Mixed-Domain Fast Simulation of RF and Microwave MEMS-based Complex Networks within Standard IC Development Frameworks

MS technology (MicroElectroMechanical-System) has been successfully employed since a few decades in the sensors/actuators field. Several products available on the market nowadays include MEMS-based accelerometers and gyroscopes, pressure sensors and micro-mirrors matrices. Beside such well-established exploitation of MEMS technology, its use within RF (Radio Frequency) blocks and systems/sub-systems has been attracting, in recent years, the interest of the Scientific Community for the significant RF performances boosting that MEMS devices can enable. Several significant demonstrators of entirely MEMS-based lumped components, like variable capacitors (Hyung et al., 2008), inductors (Zine-El-Abidine et al., 2003) and micro-switches (Goldsmith et al., 1998), are reported in literature, exhibiting remarkable performance in terms of large tuning-range, very high Q-Factor and low-loss, if compared with the currently used components implemented in standard semiconductor technology (Etxeberria & Gracia, 2007, Rebeiz & Muldavin, 1999). Starting from the just mentioned basic lumped components, it is possible to synthesize entire functional sub-blocks for RF applications in MEMS technology. Also in this case, highly significant demonstrators are reported and discussed in literature concerning, for example, tuneable phase shifters (Topalli et al., 2008), switching matrices (Daneshmand & Mansour, 2007), reconfigurable impedance matching networks (Larcher et al., 2009) and power attenuators (Iannacci et al., 2009, a). In all the just listed cases, the good characteristics of RF-MEMS devices lead, on one side, to very highperformance networks and, on the other hand, to enabling a large reconfigurability of the entire RF/Microwave systems employing MEMS sub-blocks. In particular, the latter feature addresses two important points, namely, the reduction of hardware redundancy, being for instance the same Power Amplifier within a mobile phone suitable both in transmission (Tx) and reception (Rx) (De Los Santos, 2002), and the usability of the same RF apparatus in compliance with different communication standards (like GSM, UMTS, WLAN and so on) (Varadan, 2003). Beside the exploitation of MEMS technology within RF transceivers, other potentially successful uses of Microsystems are in the Microwave field, concerning, e.g., very compact switching units, especially appealing to satellite applications for the very reduced weight (Chung et al., 2007), and phase shifters in order to electronically steer short and mid-range radar systems for the homeland security and monitoring applications (Maciel et al., 2007). Given all the examples reported above, it is straightforward that the employment of a proper strategy in aiming at the RF-MEMS devices/networks optimum design is a key-issue in order to gain the best benefits, in terms of performance, that such technology enables to address. This is not an easy task as the behaviour of RF-MEMS transversally crosses different physical domains, namely, electrical, mechanical and electromagnetic, leading to a large number of trade-offs between mechanical and electrical/electromagnetic parameters, that typically cannot be managed within a unique commercial simulation tool. In this chapter, a complete approach for the fast simulation of single RF-MEMS devices as well as of complex networks is presented and discussed in details. The proposed method is based on a MEMS compact model library, previously developed by the author, within a commercial simulation environment for ICs (integrated circuits). Such software tool describes the electromechanical mixed-domain behaviour typical of MEMS devices. Moreover, through the chapter, the electromagnetic characteristics of RF-MEMS will be also addressed by means of extracted lumped element networks, enabling the whole electromechanical and electromagnetic design optimization of the RF-MEMS device or network of interest. In particular, significant examples about how to acc..

Microsystem based Energy Harvesting (EH-MEMS): Powering pervasivity of the Internet of Things (IoT) – A review with focus on mechanical vibrations

The paradigm of the Internet of Things (IoT) appears to be the common denominator of all distributed sensing applications, providing connectivity, interoperability and communication of smart entities (e.g. environments, objects) within a pervasive network. The IoT demands for smart, integrated, miniaturised and low-energy wireless nodes, typically powered by non-renewable energy storage units (batteries). The latter aspect poses constraints as batteries have a limited lifetime and often their replacement is impracticable. Availability of zero-power energy-autonomous technologies, able to harvest (i.e. convert) and store part of the energy available in the surrounding environment (vibrations, thermal gradients, electromagnetic waves) into electricity to supply wireless nodes functionality, would fill a significant part of the technology gap limiting the wide diffusion of efficient and cost effective IoT applications. Given the just depicted scenario, the realisation of miniaturised Energy Harvesters (EHs) leveraging on MEMS technology (MicroElectroMechanical-Systems), i.e. EH-MEMS, seems to be a key-enabling solution able to conjugate both main driving requirements of IoT applications, namely, energy-autonomy and miniaturisation/integration.This short review outlines the current state of the art in the field of EH-MEMS, with a specific focus on vibration EHs, i.e. converters capable to convert the mechanical energy scattered in environmental vibrations, into electric power. In particular, the issues in terms of conversion performance arising from EHs scaling down, along with the challenge to extend their operability on a frequency range of vibrations as wider as possible, are going to be discussed in the following. Keywords: Energy Harvesting (EH), MEMS, Internet of Things (IoE), Ultra-Low Power (ULP), Zero-power electronic

A COMPREHENSIVE OVERVIEW OF RECENT DEVELOPMENTS IN RF-MEMS TECHNOLOGY-BASED HIGH-PERFORMANCE PASSIVE COMPONENTS FOR APPLICATIONS IN THE 5G AND FUTURE TELECOMMUNICATIONS SCENARIOS

The goal of this work is to provide an overview about the current development of radio-frequency microelectromechanical systems technology, with special attention towards those passive components bearing significant application potential in the currently developing 5G paradigm. Due to the required capabilities of such communication standard in terms of high data rates, extended allocated spectrum, use of massive MIMO (Multiple-Input-Multiple-Output) systems, beam steering and beam forming, the focus will be on devices like switches, phase shifters, attenuators, filters, and their packaging/integration. For each of the previous topics, several valuable contributions appeared in the last decade, underlining the improvements produced in the state of the art and the chance for RF-MEMS technology to play a prominent role in the actual implementation of the 5G infrastructure

Mixed-domain simulation and hybrid wafer-level packaging of RF-MEMS devices for wireless applications

In questa tesi verranno trattati sia il problema della creazione di un ambiente di simulazione a domini fisici misti per dispositivi RF-MEMS, che la definizione di un processo di fabbricazione ad-hoc per il packaging e l’integrazione degli stessi. Riguardo al primo argomento, sarà mostrato nel dettaglio lo sviluppo di una libreria di modelli MEMS all’interno dell’ambiente di simulazione per circuiti integrati Cadence c . L’approccio scelto per la definizione del comportamento elettromeccanico dei MEMS è basato sul concetto di modellazione compatta (compact modeling). Questo significa che il comportamento fisico di ogni componente elementare della libreria è descritto per mezzo di un insieme limitato di punti (nodi) di interconnessione verso il mondo esterno. La libreria comprende componenti elementari, come travi flessibili, piatti rigidi sospesi e punti di ancoraggio, la cui opportuna interconnessione porta alla realizzazione di interi dispositivi (come interruttori e capacità variabili) da simulare in Cadence c . Tutti i modelli MEMS sono implementati per mezzo del linguaggio VerilogA c di tipo HDL (Hardware Description Language) che è supportato dal simulatore circuitale Spectre c . Sia il linguaggio VerilogA c che il simulatore Spectre c sono disponibili in ambiente Cadence c . L’ambiente di simulazione multidominio (ovvero elettromeccanico) così ottenuto permette di interfacciare i dispositivi MEMS con le librerie di componenti CMOS standard e di conseguenza la simulazione di blocchi funzionali misti RF-MEMS/CMOS. Come esempio, un VCO (Voltage Controlled Oscillator) in cui l’LC-tank è realizzato in tecnologia MEMS mentre la parte attiva con transistor MOS di libreria sarà simulato in Spectre c . Inoltre, nelle pagine successive verrà mostrata una soluzione tecnologica per la fabbricazione di un substrato protettivo (package) da applicare a dispositivi RF-MEMS basata su vie di interconnessione elettrica attraverso un wafer di Silicio. La soluzione di packaging prescelta rende possibili alcune tecniche per l’integrazione ibrida delle parti RF-MEMS e CMOS (hybrid packaging). Verranno inoltre messe in luce questioni riguardanti gli effetti parassiti (accoppiamenti capacitivi ed induttivi) introdotti dal package che influenzano le prestazioni RF dei dispositivi MEMS incapsulati. Nel dettaglio, tutti i gradi di libertà del processo tecnologico per l’ottenimento del package saranno ottimizzati per mezzo di un simulatore elettromagnetico (Ansoft HFSSTM) al fine di ridurre gli effetti parassiti introdotti dal substrato protettivo. Inoltre, risultati sperimentali raccolti da misure di strutture di test incapsulate verranno mostrati per validare, da un lato, il simulatore Ansoft HFSSTM e per dimostrate, dall’altro, la fattibilit`a della soluzione di packaging proposta. Aldilà dell’apparente debole legame tra i due argomenti sopra menzionati è possibile identificare un unico obiettivo. Da un lato questo è da ricercarsi nello sviluppo di un ambiente di simulazione unificato all’interno del quale il comportamento elettromeccanico dei dispositivi RF-MEMS possa essere studiato ed analizzato. All’interno di tale ambiente, l’influenza del package sul comportamento elettromagnetico degli RF-MEMS può essere tenuta in conto per mezzo di modelli a parametri concentrati (lumped elements) estratti da misure sperimentali e simulazioni agli Elementi Finiti (FEM) della parte di package. Infine, la possibilità offerta dall’ambiente Cadence c relativamente alla simulazione di dipositivi RF-MEMS interfacciati alla parte CMOS rende possibile l’analisi di blocchi funzionali ibridi RF-MEMS/CMOS completi

A Reconfigurable Pseudohairpin Filter Based on MEMS Switches

This work presents a bandpass-reconfigurable planar pseudohairpin filter based on RF-MEMS switches. Hairpin-line structures are preferred to design microstrip filters because this class of filters offers a more compact size, and, in general, hairpin filters do not need ground connections for resonators. In this work, the U-shape resonators are arranged to obtain an interdigit capacitor to improve the coupling between the resonators. RF-MEMS switches modify the lengths of coupled resonators by adding microstrip segments to control the filter bandwidth, moving the center frequency and the return loss. An experimental hairpin tunable filter prototype based on RF-MEMS has been designed, fabricated, numerically and experimentally assessed, and compared concerning its tunability, quality factor, and capability with standard tunable filters based on PIN diodes. In conclusion, the tunable hairpin filter based on RF-MEMS switches offers the best performance in center frequency tuning range, compactness, and power consumption regarding reconfigurable filters based on standard PIN diodes switches. The obtained results are appealing and demonstrate the capabilities and potentialities of RF-MEMS to operate with the new communication standards that work at high microwave frequency bands

RF-MEMS for high-performance and widely reconfigurable passive components – A review with focus on future telecommunications, Internet of Things (IoT) and 5G applications

Abstract Since its first discussions in literature during late '90s, RF-MEMS technology (i.e. Radio Frequency MicroElectroMechanical-Systems) has been showing uncommon potential in the realisation of high-performance and widely reconfigurable RF passives for radio and telecommunication systems. Nevertheless, against the most confident forecasts sparkling around the successful exploitation of RF-MEMS technology in mass-market applications, with the mobile phone segment first in line, already commencing from the earliest years of the 2000s, the first design wins for MEMS-based RF passives have started to be announced just in late 2014. Beyond the disappointment of all the most flattering market forecasts and, on the other hand, the effective employment of RF-MEMS in niche applications (like in very specific space and defence scenarios), there were crucial aspects, not fully considered since the beginning, that impaired the success of such a technology in large-market and consumer applications. Quite unexpectedly, the context has changed rather significantly in recent years. The smartphones market segment started to generate a factual need for highly reconfigurable and high-performance RF passive networks, and this circumstance is increasing the momentum of RF-MEMS technology that was expected to take place more than one decade ago. On a broader landscape, the Internet of Things (IoT) and the even wider paradigm of the Internet of Everything (IoE) seem to be potential fields of exploitation for high-performance and highly reconfigurable passive components in RF-MEMS technology. This work frames the current state of RF-MEMS market exploitation, analysing the main reasons impairing in past years the proper employment of Microsystem technology based RF passive components. Moreover, highlights on further expansion of RF-MEMS solutions in mobile and telecommunication systems will be briefly provided and discussed

Investigation of Nonlinear Piezoelectric Energy Harvester for Low-Frequency and Wideband Applications

This paper proposes a monostable nonlinear Piezoelectric Energy Harvester (PEH). The harvester is based on an unconventional exsect-tapered fixed-guided spring design, which introduces nonlinearity into the system due to the bending and stretching of the spring. The physical–mathematical model and finite element simulations were performed to analyze the effects of the stretching-induced nonlinearity on the performance of the energy harvester. The proposed exsect-tapered nonlinear PEH shows a bandwidth and power enhancement of 15.38 and 44.4%, respectively, compared to conventional rectangular nonlinear PEHs. It shows a bandwidth and power enhancement of 11.11 and 26.83%, respectively, compared to a simple, linearly tapered and nonlinear PEH. The exsect-tapered nonlinear PEH improves the power output and operational bandwidth for harvesting low-frequency ambient vibrations

Pull-In Voltage and Stress in Fixed-Fixed Beams of RF MEMS Switches

Electrostatically actuated microelectromechanical system (MEMS) switches with fixed- fixed beams were fabricated. FEM modeling was used to calculate the contributions of stress in the fabricated beams from the measured values of pull-in voltage. The reported study provides useful guidelines to optimize the design of fixed-fixed beams, in order to reduce the stress contributions for the successful development of efficient and reliable electrostatically actuated MEMS devices

A RF-MEMS switchable CPW air-bridge

This work presents a new shunt-type ohmic contact RF-MEMS switch specifically designed as a switchable CPW air bridge. The switch can be used in coplanar waveguide (CPW) reconfigurable multimodal circuits, for a selective use of the CPW odd-mode. The bridge is anchored using folded-beam suspensions, in such a way that two points at each end of the bridge remain free to contact the ground planes of the CPW. The suspension has been designed to compensate stress gradients effects and to lower actuation voltage. In the actuated (ON) state, the switch isolation to the odd mode is better than 20dB up to 8GHz and 10dB up to 30GHz.Peer ReviewedPostprint (author’s final draft

Enhanced robustness of a bridge-type Rf-Mems switch for enabling applications in 5G and 6G communicationsr

In this paper, new suspended-membrane double-ohmic-contact RF-MEMS switch configurations are proposed. Double-diagonal (DDG) beam suspensions, with either two or three anchoring points, are designed and optimized to minimize membrane deformation due to residual fabrication stresses, thus exhibiting smaller mechanical deformation and a higher stiffness with more release force than previously designed single diagonal beam suspensions. The two-anchor DDGs are designed in two different orientations, in-line and 90¿ -rotated. The membrane may include a window to minimize the coupling to the lower electrode. The devices are integrated in a coplanar-waveguide transmission structure and fabricated using an eight-mask surface-micro-machining process on high-resistivity silicon, with dielectric-free actuation electrodes, and including glass protective caps. The RF-MEMS switch behavior is assessed from measurements of the device S parameters in ON and OFF states. The fabricated devices feature a measured pull-in voltage of 76.5 V/60 V for the windowed/not-windowed two-anchor DDG membranes, and 54 V/49.5 V for the windowed/notwindowed three-anchor DDG membranes, with a good agreement with mechanical 3D simulations. The measured ON-state insertion loss is better than 0.7 dB/0.8 dB and the isolation in the OFF state is better than 40 dB/31 dB up to 20 GHz for the in-line/90¿ -rotated devices, also in good agreement with 2.5D electromagnetic simulationsPostprint (published version