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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
[email protected] 1-805-893-8044 GaAsIC 2002 Oct. 2002, Monterey, CA
OutlineGaAs IC 2002 UCSB
• Introduction
• Transferred-substrate HBT technology
• Circuit design
• Results
• Conclusion
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
G-band Electronics (140-220 GHz)
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
cbbbCRff 8/max
Mesa HBT
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
• 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)
0
5
10
15
20
25
30
35
1 10 100Frequency, GHz
MSG
h21
Mason'sGain, U
• 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
SolutionEmbed transistors in sufficient length of on-wafer transmission line to reduce coupling
Line-Reflect-Line calibration to place measurement reference planes at device terminals
On-wafer Device Measurements
Transistor Embedded in LRL Test Structure
230 m 230 m
Corrupted 75-110 GHz measurements due toexcessive probe-to-probe coupling
• 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
Line-Reflect-Line Calibration
CG
LRZO
j
j
RF Device Measurements
• 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
RF Gains
freq (150.0GHz to 220.0GHz)
freq (75.00GHz to 110.0GHz)freq (6.000GHz to 40.00GHz)
Mesa vs. TS-HBT S-parameters
Transferred-substrate HBTDevice dimensions:
Emitter area: 0.4 x 6 m2
Collector area: 0.7 x 6.4 m2
3000 Å InGaAs Collector
Mattias Dahlstrom 2002 IPRM Conference
6-40 GHz, 75-110 GHz, 140-220 GHz 6-40 GHz
S11 – redS22- blue
S11 – redS22- blue
Verylow Ccb
Low Rbb
High Ccb
Fast C-doped mesa-HBTDevice dimensions:
Emitter 0.5 x 7 m2
Collector area: 1.6 x 12 m2
2000 Å. InP Collector
280 GHz ft, 450+ GHz fmax
Ccb Cancellation by Collector Space-Charge
collector space-charge layer
cbV
sat
cc
cbccb
base
v
TI
VT
A
V
Q
2
cb
cc
ccb V
IT
AC
Collector space charge screens field, Increasing voltage decreases velocity, modulates collector space-chargeoffsets modulation of base chargeCcb is reduced
Derivation is limited by charge control assumption
Model dynamics with uniform velocity assumption
2
,
sin
2
2sin1
c
c
cb
cc
c
c
cb
c
c
cicb V
IjV
IY
E
B C
R ex
R bb
C cbx
C cb i
C be,depl
re=1/gm
Y cb
gm
b
c
cjx
ceI )sin(
Negative Capacitance at low ωNegative Conductance
Negative Resistance Effects in Transferred-Substrate HBTs
xcbicbbbbeicbcb CCRCCRY ,,,2
12 jj
-5 10-5
0
5 10 -5
0.0001
0.00015
0.0002
5 10 15 20 25 30 35 40 45
Gc
= -
rea
l (Y
12)
freq, GHz
Ic=1 mA
Ic=2 mA
Ic=3 mA
Ic=4mA
Ic=5 mA
0
1
2
3
4
5
6
7
0 1 2 3 4 5 6
Ccb
, fF
Ic, mA
2 fF decrease
Emitter: 0.3 x 18 m2, Collector: 0.7 x 18.6 m2
Vce = 1.1 V
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
• 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
Amplifier Designs
IC Photograph: Dimensions 1.66 x 0.59 mm2
• 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
140-220 GHz VNA Measurements
UCSB 140-220 GHz VNA Measurement Set-up
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
Cell Dimensions: 690m x 350 m
150 160 170 180 190 200 210140 220
-2
0
2
4
6
-4
8
Frequency, GHz
S21
, dB
150 160 170 180 190 200 210140 220
-16
-12
-8
-4
-20
0
Frequency, GHz
S11
, S22
, dB
S11
S22
S21
Multi-stage Amplifiers Measurements
12.0 dB gain at 170 GHz 8.5 dB gain at 195 GHz
175 GHz Design 200 GHz Design
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
Simulation vs. Measurement
Measured amplifier (blue) and modeled (red) using measured transistor S-parameters
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
Future Work: Highly-scaled mesa-HBT Designs
0
5
10
15
20
25
30
1010 1011 1012
frequency (Hz)G
ain
s (d
B)
U
MAG/MSG
h21
Mattias Dahlstrom
• 2.7 m base mesa, • 0.54 m emitter junction• 0.7 m emitter contact
•Vce=1.7 V
•Jc=3.7E5 A/cm2
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
• Demonstrates potential of highly-scaled InP HBTs for G-band Electronics• Currently pursuing more manufacturable approaches for HBT scaling
AcknowledgementsThis work was supported by the ONR under grant N0014-99-1-0041
And by Walsin Lihwa Corporation
GaAs IC 2002