Reliability of RF MEMS capacitive and ohmic switches for space redundancy configurations

In this paper RF MEMS switches in coplanar waveguide (CPW) configuration designed for redundancy space applications have been analyzed, to demonstrate their reliability in terms of microwave performances when subjected to DC actuations up to one million cycles. As a result, both the investigated structures fulfill the current electrical requirements expected for redundancy logic purposes

Optical properties of structurally-relaxed Si/SiO2_2 superlattices: the role of bonding at interfaces

We have constructed microscopic, structurally-relaxed atomistic models of Si/SiO$_2$ superlattices. The structural distortion and oxidation-state characteristics of the interface Si atoms are examined in detail. The role played by the interface Si suboxides in raising the band gap and producing dispersionless energy bands is established. The suboxide atoms are shown to generate an abrupt interface layer about 1.60 \AA thick. Bandstructure and optical-absorption calculations at the Fermi Golden rule level are used to demonstrate that increasing confinement leads to (a) direct bandgaps (b) a blue shift in the spectrum, and (c) an enhancement of the absorption intensity in the threshold-energy region. Some aspects of this behaviour appear not only in the symmetry direction associated with the superlattice axis, but also in the orthogonal plane directions. We conclude that, in contrast to Si/Ge, Si/SiO$_2$ superlattices show clear optical enhancement and a shift of the optical spectrum into the region useful for many opto-electronic applications.Comment: 11 pages, 10 figures (submitted to Phys. Rev. B

Role of the electro-thermo-mechanical multiple coupling on the operation of RF microswitch

A phenomenological approach is proposed to identify some effects occurring within the structure of the microswitch conceived for radio frequency application. This microsystem is operated via a nonlinear electromechanical action imposed by the applied voltage. Unfortunately, it can be affected by residual stress, due to the microfabrication process, therefore axial and flexural behaviors are strongly coupled. This coupling increases the actuation voltage required to achieve the so-called ‘‘pull-in'' condition. Moreover, temperature may strongly affect strain and stress distributions, respectively. Environmental temperature, internal dissipation of material, thermo-elastic and Joule effects play different roles on the microswitch flexural isplacement. Sometimes buckling phenomenon evenly occurs. Literature show that all those issues make difficult an effective computation of ‘‘pull-in'' and ‘‘pull-out'' voltages for evenly distinguishing the origin of some failures detected in operation. Analysis, numerical methods and experiments are applied to an industrial test case to investigate step by step the RF-microswitch operation. Multiple electro-hermomechanical coupling is first modeled to have a preliminary and comprehensive description of the microswitch behavior and of its reliability. ‘‘Pull-in'' and ‘‘pull-out'' tests are then performed to validate the proposed models and to find suitable criteria to design the RF-MEM

Wet release technology for bulk-silicon resonators fabrication on silicon-on-insulator substrate

Stiction occurring in the release phase is a severe problem in many MEMS devices. This phenomenon is due to capillary forces and solid–solid adhesion, which develops during drying after a wet etching process. The possibilities and the limits of the use of a solvent with low surface tension is investigated in the case of MEMS resonators fabricated on silicon-on-insulator substrate. It is shown as in this case it is possible to obtain stiction-free structures without the necessity of more expensive and complicated techniques such as supercritical drying or hydrofluoric acid (HF) vapor etching. The fabrication and design limit of this solution are also investigated

A continuous flow microelectrophoretic module for protein separation

In the framework of our research work, we are developing a microfluidic system that can be used as a pre-treatment device for the sample preparation in analytical microsystems, as biosensors, for instance. Sample pre-treatment phase is usually envisaged before chemical and biological analysis. For example, if we want to perform contaminants detection in a complex matrix as milk, we must consider that the sample consists in a solution of butterfat globules and water with dissolved carbohydrates and protein complexes. If we want a bio-sensor to perform a label free detection of some target-contaminants in milk, interferents in the matrix must be removed. Proteins are an important part of these interferents, and their concentration needs to be reduced, in order to avoid fouling and consequently the inhibition of the sensor, or false positive results in the analysis. We have designed and fabricated a SPLITT flow thin fractionation device for protein separation that is now under testing with a BSA solution

Coupling of electrons to intermolecular phonons in molecular charge transfer dimers: a resonance Raman study

We report resonance Raman scattering (RRS) spectra and Raman excitation profiles (REP) of a system containing π dimers of identical molecular radical ions measured with laser excitation in resonance with the charge transfer (CT) transition. A Peierls–Hubbard (PH) Hamiltonian has been used to model the investigated system and to calculate its optical and RRS properties. Results are reported for two polyoxometallate salts of tetrathiafulvalene (TTF), namely (TTF)2(W6O19) and (TTF)2(Mo6O19) whose structures contain almost isolated (TTF+)2 dimers. The RRS spectra of (TTF)2(W6O19), measured in resonance with the CT absorption band centered at 832 nm, show three phonon modes located at 55, 90, and 116 cm−1 which are strongly resonance enhanced. These modes have been associated to the out‐of‐phase combinations of the translational motions of the two molecules composing the dimer. Such modes are effective in modulating the intradimer transfer integral, thus providing an efficient mechanism for coupling with the electronic system and for enhancement of the scattering intensity at resonance with the CT transition. The REP for the three strongly coupled modes of (TTF)2(W6O19) have been measured with laser excitation wavelengths ranging from 740 to 930 nm. Quantitative analysis of the REP data has been performed based on a perturbative solution of the PH model to second order in the electron‐molecular‐vibration (EMV) and electron‐intermolecular‐phonon (EIP) interactions. The CT absorption profile and the REP’s have been calculated using a time correlator technique and the model parameters have been optimized in order to fit the experimental REP data. Infrared vibronic absorptions of (TTF)2(W6O19), originated by the EMV coupling, have been measured and independent information on the electronic parameters of the PH model have been derived. This has made the choice of the fitting parameters used for the REP calculations rather unambiguous and has allowed us to obtain, for the first time, reliable experimental estimates of the EIP coupling constants

Influence of temperature on the actuation voltage of RF-MEMS switches

Most 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