Text-preface

FERROELECTRIC DEVICES

By KENJI UCHINO International Center for Actuators and Transducers Materials Research Laboratory The Pennsylvania State University

Marcel Dekker, Inc. New York, Basel, Hong Kong

ABOUT THE AUTHOR Kenji Uchino, a pioneer in piezoelectric actuators, is the Director of International Center for Actuators and Transducers and Professor of Electrical Engineering at The Pennsylvania State University. He is currently teaching "Ferroelectric Devices" and "Ceramic Actuators," using this textbook. After being awarded his Ph. D. degree from Tokyo Institute of Technology, Japan, Uchino became Research Associate in physical electronics department at this university. Then, he joined the Sophia University, Japan as an Associate Professor in physics in 1985. He then moved to Penn State in 1991. He was also involved with Space Shuttle Utilizing Committee in NASDA, Japan during 1986-88, and was the Vice President of NF Electronic Instruments, USA, during 1992-94. He has been consulting more than 60 Japanese, US and European industries to commercialize the piezoelectric actuators and electrooptic devices. He is the Chairman of Smart Actuator/Sensor Study Committee partly sponsored by the Japanese Government, MITI. He is also the executive associate editor for Journal of Advanced Performance Materials (Kluwer Academic) and the associate editor for Journal of Intelligent Material Systems and Structures (Technomic). He also serves as an Administrative Committee member for IEEE, Ultrasonics, Ferroelectrics, Frequency Control Society. His research interests are in solid state physics __ especially dielectrics, ferroelectrics and piezoelectrics, including basic research on materials, device designing and fabrication processes, as well as development of solid state actuators and displays for precision positioners, ultrasonic motors, projection type TV's etc. He has authored 240 papers, 30 books and 19 patents in the ceramic actuator area. In addition to his academic carrier, Uchino is an honorary member of KERAMOS (National Professional Ceramic Engineering Fraternity) and obtained the Best Movie Memorial Award as the director/producer in Japan Scientific Movie Festival (1989) of several educational video tapes on "Dynamical Optical Observation of Ferroelectric Domains" and "Ceramic Actuators."

PREFACE Ferroelectrics can be utilized in various devices such as high-permittivity dielectrics, pyroelectric sensors, piezoelectric devices, electrooptic devices and PTC components. The industries are producing large amount of simple devices, e. g. ceramic capacitors, piezoelectric igniters, buzzers and PTC thermisters continuously. But until now ferroelectric devices have failed to reach commercialization in more functional cases. In the light sensor, for example, semiconductive materials are superior to ferroelectrics in response speed and sensitivity. Magnetic devices are much more popular in the memory field, and liquid crystals are typically used for optical displays. Ferroelectric devices often fail to be developed in the cases where competitive materials exist. This is mainly due to a lack of systematic accumulation of fundamental knowledges on the materials and developmental experiences on the devices. During my 12-year teching period on "Ferroelectric Devices," I found that no suitable textbook is available in this particular field, except some professional books like multi-author paper collections. Hence, I decided to write a singleauthored textbook based on my lecture notes, including my device development philosophy. This textbook introduces the theoretical background of ferroelectric devices, practical materials, device designs, drive/control techniques and typical applications, and looks forward to the future progress in this field. Though the discovery of ferroelectricity is relatively old, since the device development is really new and interdiciplinary, it is probably impossible to cover all the recent studies in a limited-page book. Therefore, I selected only important and basic ideas to understand how to design and develop the ferroelectric devices, putting a particular focus on thin/thick film devices. Let me introduce the contents. Chapter 1 introduces the overall background, "General view of ferroelectrics," followed by the theoretical background in Chapter 2 "Mathematical treatment of ferroelectrics." Chapter 3 "Device designing and fabrication processes" provides practical designing and manufacturing of the devices. Capacitor applications are described in Chapter 4 "High permittivity devices." Chapters 5 and 6 treat thin/thick film applications, i. e. "Ferroelectric memory devices" and "Pyroelectric devices," respectively. Chapter 7 "Piezoelectric devices" deals with piezoelectric actuators and ultrasonic motors as well as acoustic transducers and piezoelectric sensors. Optical devices such as light valves, displays, wave guides and bulk photovoltaic devices are described in Chapter 8 "Electrooptic devices." In Chapters 9 and 10, we learn basic concepts of "PTC materials" and "Composite materials," and their device applications. Finally in Chapter 11 we discuss "Future of ferroelectric devices," in which the market size is estimated, and the author's strategy for developing bestseller devices is introduced. This textbook was written for graduate students and industry engineers studying or working in the fields of electronic materials, optical materials and communications,

precision machinery and robotics. Though this text is designed for a course with thirty 75-minute lectures, the reader can learn the content by himself/herself aided by the availability of examples and problems. Critical review and content corrections on this book are highly appreciated. Send the information directed to Kenji Uchino at 134 Materials Research Laboratory, The Pennsylvania State University, University Park, PA 16802-4800. Fax: 814865-2326, E-mail: [email protected] For the reader who needs detailed information on smart piezoelectric actuators and sensors, "Piezoelectric Actuators and Ultrasonic Motors" (349 pages) authored by K. Uchino, published by Kluwer Adacemic Publishers in 1997 is recommended. Even though I am the sole author of this book, it nevertherless includes the contributions of many others. I express my gratitude to my ICAT center faculty who have geneously given me their advice and help during the writing, particularly to Dr. Uma Belegundu, who worked out all the problems. Specific acknowledgement is given to Professor Jayne Giniewicz, Indiana University of Pennsylvania who reviewed and criticized the whole portion of the manuscript, and provided linguistic corrections. January, 1999 at State College, PA Kenji Uchino

CONTENTS

PREFACE CONTENTS LIST OF SYMBOLS SUGGESTED TEACHING SCHEDULE PREREQUISITE KNOWLEDGE 1.

2.

3.

4.

5.

6.

GENERAL VIEW OF FERROELECTRICS 1.1 Crystal Structure and Ferroelectricity 1.2 Origin of Spontaneous Polarization 1.3 Origin of Field Induced Strain 1.4 Electrooptic Effect 1.5 Example of Ferroelectrics 1.6 Applications of Ferroelectrics

1 2 4 9 13 18 20

MATHEMATICAL TREATMENT OF FERROELECTRICS 2.1 Tensor Representation of Physical Properties 2.2 Phenomenology of Ferroelectricity MATERIAL AND DEVICE DESIGNING AND FABRICATION PROCESSES 3.1 Material Designing 3.2 Fabrication Processes of Ceramics 3.3 Device Designing 3.4 Grain Size Effect on Ferroelectricity 3.5 Ferroelectric Domain Contributions

57 67 73 84 89

HIGH PERMITTIVITY DIELECTRICS 4.1 Ceramic Capacitors 4.2 Chip Capacitors 4.3 Hybrid Substrates 4.2 Relaxor Ferroelectrics FERROELECTRIC MEMORY DEVICES 5.1 DRAM 5.2 Non-Volatile Ferroelectric Memory PYROELECTRIC DEVICES

23 38

105 106 108 108

119 126

6.1 6.2 6.3 7.

8.

9.

10.

11.

INDEX

Pyroelectric Materials Temperature/Infrared Light Sensors Infrared Image Sensors

131 138

PIEZOELECTRIC DEVICES 7.1 Piezoelectric Materials and Properties 7.2 Pressure Sensors/Accelerometers/Gyroscopes 7.3 Piezoelectric Vibrators/Ultrasonic Transducers 7.4 Surface Acoustic Wave Devices 7.5 Piezoelectric Transformers 176 7.6 Piezoelectric Actuators 7.7 Ultrasonic Motors

139

145 158 161 174 180 197

ELECTROOPTIC DEVICES 8.1 Electrooptic Effect - Review 8.2 Transparent Electrooptic Ceramics 8.3 Bulk Electrooptic Devices 8.4 Wave Guide Modulators

221 222 230 239

PTC MATERIALS 9.1 Mechanism of PTC Phenomenon 9.2 PTC Thermistors 9.3 Grain Boundary Layer Capacitors

243 248 250

COMPOSITE MATERIALS 10.1 Connectivity 10.2 Composite Effects 10.3 PZT:Polymer Composites 10.4 PZT Composite Dampers

255 257 260 269

FUTURE OF FERROELECTRIC DEVICES 275 11.1 Market Share of Ferroelectric Devices 11.2 Reliability Issues 11.3 Development of Bestseller Devices

276 279 283 305

LIST OF SYMBOLS D E P Ps p α γ µ ε0

Electric displacement Electric field Dielectric polarization Spontaneous polarization Pyroelectric coefficient Ionic polarizability Lorentz factor Dipole moment Vacuum permittivity

ε C T0 TC G1 x xs X s c v d,g M,Q k η n r g Γ

Relative permittivity Curie-Weiss constant Curie-Weiss temperature Curie temperature (Phase transition temperature) Gibbs elastic energy Strain Spontaneous strain Stress Elastic compliance Elastic stiffness Sound velocity Piezoelectric coefficients Electrostrictive coefficients Electromechanical coupling factor Energy transmission coefficient Refractive index Primary electrooptic coefficient Secondary electrooptic coefficient Phase retardation

SUGGESTED TEACHING SCHEDULE (75 min x 30 times per semester) 0. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Course Explanation & Prerequisite Knowledge Check General View of Ferroelectrics Mathematical Treatment of Ferroelectrics Device Designing and Fabrication Processes High Permittivity Dielectrics Ferroelectric Memory Devices Pyroelectric Devices Piezoelectric Devices Electrooptic Devices PTC Materials Composite Materials Future of Ferroelectric Devices Review/Q&A

1 Time 4 Times 4 Times 3 Times 2 Times 1 Time 1 Time 7 Times 2 Times 1 Time 2 Times 1 Time 1 Time

PREREQUISITE KNOWLEDGE In order to understand ferroelectric devices, some prerequisite knowledge is expected. Try to solve the following questions without seeing the answers on the next page.

Q1 Q2

Describe the definitions of elastic stiffness c and compliance s, using a stress X - strain x relation. Indicate a shear stress X4 on the following square.

3

2 Q3 Q4 Q5 Q6 Q7 Q8

Describe the sound velocity v in a material with mass density ρ and elastic compliance s E. Calculate the capacitance C of a capacitor with area S and electrode gap t filled with a material of relative permittivity ε. Calculate the polarization P of a material with dipole density N (m-3) of dipole moment qu (C.m). Describe the Curie-Weiss law of relative permittivity ε, using a Curie-Weiss temperature T0 and a Curie-Weiss constant C. Describe the light velocity in a material with a refractive index n (c: light velocity in vacuum). Indicate the work function in the following energy band of a metal. Vacuum Level

Fermi Level

Inside of Metal

Q9 Q10

Outside

There is a voltage supply with an internal impedance Z0. Indicate the external impedance Z1 to obtain the maximum output power. Calculate the induced polarization P under an external stress X in a piezoelectric with a piezoelectric constant d.

Answer (Correct rate more than 70% of full score is expected) Q1 Q2

X = c x, x = s X x4 = 2 x23 = 2 φ

(radian)

φ

X4

Q3 Q4 Q5 Q6 Q7 Q8

φ

[0.5 point for v = 1/ ρ s E] [0.5 point for C = ε (??S / t)]

v = 1/(ρ s E)1/2 C = ε0ε (??S / t) P = Nqu ε = C / (T - T0) c' = c / n (Work function)

[0.5 point for ε = C / T]

Vacuum Level Work Function Fermi Level

Inside of Metal

Q9

Z1 = Z0 On Z1, current and voltage are given as V/(Z0 + Z1) and [Z1/(Z0 + Z1)]V, leading to the power: Power = V2.Z1/(Z0 + Z1)2 = V2/(Z0/ Z11/2 + Z11/2)2 < (1/4) V2/ Z0 The maximum is obtained when Z0 / Z11/2 = Z11/2. Hence, Z1=Z0. Z0

v Q10

Outside

P = d X (refer to x = d E)

Z1