1 carbon nanotube field-effect transistors carbon nanotube field-effect transistors and their...
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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
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
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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
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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
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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
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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
+
+ +++ _
__
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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