Understanding Frank SMART U n d SENSORS e r s Understanding t a Third Edition Randy Frank n d Now in its third edition, Understanding Smart Sensors is the most complete, up-to-date, i n and authoritative summary of the latest applications and developments impacting smart g sensors in a single volume. This thoroughly expanded and revised edition of an Artech bestseller contains a wealth of new material, including: S • Critical coverage of sensor fusion and energy harvesting; M • The latest details on wireless technology; • The roles and challenges involved with sensor apps and cloud sensing, A • Greater emphasis on applications throughout the book; • Dozens of figures and examples of current technologies from over 50 companies. R SMART Utilizing the latest in smart sensors, microelectromechanical systems (MEMS), and T microelectronic research and development, readers get the technical and practical information they need to keep their designs and products on the cutting edge. Plus, S engineers see how network (wired and wireless) connectivity continues to impact smart sensor development and the emerging need for trusted sensing. E By combining information on micromachining and microelectronics, this is the first book SENSORS N that links these two important aspects of smart sensor technology so professionals don’t have to keep multiple references on hand. This comprehensive resource also includes an extensive list of smart sensor acronyms and a glossary of key terms. With an effective S blend of historical information and the latest content, the third edition of Understanding O Smart Sensors provides a unique combination of foundational and future-changing information. R Randy Frank is the president of Randy Frank and Associates in Scottsdale, Arizona. A well- Third Edition established author and holder of three patents, Mr. Frank received his B.S. and M.S. in S electrical engineering, as well as his M.B.A. in management, from Wayne State University in Detroit, Michigan. He is a Society of Automotive Engineers Fellow, former chairman and a member of the SAE Sensors Standards Committee, an IEEE Fellow, and a former T h member of the IEEE 1451 Smart Transducer Interface standards committee. i r d E d Include bar code: i t i o ISBN-13: 978-1-60807-507-2 n ISBN-10: 1-60807-507-9 Randy Frank BOSTON LONDON www.artechhouse.com Understanding Smart Sensors Third Edition For a listing of recent titles in the Artech House Integrated Microsystems Library, turn to the back of this book. Understanding Smart Sensors Third Edition Randy Frank Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the U.S. Library of Congress. British Library Cataloguing in Publication Data A catalog record for this book is available from the British Library. ISBN-13: 978-1-60807-507-2 Cover design by Vicki Kane © 2013 Artech House All rights reserved. Printed and bound in the United States of America. No part of this book may be reproduced or utilized in any form or by any means, elec- tronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without permission in writing from the publisher. All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized. Artech House cannot attest to the accuracy of this information. Use of a term in this book should not be regarded as affecting the validity of any trademark or service mark. Given® Imaging and PillCam® are registered trademarks of Given Imaging, Ltd. 10 9 8 7 6 5 4 3 2 1 To my granddaughter, Ashley. She and her generation will benefit from improvements in today’s smart sensors, and there will still be plenty of opportunities for them to advance the technology. Contents Preface xvii CHAPTER 1 Smart Sensor Basics 1 1.1 Introduction 1 1.2 Mechanical-Electronic Transitions in Sensing 3 1.3 Nature of Sensors 4 1.4 Integration of Micromachining and Microelectronics 9 1.5 Application Example 11 1.6 Summary 13 References 13 Selected Bibliography 14 CHAPTER 2 Micromachining 17 2.1 Introduction 17 2.2 Bulk Micromachining 18 2.3 Wafer Bonding 20 2.3.1 Silicon-on-Silicon Bonding 20 2.3.2 Silicon-on-Glass (Anodic) Bonding 21 2.3.3 Silicon Fusion Bonding 22 2.3.4 Wafer Bonding for More Complex Structures and Adding ICs 22 2.4 Surface Micromachining 24 2.4.1 Squeeze-Film Damping 26 2.4.2 Stiction 26 2.4.3 Particulate Control 26 2.4.4 Combinations of Surface and Bulk Micromachining 27 2.5 Other Micromachining Techniques 28 2.5.1 The LIGA Process 28 2.5.2 Dry Etching Processes 29 2.5.3 Micromilling 30 2.5.4 Lasers in Micromachining 31 2.6 Combining MEMS with IC Fabrication 32 2.7 Other Micromachined Materials 34 2.7.1 Diamond as an Alternate Sensor Material 34 vii viii Contents 2.7.2 Metal Oxides and Piezoelectric Sensing 35 2.7.3 Films on Microstructures 36 2.7.4 Micromachining Metal Structures 37 2.7.5 Carbon Nanotube MEMS 38 2.8 MEMS Foundry Services and Software Tools 38 2.9 Application Example 40 2.10 Summary 42 References 42 Selected Bibliography 45 CHAPTER 3 The Nature of Semiconductor Sensor Output 47 3.1 Introduction 47 3.2 Sensor Output Characteristics 47 3.2.1 Wheatstone Bridge 48 3.2.2 Piezoresistivity in Silicon 49 3.2.3 Semiconductor Sensor Definitions 51 3.2.4 Static Versus Dynamic Operation 53 3.3 Other Sensing Technologies 53 3.3.1 Capacitive Sensing 53 3.3.2 Piezoelectric Sensing 54 3.3.3 The Hall-Effect 55 3.3.4 Chemical Sensors 56 3.3.5 Improving Sensor Characteristics 56 3.4 Digital Output Sensors 57 3.4.1 Incremental Optical Encoders 57 3.4.2 Digital Techniques 59 3.5 Noise/Interference Aspects 59 3.6 Low Power, Low Voltage Sensors 60 3.6.1 Impedance 61 3.7 Analysis of Sensitivity Improvement 61 3.7.1 Thin Diaphragm 61 3.7.2 Increase Diaphragm Area 61 3.7.3 Improve Topology 61 3.8 Application Example 62 3.9 Summary 64 References 64 CHAPTER 4 Getting Sensor Information Into the Microcontroller 67 4.1 Introduction 67 4.2 Amplification and Signal Conditioning 68 4.2.1 Instrumentation Amplifiers 69 4.2.2 Sleep-Mode Circuitry for Reducing Power 70 4.2.3 Rail to Rail Operational Amplifiers 71 4.2.4 Switched-Capacitor Amplifier 72 Contents ix 4.2.5 Barometer Application Circuit 73 4.2.6 4- to 20-mA Signal Transmitter 73 4.2.7 Schmitt Trigger 74 4.3 Separate Versus Integrated Signal Conditioning 75 4.3.1 Integrated Signal Conditioning 75 4.3.2 External Signal Conditioning 76 4.4 Digital Conversion 76 4.4.1 A/D Converters 77 4.4.2 Performance of A/D Converters 79 4.4.3 Implications of A/D Accuracy and Errors 80 4.5 On-Line Tool for Evaluating a Sensor Interface Design 81 4.6 Application Example 81 4.7 Summary 81 References 83 Selected Bibliography 84 CHAPTER 5 Using MCUs/DSPs to Increase Sensor IQ 85 5.1 Introduction 85 5.1.1 Other IC Technologies 85 5.1.2 Logic Requirements 86 5.2 MCU Control 86 5.3 MCUs for Sensor Interface 87 5.3.1 Peripherals 87 5.3.2 Memory 88 5.3.3 Input/Output 89 5.3.4 On-Board A/D Conversion 90 5.3.5 Power Saving Capability 90 5.3.6 Local Voltage or Current Regulation 92 5.4 DSP Control 92 5.4.1 Digital Signal Controllers 93 5.4.2 Field Programmable Gate Arrays 93 5.4.3 Algorithms Versus Look-Up Tables 93 5.5 Techniques and Systems Considerations 95 5.5.1 Linearization 95 5.5.2 PWM Control 96 5.5.3 Autozero and Autorange 96 5.5.4 Diagnostics 98 5.5.5 Reducing EMC/RFI 98 5.5.6 Indirect (Computed not Sensed) Versus Direct Sensing 98 5.6 Software, Tools, and Support 99 5.6.1 Design-in Support 99 5.7 Sensor Integration 100 5.8 Application Example 101 5.9 Summary 102 References 103