Toward Carbon Based Electronics Beyond CMOS Devices
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Transcript of Toward Carbon Based Electronics Beyond CMOS Devices
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Philip Kim
Department of PhysicsColumbia University
Toward Carbon Based ElectronicsBeyond CMOS Devices
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End of the Road map:Quest for Beyond Si CMOS Era
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SP2 Carbon: 0-Dimension to 3-Dimension
Fullerenes (C60) Carbon Nanotubes
Atomic orbital sp2
GraphiteGraphene
0D 1D 2D 3D
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Outline: Carbon Based Electronics
Material Platform: Low dimensional graphitic systems
• 1-D: Carbon Nanotubes (since 1991)• 2-D: Graphene (since 2004)
Device Concepts
Conventional: (extended or ultimate) CMOS, SET
Non-Conventional: Quantum Interference, Spintronics, valleytronics
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Graphene : Dirac Particles in 2-dimension
Band structure of graphene (Wallace 1947)
kx
ky
Ene
rgy
kx' ky'
E
kvE F
Zero effective mass particles moving with a constant speed vF
hole
electron
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Single Wall Carbon Nanotube
ky
kxkx
ky
Allowed statesMetallic nanotube
E
k1D
E
k1D
Semiconducting nanotube
Eg ~ 0.8 ev / d (nm)
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400
200
0
6040200
Length (m)
Res
ista
nce
(k
)
T = 250 K
= 8 k/m
Extremely Long Mean Free Path in Nanotubes
Multi-terminal Device with Pd contact
* Scaling behavior of resistance:R(L)
5
678
10
2
3
4
5
678
100
2
3
4
5
67
0.12 4 6 8
12 4 6 8
102 4 6 8
L (m)
R (
k)
T = 250 K400
200
0
6040200
R (
k)
L (m)
R ~ RQ
R ~ L
el
L
Ne
h
Ne
hLR
22)(
le ~ 1 m
M. Purewall, B. Hong, A. Ravi, B. Chnadra, J. Hone and P. Kim, PRL (2007)Room temperature mean free path > 0.5 m
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Nanotube FET
Band gap: 0.5 – 1 eVOn-off ratio: ~ 106
Mobility: ~ 100,000 cm2/Vsec @RTBallistic @RT ~ 300-500 nmFermi velocity: 106 m/secMax current density > 109 A/cm2
Vsd (V)0-0.4-0.8-1.2
I sd (
A)
Ph. Avouris et al, Nature Nanotechnology 2, 605 (2007)
Schottky barrier switching
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Advantages of CNTFET
• Novel architecture ->Band-to-band tunneling FET:
subthreshold slop ~ 40 meV/dB @RT
• No-dangling bond at surface -> high k-dielectric compatible
Cg ~ CQ can be attainable; small RC, low energy
• Thin body (1-2 nm) -> suppressed short channel effectchannel length ~ 10 nm has been demonstrated
Javey et al. PRL (2004).
Appenzeller et al., PRL (2002)
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Rodgers, UIUC
Aligned growth of Nanotubes
Nanotube Electronics: ChallengesPros:High mobility High on-off ratioHigh critical current densitySmall channel lengthSmall gate capacitanceLarge Fermi velocity
Con:Controlled growth
Artistic dream (DELFT)
IBM, Avouris group
Nanotube Ring Oscillators
graphene
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Discovery of Graphene
Large scale growth efforts:CVD, MBE, chemical synthesis
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Num
ber o
f Gra
phen
e Pu
blic
ation
s on
arX
iv /
mon
th
Oct 05
Jun 05
Feb 05
Oct 04
Feb 07
Oct 06
Jun 06
Feb 06
Feb 08
Oct 07
Jun 07
Dec 05
Aug 05
Apr 05
Dec 04
Apr 07
Dec 06
Aug 06
Apr 06
Apr 08
Dec 07
Aug 07
Growth of Graphene Research
Jun 08
60
50
40
30
20
10
01
2
4
6
810
2
4
6
8100
factor 4 / year
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Graphene Mobility
103
104
105
-4 -2 0 2 4
n (1012 cm-2)
Mobility (cm
2/V sec)
TC17
TC12
TC145
TC130
Mechanically exfoliated graphene
Tan et al. PLR (2007)
Scattering Mechanism?
•Ripples•Substrate (charge trap)•Absorption•Structural defects
Modulate Doped GaAs: Pfeiffer et al.
GaAs HEMT
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High mobility materials have been under intensive research as an alternative to Silicon for higher performance
mobility: Si (1,400 cm2/Vsec), InSb (77,000 cm2/Vsec)
Graphene mobility: > 100,000 cm2/Vsec @ room temperature
104
105
106
-0.2 0.0 0.2
unsuspended best
before annealing
after annealing
Density ( 1012 cm-2)
Mob
ilit
y (c
m2 /
V s
ec)
Enhanced Room Temperature Mobility of Graphene
SEM image of suspended graphene
graphene
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Low temperature direct atomic layer deposition (ALD) of HfO2 as high-κ gate dielectric
Top-gate electrode is defined with a final lithography step.
I-V measurements at two different back gate voltages show a distinct “kink” for different top-gate voltages
Transconductance can be as high as gm = 328μS (150μS/μm)
Poor on-off ratio: ~ 5-10due to zero gap in
bulk
Graphene FET characteristics
Meric, Han, Young, Kim, and Shepard, Nature Nanotech (2008)