Showing papers by "Benno Margesin published in 2009"

A general purpose reconfigurable MEMS-based attenuator for Radio Frequency and microwave applications

Abstract: In this paper we present a power attenuator for RF (RadioFrequency) and microwave signals entirely designed in MEMS (MicroElectroMechanical-System) technology. It is fabricated in the RF-MEMS technology available at Fondazione Bruno Kessler (FBK) based on a surface micromachining process. The network is realized in a low-cost manufacturing process and its dimensions are significantly compact compared to traditional implementations of RF power attenuators. More interestingly, employment of MEMS technology for such architecture enables a very large reconfigurability, making the network compatible with different standards and usable in several wireless communication systems. Electromechanical and RF behaviour of the discussed network are simulated and compared against experimental results collected by the first fabricated samples. RF measured performances are rather promising in spite a technology issue occurred during the fabrication deteriorating the attenuator low-frequency characteristic. RF modelling of such issue (already fixed in the batches being currently fabricated) is shown and discussed through this paper.

Evolution of electrical parameters of dielectric-less ohmic RF-MEMS switches during continuous actuation stress

Abstract: The evolution of the main electrical parameters of dielectric-less ohmic RF-MEMS cantilever-based switches during continuous actuation stress was investigated in this work Thanks to different designs, the main electrical parameters changes were attributed to a charging phenomena of the oxide over the substrate near the polysilicon actuator, leading to both narrowing and shifting of traditional hysteresis-like curves Recovery procedures were also analyzed Furthermore, the breakdown occurrence was also investigated, supported by both emission microscope and optical images

Dielectric charging in microwave microelectromechanical Ohmic series and capacitive shunt switches

Abstract: The charging of the dielectric used for the actuation in microelectromechanical system (MEMS) devices is one of the major failure sources for switches based on this technology. For this reason, a better understanding of such an effect is vital to improve the reliability for both ground and space applications. In this paper, the expected response of MEMS switches to unipolar and bipolar dc actuation voltages has been measured and modeled. Two configurations of MEMS switches, namely, an Ohmic series and a shunt capacitive one designed for microwave applications, have been studied as a test vehicle for charging effects related to the dc actuation pads. The recorded data have been interpreted mainly through the Poole–Frenkel effect due to charge injection when a high voltage is applied to the dielectric layer. Metal-Insulator-Metal (MIM) structures have been also considered as a complementary information for the response of the dielectric material.

A MEMS Reconfigurable Quad-Band Class-E Power Amplifier for GSM Standard

Abstract: In this work we present a reconfigurable mid-power Class-E Power Amplifier (PA) [1,2] operating at ~900MHz and ~1800MHz (GSM standard [3]) realized hybridizing one chip manufactured in AMS 0.35 ?m CMOS technology and one MEMS sub-network. The CMOS chip realizes the active part of the circuit, whereas the MEMS block (realized in FBK technology) implements a reconfigurable impedance Matching Network (MN) that transforms the 50? antenna load to the 12? impedance required by the PA in order to deliver 20dBm output power in both the GSM operating frequency bands. The prototype of the MEMS/CMOS PA we realized delivers 20dBm with 38% and 26% drain efficiencies at 900MHz and 1800MHz, respectively, demonstrating to be a feasible option compared to standard commercial solutions.

Reliability of RF MEMS switches due to charging effects and their circuital modelling

Abstract: The reliability of RF MEMS switches is typically reduced by charging effects occurring in the dielectrics. The aim of this paper is to discuss these effects, and to propose an equivalent circuit model which accounts for most of the physical contributions present in the structure.

Development of different K-band MEMS phase shifter designs for Satellite COTM Terminals

Abstract: This work presents the design, manufacturing and testing of three 5-bit K-band MEMS phase shifters based on similar architectures (combination of switched line and loaded line) but employing different MEMS switch typologies (cantilevers & air-bridges) and RF junctions (SP2T & SP4T). All devices have been monolithically manufactured on 200 µm thick high resistivity silicon substrate (4") by using the FBK MEMS process. The performance of the different devices have been compared in order to identify the best configuration to be implemented in electronically steerable phased arrays antennas for Satellite COTM (Communication On The Move) Terminals. Excellent performances were measured for the dielectric-free pad MEMS switches as well as the single bits constituting the phase shifter. The three 5-bit devices show return loss better than 15 dB for all states, with average insertion loss of 3.5dB for the clamped-clamped, SP2T-based design, 2.2 dB for the cantilever, SP2T-based device and 2.1 dB for the cantilever, SP4T-based design. The measurements of the packaged devices are on-going.

Electrical and mechanical properties of layered gold-chromium thin films for ohmic contacts in RF-MEMS switches

Abstract: The electrical contacts are the most critical part for the reliability of RF-MEMS switches. For this reason the development of new contact materials with higher hardness and low resistivity would be of great help in increasing MEMS switch reliability. In this paper a detailed study of mechanical, electrical and morphological properties of gold–chromium multilayers is presented and discussed. It will be shown how hardness of gold can be increased introducing thin layers of chromium inside the gold contact layer. However, some care must be taken, since this improvement can vanish because of thermal and oxygen plasma treatments normally involved in RF-switches fabrication, mainly due to chromium oxidation.

A micromachined gold–palladium Kelvin probe for hydrogen sensing

Abstract: In this paper we discuss the fundamental principles of the Kelvin probe apparatus; in particular, first, we find an analytical relation for the sensitivity of vibrating capacitors, so that the advantages of integration can be quantitatively estimated; second, we describe an equivalent electric circuit for vibrating capacitors, thus allowing to simulate a complete Kelvin probe with a standard electronic circuit simulator; third, we illustrate the most important issues of the electronic interface. A fundamental part of the research and technological work reported by this paper deals with the fabrication process of micromachined gold–palladium vibrating capacitors fully integrated on silicon, for hydrogen sensing applications. The relevant technological fabrication steps are explained. Preliminary experimental results of the first capacitor prototypes testing are reported as static C–V (capacitance–voltage) curves and as measurement in air of the gold–palladium work–function difference.

Novel design of a RF-MEMS tuneable capacitor based on electrostatically induced torsion

Abstract: Micro-Electro-Mechanical System (MEMS) RF switches have been one of the most interesting areas for research and development in the last years. It has been shown that they have an excellent performance in the RF and microwave frequency range and a great effort has been dedicated in designing suitable geometries and structures best suited for switching application. In parallel other devices useful for the construction of complex RF circuits have been proposed and studied. Among these tuneable capacitors are of high interest for a variety of applications. In this paper we present a new electromechanical design for a tuneable capacitor with a totally different shape from usual designs. In particular we try to exploit the effect of the small in-plane force that develops during the polarization of a parallel plate capacitor with partially overlapping plates. First prototype realizations are discussed and analyzed and as the first realization showed some problems an improved design is presented.

Automatically Generated and Experimentally Validated System-Level Model of a Microelectromechanical RF Switch

Abstract: We present a computationally efficient multi-energy domain coupled system-level model of an electrostatically actuated RF MEMS switch exposed to squeeze film damping. The physically-based model is systematically derived and calibrated on the basis of a hierarchical modeling approach. The model shows excellent agreement with measurements. Especially coupling effects, that are the increased damping and the spring softening whilst actuation, are correctly reproduced by the model. This demonstrates the power of our modeling approach and, in particular, the predictiveness w.r.t. ”real world” experiments. Furthermore, the automatically generated model is suitable for direct implementation into standard circuit simulators.

P1.7 - FEM Electromechanical Modelling of a MEMS Variable Capacitor for RF Applications

Abstract: Accurate modelling of the electromechanical behaviour of RF-MEMS devices is critical in order to predict their characteristics, and consequently how the design has to be optimized in order to overcome the trade-offs arising when dealing with specifications both in the mechanical and electrical/electromagnetic physical domains. In this work we present a complete approach to the simulation of RF-MEMS devices based on FEM (Finite Element Method) simulations performed in ANSYS TM Multiphysics.

POLYSILICON MESOSCOPIC WIRES COATED BY Pd AS H(2) SENSORS

Abstract: In this work a novel monocrystalline silicon nanowires array has been investigated and presented as hydrogen sensor, designed and fabricated by employing high resolution microfabrication techniques ...