Practical Guide to RF-MEMS E-Book

Jacopo Iannacci

• Herausgeber: Wiley-VCH
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 497

Veröffentlichungsjahr: 2013

Beschreibung

Closes the gap between hardcore-theoretical and purely experimental RF-MEMS books.

The book covers, from a practical viewpoint, the most critical steps that have to be taken in order to develop novel RF-MEMS device concepts. Prototypical RF-MEMS devices, both including lumped components and complex networks, are presented at the beginning of the book as reference examples, and these are then discussed from different perspectives with regard to design, simulation, packaging, testing, and post-fabrication modeling. Theoretical concepts are introduced when necessary to complement the practical hints given for all RF-MEMS development stages.

• Provides researchers and engineers with invaluable practical hints on how to develop novel RF-MEMS device concepts
• Covers all critical steps, dealing with design, simulation, optimization, characterization and fabrication of MEMS for radio-frequency applications
• Addresses frequently disregarded issues, explicitly treating the hard to predict interplay between the three-dimensional device structure and its electromagnetic functionality
• Bridges theory and experiment, fundamental concepts are introduced with the application in mind, and simulation results are validated against experimental results

Appeals to the practice-oriented R&D reader: design and simulation examples are based on widely known software packages such as ANSYS and the hardware description language Verilog.

Leseprobe

Contents

Foreword

Preface

1 RF-MEMS Applications and the State of the Art

1.1 Introduction

1.2 A Brief History of MEMS and RF-MEMS from the Perspective of Technology

1.3 RF-MEMS Lumped Components

1.4 RF-MEMS Complex Networks

1.5 Modeling and Simulation of RF-MEMS Devices

1.6 Packaging of RF-MEMS

1.7 Brief Overview of Exploitation of RF-MEMS in RF Systems

1.8 Conclusions

2 The Book in Brief

2.1 Introduction

2.2 A Brief Introduction to the FBK RF-MEMS Technology

2.3 An RF-MEMS Series Ohmic Switch (Dev A)

2.4 RF-MEMS Capacitive Switches/Varactors

2.5 Conclusions

3 Design

3.1 Introduction

3.2 Design Rules of the Fondazione Bruno Kessler RF-MEMS Technology

3.3 Design of an RF-MEMS Series Ohmic Switch (Dev A)

3.4 Generation of 3D Models Starting from the 2D Layout

3.5 Conclusions

4 Simulation Techniques (Commercial Tools)

4.1 Introduction

4.2 Static Coupled Electromechanical Simulation of the RF-MEMS Ohmic Switch (Dev A) in ANSYS Multiphysics™

4.3 Modal Analysis of the RF-MEMS Capacitive Switch (Dev B2) in ANSYS Multiphysics

4.4 Coupled Thermoelectromechanical Simulation of the RF-MEMS Ohmic Switch with Microheaters (Dev C) in ANSYS Multiphysics

4.5 RF Simulation (S-parameters) of the RF-MEMS Variable Capacitor (Dev B1) in ANSYS HFSS™

4.6 Conclusions

5 On-Purpose Simulation Tools

5.1 Introduction

5.2 MEMS Compact Model Library

5.3 A Hybrid RF-MEMS/CMOS VCO

5.4 Excerpts of Verilog-A Code Implemented for MEMS Models

5.5 Conclusions

6 Packaging and Integration

6.1 Introduction

6.2 A WLP Solution for RF-MEMS Devices and Networks

6.3 Encapsulation of RF-MEMS Devices

6.4 Fabrication Run of Packaged Test Structures

6.5 Electromagnetic Characterization of the Package

6.6 Influence of Uncompressed ACA on the RF Performance of Capped MEMS Devices

6.7 Conclusions

7 Postfabrication Modeling and Simulations

7.1 Introduction

7.2 Electromechanical Simulation of an RF-MEMS Varactor (Dev B2) with Compact Models

7.3 RF Modeling of an RF-MEMS Varactor (Dev B2) with a Lumped Element Network

7.4 Electromechanical Modeling of an RF-MEMS Series Ohmic Switch (Dev A) with Compact Models

7.5 Electromagnetic Modeling and Simulation of an RF-MEMS Impedance-Matching Network (Dev E) for a GSM CMOS Power Amplifier

7.6 Electromagnetic Simulation of an RF-MEMS Capacitive Switch (Dev B1) in ANSYS HFSS™

7.7 Electromagnetic Simulation of a MEMS-Based Reconfigurable RF Power Attenuator (Dev D) in ANSYS HFSS

7.8 Conclusions

Appendix A: Rigid Plate Electromechanical Transducer (Complete Model)

A.1 Introduction

A.2 Mechanical Model of the Rigid Plate with Four DOFs

A.3 Extension of the Mechanical Model of the Rigid Plate to Six DOFs

A.4 Contact Model for Rigid Plates with Four and Six DOFs

A.5 Electrostatic Model of the Rigid Plate

A.6 Electrostatic Model of the Plate with Holes

A.7 Electrostatic Model of the Fringing Effect

A.8 Viscous Damping Model

A.9 Conclusions

Appendix B: Flexible Straight Beam (Complete Model)

B.1 Mechanical Model of the Flexible Beam with Two Degrees of Freedom

B.2 Mechanical Model of the Flexible Beam with 12 DOFs

B.3 Complete Mechanical Model of the Euler Beam with 12 DOFs

B.4 Electrostatic Model of the Euler Beam with 12 DOFs

B.5 Viscous Damping Model

B.6 Conclusions

References

Index

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The Author

Dr. Jacopo Iannacci

Fondazione Bruno Kessler

Ctr. for Materials & Microsystems

via Sommarive 18

38123 Trento

Italy

All books published byWiley-VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.

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© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Boschstr. 12, 69469 Weinheim, Germany

All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any othermeans – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.

Print ISBN 978-3-527-33564-0

ePDF ISBN 978-3-527-67392-6

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Intellectual honesty is like a breeze for a sailor. It is invisible and intangible, but it makes a difference.

Intelligence is not all you need in life. You should be intelligent enough to practice it too.

J. Iannacci, June 2012.

Happiness only real when shared.

C.J. McCandless, August 1992.

To my parents, and to their unconditional presence.

Foreword

The world, as we all know it, has three dimensions. Some of us enjoyed playing with construction bricks as a child, and some still enjoy building stuff, as a hobby or for work. Through the years different branches of engineering have studied how to build complex, efficient, reliable, 3D structures, either movable or still. Indeed, the progress made in the fields of mechanical and civil engineering in recent decades is impressive, making possible the construction of amazing bridges and buildings that literally fight against the force of gravity. In parallel, the achievements obtained by electronic engineering have been continuously changing our life styles and deserve a quick recap. Since the invention of the planar fabrication process at the end of the 1950s by Jean Hoerni, and the successive demonstration of the first CMOS circuit by Frank Wanlass at the beginning of the 1960s, the evolution of microelectronic fabrication technologies has literally exploded, pushing to a few nanometers the lithographic resolution achievable nowadays, and making it possible to integrate tens of millions of transistors in a few square millimeters. However, as already mentioned, we live in a 3D world, so why not exploit the advantages offered by the planar fabrication process to build 3D, even movable structures with dimensions well below the millimeter scale? It is likely that Harvey Nathanson had the same question, and in 1964 with his team at Westinghouse he answered it by producing the first batch-fabricated electromechanical device. The device, a resonant transistor, joined for the first time a mechanical component and electronic circuitry. In other words, he gave birth to the first microelectromechanical system (MEMS). The term “microelectromechanical system” (MEMS) originated in the United States and was followed by “microsystem technology” in Europe and “micromachining” in Japan. Despite the different terminology, the essence is the demonstration that it is possible to co-integrate electrical and 3D mechanical components with dimensions (well) below 1 mm using a fabrication process to produce microelectronic devices. A couple of decades since the first MEMS demonstration, the field has experienced a huge expansion. Nowadays, extremely complex MEMS, such as high-resolution accelerometers and gyroscopes, are commonly implemented in many portable guidance and entertainment systems, and in state-of-the-art automotive and avionic applications. This is very exciting from an engineering point of view and, from a business perspective, we are speaking about multi-billion-dollar markets. In parallel to those and other kinds of successful micromachined sensors/actuators, there has been great interest in the last two decades in developing 3D devices for radio frequency (RF) applications. Good examples are transmission lines, suspended inductors, ohmic/capacitive switches, varactors, resonators, and so on. Given the superior performance demonstrated by MEMS compared with traditional solid-state/fully mechanical technologies, such as higher linearity and frequency bandwidth, smaller volume occupancy and weight, ultralow power consumption, and lower batch production cost and fabrication process complexity, it has been straightforward to exploit such kinds of devices in next-generation portable and regular telecommunications systems. As said before, these are exciting and remunerative markets! Given the great interest in the field, many books have appeared on the design of MEMS. Many of them were meant to give the reader a deep theoretical understanding of the working principles of devices. Fewer works preferred to investigate the field of reliability, showing how it is easy to damage, or even destroy, these wonderful, little, 3D movable structures if they are not properly protected from potentially critical electrical, mechanical, or environmental overstress.

The monograph of Iannacci is different from what has already been presented in the literature, filling the gap between pure theoretical books and experimental ones. Indeed, this book takes the reader by the hand, showing how to fabricate, design, simulate, and characterize electrostatic-based MEMS for RF applications. The starting point is the introduction of the Fondazione Bruno Kessler MEMS process flow and a design software tool (L-Edit) in the first chapters, with an easy to follow and practical approach. But the design and optimization of any new device requires spending some time on structure simulation. Any RF design engineer knows very well the importance of a good design and the considerable amount of time it can take to predict the response of the device. Playing with 3D movable devices, everything is complicated by the need to couple the electromechanical physics with electromagnetism. Iannacci did not forget this often cumbersome problem, and has devoted ample space to introduce the reader to many finite element method and RF simulation tools, always with a “from the scratch” approach, and always comparing simulation results with experimental data. In the end, it is worth remembering that you will sell actual devices, not just simulation data. And the differences with previous literature continue. Instead of simply introducing the basic blocks of MEMS, Iannacci provides a full description of two MEMS-based, complex systems: a GSM MEMS-based power amplifier and an RF-MEMS-based reconfigurable power attenuator. These examples can be definitely beneficial to experienced “solid-state” engineers, who can easily compare the pros and cons offered by a 3D technology, as well as to students, who can understand the possible problems in integrating different technologies, including differences and problems encountered in MEMS packaging. Despite the practical approach of the book, theory has not been forgotten, and in the appendices Iannacci describes the theoretical basis behind the electromechanical actuator, the heart of each electrostatic-based MEMS, as well as the flexible beam, that is, the suspension of the MEMS movable structure. In conclusion, the field of RF-MEMS is so ably described by Iannacci that both professionals and students, experienced or newbies, will benefit from his presentation and experimental point of view. As a last, personal, comment, I really enjoyed reading the book of my friend Jacopo. Actually, I just realized I have never called him by his surname so often as in this foreword!

Pittsburg, USA

May 2012

Augusto Tazzoli

Preface

Microelectromechanical systems (MEMS) technology is characterized by great flexibility, making it suitable for sensor and actuator applications spanning from the biomedical to the automotive sector. A rather recent exploitation of MEMS technology which emerged in the research community about 15 years ago is in the field of radio frequency (RF) passive components. RF-MEMS devices – RF-MEMS is an acronym identifying microsystem-based RF passive components – range from lumped components, such as microrelays, variable capacitors (i.e., varactors), and inductors, to complex elements based on a combination of the previously listed basic components, such as tunable filters, phase shifters, and impedance-matching tuners. All the RF-MEMS components mentioned are characterized by very high performance, for example, low loss, high quality factor (Q factor), and good isolation, as well as by wide reconfigurability. Such characteristics offer the potential to extend the operability and to boost the performance of RF systems, such as transceivers, radar systems, cell phones, and smartphones, and this is the main reason for which significant effort is now being expended (at the research and industrial level) in order to solve the issues still impeding the full integration of MEMS technology in standard RF circuits, they being mainly reliability, packaging, and integration.

Given the wide interdisciplinary behavior of MEMS and RF-MEMS devices, the aspects to be faced as well as the knowledge required to handle their development are multiple, regardless of the specific phase – design, simulation, fabrication, testing – one is dealing with. For example, the proper design of an innovative RF-MEMS component implies propaedeutic knowledge of the physics of semiconductors, structural mechanics, dynamics, electrostatics, and electromagnetism. Consequently, MEMS/RF-MEMS being a novel discipline demanding a straightforward definition of its pertinence, several remarkable handbooks and textbooks were written in the last decade, covering both the comprehensive discussion of the field as a whole and the close examination of specific device development phases, such as modeling, simulation, microfabrication, and packaging.

Since it would have made no sense to publish another text containing the theory of RF-MEMS that, in the best case, could have been as good as already existing texts, a different approach was chosen and pursued in the preparation of this book. The philosophy behind it can be summarized as follows: if relevant books dealing with the theory of RF-MEMS and hands-on texts already exist, why not aim at something in between? And this is it.

This book covers some of the most critical phases that have to be faced in order to develop novel RF-MEMS device concepts according to a very practical approach, it being the one followed by the author in the research activities he pursued in the last decade. A very limited set of RF-MEMS devices – including both lumped components and complex networks – is chosen at the beginning of the book as reference examples, and they are then discussed from different perspectives while progressing from the design to the simulation, packaging, testing, and postfabrication modeling. Theoretical bases are introduced when necessary, while several practical hints are reported concerning all the development steps discussed, providing the book with an engineering flavor.

In conclusion, given its practical approach, this book is meant to give a helping hand to a wide audience, ranging from scientists and researchers directly involved in the RF-MEMS field, to those who want to gain insight into what working in the field of microsystems for RF applications means.

Trento, Italy

June 2012

Jacopo Iannacci

1

RF-MEMS Applications and the State of the Art

Abstract: This introductory chapter provides a comprehensive overview of the state of the art in radio frequency (RF) microelectromechanical systems (MEMS) technology and its applications. The exploitation of MEMS technology in the field of RF circuits and systems (i.e., RF-MEMS) represents a rather recent exploitation of microsystems if compared with the field of sensors and actuators, and can be framed in the last 10–15 years. Firstly, the chapter discusses some of the history of MEMS technology, focusing on the development of suitable and appropriate technological steps for the manufacturing of microsystems. Subsequently, the focus is moved to RF-MEMS technology, and a comprehensive scenario of the most relevant devices manufactured with such a technology is provided. The discussion of microsystem-based RF passive components is arranged according to an increasing complexity fashion, with the basic passive lumped components, namely, switches, variable capacitors, and inductors, being presented first. Then, the potential of RF-MEMS technology is framed by showing how such basic elements can be combined in order to realize complex functional RF subblocks, such as phase shifters and filters, characterized by large reconfigurability and very high performance. To conclude this introductory chapter, information about the state of the art in modeling and packaging of RF-MEMS devices is provided, while other relevant aspects, such as testing and reliability, are not described in detail as they will not be treated in this work. A brief overview of the exploitation of RF-MEMS devices in RF systems is also given.

1.1 Introduction

What is the relationship, if it truly exists, between the progress of technology and the progress of human kind? This is one of those complicated questions that do not admit a unique answer; in fact, it is a question with no answer, according to the point of view of an engineer. Nonetheless, trying for a very short while not to be a scientist, but just a human being, which is the basis of a scientist, as well as of a lawyer, a worker, a secretary, and so on, one can maybe address, even though partially, the initial question. The intricacy between the progress of human kind and that of technology is clearly bidirectional. The advancements in technology, and their influence on the daily life of people, definitely improved, and are seamlessly improving, our conditions of life. Let us think about how radio, television, cell phones, and other equipment have brought about a revolution in our lifestyle as well as in our habits, both of which concern ourselves and our social life. Nevertheless, the same advancements have generated a series of negative consequences for human kind, outlining a fundamental paradox. What is the point if the improvement of one aspect of life causes the degradation of other traits? The point is that positive and negative consequences of each change, including the no-change option, are unavoidable. Consequently, real progress is not represented by the sole boost given by technology, but rather by the conscious evaluation of all the aspects and consequences that the employment of a new solution will cause. And this delicate aspect is not solved by the ultimate step forward taken by technology, as it is a responsibility resting on the shoulders of human beings. This is the perspective within which the progress of technology can really become progress also for human kind. These considerations apply to all the changes we have faced, are facing, and will face in the future, in technology as well as in society (concerning laws, regulations, health, etc.), and, of course, also apply to radio frequency (RF) microelectromechanical systems (MEMS) technology, which is the real topic of this book. In other words, it is time for a human being to remember to be an engineer after all.