactor prototype has been electromechanically modeled and manufactured at FBK. The electromagnetic model has also been developed on the basis of the varactor’s measured response and the fitted capacitance values have been used for the design of the phase shifter unit cell. RF full–wave simulations of the phase shifters are presented showing very high RF performance as well as small space occupation allowing their integration in electronically steerable reflectarrays
Modeling of gold microbeams for characterizing MEMS packages
No full textModeling of gold microbeams for characterizing MEMS packaging solutions in terms of strains induced to the MEMS devices as well as hermetic sealing capability is presented. The proposed test structures are meant to be manufactured by the surface micromachining front-end technology available at FBK. They are based on arrays of rectangular-shaped cantilever beams as well as clamped-clamped bridges, with a width of 20 μm and a length ranging from 100 to 400 μm, to be realized by a 2 μm thick film of electroplated gold. The resonant frequency of the microbeams is modeled by FEM simulations as a function of substrate deformations, which could be induced by the package. Clamped-clamped bridges show a linear change with respect to the square of the resonant frequency up to 1800 ppm/μstrain in case of in-plane deformations. The impact of temperature excursions is also simulated, in order to use these structures for assessing thermally induced deformations. Cantilever beams are modeled as variable capacitors to detect out-of-plane deformations. Finally, both an analytical model and FEM simulations are used to study cantilever beams as resonators for detecting pressure changes, showing an impact on the quality factor in a range from 1-2 bar down to 10^-3-10^-2 mbar
Contact Modeling of RF MEMS Switches Based On FEM Simulations
No full textThis paper presents an approach in modeling RF MEMS switches based on FEM simulations performed by means of ANSYSTM software. A two-steps simulation procedure will be introduced, consisting of a structural analysis involving contact elements and a coupled-domains analysis aiming at evaluating the combined effect of pressure, voltage and temperature. The key steps useful to perform both the kind of simulation will be highlighted
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