Multi-stage G-band (140-220 GHz) InP HBT Amplifiers

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
urteaga_at_ece.ucsb.edu 1-805-893-8044
GaAsIC 2002 Oct. 2002, Monterey, CA
2
Outline
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. 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.
• 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

• Submicron HBTs have very low Ccb (lt 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 75-110 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, 75-110 GHz, 140-220 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 Capacitance at low ?
Negative Conductance
12
Negative Resistance Effects in Transferred-Substra
te 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
?m2Vce 1.1 V
2 fF decrease
13
Amplifier Designs

• Three cascaded common-emitter stages matched to
  50?
• Designs based on measured transistor
  S-parameters
• Standard microstrip models and electromagnetic
  simulation (Agilents 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
140-220 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 Tees in probes for biasing active
  devices

UCSB 140-220 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
  140-220 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
• Vce1.7 V
• Jc3.7E5 A/cm2

19
Conclusions
UCSB
GaAs IC 2002

• Multi-stage amplifiers have been demonstrated in
  140-220 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
  N0014-99-1-0041
• And by Walsin Lihwa Corporation