THz Indium Phosphide Bipolar Transistor Technology

rodwell@ece.ucsb.edu 805-89-44, 805-89-5705 fax

IEEE Compound Semiconductor IC Symposium, October 4-7, La Jolla, California

Mark Rodwell University of California, Santa Barbara

Coauthors:

J. Rode, H.W. Chiang, P. Choudhary, T. Reed, E. Bloch, S. Danesgar, H-C Park, A. C. Gossard, B. J. Thibeault, W. Mitchell UCSB M. Urteaga, Z. Griffith, J. Hacker, M. Seo, B. Brar Teledyne Scientific Company

Why THz Transistors ?

THz Transistors: Not Just For THz Circuits

precision analog design at microwave frequencies → high-performance receivers

500 GHz digital logic → fiber optics

Higher-Resolution Microwave ADCs, DACs, DDSs

THz amplifiers→ THz radios → imaging, communications

THz Communications Needs High Power, Low Noise

Real systems with real-world weather & design margins, 500-1000m range:

3-7 dB Noise figure, 50-500 mW power/element, 64-256 element arrays

Will require:

→ InP or GaN PAs and LNAs, Silicon beamformer ICs

THz InP HBTs

THz & nm Transistors: what it's all about

Metal-semiconductor interfaces (Ohmic contacts): very low resistivity Dielectric-semiconductor interfaces (Gate dielectrics---FETs only): thin !

Ultra-low-resistivity (~0.25 W-mm2 ), ultra shallow (1 nm), ultra-robust (0.2 A/mm2 ) contacts

Mo

InGaAs

Ru

InGaAs

Heat

W

L

LK

PT

th

ln~transistor

LK

PT

th

ICIC

Available quantum states to carry current L

→ capacitance, transconductance contact resistance

Bipolar Transistor Design eW

bcWcTbT

nbb DT 22

satcc vT 2

ELlength emitter

eex AR /contact

2

through-punchce,operatingce,max cesatc TVVAvI /)(,

contacts

contactsheet

612 AL

W

L

WR

e

bc

e

ebb

e

e

E W

L

L

PT ln1

cccb /TAC

Bipolar Transistor Design: Scaling eW

bcWcTbT

nbb DT 22

satcc vT 2

ELlength emitter cccb /TAC

eex AR /contact

2

through-punchce,operatingce,max cesatc TVVAvI /)(,

contacts

contactsheet

612 AL

W

L

WR

e

bc

e

ebb

e

e

E W

L

L

PT ln1

Scaling Laws, Scaling Roadmap

HBT parameter change

emitter & collector junction widths decrease 4:1

current density (mA/mm2) increase 4:1

current density (mA/mm) constant

collector depletion thickness decrease 2:1

base thickness decrease 1.4:1

emitter & base contact resistivities decrease 4:1

scaling laws: to double bandwidth

eW

bcWcTbT

ELlength emitter

150 nm device 150 nm device

HBT Fabrication Process Must Change... Greatly

32 nm width base & emitter contacts...self-aligned

32 nm width emitter semiconductor junctions

Contacts: 1 W-mm2 resistivities 70 mA/mm2 current density ~1 nm penetration depths → refractory contacts

nm III-V FET, Si FET processes have similar requirements

Needed: Greatly Improved Ohmic Contacts

textbook with surface oxide

Interface barrier → resistance

Further intermixing during high-current operation → degradation

with metal penetration

Needed: Greatly Improved Ohmic Contacts Needed: Greatly Improved Ohmic Contacts

~5 nm Pt contact penetration (into 25 nm base)

Pt/Ti/Pd/Au

Ultra Low-Resistivity Refractory In-Situ Contacts

10-9

10-8

10-7

10-6

1018

1019

1020

1021

N-InAs

Co

nta

ct

Re

sis

tiv

ity

(W

cm

2)

concentration (cm-3

)

1017

1018

1019

1020

N-InGaAs

concentration (cm-3

)

1018

1019

1020

1021

P-InGaAs

Ir

W

Mo

concentration (cm-3

)

Mo Mo

Barasakar et al IEEE IPRM 2012

32 nm node requirements

Contact performance sufficient for 32 nm /2.8 THz node.

Low penetration depth, ~ 1 nm

In-situ: avoids surface contaminants

Refractory: robust under high-current operation

Needed: Greatly Improved Ohmic Contacts Refractory Emitter Contacts

negligible penetration

HBT Fabrication Process Must Change... Greatly

Undercutting of emitter ends

control undercut → thinner emitter

thinner emitter → thinner base metal

thinner base metal → excess base metal resistance

{101}A planes: fast

{111}A planes: slow

tall, narrow contacts: liftoff fails !

Sub-200-nm Emitter Anatomy

slide: E. Lobisser. HBT: V. Jain. Process: Jain & Lobisser

TiW

W 100 nm

Mo

High-stress emitters fall off

during subsequent lift-offs

TiW W

Single sputtered metal has

non-vertical etch profile

SiNx

Refractory contact: high-J operation

Liftoff Sputter+dry etch→ sub-200nm contacts

Sub-200-nm Emitter Anatomy

slide: E. Lobisser. HBT: V. Jain. Process: Jain & Lobisser

TiW

W 100 nm

Mo

Hybrid sputtered metal stack for

low-stress, vertical profile

W/TiW interfacial discontinuity

enables base contact lift-off

Interfacial Mo blanket-evaporated for low ρc SiNx

SiNx sidewalls protect emitter contact,

prevent emitter-base shorts during liftoff

Semiconductor wet etch

undercuts emitter contact

Very thin emitter epitaxial layer

for minimal undercut

Sub-200-nm Emitter Anatomy

slide: E. Lobisser. HBT: V. Jain. Process: Jain & Lobisser

emitter-base gap: only ~10 nm → greatly reduces link component of Rbb. emitter-base gap: only ~10 nm → greatly reduces link component of Rbb

Web = 155 nm

Wbc = 150 nm

TiW

W

Pt/Ti/Pd/Au

SiNx sidewall

RF Data: 25 nm thick base, 75 nm Thick Collector

0

5

10

15

20

25

1010

1011

1012

Gain

s (

dB

)Frequency (Hz)

H21

U

f = 530 GHz

fmax

= 750 GHz

Required dimensions obtained but poor base contacts on this run

E. Lobisser, ISCS 2012, August, Santa Barbara

DC, RF Data: 100 nm Thick Collector

0

4

8

12

16

20

24

28

32

109

1010

1011

1012

Gain

(d

B)

Frequency (Hz)

U

H21

f = 480 GHz

fmax

= 1.0 THz

Aje = 0.22 x 2.7 mm

2

Ic = 12.1 mA

Je = 20.4 mA/mm

2

P = 33.5 mW/mm2

Vcb

= 0.7 V

0

5

10

15

20

25

30

0 1 2 3 4 5

Je (

mA

/mm

2)

Vce

(V)

P = 30 mW/mm2

Ib,step

= 200 mA

BV

P = 20 mW/mm2

Aje

= 0.22 x 2.7 mm2

10-9

10-7

10-5

10-3

10-1

0

5

10

15

20

0 0.2 0.4 0.6 0.8 1I c

, I b

(A

)

Vbe

(V)

Solid line: Vcb

= 0.7V

Dashed: Vcb

= 0V

nc = 1.19

nb = 1.87

Ic

Ib

Jain et al IEEE DRC 2011

Chart 22

THz InP HBTs From Teledyne

Urteaga et al, DRC 2011, June

Towards & Beyond the 32 nm /2.8 THz Node

Base contact process: Present contacts too resistive (4Wmm2) Present contacts sink too deep (5 nm) for target 15 nm base

→ refractory base contacts

Emitter Degeneracy: Target current density is almost 0.1 Amp/mm2 (!) Injected electron density becomes degenerate. transconductance is reduced.

→ Increased electron mass in emitter

Base Ohmic Contact Penetration

~5 nm Pt contact penetration (into 25 nm base)

Base Ohmic Contact Penetration

Refractory Base Process (1)

low contact resistivity low penetration depth

low bulk access resistivity

base surface not exposed to photoresist chemistry: no contamination low contact resistivity, shallow contacts low penetration depth allows thin base, pulsed-doped base contacts

Blanket liftoff; refractory base metal Patterned liftoff; Thick Ti/Au

Refractory Base Process (2)

0 100

5 1019

1 1020

1.5 1020

2 1020

2.5 1020

0 5 10 15 20 25

do

pin

g, 1

/cm

3

depth, nm

2 nm doping pulse

1018

1019

1020

1021

P-InGaAs

10-10

10-9

10-8

10-7

10-6

10-5

Hole Concentration, cm-3

B=0.8 eV

0.6 eV0.4 eV0.2 eV

step-barrierLandauer

Co

nta

ct

Res

isti

vit

y,

W

cm

2

32 nm node requirement

Increased surface doping: reduced contact resistivity, but increased Auger recombination. → Surface doping spike at most 2-5 thick. Refractory contacts do not penetrate; compatible with pulse doping.

Degenerate Injection→ Reduced Transconductance

10-3

10-2

10-1

100

101

102

-0.3 -0.2 -0.1 0 0.1 0.2

J(m

A/m

m2)

Vbe

-

Boltzmann

(-Vbe

)>>kT/q

)./exp( kTqVJJ bes

Transconductance is high

)./exp( kTqVJJ bes

JAg Em /

Current varies exponentially with Vbe

)./exp( kTqVJJ bes

Degenerate Injection→ Reduced Transconductance

10-3

10-2

10-1

100

101

102

-0.3 -0.2 -0.1 0 0.1 0.2

J(m

A/m

m2)

Vbe

-

Fermi-Dirac

Boltzmann

(-Vbe

)>>kT/q

Transconductance is reduced

Current varies exponentially with Vbe

Degenerate Injection→ Reduced Transconductance

10-3

10-2

10-1

100

101

102

-0.3 -0.2 -0.1 0 0.1 0.2

J(m

A/m

m2)

Vbe

-

Fermi-Dirac

Highly degenerate

(Vbe

->>kT/q

Boltzmann

(-Vbe

)>>kT/q

Highly degenerate limit:

)(8

* 2

32

3

beVmq

J

2* )( beE VmJ

current varies as the square of bias

Degenerate Injection→ Reduced Transconductance

10-3

10-2

10-1

100

101

102

-0.3 -0.2 -0.1 0 0.1 0.2

J(m

A/m

m2)

Vbe

-

Fermi-Dirac

Highly degenerate

(Vbe

->>kT/q

Boltzmann

(-Vbe

)<<kT/q

Highly degenerate limit:

)(8

* 2

32

3

beVmq

J

2* )( beE VmJ

Transconductance varies as J1/2

current varies as the square of bias

JmAg EEm

*/

At & beyond 32 nm, we must increase the emitter effective mass.

...and as (m*)1/2

Degenerate Injection→Solutions

At & beyond 32 nm, we must increase the emitter (transverse) effective mass.

Other emitter semiconductors: no obvious good choices (band offsets, etc.).

Emitter-base superlattice: increases transverse mass in junction evidence that InAlAs/InGaAs grades are beneficial

Extreme solution (10 years from now): partition the emitter into small sub-junctions, ~ 5 nm x 5 nm. parasitic resistivity is reduced progressively as sub-junction areas are reduced.

IC Results

InP HBT Integrated Circuits: 600 GHz & Beyond

614 GHz fundamental VCO

340 GHz dynamic frequency divider

Vout

VEE VBB

Vtune

Vout

VEE VBB

Vtune

565 GHz, 34 dB, 0.4 mW output power amplifier

J. Hacker, TSC

M. Seo,

M. Seo, UCSB/TSC IMS 2010

204 GHz static frequency divider (ECL master-slave latch)

Z. Griffith, TSC CSIC 2010

300 GHz fundamental PLL M. Seo, TSC IMS 2011

220 GHz 90 mW power amplifier T. Reed, UCSB

600 GHz Integrated Transmitter PLL + Mixer M. Seo

Integrated 300/350GHz Receivers: LNA/Mixer/VCO

M. Seo

Chart 34

Teledyne: 560 GHz Common-Base Amplifier IC

S-parameters Output Power

•10-Stage Common-base using

inverted CPW-G architecture

•34 dB at 565 GHz

•Psat -3.9 dBm at 560 GHz

1200x230 mm2

J Hacker et al, Teledyne Scientific

90 mW, 220 GHz Power Amplifier

active area, 1.02 x 0.85 mm die: 2.42 x 1.22 mm

Reed (UCSB) and Griffith (Teledyne): CSIC 2012 Teledyne 250 nm InP HBT

-20

-10

0

10

20

210 220 230 240 250 260

Am

plif

ier

ga

ins (

dB

)

frequency (GHz)

3dB bandwidth = 240GHz

S21,mid-band

= 15.4dB

S11

S22

8-cell, 2-stage PA

PDC

= 4.46W

0

20

40

60

80

100

0 2 4 6 8 10 12 14

Po

ut , m

W

Pin

, mW8-cell, 2-stage PA PDC

= 4.46W

88mW Pout

84mW

80mW

72mW

62mW

42mW

90mW

220GHz operation

RF output power densities up to 0.5 W/mm @ 220 GHz. → InP HBT is a competitive mm-wave / sub-mm-wave power technology.

220 GHz 330mW Power Amplifier Design

0

5

10

15

20

25

30

35

40

0

50

100

150

200

250

300

350

400

-30 -25 -20 -15 -10 -5 0 5 10

Ga

in (

dB

), P

ou

t (d

Bm

)

Po

ut (m

W)

Pin (dBm)

Operating Frequency = 220 GHz

Pdc = 12 W

-20

-10

0

10

20

30

0 50 100 150 200 250 300 350 400

-20

-10

0

10

20

30

S-p

ara

me

ters

(d

B)

Frequency (GHz)

2.3 mm x 2.5 mm

T. Reed, UCSB Z. Griffith, Teledyne Teledyne 250 nm InP HBT

50-G/s Track/Hold Amplifier; 250 nm InP HBT

20.5 GHz input, 10 GHz clock

S. Daneshgar, this conference

Linearity test (third-order intercept)

Where Next ? → 2 THz Transistors, 1 THz Radios.

transmitter receiver

interconnects

DIVOUT

VEF

RFIN

VEE

C1

C2

C3

C4

Q3,4 Q5,6

Q1 Q2

Q7 Q8

Q9

Q10

Q11

L1 L2

L3 L4

L5 L6

R1

R2R3 R4

R5

R6 R7

circuits

VVEEEE VVTUNETUNE

VVOUTOUT

VVBBBB

Q3Q3 Q4Q4

Q1Q1 Q2Q2Q6Q6

C1C1 C2C2 C3C3

RREE

Q5Q5Q5Q5

LLE1E1

LLE2E2

RR11

CCVarVar CCVarVar

RR22

RR33

RR44

LLBB

LLC1C1

LLC2C2LLC3C3

LLout1out1

LLout2out2

THz and Far-Infrared Electronics

IR today→ lasers & bolometers → generate & detect

It's all about classic scaling: contact and gate dielectrics...

Far-infrared ICs: classic device physics, classic circuit design

...wire resistance,...

...heat,...

...& charge density. band structure and density of quantum states (new!).

Even 1-3 THz ICs will be feasible

(backup slides follow)

Weakly Degenerate→ Effective Added Resistance

10-3

10-2

10-1

100

101

102

-0.3 -0.2 -0.1 0 0.1 0.2

J(m

A/m

m2)

Vbe

-

Fermi-Dirac

Boltzmann

(-Vbe

)<<kT/q

Fit:

equivalent

series

resistanceeqsbe RIIIqkTV )/ln()/(

*/1 Eeq mR

At & beyond 32 nm, we must increase the emitter effective mass.

HBT Scaling Roadmap

emitter 128 64 32 nm width

4 2 1 Wmm2 access

base 120 60 30 nm contact width,

5 2.5 1.25 Wmm2 contact

collector 75 53 37.5 nm thick,

18 36 72 mA/mm2 current density

3.3 2.75 2-2.5 V, breakdown

f 730 1000 1400 GHz

fmax 1300 2000 2800 GHz

RF-ICs 660 1000 1400 GHz

digital divider 330 480 660 GHz

140 nm Device: RF Results

140 nm emitter junction

120 nm wide base contacts 75 nm thick collector 25 nm thick base

fmax impaired (780 GHz) : excessive contact penetration into base

Chiang & Rode unpublished

433 GHz f 780 GHz fmax

DC to Daylight. Far-Infrared Electronics

0.1-0.4 THz imaging systems

109

1010

1011

1012

1013

1014

1015

Frequency (Hz)

microwave

3-30 GHz

mm-wave

30-300 GHz

far-IR

(sub-mm)

0.3-3THz

mid-IR

3-30 THz

near-IR

30-450 THz

op

tica

l

45

0-9

00

TH

zHow high in frequency can we push electronics ?

...and what would be do with it ?

0.3-3 THz radio: vast capacity bandwidth, # channels

0.1-1 Tb/s optical fiber links