October 3-5, 2016

International Workshop on Power Supply On Chip

(PwrSoC 2016)

October 4, 2016

Tatsuo Morita

Automotive & Industrial Systems Company

Panasonic Corporation

Monolithic integration of

GaN power transistors

integrated with gate drivers

Potential Application for WBG semiconductors

GaN power transistors are suited for high-frequency applications.

600V/15A TO-220

600V/15A SMD

Normally-off GaN Gate Injection Transistor

(GaN-GIT)

Production

Proto-type

30V normally-off GaN-GITs

(developed in 2014)

Advantages of GaN for Power device

Comparison of material properties

x107 (cm/s)

GaN

Si

SiC

Bandgap (eV)

Maximum

Electric

Field

(MV/cm)

Electron

Mobility

Saturation

drift velocity Baliga’s

FOM

(cm2/Vs)

3

2

1

AlGaN/GaN Hetero-junction FET

GaN inherently has superior material properties for Power switching device

Unique feature of GaN is 2-Dimensional Electron Gas(2DEG) which serves

both high electron density and high electron mobility

High sheet carrier density induced by

polarization effects at the AlGaN/GaN

hetero-interface without any doping

GaN-FET can be fabricated on cost-

effective Si-substrates

Normally-on operation

Drain Source Gate

Un-doped AlGaN

Un-doped GaN

2DEG channel

Si substrate

Super-lattice Buffer

Normally-off GaN Gate Injection Transistors - GIT -

Gate Injection Transistor (GIT)

Normally-off operation

Vg=0V: p-AlGaN lifts up the potential at the channel.

Vg>Vf: Hole injectction → Electron generation →Large Drain current

Very low RonQg

RonQg of 600V GIT is 0.7 WnC which is 1/13 of that of the latest SJ-MOSFET.

Good Recovery characteritics

GIT can be operated as a free-wheeling diode with very small charging current.

Recovery characteristics

Power supply

GaN power devices used in Power supply

DC12V Bus

Isolated DC-DC converter

Non-isolated

DC-DC converter

PFC

AC-DC Power Supply

CPU

AC

100-230V

1～

1.2V

Power converter have progressed with overcoming design trade-off among

power density and efficiency, cost.

To make more advanced, GaN-FETs have been actively investigated.

・5MHz/50A GaN POL converter

reported on PCIM2014

・ GaN POL power IC integrated with gate

drivers reported on ISPSD14

1MHz resonant converter

using 600V normally-off GaNs

reported by Fraunhofer ISE

on ECSCRM2012

Totem-pole PFC using GITs

reported by Panasonic

on PCIM2014

Today’s topic

1 2 5

Frequency (MHz)

0

100

200

300

400

500

600

Siz

e (

mm

2)

Inductor

170nH

GaN

Module

Inductor

350nH

Si-MOS

Module

GaN

70nH

For smaller POL converter

Advantage by increasing frequency

Compact

Increasing frequency greatly helps to reduce the system size.

Low RonQg power device and low parasitic inductance are key

factors.

30V-class normally-off GaN-GITs

RonQg of developed 30V GaN-GIT is reached to 19.1mΩnC*1.

-> 36% smaller than that of reported Si-MOSFET*2.

*1 H. Umeda, et al., PCIM2014

*2 S. Xu, et al., International Electron Devices Meeting (IEDM) Technical Digests, 145(2009)

Impact of the parasitic inductance

Parasitic inductance on Power Loop LPower_Loop

Cout

Parasitic inductance on Gate Loop LGate_Loop

Spike voltage t

ILV DS

LoopPowerSpike

_

VDS

IDS

→limit di/dt to keep Vds under BVds

→causes gate oscillation

→generate Noise

→Reduction of Lgate_Loop also effectively increase gate charging speed

Parastic inductance on power loop (LPower_Loop) increase the spike voltage

→It limits di/dt and causes gate oscillation, increase noise.

Parastic inductance on gate loop (LGate_Loop) increase the gate charging time.

This Work : GaN-based IC with gate driver

This Work

One Chip

GaN-based IC

Inductor (L) Capacitor (C)

High-side

Transistor (Hi)

Low-side

Transistor (Lo) Si-based

Gate Drivers

Conventional

GaN transistors and GaN gate drivers are integrated to a

compact chip

-4

-2

0

2

4

6

8

10

12

14

GaN

Transistors

Vout

VinVgate driver

Gate

DriversParasitic

Inductors

L

C

L1

L2

L3

L4

Impact of Integration : Small Parasitic Inductances

Switching speed is increased by reduction of parasitic inductances

Simulated turn-on switching

waveform

0 1 2 3

Time (ns)

Vo

ltag

e (

V)

L1～L4 = 4.5nH

12.5V/ns

L1～L4 = 1nH

15.8V/ns

12V ⇒ 1.8V Iout = 6A

2MHz operation

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

0 2 4 6 8 10 12

Op

era

tio

n L

oss (

W)

Parasitic Inductance (nH)

L1+L2

(L3=L4=0)

L3+L4

(L1=L2=0)

Parasitic Inductance (nH)

Op

era

tio

n L

os

s (

W)

00.6

2 4 6 8 10 12

0.7

0.8

0.9

1

1.1

1.2

1.312V ⇒ 1.8V

Iout=6A

@ 2MHz

Simulated operation loss

Impact of Integration : Small Parasitic Inductances

Operation loss is reduced by the reduction of parasitic inductances.

Vout

Iin

tr tf

VG

D-Tr.

E-Tr.1

Vout

Iin Large Wg

E-Tr.4

DCFL

5V

Switching

Power

Device

VG

GaN Gate Driver : DCFL (Direct Coupled FET Logic)

High power consumption in GaN gate driver of DCFL.

Time Chart Circuit Design

High

Short-Circuit

Current

Flowing

Short-Circuit

Current

Charge

Current

Vout

Iin

tr tf

VG

High

5V

Switching

Power

Device

Buffer

AmplifierDCFL

VoutVG

D-Tr.

E-Tr.1

E-Tr.2

E-Tr.3

Iin Small Wg Large Wg

E-Tr.4

GaN Gate Driver : DCFL with Buffer Amplifier

Low power consumption in GaN gate driver by buffer amplifier.

Time Chart Circuit Design

Low

Short-Circuit

Current

Flowing

Short-Circuit

Current

AlGaNGaN

Buffer layer

Si Substrate

p-AlGaN

Gate

S D DS

Schottky

Gate

GaN-GIT GaN-HFET

Isolation layer

GaN Device Structure and Characteritics

0

5

10

15

20

25

30

1E-10

1E-8

1E-6

1E-4

1E-2

1E+0

1E+2

-4 -2 0 2 4 6 8

Ro

n (

Ωm

m)

Ids (

A/m

m)

Vgs (V)

GIT

GIT

HFET

HFET

0

Vgs (V)

Ids

(A

/mm

)

2 4 6 8-2-41E-10

1E-8

1E-6

1E-4

1E-2

1E+0

1E+2

0

5

10

15

20

25

30

Ro

n (

Ωm

m)

Device Characteristics Device Structure

D-mode HFET and E-mode GIT are monolithically fabricated.

Operation Characteristics of GaN Gate Driver

-2

-1

0

1

2

3

4

5

6

-50 0 50 100

Voltage (

V)

time (ns)

Vin

tr=7ns

Pulth Width：50ns

tf=5ns

Vout

Cload：1500pF

0 50 100-50-2

-1

0

1

2

3

4

5

6

time (ns)

Vo

lta

ge

(V

)

GaN gate driver is about 40% faster than Si gate driver.

0

1

2

3

4

5

6

7

8

9

10

0 20 40 60 80 100

Po

we

r C

on

su

mp

tio

n o

f G

ate

Drive

r [W

]

duty [%]

Without

buffer amplifier

duty (%)

Po

we

r C

on

su

mp

tio

n o

f G

ate

Dri

ve

r (W

)

0 20 40 60 80 100

0

1

2

3

4

5

6

7

8

9

10

t1

t2

Gate Driver

Output Voltage

Low

High

duty ratio

= t1 / t2

With buffer amplifier

98.5%

Reduction

Low Consumption of GaN Gate Driver

Power consumption is reduced about 98.5% by using GaN

DCFL with buffer amplifier.

GaN-based DC-DC Converter IC

Compact chip size is 5.1mm x 2.3mm

GaN-based IC reduces the system size

High side Transistor

Low side Transistor

Gate Driver

for High side

Gate Driver

for Low side1mm

Chip photograph Module layout with GaN-based IC

Driver

Driver

High-GIT

Low-GITInductor

Inductor

GaN-based IC

Integration

Circuit diagram

Operating Efficiencies of DC-DC Converter

Peak efficiency of 88.2% is achieved with 12V - 1.8V DC-

DC conversion at 2MHz

70

75

80

85

90

95

0 2 4 6 8 10 12

Eff

icie

ncy

(%)

Load Current (A)

1MHz

2MHz

3MHz

This work

Discrete

12V ⇒ 1.8V DCDC down conversion

Analyzed operating loss of GaN-based IC

Switching loss have been reduced 15% by using GaN-based DC-

DC converter IC.

80

82

84

86

88

90

0

0.5

1

1.5

2

2.5

1 2

Eff

icie

nc

y (

%)

Op

era

tio

nL

oss (

W)

12V ⇒ 1.8V,

Iout=6A,

@2MHz

Switching Loss

Eoss

Conduction Loss

Discrete This Work

88.2%

0.68W0.80W

87.8%

Summary

Compact GaN-based DC-DC Converter IC

with High Speed Gate Drivers for

Highly Efficient DC-DC Converters

GaN Gate Driver DCFL with buffer amplifier

Monolithically fabrication of HFET and GIT

High speed switching (tr + tf = 12ns)

GaN-based IC 5.1mm X 2.3mm Compact chip size

Peak Efficiency (12V-1.8V) : 88.2%@2MHz

This work is partially supported by the New Energy

and Industrial Technology Development Organization

(NEDO), Japan, under the Strategic Development of

Energy Conservation Technology Project.