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Transcript of D.L. Pulfrey Department of Electrical and Computer Engineering University of British Columbia...
D.L. Pulfrey
Department of Electrical and Computer EngineeringUniversity of British ColumbiaVancouver, B.C. V6T1Z4, Canada
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
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
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
E
DbSbD
E
DSCNT
),(),(),(),(
),(),()(
11
z sig
D
z
CNT
D
G
TSD
zv
dz
i
dzzQ
i
Q
)(
)(
1
max,SD
max,
S
max,
max,
)ultimate""( and
)(then
Q and If
),(),(
),(),(
)(
then
everywhere If
),(),(
),(),(),(),(
)(
b
G
bsig
SSD
E
DS
E
DS
bsig
bb
E
DS
E
DbSb
sig
v
L
vzv
QQQ
dEEzQEzQ
dEEzQEzQ
vzv
vv
dEEzQEzQ
dEEzQEzvEzQEzv
zv
2
11
11
vvsigsig and and SDSD
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
q
q
Q
Qvv
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, zQ
DQvv 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.