Topics in Applied Physics Volume 24 ( Topics in Applied Physics Founded by Helmut K.V. Lotsch Vol. 1 Dye Lasers 2nd Edition Editor: F. P. Sch~ifer Vol. 2 Laser Spectroscopy of Atoms and Molecules Editor: H. Walther Vol. 3 Numerical and Asymptotic Techniques in Electromagnetics Editor: R. Mittra Vol. 4 Interactions on Metal Surfaces Editor: R. Gomer Vol. 5 MiJssbauer Spectroscopy Editor: U. Gonser Vol. 6 Picture Processing and Digital Filtering Editor: T. S. Huang Vol. 7 Integrated Optics Editor: T. Tamir Vol. 8 Light Scattering in Solids Editor: M. Cardona Vol. 9 Laser Speckle and Related Phenomena Editor: J. C. Dainty Vol. 10 Transient Electromagnetic Fields Editor: L. t3. Felsen Vol. 11 Digital Picture Analysis Editor: A. Rosenfeld Vol. 12 Turbulence Editor: P. Bradshaw Vol. 13 High-Resolution Laser Spectroscopy Editor: K. Shimoda Vol. 14 Laser Monitoring of the Atmosphere Editor: E. D. Hinkley Vol. 15 Radiationless Processes in Molecules and Condensed Phases Editor: 1=. K. Fong Vol. 16 Nonlinear Infrared Generation Editor: Y.-R. Shen Vol. 17 Eiectroluminescence Editor: J. I. Pankove Vol. 18 Ultrashort Light Pulses. Picosecond Techniques and Applications Editor: S. L. Shapiro Vol. 19 Optical and Infrared Detectors Editor: R. J. Keyes Vol. 20 Holographic Recording Materials Editor: H. M. Smith Vol. 21 Solid Electrolytes Editor: S. Geller Vol. 22 X-Ray Optics. Applications to Solids Editor: H.-J. Queisser Vol. 23 Optical Data Processing. Applications Editor: D. Casasent Vol. 24 Acoustic Surface Waves Editor: A. A. Oliner Vol. 25 Laser Beam Propagation in the Atmosphere Editor: J. W. Strohbehn Vol. 26 Photoemission in Solids I. General Principles Editors: M. Cardona and L. Ley Vol. 27 Photoemission in Solids If. Case Studies Editors: M. Cardona and L. Ley Vol. 28 Hydrogen in Metals I. Basic Properties Editors: G. Alefeld and J. V61kl Vol. 29 Hydrogen in Metals II. Application-Oriented Properties Editors: G. Alefeld and J. V61kl Acoustic Surface Waves Edited by A. A. Oliner With Contributions by E. A. Ash G.W. Farnell H.M. Gerard A.A. Oliner A.J. Slobodnik, Jr. H.I. Smith With 198 Figures Springer-Verlag Berlin Heidelberg New York 1978 Arthur A. Oliner, Ph. D. Polytechnic Institute of New York, 333 Jay Street Brooklyn, NY 11201, USA ISBN 3-540-08575-0 Springer-Verlag Berlin Heidelberg New York ISBN 0-387-08575-0 Springer-Verlag New York Heidelberg Berlin l.,ibrary of Congress Cataloging in Publication Data. Main entry under title: Acoustic surface waves. (Topics in applied physics; v. 24). I. Acoustic surface waves. I. Oliner, Arthur A. II. Ash, E. A. QC176.8.A3A3 530.4'1 77-17957 This work is is subject to copyright. All rights are reserved, whether the whole or part of material is concerned, specifically those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine or similar means, and storage in data banks. Under § 54 of the German Copyright Law, where copies are made for other than private use, a fee is payable to the publisher, the amount of the fee to be determined by agreement with the publisher. © by Springer-Verlag Berlin lteidelberg 1978 Printed in Germany The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relewmt protective laws and regulations and therefore free ~or general use. Monophoto typesetting, offset printing and bookbinding: BriJhlsche Universitfitsdruckerei, Lahn-Giessen 2153/3130-543210 Preface Acoustic surface waves form the basis of an exciting new field of applied physics and engineering, extending to several disciplines as diverse as nonde- structive evaluation (NDE), seismology, and signal processing in electronic systems. This field, often referred to as the SAW (Surface Acoustic Wave) field, has developed enormously during the last decade, particulary within the past half-dozen years, with its principal impact on signal processing, with important applications to radar, communications and electronic warfare. The extremely low velocity, and therefore extremely small wavelength, of these (ultrasonic) acoustic waves permits them to perform functions in a very simple fashion that would be very difficult or cumbersome to accomplish using any other technology. Devices from the VHF to the low microwave frequency range employing these waves are therefore very practical, in addition to offering dramatically small size and weight, combined with ruggedness and reliability. The vitality and strength of this field derive from its interdisciplinary nature, combining the talents of solid mechanicians, solid-state physicists, and micro- wave engineers. Great strides were therefore made quickly in both the under- standing of these acoustic wave types and in the ingenious engineering deve- lopments that have followed from this understanding. This book is concerned with the fundamentals of the acoustic surface wave field, with stress on implications for signal processing. The book includes in one place the following four most important basic aspects of this field: the properties of the basic wave types, the principles of operation of the most important devices and structures, the properties of materials which affect device performance, and the ways by which the devices are fabricated. The attempt throughout has been to stress the the fundamentals so that this book is not likely to be outdated soon. Although a variety of books and journal publications have appeared which present certain basic material or contain broad reviews, there is no single published source, to our knowledge, that duplicates the intent or the contents of this book. I wish to thank my contributors, each an acknowledged expert in his own specialty in this field, for their fine cooperation in the preparation of the manuscript. I am also very grateful to Mrs. Jean B. Maher for her superb typing skill, her perceptiveness in suggesting improvements, and her creative assistance in the preparation of the index. Brooklyn, NY A. A. Oliner January, 1978 Contents 1. Introduction. By A. A. Ol iner (With 2 Figures) . . . . . . . . . . 1 1.1 An Overv iew of the Field . . . . . . . . . . . . . . . . . 2 1.2 The Organ iza t ion of This Book . . . . . . . . . . . . . . 5 References . . . . . . . . . . . . . . . . . . . . . . . . . 11 2. Types and Properties of Surface Waves. By G. W. Farnel l (With 26 Figures) . . . . . . . . . . . . . . . . . . . . . . 13 2.1 The W a v e Equa t ions . . . . . . . . . . . . . . . . . . . 14 2.2 Surface W a v e Character is t ics . . . . . . . . . . . . . . . 17 2.2.1 I so t rop i cSubs t r a t e s . . . . . . . . . . . . . . . . . 20 2.3 Plate Modes . . . . . . . . . . . . . . . . . . . . . . 22 2.4 Aniso t ropy . . . . . . . . . . . . . . . . . . . . . . . 24 2.4.1 Basal Plane of Cubic Crystals . . . . . . . . . . . . . 26 2.4.2 (110) Plane of Cubic Crystals . . . . . . . . . . . . . 29 2.4.3 (111) Plane of Cubic Crystals . . . . . . . . . . . . . 30 2.5 Power F l o w . . . . . . . . . . . . . . . . . . . . . . . 31 2.6 Piezoelectr ici ty . . . . . . . . . . . . . . . . . . . . . 35 2.6.1 Stiffened Rayle igh Waves . . . . . . . . . . . . . . . 36 2.6.2 Bleus te in-Gulyaev Wave . . . . . . . . . . . . . . . 39 2.7 P ropaga t ion in Thin Layers . . . . . . . . . . . . . . . . 41 2.7.1 Rayle igh-Type Waves . . . . . . . . . . . . . . . . 41 2.7.2 Love Waves . . . . . . . . . . . . . . . . . . . . 47 2.7.3 An i so t ropy . . . . . . . . . . . . . . . . . . . . . 48 2.8 Reflect ions . . . . . . . . . . . . . . . . . . . . . . . 49 2.9 Diffract ion . . . . . . . . . . . . . . . . . . . . . . . 54 References . . . . . . . . . . . . . . . . . . . . . . . . . 59 3. Principles of Surface Wave Filter Design. By H. M. Gera rd (With 26 Figures) . . . . . . . . . . . . . . . . . . . . . . 61 3.1 His tor ical Background . . . . . . . . . . . . . . . . . . 61 3.1.1 The Interdigi ta l (ID) Transducer . . . . . . . . . . . . 62 3.1.2 The Surface Wave Fi l ter . . . . . . . . . . . . . . . 62 3.2 Basic Design Principles . . . . . . . . . . . . . . . . . . 64 3.2.1 Review of Genera l Four i e r Synthesis (Transversal Fi l ter Theory) . . . . . . . . . . . . . . 64 Vill Contents 3.2.2 The In te rd ig i ta l (ID) T ra nsduc e r as a Transversa l F i l t e r 66 3.2.3 Surface W a v e F i l te r Des ign Presc r ip t ion . . . . . . . . 68 3.3 Equiva len t Circui t Mode l . . . . . . . . . . . . . . . . . 72 3.3.1 The Crossed -F ie ld M o d e l . . . . . . . . . . . . . . 72 3.3.2 De l t a F u n c t i o n Represen ta t ion . . . . . . . . . . . . 76 3.3.3 Acous t ic /E lec t r i c Transfer F u n c t i o n . . . . . . . . . . 76 3.3.4 The A p o d i z a t i o n Law . . . . . . . . . . . . . . . . 80 3.4 T r a n sd uce r Pe r fo rmance Charac te r i s t i cs . . . . . . . . . . . 81 3.4.1 Des ign T rade -Of f Re la t ionsh ips . . . . . . . . . . . . 81 3.4.2 F i l t e r E r ro r Charac te r i s t i cs . . . . . . . . . . . . . . 86 3.4.3 O the r Trade-Offs . . . . . . . . . . . . . . . . . . 88 3.5 S u m m a r y and Examples . . . . . . . . . . . . . . . . . 89 3.5.1 Examples . . . . . . . . . . . . . . . . . . . . . 91 Append ices . . . . . . . . . . . . . . . . . . . . . . . . . 93 References . . . . . . . . . . . . . . . . . . . . . . . . . 96 4. Fundamentals of Signal Processing Devices. By E. A. Ash (With 54 Figures) . . . . . . . . . . . . . . . . . . . . . . 97 4.1 In t roduc t ion . . . . . . . . . . . . . . . . . . . . . . 97 4.2 De lay Lines . . . . . . . . . . . . . . . . . . . . . . . 99 4.2.1 Inser t ion and Spur ious Signals . . . . . . . . . . . . 99 4.2.2 De lay Line Bandwid th . . . . . . . . . . . . . . . . 101 4.2.3 T e m p e r a t u r e Stabi l i ty . . . . . . . . . . . . . . . . 102 4.2.4 Long De lay Lines . . . . . . . . . . . . . . . . . . 103 4.3 Acoust ic Surface Wave Resona to r s . . . . . . . . . . . . . 107 4.3.1 Surface W a v e Reflectors and Transmis s ion Cavi t ies 109 4.3.2 The g o a d e d Surface Wave R e s o n a t o r . . . . . . . . . 112 4.4 S A W Delay Line Osc i l l a to rs . . . . . . . . . . . . . . . . 117 4.4.1 M o d e Con t ro l for S ing le -F requency O p e r a t i o n . . . . . 118 4.4.2 Osc i l l a to r S tabi l i ty . . . . . . . . . . . . . . . . . 119 4.4.3 Tun ing and F M Capab i l i t y . . . . . . . . . . . . . . 124 4.4.4 Mul t i f requency Opera t ion . . . . . . . . . . . . . . . 125 4.5 C o d e d " T i m e - D o m a i n " Structures . . . . . . . . . . . . . . 128 4.5.1 Pulse C o m p r e s s i o n Fi l te rs for Ch i rp R a d a r . . . . . . . 129 4.5.2 P h a s e - C o d e d Transducers . . . . . . . . . . . . . . 137 4.5.3 Signal Process ing and L inear Ch i rp Fi l te rs . . . . . . . 143 4.6 Non l inea r Signal Processing . . . . . . . . . . . . . . . . 149 4.6.1 The P i e z o e l e c t r i c C o n v o l v e r . . . . . . . . . . . . . 153 4.6.2 Acous toe lec t r i c N o n l i n e a r Signal Process ing . . . . . . . 158 4.6.3 Acous toe lec t r ic Processing with Inheren t M e m o r y . . . . 163 4.7 M u l t i p o r t Acous t ic Devices . . . . . . . . . . . . . . . . 167 4.7.1 Mul t i s t r i p Coup le r - - Basis of O p e r a t i o n . . . . . . . . 169 4.7.2 Ful l Transfer Mul t i s t r ip Coup le r . . . . . . . . . . . . 173 4.7.3 Par t ia l Transfer Mul t i s t r ip C o u p l e r . . . . . . . . . . . 174 Contents IX 4.7.4 A s y m m e t r i c a l M u l t i s t r i p C o u p l e r for Beam C o m p r e s s i o n . 177 4.7.5 Acous t ic Surface W a v e Mul t ip lexers . . . . . . . . . . 178 References . . . . . . . . . . . . . . . . . . . . . . . . . 182 5. Waveguides for Surface Waves. By A. A. Ol iner (With 15 Figures) . 187 5.1 B a c k g r o u n d and Genera l Cons ide ra t i ons . . . . . . . . . . 187 5.1.1 W h y W a v e g u i d e s ? . . . . . . . . . . . . . . . . . . 187 5.1.2 Types of W a v e g u i d e . . . . . . . . . . . . . . . . . 189 5.2 F l a t Ove r l ay Wavegu ides . . . . . . . . . . . . . . . . . 192 5.2.1 The St r ip W a v e g u i d e . . . . . . . . . . . . . . . . 192 5.2.2 The Shor t ing -S t r ip (or Av/v) Wav e g u i d e . . . . . . . . 197 5.2.3 The Slot W a v e g u i d e . . . . . . . . . . . . . . . . . 198 5.3 T o p o g r a p h i c Wavegu ides . . . . . . . . . . . . . . . . . 200 5.3.1 The Ant i symmet r i c , or F lexura l , M o d e of the Rec tangu la r Ridge W a v e g u i d e . . . . . . . . . . . . . . . . . . 201 5.3.2 The Symmetr ic , or Pseudo-Rayle igh , M o d e of the Rec tangu la r Ridge W a v e g u i d e . . . . . . . . . . . . . . . . . . 204 5.3.3 Waves G u i d e d by a P la te Edge . . . . . . . . . . . . 206 5.3.4 The W e d g e W a v e g u i d e . . . . . . . . . . . . . . . . 211 5.4 O the r Types of W a v e g u i d e . . . . . . . . . . . . . . . . . 213 5.4.1 In-Diffused Wavegu ides . . . . . . . . . . . . . . . 213 5.4.2 Rec t angu la r O v e r l ay Wavegu ides . . . . . . . . . . . 214 5.4.3 Ci rcu la r F i b e r Wa v egu id e s . . . . . . . . . . . . . . 215 5.5 S u m m a r y and Conc lus ions . . . . . . . . . . . . . . . . 217 5.5.1 S u m m a r y o f W a v e g u i d e Proper t i e s . . . . . . . . . . . 217 5.5.2 App l i ca t i ons : Actua l and Potent ia l . . . . . . . . . . . 219 References . . . . . . . . . . . . . . . . . . . . . . . . . 221 6. Materials and Their Influence on Performance. By A. J. Slobodnik, Jr. (With 67 Figures) . . . . . . . . . . . . . . . . . . . . . . 225 6.1 The Laser P robe as a Basic M e a s u r e m e n t Tool . . . . . . . 225 6.1.1 Desc r ip t ion of the Laser P robe . . . . . . . . . . . . 226 6.1.2 Laser P robe App l i ca t ions and I n t r o d u c t i o n to At tenua t ion , Beam Steering, and Dif f rac t ion . . . . . . . . . . . . 228 6.2 P r o p a g a t i o n Loss . . . . . . . . . . . . . . . . . . . . 229 6.2.1 R o o m - T e m p e r a t u r e A t t enua t i on . . . . . . . . . . . 230 6.2.2 T e m p e r a t u r e Dependence of A t t e n u a t i o n . . . . . . . . 232 6.2.3 Air a n d G a s L o a d i n g . . . . . . . . . . . . . . . . 237 6.2.4 F r e q u e n c y and Ma te r i a l D e p e n d e n c e of P r o p a g a t i o n Loss . 242 6.2.5 The Effect of Surface Qua l i t y on A t t e n u a t i o n . . . . . . 244 6.3 Diff ract ion and Beam Steer ing . . . . . . . . . . . . . . . 251 6.3.1 Review of the Theor ies . . . . . . . . . . . . . . . . 251 6.3.2 L imi t a t i ons to the Pa rabo l i c Theo ry . . . . . . . . . . 254 6.3.3 L imi t a t i ons in Us ing the A ng u l a r Spec t rum of Waves Theo ry 257 X Contents 6.3.4 Material Dependence of Diffraction and Beam Steering . . 259 6.3.5 Min imal Diffraction Cuts . . . . . . . . . . . . . . . 267 6.4 O p t i m u m Transduce r Design in the Presence of Material Limi ta t ions . . . . . . . . . . . . . . . . . . . . . . . 273 6.5 Diffraction Compensa t i on in Periodic SAW Filters . . . . . . 279 6.5.1 In t roduc t ion . . . . . . . . . . . . . . . . . . . . 279 6.5.2 Basic Theory . . . . . . . . . . . . . . . . . . . . 280 6.5.3 Correc t ion for Diffraction . . . . . . . . . . . . . . 281 6.5.4 Exper imental Invest igat ion . . . . . . . . . . . . . . 283 6.6 Coupl ing Efficiency and Tempera tu re Coefficients . . . . . . 285 6.6.1 In t roduc t ion . . . . . . . . . . . . . . . . . . . . 285 6.6.2 Tempera tu re Coefficient C o m p u t a t i o n s . . . . . . . . . 287 6.6.3 Tempera tu re Coefficient, Coupl ing Trade-Offs, and Conclus ions . . . . . . . . . . . . . . . . . . 289 6.7 Non l inea r Effects . . . . . . . . . . . . . . . . . . . . 289 6.7.1 In t roduc t ion . . . . . . . . . . . . . . . . . . . . 289 6.7.2 Nonl inea r Effects in the F u n d a m e n t a l F requency Wave . 290 6.7.3 H a r m o n i c Gene ra t ion . . . . . . . . . . . . . . . . 290 6.7.4 Detai led Power Dependence . . . . . . . . . . . . . 294 6.7.5 Mixing . . . . . . . . . . . . . . . . . . . . . . 298 6.7.6 Summary and Conclus ions Conce rn ing Non l inea r Effects . 298 6.8 Summary and Propert ies of Materials . . . . . . . . . . . . 298 References . . . . . . . . . . . . . . . . . . . . . . . . . 301 7. Fabrication Techniques for Surface Wave Devices. By H. I. Smith (With 8 Figures) . . . . . . . . . . . . . . . . . . . . . . . 305 7.1 Techniques for Exposing Pat terns in Polymer Fi lms . . . . . . 305 7.1.1 Optical Project ion Pr in t ing . . . . . . . . . . . . . . 306 7.1.2 Conven t iona l Contac t Pr in t ing . . . . . . . . . . . . 306 7.1.3 Confo rmab le -Pho tomask Contac t Pr in t ing . . . . . . . 307 7.1.4 Holographic Recording . . . . . . . . . . . . . . . 310 7.1.5 Scanning Electron Beam Li thography . . . . . . . . . 311 7.1.6 Project ion Electron Li thography . . . . . . . . . . . 313 7.1.7 X-Ray Li thography . . . . . . . . . . . . . . . . . 314 7.2 Techniques for Pa t te rn ing the Substra te . . . . . . . . . . . 314 7.2.1 Aqueous Chemical Etching . . . . . . . . . . . . . . 316 7.2.2 Plasma Etching . . . . . . . . . . . . . . . . . . . 317 7.2.3 Ion B o m b a r d m e n t Etching . . . . . . . . . . . . . . 318 7.2.4 Dop ing . . . . . . . . . . . . . . . . . . . . . . 320 7.2.5 The Li f tof fTechnique . . . . . . . . . . . . . . . . 320 7.3 Conclus ions . . . . . . . . . . . . . . . . . . . . . . . 321 References . . . . . . . . . . . . . . . . . . . . . . . . . 322 Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . 325 Contributors Ash, Eric A. Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WCIE 7JE, Great Britain Farnell, Gerald W. Department of Electrical Engineering, McGill University, Montreal, Quebec H3A, 2K6, Canada Gerard, Henry M. Building 600, M/S C-241, Hughes Aircraft Company, Fullerton, CA 92634, USA Oliner, Arthur A. Microwave Research Institute, Polytechnic Institute of New York, 333 Jay Street, Brooklyn, NY 11201, USA Slobodnik, Andrew J., Jr. Electromagnetic Sciences Division, Deputy for Electronic Technology Rome Air Development Center (AFSC), Hanscom AFB, MA 01731, USA Smith, Henry I. MIT Lincoln Laboratory, P. O. Box 73, Lexington, MA02173, USA