1

Carbon Nanotube Field-Effect Carbon Nanotube Field-Effect

TransistorsTransistors

and their possible applications and their possible applications

D.L. Pulfrey

Department of Electrical and Computer EngineeringUniversity of British ColumbiaVancouver, B.C. V6T1Z4, Canada

pulfrey@ece.ubc.ca

http://nano.ece.ubc.ca

Day 4B, May 30, 2008, Pisa

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Single-Walled Carbon NanotubeSingle-Walled Carbon Nanotube

2p orbital, 1e-

(-bonds)

Hybridized carbon atom graphene monolayer carbon nanotube

L.C. Castro

3

Chiral tubeChiral tube

a2

a1 (5,2) Tube(5,2) Tube

Structure (n,m):Structure (n,m):

VECTOR NOTATION FOR NANOTUBESVECTOR NOTATION FOR NANOTUBES

Adapted from Richard Martel

Zig-zag (6,0)Zig-zag (6,0)

Armchair (3,3)Armchair (3,3)

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From: Dresselhaus, Dresselhaus & Eklund. 1996 Science of Fullerenesand Carbon Nanotubes. San Diego, Academic Press. Adapted from Richard Martel.

Armchair

Zig-Zag

Chiral

CHIRAL NANOTUBESCHIRAL NANOTUBES

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Carbon Nanotube PropertiesCarbon Nanotube Properties

• Graphene sheet 2D E(k//,k)

– Quantization of transverse wavevectors

k (along tube circumference)

Nanotube 1D E(k//)

• Nanotube 1D density-of-states derived from [E(k//)/k]-1

• Get E(k//) vs. k(k//,k) from Tight-Binding Approximation

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E-EE-EFF (eV) (eV) vsvs. k. k|||| (1/nm)(1/nm)

(5,0) semiconducting (5,5) metallic

Eg/2

eV (nm)

80

2

d

.

d

aE CC

g

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• low m* - maybe good for tunneling transistor to reduce sub-threshold slope

• low m* and long mfp - high mobility - good for ION, gm, fT

- high conductivity - good for interconnects

- also, may help collection in polymer solar cells

• m*e = m*h - ambipolar conduction, maybe good for electroluminescence

• cylindrical shape - good for combating SCE

Properties relevant to devices discussed at PisaProperties relevant to devices discussed at Pisa

Other device possibilities:Other device possibilities:

• molecular size - may be useful as a molecular sensor

• biological compatibility - perhaps devices can be assembled via biological recognition.

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Metallic CNTs Metallic CNTs as as

interconnectsinterconnects

T. Iwai et al., (Fujitsu), 257, IEDM, 2005

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CNT-assisted organic-cell photovoltaicsCNT-assisted organic-cell photovoltaics

Keymakis, APL, 80, 112, 2002

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Is there a DIGITAL future for nanotubes?Is there a DIGITAL future for nanotubes?

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Tennenhouse04

12

H. Dai, APS, March, 2006

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Fabricated Carbon Nanotube FETsFabricated Carbon Nanotube FETs

20nm -ve SB20nm -ve SBR.V. Seidel et al., Nano Letters, Dec. 2004

50nm MOS50nm MOSA. Javey et al., Stanford

14Small m*: sub-threshold slope Small m*: sub-threshold slope improvementimprovement

Non-thermionic process:

S < 60 mV/dec !!

J. Appenzeller et al., IEEE TED, 4, 481, 2005

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Carbon Nanotube FETs for HFCarbon Nanotube FETs for HF

300 nm SB-CNFET300 nm SB-CNFETA. Le Louarn et al., APL, 90, 233108, 2007

Single-tube drawbacks:

Imax ~ A

Zout ~ k

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High-frequency Carbon Nanotube FETHigh-frequency Carbon Nanotube FET

A. Le Louarn et al., APL, 233108, 2007

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Experimental results for fExperimental results for fTT

"Ultimate"

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• Need full QM treatment to compute:

-- Q(z) within barrier regions

-- Q in evanescent states (MIGS)

-- resonance, coherence

-- S D tunneling.

Schrödinger-Schrödinger-Poisson SolverPoisson Solver

D.L. John et al., Nanotech04, 3, 65, 2004.

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Schrödinger-Poisson Schrödinger-Poisson NormalizationNormalization

S DCNT

Unbounded plane waves

)()()(

2)(

:currentLandauer andcurrent PD equatingby J.m Find

),( :define Instead,

:ionnormalizat spatial doCannot

**

1-

2

*

Q(z,E)n(z,E)ETEfq

EI

zzi

m

qEI

Ezn

dz

SL

PD

z

20

kx

kx

kz

E

METAL (many modes)

CNT (few modes)

Doubly degenerate lowest mode

MODE CONSTRICTIONMODE CONSTRICTIONandand

TRANSMISSIONTRANSMISSION

T

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Quantized Quantized ConductanceConductance

E DSee dEEfEfETM

h

qI )}(- )(){(

2

In the low-temperature limit:

Mh

qG

T

qVdEEfEfE DSSDS

2

D

2

1 if

- )}(- )({

Interfacial G: even when transport is ballistic in CNT

155 S for M=2

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Carbon nanotube FETs: model Carbon nanotube FETs: model structuresstructures

C-CNFETC-CNFETD.L. Pulfrey et al., IEEE TNT, 2007

SB-CNFETSB-CNFETK. Alam et al., APL, 87, 073104, 2005

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Propagation velocity and fPropagation velocity and fTT

dEEzQEzvEzQEzvi

dEEzQEzQzQ

E

DbSbD

E

DSCNT

),(),(),(),(

),(),()(

CC

z sig

D

z

CNT

D

G

TSD

zv

dz

i

dzzQ

i

Q

)(

)(

1

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Image charges in transistorsImage charges in transistors

QB QC

BJT: qb < |qe| max,max, bsigb

e

inbsig vv

q

q

Q

Qvv

C

BJT

FET: qg |qe| max,bsig vv

+

_

+

+

_

QB+qb QC+qcqe

+

+

+

+_

_

_

qeQS+qs QD+qd

QG+qg

FET

+

+ +++ _

__

25Comparison of vComparison of vbandband::Si NW, Si planar and Si NW, Si planar and

CNTCNT

Si NW and planar SiJ.Wang et al.,

APL, 86, 093113, 2005

(11,0) CNTTight-binding

vb,max (CNT) higher by factor of ~ 5

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FET StatusW

(um)Lg

(nm)Tox (nm)

gm (mS)

Cgg (aF)

Ft (THz)

               

Si MOS Exptl. (IBM) 80 27 1.05 108 52 0.33

C-CN coax Theor. (UBC) 80 7 2 448 37 1.93

Si MOSFET and CNFET: Si MOSFET and CNFET: comparisoncomparison

S. Lee et al., IEDM, 241, 2005

CN oxide Gate

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AMBIPOLAR CONDUCTIONAMBIPOLAR CONDUCTION

Experimental data:M. Radosavljevic et al., arXiv: cond-mat/0305570 v1

Vds= - 0.4VVgs= -0.15+0.05+0.30

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SOURCE

DRAIN

Ambipolar CNFET Gate-controlled light emission

McGuire and Pulfrey, Nanotechnology, 17, 5805, 2006

Mobile electroluminescence and the LETMobile electroluminescence and the LET

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Source Drain

Gate

Analyte

Spectrometer and/or Photodetector

Biomolecular sensing schemesBiomolecular sensing schemes

1. Electroluminescence

VGS

VDS

++

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CARBON NANOTUBES:

• size compatibility with biomolecules,

• exposed surface,

• interactions that modify band structure,

• change in LDOS.

CN biomolecular sensorsCN biomolecular sensors

Gruner, Anal. Bioanal. Chem., 384, 322, 2006

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Biomolecular sensing schemesBiomolecular sensing schemes

2. Conductance

Star et al., Nano Lett., 3(4), 459, 2003

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Alanine-Glutamine, Glycine-Glutamine: - reduces muscle  wasting in inactive patients.Arginine-Glutamine: - maintains muscle mass- boosts mucosal immunity.

Sensing amino acids, dipeptidesSensing amino acids, dipeptides

Protein building blocks

Glutamine-Glutamine:- aids glutathione biosynthesis.Tyrosine-Tyrosine:- restores Phe:Tyr ratios in patients with renal disease.

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Simulation approachSimulation approach

Molecular Dynamics

GROMACS

Density Functional Theory

ATOMISTIX• Transport

• Current

• Electroluminescence

• Atomic positions

• Electronic band structure

• LDOS as f(E, r, θ, z)

Non-Equilibrium Green's Function

ATOMISTIX

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(12,11) CNs

Dipeptides:

Asparagine (hydrophilic)

Isoleucine (hydrophobic)

MD resultsMD results

Abadir et al., IJHSE, accepted.

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Single-biomolecule detectionSingle-biomolecule detection

Asparagine (top) and isoleucine (bottom) adsorbed on CNT between Al electrodes

Abadir et al., IEEE NANO Conf.

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Self-assemblySelf-assembly of of

DNA-templated DNA-templated CNFETsCNFETs

K. Keren et al., Science, 302, 1380, 2003