Polarization Super-junction - POWDEC powdec...Conventional Si-MOS FET biasing n n G D S p p+ n + 9...

IWWPE2012, 2-nd April 2012, Hsinchu, Taiwan . POWDEC K.K.

GaN for Green Future

Polarization Super-junction

A New Concept for

GaN High-Voltage Devices

1

H. Kawai

A. Nakajima

E. M. S. Narayanan

POWDEC K.K. The University of Sheffield (UoS), present : National Institute of Advanced Industrial Science and Technology (AIST)

The University of Sheffield (UoS)



2

1. About Powdec

2. Background

Issues for Today’s GaN Power Devices

3. Polarization Super-Junction, (PSJ) Concept

4. Application to Devices

5. Results and Discussion

6. Summary

-- Contents --



3

-- About POWDEC --

Established: May 2001

Location: Oyama-city, Japan

No. of employees: 20 Powdec core technology:

GaN growth using the original large scale MOCVD equipment

Power device development using unique growth techniques such as ELO (Epitaxial lateral overgrowth), PSJ (polarization super-junction)

Powdec is managed independently of its shareholders

to pursue its business interests

Mt. Fuji

150km

Narita 70

60

Fukushima 170km



4

-- Background--

Issues for Today’s GaN Power Devices

Reliability • Current Collapse

• Not high-breakdown voltage

• Avalanche resistance

• Life-time degradation

Cost • Substrate

• Thick buffer growth

• High cost front-end process

Need a new device approach



5

-- Background--

Current Collapse

Low drain bias

High drain bias

Drain Voltage, Vd

Dra

in C

urr

en

rt, I

d

Vg

Vg

Vd

VDD

Id R

0

Id

on

Vd

VDD

R

Time

Vg

On-state

off

Vstress

Off-state On-state



Decrease of electron

S G

D

AlGaN

GaN

S G

D

AlGaN

GaN

Ele

ctr

ic F

ield

Hot electrons captured in Deep traps Hot electrons captured in AlGaN Gate leakage Electrons captured

in the surface

Trapped electrons act as the negative bias under the channel

Increase in channel resistance

High field induces “Hot electrons”

Deep trap

Leakage

Channel electron

6

-- Background--

Origin of Current Collapse



SiN/SiO2 insulator

Source FP

Gate FP

Si substrate

AlN nucleation layer

AlGaN/AlGaN buffer

S G

AlGaN GaN

High quality passivation

D GaN-cap

Thick

7

-- Background--

High field limits GaN’s potential capability.

High field induces; Current collapse Low breakdown voltage Poor life time reliability

How to amend;

Lower the Field

Lower the gate leakage

Decrease the surface trap

Decrease the deep trap



S D

AlGaN

GaN

Field plate (FP)

G

Fie

ld (

E)

without FP

with FP

Split & decrease the field

8

-- Polarization Super-junction (PSJ) --

Traditional technology : Field plate (FP)

Max.Field（MV/cm)

On

-resis

tan

ce I

ncre

ase

（R

HV-R

LV)/

RLV [%

]

VDD=300V

（Toshiba semiconductor Company、SEMI FORUM JAPAN, power device seminar)

On-resistance increase vs. Peak field strength

Gate-edge

FP-edge



E

V

V

Deple-tion

n

n+

Conventional Si-MOS FET

biasing

n

n+

G

D

S

p

p+

n+

9

Super-junction (SJ) concept

Depleted whole

E

Flat distribution

n+

n

p p

biasing

Si Super-Junction-MOS FET

n+




AlG

aN

u

-Ga

N

GaN

p-G

aN

potential

Polarization charge

Ev Ec

i-AlGaN

i-GaN hole

i-GaN ele.

Polarization charge

n+

p

p

n

GaN/AlGaN/GaN

GaN/AlGaN/GaN

Band structure

10


GaN/AlGaN/GaN Polarization(PJ) structure acts similar to a silicon super-junction

n+

p

depleted

biasing

Super-junction Si-MOS FET

i-AlGaN

i-GaN

i-GaN

depleted

Polarization charge

biasing

Polarization charge

Ec Ev

AlG

aN

u

-GaN

GaN

p-G

aN

V



Existence of high density 2-dimensional hole gas (2DHG)

sapphire

buffer

i-GaN

i-Al.23Ga.77N

i-GaN

p+GaN

***nm

***nm

***nm

Layer structure

0

5

10

15

20

25

30

50 100 150 200 250 300

Ho

le D

en

sit

y (

1e1

2 /c

m2 )

Temperature ( K )

PJ

p-GaN

1.4E13 cm-2

Temperature dependence

of hole concentration

11


PSJ

Freeze-out


GaN for Green Future F

ield

Flat distribution

12


Application to lateral devices

S D

AlGaN

GaN

G B

PSJ region

Fie

ld

with FP

without FP

S D

AlGaN

GaN

Metal FP

G

Traditional metal field-plate Polarization super-junction



p-GaN G

i-GaN

Sapphire sub.

i-AlGaN

i-GaN

B

Lp:8mm

Lsd:22mm

Lgd:17mm

3mm

S D G

i-GaN

Sapphire sub.

i-AlGaN

Lsd:22 mm

Lgd:17 mm

S D

Lg:2 mm

PSJ-FET Reference HFET

13

-- Application to FET (PSJ-FET) --

• No passivation

• No field plate

• Gate-PSJ configuration

6mm 5mm Lg:2mm



Transfer Characteristics Off-state Characteristics

10-9

10-7

10-5

10-3

0 200 400 600 800D

rain

Cu

rre

nt

[A/m

m]

Drain Voltage [V]

Vg = -15 V

Super HFET

Reference

HFET

VB = 720 V

14

-- PSJ-FET; results --

Vth = ~5 V VB = ~720 V; ref-HFET < 200 V Leak current= ~sub mA/mm@700 V

0

0.1

0.2

0.3

0

20

40

60

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

Dra

in C

urr

en

t [A

/mm

]

Gm

[m

S/m

m]

Gate Voltage [V]

Super HFET

Vd:10V

Vth:-4V

Id

GmGm

max:

55 mS/mm

PSJ-FET

PSJ-FET





0

0.1

0.2

0.3

0 5 10 15

Dra

in C

urr

en

t [A

/mm

]

Drain Voltage [V]

25

Reference HFET

150

Vg = 0 V

-2 V step℃

℃

Pinch-offed at 250 C

Id decreased due to phonon

scattering and band modulation Did not work at > 150 C

15


0

0.1

0.2

0.3

0 5 10 15

Dra

in C

urr

en

t [A

/mm

]

Drain Voltage [V]

Vg = 0 V

250

-2 V step

25

Super HFET

℃

℃




~mA/mm leak current at 250 C

10-12

10-10

10-8

10-6

10-4

10-2

0 50 100 150 200

Dra

in C

urr

en

t [A

/mm

]

Drain Voltage [V]

Vg = -15 V

250

175

10025

Super HFET

℃

℃

℃

℃

10-12

10-10

10-8

10-6

10-4

10-2

0 50 100 150 200

Dra

in C

urr

en

t [A

/mm

]

Drain Voltage [V]

100

25

Reference HFET

150Vg = -15 V

℃

℃

℃

Exponential increase with temp.

16


at off-state condition




Vd

Id

Vg=0V

Vd=+2V

measurement

Vg = -15 V

time

1 s

（20->350 V）

stress

transient

measure

17

Current collapse

Super HFET

Reference

HFET

1

2

3

4

5

6

0 100 200 300 400

Ro

nH

V / R

on

init

ial

Stress Voltage [V]

PSJ-FET


Essentially no current collapse



0

50

100

150

200

250

300

350

400

450

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

Id (

mA

/mm

)

Vgs (V)

Id saturate at Vg > -2 V VB > 830 V

18

B p-GaN

G

i-GaN

Sapphire sub.

i-AlGaN

i-GaN

Lg:2 mm

S D

Lgd=13mm

AlGaN

Source-PSJ configuration

Conv.

PSJ

Vds=10V

Vth=-4V

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

450

400

350

300

250

200

150

100

50

0

Vgs (V)


1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

0

5

10

15

20

0 500 1000

Ig (A/m

m)

Id (

mA

/mm

)

Vds (V)

Conv. Super

Conv. (VB=130V)

Super (VB=830)

500 1000 0

20

15

10

5

0

1E-2

1E-3

1E-4

1E-5

1E-6

1E-7

1E-8

1E-9

1E-10

PSJ

PSJ Ig (

A/m

m)

Ig (

A/m

m)

Vds (V)

Id



Forward I-V

Vth：1.2 V

RonA : 1.3 mWcm2

Breakdown voltage > 1.1 kV

Reverse current : ~1 mA/mm

19

Schottky barrier diode

Reverse I-V

-- PSJ Applied to a Diode--

sapphire

i-GaN

i-AlGaN

P-GaN

12um A C

0

0.05

0.1

0.15

0.2

0 0.5 1 1.5 2 2.5 3 3.5

An

od

e C

urr

en

t [A

/mm

]

Anode Voltage [ V ]

W : 50 mm

Lac

: 12 mm RonA : 1.3 mWcm2

AlGaN/GaN SBD

PSJ-SBD

AlGaN SBD

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

-1200 -1000 -800 -600 -400 -200 0

An

od

e C

urr

en

t [A

/mm

]

Anode Voltage [ V ]

W : 50 mm

Lac

: 12 mm

VB > 1.1 kV

PJ-SBD

AlGaN/GaN SBD

VB = 400V

AlGaN SBD



20

-- Discussion --

Scalability of VB with PSJ length

Super-junction predicts the linear

increase of VB with the junction length

PSJ-length; Lp

sapphire

i-GaN

i-AlGaN

P-GaN

G PSJ length

D S

Fie

ld

V

Lp

Bre

akd

ow

n v

olt

ag

e (

VB

) ** MV/cm

Scalable with PSJ-length



sapphire

i-GaN

i-AlGaN

P-GaN

G PSJ length

D S Lp

21

-- Discussion --


Acknowledgement: High-voltage measurement was supported by “Agilent Technologies International Japan Ltd.”

0.01

0.1

1

10

100

0 1 2 3 4 5 6 7

Drain current at off-state vs. PSJ length

Dra

in C

urr

en

t [ u

A/m

m ]

Drain Voltage [ kV ]

Lp = 10 um

20 um30 um

40 um

Drain-current at off-state vs.

Drain-voltages

PSJ, Lp = 30um

S D



S D

22

-- Discussion --


0

2

4

6

8

10

0 10 20 30 40 50 60 70

VB vs, PSJ length

Bre

akd

ow

n V

olt

ag

e [

kV

]

PSJ length, Lp [ mm ]

line for

eye convenience

slope = 1.4 MV/cm

sapphire

i-GaN

i-AlGaN

P-GaN

G PSJ length

D S Lp

• VB increased linearly with PSJ length. • Breakdown field was about 1.4 MV/cm,

being smaller than 3.3 MV/cm.



23

-- Discussion --

0

5

10

15

20

25

0 5 10 15 20 25

Dra

in C

urr

en

t [ m

A/m

m ]

Drain voltage [ V ]

Lp = 40um

Vg = 0 V

-2 V

-4 V

-6 V

sapphire

i-GaN

i-AlGaN

D S Lp

5um 6um LSD

Lp = 10mm Lp = 40mm

0

10

20

30

40

50

60

0 2 4 6 8 10

Dra

in C

urr

en

t [ m

A/m

m ]

Drain Voltage [ V ]

Vg = 0 V

-2 V

-4 V

-6 V

Lp = 10um

slope

RonA=

22 mWcm2

RonA=

110 mWcm2

𝑳𝑺𝑫

𝒔𝒍𝒐𝒑𝒆 𝑽𝒈=𝟎 RonA ( mW cm2 ) =



24

-- Discussion --

Comparison of on-resistance

0.1

1

10

100

1000

0.1 1 10

Ro

nA

[ mW

cm

2 ]

Breakdown voltage, VB [ kV ]

Panasonic

('07)

Si-SJ MOSFET

SiC transistors

GaN-HFET

This work (PSJ-FET)

Si-SJ MOSFET

SiC transistors

GaN-HFET

This work (PSJ-FET)

Si-SJ MOSFET

SiC transistors

GaN-HFET

This work (PSJ-FET)

Toshiba

Fuji-Ele.

Infineon

Philips

Denso

Sanken('07)

Toshiba('07)

Furukawa

UCSB('06)

USCC('06)

AIST(SIT)

Kansai Ele.Pow.

(DMOS)

Rutgers Univ.(SIT)

Si-limit

6H-SiC-limit

4H-SiC-limit

GaN-limit

SiCED

Cree(DMOS)

Rutgers Univ.(SIT)

PSJ-Diode

1mm

Panasonic 10kV GaN-HFET

sapphire

i-GaN

i-AlGaN

D S Lp

POWDEC 6kV PSJ-FET



25

-- Summary --

We proposed a new method to realize GaN

transistors and diodes enabling high-VB and

negligible current collapse.

Polarization super-junction (PSJ)

i-AlGaN

i-GaN

hole

i-GaN

electron Polarization

charge

Which consists of basically

GaN/AlGAN/GaN double hetero-

junction in which 2DHG and 2DEG

co-exist.

The PSJ system acts similar to a

silicon super-junction



26

substrate

AlN

Thick buffer layer

S G

AlGaN GaN

D GaN-cap

-- Summary --

As a consequence,

the PSJ system can eliminate the barriers

encountered in the present metal field-plate

based device system.

• Breakdown voltage

• Current collapse

• Process cost

• Epi-cost

• etc.

G S D

AlGaN GaN

p-GaN

AlN nucleation layer

B

composite substrate



27

Thank you very much

for your careful attention!!


Polarization Super-junction - POWDEC powdec...Conventional Si-MOS FET biasing n n G D S p p+ n + 9...

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Transcript of Polarization Super-junction - POWDEC powdec...Conventional Si-MOS FET biasing n n G D S p p+ n + 9...