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

OutlineIMS2001 UCSB

• Introduction

• Transferred-Substrate HBT Technology

• Circuit Design

• Results

• Conclusion

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

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

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

Device Fabrication IIMS2001

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

Device Fabrication IIIMS2001

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

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

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

• 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

• 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

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

• 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

• 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

• 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

• 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)

• 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

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