Transcript No Slide Title

Carbon Nanotube Field-Effect Transistors:
Critique of
High-Frequency Performance
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
L.C. Castro
D.L. John
Li Chen
Carbon Nanotubes

Hybridized carbon atom  graphene monolayer  carbon nanotube
1s orbital, 2e-
sp2 hybridized
orbital, 3e(-bonds)
2p orbital, 1e(-bonds)

High mobility – quasi-1D, low m*, no surface states

Small SCE - coaxial geometry
L.C. Castro
Employment of
metallic CNTs
T. Iwai et al., (Fujitsu), 257, IEDM, 2005
Fabricated Carbon Nanotube FETs
300 nm SB-CNFET
A. Le Louarn et al., APL, 90, 233108, 2007
Single-tube drawbacks:
Imax ~ A
Zout ~ k
80nm C-CNFET
A. Javey et al., Nano Lett., 5, 345, 2005
High-frequency Carbon Nanotube FET
A. Le Louarn et al., APL, 233108, 2007
Experimental results for fT
"Ultimate"
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
Ballistic transport
QCNT ( z )   QS ( z, E )  QD ( z, E ) dE

E






i D    vb ( z , E )QS ( z , E )  vb ( z , E )QD ( z , E ) dE
E
vsig and SD

v sig ( z ) 
 SD 

1
T

QG
i D
  QCNT ( z ) dz
E
dz

v ( z)
z sig
 Q
S
( z , E )  QD ( z , E ) dE
E
If vb  vb ,max everywhere
then




QS ( z , E )  QD ( z , E ) dE
z
i D



  vb ( z , E )QS ( z , E )  vb ( z , E )QD ( z , E ) dE
v sig ( z )  vb ,max
E
 Q
S
E
If QD  QS
then
and
and
( z , E )  QD ( z , E ) dE


Q S  QS
v sig ( z )  vb ,max
 SD (" ultimate" ) 
LG
vb ,max
SB-CNFET: summary of predictions
"Ultimate"
C-CNFET: summary of predictions (July 2007)
C-CNFET: summary of predictions (latest)
Regional delay times
Energy
where
most
∂Q
occurs
7.6 THz
D.L. John et al., WOCSDICE, 2007
D.L. Pulfrey et al., IEEE TNT, 2007
Image charges in transistors
BJT
FET
_
+
_
+
_
+
QC
+
QS+qs
+
+
_
qe
FET: qg  |qe|
+
_
+
QB+qb
qe
BJT: qb < |qe|
_
_
_
+
QB
QG+qg
+ + +
QC+qc
v sig  vb ,max

qe
Q

Qin
qb
 v sig  vb ,max
QD+qd
 v sig  vb ,max
Q(E,z) in CNFETs
C-CNFET
SB-CNFET
-5.5eV
v sig  vb,max

Q( D)
Q( z )
Insignificant resonance in channel
Comparison of vband:
Si NW, Si planar and CNT
Si NW and planar Si
J.Wang et al.,
(11,0) CNT
Tight-binding
APL, 86, 093113, 2005
vb,max (CNT) higher by factor of ~ 5
Si MOSFET and CNFET: comparison
CN
oxide
S. Lee et al., IEDM, 241, 2005
W
(um)
Lg
(nm)
Tox
(nm)
gm
(mS)
Cgg
(aF)
Ft
(THz)
Exptl. (IBM)
80
27
1.05
108
52
0.33
Theor. (UBC)
80
7
2
448
37
1.93
FET
Status
Si MOS
C-CN coax
Gate
Conclusions
• Multi-channel CNFETs needed for high current and for impedance matching.
• HF performance appears to be ultimately limited by vb,max.
• CNs have a vb,max advantage over Si of ~ 5 times.
• This could lead to a gm advantage (in C-CNFETs).
• Translating this advantage into superior fT and fmax will necessitate keeping
CGG low, which may be a technological issue.
• Seek applications not suited to Si.