NANOSCALE PHENOMENA IN FERROELECTRIC THIN FILMS

Transcription

1 NANOSCALE PHENOMENA IN FERROELECTRIC THIN FILMS

2 NANOSCALEPHENOMENAIN FERROELECTRIC THIN FILMS edited by Seungbum Hong Samsung Advanced Institute oftechnology, Korea SPRINGER-SCIENCE+BUSINESS MEDIA, LLC

3 Library of Congress Cataloging-in-Publication Nanoscale phenomena in ferroelectric thin films 1 edited by Seungbum Hong. p.cm. Includes bibliographical references and index. ISBN ISBN (ebook) DOI / Ferroelectric thin films. 2. Nanostructure materials. 1. Hong, Seungbum TA418.9.T45N '2-dc22 Copyright 2004 Springer Science+Business Media New York Originally published by Kluwer Academic Publishers in 2004 Softcover reprint of the hardcover 1 st edition 2004 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transrnitted in any form or by any means, electronic, mechanical, photo-copying, rnicrofilrning, recording, or otherwise, without the prior written perrnission ofthe publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Perrnissions for books published in the USA: perrnissions@wkap.com Perrnissions for books published in Europe: Printed on acid-free paper.

4 Table of Contents List of Contributors Preface Acknowledgment ix xi xiv Part I. Electrical Characterization in Nanoscale Ferroelectric Capacitor I. Testing and characterization of ferroelectric thin film capacitors In Kyeong. Yoo 1. Test Circuits 3 2. Hysteretic Property 5 3. Capacitance and Current. : 9 4. Stored Energy 9 5. Ageing Fatigue Imprint Leakage Current Electrical Degradation Breakdown Pyroelectric Effect Additional tests for commercial memory cells 29 References 37 II. Size effects in ferroelectric film capacitors: role of the film thickness and capacitor size Igo r Stolichnov 1. Introduction Size effects: role of the ferroelectric film thickness, impact of the passive layer and local charge injection Size effects: role of the capacitor size and impact of nonhomogeneou s stress Conclusions and outlook 54 Acknowledgements 55 References 55

5 vi III. Ferroelectric thin films for memory applications: nanoscale characterization by scanning force microscopy Alexei Gruverman 1. Introduction Experimental Appro ach Variations in Ferroelectric Properties at the nanosc ale PPM studies of retention behavior Nanoscale Leakage Current Mapping Conclusion 83 Acknow ledgment 84 References 84 IV. Nanoscale domain dynamics in ferroelectric thin films V. Nagarajan and R. Ramesh 1. Introduction Thin Film Materials and Characterization Polarizatio n Relaxation at the Nanoscale Nanoscale Piezoelectric and Ferroelectric Behavior Conclusions 106 Acknowledgements 107 References 108 V. Polarization switching and fatigue of ferroelectric thin films studied bypfm Seungbum Hong 1. Introduct ion Polarization switching Fatigue: suppression of switch able polarization Summary and Conclusion 130 Acknowledgments 131 References 131

6 Part II. Nano Domain Manipulation and Visualization in Ferroelectric Materials Vll VI. Domain switching and self-polarization in perovskite thin films A. Roelofs, K. Szot and R. Waser 1. Introduction PTO polycrystalline thin films on platinized silicon wafers PTO single grains Epitaxial PZT thin films on STO/LSCO The origin of self-polarization 146 References 153 VII. Dynamic-contact electrostatic force microscopy and its application to ferroelectric domain Z. G. Khim and J. Hong 1. Introduction Detection Mechanism of DC-EFM Observation of Ferroelectric Domains Control of ferroelectric domains Conclusion 179 Acknowledgements 181 References 181 VIIl Polarization and charge dynamics in ferroelectric materials with SPM S. Kalinin and D. A. Bonnell 1. Introduction Principles of Non-contact Electrostatic SPMs Domain Structure Reconstruction from SPM Origins of Domain Contrast in EFM and SSPM Polarization and Charge Dynamics on the BaTi0 3 (100) Surface Screening and Thermodynamics of Adsorption on BaTi0 3 (100) Surfaces Domain Selective Photochemical Activity on Ferroelectric Surfaces Conclusions 214

7 V111 Acknowledgements 215 References 215 IX. Nanoscale investigation of MOCVD-Pb(Zr,Ti)03 thin films using scanning probe microscopy Hironori Fujisawa and Masaru Shimizu 1. Introduction Experimental procedure 22() 3. Local Current Flow of PZT Thin Films Crystalline Structure and Ferroelectric Properties of Nanosized PZT Islands Polarization Switching Processes in Epitaxial PZT Thin Films Conclusions 234 Acknowledgements 235 References 235 X. SPM measurements of ferroelectrics at MHz frequencies Bryan. D. Huey 1. Introduction Sensitivity to cantilever Loading Periodic excitation and detection MHz measurement Techniques at the Nanoscale 252 Acknowledgements 261 References 261 XI. Application of ferroelectric domains in nanometer scale for highdensity storage devices Hyunjung Shin 1. Introduction MEMS technology and Probe-based storage systems Ferroelectric Domain writing and reading in nanometer scale Research Issues and perspective of ferroelectric domains for storage applications Summary and conclusions 276 Acknowledgments 276 References 277

8 List of Contributors Chapter 1 IN KYEONG YOO Samsung Fellow, Samsung Advanced Institute of Technology, Suwon, Korea Chapter 2 IGOR STOLICHNOV Laboratory of Ceramics, Swiss Federal Institute of Technology, Lausanne, Switzerland Chapter 3 ALEXEI GRUVERMAN North Carolina State Univer sity, Raleigh, NC, U. S. Chapter 4 V. NAGARAJAN and R. RAMESH Materials Research Science and Engine ering Center, Universit y of Maryland, College Park, MD, U. S. Chapter 5 SEUNGBUM HONG Storage Laboratory, Samsung Advanced Institu te of Technology, Suwon, Korea Chapter 6 A. ROELOFS, K. SZOT and R. WASER Center of Nanoelectronic Systems for Information Technology (CNI), IFF, Research Center Julich, D Julich, Germany Chapter 7 ZHEONG G. KHIM and JAEWAN HONG School of Physics and Nano-Science and Technology Program, Seoul National University, Seoul, Korea Interdisciplinary Chapter 8 SERGEI V. KALININ*and DAWN A. BONNELL Oak Ridge National Laboratory, Oak Ridge, TN, U. S. University of Penns ylvania, Philadelphia, PA, U. S.

9 x Chapter 9 HIRONORI FUJISAWAand MASARU SHIMIZU Department of Electrical Engineering and Computer Sciences, Himeji Institute of Technology, Hyogo, Japan Chapter 10 BRYAND. HUEY National Institute of Standards and Technology, MD, U. S. Chapter 11 HYUNJUNG SHIN School of Advanced Materials Engineering, Kookmin University, Seoul, Korea

10 Preface This book presents the recent advances in the field of nanoscale science and engineering of ferroelectric thin films. It comprises two main parts, i.e. electrical characterization in nanoscale ferroelectric capacitor, and nano domain manipulation and visualization in ferroelectric materials. Wellknown le'ading experts both in relevant academia and industry over the world (U.S., Japan, Germany, Switzerland, Korea) were invited to contribute to each chapter. The first part under the title of electrical characterization in nanoscale ferroelectric capacitors starts with Chapter 1, "Testing and characterization of ferroelectric thin film capacitors," written by Dr. I. K. Yoo. The author provides a comprehensive review on basic concepts and terminologies of ferroelectric properties and their testing methods. This chapter also covers reliability issues in FeRAMs that are crucial for commercialization of highdensity memory products. In Chapter 2, "Size effects in ferroelectric film capacitors: role ofthe film thickness and capacitor size," Dr. I. Stolichnov discusses the size effects both in in-plane and out-of-plane dimensions of the ferroelectric thin film. The author successfully relates the electric performance and domain dynamics with proposed models of charge injection and stress induced phase transition. The author 's findings present both a challenging problem and the clue to its solution of reliably predicting the switching properties for ultra-thin ferroelectric capacitors. In Chapter 3, "Ferroelectric thin films for memory applications: nanoscale characterization by scanning force microscopy," Prof. A. Gruverman focuses on the reliability issues of ferroelectric thin films such as spatial variations of imprint or local hysteresis loops, which leads to different switching behaviors from capacitor to capacitor when the capacitor scales down to the size comparable to the grain size. The author discusses another important reliability issues of retention loss and dielectric breakdown, and provides a model of nucleation triggered by built-in field at film/electrode interface and growth enhanced by polarization-dependent space charge field, which explains the stability enhancement of both positive and negative domains by selecting proper electrode materials. In Chapter 4, "Nanoscale dynamics in ferroelectric thin films," Dr. V. Nagarajan and Prof. R. Ramesh covers two seemingly independent but closely related topics of domain dynamics in model thin films and piezoelectric behavior in nanostructures. The authors have shown the important role of 90 domains and domain wall in time dependent relaxation of the remnant polarization and in gigantic piezoelectric strain at saturation

11 xii field. It is amazing to see how nano-structuring of ferroelectric materials can enhance the electromechanical properties to its intrinsic limit. In Chapter 5, "Polarization switching and fatigue of ferroelectric thin films studied by PFM," Dr. S. Hong reviewed the switching behavior and fatigue process directly observed by ferroelectric domain imaging technique on ferroelectric capacitors with top electrode. The author has analyzed the switching kinetics by comparing the domain evolution with the corresponding macroscopic electrical characteristics to find out the forward domain growth being rate limiting mechanism in switching and local freezing of polarization switching during fatigue process. The switching models applicable to nanoscale structures provide important design directions of ferroelectric thin films for future memory or storage device components. The second part of the book, under a title of "Nano Domain Manipulation and Visualization in Ferroelectric Materials", deals with the nano-structuring ferroelectric domains by controlling the nucleation stage of deposition and various domain-imaging and patterning techniques using the nano-probe as a moving electrode. In Chapter 6, "Domain switching and self-polarization in perovskite thin films," Dr. A. Roelofs, Dr. K. Szot, and Prof. R. Waser present polarization switching induced by a conducting tip in polycrystalline, island structured and epitaxial perovskite thin films. The authors show the method of 3D domain map construction by separating in-plane and out-of-plane piezoelectric signals. Intrinsic size effect of the ferroelectric phase was studied using the single grains deposited by bottom-up approach. The authors successfully related the self-polarization phenomena with formation of concentration gradient buildup near the surface caused by a chemical segregation. In Chapter 7, "Dynamic-contact electrostatic force microscopy and its application to ferroelectric domain," Prof. Z. G. Khim and Dr. 1. W. Hong reviews the novel mode of EFM named "dynamic-contact electrostatic force microscopy (DC-EFM)" where electrostatic force induced tip vibration plays the major role in contact mode. The authors present domain patterns and dynamics in TGS single crystals to find out the relaxation behavior of domains and the coincidence between crystallographic twin boundaries and domain boundaries. Finally, they explain nano-manipulation of either ferroelectric dipoles or charges in ferroelectric or charge trap media using the conducting tip as a nano-probe. In Chapter 8, "Polarization and charge dynamics in ferroelectric materials with SPM," Dr. S. V. Kalinin and Prof. D. A. Bonnell discuss the charge screening mechanism on barium titanate and its influence on EFM images. The authors reveal the interplay between fast polarization charge and slow

12 Xlll screening charge that leads to the effect of potential retention above Curie temperature and temperature induced potential inversion. They present cutting-edge results of polarization dependent photochemical activity of ferroelectric surface and ferroelectric domain patterning using SPM probe followed by domain selective metal deposition, which is a promising candidate for nano-lithography. In Chapter 9, "Nanoscale investigation of MOCVD-Pb(Zr,Ti)03 thin films using scanning probe microscopy," Dr. H. Fujisawa and Prof. M. Shimizu cover three main topics of local current flow in polycrystalline PZT thin films, ferroelectric properties of nano-sized PZT islands and polarization switching processes in epitaxial PZT thin films. The authors present important findings regarding the role of grain boundary in leakage phenomena, the size effect of ferroelectric island, and switching kinetics of nano-domains by applying the well-known Ishibashi theory to their PFM results. In Chapter 10, "SPM measurements of ferroelectrics at MHz frequencies," Dr. B. D. Huey presents the concepts behind several MHz frequency SPM investigations of ferroelectrics. The author discusses the imaging techniques based on MHz excitations of domains detected at the same or down-converted frequencies, which opens the possibility of in-situ characterization of nanosecond polarization switching with nanometer scale spatial resolution. In Chapter 11, "Applications of ferroelectric domains in nanometer scale for high-density storage devices," Dr. H. Shin reviews the current status and vision of probe based data storage using ferroelectric thin films as storage media. The author focuses on inducing polarization switching by a conductive tip and detecting piezoelectric response of each ferroelectric domain as write/read mechanism. The issues related to system integration is also discussed such as multi-probe array, x- and -y planar MEMS stage and packaging. The essence of the topics covered in each chapter is the ability to build, see and manipulate domain structures to understand the unexplained macroscopic phenomena and/or create ferroelectric thin film that shows novel and significantly improved physical, chemical properties and phenomena due to their nanoscale size. This forms the basis on which the existing technology can further improve its performance and/or a new and radical technology can evolve to change the rule of the game in the market. Nanoscale ferroelectric materials regardless of their dimensions (film, wire, island) are receiving great interests from academia and industry due to their various potential applications such as memory and storage devices (Ferroelectric Random Access Memory (FRAM), Probe-based Data Storage (PDS) System, etc), sensors (gas sensor, infrared detector, etc), and actuators

13 xiv (micro-mirrors, ultrasonic devices, etc). This book provides the compass to navigate the unknown sea of information related to the nanoscale phenomena occurring in ferroelectric thin films. The intended audience includes professional researchers and engineers in physics, electronics, chemistry, and material science who are interested either in nanotechnology or ferroelectrics. We believe that this book will set the standard as the leading book addressing fundamental questions in the area of nanoscale phenomena in thin film ferroelectrics. Therefore, we expect this to be a key book that will be used and referred by the field over the next ten years. Acknowledgment Seungbum Hong The editor is grateful for chapter reviews and suggestions of Carol Day and for essential support and constant help of Gregory Franklin at Kluwer Academic Publisher.