1. Multi-stage G-band (140-220 GHz) InP HBT Amplifiers
M. Urteaga, D. Scott, S. Krishnan, Y. Wei, M. Dahlström, Z. Griffith, N. Parthasarathy, and M. Rodwell.
Department of Electrical and Computer Engineering,
University of California, Santa Barbara
GaAsIC 2002 Oct. 2002, Monterey, CA

2. Outline Introduction Transferred-substrate HBT technology
UCSB
GaAs IC 2002
Introduction
Transferred-substrate HBT technology
Circuit design
Results
Conclusion

3. G-band Electronics (140-220 GHz)
Applications:
Wideband communication systems
Atmospheric sensing
Automotive radar
Transistor-based ICs realized through submicron device scaling
State-of-the-art InP-based HEMT Amplifiers with submicron gate lengths
3-stage amplifier with 30 dB gain at 140 GHz.
Pobanz et. al., IEEE JSSC, Vol. 34, No. 9, Sept
3-stage amplifier with dB gain from GHz
Lai et. al., IEDM, San Francisco, CA.
6-stage amplifier with 20  6 dB from GHz.
Weinreb et. al., IEEE MGWL, Vol. 9, No. 7, Sept
HBT is a vertical-transport device (vs. lateral-transport) Presents Challenges to Scaling

4. Transferred-Substrate HBTs
Substrate transfer enables simultaneous scaling of emitter and collector widths
Maximum frequency of oscillation
Previously demonstrated single-stage amplifier with 6.3 dB gain at 175 GHz
2001 GaAsIC Symposium, Baltimore, MD
This Work
Three-stage amplifier designs:
12.0 dB gain at 170 GHz
8.5 dB gain at 195 GHz
Mesa HBT
Transferred-substrate HBT

5. 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

6. Ultra-high fmax Submicron HBTs
Electron beam lithography used to define submicron emitter and collector stripes
InAlAs/InGaAs emitter-base heterojunction
400 Å InGaAs base with 4 x 1019 cm-3 Be base doping, 52 meV bandgap grading
3000 Å InGaAs collector, high fmax / f ratio
Amplifier device dimensions:
Emitter area: 0.4 x 6 m2
Collector area: 0.7 x 6.4 m2
0.3 m Emitter before polyimide planarization
Submicron Collector Stripes (typical: 0.7 um collector)

7. On-wafer Device Measurements
230 mm
Submicron HBTs have very low Ccb (< 5 fF)
Characterization requires accurate measure of very small S12
Standard 12-term VNA calibrations do not correct S12 background error due to probe-to-probe coupling
Solution
Embed transistors in sufficient length of on-wafer transmission line to reduce coupling
Line-Reflect-Line calibration to place measurement reference planes at device terminals
Transistor Embedded in LRL Test Structure
Corrupted GHz measurements due to
excessive probe-to-probe coupling

8. Line-Reflect-Line Calibration
LRL does not require accurate characterization of Open or Short calibration standards
LRL does require single-mode propagation environment
LRL does require accurate characterization of transmission line characteristic impedance
Must correct for complex characteristic impedance of Line standard due to resistive losses
Transferred-substrate process provides excellent wiring environment for on-wafer device measurements

9. RF Device Measurements
RF Gains
Singularity observed in Unilateral power gain measurements, cannot extrapolate fmax from U
Negative resistance effects observed at moderate bias currents
Maximum stable gain of 7.4 dB at 200 GHz
f = 180 GHz
Observation
TS-HBTs have very small output conductance due to low Ccb giving rise to high transistor power gains but…
Second-order transport effects in collector may lead to negative resistance phenomenon
Bias Conditions: VCE = 1.25 V, IC = 3.2 mA
Device dimensions:
Emitter area: 0.4 x 6 m2
Collector area: 0.7 x 6.4 m2

10. Mesa vs. TS-HBT S-parameters
S11 – red
S22- blue
S11 – red
S22- blue
Low Rbb
Very
low Ccb
High Ccb
6-40 GHz
6-40 GHz, GHz, GHz
Transferred-substrate HBT
Device dimensions:
Emitter area: 0.4 x 6 m2
Collector area: 0.7 x 6.4 m2
3000 Å InGaAs Collector
Fast C-doped mesa-HBT
Device dimensions:
Emitter 0.5 x 7 m2
Collector area: 1.6 x 12 m2
2000 Å. InP Collector
280 GHz ft, 450+ GHz fmax
Mattias Dahlstrom 2002 IPRM Conference

11. Ccb Cancellation by Collector Space-Charge
Collector space charge screens field, Increasing voltage decreases velocity, ® modulates collector space-charge ® offsets modulation of base charge ® Ccb is reduced
Derivation is limited by charge control assumption
Model dynamics with uniform velocity assumption
Negative Conductance
Negative Capacitance at low ω

12. Negative Resistance Effects in Transferred-Substrate HBTs
Capacitance cancellation is observed for submicron InGaAs collector HBTs
Change in curvature of real (Y12) is observed with increasing current. Effect not predicted by standard transistor hybrid-pi model where at low frequencies,
As of yet, we have been unable to fit dynamic capacitance cancellation model to measurements
Emitter: 0.3 x 18 m2, Collector: 0.7 x 18.6 m2 Vce = 1.1 V
2 fF
decrease

13. IC Photograph: Dimensions 1.66 x 0.59 mm2
Amplifier Designs
Three cascaded common-emitter stages matched to 50
Designs based on measured transistor S-parameters
Standard microstrip models and electromagnetic simulation (Agilent’s Momentum) were used to characterize matching networks
Two designs at 175 GHz and 200 GHz
IC Photograph: Dimensions 1.66 x 0.59 mm2

14. GHz VNA Measurements
HP8510C VNA with Oleson Microwave Lab mmwave Extenders
GGB Industries coplanar wafer probes with WR-5 waveguide connectors
Full-two port T/R measurement capability
Line-Reflect-Line calibration with on-wafer standards
Internal bias Tee’s in probes for biasing active devices
UCSB GHz VNA Measurement Set-up

15. Single-stage Amplifier Design
6.3 dB peak gain at 175 GHz
2001 GaAs IC Symposium, Baltimore, MD
Single stage amplifiers designs on this process run
3.5 dB gain at 175 GHz
S21
Cell Dimensions: 690m x 350 m

16. Multi-stage Amplifiers Measurements
175 GHz Design
200 GHz Design
12.0 dB gain at 170 GHz
8.5 dB gain at 195 GHz

17. Simulation vs. Measurement
Circuit simulations predicted
20 dB gain at 175 GHz
14.5 dB gain at 200 GHz
Measured transistors show higher extrinsic emitter resistance, lower power gain than those used in design
Re-simulate amplifiers using measured transistor S-parameters
Good agreement with measured amplifiers confirms passive network design
Measured amplifier (blue) and modeled (red) using measured transistor S-parameters

18. Future Work: Highly-scaled mesa-HBT Designs
Mattias Dahlstrom
Transferred-substrate HBTs enabled aggressive device scaling
but…
They are hard to yield/manufacture
High Carbon base doping allows for aggressive scaling of lateral dimensions of mesa HBTs
Moderate power gains have been measured in GHz band
~ 5 dB MSG at 175 GHz
Tuned circuit designs in technology appear feasible
2.7 mm base mesa,
0.54 mm emitter junction
0.7 mm emitter contact
Vce=1.7 V
Jc=3.7E5 A/cm2

19. Conclusions UCSB GaAs IC 2002 Acknowledgements
Multi-stage amplifiers have been demonstrated in GHz
12.0 dB Gain at 175 GHz
8.5 dB Gain at 200 GHz
Demonstrates potential of highly-scaled InP HBTs for G-band Electronics
Currently pursuing more manufacturable approaches for HBT scaling
Acknowledgements
This work was supported by the ONR under grant N
And by Walsin Lihwa Corporation