Showing papers by "Benno Margesin published in 2011"

A flexible technology platform for the fabrication of RF-MEMS devices

Abstract: The paper reports about the technology platform for the fabrication of RF-MEMS devices developed at FBK. The most important process features, requirements and possible applications are presented and described. The basic fabrication process, together with some of the more important process variations and its capabilities are reported. Finally, some examples of produced devices and their performances are briefly presented.

Influence of beam geometry on the dielectric charging of RF MEMS switches

Abstract: This 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.

Effect of the substrate on RF power-handling capability of micro-electromechanical capacitive switches

Abstract: RF power-handling capacity of micro-electromechanical capacitive switches was modeled by multiphysics finite-element analysis. Coupled electromechanical, electrothermal and thermomechanical models were constructed by using commercially available software. Simulations by using the models were validated by small- and large-signal RF measurements. The measurements showed that the power-handling capacity of the switches depended on not only the properties of the membrane (the movable part of the switches), but also the substrate properties and the circuit environment. These effects were captured in a compacted model, which could be used to guide the improvement of the power-handling capacity of the switches.

Terahertz microsensor for biomedical applications

Abstract: A low-cost integrated microsensor for biomedical applications is proposed. It is composed by an antenna-coupled microbolometer as detector, which is coupled to a specifically designed integrated circuit for biasing and readout. The main features are fast response to radiation, device level reference sensor, and electronic time-correlation for pulsed sources. The detector and the integrated circuits have been fabricated in a custom MEMS technology and a standard CMOS technology, respectively. First electrical measurements show properly operating devices.

Variable isotropy Deep RIE process for through wafer via holes manufacturing

Abstract: This paper reports a method on the manufacturing of through wafer via holes in silicon with tapered walls by Deep Reactive Ion Etching (DRIE) using the opportunity to change the isotropy in the DRIE equipments during processing. By using consecutively anisotropic and isotropic etching steps it is possible to enlarge the dimension of via holes on one side of the wafer, while on the other side dimension is set by the initial etching window. The method was used for two etching windows sizes (100μm and 20μm respectively) on 200μm and 300μm thick wafers. The aim was to manufacture tapered walls via having a good control over the walls angle. Different Bosch process recipes providing different walls roughness were used. Via holes with tapered walls (2° to 22°) were manufactured using this method. An angle deviation smaller than 10% of the manufactured via holes along the wafers was observed.

Design and characterization of an active recovering mechanism for high-performance RF MEMS redundancy switches

Abstract: This paper presents the design and characterization of an active push/pull toggle RF micro-electro-mechanical systems (MEMS) switch for satellite redundancy networks. The actively controlled pull-up mechanism allows for extended restoring capabilities of the switch in case of ON-state stiction. As a proof of concept an active push/pull MEMS capacitive switch was modeled, designed, and manufactured in shunt configuration on a 50 Ω coplanar transmission line. RF measurement results show a return loss better than 15 dB in the 0.1–40 GHz range and an insertion loss better than 0.5 dB over the same range. The restoring capability of the switch was experimentally proved up to 9 h, and a predictive model was proposed for the estimation of the switch time to failure.

Gold-based thin multilayers for ohmic contacts in RF-MEMS switches

Abstract: In RF-MEMS switches many reliability issues are related to the metal contacts in the switching area. The characteristics of this contact influence not only contact resistance and insertion loss, but also the most relevant switch failure mechanisms that are wear of ohmic contact, adhesion and stiction. Gold is widely used for this purpose because of its good conductivity and chemical inertness, but is a soft metal, and the development of hard contact materials with low resistivity is of great interest for RF-MEMS switch reliability. It is possible to increase the contact hardness preserving the convenient gold properties alternating gold layers with thin layers of different metals. The material becomes harder not only by simple alloying but also by the presence of interfaces which act as barriers for mechanical dislocation migration. A detailed study of mechanical, electrical and morphological properties of gold-chromium, gold-platinum and gold-palladium multilayers is presented and discussed. It is found that the annealing treatments are important for tuning hardness values, and a careful choice of the alloying metal is essential when the material is inserted in a real switch fabrication cycle, because hardness improvements can vanish during oxygen plasma treatments usually involved in RF-switches fabrication. Platinum is the only metal tested that is unaffected by oxidation, and also modifies the chromium adhesion layer diffusion on the contact surface.

MEMS technology for RF passive components

Abstract: In this work a wide overview on the exploitation of MEMS technology (MicroElectroMechanical-Systems) for Radio Frequency (i.e. RF-MEMS) and telecommunication systems is provided. In the last 10-15 years MEMS technology proved to be a valuable solution for the realization of passive components for RF circuits, like variable capacitors (i.e. varactors), inductors, switches (i.e. micro-relays), as well as more complex networks, like RF filters, impedance matching tuners etc., with remarkable characteristics in terms of low-loss, high Q-factor (quality factor), and large reconfigurability. The integration within RF circuits and platforms, of passive lumped elements and networks with such prominent characteristics, would lead to a significant increase of performance and reconfigurability of the whole system (e.g. mobile handset, satellite, radar, and so on).

Modeling and characterization of a circular-shaped energy scavenger in MEMS surface micromachining technology

Abstract: This work reports the analysis, modeling and characterization of an electrostatic vibration-to-electric energy scavenger. The scavenger was manufactured by the FBK in-house foundry by using a MEMS (Micro-Electro- Mechanical System) surface micro-machining technology. Extensive finite element analyses (FEA) were performed for the compact modeling of the device and presented here. The scavenger was characterized by means of dynamical measurements as a further validation of the FE model. A random vibration analysis is also utilized for the emulation of the real device operating conditions.

Modeling of gold microbeams for characterizing MEMS packages

Abstract: Modeling 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.

The MARE project: A new 187Re neutrino mass experiment with sub eV sensitivity

Abstract: A large worldwide collaboration is growing around the project of Micro-calorimeter Arrays for a Rhenium Experiment (MARE) for a direct calorimetric measurement of the neutrino mass with a sensitivity of about 0.2 eV/c 2 . Many groups are joining their experience and technical expertise in a common effort towards this challenging experiment which will use the most recent and advanced developments of the thermal detection technique.

Fabrication of through-wafer interconnections by gold electroplating

Abstract: A new method for conductive via's using gold electroplating is presented. Tapered walls through wafer via (TWV) holes were made using a variable isotropy DRIE process, with a very good control over the obtained angles — angles of 11.3° and 21.8° were obtained with errors smaller than 10%. Barrier and seed layers were deposited in via's performed by PVD (Physical Vapor Deposition) techniques with a very good coverage of the walls. Finally, gold electroplating was used to fill the narrow part of via's.