Transcript Slide 1
Carbon Nanotube Field-Effect Transistors and their possible applications
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D.L. Pulfrey
Department of Electrical and Computer Engineering University of British Columbia Vancouver, B.C. V6T1Z4, Canada [email protected]
http://nano.ece.ubc.ca
Day 4B, May 30, 2008, Pisa
Single-Walled Carbon Nanotube Hybridized carbon atom graphene monolayer carbon nanotube 2 L.C. Castro 2p orbital, 1e ( -bonds)
VECTOR NOTATION FOR NANOTUBES Adapted from Richard Martel a 1 a 2 Zig-zag (6,0) Chiral tube Structure (n,m): (5,2) Tube Armchair (3,3) 3
CHIRAL NANOTUBES
Armchair Zig-Zag Chiral
From: Dresselhaus, Dresselhaus & Eklund. 1996 Science of Fullerenes and Carbon Nanotubes. San Diego, Academic Press. Adapted from Richard Martel .
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Carbon 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 5
E-E F (eV) vs . k || (1/nm) 6 E g /2 (5,0) semiconducting (5,5) metallic
E g
2
a CC
d
0
.
8
d
(nm) eV
Properties relevant to devices discussed at Pisa 7 • low m* - maybe good for tunneling transistor to reduce sub-threshold slope • low m* and long mfp - high mobility - good for I ON , g m , f T - 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 Other device possibilities: • molecular size - may be useful as a molecular sensor • biological compatibility biological recognition.
- perhaps devices can be assembled via
T. Iwai et al., (Fujitsu), 257, IEDM, 2005
Metallic CNTs as interconnects 8
CNT-assisted organic-cell photovoltaics 9 Keymakis, APL, 80, 112, 2002
Is there a DIGITAL future for nanotubes?
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Tennenhouse04 11
H. Dai, APS, March, 2006 12
Fabricated Carbon Nanotube FETs 13 20nm -ve SB R.V. Seidel et al., Nano Letters, Dec. 2004 50nm MOS A. Javey et al., Stanford
Small m*: sub-threshold slope improvement 14 Non-thermionic process: S < 60 mV/dec !!
J. Appenzeller et al., IEEE TED, 4, 481, 2005
Carbon Nanotube FETs for HF 15 300 nm SB-CNFET
A. Le Louarn et al., APL, 90, 233108, 2007
Single-tube drawbacks: I max ~ A Z out ~ k
High-frequency Carbon Nanotube FET 16
A. Le Louarn et al., APL, 233108, 2007
Experimental results for f T "Ultimate" 17
• Need full QM treatment to compute: - Q(z) within barrier regions - Q in evanescent states (MIGS) -- resonance, coherence - S D tunneling.
Schrödinger-Poisson Solver 18
D.L. John et al., Nanotech04, 3, 65, 2004.
Schrödinger-Poisson Normalization S CNT D Unbounded plane waves Cannot do spatial normalizat ion :
z
*
dz
Instead, define :
n
(
z
,
E
) Find 1 by equating 2 PD current and Landauer current
I PD
(
E
)
q
2
m i
z
* *
z
:
I L
(
E
)
q
f S
(
E
)
T
(
E
)
n(z,E)
Q(z,E)
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MODE CONSTRICTION and TRANSMISSION E T CNT (few modes) k x METAL (many modes) Doubly degenerate lowest mode k x k z 20
Quantized Conductance
I e
2
q h M
E T e
(
E
){
f S
(
E
) -
f D
(
E
)}
dE
In the low-temperature limit:
E
{ if
f S T
(
E
) 1
f D
(
E
)}
dE
S
D
qV DS G
2
q
2
h M
Interfacial G: even when transport is ballistic in CNT 155 S for M=2 21
Carbon nanotube FETs: model structures SB-CNFET
K. Alam et al., APL, 87, 073104, 2005
22 C-CNFET
D.L. Pulfrey et al., IEEE TNT, 2007
Propagation velocity and f T 23
Q CNT
i D
(
z
)
E
v b
E
Q S
(
z
, (
z
,
E
)
Q S E
) (
z
,
E
)
Q D
(
z
,
E
)
dE v b
(
z
,
E
)
Q D
(
z
,
E
)
dE
SD
1
T
Q G
i D
z
Q CNT
i D
(
z
)
dz
z dz v sig
(
z
)
Image charges in transistors
_ _ _
Q B
_
BJT
_
Q B +q b q e BJT: q b < |q e | FET
+ + +
Q G +q g
+ + + _ + _ _
Q C Q S +q s
+ + + +
FET: q g |q e | Q C +q c
v sig
v b
, max
Q
Q in
q q b e
v sig
v b
, max q e Q D +q d
v sig
v b
, max
+
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Comparison of v band : Si NW, Si planar and CNT 25 Si NW and planar Si
J.Wang et al., APL, 86, 093113, 2005
(11,0) CNT
Tight-binding
v b,max (CNT) higher by factor of ~ 5
Si MOSFET and CNFET: comparison 26 CN oxide Gate
S. Lee et al., IEDM, 241, 2005
FET Status W (um) Si MOS C-CN coax Exptl. (IBM) Theor. (UBC) 80 80 Lg (nm) Tox (nm) gm (mS) 27 7 1.05
2 108 448 Cgg (aF) Ft (THz) 52 37 0.33
1.93
27 AMBIPOLAR CONDUCTION Experimental data: M. Radosavljevic et al., arXiv: cond-mat/0305570 v1 Vds= - 0.4V
Vgs= -0.15
+0.05
+0.30
Mobile electroluminescence and the LET DRAIN SOURCE Ambipolar CNFET Gate-controlled light emission McGuire and Pulfrey, Nanotechnology, 17, 5805, 2006 28
Source Biomolecular sensing schemes 1. Electroluminescence Spectrometer and/or Photodetector Analyte Drain Gate + V GS V DS + 29
CN biomolecular sensors CARBON NANOTUBES: • size compatibility with biomolecules, • exposed surface, • interactions that modify band structure, • change in LDOS. Gruner, Anal. Bioanal. Chem., 384, 322, 2006 30
2. Conductance Biomolecular sensing schemes Star
et al.,
Nano Lett., 3(4), 459, 2003 31
Sensing amino acids, dipeptides Protein building blocks Alanine-Glutamine, Glycine-Glutamine: - reduces muscle wasting in inactive patients.
Arginine-Glutamine: - maintains muscle mass - boosts mucosal immunity.
Glutamine-Glutamine: - aids glutathione biosynthesis.
Tyrosine-Tyrosine: - restores Phe:Tyr ratios in patients with renal disease.
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Simulation approach Molecular Dynamics GROMACS Density Functional Theory ATOMISTIX Non-Equilibrium Green's Function ATOMISTIX • Atomic positions • Electronic band structure • LDOS as f(E, r, θ, z) • Transport • Current • Electroluminescence 33
(12,11) CNs Asparagine (hydrophilic) Dipeptides: Isoleucine (hydrophobic) Abadir et al., IJHSE, accepted.
MD results 34
Single-biomolecule detection 35 Asparagine (top) and isoleucine (bottom) adsorbed on CNT between Al electrodes Abadir et al., IEEE NANO Conf.
Self-assembly of DNA-templated CNFETs
K. Keren et al., Science, 302, 1380, 2003 36