Urteaga et al, 2001 Device Research Conference, June, Notre Dame, Illinois Characteristics of Submicron HBTs in the 140-220 GHz Band M. Urteaga, S. Krishnan,

Urteaga et al, 2001 Device Research Conference, June, Notre Dame, Illinois

Characteristics of Submicron HBTs in the 140-220 GHz Band

M. Urteaga, S. Krishnan, D. Scott, T. Mathew, Y. Wei, M. Dahlstrom, S. Lee, M. Rodwell.

Department of Electrical and Computer Engineering,

University of California, Santa Barbara

[email protected] 1-805-893-8044 DRC, June 2001, South Bend, IN


Ultra-high fmax Transferred-Substrate HBTs

• Substrate transfer provides access to both sides of device epitaxy

• Permits simultaneous scaling of emitter and collector widths

• Maximum frequency of oscillation

• Sub-micron scaling of emitter and collector widths has resulted in record values of extrapolated fmax

• Extrapolation begins where measurements end

• New 140-220 GHz Vector Network Analyzer (VNA) extends device measurement range

0

5

10

15

20

25

30

10 100 1000

Gai

ns,

dB

Frequency, GHz

fmax = 1.1 THz ??

f = 204 GHz

Mason's gain, U

H21

MSG

Emitter, 0.4 x 6 m2

Collector, 0.7 x 6 m2

Ic

= 6 mA, Vce

= 1.2 V

3000 Å collector400 Å base with 52 meV gradingAlInAs / GaInAs / GaInAs HBT

cbbbCRff 8/max


High Frequency Device Characterization

MotivationCharacterize transistors to highest measurable frequency Develop an accurate methodology for ultra-high frequency transistor measurements

ResultsMeasured submicron transistors DC-45 GHz, 75-110 GHz, 140-220 GHz bands

Observed singularity in Unilateral Power Gain

Submicron HBTs have very high power gain,

but fmax can’t be determined


InGaAs 1E19 Si 1000 Å

Grade 1E19 Si 200 Å

InAlAs 1E19 Si 700 Å

InAlAs 8E17 Si 500 Å

Grade 8E17 Si 233 Å

Grade 2E18 Be 67 Å

InGaAs 4E19 Be 400 Å




InAlAs UID 2500 Å

S.I. InP

400 A base, 4* 1019/cm3 3000 A collector

InGaAs/InAlAs HBT Material System

Layer StructureAlInAs/GaInAs graded base HBT

Band diagram under normal operating voltagesVce = 0.9 V, Vbe= 0.7 V

• 500 Å 5E19 graded base (Eg = kT), 3000 Å collector

-2

-1.5

-1

-0.5

0

0.5

0 1000 2000 3000 4000 5000 6000

Distance, Å

Gradedbase

Collector depletion regionEmitter

Schottkycollector

2kT base bandgap grading

Band diagram at Vbe = 0.7 V, Vce = 0.9 V


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 emitters and collectors

• Minimum feature sizes 0.2 m emitter stripe widths 0.3 m collector stripe widths

• Improved collector-to-emitter alignment using local alignment marks

• Aggressive scaling of transistor dimensions predicts progressive improvement of fmax

As we scale HBT to <0.4 um, fmax keeps increasing,measurements become very difficult

0.3 m Emitter before polyimide planarization

Submicron Collector Stripes(typical: 0.7 um collector)


Stabilize transistor and simultaneously match input and output of device

Approximate value for hybrid- model

To first order MSG does not depend on f or Rbb

Simultaneously match input and output of device

K = Rollet stability factor

How do we measure fmax?

1KKS

S 2

12

21 MAG

cexcb

12

21

12

21

qIkTRωC

1

Y

Y

S

SMSG

For Hybrid- model, MSG rolls off at 10 dB/decade, MAG has no fixed slopeCANNOT be used to accurately extrapolate fmax

Maximum Available Gain

Transistor must be unconditionally stable or MAG does not exist

Maximum Stable Gain

g e n e r a t o r

lo s s le s sm a t c h in gn e tw o rk

R g e n

V g e n

lo s s le s sm a tc h in gn e tw o rk

R L

lo a d

g e n e r a t o r

lo s s le s sm a t c h in gn e tw o rk

R g e n

V g e n

lo s s le s sm a tc h in gn e tw o rk

R L

lo a d

r e s is t iv elo s s

( s ta b iliz -a t io n )


Use lossless reactive feedback to cancel device feedback and stabilize the device, then match input/output.

12212211

2

1221

GGGG4

YY

U

Unilateral Power Gain

Mason’s Unilateral Power Gain

0

5

10

15

20

25

30

35

40

1 10 100

Gai

ns, d

B

Frequency, GHz

MAG/MSGcommon base

U: all 3

MAG/MSGcommon collector

MAG/MSGcommon emitter

For Hybrid- model, U rolls off at 20 dB/decade

ALL Power Gains must be unity at fmax

U is not changed by pad reactances

g e n e ra to r

lo s s le s sm a tc h in gn e two rk

R g e n

Vg e n

lo s s le s sm a tc h in gn e two rk

R L

lo a d

s e rie sfe e d b a c k

s h un tfe e d b a c k


Negative Unilateral Power Gain ???

YES, if denominator is negative

This may occur for device with a negative output conductance (G22) or some positive feedback (G12)

12212211

2

1221

GGGG4

YY

U

1221L2211

2

1221

GGGGG4

YY

U

2-portNetwork G L

Select GL such that denominator is zero:

Can U be Negative?

What Does Negative U Mean?

Device with negative U will have infinite Unilateral Power Gain with the addition of a proper source or load impedance

AFTER Unilateralization• Network would have negative output resistance

• Can support one-port oscillation

• Can provide infinite two-port power gainU

Simple Hybrid- HBT model will NOT show negative U


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

Solution

Embed transistors in sufficient length of transmission line to reduce coupling

Place calibration reference planes at transistor terminals

Line-Reflect-Line Calibration

Standards easily realized on-wafer

Does not require accurate characterization of reflect standards

Characteristics of Line Standards are well controlled in transferred-substrate microstrip wiring environment

Accurate Transistor Measurements Are Not Easy

Transistor in Embedded in LRL Test Structure

230 m 230 m

Corrupted 75-110 GHz measurements due toexcessive probe-to-probe coupling


• HP8510C VNA used with Oleson Microwave Lab mmwave Extenders

• Extenders connected to GGB Industries coplanar wafer probes via short length of WR-5 waveguide

• Internal bias Tee’s in probes for biasing active devices

• Full-two port T/R measurement capability

• 75-110 GHz measurement set-up uses same waveguide-to-probe configuration with internal HP test set

140-220 GHz On-Wafer Network Analysis

UCSB 140-220 GHz VNA Measurement Set-up


140 150 160 170 180 190 200 210 220

freq, GHz

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0.30

freq (75.00GHz to 110.0GHz)

Can we trust the calibration ?

freq (140.0GHz to 220.0GHz)

S11 of throughAbout –40 dB

140-220 GHz calibration looks OK75-110 GHz calibration looks Great

S11 of openAbout 0.1 dB / 3o error

dBS21 of through line is off by less than 0.05 dB

S11 of openS11 of short S11 of through

75 80 85 90 95 100 105 110

freq, GHz

-70

-65

-60

-55

-50

-45

-40

Probe-Probe couplingis better than –45 dB


1E10 1E11 1E12

Freq.

-5

0

5

10

15

20

25

30

35

40

RF G

ains

U

MAG/MSG

h21 S11

S22

-6 -4 -2 0 2 4 6

freq (6.000GHz to 45.00GHz)freq (75.00GHz to 110.0GHz)freq (140.0GHz to 220.0GHz)freq (6.000GHz to 45.00GHz)freq (75.00GHz to 110.0GHz)freq (140.0GHz to 220.0GHz)

S12*20

S21Emitter: 0.3 x 18 m2, Collector: 0.7 x 18.6 m2

Ic = 5 mA, Vce = 1.1 V

0.3 m Emitter / 0.7 m Collector HBTs: Negative U

Gains are high at 200 GHzbut fmax can’t be determined

Negative U


0 20 40 60 80 100 120 140 160 180 200 220

Freq. GHz

0.00

0.02

0.04

0.06

0.08

0.10

0 20 40 60 80 100 120 140 160 180 200 220

Freq. GHz

-0.0035

-0.0030

-0.0025

-0.0020

-0.0015

-0.0010

-0.0005

0.0000

0.0005

0 20 40 60 80 100 120 140 160 180 200 220

Freq. GHz

-0.0015

-0.0010

-0.0005

0.0000

0.0005

Real (Y11)

0.3 m Emitter / 0.7 m Collector HBTs: Negative Output Conductance

Real (Y12)

Real (Y21)

0 20 40 60 80 100 120 140 160 180 200 220

Freq. GHz

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

Real (Y22)

Negative Y22Emitter: 0.3 x 18 m2, Collector: 0.7 x 18.6 m2

Ic = 5 mA, Vce = 1.1 V


1E10 1E11 1E12

Freq.

-5

0

5

10

15

20

25

RF G

ains

U

MAG/MSG

h21

S11

S22

-4 -3 -2 -1 0 1 2 3 4

freq (6.000GHz to 45.00GHz)freq (75.00GHz to 110.0GHz)freq (140.0GHz to 220.0GHz)freq (6.000GHz to 45.00GHz)freq (75.00GHz to 110.0GHz)freq (140.0GHz to 220.0GHz)

S12*20S21

0.4 m Emitter / 1.0 m Collector HBTs

Emitter: 0.4 x 6 m2, Collector: 1.0 x 6.6 m2

Ic = 3 mA, Vce = 1.1 V


0 20 40 60 80 100 120 140 160 180 200 220

Freq. GHz

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0 20 40 60 80 100 120 140 160 180 200 220

Freq. GHz

-0.0006

-0.0004

-0.0002

0.0000

0.0002

0.0004

0 20 40 60 80 100 120 140 160 180 200 220

Freq. GHz

-0.0014

-0.0012

-0.0010

-0.0008

-0.0006

-0.0004

-0.0002

0.0000

Real (Y11)

Real (Y22)

0 20 40 60 80 100 120 140 160 180 200 220

Freq. GHz

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.4 m Emitter / 1.0 m Collector HBTs

Negative Y22

Real (Y12)

Real (Y21)


-10 -8 -6 -4 -2 0 2 4 6 8 10

freq (6.000GHz to 45.00GHz)freq (75.00GHz to 110.0GHz)freq (6.000GHz to 45.00GHz)freq (75.00GHz to 110.0GHz)

S21

S12*30

Less scaled devices show expected power gain rolloff

S11S22

1E10 1E11 1E12

Freq.

-5

0

5

10

15

20

25

RF G

ains

U

MAG/MSG

h21

Emitter: 0.5 x 8.0 m2, Collector: 1.2 x 8.6 m2

Ic = 4 mA, Vce = 1.8 VInP/InGaAs/InP DHBT


Submicron HBTs have Extremely Low Parasitics

Extremely High Power Gains

High fmax HBTs are hard to measure

Probe-to-Probe coupling can cause errors in S21

Highly scaled transistors show a negative unilateral power gain

coinciding with a negative output conductance

Cannot extrapolate fmax from measurements of U but…

Device has ~ 8 dB MAG at 200 GHz

Single-stage amplifiers with 6.3 dB gain at 175 GHz have been fabricated(To be presented 2001 GaAs IC Conference Baltimore, MD)

Possible sources of Negative Output Conductance

Dynamics of capacitance cancellation

Dynamics of base-collector avalanche breakdown

Measurement Errors (We hope we’ve convinced you otherwise)

Conclusions


This work was supported by the ONR under grant N0014-99-1-0041

And the AFOSR under grant F49620-99-1-0079

Acknowledgements

Documents

Urteaga et al, 2001 Device Research Conference, June, Notre Dame, Illinois Characteristics of Submicron HBTs in the 140-220 GHz Band M. Urteaga, S. Krishnan,