High current (100mA) InP/InGaAs/InP
DHBTs with 330 GHz fmax
Yun Wei, Sangmin Lee, Sundararajan
Krishnan, Mattias Dahlström, Miguel Urteaga,
Mark Rodwell
Department of Electrical and Computer
Engineering, University of California
yunwei@ece.ucsb.edu tel: 805-893-8044, fax 805-893-3262
High-Breakdown vs. High-Power HBTs
Wideband HBTs: high frequency amplification
millimeter-wave power amplifiers (60, 94 GHz, …)
modulator driver amplifiers for fiber optics
need high breakdown voltages DHBTs
DHBTs will operate at high power density
logic: > 200 kA/cm2 , 1.4 Volts 280 kW/cm2
mm-wave power: 100 kA/cm2 , 3 Volts 300 kW/cm2
self-heating, thermal failure, thermal runaway
In high current devices,
thermal runaway limits usable breakdown to well below BVCEO
Ultra-high fmax Transferred-Substrate HBTs
Miguel Urteaga
• Substrate transfer provides access to
both sides of device epitaxy
• Permits simultaneous scaling of
emitter and collector widths
• Maximum frequency of oscillation
f / 8RbbCcb
• Sub-micron scaling of emitter and
collector widths has resulted in record
values of mm-wave power gain
40
Transistor Gains, dB
 f max 
Collector:
3000 A thickness ,
30
unbounded U
U
16
3
10 /cm doping
Collector pulse
doping:
50 A thickness
20
MSG/MAG
U 1017/cm3 doping,
250 A from base
10
H
Vce = 1.1 V, Ic=5 mA
0
21
0.3 m x 18 m emitter,
0.7 m x 18.6 m collector,
10
100
Frequency, GHz
1000
Components of Rbb and Ccb
Pulfrey / Vaidyanathan
Rhoriz   sWbc / 2 LE
Ccb ,e  LeWe / Tc
Rx  Rhoriz  Rvert Rcont  Rcont!
MBE DHBT layer structure
InGaAs 1E19 Si 500 Å
collector
substrate
Grade 1E16 Si 480 Å
InP 2E18 Si 20 Å
InP 1E16 Si 2500 Å
Multiple stop etch layers
Buffer layer 2500 Å
base
Grade 2E18 Be 67 Å
InGaAs 4E19 Be 400 Å
emitter
Grade 1E19 Si 200 Å
InP 1E19 Si 900 Å
InP 8E17 Si 300 Å
Grade 8E17 Si 233 Å
Band profile
Bias at Vbe=0.7 V, Vce=1.5 V
Transferred-Substrate HBT Process Flow
• emitter metal
• emitter etch
• self-aligned base
• mesa isolation
• polyimide planarization
• interconnect metal
• silicon nitride insulation
• spin Benzocyclobutene, etch vias
• electroplate gold
• bond to carrier wafer with solder
• remove InP substrate
• collector metal
• collector recess etch
0.4 m T.S. DHBT
UCSB
Sangmin Lee
35
fmax = 425 GHz,
ft = 139 GHz
30
20
15
10
5
0
1.E+09
1.E+10
1.E+11
1.E+12
Frequency (Hz)
6.0
Vce(sat) ~1 V at 1.8 mA/m2
2
33.0
at 66.0
GHz input
BVGHz static
= 8 divider
V at Joutput
=0.4
mA/m
3.0
CEO
E
Ic(mA)
5.0
4.0
Ic(mA)
h21, U (dB)
25
3.0
2.0
2.0
1.0
1.0
0.0
0.0
0
0
0.5
1
1.5
Vce(V)
2
2.5
3
1
2
3
4
5
6
7
Vce(V)
Unlike power HEMTs, breakdown is high even at high current
8
9
ARO
MURI
Restrictions on DHBT sizing:
distributed base feed resistance
UCSB
Yun Wei
emitter
base contact
base
base feed-in contact
Self-aligned base contact thickness=0.08 m
base feed sheet resistance:
s=0.3 /•
significant for > 8 um emitter finger length
Large Area HBTs:
big Ccb, small Rbb,
even small excess Rbb substantially reduces fmax
ARO
MURI
Thermal runaway within a finger
UCSB
Yun Wei
emitter
With long emitter finger, current-crowding can occur within finger
• Long finger: temperature can vary along length of emitter finger
loss of strong thermal coupling
•Temperature gradients along finger results in nonuniform current distribution
center of stripe gets hotter carries more current gets hotter …
Premature Kirk-effect-induced collapse in ft.
• contact variation along emitter finger
ARO
MURI
Multi-finger DHBT thermal coupling:
thermal instability between fingers
UCSB
Yun Wei
Collector contact
Collector (InP)
Base (InGaAs)
Emitter (InP)
SiN
Au via
Heat flow
Carrier wafer
Ic
Ic
T
T
Steady state current and temperature
distribution when thermally stable
thermal instability further increases
current non-uniformity
ARO
MURI
Current hogging observation: multi-finger DHBT UCSB
Yun Wei
0.05
0.04
0.03
0.02
0.01
0
0
0.5
1
1.5
W. Liu, H-F Chau, E. Beam III, "Thermal properties and thermal instabilities of InP-based heterojunction bipolar transistors", IEEE Transactions on Electron Devices, vol.43,
(no.3), IEEE, March 1996. p.388-95.
2
ARO
MURI
Multi-finger DHBTs: poor performance
due to current instabilities
UCSB
Yun Wei
thermally driven current instability  collapse
120
25
I , mA
100
c
80
b
15
10
60
5
40
0
c
I , mA
I step = 300 A
20
0
I step = 380 A
20
1
2
3
4
V , Volts
5
6
ce
b
0
0
1
2
3
V , Volts
4
5
ce
25
low fmax due to
premature Kirk effect (current hogging)
excess base feed resistance
Jc=5e4 A/cm2
Vce=1.5 V
20
Gains, dB
8 finger common emitter DHBT
Emitter size: 16 um x 1 um
Ballast resistor (design):9 Ohm/finger
U
15
H
21
10
f
=120 GHz
max
5
f =91 GHz

0
10
10
Frequency, Hz
10
11
ARO
MURI
DHBT thermal stability: multiple emitter fingers
UCSB
Yun Wei
Assume initial temperatu re difference T between 2 fingers
dVbe
 1.1 mV/K at constant I c
dT
dVbe
1
T  Vbe 
T  I C 
Vbe
dT
Rex  Rballast  kT / qI E
 P  VCE I C  T   JAP
Unstable unless
dVbe
VCE JA
K thermal stability 
1
dT Rex  Rballast  kT / qI E
ARO
MURI
Multi-finger DHBT thermal resistance
Vbe fixed I
  JA
c
UCSB
dVbe dT dP

VCE   1.1 mV/K   JA I CVCE
dT dP dVCE
dVbe

dVCE
fixed I c
1

I C  1.1 mV/K 
Ic
Ib
Vbe
Vce
Yun Wei
ARO
MURI
Multi-finger DHBT mutual thermal resistance
UCSB
Yun Wei
mutual-heating thermal resistance ( thermal coupling between finger i and k):

th _ jk

V
(dV / dT )I V
bei
be
cek
0.01
Vce_j=3V
finger i
Icj, A
finger k
ck
Ib_k Ib_j
Vce_k
V
ce_j
0.001
0.0001
0.62
Vce_j=1V
Vce_k=1V
Vce_k=2V
Vce_k=3V
Vce_j
measure variation of Vbe
on one finger
while varying Vce
on a different finger
=2V
0.63
0.64
0.65
V ,V
bej
0.66
0.67
0.68
ARO
MURI
UCSB
Multi-finger DHBT design
7 m
5 m
Yun Wei
1 m
16 m
18 m
24 m
20 m
•4 finger structure
2 m
•Reduced base series resistance
•No current crowding observed
•Self-heating thermal resistance: th=3OC/mW
•Mutual thermal coupling resistance: th=0.03OC/mW
•AlN as carrier wafer to improve the thermal conductivity
•Rballast=8 gives KT=0.8 at Jc=1mA/m2 and Vce=3.5V
ARO MURI
Large current high breakdown voltage
broadband InP DHBT
UCSB
Yun Wei
4-finger device
4 x ( 1 m x 16 m emitter )
4 x ( 2 m x 20 m collector )
~4 Ohm ballast per emitter finger
fmax>330 GHz,
Vbrceo>7 V, Jmax>1x105 A/cm2
64 m2 common emitter DHBT
70
30
Ibstep=300uA
A =64 um
2
U, MAG/M SG, h21, dB
60
E
10
Ib step=59 uA
8
40
Ic, mA
Ic, m A
50
6
30
4
20
2
10
0
0
1
2
3
4
5
6
2
3
4
Vce, V
5
I =57m A
U
C
20
V =2.5V
ce
M SG /MAG
15
10
h21
5
f =107 GHz f
T
max
=371 GHz
0
0
1
2
E
25
7
Vce, V
0
A =64um
6
7
10
0
10
1
10
2
Frequency, G Hz
10
3
Large current high breakdown voltage
broadband InP DHBT
ARO MURI
UCSB
Yun Wei
4-finger device
4 x ( 1 m x 16 m emitter )
4 x ( 2 m x 20 m collector )
~8 Ohm ballast per emitter finger
fmax>330 GHz,
Vbrceo>7 V, Jmax>1x105 A/cm2
64 m2 common base DHBT
70
AE=64 um2
AE=64 um2
60
7
Ic=60 mA
6
5
40
Ic, mA
Ic, mA
50
30
MSG/MAG
U
4
3
2
20
1
0
10
0
2
4
6
Vcb, V
8
0
0
2
Vc,
Vcb,VV
4
6
8
Vcb=2.5 V
ARO MURI
Large current high breakdown voltage
broadband InP DHBT
UCSB
Yun Wei
8-finger device
8 x ( 1 m x 16 m emitter )
8 x ( 2 m x 20 m collector )
~8 Ohm ballast per emitter finger
fmax>330 GHz,
Vbrceo>7 V, Jmax>1x105 A/cm2
128 m2 common base DHBT
30
140
A =128 um
120
25
U, MSG/MAG, dB
14
12
10
80
Ic, m A
Ic, mA
100
60
8
6
4
40
2
0
-1
20
AE=128um2
2
E
IC=100mA
20
15
Vcb=2.9V
MSG/MAG
U
10
5
0
1
2
3
4
5
6
fmax=330 GHz
7
Vcb, V
0
0
2
4
Vcb, V
6
8
10
0 0
10
10
1
10
2
Frequency, GHz
10
3
Hybrid- model extraction:
as expected, very low Rbb , very high Ccb
ARO
MURI
UCSB
Yun Wei
AE=4 fingers x 16um2/finger
Ic=57mA, Vce=2.2 V
30
S21
U
20
hbt_tb..S(2,1)
hbt_tb_w..S(2,1)
S(2,1)
dB(baseline..S(1,1))
hbt_tb..U
dB(hbt_tb..h21)
hbt_tb_w..U
dB(hbt_tb_w..h21)
U
dB(h21)
25
15
h21
10
m2
freq=109.0GHz
dB(baseline..S(1,1))=<invalid>
5
-20
-15
-10
-5
0
5
10
15
20
m1
freq=342.0GHz
dB(baseline..S(1,1))=<invalid>
m2
m1
Ccbi=23.7 fF
Rbb=1.6 Ohm
Rex=1.2 Ohm
fmax=342 GHz
fT=109 GHz
0
1E9
1E10
1E11
1E12
freq (1.000GHz to 110.0GHz)
freq (75.00GHz to 110.0GHz)
freq (1.000GHz to 30.00GHz)
S12
S22
hbt_tb..S(1,2)
hbt_tb_w..S(1,2)
S(1,2)
S11
freq (1.000GHz to 110.0GHz)
freq (75.00GHz to 110.0GHz)
freq (1.000GHz to 30.00GHz)
hbt_tb..S(2,2)
hbt_tb_w..S(2,2)
S(2,2)
hbt_tb..S(1,1)
hbt_tb_w..S(1,1)
S(1,1)
freq, Hz
freq (1.000GHz to 110.0GHz)
freq (75.00GHz to 110.0GHz)
freq (1.000GHz to 30.00GHz)
-0.15
-0.10
-0.05
0.00
0.05
0.10
freq (1.000GHz to 110.0GHz)
freq (75.00GHz to 110.0GHz)
freq (1.000GHz to 30.00GHz)
0.15
Large signal DHBT model with self-heating consideration
-Spice model frame + small signal extraction
Spice parameters are
extracted from DC
Measurement
AE=1x16 m2
Common emitter
Distributed parasitic
elements are obtained
from Small signal
Modeling
Thermal effect is
emulated with powercontrolled-shunt-feed
back, given the
measured thermal
resistance.
Vbe
regression
current gain collapse
Large signal DHBT model with self-heating consideration
-Comparison of DC and RF simulation and measurement
70
measured
30
60
simulation
50
U
20
Ic, m A
dB(hbt_tb_w..h21)
dB(hbt_tb..h21)
dB(h21)
U
hbt_tb..U
hbt_tb_w..U
25
15
h21
10
40
30
20
5
10
1E10
1E11
1E12
0
0
freq, Hz
-0.05
0.00
3
4
5
6
7
S21
0.05
freq (1.000GHz to 30.00GHz)
freq (75.00GHz to 110.0GHz)
freq (1.000GHz to 110.0GHz)
0.10
hbt_tb_w..S(2,1)
hbt_tb..S(2,1)
S(2,1)
S(1,2)
hbt_tb_w..S(1,2)
hbt_tb..S(1,2)
-0.10
2
Vce,V
S12
-0.15
1
0.15
-20
-15
-10
-5
0
5
10
freq (1.000GHz to 110.0GHz)
freq (1.000GHz to 30.00GHz)
freq (75.00GHz to 110.0GHz)
15
20
S(2,2)
hbt_tb_w..S(2,2)
hbt_tb..S(2,2)
hbt_tb..S(1,1)
hbt_tb_w..S(1,1)
S(1,1)
0
1E9
S11
S22
freq (1.000GHz to
freq (75.00GHz to
freq (1.000GHz to
freq (1.000GHz to
freq (75.00GHz to
freq (1.000GHz to
110.0GHz)
110.0GHz)
30.00GHz)
30.00GHz)
110.0GHz)
110.0GHz)
Further power improvement of multi-finger DHBT
-multi-finger structure with partitioned emitter fingers
How to further improve the power?
•
Lumped 4-finger units using transmission line good, but area consuming
•
More parallel fingers on single mesa  layout difficulties with putting ballast resistor
temperature variation between fingers increases
•
How about increase emitter length?
•
Excess base feed resistance additional base metal evaporation, solved!
•
Current crowding within finger and current hogging between fingers big problem but can
be solved now.
Partitioned emitter fingers
•Long emitter finger is formed by several
interconnected emitter islands in 1.5 um
Contact metal
spacing in longitude direction.
•Emitter stripe length L0 is chosen that no
current crowding happens within the
emitter stripe.
•Common collector and collector contact.
Advantage: very thermal stable
Disadvantage: a little increase of Ccbx
collector
base
emitter
emitter
Interconnection
metal
-can also be applied for power mesa HBTs
where parallel emitter fingers will
substantially increase Ccb.
Thermal via
L0
1.5um
L0
Some recent results with
multi-finger structure with partitioned emitter fingers
Current collapse experiments with
4finger x (1umx32um)/finger DHBT
Different emitter structure:
•unit 1um x 32 um current collapse
observed
•partitioned in 4, 1um x 8 um each
stripe no current collapse
•same measured thermal resistance
burned
partitioned emitter, 4 stripes, 1umx8um/stripe
0.05
0.04
0.015
unstable
no partitioned emitter
0.014
3 finger Ic(A)
0.03
0.02
0.005
0.012
0.03
0.01
0.025
0.008
0.02
0.006
0.015
0.004
0.01
0.01
0.002
0.005
0
0
0
0.4
0.8
1.2
1.6
Vce(V)
2
2.4
2.8
0
0
0
0.4
0.8
1.2
Vce(V)
1.6
2
2.4
edge finger Ic(A)
0.01
edge finger Ic(A)
0.04
3 fingers Ic(A)
0.035
Some recent results with
multi-finger structure with partitioned emitter fingers
dB(baseline..S(1,1))
our_maxg
U
dB(h21)
25
New High current DHBT(common base)*
20
15
10
5
m1
0
1E9
1E10
1E11
1E12
freq, Hz
Single finger
DHBT-16m1
um emitter -no partitioned
freq=359.0GHz
dB(baseline..S(1,1))=<invalid>
fmax =359 GHz
25
dB(h21)
dB(baseline..S(1,1))
our_maxg
U
20
15
10
5
m1
0
1E9
1E10
m1
1E11
1E12
freq, Hz
freq=327.0GHz
Single finger DHBT-16
um emitter-partitioned in 4
dB(baseline..S(1,1))=<invalid>
fmax =327 GHz
fmax
dose not changed much with small excess Ccbx
8 fingers
Single finger: WE=1 um, LE =4x8 um
Maximum measured:
Ic_max=250 mA Vce=2.3 V
*no RF measurable device for this processing
Conclusions
Wideband Power DHBT:
power density: 100 kA/cm2 , 3 Volts 300 kW/cm2
bandwidth: >330 GHz
size: 128 um2 emitter area
Wideband Power applications: (60, 94 GHz, 200 GHz…)
millimeter-wave amplifiers
modulator driver amplifiers for fiber optics