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

Chromium in MEMS Technology

This chapter has the purpose to address several topics where chromium can be encountered in MEMS technology, and the different ways to exploit its unique properties in the fabrication of MEMS and more in general microsystem devices. The aim of this choice is also to collect in a clear and organized way many specific knowledge that can normally be found only scattered around in different and diverse sources of scientific and technological information. The structure of the chapter can be described as follows: first a short introductory section where it is explained what is MEMS technology, what are the general principles of MEMS microfabrication, and the types of devices that can be produced by this technology. Then a brief review of chromium chemical properties relevant for MEMS, also with reference of its compounds, including oxidation behavior and chemical etching properties is given. It follows a discussion on mechanical and physical properties of this metal, and a summary of common deposition techniques (PVD, sputtering, electroplating) for chromium and its compounds. A core section about different uses of chromium in MEMS technology is then presented: chromium for masks in photolithography, chromium as adhesion layer for structural and noble metals, chromium as structural material in thin film resistors and other less frequent uses. Finally a short section on chromium alloys and their exploitation in MEMS applications is reported

Electrochemically oxidised porous silicon microcavities

Ageing effects in porous silicon microcavities result in emission enhancement and resonance peak blueshift. In this paper we propose electrochemical oxidation as a method to control these effects. Properties of porous silicon microcavities obtained after anodic oxidation are compared to those of microcavities aged in air for several months. This evidences that emission enhancement and resonance peak shift are two different phenomena and the effects of anodic and naturally oxidation are not the same. A significant suppression of peak shift due to ageing is achieved, and the extent of this stabilisation increases with the oxidation time, but for long oxidation times the microcavity properties are degraded

Porous silicon microcavities as optical chemical sensors

The optical properties of porous silicon microcavities are strongly dependent on the environment. For highly luminescent samples, both the luminescence intensity and the peak position are affected by organic substances, giving the possibility to obtain dual-parameter optical sensors. While the peak position depends on the organic compound refractive index, luminescence intensity depends on its low-frequency dielectric constant. This allows the discrimination between different organic substances. This sensor is particularly interesting for solvents with low dielectric constant, where the response of electrical sensors is very weak

All porous silicon microcavities: growth and physics

The spontaneous emission of a material can be controlled by placing it in a micron-sized optical cavity. In this paper we introduce the subject and we discuss the realization, the physics and perspective applications of all porous silicon microcavities. The emission properties of the cavities have been characterized as a function of the temperature, of the excitation power and of the response time. Coupled microcavities are demonstrated. Modeling of the structure have been performed on the basis of a transfer matrix approximation