GOMAC, March 25, 2010, Reno, NV.

THz Bipolar Transistors: Design and Process Technologiesg g

Mark Rodwell University of California, Santa Barbara

E L bi V J i A B k M S B J Thib ltE. Lobisser, V. Jain, A. Baraskar, M. Seo, B. J. Thibeault,University of California, Santa BarbaraM. Seo, Z. Griffith, J. Hacker, M. Urteaga, Richard Pierson, B. BrarT l d S i tifi CTeledyne Scientific Company

rodwell@ece.ucsb.edu 805-893-3244, 805-893-5705 fax

WhWhyTH T i ?THz Transistors ?

Why Build THz Transistors ?500 GHz digital logic→ fiber optics

THz amplifiers→ THz radios i i i → imaging, sensing,

communications

precision analog design at microwave frequencies→ high-performance receivers

Higher-Resolution Microwave ADCs, DACs, DDSs→ high-performance receivers DDSs

Why Bipolars for Fast Analog Applications ?

digital frequency synthesis mm-wave jammer on chipdigital frequency synthesis mm-wave phased arrays

jammer on chip

high resolution ADCs and DACs for 2-20, 38 GHzBJTs, particularly InP,h hi h b kdCMOS does not serve all ICs

low analog gainlow analog precision

high Cds /Cgs , high Cgd /Cgs→ less bandwidth

have high breakdown

g plow breakdown voltage

0.35 fF0.7 fF

→ less bandwidth than f suggests

0.7 fF

H M k How to Make TH T iTHz Transistors

Changes required to double transistor bandwidthHBT parameter changeHBT parameter changeemitter & collector junction widths decrease 4:1current density (mA/m2) increase 4:1current density (mA/m) constant

eW

cu e t de s ty ( / ) co s acollector depletion thickness decrease 2:1base thickness decrease 1.4:1emitter & base contact resistivities decrease 4:1 ELlength emitter

FET parameter change

Egnearly constant junction temperature → linewidths vary as (1 / bandwidth)2

gate length decrease 2:1current density (mA/m), gm (mS/m) increase 2:1channel 2DEG electron density increase 2:1

GL

gate-channel capacitance density increase 2:1dielectric equivalent thickness decrease 2:1channel thickness decrease 2:1channel densit of states increase 2 1 channel density of states increase 2:1

source & drain contact resistivities decrease 4:1 GW widthgate

constant voltage, constant velocity scaling fringing capacitance does not scale → linewidths scale as (1 / bandwidth )

256 nm GenerationInP HBT 8

10

m230

40

UH

150 nm thick collectorZ. Griffith

0

2

4

6

0 1 2 3 4 5

mA/

0

10

20dB

H21

f = 424 GHz

fmax

= 780 GHz340 GHz dynamic frequency dividerM. Seo, UCSB/TSC

30 109

1010

1011

1012

H21

0 1 2 3 4 5V

ce

0109 1010 1011 1012

Hz

20

70 nm thick collector

10

20

dBf = 560 GHz

fmax

= 560 GHz

U

5

10

15

mA

/m

2

340 GHz VCOVtuneVtune

E. LindM. Seo, UCSB/TSC

0109 1010 1011 1012

Hz

00 1 2 3 4

Vce

4030

60 nm thick collectorVout

VEE VBB

Vout

VEE VBB

20

30

dB

U

H21

f 218 GH 10

20

30

mA/m

2

324 GHz amplifier J. Hacker, TSCZ. Griffith

0

10

109 1010 1011 1012

Hz

ft = 660 GHz

fmax

= 218 GHz

0

10

0 1 2 3

m

Vce

InP Bipolar Transistor Scaling Roadmap

emitter 512 256 128 64 32 nm width16 8 4 2 1 2 16 8 4 2 1 m2 access

base 300 175 120 60 30 nm contact width, 20 10 5 2 5 1 25 m2 contact 20 10 5 2.5 1.25 m2 contact

collector 150 106 75 53 37.5 nm thick, 4.5 9 18 36 72 mA/m2 current density4.5 9 18 36 72 mA/m current density4.9 4 3.3 2.75 2-2.5 V, breakdown

f 370 520 730 1000 1400 GHz eWfmax 490 850 1300 2000 2800 GHz

power amplifiers 245 430 660 1000 1400 GHz digital 2:1 divider 150 240 330 480 660 GHz

e

bcWcTbT

Conventional ex-situ contacts are a messTHz transistor bandwidths: very low resistivity contacts are required

textbook contact with surface oxide with metal penetration

THz transistor bandwidths: very low-resistivity contacts are required

Interface barrier → resistanceInterface barrier resistanceFurther intermixing during high-current operation → degradation

In-Situ Refractory Ohmics on Regrown N-InGaAs

4

5

)

In-situ Mo on n-InAs In-situ Mo on n-InGaAs6

8

)

2

3

esis

tanc

e (

2

4

esis

tanc

e (

0

1

0 0.5 1 1.5 2 2.5 3 3.5

Re

ρc = 0.6 ± 0.4 Ω·µm2

n = 1×1020 cm-3

ρc = 1.0 ± 0.6 Ω·µm2

n = 5×1019 cm-3

0

2

0 0.5 1 1.5 2 2.5 3 3.5

Re

Gap Spacing (m)

In-situ emitter contacts good

Gap Spacing (m)HAADF-STEM*

InGaAsthIn situ emitter contacts good

enough for 64 nm node Interface

InGaAs

regrowth

2 nm

InGaAs

TEM by Dr. J. Cagnon, Stemmer Group, UCSB

A. Baraskar

Process Must Change Greatly for 128 / 64 / 32 nm Nodes

control undercut→ thinner emitter thinner emitter

→ thinner base metalthinner base metal→ excess base metal resistance

Undercutting of emitter endsg101A planes: fast

111A planes: slow

128 / 64 nm process: Dry-Etched Emitter Metal

In-situ MBE emitter contacts:refractory→ high Jlow contact : ~0.7 -m2

Refractory emitter contactdry-etched→ nm resolutionrefractory→ high currentW t/d t h d itt Wet/dry etched emitter dry-etched→ nm resolutionconventional base liftoffhigh penetration→ thick baseshigh penetration→ thick basesmoderate contact ~4-m2

yield issues ?

V. JainE. Lobisser

Dry-Etched W/TiW Emitter Contact Process

Sputtered W/ Ti0.1W0.9processpVertical ICP etch profileLow-stress filmLow stress filmGood adhesion between layersRefractory Refractory MetalsW/TiW bilayer:stress and etch bias compensation

V. JainE. Lobisser

Sub-100 nm devices: lifted-off base metal

After Sidewall EtchAfter Sidewall Etch Base Contact Post and Mesa EtchBase Contact Post and Mesa Etch

V. JainE. Lobisser

After Sidewall EtchAfter Sidewall Etch Base Contact, Post and Mesa EtchBase Contact, Post and Mesa Etch

Device Isolation EtchDevice Isolation Etch HBT before BCB processingHBT before BCB processing

Sub-100 nm devices: lifted-off base metal V. JainE. Lobisser

Sub-100 nm devices: lifted-off base metal V. JainE. Lobisser

15 MAG/MSG

10

15

dB)

UA

je= 0.11m x 3.5m

Ic = 9.1mA; V

ce = 1.75V

Je = 23.6mA/m2; V

cb = 0.7V

MAG/MSG

30

40

dB)

Aje

= 0.11m x 3.5m

U

H

MAG/MSGft = 400 GHz

f = 660 GHz

5Gai

n (d

H21

fmax

= 660 GHz10

20

Gai

n (d

Ic = 8.9mA; V

ce = 1.74V

H21

max

2

01011 1012

freq (Hz)

ft = 465 GHz

0109 1010 1011 1012

freq (Hz)

c ceJ

e = 23.1mA/m2; V

cb = 0.7V

40

50

60

m2 )

50 mW/m240 mW/m2

Aje = 0.11m x 3.5m

I = 0.2 mA600

750

600

750

Hz) ft

: Vcb

= 0 V: V

cb = 0.7 V

10

20

30

J e (mA

/um

Vcb

= 0 V

Ib,step

0.2 mA

300

450

300

450f m

ax (G

H

t (GH

z)

0

10

0 1 2 3V

ce (V)

Ib = 0.01 mA

Peak ft/f

max

1500 5 10 15 20 25 30 35

150

Je (mA/m2)

128 / 64 nm process: Sputtered Refractory Base

In-situ MBE emitter contacts:refractory→ high Jlow contact : ~0.7 -m2

Refractory emitter contactdry-etched→ nm resolutionrefractory→ high currentW t/d t h d itt Wet/dry etched emitter dry-etched→ nm resolutionRefractory base contactslow penetration→ thin baseslow penetration→ thin baseslow contact ~2.5 -m2

self-aligned/ liftoff-free

V. JainE. Lobisser

In-Situ Refractory Ohmics on P-InGaAs

Metal Contact ρc (Ω-µm2) ρh (Ω-µm)In-situ Ir 1.0 ± 0.7 11.5 ± 3.3

20Iridium

10

15ta

nce

()

WR

R ShCC

22

5Res

ist

W0

0 1 2 3 4Gap Spacing (m)

In-situ base contacts good enough for 32 nm nodeRemaining work: contacts on processed surfaces

contact thermal stability & reliability A. Baraskar

Benefits of refractory base contacts

100 nm InGaAs grown in MBE

15 nm Pd/Ti diffusion

30 nm Mo

After 250°C anneal, Pd/Ti/Pd/Au diffuses 15nm into semiconductordeposited Pd thickness 2 5nmdeposited Pd thickness: 2.5nmbase now 30 nm thick: observed to degrade with thinner bases

Refractory Mo contacts do not diffuse measurablyRefractory Mo contacts do not diffuse measurablyRefractory, non-diffusive metal contacts for thin base semiconductor

A.. Baraskar

Sputtered Process for in-situ base contacts

• Blanket ex-situ Pd/W contacts• Planarization and etch back 15

20

)

Iridium

• Low contact resistivity• Lift-off free and Au free base process• Self-aligned process for thin emitters

10

esis

tanc

e (

Self aligned process for thin emitters • Enables refractory, in-situ base contacts

0

5

0 1 2 3 4

Re

ρc =1.0 ± 0.7 Ω-µm2

0 1 2 3 4Gap Spacing (m)

Planarization boundary

SiNx Sidewall

V. JainE. Lobisser

Sub-100 nm HBTs : planarized base contact

Emitter projecting from PR forEmitter projecting from PR forplanarization planarization Planarized EmitterPlanarized Emitter

Base Contact, Post and Mesa EtchBase Contact, Post and Mesa Etch Contact Via EtchContact Via Etch

V. JainE. Lobisser

670 GHz Transceiver Simulations in 128 nm InP HBT transmitter exciter Simulations @ 670 GHz (128 nm HBT)transmitter exciter

5

10

15

20

LNA: 9.5 dB Fmin at 670 GHz

20

30

S(2,

1))

f(2)

f(2)

Simulations @ 670 GHz (128 nm HBT)PA: 9.1 dBm Pout at 670 GHz

receiver

128nm-8 -6 -4 -2 0 2 4 6 8-10 10

-5

0

5

-10640 660 680 700620 720

10

0

SP.freq, GHz

dB(S

freq GHz

nf n

128nm

VCO50

(1 H

z)

free-runningVCO:-50 dBc (1 Hz)@ 100 Hz offsetat 620 GHz (phase 1)

-150

-100

-50

0

101 102 103 104 105 106 107

PLL

sing

le-s

ideb

and

phas

e no

ise

spec

tral d

ensi

ty, d

Bc free running

VCO

closed-loop VCO noise

multiplied reference noise

Total PLLphase noise

3-layer thin-film THz interconnectsthick-substrate--> high-Q TMICthin -> high-density digital

10 10 10 10 10 10 10offset from carrier, Hz

-1.05

-1

-0.95

-0.9690 GHz Input

t , V

out_

bar

-1.05

-1

-0.95

-0.9

950 GHz Input

ut, V

out_

bar

Dynamic divider:novel design,simulates to 950 GHzg y g

-1.2

-1.15

-1.1

195 10-12 197.5 10-12 200 10-12

Vou

time, seconds

-1.2

-1.15

-1.1

195 10-12 197.5 10-12 200 10-12

Vou

time, seconds

simulates to 950 GHz

30

n (d

B)

Mixer:

-10.00 -5.000 0.0000 5.000 -15.00 10.00

0

5

10

15

20

25

-5

LO Power

Noi

se F

igur

e, C

onve

rsio

n G

ainMixer:

10.4 dB noise figure11.9 dB gain

InP HBT Fundamental Oscillators to > 340 GHzM. Seo UCSBM. Rodwell UCSBM. Urteaga TSCTSC HBT Technology

Differential Topology, Cascode output buffer, ECL outputsFixed frequency and voltage controlled designs

VVOUTOUT

Q3Q3 Q4Q4Q5Q5Q5Q5

RR11

RR33LLout1out1

LLout2out2

VtuneVtune

Q3Q QQ

Q1Q1 Q2Q2Q6Q6

RR22

RR44

LLBB

LLC1C1

LLC2C2LLC3C3

VEE VBBVEE VBB

RREE

LLE1E1

LLE2E2

CCVarVar CCVarVar

Vout

VEE VBB

Vout

VEE VBB

VVEEEE VVTUNETUNE VVBBBB

C1C1 C2C2 C3C3

EE

InP HBT 331 GHz Dynamic Frequency Dividers M. Seo UCSBM. Rodwell UCSBM. Urteaga TSC Z. Griffith TSCTSC HBT Technology

Topology: Double-balanced mixer with emitter follower feedback and resonant loading

Modified version of modern dynamic divider (H.M. Rein)

Circuit Schematic

y ( )

Inverted microstrip wiring Design variations with input for external clock

source and with integrated fixed frequency and voltage controlled oscillators for testing.

O t t t ith 331 2 GH l k i t Chi h t hOutput spectrum with 331.2 GHz clock input Chip photograph“Signal Identification” test at fIN= 331.2 GHz

THz 240 GHz PA DesignT. Reed UCSBM. Urteaga TSCZ. Griffith TSCTSC HBT Technology

Teledyne InP HBTs We=256nm, Tc=150nmTwo-finger design achieves S21 = 4.9dB @ 238GHz

TH T iTHz Transistors

THz Integrated Circuits

Device scaling (Moore's Law) is not yet over.

Scaling→ multi-THz transistors

Challenges in scaling:

Scaling→ multi-THz transistors.

g gcontacts, dielectrics, heat

M l i TH iMulti-THz transistors:for systems at very high frequenciesfor better performance at moderate frequenciesfor better performance at moderate frequencies

Vast #s of THz transistorscomplex systemsnew applications.... imaging, radio, and more

end

On-Wafer TRL Calibration Envirnoment

Ref Plane for TRL

Ref Plane for TRL

0.5-67GHz Data: Lumped Pads, Off Wafer LRRM Cal.

m7Ft_fit = 400GHz Fmax_fit = 660GHz

Standard Off Wafer OSLTOpen & Short Pad Cap Extraction

Open Short

THTHzBi l T i Bipolar Transistors

Sub-100 nm devices: lifted-off base metal V. JainE. Lobisser

15 MAG/MSG

10

15

dB)

UA

je= 0.11m x 3.5m

Ic = 9.1mA; V

ce = 1.75V

Je = 23.6mA/m2; V

cb = 0.7V

MAG/MSG

30

40

dB)

Aje

= 0.11m x 3.5m

U

H

MAG/MSGft = 400 GHz

f = 660 GHz

5Gai

n (d

H21

fmax

= 660 GHz10

20

Gai

n (d

Ic = 8.9mA; V

ce = 1.74V

H21

max

01011 1012

freq (Hz)

ft = 465 GHz

0109 1010 1011 1012

freq (Hz)

c ceJ

e = 23.1mA/m2; V

cb = 0.7V

600

750

600

750

Hz) ft

: Vcb

= 0 V: V

cb = 0.7 VS21/5

S12x5S21/5

S12x5

300

450

300

450f m

ax (G

H (GH

z)--- : Measured x : Simulated--- : Measured x : Simulated

1500 5 10 15 20 25 30 35

150

Je (mA/m2)

S11 S22S11 S22

Sub-100 nm devices: lifted-off base metal V. JainE. Lobisser

60 40 mW/m210-2

40

50

60

um2 )

50 mW/m240 mW/m

Aje = 0.11m x 3.5m

Ib,step

= 0.2 mA10-4

10

A)

Ic

Ib

Solid Line: Vcb

= 0 VDashed Line: V

cb = 0.7 V

10

20

30

J e (mA

/u

Vcb

= 0 V

, p

10-8

10-6

I b, Ic (A b

nc = 1.41

nb = 3.04

00 1 2 3

Vce

(V)

Ib

= 0.01 mA

Peak ft/f

max

10-10

0 0.2 0.4 0.6 0.8 1V

be (V)

8

6

7

8

F)

Vcb

= 0 V

4

5

6C

cb (f

F

Vcb

= 0.4 V

V 0 V3 0 5 10 15 20 25 30

Je (mA/m2)

Vcb

= 0.7 V

2008 UCSB Dry-Etched Ti/TiW Emitter Process

SiO23 4

BHF

Litho patternmetal

sidewall dry etch wet etch

TiW

I G A ++Ti

I G A InGaAs n++InGaAs n++

InGaAs p++ Base

InP n

InGaAs p++ Base InGaAs p++ Base InGaAs p++ Base InGaAs p++ Base

InP nInGaAs n++ InGaAs n++

InP n InP n

30 109

1010

1011

1012

U

H21 Worked well @ 200 nm

base contactby liftoff

10

20

dB

f = 560 GHz

fmax

= 560 GHz

U

Low yield @ 128 nm:stress→ poor adhesion

0109 1010 1011 1012

HzSubstantial revisionrequired