Carbon Nanotube Field-Effect Transistors

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Carbon Nanotube Field-Effect Transistors and
their possible applications
Day 4B, May 30, 2008, Pisa
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Single-Walled Carbon Nanotube

• Hybridized carbon atom ? graphene monolayer ?
  carbon nanotube

L.C. Castro
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VECTOR NOTATION FOR NANOTUBES
Zig-zag (6,0)
Chiral tube
Armchair (3,3)
Adapted from Richard Martel
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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

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E-EF (eV) vs. k (1/nm)
Eg/2
(5,0) semiconducting
(5,5) metallic
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Properties relevant to devices discussed at Pisa

• 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
• me mh - 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 - perhaps devices can
  be assembled via biological recognition.

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Metallic CNTs as interconnects
T. Iwai et al., (Fujitsu), 257, IEDM, 2005
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CNT-assisted organic-cell photovoltaics
Keymakis, APL, 80, 112, 2002
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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 FETs
20nm -ve SB R.V. Seidel et al., Nano Letters,
Dec. 2004
50nm MOS A. Javey et al., Stanford
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Small m sub-threshold slope improvement
Non-thermionic process S lt 60 mV/dec !!
J. Appenzeller et al., IEEE TED, 4, 481, 2005
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Carbon Nanotube FETs for HF
300 nm SB-CNFET A. Le Louarn et al., APL, 90,
233108, 2007
Single-tube drawbacks Imax ?A Zout k?
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High-frequency Carbon Nanotube FET
A. Le Louarn et al., APL, 233108, 2007
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Experimental results for fT
"Ultimate"
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Schrödinger-Poisson Solver

• Need full QM treatment to compute
• -- Q(z) within barrier regions
• -- Q in evanescent states (MIGS)
• -- resonance, coherence
• -- S ? D tunneling.

D.L. John et al., Nanotech04, 3, 65, 2004.
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Schrödinger-Poisson Normalization
S
D
CNT
Unbounded plane waves
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MODE CONSTRICTION and TRANSMISSION
Doubly degenerate lowest mode
T
CNT (few modes)
METAL (many modes)
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Quantized Conductance
In the low-temperature limit
Interfacial G even when transport is ballistic
in CNT
155 ?S for M2
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Carbon nanotube FETs model structures
SB-CNFET K. Alam et al., APL, 87, 073104, 2005
C-CNFET D.L. Pulfrey et al., IEEE TNT, 2007
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Propagation velocity and fT
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Image charges in transistors
BJT
_

_

_

QB
QC
FET qg ? qe
BJT qb lt qe
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Comparison of vbandSi NW, Si planar and CNT
(11,0) CNT Tight-binding
Si NW and planar Si J.Wang et al., APL, 86,
093113, 2005
vb,max (CNT) higher by factor of 5
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Si MOSFET and CNFET comparison
S. Lee et al., IEDM, 241, 2005
FET Status W (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
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AMBIPOLAR CONDUCTION
Experimental data M. Radosavljevic et al.,
arXiv cond-mat/0305570 v1
Vds - 0.4V Vgs -0.15 0.05 0.30
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Mobile electroluminescence and the LET
DRAIN
SOURCE
Ambipolar CNFET
Gate-controlled light emission
McGuire and Pulfrey, Nanotechnology, 17, 5805,
2006
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Biomolecular sensing schemes
1. Electroluminescence
Spectrometer and/or Photodetector
Analyte
Source
Drain
Gate


VDS
VGS
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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
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Biomolecular sensing schemes
2. Conductance
Star et al., Nano Lett., 3(4), 459, 2003
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Sensing amino acids, dipeptides
Protein building blocks
Alanine-Glutamine, Glycine-Glutamine - reduces
muscle  wasting in inactive patients. Arginine-Glu
tamine - maintains muscle mass - boosts mucosal
immunity.
Glutamine-Glutamine - aids glutathione
biosynthesis. Tyrosine-Tyrosine - restores
PheTyr ratios in patients with renal disease.
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Simulation approach
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MD results
(12,11) CNs Dipeptides
Asparagine (hydrophilic)
Isoleucine (hydrophobic)
Abadir et al., IJHSE, accepted.
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Single-biomolecule detection
Asparagine (top) and isoleucine (bottom) adsorbed
on CNT between Al electrodes
Abadir et al., IEEE NANO Conf.
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Self-assembly of DNA-templated CNFETs
K. Keren et al., Science, 302, 1380, 2003