1,721,070 research outputs found
Instability and Drift Phenomena in Switching RF-MEMS Microsystems
No full textMEMS switches include mobile beams in their mechanical structure and these suspended parts are essential for the device functioning. This paper illustrates the most important instability phenomena related to MEMS switches. Starting from the most important instability exploited in these devices—the electrical actuation—the paper also analyzes other important effects related to instability phenomena, which are very common in this type of technology. Instabilities due to dielectric charge trapping, fabrication tolerances, mechanical deformation, contact wear, and temperature variation are duly analyzed, giving a comprehensive view of the complexity encountered in the reliable functioning of these apparently simple devices
Chromium in MEMS Technology
No full textThis 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
All porous silicon microcavities: growth and physics
No full textThe 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
Porous silicon microcavities as optical chemical sensors
No full textThe 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
Porous Silicon Microcavities as Optical and Electrical Chemical Sensors
No full textThe optical and electrical 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, which also strongly modify the electrical conductivity, giving the possibility to obtain a multi-parametric optical/electrical sensor. The peak position depends on the refractive index of the organic compound, whereas the luminescence intensity depends on its low frequency dielectric constant. Electrical properties depend on the dipole moment of the molecules. This allows discriminating between different organic substances
Effect of temperature on stress and stress gradient during final release process in gold suspended MEMS structures
No full textIn this paper will be shown that the conditions of the final oxygen plasma process strongly influence the shape of MEMS suspended gold structures.
The structures examined have typically a thickness of 1.8 microns, and are produced by patterned gold electrodeposition above a sacrificial photoresist layer which is then removed by oxygen plasma ashing. In general, deformations are strongly reduced lowering the temperature, but the release time increases abruptly. A simple model is presented to explain the experimental observation, and from it can be deduced that yield and inelastic relaxation are critical phenomena responsible for most of the deviations from the ideal planar shape of MEMS structures
Effects of the mixing of charge transfer and molecular excitations on the resonance Raman properties of symmetric radical dimers
No full textThe mixing of charge transfer (CT) and molecular excitation (ME) states in a molecular radical dimer is investigated based on a model Hamiltonian for a dimer with two orbitals per site filled with two electrons. The CT/ME mixing brings about an intensity enhancement of intramolecular modes in the Raman spectra resonant with the CT absorption. The relevant parameter for this effect is the transfer integral tab for the hopping of one electron from orbital a in one molecule to orbital b in the other. This theoretical prediction is confirmed by Raman excitation profiles measured for the cation radical salt (TTF)2(W6O19)
A Simple Nondestructive Radio Frequency Measurement Technique for the Analysis of Liquids
No full textAbstract—Dielectric resonators (DRs) are widely used in microwave and millimeter-wave applications, including antennas and bandpass filters. In this study, we exploit the properties of these resonators in a different way, demonstrating how a common container filled with liquid can be assimilated to a DR. The typical properties of DRs are used to investigate the physical and chemical properties of the content and their evolution, providing a contactless, noninvasive, and nondestructive evaluation (NDE)
of its characteristics. The level of the liquid, its conductivity, and dielectric constant can be easily determined in real time, and used as parameters for in-line monitoring, quality control, and chemical composition assessment. Results are reported using a common wine bottle as a container, but are very easily transferable to other types of liquid containers, including plastic
bottles or larger containers
Wet release technology for bulk-silicon resonators fabrication on silicon-on-insulator substrate
No full textStiction 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
Elaboration, characterization and aging effects of porous silicon microcavities formed on lightly p-type doped substrates
No full textIn this paper we present and discuss the realization and optical characterization of porous silicon microcavities formed on p−-type doped substrates. We produce porous silicon microcavities with a very narrow bandwidth (5.5 nm) and a good ratio of the peak to background emission, reaching at the same time a high emission quantum efficiency. The effects of etching parameters such as electrolyte temperature and viscosity are presented as well as changes due to aging. The properties of microcavities are improved when the viscosity of the electrolyte is increased by adding glycerol to the etching solution. Lowering
the etching temperature does not lead to appreciable improvement. Aging has been shown to simply shift the luminescence of microcavities without significant deterioration. Emission properties are mainly shown, including stationary and time-resolved measurements of photoluminescence
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