Integration of Ferroelectric and Piezoelectric Thin Films E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 524

Veröffentlichungsjahr: 2013

Beschreibung

This book contains four parts. The first one is dedicated to concepts. It starts with the definitions and examples of what is piezo-pyro and ferroelectricity by considering the symmetry of the material. Thereafter, these properties are described within the framework of Thermodynamics. The second part described the way to integrate these materials in Microsystems. The third part is dedicated to characterization: composition, structure and a special focused on electrical behaviors. The last part gives a survey of state of the art applications using integrated piezo or/and ferroelectric films.

Leseprobe

Table of Contents

Preface

General Introduction

Chapter 1. Dielectricity, Piezoelectricity, Pyroelectricity and Ferroelectricity

1.1. Crystal structure

1.2. Piezoelectricity, pyroelectricity and ferroelectricity definitions

1.3. Simplified examples

1.4. Three typical structures: wurtzite, ilmenite and perovskite

1.5. Bibliography

Chapter 2. Thermodynamic Study: a Structural Approach

2.1. History

2.2. Revisiting statistical thermodynamics

2.3. State functions

2.4. Linear equations — piezoelectricity

2.5. Non linear equations — electrostriction

2.6. Bibliography

Chapter 3. Ferroelectric-paraelectric Phase Transition Thermodynamic Modeling

3.1. Hypothesis on Gibbs’ elastic energy

3.2. Second-order transition

3.3. Effects of stresses

3.4. First-order transition

3.5. Conclusion

3.6. Bibliography

Chapter 4. Mechanical Formalism

4.1. Introduction

4.2. Hooke’s law

4.3. Definitions of local strains

4.4. Definition of local strains

4.5. Stress-strain relation

4.6. Elastic energy density

4.7. Expression of the elasticity tensor as a function of elements of symmetry

4.8. Bibliography

Chapter 5. Dielectric Formalism

5.1. Introduction

5.2. The dielectric effect seen by Faraday

5.3. Electric polarization and displacement

5.4. The dielectric constant

5.5. The local field in dielectrics: polarization catastrophe

5.6. Dielectric relaxation

5.7. Electric energy density

5.8. Bibliography

Chapter 6. Piezoelectric Formalism

6.1. Thermodynamic equations

6.2. Reducing coefficients using crystal symmetry

6.3. One-dimensional microscopic model

6.4. Electromechanical coupling coefficient

6.5. Piezoelectric coefficients of key materials

6.6. Calculating coupling as a function of crystal orientation

6.7. Piezoelectric coefficients in the case of ferroelectric materials

6.8. Relation between piezoelectric formalism and matter

6.9. Bibliography

Chapter 7. Acoustic Formalism

7.1. Propagation of bulk waves

7.2. Bulk wave resonator

7.3. Bulk acoustic waves filter

7.4. Bibliography

Chapter 8. Electrostrictive Formalism

8.1. Foundations of electrostriction

8.2. Thermodynamic model of electrostriction — case of the resonator

8.3. The electrostriction tensor

8.4. Microscopic model of electrostriction

8.5. Electrostrictive resonator

8.6. Bibliography

Chapter 9. Electric Characterization

9.1. Static piezoelectric characterization of thin films

9.2. Piezoelectric and atomic force microscopy

9.3. Ferroelectric measurement

9.4. Dielectric measurement

9.5. Leakage current in metal/insulator/metal structures

9.6. Bibliography

Chapter 10. Piezoelectric Resonators and Filters

10.1. Acoustic resonators: principle and history

10.2. BAW technology

10.3. CRF technology

10.4. Bibliography

Chapter 11. High Overtone Bulk Acoustic Resonator (HBAR)

11.1. About HBAR

11.2. Technology

11.3. Examples of implementations

11.4. Conclusions about HBAR

11.5. Bibliography

Chapter 12. Electrostrictive Resonators

12.1. Introduction

12.2. State of the art

12.3. Experimental implementations

12.4. Simulation of a filter with electrostrictive resonators

12.5. Status of perovskite electrostrictive resonators

12.6. PZT-based tunable frequency ferroelectric acoustic resonator

12.7. Nonlinear effect in piezoelectric AlN

12.8. Conclusion with electrostriction

12.9. Bibliography

Chapter 13. Thin Film Piezoelectric Transducers

13.1. Introduction

13.2. State of the art

13.3. Resonant membranes

13.4. Resonant micromirror

First published 2011 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:

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© ISTE Ltd 2011

The rights of Emmanuel Defaÿ to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.

Library of Congress Cataloging-in-Publication Data

Integration of ferroelectric and piezoelectric thin films: concepts and applications for microsystems / edited by Emmanuel Defaÿ. p. cm. Includes bibliographical references and index. ISBN 978-1-84821-239-8 1. Piezoelectric devices--Materials. 2. Ferroelectric thin films. 3. Miniature electronic equipment-- Materials. I. Defaÿ, Emmanuel. TK7872.P54I58 2011 621.3815′2--dc22

2010048939

British Library Cataloguing-in-Publication Data

Preface

The idea of this book came about in 2008 following a discussion with Michel Bruel about the works on materials of the perovskite family carried out at the CEA-LETI, the Electronics and Information Technology Laboratory of the French Atomic Energy Commission, at the Minatec campus in Grenoble, France. It quickly occurred to us that we should gather the studies concerning this field we have been involved in since the beginning of the 2000s in one document. Upon reflection, it seemed interesting to extend the theme of the book to piezoelectric materials in order to include the thematics of acoustic resonators, about which we also had some excellent realizations. Several people also came to assist in writing this book, taking care of a section or a chapter corresponding to their field of speciality.

In this book about piezoelectric thin films, I wanted to cover the rather exhaustive theoretical bases, associating them with state-of-the-art applications in 2010. Of course, there are reference books on piezoelectric materials, such as the piezoelectricity standards (IEEE Standard on Piezoelectricity, ANSI/IEEE Std 176–1987) or Royer and Dieulessaint's famous book (Ondes Élastiques dans les Solides [Elastic Waves in Solids], Masson, Paris, 1974). There are also very good books on the ferroelectric phenomenon, such as Lines and Glass (M.E Lines, A.M. Glass, Principles and Applications of Ferroelectrics and Related Materials, Clarendon Press, Oxford, 1977) or more recently Dragan Damjanovic's article (D. Damjanovic, “Ferroelectric, dielectric and piezoelectric properties of ferroelectric thin films and ceramics”, Rep. Prog. Phys., Vol. 61, pp. 1267–1324, 1998).

To me it seemed worth gathering together the two pillars necessary for a deep understanding of piezoelectric films, while at the same time adding other essential notions:

– the stress-strain mechanical formalism;

– the dielectric formalism; and also

– an important issue of acoustic wave propagation.

The notion of thermodynamic equilibrium is also largely detailed in order to properly stress the foundations of piezoelectricity that originate from the energy exchange between the electrical and mechanical field. The nonlinear phenomenon of electrostriction, essential for describing perovskite materials like PZT, is also described.

The typical reader of this book is a student, researcher or engineer wishing to approach the field of piezoelectricity from the basics. He or she can clearly start reading from any chapter, as they are largely independent. Nevertheless, we took special care to see to it that the notations chosen are compatible between chapters, to ensure a coherent overall reading. Indeed, the different fields necessary for describing piezoelectricity generally present identical notations that can cause confusion. I hope that this book will bring some pertinent information to the interested reader through piezoelectric microsystems, and that he or she will share part of the pleasure we had in writing it.

To conclude, I would like to thank the people who participated in developing this book, either through direct contribution or indirect assistance. I will start with Michel Bruel, one of the figureheads of LETI, and Marc Aïd, the person in charge of the radiofrequency components laboratory, and Claude Massit then Buno Mourey, successively in charge of the microsystems department of LETI, who were a constant support throughout these few months of work. Next I would like to thank Alexandre Reinhardt (acoustics) and Gwenaël LeRhun (electrical characterization), two of my closest colleagues, who were the first to agree to participate in this book. Emilien Bouyssou of STMicroelectronics in Tours (electrical measurements, accuracy) also quickly agreed, benefiting us with information on the industrial approach for integrating PZT in silicon technology. Christophe Billard (RF filters), Mathieu Pijolat, Chrystel Deguet and Sylvain Ballandras (HBAR), Matthieu Cueff, Fabien Filhol and Patrice Rey (actuators), Brice Ivira, Nizar Ben Hassine and Alexandre Volatier (electrostriction) and Christophe Zinck (ferroelectric resonators) were of great assistance for contributions in their fields. I must also thank Sylvain Ballandras (Franche-Comté Electronics, Mechanics, Thermal transfers, Optics, Science and Technology — Femto-ST), Paul Muralt (Swiss Federal Institute of Technology Lausanne — EPFL), Brahim Dkhil (Centrale Paris) and Jens Kreisel (Grenoble Institute of Technology — INPG) for their constant support and the positive energy they were able to and still can communicate to me. I would also like to thank José Olivarès for the many discussions we had, especially on the subject of statistical thermodynamics.

This book is also the result of two excellent projects that we produced with Pascal Ancey (STMicroelectronics in Crolles) and Lianjiu Liu (Freescale): thanks go to them.

I would also like to thank all the people who contributed to producing the mechanisms displayed. Although it is impossible to name them all, I am thinking of François Perruchot, Aurélien Suhm, Guy Parat, Aude Lefèvre, Patrice Gergaud, Denis Pellissier, Amy N'Hary, Laurent Figuière, François Chapuis, Xiaohong Zhu, Sylvia Sanchez, Julie Abergel, David Pinceau, David Wolozan, Fabien Dumont, Grégory Caruyer, Patrick Emery, Julie Guillan, Benoit Guigues, Frédéric Domingue, Patrick Lassagne, Pierre-Antoine Deléan and Marie Thérèse Delaye, as well as LETI's silicon platform.

Finally, my thoughts go to my wife and my two daughters for their perpetual patience and their support.

Emmanuel DEFAŸ

January 2011

General Introduction

The piezoelectric effect was discovered by the Curie brothers in 1880. Since then, many applications have come into being: time base, precision actuators, sonar, echographic probe and, more recently, radio-frequency filters for mobile phones. This field is set to be further developed because of the growing need for actuators and sensors of all sorts, especially for communication and healthcare. Piezoelectricity is very well adapted to these fields as it links the electrical or electronic world to the mechanical world in a linear manner. This is why mastering good piezoelectric materials is fundamental for developing these applications. In the microsystems framework, great advances in thin-film piezoelectric materials have been achieved since the middle of the 1990s. Lead zirconate titanate (Pb(Zr,Ti)O3 called PZT) and aluminum nitride (AlN) are, today, the spearheads of these thin-film materials, as we will see in detail in this book.

This book begins with a chapter that endeavors to specify the microscopic properties of dielectrics: ferroelectricity, piezoelectricity, pyroelectricity and electrostriction. Certain notions of crystallography are taken up, since the crystalline nature of matter produces a good part of these properties.

Chapter 2 is devoted to thermodynamic notions indispensable for the precise description of the state of equilibrium and energy exchanges. It is this approach that enables us to define electromechanical coupling.

Next, we take on the description of paraelectric-ferroelectric phase transition, which is very useful for describing the piezoelectrics of ferroelectric nature, such as those of the perovskite family (PZT, for example).

Chapter 4 is dedicated to the study of stress-strain relations, indispensable for putting the piezoelectric effect in the form of an equation.

Chapter 5 describes dielectric materials by adding stresses to the main fields, such as electric displacement. The notion of dielectric relaxation is also taken up. Once these bases have been expanded on, we go into detail about the piezoelectric formalism in a macroscopic but also microscopic way, even if the latter is less useful for applications in Chapter 6.

Chapter 7 is a rather detailed exposition on the acoustic formalism adapted to piezoelectric films. Acoustic filters and the main applications of acoustic resonators are also approached from an analytical angle.

Chapter 8 is dedicated to electrostrictive nonlinear effect, less well-known, but very important for describing the piezoelectric linear effect of perovskites and increasingly used in applications.

The next chapter endeavors to describe the principle means of electric characterizations of these piezoelectric films: macroscopic then local piezoelectric measurements, ferroelectric, dielectric measurement and finally, leakage current measurement.

Next we move on to the application chapters. Chapter 10 is reserved for resonators and filters that use piezoelectric thin films. This application is currently the most beautiful industrial piezoelectric film success. Chapter 11, most of all, is devoted to electrostrictive thin films used for variable frequency resonators. Although this solution is not yet industrially exploited, it constitutes a real alternative for the future. Chapter 12 discusses electrostrictive resonators. The last chapter describes some thin-film piezoelectric transducers, after having given a few figures of merit essential for choosing materials depending on the function of the target applications.

Chapter 1

Dielectricity, Piezoelectricity, Pyroelectricity and Ferroelectricity1

1.1. Crystal structure

The notions of piezoelectricity, pyroelectricity and ferroelectricity are closely linked to the crystalline nature of materials. Indeed, the study of the crystal structure of materials enables us to see what arrangements of atoms are susceptible to showing one or other property. We will discuss some core notions of crystallography in order to bring out the main conclusions that can be drawn from this approach [ESN 94].

A crystal is defined as follows: the atoms that make up a crystal form a pattern that periodically repeats itself in the three spatial dimensions. A crystal is an object whose dimensions are large compared to the atoms that constitute it. The periodicity of its structure results in the properties of the crystal being identical, depending on the dimensions and planes given, no matter the initial reference point. This is what we call translational symmetry. This notion is important as it will enable us to implement symmetry operations that will be used to classify the crystals.

As a simple example of a periodicity-based property, let us cite silicon cleavage, which is always split in the same directions, or the hexagonal structure of quartz crystals that is visible to the naked eye.

The notions that constitute the foundations of the study of crystallography are the lattice and pattern of a crystal. The lattice is made up of points called nodes that periodically repeat themselves in space, but the lattice does not contain any atoms. The atoms of the crystal belong to the pattern that is attached to the lattice node.

Figure 1.1 is a diagram representing a crystal with its lattice and its pattern.

To help with comprehension, it is useful to start with a classic example: sodium chloride (NaCl). Crystal packing is made up of a regular succession Na+ and Cl− ions in the three spatial dimensions, as represented in Figure 1.2.

Figure 1.2.Crystal packing of NaCl

More specifically, we can say that the NaCl consists of the spatial packing of cubes, such as C (Na+1, Na+2, Na+5, Na+4, Na+10, Na+11, Na+14, Na+13). On the other hand, it is not possible from cube (Na+1, Cl−1, Na+3, Cl−2, Cl−5, Na+6, Cl−7, Na+7). Packing can be initiated from several equal points of the lattice. In this case, they are points on the corners of the cube C (Na+1, Na+2, Na+5…) or those that are in the center of the faces of C (Na+3, Na+6, Na+7…).

It is these nodes that constitute the lattice called the translational lattice. A pattern is attached to each node. Here, the latter is made up of a pair of ions Na+ and Cl−. For example, Na+1−Cl−1 or Na+1−Cl−2 or even Na+1−Cl−5. The structure of NaCl can be described as two interpenetrating face-centered cubic lattices with a gap between them of a distance a/2 in one of the three spatial dimensions, depending on the pattern chosen (x axis if Na+1−Cl−1).

This description is not the most compact possible, although it is the simplest. The face-centered cubic lattice constitutes a multiple lattice.

This means that several patterns are contained in one lattice. There are four of them here (each corner node counts for 1/8 and each node on a face counts for 1/2). Nevertheless, it is possible to define, for each packing, an elementary lattice that contains only one pattern.

Figure 1.3.Trigonal elementary lattice of the face-centered cubic packing of NaCl

In the case of NaCl (and face-centered cubic in general), this lattice is illustrated in .