d.l. pulfrey department of electrical and computer engineering university of british columbia...
TRANSCRIPT
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
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
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
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
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.