Understanding smart sensors second editi

Understanding Smart Sensors
Second Edition


For a listing of recent titles in the Artech House Sensors Library,
turn to the back of this book.


Understanding Smart Sensors
Second Edition

Randy Frank

Artech House
Boston • London


Library of Congress Cataloging-in-Publication Data
Frank, Randy.
Understanding smart sensors / Randy Frank.—2nd ed.
p.
cm.—(Artech House sensors library)
Includes bibliographical references and index.
ISBN 0-89006-311-7 (alk. paper)
1. Detectors—Design and construction.
2. Programmable controllers.
3. Signal processing—Digital techniques.
4. Semiconductors.
5. Application specific integrated circuits.
I. Title.

TA165.F724 2000
681’.2—dc21
00-021296
CIP

British Library Cataloguing in Publication Data
Frank, Randy
Understanding smart sensors.—2nd ed.—(Artech House sensors library)
1. Detectors—Design and construction
2. Programmable controllers
3. Signal processing—Digital techniques
4. Application specific integrated circuits
I. Title
681.2
ISBN 1-58053-398-1
Cover and text design by Darrell Judd
Cover image courtesy of Sandia National Laboratories
© 2000 ARTECH HOUSE, INC.
685 Canton Street
Norwood, MA 02062
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, electronic 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.
International Standard Book Number: 0-89006-311-7
Library of Congress Catalog Card Number: 00-021296
10 9 8 7 6 5 4 3 2 1

This Page Intentionally Left Blank


Dedicated to the memory of the one person who would have loved to see this book
but did not—my father, Carl Robert Frank.


Contents
Preface

1

xix

Smart Sensor Basics

1

1.1
1.2
1.3
1.4

Introduction

1

Mechanical-Electronic Transitions in Sensing

4

Nature of Sensors

5

Integration of Micromachining and
Microelectronics

11

1.5

Summary

15

References

16

Select Bibliography

16

Micromachining

17

Introduction

17

Bulk Micromachining

19

Wafer Bonding

21

Silicon-on-Silicon Bonding

22

Silicon-on-Glass (Anodic) Bonding

23

Silicon Fusion Bonding

24

2
2.1
2.2
2.3
2.3.1
2.3.2

2.3.3

vii


viii

Understanding Smart Sensors

2.3.4

Wafer Bonding for More Complex Structures and
Adding ICs

25

2.4
2.4.1
2.4.2
2.4.3
2.4.4

Surface Micromachining

25

Squeeze-Film Damping

29

Stiction

29

Particulate Control

30

Combinations of Surface and
Bulk Micromachining

30

2.5
2.5.1
2.5.2
2.5.3
2.5.4
2.5.5
2.6
2.6.1
2.6.2
2.6.3
2.6.4
2.7

Other Micromachining Techniques

31

LIGA Process

32

Dry-Etching Processes

32

Micromilling

36

Lasers in Micromachining

36

Chemical Etching and IC Technology

37

Other Micromachined Materials

40

Diamond as an Alternative Sensor Material

41

Metal Oxides and Piezoelectric Sensing

41

Films on Microstructures

42

Micromachining Metal Structures

43

Summary

44

References

44

The Nature of Semiconductor Sensor Output

49

Introduction

49

Sensor Output Characteristics

49

Wheatstone Bridge

50

Piezoresistivity in Silicon

52

Semiconductor Sensor Definitions

54

Static Versus Dynamic Operation

57

Other Sensing Technologies

57

Capacitive Sensing

58

Piezoelectric Sensing

59

3
3.1

3.2
3.2.1
3.2.2
3.2.3
3.2.4
3.3
3.3.1
3.3.2


Contents

3.3.3
3.3.4
3.3.5
3.4
3.4.1
3.4.2
3.5
3.6
3.6.1
3.7
3.7.1
3.7.2
3.7.3
3.8
4
4.1
4.2
4.2.1

4.2.2
4.2.3
4.2.4
4.2.5
4.2.6
4.2.7
4.2.8
4.3
4.3.1
4.3.2
4.4

ix

Hall Effect

60

Chemical Sensors

60

Improving Sensor Characteristics

61

Digital Output Sensors

62

Incremental Optical Encoders

63

Digital Techniques

64

Noise/Interference Aspects

65

Low-Power, Low-Voltage Sensors

66

Impedance

67

Analysis of Sensitivity Improvement

67

Thin Diaphragm

67

Increased Diaphragm Area

67

Combined Solution: Micromachining and
Microelectronics

68

Summary

68

References

69

Getting Sensor Information Into the MCU

71

Introduction

71

Amplification and Signal Conditioning

72

Instrumentation Amplifiers

73

SLEEPMODE™ Operational Amplifier

75

Rail-to-Rail Operational Simplifiers

76

Switched-Capacitor Amplifier

77

Barometer Application Circuit

79

4- to 20-mA Signal Transmitter

79

Schmitt Trigger

79

Inherent Power-Supply Rejection

81

Separate Versus Integrated Signal Conditioning

82

Integrated Passive Elements

83

Integrated Active Elements

84

Digital Conversion

86


x

Understanding Smart Sensors

4.4.1
4.4.2
4.4.3
4.5

A/D Converters

87

Performance of A/D Converters

89

Implications of A/D Accuracy and Errors

90

Summary

91

References

91

Using MCUs/DSPs to Increase Sensor IQ

93

5.1
5.1.1
5.1.2
5.2
5.3
5.3.1
5.3.2
5.3.3
5.3.4
5.3.5
5.3.6

5.3.7
5.4
5.4.1
5.5
5.5.1
5.5.2
5.5.3
5.5.4
5.5.5

Introduction

93

Other IC Technologies

93

Logic Requirements

94

MCU Control

95

MCUs for Sensor Interface

96

Peripherals

96

Memory

97

Input/Output

98

Onboard A/D Conversion

99

5.5.6

5

5.6
5.7

Power-Saving Capability

101

Local Voltage or Current Regulation

103

Modular MCU Design

103

DSP Control

104

Algorithms Versus Lookup Tables

106

Techniques and Systems Considerations

107

Linearization

108

PWM Control

108

Autozero and Autorange

109

Diagnostics

111

Reducing Electromagnetic Compatibility and
Radio Frequency Interference

111

Indirect (Computed, Not Sensed) Versus Direct
Sensing

112

Software, Tools, and Support

112

Sensor Integration

113


Contents

5.8
6
6.1
6.2
6.2.1
6.2.2

6.3
6.4
6.4.1
6.4.2
6.4.3
6.5
6.5.1
6.5.2
6.5.3
6.6
6.7
6.7.1
6.7.2
6.8
6.8.1
6.8.2
6.8.3
6.8.4
6.8.5
6.9
6.9.1
6.9.2
6.9.3

xi

Summary

116

References

116

Communications for Smart Sensors

119

Introduction

119

Definitions and Background

119

Definitions

119

Background

120

Sources (Organizations) and Standards

122

Automotive Protocols

123

SAE J1850

125

CAN Protocol

126

Other Automotive Protocols

129

Industrial Networks

130

Industrial Usage of CAN

130

LonTalk™ Protocol

131

Other Industrial Protocols

132

Office/Building Automation

133

Home Automation

134

CEBus

135

LonTalk™

135

Protocols in Silicon

135

MCU With Integrated SAE J1850

135

MCU With Integrated CAN

137

Neuron® Chips and LonTalk™ Protocol

139

MI-Bus

141

Other MCUs and Protocols

142

Other Aspects of Network Communications

142

MCU Protocols

143

Transition Between Protocols

143

Transition Between Systems

144


xii

Understanding Smart Sensors

6.9.4
6.10
7
7.1
7.1.1
7.1.2
7.1.3
7.2
7.3
7.4
7.5
7.6
7.6.1
7.7
7.7.1
7.7.2
7.8
7.9
8
8.1
8.1.1
8.1.2
8.2
8.2.1
8.2.2
8.2.3
8.2.4
8.3

The Protocol as a Module

145

Summary

146

References

146

Control Techniques

149

Introduction

149

Programmable Logic Controllers

150

Open- Versus Closed-Loop Systems

150

PID Control

150

State Machines

154

Fuzzy Logic

155

Neural Networks

157

Combined Fuzzy Logic and Neural Networks

160

Adaptive Control

161

Observers for Sensing

162

Other Control Areas

164

RISC Versus CISC

165

Combined CISC, RISC, and DSP

167

The Impact of Artificial Intelligence

168

Summary

169

References

170

Transceivers, Transponders, and Telemetry

173

Introduction

173

The RF Spectrum

174

Spread Spectrum

177

Wireless Data and Communications

179

Wireless Local Area Networks

180

FAX/Modems

180

Wireless Zone Sensing

181

Optical Signal Transmission

182

RF Sensing

183

Contents

8.3.1
8.3.2
8.3.3
8.3.4
8.3.5
8.3.6
8.3.7
8.3.8
8.3.9
8.4
8.5
8.6
9
9.1
9.2
9.2.1
9.2.2
9.2.3
9.2.4
9.2.5
9.2.6
9.3
9.3.1
9.3.2
9.3.3
9.3.4
9.3.5

9.3.6
9.3.7

xiii

Surface Acoustical Wave Devices

183

Radar

183

Global Positioning System

185

Remote Emissions Sensing

186

Remote Keyless Entry

187

Intelligent Transportation System

188

RF-ID

191

Other Remote Sensing

192

Measuring RF Signal Strength

192

Telemetry

192

RF MEMS

195

Summary

196

References

197

MEMS Beyond Sensors

201

Introduction

201

Micromachined Actuators

203

Microvalves

203

Micromotors

203

Micropumps

206

Microdynamometers

208

Microsteam Engines

210

Actuators in Other Semiconductor Materials

210

Other Micromachined Structures

211

Cooling Channels

211

Microoptics

213

Microgrippers

214

Microprobes

214

Micromirrors

215

Heating Elements

217

Thermionic Emitters

217


xiv

Understanding Smart Sensors

9.3.8
9.3.9
9.3.10
9.3.11
9.3.12
9.4
10
10.1
10.2
10.2.1
10.3
10.3.1
10.3.2
10.3.3
10.3.4
10.4
10.4.1
10.4.2
10.4.3
10.4.4

10.5
10.5.1
10.5.2
10.6
10.7
11
11.1

Field Emission Displays

219

Unfoldable Microelements

219

Micronozzles

221

Interconnects for Stacked Wafers

222

Nanoguitar

222

Summary

223

References

223

Packaging, Testing, and Reliability
Implications of Smarter Sensors

227

Introduction

227

Semiconductor Packaging Applied to Sensors

228

Increased Pin Count

231

Hybrid Packaging

231

Ceramic Packaging and Ceramic Substrates

232

Multichip Modules

232

Dual-Chip Packaging

233

Ball Grid Array Packaging

234

Packaging for Monolithic Sensors

235

Plastic Packaging

236

Surface-Mount Packaging

236

Flip-Chip

237

Wafer-Level Packaging

238

Reliability Implications

239

The Physics of Failure

242

Wafer-Level Sensor Reliability

243

Testing Smarter Sensors

244

Summary

245

References

246

Mechatronics and Sensing Systems

249

Introduction

249


Contents

11.1.1
11.2
11.3
11.3.1
11.3.2
11.3.3
11.3.4
11.4
11.4.1
11.4.2
11.4.3
11.5
11.5.1
11.5.2
11.5.3
11.6

xv

Integration and Mechatronics

250

Smart-Power ICs

250

Embedded Sensing

252

Temperature Sensing

252

Current Sensing in Power ICs

256

Diagnostics

256

MEMS Relays

261

Sensing Arrays

261

Multiple Sensing Devices

261

Multiple Types of Sensors

264

An Integrated Sensing System

265

Other System Aspects

265

Batteries

266

Field Emission Displays

266

System Voltage Transients, Electrostatic Discharge,
and Electromagnetic Interference
267
Summary

270

References

270

Standards for Smart Sensing

273

12.1
12.2

Introduction

273

Setting the Standards for Smart Sensors and
Systems

273

12.3
12.3.1
12.3.2
12.3.3
12.4
12.4.1
12.4.2
12.4.3
12.4.4

IEEE 1451.1

276

Network-Capable Application Processor

276

Network Communication Models

278

The IEEE 1451.1 Example

280

IEEE 1451.2

281

STIM

282

Transducer Electronic Data Sheet

284

TII

285

Calibration/Correction Engine

286

12


xvi

Understanding Smart Sensors

12.4.5
12.4.6
12.5
12.6
12.7
12.8
13
13.1
13.2
13.3
13.3.1
13.3.2
13.4
13.4.1
13.4.2
13.5
13.6

13.6.1
13.6.2
13.7
14
14.1
14.2
14.3
14.4
14.4.1
14.4.2
14.4.3

Sourcing Power to STIMs

289

Representing Physical Units in the TEDS

289

IEEE P1451.3

291

IEEE P1451.4

292

Extending the System to the Network

293

Summary

295

References

295

The Implications of Smart Sensor Standards

297

Introduction

297

Sensor Plug-and-Play

297

Communicating Sensor Data Via Existing Wiring 300
Ethernet

300

Sensing by Modem

300

Automated/Remote Sensing and the Web

301

Wireless Protocol

302

Remote Diagnosis

302

Process Control Over the Internet

303

Alternative Standards

305

Airplane Networks

306

Automotive Safety Network

306

Summary

308

References

308

The Next Phase of Sensing Systems

311

Introduction

311

Future Semiconductor Capabilities

313

Future System Requirements

315

Not-So-Futuristic Systems

317

Fabry-Perot Interferometer

317

HVAC Sensor Chip

318

Speech Recognition and Micromicrophones

319


Contents

14.4.4
14.4.5
14.4.6
14.4.7
14.4.8
14.5
14.5.1
14.6
14.7
14.8

xvii

Electrostatic Mesocooler

320

Microangular Rate Sensors

321

MCU With Integrated Pressure Sensor

321

Wireless Sensing in the Networked Vehicle

323

Personal ID Smart Sensor

324

Software, Sensing, and the System

325

CAD for MEMS

325

Alternative Views of Smart Sensing

326

The Smart Loop

328

Summary

329

References

330

List of Acronyms and Abbreviations

333

Glossary

351

Selected Bibliography

367

Books and Journals

367

Web Sites

368

About the Author

373

Index

375


This Page Intentionally Left Blank


Preface
The number one challenge facing engineers is rapidly changing technology,
according to a 1999 survey [1]. IBM estimates that more data has been generated in the past 30 years than in the previous 5,000 years! There certainly is no
lack of available information on what is happening and the ongoing activities in
the area of sensing, micromachining, and microelectromechanical systems
(MEMS). The difficulty comes in making effective decisions as users of the
technology or establishing a long-range plan of where a company might use
existing and future products to develop end-user products. This book condenses the existing material into a highly readable format and links the variety
of ongoing activities in the smart sensor and MEMS area.
According to Dana Gardner and as noted in the first edition of this book,
“By the year 2000, 50% of all engineers will design with sensors, up from 16%
who routinely used them at the beginning of the decade” [2]. I do not know if
that prediction came true, but the 1990s certainly should be remembered as the
decade when MEMS technology accelerated from the laboratory into production and the decade that established smart sensors through the IEEE 1451 standard. Micromachining technology will continue to be the primary reason for
sensors achieving cost breakthroughs that allow widespread sensor usage. At the
heart of most smart sensors will be digital integrated circuit technology.
Embedded microcontrollers already play a hidden role in most of the
common activities that occur in our daily lives. Use a cellular phone, receive a
page, watch television, listen to a compact disc, or drive a current model car

and you have the assistance of embedded microcontrollers. For example, there
are a dozen or so microcontrollers in a typical car, over 50 if you drive a wellequipped luxury vehicle. Semiconductor sensors provide many of the inputs to
xix


xx

Understanding Smart Sensors

those devices. The number of sensors and the intelligence level are increasing to
keep up with increasing control complexity.
Semiconductor sensors initially were developed to provide easier-tointerface, lower-cost, and more reliable inputs to electronic control systems.
The microcontrollers at the heart of these systems have increased in complexity
and capability while drastically achieving reduced cost per function. Semiconductor technology has also been applied to the input side for a few sensor
inputs (pressure, temperature, acceleration, optoelectronics, and Hall-effect
devices) but is just starting to broaden in scope (level of integration) and sensed
parameters and to achieve some of the cost-reduction benefits from integration.
The system outputs have done a better job of keeping up with advances
in semiconductor technology. The term smart power refers to semiconductor
power technologies that combine an output power device(s) with control circuitry on the same silicon chip. Both input and output devices are receiving
greater focus, the capability of combining technologies is being extended, and
the need for systems-level communications is finally making smart sensors a
reality.
Wen Ko of Case Western Reserve University established a vision for intelligent sensors [3], but Joe Giachino of Ford Motor Company is frequently
given credit for the term smart sensor, based on his 1986 paper [4]. Several others, including Middelhoek and Brignell, claim part of the credit for pioneering
the concept of smart sensors with capabilities beyond simple signal conditioning. The communication of sensory information is finally requiring consensus
for the true meaning of smart sensor.
The ultimate capabilities of new smart sensors will undoubtedly go far
beyond today’s projections. An understanding of what is possible today and
what can be expected in the future is necessary to take the first step toward

smarter sensing systems. This book is intended to provide the reader with
knowledge regarding a broad spectrum of possibilities based on current industry, university, and national laboratories’ R&D efforts in smart sensors. It discusses many recent developments that will affect sensing technology and future
products.
In this second edition, every chapter has been reviewed, and new, more
current material has been added. The recent balloting and acceptance of IEEE
1451.1 and 1451.2 provided the impetus for updating the first edition.
Chapters 12 and 13 address those important additions to the future of smart
sensing.
I would like to extend my sincere appreciation to Mark Shaw, whose concept of the phases of integration became an underlying theme for this book
and, I believe, the way that smart sensing will evolve. It certainly has held true


Preface

xxi

for well over 6 years. A number of other people played an important role in
making this book a reality:
•
•
•
•

•

Ray Weiss of Computer Design magazine provided methodology guidance and was the prime mover.
Mark Walsh and the team at Artech House were very supportive at
every step in the process.
Lj Ristic, Mark Shaw, Cindy Wood, and Mark Reinhard from
Motorola Semiconductor Products Sector provided chapter reviews.

Carl Helmers and the folks at Sensors magazine and Sensors Expo provided many publishing opportunities that were helpful in documenting several aspects of smart sensors.
Sandia National Laboratories provided material for cover artwork.

Finally, this book would not have been possible without the critical
evaluation, tolerance, and encouragement of my wife, Rose Ann. Any expression of appreciation is small compared to the sacrifices she made.

References
[1]

Design News, Jan. 18, 1999, p. 74.

[2]

Gardner, D. L., “Accelerometers for Exotic Designs,” Design News, July 17, 1989, p. 55.

[3]

Ko, W. H., and C. D. Fung, “VLSI and Intelligent Transducers,” Sensors and Actuators, 2
(1982), pp. 239–250.

[4]

Giachino, J. M., “Smart Sensors,” Sensors and Actuators, 10 (1986), pp. 239–248.


1
Smart Sensor Basics
A rose by any other name would smell as sweet.
—William Shakespeare
A rose with a microcontroller would be a smart rose.

—Randy Frank

1.1 Introduction
Just about everything today in the technology area is a candidate for having the
prefix smart added to it. The term smart sensor was coined in the mid-1980s,
and since then several devices have been called smart sensors. The intelligence
required by such devices is available from microcontroller unit (MCU), digital
signal processor (DSP), and application-specific integrated circuit (ASIC) technologies developed by several semiconductor manufacturers. Some of those
same semiconductor manufacturers are actively working on smarter silicon
devices for the input and output sides of the control system as well. The term
microelectromechanical system (MEMS) is used to describe a structure created
with semiconductor manufacturing processes for sensors and actuators. To
understand what is occurring today when advanced microelectronic technology
is applied to sensors, a brief review of the transitions that have occurred is
in order.
Before the availability of microelectronics, the sensors or transducers used
to measure physical quantities, such as temperature, pressure, and flow, usually
were coupled directly to a readout device, typically a meter that was read by an
1


2

Understanding Smart Sensors

observer. The transducer converted the physical quantity being measured to a
displacement. The observer initiated system corrections to change the reading
closer to a desired value. The typical blocks of a measurement system are shown
in Figure 1.1 [1].
Many home thermostats, tire pressure gauges, and factory flow meters

still operate in the same manner. However, the advent of microprocessor technology initiated the requirement for sensors to have an electrical output that
could be more readily interfaced to provide unattended measurement and
control. That also required the analog signal level to be amplified and converted to digital format prior to being supplied to the process controller.
Today’s MCUs and analog-to-digital (A/D) converters typically have a 5V
power supply, which has dictated the supply voltage for many amplified
and signal conditioned sensors. However, the reduction in the supply voltage
from 5V to 3.3V and even lower voltages and the presence of more than one
voltage in a system pose challenges not typically associated with even the smartest sensors. Separate integrated circuits (ICs) are available to handle the variety
of voltages and resolve the problem, but they add to system and sensor
complexity.
Commonly used definitions for the terms sensor and transducer must be
the first in the list of many terms that will be defined. A transducer is a device
that converts energy from one domain into another, calibrated to minimize the
errors in the conversion process [2]. A sensor is a device that provides a useful
output to a specified measurand. The sensor is a basic element of a transducer,
but it also may refer to a detection of voltage or current in the electrical regime
that does not require conversion. Throughout this book, the terms are used
synonymously, because energy conversion is part of every device that is discussed. The mechanical measurements that require a transducer to provide an
electrical output are listed in Table 1.1.

Calibration
input

Auxiliary
power (not always
required)

Auxiliary
power (usually
required)

Indicator

Measurand

Sensor/
transducer

Signal
conditioner

Recorder
Processor
Controller

Figure 1.1 General sensing system.


Smart Sensor Basics

3

Table 1.1
Mechanical Measurements
Measurement

Typical/Common Techniques

Displacement/position

Variable reluctance, Hall effect, optoelectronic

Temperature

Thermistor, transistor base-emitter voltage (Vbe)

Pressure

Piezoresistive, capacitive

Velocity (linear/angular)

Variable reluctance, Hall effect, optoelectronic

Acceleration

Piezoresistive, capacitive, piezoelectric

Force

Piezoresistive

Torque

Optoelectronic

Mechanical impedance

Piezoresistive

Strain

Piezoresistive

Flow

∆ pressure, or delta pressure

Humidity

Resistive, capacitive

Proximity

Ultrasonic

Range

Radar

Liquid level

Ultrasonic

Slip

Dual torque

Imminent collision

Radar

The definition of smart sensor (intelligent transducer) has not been as
widely accepted and is subject to misuse. However, an Institute of Electrical
and Electronics Engineers (IEEE) committee has been actively consolidating
terminology that applies to microelectronic sensors. The recently approved
IEEE 1451.2 specification defines a smart sensor as a sensor “that provides
functions beyond those necessary for generating a correct representation of a
sensed or controlled quantity. This function typically simplifies the integration
of the transducer into applications in a networked environment” [2]. That definition provides a starting point for the minimum content of a smart sensor.
Future smart sensors will be capable of much more, and additional classifications (e.g., smart sensor type 1) may be required to differentiate the products.
Chapter 12 addresses the IEEE-approved smart transducer interface for sensors
and actuators that establishes a standard for transducer-to-microprocessor communication protocols in a transducer electronic data sheet (TEDS) format.
That standard and others will provide further definition and differentiation for