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

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

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5

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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