185 GHz Monolithic Amplifier in
InGaAs/InAlAs Transferred-Substrate
HBT Technology
M. Urteaga, D. Scott, T. Mathew, S. Krishnan, Y.
Wei, M. Rodwell.
Department of Electrical and Computer Engineering,
University of California, Santa Barbara
urteaga@ece.ucsb.edu 1-805-893-8044
IMS2001 May 2001, Phoenix, AZ
IMS2001
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•
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•
•
Outline
UCSB
Introduction
Transferred-Substrate HBT Technology
Circuit Design
Results
Conclusion
IMS2001
Transferred-Substrate HBTs
• Substrate transfer allows
simultaneous scaling of emitter and
collector widths
• Maximum frequency of oscillation

f max 
ft / 8RbbCcb
• Sub-micron scaling of emitter and
collector widths has resulted in record
values for extrapolated fmax (>1 THz)
Mason's
gain, U
3000 Å collector
400 Å base with 52 meV
grading
AlInAs / GaInAs / GaInAs
HBT
25
Gains, dB
• Promising technology for ultra-high
frequency tuned circuit applications
30
20
MSG
15
H21
10
5
Emitter, 0.4 x 6 mm2
Collector, 0.7 x 6 mm2
fmax
= 1.1 THz ??
ft = 204 GHz
Ic = 6 mA, Vce = 1.2 V
0
10
100
Frequency, GHz
1000
IMS2001
Ultra-high Frequency Amplifiers
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Applications for electronics in 140-220 GHz frequency band
 Wideband communication systems
 Atmospheric sensing
 Automotive radar
•
Amplifiers in this frequency band realized in InP-based HEMT technologies
 3-stage amplifier with 30 dB gain at 140 GHz.


•
Pobanz et. al., IEEE JSSC, Vol. 34, No. 9, Sept. 1999.
3-stage amplifier with 12-15 dB gain from 160-190 GHz
Lai et. al., 2000 IEDM, San Francisco, CA.
6-stage amplifier with 20  6 dB from 150-215 GHz.
Weinreb et. al., IEEE MGWL, Vol. 9, No. 7, Sept. 1999.
This Work:
 Single-stage tuned amplifier with 3.0 dB gain at 185 GHz
 First HBT amplifier in this frequency range
 Gain-per-stage is comparable to HEMT technology
IMS2001
InGaAs/InAlAs HBT Material System
Layer Structure
Band Diagram
InGaAs 1E19 Si 1000 Å
Grade 1E19 Si 200 Å
InAlAs 1E19 Si 700 Å
InAlAs 8E17 Si 500 Å
Grade 8E17 Si 233 Å
Grade 2E18 Be 67 Å
InGaAs 4E19 Be 400 Å
2kT base bandgap grading
InGaAs 1E16 Si 400 Å
InGaAs 1E18 Si 50 Å
InGaAs 1E16 Si 2550 Å
Bias conditions for the band diagram
InAlAs UID 2500 Å
S.I. InP
Vbe = 0.7 V
Vce = 0.9 V
IMS2001
Device Fabrication I
IMS2001
Transferred-Substrate Process Flow
• emitter metal
• emitter etch
• self-aligned base
• mesa isolation
• polyimide planarization
• interconnect metal
• silicon nitride insulation
• Benzocyclobutene, etch vias
• electroplate gold
• bond to carrier wafer with solder
• remove InP substrate
• collector metal
• collector recess etch
IMS2001
Device Fabrication II
IMS2001
Ultra-high fmax Devices
• Electron beam lithography used to define
submicron emitters and collectors
• Minimum feature sizes
 0.2 mm emitter stripe widths
 0.3 mm collector stripe widths
• Improved collector-to-emitter alignment
using local alignment marks
0.3 mm Emitter before polyimide planarization
Future Device Improvements
• Carbon base doping
 na >1.0 x 1020 cm-3
 significant reduction in Rbb
• DHBTs with InP Collectors
 Greater than 6 V BVCEO
0.4 mm Collector Stripe
Device Measurements
IMS2001
DC Measurements
Measured RF Gains
3
25
2.5
Ib steps = 15 uA
Gain (dB)
2
Ic
(m
A)
U
20
1.5
1
0.5
15
MAG/
MSG
10
h21
5
0
0
-5
1E10
-0.5
0
0.2
0.4
0.6
0.8
Vce (V)
1
• Device dimensions:
 Emitter area: 0.4 x 6 mm2
 Collector area: 0.7 x 6.4 mm2
•  = 20
• BVCEO = 1.5 V
1E11
1E12
Frequency (Hz)
1.2
• Bias Conditions:
 VCE = 1.2 V, IC = 4.8 mA
• ft = 160 GHz
• Measurements of unilateral power gain in
140-220 GHz frequency band appear to show
unphysical behavior
IMS2001
Amplifier Design
Simulation Results
S21, dB
7.5
• Shunt R-C network at output
provides low frequency stabilization
5.0
0
2.5
-10
0.0
-30
-5.0
-40
140
150
• Designed using hybrid-pi model
derived from DC-50 GHz
measurements of previous
generation devices
• Electromagnetic simulator
(Agilent’s Momentum) was used to
characterize critical passive
elements
-20
S11,
S22
-2.5
• Simulations predicted 6.2 dB gain
10
S21
S11, S22, dB
• Simple common-emitter design
conjugately matched at 200 GHz
using shunt-stub tuning
160
170
180
190
200
210
220
Frequency, GHz
Circuit Schematic
50
0.2pF
80
1.2ps
30
0.2ps
IN
OUT
80
1.2ps
50
30
1.2ps
50

0.6ps
IMS2001 Design Considerations in Sub-mmwave Bands
• Transferred-substrate technology provides
low inductance microstrip wiring environment
 Ideal for Mixed Signal ICs
• Advantages for MMIC design:
 Low via inductance
 Reduced fringing fields
• Disadvantages for MMIC design:
 Increased conductor losses
• Resistive losses are inversely proportional
to the substrate thickness for a given Zo
• Amplifier simulations with lossless matching
network showed 2 dB more gain
• Possible Solutions:
 Use airbridge transmission lines
 Find optimum substrate thickness
IMS2001
140-220 GHz VNA Measurements
• HP8510C VNA used with Oleson
Microwave Lab mmwave Extenders
• Extenders connected to GGB
Industries coplanar wafer probes via
short length of WR-5 waveguide
• Internal bias Tee’s in probes for
biasing active devices
• Full-two port T/R measurement
capability
• Line-Reflect-Line calibration performed
using on-wafer transmission line
standards
UCSB 140-220 GHz VNA Measurement Set-up
IMS2001
Amplifier Measurements
• Measured 3.0 dB peak gain at 185 GHz
Measured Gain
4
3
• Device dimensions:
 Emitter area: 0.4 x 6 mm2
 Collector area: 0.7 x 6.4 mm2
S21 (dB)
2
• Device bias conditions:
 Ic= 3.0 mA, VCE = 1.2 V
1
0
-1
-2
-3
-4
-5
140
150
160
170
180
190
200
210
220
Freq. (GHz)
Measured Return Loss
0
-2
S22
S11, S22 (dB)
-4
-6
S11
-8
-10
-12
-14
-16
Cell Dimensions: 690mm x 350 mm
-18
140
150
160
170
180
190
Freq. (GHz)
200
210
220
IMS2001
Simulation vs. Measurement
Simulation versus Measured Results
• Amplifier designed for 200 GHz
7.5
• Peak gain measured at 185 GHz
5.0
• Possible sources for discrepancy:
2.5
S21, dB
Meas.
0.0
-2.5
-5.0
140
150
160
170
180
190
200
210
220
Frequency, GHz
0
-5
-10
S11,S22, dB
 Matching network design
 Device model
Sim.
-15
Meas.
-20
Sim.
-25
-30
-35
-40
140
150
160
170
180
190
Frequency, GHz
200
210
220
IMS2001
Matching Network Design
Matching Network Breakout
• Breakout of matching network without
Simulation Vs. Measurement
active device was measured on-wafer
• Measurement compared to circuit
simulation of passive components
• Simulations show good agreement
with measurement
• Verifies design approach of combining
E-M simulation of critical passive
elements with standard microstrip
models
S11
S21
S22
freq (140.0GHz to 220.0GHz)
Red- Simulation
Blue- Measurement
IMS2001
Device Modeling I: Hybrid-Pi Model
• Design used a hybrid-pi device model
based on DC-50 GHz measurements
HBT Hybrid-Pi Model
Derived from DC-50 GHz Measurements
• Measurements of individual devices in
140-220 GHz band show poor
agreement with model
• Discrepancies may be due to
weakness in device model and/or
measurement inaccuracies
1.59
17
43
45
0.4
• Device dimensions:
 Emitter area: 0.4 x 6 mm2
 Collector area: 0.7 x 6.4 mm2
• Bias Conditions:
 VCE = 1.2 V, IC = 4.8 mA
7.0
9.5
281
0.60
76
0.126
Device Modeling II: Model vs. Measurement
IMS2001
S21
• Measurements and simulations of device
S-parameters from 6-45 GHz and 140-220 GHz
• Large discrepancies in S11 and S22
• Anomalous S12 believed to be due to
excessive probe-to-probe coupling
-5
-4
-3 -2
-1
0
1
2
3
4
5
Red- Simulation
Blue- Measurement
S11, S22
freq (140.0GHz to 220.0GHz)
freq (6.000GHz to 45.00GHz)
freq (6.000GHz to 45.00GHz)
freq (140.0GHz to 220.0GHz)
S12
-0.15 -0.10 -0.05
0.00
0.05
0.10
freq (140.0GHz to 220.0GHz)
freq (6.000GHz to 45.00GHz)
freq (6.000GHz to 45.00GHz)
freq (140.0GHz to 220.0GHz)
0.15
IMS2001
Simulation vs. Measurement
UCSB
Simulation versus Measured Results
• Simulated amplifier using measured
Simulation Using Measured Device S-parameters
7.5
device S-parameters in the 140-220 GHz
band
S21, dB
• Simulations show better agreement with
measured amplifier results
Sim.
5.0
• Results point to weakness in hybrid-pi
model used in the design
Meas.
0.0
-2.5
-5.0
140
150
160
170
180
190
200
210
220
210
220
Frequency, GHz
0
-5
Meas.
-10
S11,S22, dB
• Improved device models are necessary
for better physical understanding but
measured S-parameter can be used in
future amplifier designs
2.5
-15
Sim.
-20
-25
-30
-35
-40
140
150
160
170
180
190
Frequency, GHz
200
IMS2001
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•
•
Conclusions
UCSB
Demonstrated first HBT amplifier in the 140-220 GHz frequency band
Simple design provides direction for future high frequency MMIC work in
transferred-substrate process
Observed anomalies in extending hybrid-pi model to higher frequencies
Future Work
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Multi-stage amplifiers and oscillators
Improved device performance for higher frequency operation
Acknowledgements
This work was supported by the ONR under grant N0014-99-1-0041
And the AFOSR under grant F49620-99-1-0079