![Page 1: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/1.jpg)
Scaling of High Frequency III-V Transistors
[email protected] 805-893-3244, 805-893-5705 fax
Short Course, 2009 Conference on InP and Related Materials, Newport Beach, CA, May 10-14
Mark Rodwell University of California, Santa Barbara
![Page 2: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/2.jpg)
THz Transistors
Transistor bandwidths are increasing rapidly.
Si MOSFETs will soon reach 500+ GHz cutoff frequencies.
It is now clear III-V bipolar transistors can reach ~2-3 THz cutoff frequencies.
III-V FETs have comparable potential, but the prospects and analysis are less clear.
The limits to transistor bandwidth are:contact resistivities
gate dielectric capacitance densities.device and IC power density & thermal resistance.
challenges in reliably fabricating small devices.
![Page 3: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/3.jpg)
WhyTHz Transistors ?
![Page 4: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/4.jpg)
Why Build THz Transistors ?
THz amplifiers→ THz radios→ imaging, sensing, communications
precision analog design at microwave frequencies→ high-performance receivers
500 GHz digital logic→ fiber optics
Higher-Resolution Microwave ADCs, DACs, DDSs
![Page 5: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/5.jpg)
PerformanceFigures of Merit
![Page 6: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/6.jpg)
Transistor figures of Merit / Cutoff Frequencies
H21=short-circuit current gain
gain
s, d
B
MAG = maximum available power gain:impedance-matched
U= unilateral power gain:feedback nulled, impedance-matched
fmax
power-gaincutoff frequency
fcurrent-gaincutoff frequency
![Page 7: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/7.jpg)
What Determines Gate Delay ?
cexLOGIC
LOGIC
Ccb
becbi
becbC
LOGIC
IRq
kTV
V
IR
CCR
CCI
V
4
leastat bemust swing logic The
resistance base the through
charge stored
collector base Supplying
resistance base the through
charging ecapacitanc on Depleti
swing logic the through
charging ecapacitanc on Depleti
:by ermined Delay DetGate
bb
depletion,bb
depletion,
JVR
v
T
A
A
V
V
I
VC
T)V(VvεJ
CI
CCIV
f
ex
electron
C
CE
LOGIC
C
LOGICcb
cceceelectronKirk
cbC
becbCLOGIC
cb
highat low for low very bemust
22
/2
objective. design key HBTa is / High
total.of 80%-55% is
withcorrelated not well Delay
delay; totalof 25%-10y typicall)(
logic
emitter
collector
min,
2depletion full,operating ,max,
depl,
![Page 8: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/8.jpg)
HBT Design For Digital & Mixed-Signal Performance
from charge-control analysis:
)./5.05.0(
)/5.05.05.0(
)/5.05.0)(/(
)66)(/(
LCfcbijebb
LCfcbicbxex
LCfcbicbxjeC
fcbicbxjeCLgate
VICCR
VICCR
VICCCqIkT
CCCIVT
analog ICs have similar bandwidth constraints...
![Page 9: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/9.jpg)
High-FrequencyElectron Device
Design
![Page 10: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/10.jpg)
Simple Device Physics: Resistance
Good approximation for contactwidths less than 2 transfer lengths.
A
TR bulk
bulk resistance
AR contact
contact resistance-perpendicular
L
W
AR sheet
contact
3
'
contact resistance- parallel
![Page 11: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/11.jpg)
Simple Device Physics: Depletion Layers
capacitance
T
AC
transit time
v
T
2
space-chargelimited current
2
22
max depletionapplied VVT
v
A
I
2 where
max
depletionapplied VVI
C
T
VCI
![Page 12: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/12.jpg)
Simple Device Physics: Thermal Resistance
Exact
L
W
WK
W
L
LKR
th
thth
1
1
sinh1
sinh1
Carslaw & Jaeger 1959
LKW
L
LKR
ththth
1ln
1
junctionnear
flowheat lcylindrica
Long, Narrow StripeHBT Emitter, FET Gate
junction fromfar
flowheat spherical
LKLKR
ththth
1
4
1
surfacenear
flowheat planar
Square ( L by L ) IC on heat sink
surface fromfar
flowheat spherical
![Page 13: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/13.jpg)
Simple Device Physics: Fringing Capacitance
5.1T
W
L
C
wiring capacitance
plate-parallel fringing
)3 to(1
/ and / of
function varying-slowly
21 GWGWL
C
FET parasitic capacitances
LC / ~/ LCparasitic
VLSI power-delay limits FET scaling constraints
![Page 14: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/14.jpg)
Electron Plasma Resonance: Not a Dominant Limit
*2kinetic
1
nmqA
TL
T
AC
ntdisplaceme
m
dielecic L
Rf
2
1
2
1
frequency scattering
kinetic
bulk
mnmqA
TR
*2bulk
1
2
1
2/1
frequency relaxation dielectric
bulkntdisplaceme
RC
fdielecicntdisplacemekinetic
2/1
frequencyplasma
CLf plasma
THz 800 THz 7 THz 74319 cm/105.3
InGaAs-
n
319 cm/107
InGaAs-
pTHz 80 THz 12 THz 13
![Page 15: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/15.jpg)
Electron Plasma Resonance: Not a Dominant Limit
*2kinetic
1
nmqA
TL
T
AC
ntdisplaceme
m
dielecic L
Rf
2
1
2
1
frequency scattering
kinetic
bulk
mnmqA
TR
*2bulk
1
2
1
2/1
frequency relaxation dielectric
bulkntdisplaceme
RC
fdielecicntdisplacemekinetic
2/1
frequencyplasma
CLf plasma
THz 800 THz 7 THz 74319 cm/105.3
InGaAs-
n
319 cm/107
InGaAs-
pTHz 80 THz 12 THz 13
![Page 16: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/16.jpg)
Electron Plasma Resonance: Not a Dominant Limit
*2kinetic
1
nmqA
TL
T
AC
ntdisplaceme
m
dielecic L
Rf
2
1
2
1
frequency scattering
kinetic
bulk
mnmqA
TR
*2bulk
1
2
1
2/1
frequency relaxation dielectric
bulkntdisplaceme
RC
fdielecicntdisplacemekinetic
2/1
frequencyplasma
CLf plasma
THz 800 THz 7 THz 74319 cm/105.3
InGaAs-
n
319 cm/107
InGaAs-
pTHz 80 THz 12 THz 13
![Page 17: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/17.jpg)
Electron Plasma Resonance: Not a Dominant Limit
*2kinetic
1
nmqA
TL
T
AC
ntdisplaceme
m
dielecic L
Rf
2
1
2
1
frequency scattering
kinetic
bulk
mnmqA
TR
*2bulk
1
2
1
2/1
frequency relaxation dielectric
bulkntdisplaceme
RC
fdielecicntdisplacemekinetic
2/1
frequencyplasma
CLf plasma
THz 800 THz 7 THz 74319 cm/105.3
InGaAs-
n
319 cm/107
InGaAs-
pTHz 80 THz 12 THz 13
![Page 18: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/18.jpg)
Frequency Limitsand Scaling Laws of (most) Electron Devices
width
lengthlog
length
power
thicknessarea /
length
width
4area
area/
thickness/area
thickness
2limit-charge-space max,
T
I
R
R
C
sheetcontactbottom
contacttop
To double bandwidth, reduce thicknesses 2:1 Improve contacts 4:1reduce width 4:1, keep constant lengthincrease current density 4:1
topR
bottomR
PIN photodiode
![Page 19: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/19.jpg)
parameter change
collector depletion layer thickness decrease 2:1
base thickness decrease 1.414:1
emitter junction width decrease 4:1
collector junction width decrease 4:1
emitter contact resistance decrease 4:1
current density increase 4:1
base contact resistivity decrease 4:1
Changes required to double transistor bandwidth:
Linewidths scale as the inverse square of bandwidth because thermal constraints dominate.
eW
bcWcTbT
ELlength emitter
Bipolar Transistor Scaling Laws
![Page 20: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/20.jpg)
parameter change
gate length decrease 2:1
gate dielectric capacitance density increase 2:1
gate dielectric equivalent thickness decrease 2:1
channel electron density increase 2:1
source & drain contact resistance decrease 4:1
current density (mA/m) increase 2:1
Changes required to double transistor bandwidth:
Linewidths scale as the inverse of bandwidth because fringing capacitance does not scale.
FET Scaling Laws
GW widthgate
GL
![Page 21: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/21.jpg)
THz & nm Transistors: it's all about the interfaces
Metal-semiconductor interfaces (Ohmic contacts): very low resistivity
Dielectric-semiconductor interfaces (Gate dielectrics): very high capacitance density
Transistor & IC thermal resistivity.
![Page 22: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/22.jpg)
BipolarTransistors
![Page 23: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/23.jpg)
Indium Phosphide Heterojunction Bipolar Transistors
Z. GriffithE. Lind
![Page 24: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/24.jpg)
Bipolar Transistor Operation
cI
beV ceV
voltagecollector with little varies
it through pass base reaching electrons allAlmost
)/exp(
al)(exponenti thermalison distributienergy emitter Because
c
bec
I
kTqVI
![Page 25: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/25.jpg)
Transistor Hybrid-Pi equivalent circuit model
nkTqIg Em /
)( cbmjebe gCC
mbe gR /
![Page 26: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/26.jpg)
Cutoff frequencies in HBTs
collex
Ebc
Ejecollectorbase RR
qI
kTC
qI
kTC
f
2
1
nbbase DT 22 effccollector vT 2
cbibbCR
ff
8max
![Page 27: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/27.jpg)
Epitaxial Layer Structure
![Page 28: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/28.jpg)
emitter
emittercap
gradedbase
collector
subcollector
Epitaxy: InP Emitter, InGaAs Base, InP Collector, Both Junctions GradedKey Features:
N++ InGaAs emitter contact layer
InP emitter
InGaAs/InAlAs superlattice e/b grade
InGaAs graded basebandgap or doping grade
BC setback layer
InGaAs/InAlAs superlattice b/c grade
InP collector
InGaAs etch-stop layerthin for heat conduction
InP subcollector
Layer Material Doping Thickness (nm)
Emitter cap In0.53Ga0.47As 8 1019 cm-3: Si 25
N+ emitter InP 8 1019 cm-3: Si 50
N- emitter InP 1 1018 cm-3: Si 20
Emitter-base grade In0.53Ga0.47As / In0.52Al0.48As,
1.6 nm period N: 1 1017 cm-3: Si
24
Emitter-base grade In0.53Ga0.47As / In0.52Al0.48As,
1.5 nm period P: 8 1017 cm-3: C 1
Base In0.53Ga0.47As P: 7-4 1019 cm-3: C 24.5
Setback In0.53Ga0.47As N: 9 1016 cm-3: Si 4.5
Base-collector grade
In0.53Ga0.47As / In0.52Al0.48As, 1.6 nm period
N: 9 1016 cm-3: Si 15
Pulse doping InP 6 1018 cm-3: Si 3
Collector InP N: 2 1016 cm-3: Si 82
etch-stop In0.53Ga0.47As N: 8 1019 cm-3: Si 5
Subcollector InP N: 8 1019 cm-3: Si ~200
M. DahlstromZ. Griffith UCSB
M. UrteagaTSC
![Page 29: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/29.jpg)
emitter
emittercap
gradedbase
collector
subcollector
Epitaxy with Abrupt BE Junction
Similar design
Abrupt E/B junction (no e/b grade)
Advantages:ease of stopping emitter etch on base→ good base contacts
Disadvantages:Increased Vbe .Cannot make e/b ledge.
Layer Material Doping Thickness (nm)
Emitter cap In0.53Ga0.47As 8 1019 cm-3: Si 25
N+ emitter InP 8 1019 cm-3: Si 50
N- emitter InP 1 1018 cm-3: Si 20
N- emitter InP N: 1 1017 cm-3: Si 24
Emitter-base grade In0.53Ga0.47As / In0.52Al0.48As,
1.5 nm period P: 8 1017 cm-3: C 1
Base In0.53Ga0.47As P: 7-4 1019 cm-3: C 24.5
Setback In0.53Ga0.47As N: 9 1016 cm-3: Si 4.5
Base-collector grade
In0.53Ga0.47As / In0.52Al0.48As, 1.6 nm period
N: 9 1016 cm-3: Si 15
Pulse doping InP 6 1018 cm-3: Si 3
Collector InP N: 2 1016 cm-3: Si 82
etch-stop In0.53Ga0.47As N: 8 1019 cm-3: Si 5
Subcollector InP N: 8 1019 cm-3: Si ~200
M. DahlstromZ. GriffithE. Lind
![Page 30: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/30.jpg)
Alternative Grades for Thinner Epitaxy
Common Grade in LiteratureInGaAs/InAlAs 18 nm thick, 1.5 nm period
Sub-monolayer Grade0.15 nm InAlAs, (0.15 to 0.165 nm InGaAs)10.8 nm thick
Strained InxGa1-xAs Grade
InGaAs/GaAs 6 nm
E . LindZ. Griffith
![Page 31: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/31.jpg)
Other Methods of Grading the Junctions
IEDM 2001
InGaAs/InGaAsP/InP grade InP/GaAsSb/InP DHBT
-suitable for MOCVD growth
- excellent results
- does not need B/C grading
- E/B band alignment through GaAsSb alloy ratio (strain)
or InAlAs emitter
![Page 32: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/32.jpg)
Transport Analysis
![Page 33: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/33.jpg)
Approximate Carrier Transit Times eW
bcWcTbT
exitbnbb vTDT 22
satcc vT 2
ELlength emitter
TimeTransit Base
TimeTransit Collector
![Page 34: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/34.jpg)
Base Transit Time with Graded Base
gbg
g
LWsatgngngbb
EkTWL
L
evLDLDLW gb
/
:length grading theis where
1/// /2
fs 35/
ifcorrect modeldiffusion -Drift* kTmDτ nmb
cm/s 103
secV/cm 40
:Assumes
7
2
exit
N
v
D
Dino Mensa
![Page 35: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/35.jpg)
Base Transit Time: Grading Approaches Dino MensaMiguel UrteagaMattias Dahlström
Compositional grading: strained graded InGaAs base
Doping grading unstrained In0.53Ga0.47As base
(strained) AsGaIn AsGaIn
:drop potential meV 52
0.470.530.5450.455
/cm105~ to/cm108~
:from varieddoping Carbon319319
![Page 36: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/36.jpg)
V=0
TcTc/2
-
-+ +
V=0
Tc/4
+ +
-
-
+ +
-
-
-
-
+
+
Collector Transit TimeT. Ishibashi
base.near velocity tosensitive more is
2)(
)/1(
sketch) (refer to ticselectrosta elementary From
c
0
c
CT
eff
cc
v
Tdx
xv
Tx
.scattering L- todue decreasesthen
high, is velocity initial as ,Fortuitous
layers nm 200-70~for cm/s103.5 :InP
:voltagecollector .density vscurrent Kirk fromor ata,d RF fit tobest From7
![Page 37: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/37.jpg)
Space-Charge Limited Current Density → Ccb charging time
Collector Field Collapse (Kirk Effect)
Collector Depletion Layer Collapse
)2/)(/( 2 cdsatcb TqNvJV
)2/)(( 2min, cTqNV dcb
eff
C
CECE
LOGICCLOGICcCLOGICcb v
T
A
A
VV
VIVTAIVC
2/
emitter
collector
min,
collector
2
min,max /)2(2 ccbcbeff TVVvJ
cecbbe VVV )( hence , that Note
Collector capacitance charging time scales linearly with collector thickness if J = Jmax
![Page 38: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/38.jpg)
Space-Charge-Limited Current (Kirk effect) in DHBTs
ceV
Jff
increased with
increases esholdeffect thr-Kirk
highat and in Decrease max
CEEeffective
effectivesat
c
c
ce
satce
TWLA
Av
TR
dI
dV
JV
2
is areaflux current
collector effective thewhere
2
increased with in Increase2
chargespace
,
2min,
2min,max
/)(2
/)2(2
ccecesat
ccbcbsat
TVVv
TVVvJ
100
200
300
400
500
0 2 4 6 8 10 12
f (
GH
z)
Je (mA/um2)
f, -0.3 V
cb
0.0 Vcb
-0.2 Vcb
0.2 Vcb
0.6 Vcb
0
2
4
6
8
10
12
14
16
0 0.5 1 1.5 2 2.50
5
10
15
20
25
30
35
40
J e (m
A/
m2 )
Vce
(V)
Ajbe
= 0.6 x 4.3 m2
Ib step
= 180 uA
Vcb
= 0 V
Ic (mA
)
Peak ft, f
max
![Page 39: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/39.jpg)
Current-induced Collector Velocity Overshoot
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2 2.5 3 3.5
tau e
c, ps
inverse current density, 1/J,m2/mA
J=0
J= 8 mA/um2
300 Å InGaAs base
2000 Å InP collector
280 GHz peak f
bias. with of variation todue and),/ asnot vary does often (1/current bias hfactor witideality emitter in modulation toduepart in also is variationnonlinear observed :CAUTION ec jeEexm CqInkTRg
not
is metransit ticollector of definitioncorrect
toalproportionexactly not is )(
)/1(
metransit ticollector reduced
collector ofpart early in )( increases
,scattering L- reducescurrent Increased
cc
0
c
base
c
base
c
T
ccbase
I
Q
I
Q
Idxxv
TxIQ
xv
C
Nakajima, H. "A generalized expression for collector transit time of HBTstaking account of electron velocity modulation," Japanese Journal ofApplied Physics, vo. 36, Feb. 1997, pp. 667-668
T. Ishibashi
![Page 40: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/40.jpg)
Transit time Modulation Causes Ccb Modulation
),(//1)(constant0 cbccbc
T
celectronsbase
holesbase VIfTAVdxTxAxqnQQ c
cb
f
c
cb
c
holesbasef
cb
holesbasecb VI
C
I
Q
V
QC
Camnitz and Moll, Betser & Ritter, D. Root holesbaseb ΔQI ,
E
drift collectorbase
-
+
+
+
+
-
-
-
--
-
-
-2
-1
0
1
2
0 100 200 300 400
eV
nm
L
-2
-1
0
1
2
0 100 200 300 400
eV
nm
0 0 ccbcbf ICV
:Modulation Velocity Collector
0 0 ccbcbf ICV
: Effect Kirk
2
3
4
5
6
7
8
0 2.5 5 7.5 10 12.5
Ccb
/Ae (
fF/
m2 )
Je (mA/m2)
-0.2 V
0.0 V
0.2 V
Vcb
= 0.6 V
cbb
cb
Vτ
C
by of modulation and-
collector into pushout base-
both to due is in Increase
100
200
300
400
500
0 2 4 6 8 10 12
f (
GH
z)
Je (mA/um2)
f, -0.3 V
cb
0.0 Vcb
-0.2 Vcb
0.2 Vcb
0.6 Vcb
DHBTs InP in effect weak-
SHBTs InGaAs in effect strong-
reduced with in Increase cbcbc CVτ
![Page 41: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/41.jpg)
Emitter-Base Junction Effects
Electron degeneracy contributes 1 - μm2
equivalent series resistance
10-3
10-2
10-1
100
101
102
-0.3 -0.2 -0.1 0 0.1 0.2
J(m
A/u
m^2
)
Vbe
-
Fermi-Dirac
Equivalent series resistance approximation
Boltzmann
)(
)(
xnq
J
x
xE
n
fn
Space-charge storage
need thin layer to avoid substantial charge storage delays
Voltage drops in depletion region
need thin layer &high electron density ).08.0/(emitter InPfor
eV 1.0m
mA130
2
)(*
limit degenerateHighly
0*
2
2
32
2
mm
EE
EEqmJ
cf
cf
RodwellLundstrom.
![Page 42: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/42.jpg)
RC parasitics
![Page 43: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/43.jpg)
Simple Device Physics: Resistance
Good approximation for contactwidths less than 2 transfer lengths.
A
TR bulk
bulk resistance
AR contact
contact resistance-perpendicular
L
W
AR sheet
contact
3
'
contact resistance- parallel
![Page 44: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/44.jpg)
HBT RC Parasitics
base contact width < 2 transfer lengths
→ simple analysis
Limiting case of Pulfrey / Vaidyanathanfmax model.
![Page 45: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/45.jpg)
HBT RC Parasitics
emitteremittercontactex AR /,
Eesspread LWR 12/ ELlength emitter
Egapsgap LWR 4/
Ebcscontactspread LWR 6/,
contactsbasebcbasecontactcontact AWR _, /
cemitterecb TAC /,
cgapgapcb TAC /,
ccontactsbasecontactcb TAC /_,
![Page 46: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/46.jpg)
Base-Collector Time Constant & Fmax.
where8max
cbibbCR
ff
)(
)2/(
,,
,,
,
spreadgapcontactspreadcontactecb
gapcontactspreadcontactgapcb
contactcontactcbcbibbcb
RRRRC
RRRC
RCCR
![Page 47: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/47.jpg)
Relationship to Equivalent Circuit Model
contactspreadcontactgapspreadbb RRRRR ,
contactcbgapcbecbcbicbx CCCCC ,,,
)(
)2/(
,,
,,,
spreadgapcontactspreadcontactecb
gapcontactspreadcontactgapcbcontactcontactcbcbibb
RRRRC
RRRCRCCR
![Page 48: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/48.jpg)
Device Design
Device Scaling
![Page 49: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/49.jpg)
Simple Device Physics: Thermal Resistance
Exact
L
W
WK
W
L
LKR
th
thth
1
1
sinh1
sinh1
Carslaw & Jaeger 1959
LKW
L
LKR
ththth
1ln
1
junctionnear
flowheat lcylindrica
Long, Narrow StripeHBT Emitter, FET Gate
junction fromfar
flowheat spherical
LKLKR
ththth
1
4
1
surfacenear
flowheat planar
Square ( L by L ) IC on heat sink
surface fromfar
flowheat spherical
![Page 50: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/50.jpg)
Bipolar Transistor Design eW
bcWcTbT
nbb DT 22
satcc vT 2
ELlength emitter
eex AR /contact
2through-punchce,operatingce,max cesatc TVVAvI /)(,
contacts
contactsheet 612 AL
W
L
WR
e
bc
e
ebb
e
e
E W
L
L
PT ln1
cccb /TAC
![Page 51: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/51.jpg)
Bipolar Transistor Design: Scaling eW
bcWcTbT
nbb DT 22
satcc vT 2
ELlength emitter cccb /TAC
eex AR /contact
2through-punchce,operatingce,max cesatc TVVAvI /)(,
contacts
contactsheet 612 AL
W
L
WR
e
bc
e
ebb
e
e
E W
L
L
PT ln1
![Page 52: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/52.jpg)
parameter change
collector depletion layer thickness decrease 2:1
base thickness decrease 1.414:1
emitter junction width decrease 4:1
collector junction width decrease 4:1
emitter contact resistance decrease 4:1
current density increase 4:1
base contact resistivity decrease 4:1
Changes required to double transistor bandwidth:
Linewidths scale as the inverse square of bandwidth because thermal constraints dominate.
eW
bcWcTbT
ELlength emitter
Bipolar Transistor Scaling Laws
![Page 53: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/53.jpg)
0
20
40
60
80
100
120
140
100 200 300 400 500 600 700
jun
ctio
n t
em
pe
ratu
re r
ise
, K
elv
in
master-slave D-Flip-Flop clock frequency, GHz
substrate: cylindrical+spherical regions
substrate: planar region
package
total
Thermal Resistance Scaling : Transistor, Substrate, Package
2substrate
2/11ln
D
DT
K
P
DLK
P
W
L
LK
PT sub
InPEInPe
e
EInP
junctionnear
flowheat lcylindrica
eLr for
flow spherical
2/for
flowplanar
HBTDr
callylogarithmi
increases
variation
antinsignificconstant is if
lly quadratica increases
subT
.)(bandwidth
as scales
density,Power
h.1/bandwidt
as scale
lenghts Wiring
2
chipCu
chippackage WK
PT
1
4
1
)/GHz 150( m 40 clocksub fT
IC CML HBT-2000
![Page 54: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/54.jpg)
0
20
40
60
80
100
120
140
100 200 300 400 500 600 700
jun
ctio
n t
em
pe
ratu
re r
ise
, K
elv
in
master-slave D-Flip-Flop clock frequency, GHz
substrate: cylindrical+spherical regions
substrate: planar region
package
total
Thermal Resistance Scaling : Transistor, Substrate, Package
2substrate
2/11ln
D
DT
K
P
DLK
P
W
L
LK
PT sub
InPEInPe
e
EInP
junctionnear
flowheat lcylindrica
eLr for
flow spherical
2/for
flowplanar
HBTDr
callylogarithmi
increases
variation
antinsignificconstant is if
lly quadratica increases
subT
.)(bandwidth
as scales
density,Power
h.1/bandwidt
as scale
lenghts Wiring
2
chipCu
chippackage WK
PT
1
4
1
)/GHz 150( m 40 clocksub fT
IC CML HBT-2000Probable best solution: Thermal Vias ~500 nm below InP subcollector...over full active IC area.
![Page 55: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/55.jpg)
InP Bipolar Transistor Scaling Roadmap
emitter 512 256 128 64 32 nm width16 8 4 2 1 m2 access
base 300 175 120 60 30 nm contact width, 20 10 5 2.5 1.25 m2 contact
collector 150 106 75 53 37.5 nm thick, 4.5 9 18 36 72 mA/m2 current density4.9 4 3.3 2.75 2-2.5 V, breakdown
f 370 520 730 1000 1400 GHzfmax 490 850 1300 2000 2800 GHz
power amplifiers 245 430 660 1000 1400 GHz digital 2:1 divider 150 240 330 480 660 GHz
industry university→industry
university2007-8
appearsfeasible
maybe
eW
bcWcTbT
![Page 56: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/56.jpg)
Can we make a 1 THz SiGe Bipolar Transistor ?
InP SiGeemitter 64 18 nm width
2 1.2 m2 access
base 64 56 nm contact width, 2.5 1.4 m2 contact
collector 53 15 nm thick 36 125 mA/m2 2.75 ??? V, breakdown
f 1000 1000 GHzfmax 2000 2000 GHz
PAs 1000 1000 GHz digital 480 480 GHz(2:1 static divider metric)Assumes collector junction 3:1 wider than emitter.Assumes SiGe contacts 2:1 wider than junctions
Simple physics clearly drives scaling transit times, Ccb/Ic → thinner layers, higher current density high power density → narrow junctions small junctions→ low resistance contacts
Key challenge: Breakdown 15 nm collector → very low breakdown
(also need better Ohmic contacts)
![Page 57: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/57.jpg)
HBT Design For Digital & Mixed-Signal Performance
from charge-control analysis:
)./5.05.0(
)/5.05.05.0(
)/5.05.0)(/(
)66)(/(
LCfcbijebb
LCfcbicbxex
LCfcbicbxjeC
fcbicbxjeCLgate
VICCR
VICCR
VICCCqIkT
CCCIVT
![Page 58: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/58.jpg)
InP HBT: Status
![Page 59: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/59.jpg)
0
200
400
600
800
1000
0 200 400 600 800 1000
Teledyne DBHT
UIUC DHBT
NTT DBHT
ETHZ DHBT
UIUC SHBT
UCSB DHBT
NGST DHBT
HRL DHBT
IBM SiGe
Vitesse DHBT
f ma
x (G
Hz)
ft (GHz)
600 GHz
500GHz maxff
Updated Sept. 2008
800 GHz
900 GHz
700 GHz
400GHz
InP DHBTs: September 2008
)(
),/(
),/(
),/(
hence ,
:digital
gain, associated ,F
:amplifiers noise low
mW/
gain, associated PAE,
:amplifierspower
)11(
2/) (
alone or
min
1max
max
max
max
cb
cbb
cex
ccb
clock
ττ
VIR
VIR
IVC
f
m
ff
ff
ff
ff
:metrics better much
:metrics popular
250 nm
600nm
350 nm
250 nm
125 nm
![Page 60: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/60.jpg)
512 nm InP DHBT
Production
DDS IC: 4500 HBTs 20-40 GHz op-amps
500 nm mesa HBT 150 GHz M/S latches 175 GHz amplifiers
LaboratoryTechnology
Teledyne / BAE Teledyne / UCSB
UCSB UCSB / Teledyne / GCS
500 nm sidewall HBT
f = 405 GHz
fmax = 392 GHz
Vbr, ceo = 4 V
Teledyne
20 GHz clock53-56 dBm OIP3 @ 2 GHzwith 1 W dissipation
( Teledyne )
Z. GriffithM. UrteagaP. RowellD. PiersonB. BrarV. Paidi
![Page 61: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/61.jpg)
256 nm GenerationInP DHBT
0
10
20
30
109 1010 1011 1012
109
101
0
101
1
1012
dB
Hz
f = 560 GHz
fmax
= 560 GHz
U
H21
0
10
20
30
40
109 1010 1011 1012
dB
Hz
UH21
f = 424 GHz
fmax
= 780 GHz
0
5
10
15
20
0 1 2 3 4V
ce
mA
/m
20
10
20
30
40
109 1010 1011 1012
dB
Hz
U
H21
ft = 660 GHz
fmax
= 218 GHz
0
10
20
30
0 1 2 3
mA
/m
2
Vce
150 nm thick collector
70 nm thick collector
60 nm thick collector
200 GHz master-slavelatch design
Z. Griffith, E. Lind
J. Hacker, M. Jones
324 GHzAmplifier
![Page 62: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/62.jpg)
324 GHz Medium Power Amplifiers in 256 nm HBT
ICs designed by Jon Hacker / Teledyne
Teledyne 256 nm process flow-
Hacker et al, 2008 IEEE MTT-S
~2 mW saturated output power
0
10
20
30
40
Cu
rre
nt,
mA
-20
-10
0
10
20
Gai
n (
dB
), P
ow
er
(dB
m),
PA
E (
%)
-20 -15 -10 -5 0 5
Input Power (dBm)
O utput Pow er (dBm )
G ain (dB)
D ra in C urrent (m A )
P AE (% )
![Page 63: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/63.jpg)
128 / 64 / 32 nm HBT Technologies
![Page 64: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/64.jpg)
Conventional ex-situ contacts are a mess
textbook contact with surface oxide
Interface barrier → resistance
Further intermixing during high-current operation → degradation
with metal penetration
THz transistor bandwidths: very low-resistivity contacts are required
![Page 65: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/65.jpg)
Improvements in Ohmic Contacts
128 nm generation requires ~ 4 - μm2 emitter & base resistivities
64 nm generation requires ~ 2 - μm2
Contacts to N-InGaAs*:Mo MBE in-situ 2.2 (+/- 0.5) - μm2
TiW ex-situ / NH4 pre-clean ~2.2 - μm2
variable between process runs
Contacts to P-InGaAs:Mo MBE in-situ below 2.5 - μm2
Pd/Ti... ex-situ ~4 - μm2
...far better contacts coming...
*measured emitter resistance remains higher than that of contacts.
A.. CrookV. JainA. BaraksharM. WisteyU. Singisetti
S. Bank
![Page 66: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/66.jpg)
Mo Emitter Contacts: Robust Integration into Process Flow
Proposed Process Integration:M. WisteyA. BaraksharU. SingisetttiV. Jain
![Page 67: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/67.jpg)
Process Must Change Greatly for 128 / 64 / 32 nm Nodes
Undercutting of emitter ends
control undercut→ thinner emitter thinner emitter
→ thinner base metalthinner base metal→ excess base metal resistance
{101}A planes: fast
{111}A planes: slow
![Page 68: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/68.jpg)
128 nm Emitter Process: Dry Etched Metal & Semiconductor
SiO2
TiW
InGaAs n++
InGaAs p++ Base
InP n
CrSF6/Ar ICP Cl2/N2 ICPSiNx sidewall
Wet Etch
HCl:H3PO4BHF
Ti
a b c d e
InGaAs p++ Base InGaAs p++ Base InGaAs p++ Base InGaAs p++ Base
InP n
InGaAs n++ InGaAs n++
Litho patternmetal
sidewall dry etch wet etch
0
10
20
30
109 1010 1011 1012
10
9
10
10
101
1
10
12
dB
Hz
f = 560 GHz
fmax
= 560 GHz
U
H21
0
5
10
15
20
0 1 2 3 4V
cem
A/
m2
results @ c.a. 200 nm emitter metal width
E. Lind
![Page 69: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/69.jpg)
Planarization E/B Processes for 64 & 32 nm
Planarization boundary
E; LobisserV. JainG. Burek
![Page 70: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/70.jpg)
III-V FET Scaling
![Page 71: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/71.jpg)
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
All lengths, widths, thicknesses reduced 2:1
S/D contact resistivity reduced 4:1
oxgm TvWg /~/
oxgggs TLWC /~/
~/, gfgs WC
subcgsb TLWC /~/
If Tox cannot scale with gate length,
Cparasitic / Cgs increases,
gm / Wg does not increase
hence Cparasitic /gm does not scale
~/ ggd WC
![Page 72: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/72.jpg)
FET scaling: Output Conductance & DIBL effects) D.O.S.neglects expression ( gsC
gchd WC ~
dschdgsgsd VCVCQQI where/
/~ oxgggs TLWC
transconductance
→ Keep Lg / Tox constant as we scale Lg
output conductance
![Page 73: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/73.jpg)
parameter change
gate length decrease 2:1
gate dielectric capacitance density increase 2:1
gate dielectric equivalent thickness decrease 2:1
channel electron density increase 2:1
source & drain contact resistance decrease 4:1
current density (mA/m) increase 2:1
Changes required to double transistor bandwidth:
FET Scaling Laws
GW widthgate
GL
![Page 74: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/74.jpg)
III-V MOSFETs for VLSI
What is it ?MOSFET with an InGaAs channel
What are the problems ?low electron effective mass→ constraints on scaling !must grow high-K on InGaAs, must grow InGaAs on Si
Our focus today is III-V FET scaling generally
Why do it ?low electron effective mass→ higher electron velocitymore current, less charge at a given insulator thickness & gate lengthvery low access resistance
![Page 75: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/75.jpg)
Low Effective Mass Impairs Vertical Scaling
Shallow electron distribution needed for high gm / Gds ratio.
./ 2*2wellTmL
Only one vertical state in well. Minimum ~ 5 nm well thickness.→ constrains gate length scaling.
For thin wells, only 1st state can be populated.For very thin wells, 1st state approaches L-valley.
Energy of Lth well state
![Page 76: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/76.jpg)
Density-Of-States Capacitance
Two implications:
- With Ns >1013/cm2, electrons populate satellite valleys - Transconductance limited by finite state density
and n is the # of band minima
)//( 2* nmnEE swellf
2*2 / where nmqcdos
dosswellf cVV /
Fischetti et al, IEDM2007
Solomon & Laux , IEDM2001
motion) nalbidirectio(
![Page 77: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/77.jpg)
Drive Current in the Ballistic & Degenerate Limits
2/3*
,
2/1*2/3
)/()/(1 where,
V 1m
mA84
ooxodos
othgs
mmncc
mmnK
VVKJ
0
0.05
0.1
0.15
0.2
0.25
0.01 0.1 1
K
m*/mo
1.0 nm, n=1
0.8 nm, n=1
0.7 nm, n=6 0.4 nm, n=6
EOT includes wavefunction depth (0.5 nm for 3.5 nm InGaAs well)
n = # band minimacdos,o = density of states capacitance for m*=mo & n=1
Error bars on Si data points correct for (Ef-Ec)>> kT approximation
![Page 78: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/78.jpg)
HEMT Scaling Challenge: Low Gate Barrier
Tunneling through barrier→ sets minimum thickness
Source DrainGate
Ec
Ewell-
EF
Ec
Ewell-
EF
Gate barrier is low: ~0.6 eV
Emission over barrier→ limits 2D carrier density
K Shinohara
eV 6.0~)( ,cm/10At 213cfs EEN
![Page 79: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/79.jpg)
Ec
Ewell-
EF
N+ caplayer
HEMT Scaling Challenge: High Access Resistance
low leakage: need high barrier under gate
Source DrainGate
Ec
Ewell-
EF
Gate barrier also lies under source / drain contacts
low resistance: need low barrier under contacts
widegap barrier layer
N+ layer
K Shinohara
![Page 80: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/80.jpg)
THz III-V FET Scaling: What Must Be Done
As gate length is reduced...
channel thickness should be reduced...
barrier thickness should be reduced...
target gm/Wg and Id/Wg
should be increased...
source and drain access resistivity should be reduced...
We face serious difficulties in doing these.
parameter change
gate length decrease 2:1
gate dielectric capacitance density increase 2:1
gate dielectric equivalent thickness decrease 2:1
channel electron density increase 2:1
source & drain contact resistance decrease 4:1
current density (mA/m) increase 2:1
Changes required to double transistor bandwidth:
FET Scaling Laws
GW widthgate
GL
![Page 81: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/81.jpg)
substrate
barrier
sidewall
metal gate
quantum well / channel
gate dielectric
N+ source N+ drain
source contact drain contact
A MOSFET Might Scale Better than a HEMT
no gate barrier under S/D contacts
high-K gatebarrier
Overlap between gateand N+ source/drain
![Page 82: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/82.jpg)
Interconnects
![Page 83: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/83.jpg)
kz
Parasitic slot mode
-V 0V +V
0V
Coplanar WaveguideNo ground viasNo need (???) to thin substrate
Parasitic microstrip mode
+V +V +V
0V
Hard to ground IC to package
substrate mode coupling or substrate losses
ground plane breaks → loss of ground integrity
Repairing ground plane with ground straps is effective only in simple ICsIn more complex CPW ICs, ground plane rapidly vanishes → common-lead inductance → strong circuit-circuit coupling
40 Gb/s differential TWA modulator drivernote CPW lines, fragmented ground plane
35 GHz master-slave latch in CPWnote fragmented ground plane
175 GHz tuned amplifier in CPWnote fragmented ground plane
poor ground integrity
loss of impedance control
ground bounce
coupling, EMI, oscillation
III-V:semi-insulating substrate→ substrate mode coupling
Siliconconducting substrate→ substrate conductivity losses
![Page 84: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/84.jpg)
kz
Classic Substrate Microstrip
Strong coupling when substrate approaches ~d / 4 thickness
H
W Thick Substrate → low skin loss
Hrskin 2/1
1
Zero ground inductance in package
a
Brass carrier andassembly ground
interconnectsubstrate
IC with backsideground plane & vias
near-zeroground-groundinductance
IC viaseliminateon-wafergroundloops
High via inductance
12 pH for 100 m substrate -- 7.5 @ 100 GHz
TM substrate mode coupling
Line spacings must be ~3*(substrate thickness)
lines must be widely spaced
ground vias must be widely spaced
all factors require very thin substrates for >100 GHz ICs→ lapping to ~50 m substrate thickness typical for 100+ GHz
No ground planebreaks in IC
![Page 85: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/85.jpg)
fewer breaks in ground plane than CPW
III-V MIMIC Interconnects -- Thin-Film Microstrip
narrow line spacing → IC density
... but ground breaks at device placements
still have problem with package grounding
thin dielectrics → narrow lines → high line losses → low current capability → no high-Zo lines
H
W
HW
HZ
r
oo 2/1
~
...need to flip-chip bond
no substrate radiation, no substrate losses
InP mm-wave PA (Rockwell)
![Page 86: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/86.jpg)
No breaks in ground plane
III-V MIMIC Interconnects -- Inverted Thin-Film Microstrip
narrow line spacing → IC density
... no ground breaks at device placements
still have problem with package grounding
thin dielectrics → narrow lines → high line losses → low current capability → no high-Zo lines
...need to flip-chip bond
Some substrate radiation / substrate losses
InP 150 GHz master-slave latch
InP 8 GHz clock rate delta-sigma ADC
![Page 87: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/87.jpg)
No clean ground return ? → interconnects can't be modeled !
35 GHz static divider interconnects have no clear local ground return interconnect inductance is non-local interconnect inductance has no compact model
InP 8 GHz clock rate delta-sigma ADC
8 GHz clock-rate delta-sigma ADC thin-film microstrip wiring every interconnect can be modeled as microstrip some interconnects are terminated in their Zo some interconnects are not terminated ...but ALL are precisely modeled
![Page 88: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/88.jpg)
VLSI Interconnects with Ground Integrity & Controlled Zo
negligible breaks in ground plane
narrow line spacing → IC density
negligible ground breaks @ device placements
still have problem with package grounding
thin dielectrics → narrow lines → high line losses → low current capability → no high-Zo lines
...need to flip-chip bond
no substrate radiation, no substrate losses
![Page 89: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/89.jpg)
Conclusions
![Page 90: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/90.jpg)
Few-THz Transistors
Scaling limits: contact resistivities, device and IC thermal resistances.
Few-THz InP Bipolar Transistors: can it be done ?
62 nm (1 THz f, 1.5 THz fmax ) scaling generation is feasible.700 GHz amplifiers, 450 GHz digital logic
Is the 32 nm (1 THz amplifiers) generation feasible ?
Few-THz InP Field-Effect Transistors: can it be done?
challenges are gate barrier, vertical scaling,source/drain access resistance, increased gm and drive current.
2DEG carrier concentrations must increase.
S/D regrowth offers a path to lower access resistance.
Solutions needed for gate barrier: maybe even MOSFET ?
![Page 91: Scaling of High Frequency III-V Transistors rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax Short Course, 2009 Conference on InP and Related Materials,](https://reader036.vdocuments.us/reader036/viewer/2022062804/56649e355503460f94b234d1/html5/thumbnails/91.jpg)
What Would We Do With Them ?
THz amplifiers→ THz radios→ imaging, sensing, communications
precision analog design at microwave frequencies→ high-performance receivers
500 GHz digital logic→ fiber optics
Higher-Resolution Microwave ADCs, DACs, DDSs