developing bipolar transistors for sub-mm-wave amplifiers
TRANSCRIPT
Developing Bipolar Transistors for Sub-mm-Wave Amplifiers and Next-Generation (300 GHz) Digital Circuits
[email protected] 805-893-3244, 805-893-5705 fax
CollaboratorsZ. Griffith, E. Lind, V. Paidi, N. Parthasarathy, C. Sheldon, U. SingisettiECE Dept., University of California, Santa BarbaraProf. A. Gossard, Dr. A. Jackson, Mr. J. EnglishMaterials Dept., University of California, Santa BarbaraM. Urteaga, R. Pierson , P. RowellRockwell Scientific CompanyX. M. Fang, D. Lubyshev, Y. Wu, J. M. Fastenau, W.K. Liu International Quantum Epitaxy, Inc.Lorene Samoska, Andy FungJet Propulsion Laboratories S. Lee, N. Nguyen, and C. NguyenGlobal Communication Semiconductors
Plenary, Device Research Conference, State College, PA, June 26, 2006
SponsorsJ. Zolper, S. Pappert, M. RoskerDARPA (TFAST, ABCS, SMART)I. Mack, D. Purdy, M. YoderOffice of Naval Research
Mark Rodwell University of California, Santa Barbara
Our Specific Focus :
So, how can we build next-generation ICs ?
- 600 GHz amplifiers.
- 300 GHz digital clock rate.
Present III-V transistors have enabled
- 300 GHz amplifiers.
- 150 GHz clock rate digital ICs.
More Generally :
What do we mean by THz transistors ?
What are they for ?
How do we make them ?
Can we build THz transistors ?
What are the frequency limitsof bipolar integrated circuits ?
High-Resolution Microwave ADCs and DACs
THz Transistors: What Are They For ?
340 GHz & 600 GHz imaging systems
mm-wave radio: 40+ Gb/s on 250 GHz carrier
320 Gb/s fiber optics& adaptive equalizers for 40 Gb/s ...
Why develop transistors for mm-wave & sub-mm-wave applications ?→ compact ICs supporting complex high-frequency systems.
THz Transistors: What does this mean ?
A 1 THz current-gain cutoff frequency (fτ ) alone has little valuea transistor with 1000 GHz fτ and 100 GHz fmax cannot amplify a 101 GHz signal.
RF-ICs & MIMICs need high power-gain cutoff frequency (fmax )impedance matching is hard if fτ is low.
100+ GHz digital also needslow (Cdepletion ΔV / I ) and low (I*Rparasitic /ΔV ) .
So, how do we make a transistor with>1 THz fτ >1 THz fmax<50 fs CΔV / I charging delays ?
Key Performance Parameters for MMICs / RF-IC's
0
5
10
15
20
25
30
10 100 1000
MSG
/MA
G, d
B
Frequency, GHz
Common base
Common Collector
Common emitter
U
MIMIC / RF-ICs need gain ---hence fmax
Power amplifiers need breakdown voltage & power density
Low-Noise amplifiers need moderate associated gain and low noise
Γ++⋅⎟⎟⎠
⎞⎜⎜⎝
⎛⋅+≈ )(21min, igSmiHEMT RRRg
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( )( ) maxminmaxmax 81 IVVP −=
fmax
Key Performance Parameters for Fast Logic
clock clock clock clock
inin
out
out
( )
( )
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⎟⎟⎠
⎞⎜⎜⎝
⎛+⋅>Δ
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depl,
Δ
⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎟⎠
⎞⎜⎜⎝
⎛Δ=
Δ⇒
+=
+Δ
+
τ
ττ
Design HBTs for fast logic, not for high ft & fmax
HBT Scaling LawsHBT Scaling Roadmaps
Bipolar Transistor Scaling Laws
unchangedbase contact resistivity(if contacts do not lie above collector junction)
decrease 4:1base contact resistivity(if contacts lie above collector junction)
increase 4:1current densitydecrease 4:1emitter resistance per unit emitter areadecrease 4:1collector junction widthdecrease 4:1emitter junction widthdecrease 1.414:1base thicknessdecrease 2:1collector depletion layer thicknessrequired changekey device parameter
Goal: double transistor bandwidth when used in any circuit→ keep constant all resistances, voltages, currents→ reduce 2:1 all capacitances and all transport delays
Epitaxial scaling: layer thicknessesLithographic scaling: junction dimensionsResistance scaling: contact resistance and thermal resistance
InP HBT Scaling Roadmaps
Key scaling challengesemitter & base contact resistivitycurrent density→ device heatingcollector-base junction width scaling& Yield !
key figures of merit
for logic speed
Present Status of Fast III-V Transistors
)( ),/( ),/( ),/(
hence , :digital
gain, associated ,F :amplifiers noise low
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0
100
200
300
400
500
600
700
800
0 100 200 300 400 500 600 700 800
RSCUIUC_SHBTNTTFujitsu HEMTSFUUIUC_DHBTUCSB 500 nmNGSTPohangHRLIBM SiGeVitesseUCSB 250 nm
f max
(GH
z)
ft (GHz)
500 GHz400 GHz300 GHz200 GHz maxffτ=
Updated July 5 2006
250 nm
Red = manufacturable technology for 10,000- transistor ICs
500 nm
E. Lind et al, this conference
Scaling Generations
emitter 500 nm width16 Ω⋅μm2 contact ρ
base 300 width, 20 Ω⋅μm2 contact ρ
collector 150 nm thick, 5 mA/μm2 current density5 Vbreakdown
fτ 400 GHzfmax 500 GHz
power amplifiers 250 GHz digital clock rate 160 GHz(static dividers)
2005: InP DHBTs @ 500 nm Scaling Generation
emitter 500 250 nm width16 9 Ω⋅μm2 contact ρ
base 300 150 width, 20 10 Ω⋅μm2 contact ρ
collector 150 100 nm thick, 5 10 mA/μm2 current density5 3.5 Vbreakdown
fτ 400 500 GHzfmax 500 700 GHz
power amplifiers 250 350 GHz digital clock rate 160 230 GHz(static dividers)
2006: 250 nm Scaling Generation, 1.414:1 faster
emitter 500 250 125 nm width16 9 4 Ω⋅μm2 contact ρ
base 300 150 75 width, 20 10 5 Ω⋅μm2 contact ρ
collector 150 100 75 nm thick, 5 10 20 mA/μm2 current density5 3.5 3 V breakdown
fτ 400 500 700 GHzfmax 500 700 1000 GHz
power amplifiers 250 350 500 GHz digital clock rate 160 230 330 GHz(static dividers)
125 nm Scaling Generation→ almost-THz HBT
emitter 500 250 125 63 nm width16 9 4 2.5 Ω⋅μm2 contact ρ
base 300 150 75 70 nm width, 20 10 5 5 Ω⋅μm2 contact ρ
collector 150 100 75 53 nm thick, 5 10 20 35 mA/μm2 current density5 3.5 3 2.5 V breakdown
fτ 400 500 700 1000 GHzfmax 500 700 1000 1500 GHz
power amplifiers 250 350 500 750 GHz digital clock rate 160 230 330 450 GHz(static dividers)
65 nm Scaling Generation→beyond 1-THz HBT
Scaling Challenges
Reducing Contact Resistivity
Pd or Pt solid-phase-reaction contacts
extrinsic base
intrinsic base
drift collector
N+ sub collector
S.I. InP substrate
pedestal
current-block layer
regrown emitter
emitter contact
base contact
Regrowth for wider emitter contacts
basedrift collector
sub-collector
We
Te
Wrap-around emitter contact
nm 200at m-1
21
2
=Ω=
⋅=
e
eex
e
bulkcontact
eex
WAR
WLR
μ
ρρ
ErAs in-situ MBE emitter contactsgrown in-situ by MBE
no oxides, no contaminants
Lattice matched few defect states no Fermi level pinning
Thermodynamically stable little intermixing
Zimmerman, Gossard & Brown
Q. G. Sheng, J. Appl. Phys. (1993)A Guivarc’h, J. Appl. Phys. (1994)
*A. Guivarc’h, Electron. Lett.(1989)**C.J.Palmstrøm Appl. Phys. Lett. (1990)
TEM : Lysczek, Robinson, & Mohney, Penn State Sample: Urteaga, RSC
E. F. Chor et al , JAP 2000
Emitter-Base Degeneracy → 1.5 Ω−μm2 Effective Junction 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
- φ
Fermi-Dirac
Equivalent series resistance approximation
Boltzmann
fnEcE
Degeneracy contributes ~ 1-2 Ω-μm2
to observed emitter resistivity (?).
Solutions: higher mass emitter ?superlattice emitter ?
*2
2
132
2*
2
2
/1 ,InPfor m 5.1
)()/ln()/( model resistance series eApproximat
d]unpublishe , Lundstrom& [Liang
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integral Dirac- Fermimodel, ballistic :ApproachBetter
mmA/ 22 :envelope ofBack
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∝−Ω=
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ρμρ
ρφ
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μ
μ
hthanks to Bill Frensley for BandProf !
Temperature Rise Within Transistor & Substrate
re temperatujunction Increased1:2 decreases spacingransistor t
1:4 decreases dthemitter wi rateclock digital in doubling eachFor
→HBT
e
DW
⎟⎠⎞
⎜⎝⎛ −
⋅+⎟⎟⎠
⎞⎜⎜⎝
⎛−+⎟⎟
⎠
⎞⎜⎜⎝
⎛≅Δ 2substrate
2/11lnD
DTK
PDLK
PWL
LKPT sub
InPEInPe
e
EInP ππ
eLr < junctionnear flowheat lcylindrica
2/for flowheat spherical
HBTe DrL << 2/for flowheat planar
HBTDr >
scaling withcallylogarithmi
increases
scaling withvariationnegligible
constant is IF scaling with
llyquadratica increases
subT
Temperature Rise Within Transistor & Substrate
⎟⎠⎞
⎜⎝⎛ −
⋅+⎟⎟⎠
⎞⎜⎜⎝
⎛−+⎟⎟
⎠
⎞⎜⎜⎝
⎛≅Δ 2substrate
2/11lnD
DTK
PDLK
PWL
LKPT sub
InPEInPe
e
EInP ππ
0
20
40
60
80
100
120
140
100 200 300 400 500 600 700
tem
pera
ture
rise
in s
ubst
rate
, Kel
vin
master-slave D-Flip-Flop clock frequency, GHz
( )clocksub fT GHz/ 160 m 15 ×= μ
rate.clock digital GHz 300at even rise re temperatusubstrate acceptable allows
thicknesssubstrate reducingy Agressivel subT
junctionnear flowheat lcylindrica
eLr >for flowspherical
2/for flowplanar
HBTDr >
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variationantinsignific
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ICs digital GHz 150
eddemonstrat from scaled etc.
densities,power rates,clock
lenghts, Wiring
Temperature Rise Within Package
chipCu
chippackage WK
PT ⎟
⎠⎞
⎜⎝⎛ +≅Δ
211
RiseeTemperatur PackageTotal
π
0
50
100
150
200
100 200 300 400 500 600
pack
age
tem
pera
ture
rise
, Kel
vin
fclock,
GHz
12 mA per transistor (25 Ω logic load resistor)
3 mA per transistor (100 Ω logic load resistor)
n)dissipatior transisto( 1.5 power IC rs/IC transisto1000
bias V 2 )GHz/ (150 m 20 :spacing Transistor
:sAssumption
×=
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ce
clock
Vfμ
rate.clock digital GHz 300at evenIC / rs transisto1000 with
rise re temperatupackage acceptableloading) (100stor per transi mA 3At Ω
1:2 decrease dimensions chip 1:2 decrease spacings BT H
rateclock digital in doubling eachFor
chip
HBT
WD
→
Scaling of Breakdown Voltage with InP/InGaAs InP DHBTs
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
0 10 20 30 40 50 60 70 80
60 nm thick collector
Ene
rgy
(eV
)
distance (nm)
collector
base
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
0 20 40 60 80 100 120 140 160
120 nm thick collector
Ene
rgy
(eV
)
distance (nm)
collector
base
If collector is thinned without thinninggrade and setback layers...
..then Zener tunneling through grade& setback layers can reduce BVCEO
Or, should we simply thin the grade, using fewer superlattice periods ?
Type-2 DHBT: InGaAsSb baseType-1 DHBT: InGaAs base
Should we switch from type-I DHBT to type-2, eliminating the grade but sacrificing base transport ?
...or other approaches...
Erik Lind
Breakdown Voltage: What do we really need ?
0
2
4
6
8
10
0 1 2 3 4 5 6 7 8
J e (
mA
/μm
2 )
Vce
(V)
6.8 V BVCEO
( )( ) maxminmaxmax 81 IVVP −=
0
2
4
6
8
10
0 1 2 3 4 5 6 7 8
J e (
mA
/μm
2 )
Vce
(V)
6.8 V BVCEO
10 mW/um2
20 mW/um2
( )( ) maxminmaxmax 81 IVVP −=
Breakdown Voltage: What do we really need ?
0
2
4
6
8
10
0 1 2 3 4 5 6 7 8
J e (
mA
/μm
2 )
Vce
(V)
( )( ) maxminmaxmax 81 IVVP −=
!
Breakdown Voltage: What do we really need ?
0
2
4
6
8
10
0 1 2 3 4 5 6 7 8
J e (
mA
/μm
2 )
Vce
(V)
( )( ) maxminmaxmax 81 IVVP −=
Breakdown Voltage: What do we really need ?
max&high ffτ max& low ffτ
bandwidth decreases at high Vce due to velocity-field characteristics
Scaling challenges: What looks easy, what looks hard ?
unchangedbase contact resistivity(if contacts do not lie above collector junction)
decrease 4:1base contact resistivity(if contacts lie above collector junction)
increase 4:1current density
decrease 4:1emitter resistance per unit emitter areadecrease 4:1collector junction width
decrease 4:1emitter junction widthdecrease 1.414:1base thicknessdecrease 2:1collector depletion layer thicknessrequired changekey device parameter
Hard:Thermal resistance (ICs)Emitter contact + access resistanceYield in deep submicron processesContact electromigration (?), dark-line defects (?)
Probably not as hard :Maintaining adequate breakdown for 3 V operation...
Frequency Limitsand Scaling Laws of (most) Electron Devices
bottomR
topR
lenght stripe/1
area/thickness/area
thickness
∝
∝∝∝
bottom
contacttop
R
RC
ρ
τ
Applies whenever AC signals are removed though Ohmic contactsSemiconductor lasers avoid R/C/τ limits by radiating through end facets
capacitanceresistance transit time
device bandwidth
applies to:transistors: BJTs & HBTs, MOSFETS & HEMTs, Schottky diodes, photodiodes, photo mixers, RTDs,
Mesa HBTs
Mesa DHBTs at the 500-600 nm Scaling Generation
1.3 μm base-collector mesa1.7 μm base-collector mesa
Zach Griffith
600 nm emitter width
β ≈ 40, VBR,CEO = 3.9 V. Emitter contact Rcont < 10 Ω⋅μm2
Base : Rsheet = 610 Ω/sq, Rcont = 4.6 Ω⋅μm2
Collector : Rsheet = 12.1 Ω/sq, Rcont = 8.4 Ω⋅μm2
Vcb
= -0.3 V
0
2
4
6
8
10
0 2.5 5 7.5 10 12.50
5
10
15
20
25
Ccb
/Ae (
fF/μ
m2 )
Je (mA/μm2)
Ccb (fF
)
-0.2 V
0.0 V
0.2 V
Vcb
= 0.6 V
Ajbc
= 1.3 x 6.5 μm2
Ccb
/Ic=0.2 ps/V
0.4 ps/V
0.6 ps/V
0.8 ps/V
1.0 ps/V1.5ps/V
Ajbe
= 0.6 x 4.3 μm2
0
5
10
15
20
25
30
35
109 1010 1011 1012
Gai
ns (d
B)
Frequency (Hz)
U
Ajbe
= 0.6 x 4.3 um2
Ic = 20.6 mA, V
ce = 1.53 V
Je = 8.0 mA/um2, V
cb= 0.6 V
ft = 450 GHz, f
max = 490 GHz
h21
10-12
10-10
10-8
10-6
10-4
0.01
0 0.25 0.5 0.75 1
I b, Ic (A
)
Vbe
(V)
VCB
= 0.0 V (dashed)V
CB = 0.3 V (solid)
Ic
Ib
nc = 1.12
nb = 1.41
Gummel characteristics
InP DHBT: 600 nm lithography, 120 nm thick collector, 30 nm thick baseZach Griffith
Average β ≈ 50, BVCEO = 3.2 V, BVCBO = 3.4 V (Ic = 50 μA)Emitter contact (from RF extraction), Rcont ≈ 8.6 Ω⋅μm2
Base (from TLM) : Rsheet = 805 Ω/sq, Rcont = 16 Ω⋅μm2
Collector (from TLM) : Rsheet = 12.0 Ω/sq, Rcont = 4.7 Ω⋅μm2
InP DHBT: 600 nm lithography, 75 nm thick collector, 20 nm base
Peak fτ
Peak fmax10-12
10-10
10-8
10-6
10-4
0.01
0 0.2 0.4 0.6 0.8 1
I b, Ic (A
)
Vbe
(V)
VCB
= 0.0 V (dashed)V
CB = 0.3 V (solid)
Ic
Ib
nc = 1.15
nb = 1.47
0.0
4.0
8.0
12.0
16.0
20.0
0 0.25 0.5 0.75 1 1.25
J e (m
A/μ
m2 )
Vce
(V)
Vcb
= 0 V
DC characteristics
RF characteristics
Aje = 0.65 × 4.3 μm2 , Ib,step = 175 μA
Zach Griffith
Variation of Transistor Bandwidth with Scaling
0
100
200
300
400
500
600
700
800
0 100 200 300 400 500 600 700 800
f max
(GH
z)
ft (GHz)
500 GHz400 GHz300 GHz200 GHz maxffτ=
Updated July 5 2006
)( ),/( ),/( ),/(
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
ττVIRVIRIVC
f
m
ff
ff
ffff
+ΔΔ
Δ
+
+
−
μ
τ
τ
τ
τ
:metrics better much
:metrics popular
Variation of Transistor Bandwidth with Scaling
0
100
200
300
400
500
600
700
800
0 100 200 300 400 500 600 700 800
f max
(GH
z)
ft (GHz)
500 GHz400 GHz300 GHz200 GHz maxffτ=
Updated July 5 2006epitaxial scaling
)( ),/( ),/( ),/(
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
ττVIRVIRIVC
f
m
ff
ff
ffff
+ΔΔ
Δ
+
+
−
μ
τ
τ
τ
τ
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Variation of Transistor Bandwidth with Scaling
0
100
200
300
400
500
600
700
800
0 100 200 300 400 500 600 700 800
f max
(GH
z)
ft (GHz)
500 GHz400 GHz300 GHz200 GHz maxffτ=
Updated July 5 2006epitaxial scaling
epita
xial,
lithog
raphic
,
& conta
ct res
istan
ce
scali
ng
)( ),/( ),/( ),/(
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
ττVIRVIRIVC
f
m
ff
ff
ffff
+ΔΔ
Δ
+
+
−
μ
τ
τ
τ
τ
:metrics better much
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?
?
7.5 mW output power
175 GHz Amplifiers with 300 GHz fmax Mesa DHBTs
7 dB gain measured @ 175 GHz
2 fingers x 0.8 um x 12 um, ~250 GHz fτ, 300 GHz fmax , Vbr ~ 7V, ~ 3 mA/um2 current density
V. Paidi, Z. Griffith, M. Dahlström
-10
-5
0
5
10
15
140 150 160 170 180 190 200
S 21, S
11, S
22 d
B
Frequency, GHz
S21
S11
S22
7-dB small-signal gain at 176 GHz8.1 dBm output power at 6.3 dB gain
0.860.740.990.59psec / VCcb/Ic
3583010.6
4.40.5 x 4.5
clock current steering
GHzGHz
V
mA/μm2
μm2
units
280268358fmax
280260301fτ
1.700.6Vcb
4.44.46.9currentdensity
0.5 x 5.50.5 x 4.50.5 x 3.5size
clock emitter
followers
data emitter
followers
data current steering
UCSB / RSC / GCS 150 GHz Static Frequency Dividers
-40
-30
-20
-10
0
10
20
0 20 40 60 80 100 120 140 160
Min
imum
inpu
t pow
er (d
Bm
)
frequency (GHz)
IC design: Z. Griffith, UCSBHBT design: RSC / UCSB / GCSIC Process / Fabrication: GCSTest: UCSB / RSC / Mayo
-80
-70
-60
-50
-40
-30
74.9975 74.9987 75.0000 75.0012 75.0025
Out
put P
ower
(dB
m)
frequency (GHz)
-90
-80
-70
-60
-50
-40
-30
-20
-10
0.00 19.00 38.00 57.00 76.00
Out
put P
ower
(dBm
)
frequency (GHz)
probe station chuck @ 25°C
PDC,total = 659.8 mWdivider core without output buffer ≈ 594.7 mW
4:1 Mux in Vitesse VIP3 InP HBT Process
160 Gb/s
150 Gb/s
T. Swahn et al
250 nm scaling generation DHBTs
• 100 % I-line lithography• Emitter contact resistance reduced 40%: from 8.5 to 5 Ω⋅μm2
• Base contact resistance is < 5 Ω⋅μm2 --hard to measure • Recall, 1/8 μm scaling generation needs ≤ 5 Ω⋅μm2 emitter ρc
Zach Griffith
0.30 µm emitter junction, Wc/We ~ 1.6Zach Griffith
First mm-wave results with 250 nm InP DHBTs
150 nm material250 nm emitter width
fτ = 420 GHzfmax = 650 GHz~6 V breakdown30 mW/um2 power handling
results to be presented postdeadline this conference, E. Lind, Z. Griffith et al
Erik Lind
Epitaxial scaling at 250 nm design rules
0
100
200
300
400
500
600
700
800
0 100 200 300 400 500 600 700 800
f max
(GH
z)
ft (GHz)
500 GHz400 GHz300 GHz200 GHz maxffτ=
Updated July 5 2006
?
?
Vcb
= 0.0 V-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
0 10 20 30 40 50 60 70 80
Ene
rgy
(eV
)
distance (nm)
collector
valence band
Γ-electron valley
base
Je = 0, 5, 10, 15, 20, 25 mA/μm2
60 nm thick collector
process failurenew fab run in progress
Vcb
= 0.0 V-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
0 20 40 60 80 100 120 140
Ene
rgy
(eV
)
distance (nm)
collector
valence band
Γ-electron valley
base
Je = 0, 2.5, 5.0, 7.5, 10, 12.5 mA/μm2
100 nm thick collector
fτ / fmax, proj ~ 575/550 GHzat 250 nm emitter width
Zach Griffith
330 GHz Cascode Power Amplifiers In Design
Psat = 50 mW (17 dBm) 10-dB associated power gainuse 650 GHz fmax transistors
-5
0
5
10
15
20
0
0.05
0.1
0.15
0.2
0.25
-15 -10 -5 0 5 10
Gai
n (d
B), O
utpu
t Pow
er (d
Bm
)
PAE (%
)
Input Power, dBm
PAE
Gain
Output Power
-10
-5
0
5
10
15
260 280 300 320 340 360
S 21, S
11, S
22 (
dB )
Frequency, GHz
S21
S11
S22
Navin Parthasarathy
Manufacturable Process Flows
At a given scaling generation, intelligent choice of device geometry reduces extrinsic parasitics
Parasitic Reduction for Improved InP HBT Bandwidth
SiO2 SiO2
P base
N+ subcollector
N-thick extrinsic base : low resistancethin intrinsic base: low transit time
wide emitter contact: low resistancenarrow emitter junction: scaling (low Rbb/Ae)
wide base contacts: low resistancenarrow collector junction: low capacitance
Much more fully developed in Si…
⎟⎟⎠
⎞⎜⎜⎝
⎛ ⋅=
Wr
LR bulk
bulk2ln2
πρ
LrR c
contact πρ2
=
These are planar approximations toradial contacts:
extrinsicbase
extrinsicemitter
N+ subcollector
extrinsicbase
⎥⎦
⎤⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛+=
bulk
contactbulk
WLR
ρρ
πρ ln34.12
mintotal,
→ greatly reduced access resistance
Polycrystalline Extrinsic Emitter D. Scott, Y. Wei
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0 0.5 1 1.5
Ibstep
=100 uA
I C(A
)
VCE
(V)
Self-aligned, AE_junction
=0.3 um x 4 um
0
5
10
15
20
25
30
1 10 100 1000
IC=9.72 mA
VCE
=1.2 V
U, M
SG/M
AG, h
21 (d
B),
K
Frequency (GHz)
U
h21MAG/MSG
K
fT=280 GHzf
MAX=148GHz
Emitter junction area: 0.3 x 4 μm2
ApproachWide emitter contact for low emitter access resistanceThick extrinsic base for low base resistanceSelf-aligned refractory base contacts
Enabling TechnologyLow-resistance polycrystalline InAsIn-band Fermi-level pinning eliminates barriers
ChallengesVery complex processHydrogen passivationResistance of Refractory contacts
Self-aligned Sidewall Spacer (S3) Manufacturable HBT Process
Self-aligned contacts are critical to submicron device scaling. Eliminates lithography alignment tolerance.
RSC’s S3 HBT process utilizes electroplated contacts with dielectric sidewalls. Eliminates low yield liftoff processes from base-emitter junction formation.
Electroplated base contact is selectively deposited on the base semiconductor.
Process enables deep submicron scaling while maintaining high levels of performance and yield
Emitter Contact
Base Contact
Dielectric Sidewall
Electroplate emitter contact Etch emitter semiconductor
Dielectric sidewall deposition Base contact patterning
Selectively deposit base metal
S3 Process Flow
SEM Cross-Section of B-E Junction
10 11 120
10
20
30
40
Frequency (GHz)
|H21
|(red
), U
(blu
e) (d
B)
fτ = 405GHzfmax = 392 GHz
RF Gains
JE = 6.5 mA/um2
VCE = 1.5 V
Miguel Urteaga, Richard Pierson, Petra RowellKeisuke Shinohara, Berinder Brar
VIP-2 HBT structure: Dielectric Sidewall
Dielectric Spacer allows tightly controlled separation between Emitter and Base to minimize Rbx and Cbcx
B
C
Cross section
LayoutE B
E
C
Note that the basevia is “folded” on topof the transistor toreduce Cbc
Minh Le et al
G. He, J. Howard, M. Le, P. Partyka, B. Li, G. Kim, R. Hess, R. Bryie, R. Lee, S. Rustomji, J. Pepper, M. Kail, M. Helix, R. Elder, D. Jansen, N. Harff, J. Prairie, E. Daniel, and B. Gilbert, “Self-Aligned InP DHBT with ft and fmax over 300 GHz in a new manufacturable technology,” IEEE Electron Device Lett., vol. 25, no. 8, pp. 520–522, Aug. 2004.
Low-Power High-Speed Logic → Small Pad Capacitance
ECL with impedance-matched 50 Ohm bus:25 Ohm load→ switch 12 mA 12 mA x 7 x 4 V = 336 mW/latch
CML with impedance-matched 50 Ohm bus:25 Ohm load→ switch 12 mA 12 mA x 3 x 3 V = 108 mW/latch
Low-Power CML100 Ohm loaded → switch 3 mA 3 mA x 3 x 3 V = 27 mW/latch
base pad capacitance key parasitic in low power bipolar logicCML operates at lower Vce → reduced Kirk-effect-limited current
12 mA12 mA 12 mA
50 Ohm bus 50 Ohm 50 Ohm
12 mA
50 Ohm bus 50 Ohm 50 Ohm
50 Ohm bus100 Ohm
3 mA
3 mA 3 mA
padcbwiring CC ,low ,low power low @ speed High =
100 Ohm
0
5
10
15
20
25
-0.4 -0.2 0.0 0.2 0.4 0.60.00
1.55
3.10
4.65
6.20
7.75
9.30
Ccb
(fF)
Vcb
(V)
Ccb / A
e (fF/um2)
mesa
implanted sub-collector
implanted sub-collector + pedestal
Ajbc
= 1.3 x 8.5 um2
Subcollector & Pedestal Implant
Fe
N+S.I.
N+
Epitaxial growth JunctionFabrication
N+ N+FeFe
N+S.I.
N+N+ N+Fe
Pedestal Implant
Fe
N+S.I.
N+N+ N+Fe
Fe Implant
S.I.
Fe
Subcollector Implant
N+S.I.
Fe
Subcollector implant eliminates Ccbin base pad area .Pedestal further reduces Ccb.
Navin Parthasarathy
0
5
10
15
20
0 1 2 3 4 5 6 70
5
10
15
20
I c (mA)
VCE
(V)
Ib start
= 50 μA
Ib step
= 100 μA
β ~ 40
BVCEO
= 6.8V
0
5
10
15
20
25
30
35
109 1010 1011 1012
Gai
ns (d
B)
Frequency (Hz)
ft = 352 GHz, f
max = 403 GHz
Uh
21
10-12
10-10
10-8
10-6
10-4
0.01
0 0.2 0.4 0.6 0.8 1I b, I
c (A)
Vbe
(V)
VCB
= 0.3 V (solid)
VCB
= 0.0 V (dashed)
Ic
nc = 1.18
Ajbe
= 0.65 x 4.3 μm2
Ib
50 pA
nb = 1.53
Without Ccb reduction fmax = 51 GHz
Fe
N+.I.
N+
onation
N+ N+Fe
With Pedestal fmax = 61.2 GHz (measured)fmax ~ 100 GHz (simulated)
Pdivider core, ≈ 31 mW(includes emitter follower buffers)
Device technology, other higher-speed circuits, M. Urteaga, K. Shinohara, R. Pierson, P. Rowell, B. Brar, Z. Griffith, N. Parthasarathy, M. Rodwell" InP DHBT IC Technology with Implanted Collector-Pedestal and Electroplated Device Contacts" ,submitted to IEEE CSIC Symposium
Low-Power IC Design: Z. Griffith, N. Parthasarathy, M. Rodwell, M. Urteaga, K. Shinohara, P. Rowell, R. Pierson, and B. Brar"An Ultra Low-Power ( ≤ 13.6 mW/latch) Static Frequency Divider in an InP/InGaAs DHBT Technology" , 2006 IEEE IMS Symposium
Ultra low power CML Static Frequency Divider: RSC S3 Process with Pedestal
Frequency Limits of Bipolar Integrated Circuits
500 nm generation: Done~475 GHz ft & fmax150 GHz static dividers (digital ICs)
250 nm results coming very soon. expect ~225 GHz digital clock rate, 300-400 GHz amplifiers
125 nm devices are the next target . → 300 GHz digital clock rate, 600 GHz amplifiers
THz transistors will come The approach is scaling.The limits are contact & thermal resistance
serious challenge: volume applications to support development