VLSI Custom Microelectronics: Digital: Analog, and Mixed-Signal

479 Pages·1998·3.032 MB·English

by  Stanley L. Hurst

ULSl CUSTOM MI CR OELECTR ON ICS
DIGITAL, ANALOG, AND MIXED-SIGNAL
STANLEY 1. HURST
Faculty of Technology (Retired)
The Open University
Milton Keynes, England
MARCEl
-
MARCELD EKKERI,N C. NEWY ORK BASEL
DEKKER
Library of Congress Cataloging-in-Publication Data
Hurst, S. L. (Stanley Leonard)
VLSI custom microelectronics : digital, analog, and mixed-signal /
Stanley L. Hurst.
p. cm.
Includes bibliographical references and index.
ISBN 0-8247-0220-4 (alk. paper)
1. Integrated circuits—Very large scale integration—Design and
construction—Data processing. 2. Computer-aided design.
I. Title
TK7874.75.H87 1998
621.39′5—dc21 98-31682
CIP
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Preface
Initsshortlifespan,microelectronicshasbecomethemostcomplexofourevery-
day technologies,embracing asitdoes physics,chemistry, materials,thermody-
namics, and micromechanical engineering, as well as electrical and electronic
engineering and computer science. No one person can hope to be expert in all
these diverse aspects.
Yetinspiteofallthiscomplexityandsophistication,weoftentaketheend
productsforgranted.Nowadays,ourhomescontaintensofthousandsoftransis-
tors in domestic appliances, communications, and entertainment equipment, to
addtothevastrangeofapplicationsinindustrial,military,space,andcommercial
products. To make all this possible has required the simultaneous evolution of
not onlytheability to fabricatethe microelectroniccircuitsthemselves,but also
theabilitytodesignthemwithouterrorsinthefirstplaceandtotestthemappro-
priately during and after production.
Thisisnotatextdetailingsilicondesignandfabricationmethods.Instead,
itisprincipallyconcernedwiththeimportantbranchofmicroelectronicsdealing
withcustomcircuits,wherebyspecificcircuitdesignsrequiredbyoriginalequip-
ment manufacturers can be realized rapidly and economically in possibly small
production quantities. Theterm application-specific IC (ASIC)has been widely
used up to now, but the more accurate term user-specific IC (USIC) is now in-
creasingly used. Custom circuits have only become viable with the maturity of
both the circuit fabrication methods and the computer-aided design resources
necessary for their design and test, thus releasing the circuit designer from per-
sonal involvement in the range and depth of detail involved.
However,havingsaidthis,itisthehallmarkofagoodengineertobeaware
ofall theaspectsinvolvedeven thoughheorshemay notneed—orindeed,not
beable—todoanythingaboutthem.Thistextadoptsthisapproach,andattempts
to give a comprehensive overview of all aspects of custom electronics, includ-
ing the very important but difficult managerial decisions of when or when not
to use it.
The concept of custom microelectronic circuits is not new; it has been
almostthreedecadessinceitssimpleconception,butitprobablydidnotachieve
verygreatprominenceuntiltheearly1980s.Theintroductionofthemicroproces-
sor as a readily available standard off-the-shelf part delayed the wider adoption
of custom microelectronics and still is a major force in all the initial ‘‘how-
shall-we-make-it’’productdesigndecisions.Nevertheless,customICsoffertheir
particular technical oreconomic advantages, and everyproduct designer should
be aware of the strengths as well as the weaknesses of both custom and other
design styles. These are the matters we shall consider in the pages of this text.
It is assumedthat the readerwill be familiar with theprinciples ofmicro-
electronic devices, semiconductor physics, basic electronic circuits, and system
designascoveredinmanystandardteachingtexts.Forreadersrequiringamore
detailedtreatmentthanisgivenhere,specifictextsdealingsolelywithsuchareas
asdevicephysics,computer-aideddesign,orotheraspects,shouldbeconsulted.
Regrettably, no one book (and no one author!) can cover all these aspects in
depth, but it is hoped that the references contained in these pages will point to
such additional in-depth information.
Theprinciplesofcustommicroelectronicsarenowwellestablished,butin
common with the whole of the microelectronics industry, there is a continual
evolutionincomplexityofdevices,inobsolescenceofparticularcomponentsand
CADresources,andintheriseandfallofindustrialcompaniesthatmakeupthe
customcircuitsfield.Itisthereforeinevitablethatsomeofthecommercialprod-
uctsdescribedinthistextwillnolongercontinuetorepresentthestatusquo,but
the basic educational points being made using these illustrations should remain
valid. It is therefore hoped that this book will enable readers to appreciate the
broadspectrumofcustommicroelectronicsandwillserveasanappropriaterefer-
ence to whatever newer products and design strategies evolve in this field.
Stanley L. Hurst
Contents
Preface
1 INTRODUCTION: THE MICROELECTRONICS EVOLUTION
1.1 Initial History
1.2 The Continuing Evolution
1.3 CAD Developments
1.4 Why Custom Microelectronics?
1.5 Summary
1.6 References
2 TECHNOLOGIES AND FABRICATION
2.1 Bipolar Silicon Technologies
2.2 Unipolar Silicon Technologies
2.3 Memory Circuits
2.4 BiCMOS Technology
2.5 Gallium-Arsenide Technology
2.6 A Comparison of Available Technologies
2.7 References
3 STANDARD OFF-THE-SHELF ICs
3.1 Nonprogrammable SSI, MSI and LSI Digital ICs
3.2 Standard Analog ICs
3.3 Microprocessors
3.4 Memory
3.5 Programmable Logic Devices
3.6 Logic Cell Arrays (LCAs)
3.7 Specialized Application-Specific Standard Parts (ASSPs)
3.8 Summary
3.9 References
4 CUSTOM MICROELECTRONIC TECHNIQUES
4.1 Full Hand-Crafted Custom Design
4.2 Standard Cell Techniques
4.3 Gate Array Techniques
4.4 Maskless Fabrication Techniques
4.5 Summary and Technical Comparisons
4.6 References
5 COMPUTER-AIDED DESIGN
5.1 IC Design Software
5.2 IC Simulation Software
5.3 Silicon Compilers
5.4 CAD Hardware Availability
5.5 CAD Software Availability
5.6 CAD Costs
5.7 Summary
5.8 References
6 TEST PATTERN GENERATION AND
DESIGN-FOR-TESTABILITY
6.1 Introduction
6.2 Basic Testing Concepts
6.3 Digital Test Pattern Generation
6.4 Test Pattern Generation for Memory and Programmable
Logic Devices
6.5 Microprocessor Testing
6.6 Design-for-Testability (DFT) Techniques
6.7 PLA Design-for-Testability Techniques
6.8 I/O Testing and Boundary Scan
6.9 Further Testing Concepts
6.10 The Silicon Area Overheads of DFT
6.11 Summary
6.12 References
7 THE CHOICE OF DESIGN STYLE: TECHNICAL AND
MANAGERIAL CONSIDERATIONS
7.1 The Microelectronic Choices
7.2 Packaging
7.3 Time to Market
7.4 Financial Considerations
7.5 Summary
7.6 References
8 CONCLUSIONS
8.1 The Present Status
8.2 Future Developments
8.3 Final Summary
8.4 References
APPENDIX A: The Elements and Their Properties
APPENDIX B: Fabrication and Yield
APPENDIX C: The Principal Equations Relating to Bipolar
Transistor Performance
APPENDIX D: The Principal Equations Relating to Unipolar
(MOS) Transistor Performance
Symbols and Abbreviations
1
Introduction: The Microelectronics
Evolution
Thedevelopmentofmicroelectronicsspanslessthanonehalfcentury—lessthan
one person’s life expectancy—but during this short period it has become the
most pervasive technology that has yet been developed. It touches all aspects
of our lives, embracing communications, transportation, entertainment, medical
matters,comfortandsafety,andyetmanyprofessionaldesignengineershavestill
tobecomeinvolvedinthedesignoforiginalproductsusingthefulladvantagesof
microelectronics.
In this introductory chapter we will survey the developments which have
ledtothepresentlevels ofmicroelectronicexpertise. AsnotedinthePreface,it
will be assumedthatthe readerisalready familiar withbasic electronic compo-
nents, particularly bipolar and MOS transistors, and also with basic electronic
circuit configurations and semiconductor physics. We will not attempt to deal
with these important fundamentals in any depth, but instead we will attempt to
coverthesubjectinawaythatisrelevanttoadesignengineerwhoincorporates
microelectronicsasameansofproducingnewandinnovativecompanyproducts.
The commercial hardware and software which may be mentioned in this text
must not be taken as representative of what may be available now and in the
future,sincebothareinacontinuousdynamicstateofrapidchangeanddevelop-
ment,butratherareusedinthefollowingpagesasillustrationsoftheprinciples
and practice of the areas being discussed.
1.1 INITIAL HISTORY
Thedevelopmentofthefirsttransistorin1948wasthestartofthemicroelectron-
ics evolution [1], although it was not until about the mid-1950s that suitable
discrete devices became available for use in industrial equipments. Early com-
mercial devices were germanium junction transistors, where the collector and
emitter regions were diffused from opposite sides into the base region to form
thepnpornpnconstruction.Althoughgermaniumhasahigherholeandelectron
mobility than silicon—0.39 and 0.19 m2 V(cid:1)1 s(cid:1)1, respectively, for germanium
compared with 0.14 and 0.05 m2 V(cid:1)1 s(cid:1)1 for silicon, thus making it easier to
achievehigh-frequencyperformance—thepoorertemperaturecharacteristicsand
the inability to protect the critical transistor perimeters (the ‘metallurgicaljunc-
tions’)ofgermaniummeantthatsiliconwouldbecomethedominantmicroelec-
tronic technology from the 1960s onwards.
Details of germanium versus silicon and other III/IV compounds may be
foundinmanystandardtextbooks[2–5].Thegradualdominanceofsilicontech-
nology was principally due to the development of planar fabrication, whereby
allthefabricationstepsaremadeononesurface(plane)ofthesiliconwafer(see
Chapter2)silicondioxideprovidingthekeytotheprotectionofthemetallurgical
junctionsaswellasprovidinggoodisolationbetweenareaswhererequired.Sili-
conwasinitiallymoredifficulttoprocessthangermanium[6],whichaccounted
in part for germanium being the first commercially used technology.
Thefirstpersontoperceivethepossibilityofafullyinterconnectedmono-
lithiccircuit,ratherthanthefabricationofdiscretesemiconductordeviceswhich
weretheninterconnectedbywiresorotherseparatemeans,wasprobablyG.W.A.
Dummerofthe(then) RoyalRadarEstablishment at GreatMalvern,Englandin
1952 [7–9]; however, the bulk of the development work was pioneered in the
UnitedStates,particularlybyJackKilbyofTexasInstruments,followedbyother
companies such as Fairchild and Sprague. By 1962 small scale integrated (SSI)
packages were becoming widely available for industrial use.
1.2 THE CONTINUING EVOLUTION
Sincethe1960sthehistoryofsilicontechnologyhasbeenoneofcontinuousand
rapidevolutionbaseduponplanartechniques.Duringthefollowingtwodecades
chipcomplexityincreasedfromtheinitialsmallscaleintegration(SSI)capability
throughmedium scale integration(MSI)andlargescale integration(LSI) tothe
present status of very large scale and ultra large scale integration (VLSI and
ULSI). This is indicated in the classic illustration shown in Figure 1.1 [10,11].
Sincethesiliconarearequiredfortransistorsislessthanthatrequiredforresistors
andcapacitors,theimpactofthisevolutiononelectroniccircuitdesignhasbeen
toencouragetheuseofactiveratherthanpassivedevices.Thischangeofempha-
sishasinitsturngivenrisetogreatlyimprovedcircuitperformance,sincemuch
moreoverallgainisreadilyavailableforcircuitdesignsthanwasthecasewhen
separateandrelativelyexpensiveactivedeviceswerenecessary.Theoperational
Fig. 1.1 The classic Moore’s Law graph, showing the increase in maximum possible
capability per single IC chip over the three decades since 1960. SSI is usually taken as
tens of transistors, MSI as hundreds of transistors, LSI as thousands, and VLSI as tens
ofthousandsoftransistors upwards.
amplifierandthemicroprocessor(seeChapter3)arebothgoodexamplesofthis
evolution.
The increase in capability shown in Figure 1.1 combines two effects,
namely the growth in possible wafer size and chip area and the decrease in on-
chip feature size. The improvements in these two parameters together combine
to give the overall increase in capability per IC, with over 107 transistors now
available on a single chip. At the same time performance and costs have im-
proved, as indicated in Figure 1.2. These developments are still continuing, but
possibly at a slower rate as device geometries become deep submicron and the
limitsofwell-establishedphotolithographictechniquesapproachtheirtheoretical
limit.The escalatingcostoffabricationlines tomanufacture state-of-the-artmi-
croelectronic circuits may also have a future slow-down effect on the rate of
increase of larger and more complex ICs.