D.L. Pulfrey

D.L. Pulfrey

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

pulfrey@ece.ubc.ca

Carbon Nanotube Field-Effect Carbon Nanotube Field-Effect Transistors:Transistors:Critique ofCritique of

High-Frequency PerformanceHigh-Frequency Performance

L.C. CastroD.L. JohnLi Chen

http://nano.ece.ubc.ca

sp2 hybridized orbital, 3e-

(-bonds)2p orbital, 1e-

(-bonds)

1s orbital, 2e-

Hybridized carbon atom graphene monolayer carbon nanotube

Carbon Nanotubes

High mobility – quasi-1D, low m*, no surface states Small SCE - coaxial geometry

L.C. Castro

Employment of Employment of metallic CNTsmetallic CNTs

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

Fabricated Carbon Nanotube FETsFabricated Carbon Nanotube FETs

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

80nm C-CNFET80nm C-CNFETA. Javey et al., Nano Lett., 5, 345, 2005

Single-tube drawbacks:

Imax ~ A

Zout ~ k

High-frequency Carbon Nanotube FETHigh-frequency Carbon Nanotube FET

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

Experimental results for fExperimental results for fTT

"Ultimate"

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

Ballistic transport Ballistic transport

dEEzQEzvEzQEzvi

dEEzQEzQzQ

EDbSbD

EDSCNT

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

),(),()(

11

z sig

D

zCNT

D

G

TSD

zvdz

i

dzzQ

iQ

)(

)(

1

max,SD

max,

S

max,

max,

)ultimate""( and

)(then Q and If

),(),(

),(),()(

then

everywhere If

),(),(

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

b

G

bsig

SSD

EDS

EDS

bsig

bb

EDS

EDbSb

sig

vL

vzvQQQ

dEEzQEzQ

dEEzQEzQvzv

vv

dEEzQEzQ

dEEzQEzvEzQEzvzv

2

11

11

vvsigsig and and SDSD

SB-CNFET: summary of predictionsSB-CNFET: summary of predictions

"Ultimate"

C-CNFET: summary of predictions (July C-CNFET: summary of predictions (July 2007)2007)

C-CNFET: summary of predictions (latest)C-CNFET: summary of predictions (latest)

D.L. John et al., WOCSDICE, 2007

Energy where

most ∂Q occurs

D.L. Pulfrey et al., IEEE TNT, 2007

Regional delay timesRegional delay times

7.6 THz

Image charges in transistorsImage charges in transistors

QB QC

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

e

inbsig vv

qq

QQvv

1

BJT

FET: qg |qe| max,bsig vv

+

_

+

+

_

QB+qb QC+qcqe

++

++

_

_

_

qeQS+qs QD+qd

QG+qg

FET

+

+ +++ _

__

Q(E,z) in CNFETsQ(E,z) in CNFETs

-5.5eV

SB-CNFET C-CNFET

Insignificant resonance in channel)()(

max, zQDQvv bsig

1

Comparison 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

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

ConclusionsConclusions

• Multi-channel CNFETs needed for high current and for impedance matching.

• HF performance appears to be ultimately limited by vb,max.

• CNs have a vb,max advantage over Si of ~ 5 times.

• This could lead to a gm advantage (in C-CNFETs).

• Translating this advantage into superior fT and fmax will necessitate keeping

CGG low, which may be a technological issue.

• Seek applications not suited to Si.