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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
[email protected] 1-805-893-8044 IMS2001 May 2001, Phoenix, AZ
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OutlineIMS2001 UCSB
• Introduction
• Transferred-Substrate HBT Technology
• Circuit Design
• Results
• Conclusion
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Transferred-Substrate HBTs
• Substrate transfer allows simultaneous scaling of emitter and collector widths
• Maximum frequency of oscillation
• Sub-micron scaling of emitter and collector widths has resulted in record values for extrapolated fmax (>1 THz)
• Promising technology for ultra-high frequency tuned circuit applications
0
5
10
15
20
25
30
10 100 1000
Gai
ns,
dB
Frequency, GHz
fmax = 1.1 THz ??
f = 204 GHz
Mason's gain, U
H21
MSG
Emitter, 0.4 x 6 m2
Collector, 0.7 x 6 m2
Ic
= 6 mA, Vce
= 1.2 V
IMS2001
3000 Å collector400 Å base with 52 meV gradingAlInAs / GaInAs / GaInAs HBT
cbbbCRff 8/max
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Ultra-high Frequency AmplifiersIMS2001
• 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
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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
InGaAs 1E16 Si 400 Å
InGaAs 1E18 Si 50 Å
InGaAs 1E16 Si 2550 Å
InAlAs UID 2500 Å
S.I. InP
Bias conditions for the band diagram
Vbe = 0.7 V
Vce = 0.9 V
InGaAs/InAlAs HBT Material SystemIMS2001
Layer StructureAlInAs/GaInAs graded base HBT
Band diagram under normal operating voltagesVce = 0.9 V, Vbe= 0.7 V
• 500 Å 5E19 graded base (Eg = kT), 3000 Å collector
-2
-1.5
-1
-0.5
0
0.5
0 1000 2000 3000 4000 5000 6000
Distance, Å
Gradedbase
Collector depletion regionEmitter
Schottkycollector
Band Diagram
2kT base bandgap grading
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Device Fabrication IIMS2001
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Transferred-Substrate Process FlowIMS2001
• 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
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Device Fabrication IIIMS2001
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Ultra-high fmax Devices
• Electron beam lithography used to define submicron emitters and collectors
• Minimum feature sizes 0.2 m emitter stripe widths 0.3 m collector stripe widths
• Improved collector-to-emitter alignment using local alignment marks
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
IMS2001
0.3 m Emitter before polyimide planarization
0.4 m Collector Stripe
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Device MeasurementsIMS2001
-0.5
0
0.5
1
1.5
2
2.5
3
0 0.2 0.4 0.6 0.8 1 1.2
Ic(mA)
Vce (V)
Ib steps = 15 uA
1E10 1E11 1E12
Frequency (Hz)
-5
0
5
10
15
20
25
Gain
(dB
) MAG/MSG
h21
U
DC Measurements Measured RF Gains
• Device dimensions: Emitter area: 0.4 x 6 m2
Collector area: 0.7 x 6.4 m2
• = 20
• BVCEO = 1.5 V
• Bias Conditions: VCE = 1.2 V, IC = 4.8 mA
• f = 160 GHz
• Measurements of unilateral power gain in 140-220 GHz frequency band appear to show unphysical behavior
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140 150 160 170 180 190 200 210 220
Frequency, GHz
-5.0
-2.5
0.0
2.5
5.0
7.5
S21, dB
-40
-30
-20
-10
0
10
S11, S
22, d
B
• Simple common-emitter design conjugately matched at 200 GHz using shunt-stub tuning
• Shunt R-C network at output provides low frequency stabilization
• Simulations predicted 6.2 dB gain
• 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
Simulation Results
0.2pF
50 301.2ps
50
300.2ps
801.2ps
0.6ps
801.2ps
50
IN
OUT
S21
Circuit Schematic
S11,S22
Amplifier DesignIMS2001
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• 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 Design Considerations in Sub-mmwave Bands
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• 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
140-220 GHz VNA MeasurementsIMS2001
UCSB 140-220 GHz VNA Measurement Set-up
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Amplifier Measurements
• Measured 3.0 dB peak gain at 185 GHz
• Device dimensions: Emitter area: 0.4 x 6 m2
Collector area: 0.7 x 6.4 m2
• Device bias conditions: Ic= 3.0 mA, VCE = 1.2 V
Measured Gain
Measured Return Loss
IMS2001
140 150 160 170 180 190 200 210 220
Freq. (GHz)
-5
-4
-3
-2
-1
0
1
2
3
4
S21 (
dB
)
140 150 160 170 180 190 200 210 220
Freq. (GHz)
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
S11, S
22 (
dB
)S11
S22
Cell Dimensions: 690m x 350 m
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• Amplifier designed for 200 GHz
• Peak gain measured at 185 GHz
• Possible sources for discrepancy: Matching network design Device model
Simulation versus Measured Results
Meas.
Sim.
140 150 160 170 180 190 200 210 220
Frequency, GHz
-5.0
-2.5
0.0
2.5
5.0
7.5
S21
, dB
140 150 160 170 180 190 200 210 220
Frequency, GHz
-40
-35
-30
-25
-20
-15
-10
-5
0
S11,S
22, dB Meas.
Sim.
Simulation vs. MeasurementIMS2001
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• Breakout of matching network without 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
Matching Network BreakoutSimulation Vs. Measurement
freq (140.0GHz to 220.0GHz)
S21
S22
S11
Red- SimulationBlue- Measurement
Matching Network DesignIMS2001
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• Design used a hybrid-pi device model based on 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
• Device dimensions: Emitter area: 0.4 x 6 m2
Collector area: 0.7 x 6.4 m2
• Bias Conditions: VCE = 1.2 V, IC = 4.8 mA
HBT Hybrid-Pi ModelDerived from DC-50 GHz Measurements
Device Modeling I: Hybrid-Pi ModelIMS2001
1.59
43
7.0
45
9.5
17
0.4
281
0.60
0.126
76
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• 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
Red- SimulationBlue- Measurement
IMS2001 Device Modeling II: Model vs. Measurement
S11, S22
-5 -4 -3 -2 -1 0 1 2 3 4 5
freq (140.0GHz to 220.0GHz)freq (6.000GHz to 45.00GHz)freq (6.000GHz to 45.00GHz)freq (140.0GHz to 220.0GHz)
S21
S12
-0.15 -0.10 -0.05 0.00 0.05 0.10 0.15
freq (140.0GHz to 220.0GHz)freq (6.000GHz to 45.00GHz)freq (6.000GHz to 45.00GHz)freq (140.0GHz to 220.0GHz)
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• Simulated amplifier using measured device S-parameters in the 140-220 GHz band
• Simulations show better agreement with measured amplifier results
• Results point to weakness in hybrid-pi model used in the design
• Improved device models are necessary for better physical understanding but measured S-parameter can be used in future amplifier designs
Simulation versus Measured ResultsSimulation Using Measured Device S-parameters
Meas.
Sim.
140 150 160 170 180 190 200 210 220
Frequency, GHz
-5.0
-2.5
0.0
2.5
5.0
7.5
S21
, dB
140 150 160 170 180 190 200 210 220
Frequency, GHz
-40
-35
-30
-25
-20
-15
-10
-5
0
S11,S
22, dB
Meas.
Sim.
Simulation vs. MeasurementIMS2001 UCSB
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ConclusionsIMS2001 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• Multi-stage amplifiers and oscillators• Improved device performance for higher frequency operation
AcknowledgementsThis work was supported by the ONR under grant N0014-99-1-0041
And the AFOSR under grant F49620-99-1-0079