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@ece.ucsb.edu 1-805-893-8044
GaAsIC 2002 Oct. 2002, Monterey, CA
GaAs IC 2002
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Outline
UCSB
Introduction
Transferred-substrate HBT technology
Circuit design
Results
Conclusion
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
Transferred-Substrate HBTs
• Substrate transfer enables simultaneous
scaling of emitter and collector widths
Mesa HBT
• Maximum frequency of oscillation

f max 
f / 8RbbCcb
• 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
Transferred-substrate HBT
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
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
0.3 m Emitter before polyimide planarization
• Amplifier device dimensions:
Emitter area: 0.4 x 6 m2
Collector area: 0.7 x 6.4 m2
Submicron Collector Stripes
(typical: 0.7 um collector)
On-wafer Device Measurements
• Submicron HBTs have very low Ccb
(< 5 fF)
230 m
230 m
• 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
Transistor Embedded in LRL Test Structure
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
Corrupted 75-110 GHz measurements due to
excessive probe-to-probe coupling
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
R  j L
ZO 
G  j C
Transferred-substrate process provides excellent wiring
environment for on-wafer device measurements
RF Device Measurements
• 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
RF Gains
40
U
30
Gains (dB)
• Singularity observed in Unilateral
power gain measurements, cannot
extrapolate fmax from U
• Negative resistance effects
observed at moderate bias currents
MSG
20
h21
10
0
-10
10
10
10
11
10
12
frequency
• 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
Mesa vs. TS-HBT S-parameters
S11 – red
S22- blue
S11 – red
S22- blue
Low Rbb
Very
low Ccb
High Ccb
freq (150.0GHz to 220.0GHz)
freq75-110
(75.00GHz
to 110.0GHz)
6-40 GHz,
GHz,
140-220 GHz
6-40 GHz
freq (6.000GHz to 40.00GHz)
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
Ccb Cancellation by Collector Space-Charge
Vcb
Qbase A
  I cTc 




Vcb
Tc Vcb  2vsat 
 Ccb 

A
 Ic c
Tc
Vcb
collector space-charge layer
Collector space charge screens field, Increasing voltage decreases velocity,
modulates collector space-charge
offsets modulation of base charge
Ccbx
Ccb is reduced
Ccbi
Derivation is limited by charge control assumption
Ycb
Rbb
B
C
Model dynamics with uniform velocity assumption
Ycb,i 
 I c  c  sin 2c 
  sin c 
1 
  jI c c 

c Vcb 
2c 
Vcb  c 
Negative Conductance
2

sin(  c ) 

I x  e  j c

c


Cbe,depl
gmb
Negative Capacitance at low ω
Rex
E
re=1/gm
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,


 Y12  Rcb  j 2Ccb,iCbe Rbb  jCcb,i  Ccb, x 
As of yet, we have been unable to fit dynamic capacitance cancellation model to
measurements
0.0002
7
6
2 fF
decrease
0.00015
Gc = - real (Y12)
Ccb, fF
5
Emitter: 0.3 x 18 m2,
Collector: 0.7 x 18.6 m2
Vce = 1.1 V
4
3
2
Ic=1 mA
0.0001
Ic=2 mA
5 10 -5
Ic=3 mA
Ic=4mA
0
1
Ic=5 mA
0
-5 10
0
1
2
3
Ic, mA
4
5
6
-5
5
10
15
20
25
freq, GHz
30
35
40
45
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
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 Tee’s in probes for
biasing active devices
UCSB 140-220 GHz VNA Measurement Set-up
Single-stage Amplifier Design
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6
2001 GaAs IC Symposium, Baltimore, MD
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Single stage amplifiers designs on this
process run
• 3.5 dB gain at 175 GHz
S21, dB
• 6.3 dB peak gain at 175 GHz
S21
2
0
-2
-4
140 150 160 170 180 190 200 210 220
Frequency, GHz
0
S22
S11, S22, dB
-4
-8
S11
-12
-16
Cell Dimensions: 690m x 350 m
-20
140 150 160 170 180 190 200 210 220
Frequency, GHz
Multi-stage Amplifiers Measurements
175 GHz Design
200 GHz Design
20
20
S21
S21
10
0
0
dB
dB
10
-10
-10
S11
-20
S11
-20
S22
-30
140
S22
-30
150
160
170
180
190
200
210
frequency (GHz)
12.0 dB gain at 170 GHz
220
140
150
160
170
180
190
200
210
frequency (GHz)
8.5 dB gain at 195 GHz
220
Simulation vs. Measurement
Circuit simulations predicted
• 20 dB gain at 175 GHz
• 14.5 dB gain at 200 GHz
Re-simulate amplifiers using
measured transistor S-parameters
Good agreement with measured
amplifiers confirms passive network
design
S21
10
0
-10
dB
Measured transistors show higher
extrinsic emitter resistance, lower
power gain than those used in
design
20
S11
-20
S22
-30
-40
-50
140
150
160
170
180
190
200
210
frequency (GHz)
Measured amplifier (blue) and
modeled (red) using measured
transistor S-parameters
220
Future Work: Highly-scaled mesa-HBT Designs
Mattias Dahlstrom
30
Transferred-substrate HBTs enabled
aggressive device scaling
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
20
Gains (dB)
They are hard to yield/manufacture
U
25
but…
• 2.7 m base mesa,
• 0.54 m emitter junction
• 0.7 m emitter contact
•Vce=1.7 V
•Jc=3.7E5 A/cm2
MAG/MSG
15
h21
10
5
0
10
10
10
11
frequency (Hz)
10
12
GaAs IC 2002
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Conclusions
UCSB
Multi-stage amplifiers have been demonstrated in 140-220 GHz
– 12.0 dB Gain at 175 GHz
– 8.5 dB Gain at 200 GHz
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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