Device Research Conference 2006

Erik Lind, Zach Griffith and Mark J.W. RodwellDepartment of Electrical and Computer EngineeringUniversity of California, Santa Barbara, CA, 93106-9560, USA

Xiao-Ming Fang, Dmitri Loubychev, Ying Wu, Joel M. Fastenau, and Amy LiuIQE Inc. 119 Bethlehem, PA 18015, USA

lind@ece.ucsb.edu, 805-893-3273, 805-893-3262 fax

250 nm InGaAs/InP DHBT with 650 GHz fmax and 420 GHz ft,

operating above 30 mW/μm2

InP/InGaAs Double Heterostructure Bipolar Transistor

• Mesa DHBTs for high speed applications

•Abrubt InP-InGaAs emitter base junction•InGaAs base provides good hole mobility•Setback and Grade used for BC junction

•InP collector

Subcollector

•Base

Emitter

Collector

S.I. InP

• Objective: Improve DHBT performance by lateral scaling of emitter-base junction!

Fast bipolar transistors

0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700 800

RSC

UIUC DHBT

NTT

Fujitsu HEMT

SFU

UIUC SHBT

UCSB

NGST

Pohang

HRL

IBM SiGe

Vitesse

f ma

x (G

Hz)

ft (GHz)

500 GHz400 GHz300 GHz200 GHz maxff

Updated June 2006

600 GHz

UCSB 0.25μm

UCSB 0.6μm

Standard figures of merit / Effects of Scaling

Small signal current gain cut-off frequency (from H21)

bccexbcjec

Bcb CRRCC

qI

Tnk

f

2

1

icbCR

ff

bb ,8max

VI

C

c

cb

Charging time for digital logic

•Power gain cut-off frequency (from U)

Thinning epitaxial layers (vertical scaling) reduces base and collector transit times… But increases capacitances

Increase current density and reduce resistances.

Reduce Rbb and Ccb,i through lateral scaling

Higher Jkirk, dimished self-heating due to current increased current spreading

Fabrication I – Epitaxial Stack: 150 nm Collector

Title

Thickness (nm) Material Doping cm-3 Description

5 In0.85Ga0.15As 51019 : Si Emitter cap

15 InxGa1-xAs > 41019 : Si Emitter cap grading

20 In0.53Ga0.47As 41019 : Si Emitter

80 InP 31019 : Si Emitter

10 InP 81017 : Si Emitter

40 InP 81017 : Si Emitter

30 InGaAs 7-41019 : C Base

15 In0.53Ga0.47 As 3.51016 : Si Setback

24 InGaAs / InAlAs 3.51016 : Si B-C Grade

3 InP 2.751018 : Si Pulse doping

108 InP 3.51016 : Si Collector

5 InP 11019 : Si Sub Collector

6.5 In0.53Ga0.47 As 21019 : Si Sub Collector

300 InP 21019 : Si Sub Collector

Substrate SI : InP

• 150 nm collector

• 30 nm base, graded carbon doping

• Thin, 6.5nm InGaAs subcollector

•High fmax device with moderate fτ

• High Vceo

• Investigate Jmax increase due to improved thermal capabilities and current spreading – increase in fτ

-2

-1

0

1

2

100 150 200 250 300 350 400

Ene

rgy

(eV

)

Position (nm)

Vbe

=0.9V

Vcb

=0.6V

Grade

Setback

Emitter Base Collector

Sub-collector

Fabrication II – Lateral Scaling

Fabrication Details:

• I-line optical lithography

• All wet etch, lift-off based process

• 250 nm emitter / base junction

• Reduction in Cbc by removing semiconductor under base pad

• BCB passivation

DHBT before BCB passivation Emitter Metal Removed

Base contact

Emitter Mesa

We=250 nm

Base contact

Emitter Contact

We=400nm

RF and DC performance

• Summary of device parameters—

• Average 25, VBR, CEO ~ 5 V (@ 1kA/μm2)

• fmax=650 GHz

• ft=420 GHz

• Operates at power densities above 30mW/μm2

0

5

10

15

20

0 1 2 3 4 5 6

J e (m

A/

m2 )

Vce

(V)

Ajbe

= 0.25 x 2.1 m2

Ib step

= 100 uA

Peak ft, f

max

30 mW/m2

10-12

10-10

10-8

10-6

10-4

0.01

0 0.2 0.4 0.6 0.8 1

I b, I c (

A)

Vbe

(V)

VCB

= 0.0 V

Ic

Ib

nc = 1.15

nb = 1.6

Ajbe

= 0.5 x 7.1 m2

0

5

10

15

20

25

30

35

109 1010 1011 1012

Gai

ns

(dB

)

Frequency (Hz)

ft = 420 GHz, f

max = 650 GHz

U

H21A

jbe = 0.25 x 3.1 um2

Ic = 9.0 mA, V

ce = 1.58 V

Je = 12.0 mA/um2, V

cb= 0.6 V

MSG/MAG

650 GHz

420 GHz

Vceo

ft, fmax and CCb variation

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

0 3 6 9 12 15

f max

(G

Hz)

Je (mA/m2)

Vcb

=-0.3V

Aje = 0.25 x 3.1 m2

0.0V

0.2V

0.6V

0.4V

0.0

100.0

200.0

300.0

400.0

500.0

0 3 6 9 12 15

f t (G

Hz)

Je (mA/m2)

Vcb

=-0.3V

Aje = 0.25 x 3.1 m2

0.0V

0.2V

0.6V

• Jkirk 12 mA/μm2 (@ Vcb=0.6V)

• Limited by collector doping and thermal effects

• Ccb/Ic=0.30 pS

ft fmax

Aje

= 0.25 x 3.1 m2

Vcb

= -0.3 V

2

4

6

8

10

12

0 4 8 12 16

2

3

4

5

6

7

8

9

Ccb

/Aje (

fF/

m2 )

Je (mA/m2)

Ccb (fF

)

0.0 V

0.2 V

Vcb

= 0.6 V, A

jc= 1 x 5 m2

0.4 V

Cbc

Small signal equivivalent circuit at maximum ft, fmax

Summary resistive elements

• Emitter contact (from RF extraction), Rcont 5.0 m2

• Base (from TLM) : Rsheet = 635 /sq, Rcont < 5.0 m2

• Collector (from TLM) : Rsheet = 12.7 /sq, Rcont = 10.0 m2

freq (1.000GHz to 67.00GHz)

S22

dS

11d

S21

d/20

S12

d*5

_403

_610

GH

z_ex

trac

tion_

revi

sed.

.S(1

,1)

_403

_610

GH

z_ex

trac

tion_

revi

sed.

.S(1

,2)*

5_4

03_6

10G

Hz_

extr

actio

n_re

vise

d..S

(2,1

)/20

_403

_610

GH

z_ex

trac

tion_

revi

sed.

.S(2

,2)

S21/20S12x5

S11 S22

Ccb,ex= 2.34 fF

Rcb= 55 k

Ccb,ex= 0.96fFRbb= 45.5

Rbe= 110

Rex= 6.7

Rc= 1.5

Collector

Emitter

Base

Cje+Cdiff= 27.3+56 fF

gme-jf

0.20e-j0.29pS

1-67 GHz Aje=0.253.1μm2

Ic=9mA

Vce=1.56V

• Total delay time: 1/2πfτ= 0.38 pS

• Base and collector transit times = 0.29pS

• Terms related to Ccb = 38 fS

• Larger bandwidth through vertical scaling

Breakdown mechanism for Type-I InP DHBTs

10-9

10-8

10-7

10-6

10-5

10-4

-1 0 1 2 3 4 5 6

Aje=0.45x7.1m2, A

jc=1.4x10.1m2

|Ib

as

e|

Vcb

Ie=120A

Ie=5.6A

Ie=250nA

Ib=Ib(Vcb=0) - (M-1) αIe – Izener

• Breakdown essentially set by tunneling through setback region

• BVceo ~ 5V

• Proper design of setback and grade is needed for vertical scaling of the collector

zenercbb IIMII 10

-2

-1.5

-1

-0.5

0

0.5

1

1.5

100 150 200 250

Energ

y (e

V)

Position (nm)

Vbe

=0.9V

Vcb

=5.1V

EmitterInP

BaseInGaAs

Grade

SetbackInGaAs

10-3

10-2

10-1

100

101

102

103

0 1 2 3 4 5 6

I cbo (

A/c

m2 )

Vcb

(V)

Simulation

Ajc = 1.5 x 10 m2

Measured Data

Impact Ionization

Band to band tunneling

Comparison with 0.6μm 150nm Tc UCSB DHBT

0

5

10

15

20

25

30

35

109 1010 1011 1012

Gai

ns

(dB

)

Frequency (Hz)

ft = 391 GHz, f

max = 505 GHz

U

h21

Ajbe

= 0.6 x 4.3 um2

Ic = 13.2 mA, V

ce = 1.54 V

Je = 5.17 mA/um2, V

cb= 0.6 V

200

300

400

500

1 2 3 4 5 6

GH

z

Je (mA/um2)

ft

fmax

Vcb

= 0.6 V

• Emitter Width – 0.6 m

• Emitter contact - Rcont 10.1 m2

• Base Contact - Rcont 9.6 m2

• Jkirk ~ 5.5 mA/m2 (Pmax ~ 15 mW/m2)

• f / fmax = 391,505 GHzGriffith et al., IEEE Electron Device Letters, Vol. 26, Jan 2005

2004 2006

• Emitter Width – 0.25 m

• Emitter contact - Rcont 5.0 m2

• Base Contact - Rcont < 5.0 m2

• Jkirk ~ 12 mA/m2 (Pmax ~ 30 mW/m2)

• f / fmax = 420,650 GHz

0

5

10

15

20

25

30

35

109 1010 1011 1012

Ga

ins

(dB

)

Frequency (Hz)

ft = 420 GHz, f

max = 650 GHz

U

H21A

jbe = 0.25 x 3.1 um2

Ic = 9.0 mA, V

ce = 1.58 V

Je = 12.0 mA/um2, V

cb= 0.6 V

MSG/MAG

0

5

10

15

20

0 1 2 3 4 5 6

J e (m

A/

m2 )

Vce

(V)

Ajbe

= 0.25 x 2.1 m2

Ib step

= 100 uA

Peak ft, f

max

30 mW/m2

Comparison with SHBT and GaAsSb technologies

• Type I InP DHBTs combines high f / fmax with high power densities and breakdown voltages

• InP SHBTs (utilizing InGaAs collector) have very high ft and fmax, but low breakdown voltages.

• InP Type-II DHBTs (InP/GaAsSb/InP) have high breakdown, but fmax is low due to base resistance.

InP SHBT—InGaAs base and collector (55nm)

Type-II DHBT—GaAsSb base, InP collector (150nm)

H.G. Liu et al., IEEE TED, Vol. 53, No. 3, 2006

W. Hafez et al., APL, Vol. 87, 2006

f / fmax = 710 / 340 GHz Type-I DHBT—InGaAs base, InP collector, ternary B-C grading

f / fmax = 420 / 650 GHz

f / fmax = 380 / 250 GHz

BVceo ~ 1.75V

Parameter scaling law

Gen. 2 Gen. 3 Gen. 4

MS-DFF speed 158 GHz 230 GHz 330 GHz

Emitter Width 1/ 500 nm 250 nm 125 nm Resistivity 1/ 15 -m2 7.5 -m2 5 -m2

Base Thickness 1/ 300Å 250 Å 212 Å Doping 7 1019 /cm2 7 1019 /cm2 7 1019 /cm2 Sheet resistance 500 600 Contact 1/ 20 -m2 10 -m2 -m2

Collector Width 1/ 1.1 m 0.54 m m Thickness 1/ 1500 Å 1060 Å 750 Å Current Density 5

mA/m2 10 mA/m2

20 mA/m2

Acollector/Aemitter 2.8 2.8 2.8

f 371 GHz 517 GHz 720 GHz

maxf 483 GHz 724 GHz 1.06 THz

EE LI / 2.4 mA/m

2.4 mA/m

2.4 mA/m

f 1/ 340 fs 250 fs 170 fs

ccb IC / 1/ 440 fs/V 310 fs/V 220 fs/V

ccb IVC /logic 1/ 130 fs 94 fs 66 fs

)//( logic cbb IVR 0.66 0.51 0.41

)/( logic Cje IVC 1/ 350 fs 250 fs 180 fs

)//( logic cex IVR 0.24 0.24 0.24

Bipolar Transistor Scaling Laws & Scaling Roadmaps

key device parameter required change

collector depletion layer thickness decrease 2:1

base thickness decrease 1.414:1

emitter junction width decrease 4:1

collector junction width decrease 4:1

emitter resistance per unit emitter area decrease 4:1

current density increase 4:1

base contact resistivity (if contacts lie above collector junction)

decrease 4:1

base contact resistivity (if contacts do not lie above collector junction)

unchanged

Scaling Laws:design changes required to double transistor bandwidth

WE

WBC

WEB

x

L E

base

emitter

base

collector

WC

key figu

res of m

erit

for lo

gic sp

eed

Technology Roadmap through 330 GHz digital clock rate

• The current device is Gen 2.5.

• Key enabling technologies for the THz transistor

0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700 800

RSC

UIUC DHBT

NTT

Fujitsu HEMT

SFU

UIUC SHBT

UCSB

NGST

Pohang

HRL

IBM SiGe

Vitesse

f ma

x (G

Hz)

ft (GHz)

500 GHz400 GHz300 GHz200 GHz maxff

Updated June 2006

600 GHz

Present Status of Fast Transistors

)(

),/(

),/(

),/(

hence ,

:digital

gain, associated ,F

:amplifiers noise low

mW/

gain, associated PAE,

:amplifierspower

)11(

2/) (

alone or

min

1max

max

max

max

cb

cbb

cex

ccb

clock

ττ

VIR

VIR

IVC

f

m

ff

ff

ff

ff

:metrics better much

:metrics popular

UCSB 0.25μm

UCSB 0.6μm

Conclusion

• First generation of UCSB 250nm DHBT device

• ft/fmax = 420/650 GHz

• Record fmax for a DHBT

• High power density ~ 30 mW/ μm2

• High Kirk threshold ~ 12 mA/ μm2

• High BVeco ~ 5V

• Further scaling is feasible

This work was supported by the DARPA SWIFT program, the ONR under N0001-40-4-10071, DARPA TFAST program N66001-02-C-8080, and a grant by the Swedish Research Council.