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Transcript of D.L. Pulfrey, D.L. John, L.C. Castro Department of Electrical and Computer Engineering University of...
D.L. Pulfrey, D.L. John, L.C. Castro
Department of Electrical and Computer EngineeringUniversity of British ColumbiaVancouver, B.C. V6T1Z4, Canada
Performance Predictions forPerformance Predictions forCarbon Nanotube Field-Effect TransistorsCarbon Nanotube Field-Effect Transistors
Single-Walled Carbon NanotubeSingle-Walled Carbon Nanotube
2p orbital, 1e-
(-bonds)
Hybridized carbon atom graphene monolayer carbon nanotube
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)
d
aE CCg
2
• NANOSCALE -- no photolithography
•BANDGAP TUNABILITY -- 0.5-1.5eV
• METALS AND SEMICONDUCTORS -- all-carbon ICs
• BALLISTIC TRANSPORT -- 20-300nm
• STRONG COVALENT BONDING
-- strength and stability of graphite
-- no surface states (less scattering, compatibility with many insulators)
• HIGH THERMAL CONDUCTIVITY
-- almost as high as diamond (dense circuits)
• SELF-ASSEMBLY -- biological, recognition-based assembly
Compelling Properties of Carbon NanotubesCompelling Properties of Carbon Nanotubes
Self-assembly of DNA-templated CNFETsSelf-assembly of DNA-templated CNFETs K.Keren et al., Technion.
Self-assembly of DNA-templated CNFETsSelf-assembly of DNA-templated CNFETs K.Keren et al., Technion.
CLOSED COAXIAL NANOTUBE FET STRUCTURECLOSED COAXIAL NANOTUBE FET STRUCTURE
chirality: (16,0)
radius: 0.62 nm
bandgap: 0.63 eV
length: 15 - 100 nm
oxide thickness: (RG-RT): 2 - 6 nmq
VLV
qV
qVzRV
DDS
S
GGSG
),(
)0,(
),(
:ConditionsBoundary
kx
kx
kz
E
METAL (many modes)
CNT (few modes)
Doubly degenerate lowest mode
MODE CONSTRICTIONMODE CONSTRICTIONandand
TRANSMISSIONTRANSMISSION
T
Interfacial G: even when transport is ballistic in CNT
155 S for M=2
CURRENT in 1-D SYSTEMSCURRENT in 1-D SYSTEMS
E DSeeee
zz
z
E eSee
dEEfEfETh
qIII
dk
dE
hv
dE
dk
dE
dNEg
dEEvEgETEfEMqvqnI
)}(- )(){(4
)modes 2(
2
modes) 2 ng(consideri m.eV / states 2
)( DOS
)()()()()()1D()1D(
The Landauer currentThe Landauer current
General non-equilibrium General non-equilibrium casecase
E
f(E)
EFS
0.5
E
f(E)
EFD
0.5
g(E)
E
1D DOS
Non-equilib f(E-EC,z)
Q(z,E)=qf(E-EC,z)g(E-EC,z)
)(
)(
,
,
,,
midzcs
midC
midCSGSmidC
VfT
TfQ
VVCQ
Solve:Solve:1. Self-consistent SP2. Compact model
Quantum-Quantum-mechanical mechanical treatmenttreatment
• Need full QM treatment to compute:
-- Q(z) within barrier regions
-- Q in evanescent states (MIGS)
-- resonance, coherence
-- S D tunneling.
Emid
Transmission Probability TTransmission Probability TSS Comparison Comparison
Emid
VGS=VDS=0.4 V
CM1CM2
SP
D.L. John et al., Nanotech04, March 2004
VGS=0.4V
CM1
CM2
SP
L.C. Castro et al., Nanotechnology, submitted.
Drain I-V ComparisonDrain I-V Comparison
I-V dependence on S,D I-V dependence on S,D workfunctionworkfunction
Negative barrier(p-type) device
Positive barrier (p-type) device
VGS = -0.4 V
nm/A5
D.L. John et al., Nanotech04, March 2004
nm/A4.0
15nm Intel
continuous2
)( :1D
)( :2D
),()()(
2
2
,2
0
Q
metalQ
CSeCS
CSQ
CE
mEg
mqC
mEg
dEqVEfEgqQV
VQC
Quantum Quantum CapacitanceCapacitance
gate
insulator
nanotube
Cins
CQ
source
- - + -- - + -
Q
"Quantum" Capacitance in "Quantum" Capacitance in CNCN
D.L. John et al., JAP, submitted.
VDS=0.2V
Band Band 11
Band 2Band 2
VDS=0
Transconductance: the Ultimate LimitTransconductance: the Ultimate Limit
)}(- )({)(4
)}(- )(){(2
2
DSCDCSinsQ
insCm
E DSDSee
qVEfEfCC
CET
h
qg
dEqVEfEfETMh
qI
C
E
f(E)
EFS
0.5
E
f(E)
EFD
0.5
EC
nm/S05
nm/S1
15nm Intel
CONCLUSIONSCONCLUSIONS
• CNs have excellent thermal and mechanical properties.
• CNFETs can be self-assembled via biological recognition.
• QMR is important in negative-barrier SB-CNFETs.
• High DC currents and transconductances are feasible.
• Capacitance is not quantized.
• CNFETs deserve serious study as molecular transistors.