描述
开 本: 16开纸 张: 胶版纸包 装: 精装是否套装: 否国际标准书号ISBN: 9787030322630
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《纳电子学(纳米线分子电子学和纳米器件)(精)》(作者印纽斯基)汇集了30多位国际纳电子器件研究领域的学者和专家，他们长期在世界上(美国、意大利、加拿大、瑞士、德国等国)的**大学、国际知名研究机构和工业界从事纳电子学的教学、研究及实践工作。他们的研究工作属于国际一流水平，各章节内容基本基于各位作者自己的研究工作。本书由三个基本独立的部分组成：纳米线、分子电子器件和纳米器件，介绍了纳电子学的一些重要研究领域，对于从事相关领域研究的科研人员有一定的参考价值，可以作为研究人员和工程技术人员的参考书。但全书系统性不强，内容稍显杂乱，不适合作为本科生或研究生的教科书。
内容简介
纳电子学：纳米线，分子电子学和纳米器件详述了纳电子学的*进展，包括纳米线、分子电子学，以及纳米器件等内容。全书汇集了多个国家该领域的专家，主要讨论了*的技术及新兴的材料，比如碳纳米管和量子点器件。纳电子学：纳米线，分子电子学和纳米器件还纵览了纳米器件在下一代技术中的应用。
目 录
作者列表
前言
第一部分 纳米线
第1章 用于纳电子应用的金属纳米线的电特性
1.1 引言
1.2 金属纳米线的电阻
1.3 金属纳米线的失效机制
1.4 小结
第2章 波纹状铜互联线电迁移缺陷成核对构造和微观结构的依赖性
2.1 引言
2.2 电迁移
2.3 金属的纹理
2.4 实验装置
2.5 案例1
2.6 案例2
2.7 案例3
2.8 失效机制
第3章 CMOS集成电路中的碳纳米管互联线
3.1 引言
3.2 互联线尺寸缩小趋势
3.3 碳纳米管互联线
3.4 用于检验碳纳米管互联线性能的CMOS实验平台
3.5 片上多层碳纳米管互联线性能分析
3.6 结论和展望
第4章 纳米线集成电路的进展和挑战
4.1 引言
4.2 单壁碳纳米管合成
4.3 纳米线性能表征
4.4 纳米线组合
4.5 用于电子学、光电子学和传感器的可印刷纳米线
4.6 结论和展望
第二部分 分子电子学
第5章 印刷有机电子学:从材料到线路
5.1 引言
5.2 用于有机电子学的材料
5.3 基于印花的制造工艺
5.4 有机薄膜器件
5.5 结论
第6章 一维纳米结构化学传感
6.1 引言
6.2 半导电性金属氧化物纳米线的传感
6.3 金属氧化物纳米管传感
6.4 用于传感的聚合物纳米线
6.5 金属纳米线生物传感
6.6 结论
6.7 未来展望
第7章 纳米器件结构和复杂有机电子学的横截面制造和分析
7.1 引言
7.2 器件横截面制备和成像考虑
7.3 案例
7.4 未来展望和结论
第8章 纳米颗粒掺杂的导电聚合物的微细加工和应用
8.1 引言
8.2 填充系数和穿流淘值
8.3 纳米颗粒形状和材料
8.4 用于微系统的导电性纳米合成聚合物:制备和微成型
8.5 导电性纳米合成聚合物在微系统中的应用
8.6 总结和未来方向
第9章 用于三极管和存储器的有机纳米结构中的单电子导电性
9.1 引言
9.2 工作在4K的三极管
9.3 室温非有机三极管
9.4 室温有机三极管
9.5 基于有机单电子三极管的室温存储器
9.6 专利
9.7 结论
第10章 合成超分子生物电子纳米结构的最新进展
10.1 用于制造自组装材料的“超分子合成子”
10.2 Pi电子材料的一维超分子集合
10.3 用于生物材料的导电性聚合物
10.4 生物纳米结构中的肤—低聚喔吩配对
10.5 总结
第三部分 纳米器件
第11章 用于高级鲤离子电池的纳米结构电极材料的新进展
11.1 引言
11.2 纳米结构阴极材料
11.3 纳米结构阳极材料
11.4 结论
第12章 基于碳纳米管的量子点器件
12.1 引言
12.2 单电子器件理论
12.3 基于碳纳米管的量子点器件制备
12.4 结论
第13章 作为电机械促动器的单个碳纳米管:仿真和初步试验
13.1 引言
13.2 理论和仿真工作
13.3 单个碳纳米管的促动试验
13.4 结论及未来方向
第14章 纳米尺度的小信号电测量
14.1 引言
14.2 纳米技术实验回顾
14.3 用于纳米尺度测量的小信号测量技术
14.4 氮化嫁纳米线路的电子输运特性
14.5 结论
第15章 纳米ESD:纳米电子学时代的静电放电
15.1 引言
15.2 光刻板
15.3 磁记录
15.4 微电机械
15.5 二极管
15.6 硅纳米线
15.7 碳纳米管
15.8 结论
第16章 纳米封装
16.1 引言
16.2 纳米粒子
16.3 碳纳米管
16.4 健康和环境
16.5 结论
索引
前言
第一部分 纳米线
第1章 用于纳电子应用的金属纳米线的电特性
1.1 引言
1.2 金属纳米线的电阻
1.3 金属纳米线的失效机制
1.4 小结
第2章 波纹状铜互联线电迁移缺陷成核对构造和微观结构的依赖性
2.1 引言
2.2 电迁移
2.3 金属的纹理
2.4 实验装置
2.5 案例1
2.6 案例2
2.7 案例3
2.8 失效机制
第3章 CMOS集成电路中的碳纳米管互联线
3.1 引言
3.2 互联线尺寸缩小趋势
3.3 碳纳米管互联线
3.4 用于检验碳纳米管互联线性能的CMOS实验平台
3.5 片上多层碳纳米管互联线性能分析
3.6 结论和展望
第4章 纳米线集成电路的进展和挑战
4.1 引言
4.2 单壁碳纳米管合成
4.3 纳米线性能表征
4.4 纳米线组合
4.5 用于电子学、光电子学和传感器的可印刷纳米线
4.6 结论和展望
第二部分 分子电子学
第5章 印刷有机电子学:从材料到线路
5.1 引言
5.2 用于有机电子学的材料
5.3 基于印花的制造工艺
5.4 有机薄膜器件
5.5 结论
第6章 一维纳米结构化学传感
6.1 引言
6.2 半导电性金属氧化物纳米线的传感
6.3 金属氧化物纳米管传感
6.4 用于传感的聚合物纳米线
6.5 金属纳米线生物传感
6.6 结论
6.7 未来展望
第7章 纳米器件结构和复杂有机电子学的横截面制造和分析
7.1 引言
7.2 器件横截面制备和成像考虑
7.3 案例
7.4 未来展望和结论
第8章 纳米颗粒掺杂的导电聚合物的微细加工和应用
8.1 引言
8.2 填充系数和穿流淘值
8.3 纳米颗粒形状和材料
8.4 用于微系统的导电性纳米合成聚合物:制备和微成型
8.5 导电性纳米合成聚合物在微系统中的应用
8.6 总结和未来方向
第9章 用于三极管和存储器的有机纳米结构中的单电子导电性
9.1 引言
9.2 工作在4K的三极管
9.3 室温非有机三极管
9.4 室温有机三极管
9.5 基于有机单电子三极管的室温存储器
9.6 专利
9.7 结论
第10章 合成超分子生物电子纳米结构的最新进展
10.1 用于制造自组装材料的“超分子合成子”
10.2 Pi电子材料的一维超分子集合
10.3 用于生物材料的导电性聚合物
10.4 生物纳米结构中的肤—低聚喔吩配对
10.5 总结
第三部分 纳米器件
第11章 用于高级鲤离子电池的纳米结构电极材料的新进展
11.1 引言
11.2 纳米结构阴极材料
11.3 纳米结构阳极材料
11.4 结论
第12章 基于碳纳米管的量子点器件
12.1 引言
12.2 单电子器件理论
12.3 基于碳纳米管的量子点器件制备
12.4 结论
第13章 作为电机械促动器的单个碳纳米管:仿真和初步试验
13.1 引言
13.2 理论和仿真工作
13.3 单个碳纳米管的促动试验
13.4 结论及未来方向
第14章 纳米尺度的小信号电测量
14.1 引言
14.2 纳米技术实验回顾
14.3 用于纳米尺度测量的小信号测量技术
14.4 氮化嫁纳米线路的电子输运特性
14.5 结论
第15章 纳米ESD:纳米电子学时代的静电放电
15.1 引言
15.2 光刻板
15.3 磁记录
15.4 微电机械
15.5 二极管
15.6 硅纳米线
15.7 碳纳米管
15.8 结论
第16章 纳米封装
16.1 引言
16.2 纳米粒子
16.3 碳纳米管
16.4 健康和环境
16.5 结论
索引
在线试读
CHAPTER1 Electrical Properties of Metallic Nanowires for Nanoelectronic Applications
Carmen M. Lilley and Qiaojian Huang
Manyresearchershavefocusedonmetallicnanowire(NW)materials,suchasCu,Ag,andAunanowires,asbasicmaterialbuildingblocksfornanoelectronics.Thischapterwaswrittenwiththeintentionofprovidinganoverviewofelectricalpropertiesofmetallicnanowirematerialsusefultoresearchersandengineers.Researchersmay.ndtheinformationusefulindesigningnanoscaleelectricalsystemsbe-foretheyfabricatedevices.Thechapterisdividedsothatwebeginwithanoverviewofbasicelectricalproperties,suchaselectricalre-sistivityandthermalcoef.cientsofresistivity.Inaddition,wediscussparametersthatin.uencetheelectricalpropertiesatthenanoscale,suchassizeandsurfaceeffects.Finally,thischapterconcludeswithadiscussiononthefailurepropertiesofmetallicnanowires,suchasfailurefromJouleheatingandelectromigration,sothatthereliabil-ityofmaterialsystemcomponentscanbeconsideredinthedesignofnanoscaleelectricalsystems.
1.1 Introduction
Nanowireshaveawiderangeofapplicationsinelectronicsystems,forexampleasinterconnectwiresin.eld-effecttransistors,1 resonators,2.5nanomagnets,6.8and spintronic systems.9,10Nanowiresarealsocriticalcomponentsusedinthedesignofnanoelectrome-chanicalsystems(NEMSs),wheretheyhaveapplicationsasintercon-nectsincircuitsandsensorstodetectchemicalorbiologicalagents.
Aconsiderablechallengeisthesuccessfulintegrationofthesetypesofnanotechnologyintolargerscalesystemswithmultipleplatformsofintegration,sothatthenanosystemscaninteractwiththemacroscaleworld.Microscaleelectricalsystemsarealogicalchoiceasthe.rstplatformforintegrationofnanosystems,becausetheyaretheclosesttothenanosystemlengthscaleamongcurrentmanufacturedelec-tronicproducts.Thismakesmicrosystemsthebestcandidateasaplatformforintegrationandalinkforcontrolledinteractionwiththemacroscaleworld.Thesuccessfulintegrationofnanosystemsintomi-croscaleelectronicsdependsonstablematerialpropertiesthatarereli-ableforatleasta10-yearlifecycle(withgreaterthanatrillioncyclesofoperation).11 However,mostnanoscalesystemsfabricatedtodatearepronetomaterialinstabilities(forexample,oxidationofsurfacesoragglomerationofquantumdotsorcarbonnano.bers)thatnegativelyaffecttheirusefulness.
Therehasbeenmuchresearchintheareaofmodelingandchar-acterizationofsurfacepropertiesandcrystallinestructureofmetallicnanowiresandhowthesepropertiesin.uencetheirelectricalproper-ties.Withinthenanoscaledomain,forinstance,therehasbeencon-siderableresearchonthesizedependenceofelectricalresistivity.Forexample,asananowire’scriticaldimensiondecreasesfromhundredstotensofnanometers,theirelectricalresistivitywillincreasebecauseofsizeandsurfaceeffects.Asthecriticaldimensionsdecreasefurther,todimensionssmallerthan1nm,theirelectrontransportpropertieswillexhibitauniqueshifttoquantizedbehaviorthatcanonlybemodeledbyquantummechanics.Todate,however,thereislimitedresearchonthelong-termstabilityoftheseproperties.Itshouldbenotedthatthesurfaceandstructuralpropertiesofnanomaterialsmayleadtounexpectedmaterialfailures,whichareasigni.cantobstacletothereliabilityofthesematerialsystems.
Someofthemostcommonmetallicnanowirematerialsusedbyresearchersareface-centeredcubic(FCC)metalssuchascopper(Cu),silver(Ag),andgold(Au)synthesizedbybottom-upandtop-downapproaches.Foramonolithicnanowire,theelectricalandfailurepropertiesofthenanowirewillvarywithsizeandsurfaceproper-ties.Therefore,thischaptergivesanoverviewofelectricalproper-tiesofCu,Ag,andAunanowirematerialswithcriticaldimensionsofa10-to100-nmsizescale.Thein.uenceofsizeandsurfaceonthematerialpropertiesisalsodiscussed.Theaimofthischapteristoprovidethereaderwithpracticalinformationonmaterialprop-ertyconsiderationsofmetallicnanowireswhenplanningtodesignananoelectronicsystem.Inaddition,byprovidinginformationonfailureproperties,scientistsandengineerswillbeabletoincorpo-ratereliabilityofmaterialcomponentsintotheirdesignprocesses.Itisexpectedthatscientistsandengineerswill.ndthisinformationuseful for the practical design and fabrication of nanoelectronic systems.
1.1.1 Size and Surface Effects on Electrical Properties of Nanowires
Figure1.1illustratesthepercentageofsurfaceatomswithrespecttobulkatomsforanFCCclose-packednanoparticleofCuwithdi-ametersrangingfrom0.25to50.9nm.12 Ascanbeseen,theratioofsurfaceatomstobulkatomsbecomesincreasinglylargeastheparti-clesbecomesmaller.Therehasbeenmuchfocusonhowsurfacein-.uencesthematerialpropertiesofnanoscalestructures,wheresomeofthesesurfaceeffectsmayleadtochangesintheelectrical13,14or mechanical15.18propertiesofNWs.Forexample,apparentvariationsinmeasuredelasticmodulusforNWshavebeenattributedtoacom-binationofeffectsfromsurfacestressandsurfaceelasticity;seeforexampleRefs.15,16,and18.Inaddition,sizehasbeenfoundtoin-.uencetheelectricalresistivityofnanowires.Forexample,itisnowwellknownthatnanowireswithdimensionsbelow10nmcanex-hibitquantizedresistivitybehavior;andthisbehaviorhasbeenstud-iedextensivelyusingmoleculardynamicsimulationmethods.Fornanowiresizeslargerthan10nm,electronsurfacescatteringandelec-trongrainboundaryscatteringhavebeenshowntocauseanonlinearchangeintheelectricalresistivity.Fortheselargernanowirediame-ters,thewell-establishedkinetictheory(commonlyreferredtoastheFuchs-Sondheimertheory)hasbeenusedtomodeltheeffectsfromelectronsurfacescattering,andMayadas-Schatzkestheoryhasbeenusedtomodeltheeffectsfromelectrongrainboundaryscattering.
% of Surface Atoms
110 100 90 80 70 60 50 40 30 20 10 0
0 1020304050 Diameter (nm) of FCC Cu Nanoparticle
FIGURE1.1GraphofthepercentageofsurfaceatomswithrespecttobulkatomsforFCCclose-packedCunanoparticles.
InSection1.2,wepresentareviewofthesetheoreticalmodelsforsizeandsurfaceeffectsontheelectricalresistivityofananowire.
1.1.2 Stability of Nanomaterial Properties—Surface Matters
Adsorptionofsurfacecontaminantsisanothertypeofsurfaceeffectthatmaycausechangesinmaterialpropertiesatthenanoscale.Forexample,variationsintensilestrengthofAuNWswereattributedtothepresenceofcarbon(C),oxygen(O),andnitrogen(N).17 Sim-ilarly,exposuretoairorothersourcesofcontaminantsmayaffectthemeasuredresistanceandlong-termreliabilityofmetalNWs.14,19Forexample,researchershavefoundthattheagingmechanismsforpermalloys,suchasthoseofnickel(Ni)andiron(Fe),werearesultofoxidationanddiffusionofthisoxygenintothebulkNWmaterial.Thisoxidationandthesubsequentdiffusionofoxygencausetheelectricalresistivityofthenanowiretoincrease.Consequently,itwasfoundthatcappingthenanowiresurface,suchaswithathinsurface.lmofgold(15nm),preventedsurfaceoxidationandthusalsotheincreaseinelectricalresistance.19 However, Au has very high mobility and can readily contaminate silicon-on-insulator (SOI) devices at the wafer level.20 Therefore,itisunlikelythatAuwouldbeusedtofabricatenanoscaleelectronicsthatwouldbeintegratedintomicroelectronicsinacommercialfabricationsetting.Aspreviouslymentioned,thereislimitedpublishedresearchonthestabilityofnanoscalematerialproperties.However,researchersshouldtakenote:surfacecontami-nantsmayaffecttheirdesignofnanoscaleelectronicsystems,andtheymay.nditusefultoidentifythesurfacecompositionofthenanoma-terialsasawaytoidentifywhethersurfacecontaminantshaveanysigni.cantimpactontheirdesigns.
Asdiscussedpreviously,therelativeratioofsurfaceatomstobulk(orvolume)atomsinnanoscalesystemsincreasesdramaticallyasthenanostructuresdecreaseinsize.Thismayalsoin.uencemate-rialdiffusionatthesurface,becausetherearemoreatomspositionedatthesurface,andthesesurfaceatomsmaybedetachedmoreeas-ilyfromtheirequilibriumpositions.Thiswouldresultinmaterialshavingsurfacediffusionatlowertemperaturesascomparedtobulktemperatures.21 Thislowerdiffusiontemperature(orenhanceddif-fusivity)hasanimportantimpactonthestabilityofananowire.Forexample,Karabacaketal.recentlypublishedapremeltingtempera-tureof673to773Kforcoppernanorodarrayswithadiameterofapproximately100nm.21 Thispremeltingtemperaturerangeislowerthanthebulkmeltingtemperatureandisbelievedtobearesultofthenanowiresize.Otherresearchershavealsofoundthatalthoughthecurrent-to-failuredensityincreasesaswiresbecomesmaller,themeantemperaturetofailuremayactuallydecreaseascomparedtothebulkmelting temperatures.21,22Adecreaseinthetemperatureformaterialdiffusivitythereforemayaffectthemateriallifetimewheretheymayfailfromsucheffectsaselectromigration.
1.2 Electrical Resistivity of Metallic Nanowires
1.2.1 Electron Surface Scattering
Aspreviouslymentioned,sizeeffectsonelectricalresistivityformetal-licnanowireshavebeenmodeledbyvariousresearchersusingtwowell-establishedtheories,Fuchs-Sondheimerforelectronsurfacescat-tering,andMayadas-Schatzkesforgrainboundaryscattering.Thissectionprovidesabriefoverviewofthesetheories,andtheirappli-cationtoexperimentalresultsisdiscussedinthefollowingsection.Fuchs-Sondheimertheoryisalsocalledkinetictheoryandisawell-establishedtheorytomodelnonlinearchangesinelectricalresistivityforthin.lms.23,24Chambersappliedthistheorytomodeltheelec-tricalresistanceofwires.25 Herein,wewillpresenttheanalysisforatrapezoidalnanowiresystemusingChambers’sapproach,becausethismoregeneralgeometrycanbeappliedtomodelsquare,rectangu-lar,trapezoidal,andtriangularnanowires(allofwhichcanresultfromvariousnanofabricationmethods).Thevariablepisusedtocharac-terizetheprobabilityofelasticelectronre.ectionatthesurfacewherep=1foratotalelasticre.ectionandp=0forapurelydiffusescatter-ingandiscalledtheelectronsurfacescatteringcoef.cient.Forpurelyspecularscattering(p=0),thetheoreticalresistivitycanbeexpressedas
2ππ
ρo 32 .LOP
(p=0,λ)=dsdφdθsinθcosθ1.exp
ρFS4πsλ
s 00
(1.1)
whereρoisthebulkresistivityofthematerial,λistheelectronmeanfreepathofthematerial,sisthecross-sectionalsurfaceareaofthewire,pointOisonthesurfaceofacross-sectionalareaofthewire,andPisapointlocatedonthewiresurface.ThevectorOPconnectspointOtopointPandhasthelengthLOP.ThevectorOP. is the projection of the vector OP onto surface s. The angle φ is the radial angle for OP., and θ is the azimuthal angle of vector OP. Equation
(1.1)isintegratedoverallpointsonthesurfaces.Inessence,themeanfreepathforelectronsisreducedduetoelectronsurfacescatteringonthewiresurfacewhichcausesanincreaseinresistivityforthewireascomparedtothebulkmaterial.
(B )
TheequationfortheelectricalresistivityofatrapezoidalwireisgiveninEq.(1.2).ToderivethisequationfromEq.(1.1),we.rstconsiderapointOinthecrosssectionandelectronspassingthroughitinthedirectionofOP,wherePisonthetopwiresurface,asshowninFig.1.2.TheintegrationofEq.(1.1)isoveralllocationsthroughoutthewirecrosssections,withLOPbeingthedistancefromthelocationofpointOinthecrosssectiontothepointPonthewiresurfaceinthedirectionoftheazimuthalangleθandtheradialangleφ.Fromthiscalculation,theresultantelectronmeanfreepathinthewireisreducedtoλ[1.exp(.Lλ OP )] because of electron scattering on the wire surface.25 InFig.1.2,thedimensions2a,2b,andharethetopwidth,bottomwidth,andheightforthetrapezoidalwire,respectively.Thebottomangleofthetrapezoidwireisgivenby
h
α = arctan (1.2)
b . a
Thecross-sectionareaofthetrapezoidwireiswrittenas
(2a+2b)h
s==(a+b)h(1.3)
2
Byexaminingthein-planecrosssectionoftrapezoidABCD(thesur-faces)andtheprojectionofOP(OP.)fromtheelectrontravelingpath,
Carmen M. Lilley and Qiaojian Huang
Manyresearchershavefocusedonmetallicnanowire(NW)materials,suchasCu,Ag,andAunanowires,asbasicmaterialbuildingblocksfornanoelectronics.Thischapterwaswrittenwiththeintentionofprovidinganoverviewofelectricalpropertiesofmetallicnanowirematerialsusefultoresearchersandengineers.Researchersmay.ndtheinformationusefulindesigningnanoscaleelectricalsystemsbe-foretheyfabricatedevices.Thechapterisdividedsothatwebeginwithanoverviewofbasicelectricalproperties,suchaselectricalre-sistivityandthermalcoef.cientsofresistivity.Inaddition,wediscussparametersthatin.uencetheelectricalpropertiesatthenanoscale,suchassizeandsurfaceeffects.Finally,thischapterconcludeswithadiscussiononthefailurepropertiesofmetallicnanowires,suchasfailurefromJouleheatingandelectromigration,sothatthereliabil-ityofmaterialsystemcomponentscanbeconsideredinthedesignofnanoscaleelectricalsystems.
1.1 Introduction
Nanowireshaveawiderangeofapplicationsinelectronicsystems,forexampleasinterconnectwiresin.eld-effecttransistors,1 resonators,2.5nanomagnets,6.8and spintronic systems.9,10Nanowiresarealsocriticalcomponentsusedinthedesignofnanoelectrome-chanicalsystems(NEMSs),wheretheyhaveapplicationsasintercon-nectsincircuitsandsensorstodetectchemicalorbiologicalagents.
Aconsiderablechallengeisthesuccessfulintegrationofthesetypesofnanotechnologyintolargerscalesystemswithmultipleplatformsofintegration,sothatthenanosystemscaninteractwiththemacroscaleworld.Microscaleelectricalsystemsarealogicalchoiceasthe.rstplatformforintegrationofnanosystems,becausetheyaretheclosesttothenanosystemlengthscaleamongcurrentmanufacturedelec-tronicproducts.Thismakesmicrosystemsthebestcandidateasaplatformforintegrationandalinkforcontrolledinteractionwiththemacroscaleworld.Thesuccessfulintegrationofnanosystemsintomi-croscaleelectronicsdependsonstablematerialpropertiesthatarereli-ableforatleasta10-yearlifecycle(withgreaterthanatrillioncyclesofoperation).11 However,mostnanoscalesystemsfabricatedtodatearepronetomaterialinstabilities(forexample,oxidationofsurfacesoragglomerationofquantumdotsorcarbonnano.bers)thatnegativelyaffecttheirusefulness.
Therehasbeenmuchresearchintheareaofmodelingandchar-acterizationofsurfacepropertiesandcrystallinestructureofmetallicnanowiresandhowthesepropertiesin.uencetheirelectricalproper-ties.Withinthenanoscaledomain,forinstance,therehasbeencon-siderableresearchonthesizedependenceofelectricalresistivity.Forexample,asananowire’scriticaldimensiondecreasesfromhundredstotensofnanometers,theirelectricalresistivitywillincreasebecauseofsizeandsurfaceeffects.Asthecriticaldimensionsdecreasefurther,todimensionssmallerthan1nm,theirelectrontransportpropertieswillexhibitauniqueshifttoquantizedbehaviorthatcanonlybemodeledbyquantummechanics.Todate,however,thereislimitedresearchonthelong-termstabilityoftheseproperties.Itshouldbenotedthatthesurfaceandstructuralpropertiesofnanomaterialsmayleadtounexpectedmaterialfailures,whichareasigni.cantobstacletothereliabilityofthesematerialsystems.
Someofthemostcommonmetallicnanowirematerialsusedbyresearchersareface-centeredcubic(FCC)metalssuchascopper(Cu),silver(Ag),andgold(Au)synthesizedbybottom-upandtop-downapproaches.Foramonolithicnanowire,theelectricalandfailurepropertiesofthenanowirewillvarywithsizeandsurfaceproper-ties.Therefore,thischaptergivesanoverviewofelectricalproper-tiesofCu,Ag,andAunanowirematerialswithcriticaldimensionsofa10-to100-nmsizescale.Thein.uenceofsizeandsurfaceonthematerialpropertiesisalsodiscussed.Theaimofthischapteristoprovidethereaderwithpracticalinformationonmaterialprop-ertyconsiderationsofmetallicnanowireswhenplanningtodesignananoelectronicsystem.Inaddition,byprovidinginformationonfailureproperties,scientistsandengineerswillbeabletoincorpo-ratereliabilityofmaterialcomponentsintotheirdesignprocesses.Itisexpectedthatscientistsandengineerswill.ndthisinformationuseful for the practical design and fabrication of nanoelectronic systems.
1.1.1 Size and Surface Effects on Electrical Properties of Nanowires
Figure1.1illustratesthepercentageofsurfaceatomswithrespecttobulkatomsforanFCCclose-packednanoparticleofCuwithdi-ametersrangingfrom0.25to50.9nm.12 Ascanbeseen,theratioofsurfaceatomstobulkatomsbecomesincreasinglylargeastheparti-clesbecomesmaller.Therehasbeenmuchfocusonhowsurfacein-.uencesthematerialpropertiesofnanoscalestructures,wheresomeofthesesurfaceeffectsmayleadtochangesintheelectrical13,14or mechanical15.18propertiesofNWs.Forexample,apparentvariationsinmeasuredelasticmodulusforNWshavebeenattributedtoacom-binationofeffectsfromsurfacestressandsurfaceelasticity;seeforexampleRefs.15,16,and18.Inaddition,sizehasbeenfoundtoin-.uencetheelectricalresistivityofnanowires.Forexample,itisnowwellknownthatnanowireswithdimensionsbelow10nmcanex-hibitquantizedresistivitybehavior;andthisbehaviorhasbeenstud-iedextensivelyusingmoleculardynamicsimulationmethods.Fornanowiresizeslargerthan10nm,electronsurfacescatteringandelec-trongrainboundaryscatteringhavebeenshowntocauseanonlinearchangeintheelectricalresistivity.Fortheselargernanowirediame-ters,thewell-establishedkinetictheory(commonlyreferredtoastheFuchs-Sondheimertheory)hasbeenusedtomodeltheeffectsfromelectronsurfacescattering,andMayadas-Schatzkestheoryhasbeenusedtomodeltheeffectsfromelectrongrainboundaryscattering.
% of Surface Atoms
110 100 90 80 70 60 50 40 30 20 10 0
0 1020304050 Diameter (nm) of FCC Cu Nanoparticle
FIGURE1.1GraphofthepercentageofsurfaceatomswithrespecttobulkatomsforFCCclose-packedCunanoparticles.
InSection1.2,wepresentareviewofthesetheoreticalmodelsforsizeandsurfaceeffectsontheelectricalresistivityofananowire.
1.1.2 Stability of Nanomaterial Properties—Surface Matters
Adsorptionofsurfacecontaminantsisanothertypeofsurfaceeffectthatmaycausechangesinmaterialpropertiesatthenanoscale.Forexample,variationsintensilestrengthofAuNWswereattributedtothepresenceofcarbon(C),oxygen(O),andnitrogen(N).17 Sim-ilarly,exposuretoairorothersourcesofcontaminantsmayaffectthemeasuredresistanceandlong-termreliabilityofmetalNWs.14,19Forexample,researchershavefoundthattheagingmechanismsforpermalloys,suchasthoseofnickel(Ni)andiron(Fe),werearesultofoxidationanddiffusionofthisoxygenintothebulkNWmaterial.Thisoxidationandthesubsequentdiffusionofoxygencausetheelectricalresistivityofthenanowiretoincrease.Consequently,itwasfoundthatcappingthenanowiresurface,suchaswithathinsurface.lmofgold(15nm),preventedsurfaceoxidationandthusalsotheincreaseinelectricalresistance.19 However, Au has very high mobility and can readily contaminate silicon-on-insulator (SOI) devices at the wafer level.20 Therefore,itisunlikelythatAuwouldbeusedtofabricatenanoscaleelectronicsthatwouldbeintegratedintomicroelectronicsinacommercialfabricationsetting.Aspreviouslymentioned,thereislimitedpublishedresearchonthestabilityofnanoscalematerialproperties.However,researchersshouldtakenote:surfacecontami-nantsmayaffecttheirdesignofnanoscaleelectronicsystems,andtheymay.nditusefultoidentifythesurfacecompositionofthenanoma-terialsasawaytoidentifywhethersurfacecontaminantshaveanysigni.cantimpactontheirdesigns.
Asdiscussedpreviously,therelativeratioofsurfaceatomstobulk(orvolume)atomsinnanoscalesystemsincreasesdramaticallyasthenanostructuresdecreaseinsize.Thismayalsoin.uencemate-rialdiffusionatthesurface,becausetherearemoreatomspositionedatthesurface,andthesesurfaceatomsmaybedetachedmoreeas-ilyfromtheirequilibriumpositions.Thiswouldresultinmaterialshavingsurfacediffusionatlowertemperaturesascomparedtobulktemperatures.21 Thislowerdiffusiontemperature(orenhanceddif-fusivity)hasanimportantimpactonthestabilityofananowire.Forexample,Karabacaketal.recentlypublishedapremeltingtempera-tureof673to773Kforcoppernanorodarrayswithadiameterofapproximately100nm.21 Thispremeltingtemperaturerangeislowerthanthebulkmeltingtemperatureandisbelievedtobearesultofthenanowiresize.Otherresearchershavealsofoundthatalthoughthecurrent-to-failuredensityincreasesaswiresbecomesmaller,themeantemperaturetofailuremayactuallydecreaseascomparedtothebulkmelting temperatures.21,22Adecreaseinthetemperatureformaterialdiffusivitythereforemayaffectthemateriallifetimewheretheymayfailfromsucheffectsaselectromigration.
1.2 Electrical Resistivity of Metallic Nanowires
1.2.1 Electron Surface Scattering
Aspreviouslymentioned,sizeeffectsonelectricalresistivityformetal-licnanowireshavebeenmodeledbyvariousresearchersusingtwowell-establishedtheories,Fuchs-Sondheimerforelectronsurfacescat-tering,andMayadas-Schatzkesforgrainboundaryscattering.Thissectionprovidesabriefoverviewofthesetheories,andtheirappli-cationtoexperimentalresultsisdiscussedinthefollowingsection.Fuchs-Sondheimertheoryisalsocalledkinetictheoryandisawell-establishedtheorytomodelnonlinearchangesinelectricalresistivityforthin.lms.23,24Chambersappliedthistheorytomodeltheelec-tricalresistanceofwires.25 Herein,wewillpresenttheanalysisforatrapezoidalnanowiresystemusingChambers’sapproach,becausethismoregeneralgeometrycanbeappliedtomodelsquare,rectangu-lar,trapezoidal,andtriangularnanowires(allofwhichcanresultfromvariousnanofabricationmethods).Thevariablepisusedtocharac-terizetheprobabilityofelasticelectronre.ectionatthesurfacewherep=1foratotalelasticre.ectionandp=0forapurelydiffusescatter-ingandiscalledtheelectronsurfacescatteringcoef.cient.Forpurelyspecularscattering(p=0),thetheoreticalresistivitycanbeexpressedas
2ππ
ρo 32 .LOP
(p=0,λ)=dsdφdθsinθcosθ1.exp
ρFS4πsλ
s 00
(1.1)
whereρoisthebulkresistivityofthematerial,λistheelectronmeanfreepathofthematerial,sisthecross-sectionalsurfaceareaofthewire,pointOisonthesurfaceofacross-sectionalareaofthewire,andPisapointlocatedonthewiresurface.ThevectorOPconnectspointOtopointPandhasthelengthLOP.ThevectorOP. is the projection of the vector OP onto surface s. The angle φ is the radial angle for OP., and θ is the azimuthal angle of vector OP. Equation
(1.1)isintegratedoverallpointsonthesurfaces.Inessence,themeanfreepathforelectronsisreducedduetoelectronsurfacescatteringonthewiresurfacewhichcausesanincreaseinresistivityforthewireascomparedtothebulkmaterial.
(B )
TheequationfortheelectricalresistivityofatrapezoidalwireisgiveninEq.(1.2).ToderivethisequationfromEq.(1.1),we.rstconsiderapointOinthecrosssectionandelectronspassingthroughitinthedirectionofOP,wherePisonthetopwiresurface,asshowninFig.1.2.TheintegrationofEq.(1.1)isoveralllocationsthroughoutthewirecrosssections,withLOPbeingthedistancefromthelocationofpointOinthecrosssectiontothepointPonthewiresurfaceinthedirectionoftheazimuthalangleθandtheradialangleφ.Fromthiscalculation,theresultantelectronmeanfreepathinthewireisreducedtoλ[1.exp(.Lλ OP )] because of electron scattering on the wire surface.25 InFig.1.2,thedimensions2a,2b,andharethetopwidth,bottomwidth,andheightforthetrapezoidalwire,respectively.Thebottomangleofthetrapezoidwireisgivenby
h
α = arctan (1.2)
b . a
Thecross-sectionareaofthetrapezoidwireiswrittenas
(2a+2b)h
s==(a+b)h(1.3)
2
Byexaminingthein-planecrosssectionoftrapezoidABCD(thesur-faces)andtheprojectionofOP(OP.)fromtheelectrontravelingpath,
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