Post on 22-Jan-2021
transcript
III-V FET Channel Designs for High Current Densities and Thin Inversion Layers
rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax
Mark Rodwell University of California, Santa Barbara
Coauthors:
W. Frensley: University of Texas, Dallas
S. Steiger, S. Lee, Y. Tan, G. Hegde, G. KlimekNetwork for Computational Nanotechnology, Purdue University
E. Chagarov, L. Wang, P. Asbeck, A. Kummel, University of California, San Diego
T. BoykinUniversity of Alabama, Huntsville
J. N. SchulmanThe Aerospace Corporation, El Segundo, CA.
2010 IEEE Device Research Conference, June 21-23, Notre Dame, Indiana
Acknowledgements: Herb Kroemer (UCSB), Bobby Brar (Teledyne) Art Gossard (UCSB), John Albrecht (DARPA)
Thin, high current density III-V FET channels
InGaAs, InAs FETsTHz & VLSI need high currentlow m*→ high velocities
Density of states bottleneck (Solomon & Laux IEDM 2001)
→ For < 0.6 nm EOT, silicon beats III-Vs
FET scaling for speed requires increased charge densitylow m* →low charge density
Open the bottle !
low transport mass → high vcarrier
multiple valleys or anistropic valleys → high DOSUse the L valleys.
Simple FET ScalingGoal: double transistor bandwidth when used in any circuit
→ reduce 2:1 all capacitances and all transport delays
→ keep constant all resistances, voltages, currents
)/(~/ gggsgm WLCvWg
ggggsggs LLWCWC )/(/
~/, gfgs WC
~/ ggd WC
. ),/( ),/( , )/( doublemust wespeed, double To D sgggsggm nWLCWIWg
must increase gate
capacitance/area
must reduce
gate length
gate-source, gate-drain
fringing capacitances:
0.15-0.25 fF/mm
laws in constant-voltage limit:
FET Scaling Laws
GW widthgate
GL
FET parameter change
gate length decrease 2:1
current density (mA/mm), gm (mS/mm) increase 2:1
channel 2DEG electron density increase 2:1
electron mass in transport direction constant
gate-channel capacitance density increase 2:1
dielectric equivalent thickness decrease 2:1
channel thickness decrease 2:1
channel density of states increase 2:1
source & drain contact resistivities decrease 4:1
Current densities should double
Charge densities must double
Changes required to double device / circuit bandwidth.
Semiconductor Capacitances Must Also Scale
inversiondepth /Tc
oxc
)( thgs VV
2*2 2/ gmqcdos
)2/()()(charge channel 2* gmEEqVVcqn wellfwellfdoss
motion) onalunidirecti(
scale. both alsomust states ofdensity & thicknessInversion
qEE wellf /)(
Calculating Current: Ballistic Limit
fvv )3/4( velocity electron mean
2/3
2/3
,
2/1
V 1)/*()/(1
)/*(
m
mA 84
thgs
ooxodos
oVV
mmgcc
mmgJ
m
minima band of # theis where, )/*(2/* ,
22 gmmgcgmqc oodosdos
thgs
dosequiv
equivdos
cfdos VVcc
ccVVc
s :charge Channel
2/* through velocity Fermidetermines
toapplied voltage voltage FermiChannel
2
ffff
dos
vmqVEv
c
Do we get highest current with high or low mass ?
Natori
InGaAs MOSFETs: superior Id to Si at large EOT.
InGaAs MOSFETs: inferior Id to Si at small EOT.
2/3*
,
2/1*
1
2/3
1
)/()/(1 where,
V 1m
mA84
oequivodos
othgs
mmgcc
mmgK
VVKJ
m
Drive current versus mass, # valleys, and EOT
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.01 0.1 1
no
rma
lized
drive c
urr
en
t K
1
m*/mo
g=2
EOT=1.0 nmEOT includes the wavefunction depth term
(mean wavefunction depth*SiO2
/semiconductor
)
0.6 nm
0.4 nm
g=1
InGaAs <--> InP Si
0.3 nm
/EOTε
)/c/c(c oxequiv
2SiO
1
depth
11
Solomon / Laux Density-of-States-Bottleneck → III-V loses to Si.
2/1*
,
2/1
0
*
2
2/1
72 1 whereVolt 1
cm/s 1052.2
oeq
odos
thgs
g
D
chch
m
mg
c
c
m
mK
VV
LK
I
Q
Transit delay versus mass, # valleys, and EOT
0
0.5
1
1.5
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
No
rma
lize
d t
ran
sit d
ela
y K
2
m*/mo
EOT=1.0 nm
EOT includes wavefunction depth term
(mean wavefunction depth*SiO2
/semiconductor
)
0.6 nm
0.4 nm
g=1, isotropic bands
g=2, isotropic bands
1 nm
0.4 nm
0.6 nm
/EOTε
)/c/c(c oxequiv
2SiO
1
semi
11
Low m* gives lowest transit time, lowest Cgs at any EOT.
Low effective mass also impairs vertical scaling
Shallow electron distribution needed
for high Id, high gm / Gds ratio,
low drain-induced barrier lowering.
./ 2*2
wellTmL
Only one vertical state in well.
Minimum ~ 3 nm well thickness.
→ Hard to scale below 10-16 nm Lg.
For thin wells,
only 1st state can be populated.
For very thin wells,
1st state approaches L-valley.
Energy of Lth well state
substrate material
III-V Band Properties, normal {100} Wafer
X L
valleys tocomparable are masses nsversevalley tra-L
eV 0.28 0.075 1.90
eV 0.57 0.050 0.65
eV 0.47 0.062 1.23
/ /
valley L
EEmmmm Lotol
Si Si
GaAs GaAs
InP InAs
InP AsGaIn
substrate material
0.50.5
---
0.067
0.026
0.045
/
valley
*
omm
(negative) 0.19 0.92
eV 0.47 0.22 1.30
eV 0.87 0.16 1.13
eV 0.83 0.19 1.29
/ /
valley
EEmmmm
X
xotol
substrate material
Consider instead: valleys in {111} Wafer
X L
---
0.067
0.026
0.045
/
valley
*
omm
(negative) 0.19 0.92
eV 0.47 0.22 1.30
eV 0.87 0.16 1.13
eV 0.83 0.19 1.29
/ /
valley
EEmmmm
X
xotol
eV 0.28 0.075 1.90
eV 0.57 0.050 0.65
eV 0.47 0.062 1.23
/ /
valley L
EEmmmm Lotol
Si Si
GaAs GaAs
InP InAs
InP AsGaIn
substrate material
0.50.5
mass verticalmoderate have valleys L three& valleysX
mass verticalhigh has valley Lone :nOrientatio
substrate material
Valley in {111} wafer: with quantization in thin wells
X L
mass erselow transv valley; L[111]Selects
---
0.067
0.026
0.045
/
valley
*
omm
(negative) 0.19 0.92
eV 0.47 0.22 1.30
eV 0.87 0.16 1.13
eV 0.83 0.19 1.29
/ /
valley
EEmmmm
X
xotol
eV 0.28 0.075 1.90
eV 0.57 0.050 0.65
eV 0.47 0.062 1.23
/ /
valley L
EEmmmm Lotol
Si Si
GaAs GaAs
InP InAs
InP AsGaIn
substrate material
0.50.5
eV 0.07 0.10 1.30
eV 0.28 0.075 1.90
eV 0.47 0.062 1.23
/ /
valleyL
EEmmmm Lotol
GaSb
GaAs
AsGaIn
material
0.50.5
---
nm 4
nm 2
(?) nm 1
alignment L
for thickness Well
material
{111} -L FET: Candidate Channel Materials
Ge
GaSb
GaAs
AsGaIn
material
0.50.5
0.039
0.067
0.045
/
valley
*
omm
(negative) 0.08 1.58
eV 0.07 0.10 1.30
eV 0.28 0.075 1.90
eV 0.47 0.062 1.23
/ /
valleyL
EEmmmm Lotol
Standard III-V FET: valley in [100] orientation
3 nm GaAs wellAlSb barriers
=0 eV
L=177 meVX[100]= 264 meVX[010] = 337 meV
-1
-0.5
0
0.5
1
1.5
2
LE
ne
rgy,
eV
X[010]X[100]L
Wa
ve
fun
ctio
ns
-1
1st Approach: Use both and L valleys in [111]
-1
XL[111]
L[111]
L[111]
L[111]
-1
2.3 nm GaAs wellAlSb barriers[111] orientation
= 41 meVL[111] (1)= 0 meVL[111] (2)= 84 meV
L[111] , etc. =175 meVX=288 meV
2/3*
,
2/1*
1
2/3
1
)/()/(1 where,
V 1m
mA84
oequivodos
othgs
mmgcc
mmgK
VVKJ
m
Combined -L wells in {111} orientation vs. Si
2 nm GaAs /L well→ g =2, m*/m0=0.07
4 nm GaSb /L well→ m*/m0=0.039, mL,t*/m0=0.1
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.01 0.1 1
Norm
aliz
ed
curr
ent
density K
1
m*/mo
g=2
EOT=1.0 nmEOT includes the wavefunction depth term
(mean wavefunction depth*SiO2
/semiconductor
)
0.6 nm
0.4 nm
GaAs Si
0.3 nm
GaSb
combined ( -L) transport
/EOTε
)/c/c(c oxequiv
2SiO
1
semi
11
2nd Approach: Use L valleys in Stacked Wells
Three 0.66 nm GaAs wells0.66 nm AlSb barriers [111] orientation
L[111](1) = 0 meVL[111](2)= 61 meVL[111](3)= 99 meV
=338 meVL[111], etc =232 meVX=284 meV
-1
X
L[111]L[111]
All
L[111]
-1
Increase in Cdos with 2 and 3 wells
1
1.5
2
2.5
3
0.01 0.1 1
1 nm well pitch2 nm well pitch3 nm well pitch
Cd
os,N
-well/C
do
s,1
-we
ll
m*/mo
2 wells
3 wells
3 High Current Density (111) GaAs/AlSb Designs(111) orientation
-1
-0.5
0
0.5
1
1.5
2
L
En
erg
y,
eV
X[010]X[100]L
-1
XL[111]
L[111]
L[111]
-1
XL[111]L[111]
L[111]
-1
X
L[111]L[111]
Wa
ve
fun
ctio
ns
-1
L[111]
-1
both L[111]
-1
All
L[111]
-1
0 1 2 3 4 5 6 7
0 100
2 1019
4 1019
6 1019
8 1019
1 1020
Cha
rge
de
nsity,
1/c
m3
position, nm0 1 2 3 4 5 6 7
position, nm0 1 2 3 4 5 6 7
-1
position, nm0 1 2 3 4 5 6 7
-1
position, nm
0
2 1012
4 1012
6 1012
8 1012
-0.2 -0.1 0 0.1 0.2 0.3
Ns (
1/c
m2)
(Vgs
-Vth
), V
L valleys filling
-0.2 -0.1 0 0.1 0.2 0.3
0
(Vgs
-Vth
), V-0.2 -0.1 0 0.1 0.2 0.3
0
(Vgs
-Vth
), V-0.2 -0.1 0 0.1 0.2 0.3
0
(Vgs
-Vth
), V
3 nm GaAs wellAlSb barriers
2.3 nm GaAs wellAlSb barriers
Two 0.66 nm GaAs wells0.66 nm AlSb barriers
Three 0.66 nm GaAs wells0.66 nm AlSb barriers
(100) orientation
Concerns
Nonparabolic bands reduce bound state energies
1-2 monolayer fluctuations in growth→ scattering→ collapse in mobility
Failure of effective mass approximation:1-2 nm wells
Purdue Confirmation
Purdue Confirmation Steiger, Klimeck, BoykinRyu, Lee, Hegde, Tan
1-D FET array = 2-D FET with high transverse mass
Weak coupling → narrow transverse-mode energy distribution→ high density of states
2-D FET 1-D Array FET
3rd Approach: High Current Density L-Valley MQW FINFETs
0
1
2
3
4
5
6
7
8
0.01 0.1 1
Dra
in c
urr
ent, m
A/m
m
m*/mo
Vgs
-Vth=0.3 V
0.3 nm EOT0.6 nm EOT
EOT includes wavefunction depth term
(mean wavefunction depth*SiO2
/semiconductor
)
5 nm well pitch
2.5 nm well pitch
2
2*
22
min,min,2
energiesvalley iWm
qVE ii
i
if VVgq
I min,
2
current
i
min,
*2 :charge ifch VVqmgl
Q
oxchfgs CQVV / : voltagegate
4th Approach: {110} Orientation→ Anisotropic Bands
locitycarrier vehigh transport toparallel mass plane-in Low
states ofdensity high transportlar toperpendicu mass plane-inHigh
populate valleysmass verticalmoderate: ]1L[11 [111], L
locitycarrier ve low transport toparallel mass plane-inHigh
depopulate mass verticallow :11]1[ 1],1[1 L
valleys.undesired and desiredbetween separationenergy moderateonly :Challenge
transport
Asbeck P.
2/32/1
||
2/1
,
2/12/1
1
2/3
1
)/()/(1
)/( where,
V 1m
mA84
oequivodos
othgs
mmmgcc
mmgK
VVKJ
m
Anisotropic bands, e.g. {110}
0
0.1
0.2
0.3
0.4
0.5
0.6
0.01 0.1 1
no
rma
lized d
rive c
urr
en
t K
1
m*/mo
EOT=1.0 nm
EOT includes wavefunction depth term
(mean wavefunction depth*SiO2
/semiconductor
)
0.6 nm
0.4 nm
g=2, mperpendicular
/m0=0.70.3 nm
g=2, m perpendicular
/m0=0.6
g=2, m perpendicular
/m0=0.5
Transport in {110}
oriented L valleys
1.58/ ,081.0/ ,2 :Ge 1.9/ ,075.0/ ,2 :GaAs
nsport valley tra-L with MOSFETs {110} Ge and GaAs
olotolot mmmmnmmmmn
/EOTε
)/c/c(c oxequiv
2SiO
1
semi
11
THz FET scaling: with & without increased DOS
Gate length nm 50 35 25 18 13 9
Gate barrier EOT nm 1.2 0.83 0.58 0.41 0.29 0.21
well thickness nm 8.0 5.7 4.0 2.8 2.0 1.4
S/D resistance Wmm 210 150 100 74 53 37
effective mass *m0 0.05 0.05 0.05 0.08 0.08 0.08
# band minima
canonical
fixed DOS
stepped #
1
1
1
1.4
1
1
2
1
1
2.8
1
2
4
1
3
5.7
1
3
Scaled FET performance: fixed vs. increasing DOS
0
500
1000
1500
2000
2500
3000 canonical scaling
stepped # of bands
transport only
f ,
GH
z
0
500
1000
1500
2000
2500
3000
3500
4000
f ma
x,
GH
z
0
0.5
1
1.5
2
2.5
0 10 20 30 40 50 60
dra
in c
urr
ent
density,
mA
/mm
gate length, nm
200 mV gate overdrive
0
200
400
600
800
1000
0 10 20 30 40 50 60
SC
FL
sta
tic d
ivid
er
clo
ck r
ate
, G
Hz
gate length, nm
f fmax
mA/mm→ VLSI metricSCFL divider speed
Increased density of states needed for high drive current, fast logic @ 16, 11, 8 nm nodes
10 nm / 3 THz III-V FETs: Challenges & Solutions
gate dielectric:decrease EOT 2:1
S/D access regions:decrease resistivity 2:1
channel: keep same velocity, butthin channel 2:1increase density of states 2:1
S/D regrowthWistey et alSingisetti et al
L
To double the bandwidth:
(end)
Purdue Confirmation
MOSFET Scaling Laws
circuitarbitrary an in bandwidth increased 1:for required Changes
:laws scalingvelocity -constant / voltage-Constant
parameter law parameter law
gate lengthg
L , source-drain contact lengths
DSL
/(nm)
1 gate-channel capacitance chg
C
1]/1/1/1[ DOSsemiox
CCC (fF)
1
gate width g
W (nm) 1 transconductance ginjectionchgm
LvCg /~
(mS) 0
equivalent oxide thickness oxideSiOoxeq
TT /2
(nm)
1 gate-source, gate-drain fringing capacitances
gfgsWC
, ,
ggdWC (fF)
1
dielectric capacitance eqggSiOox
TWLC /2
(fF) 1 S/D access resistances s
R , d
R (W ) 0
S/D contact resistivity gs
WR / , gd
WR / ( mmW ) 1
inversion thickness 2/~wellinv
TT (nm) 1 S/D contact resistivity c
( 2mmW ) 2
semiconductor capacitance
invggsemisemiTWLC / (fF)
1 drain current )(~thgsmd
VVgI (mA) 0
DOS capacitance 2*2 2/
ggDOSWLnmqC (fF)
1 drain current density ( mmA/m ) 1
electron density s
n (-2cm ) 1 temperature rise (one device, K) 1~
gW
2.0 nm GaAs well, AlAs barriers, on {111} GaAs
0
0.2
0.4
0.6
0.8
1
1.2
10-10
10-9
10-8
Bo
un
d s
tate
ene
rgy,
eV
well thickness, meters
L(l) valley
valley
. nm 7-5 ~at ticselectrosta good wellnm 2
doubles minima band two
locitycarrier ve high*low
075.0/ : l) L(067.0/* :
populated. bothminima L(l)and : wellnm 2
*
lateral
g
dos
oo
L
c
m
mmmm
GaSb well, AlSb barriers, on {110} GaSb
0
0.1
0.2
0.3
0.4
0.5
0.6
10-10
10-9
10-8
GaSb well, AlSb barriers, on (110) GaSb
Bo
un
d s
tate
en
erg
y,
eV
well thickness, meters
L [111],
L[11-1]
L [1-11],
L[-111]
X [001]
X [100],
X[010]