Richard McMahon University of Cambridge

Wide Band-Gap (SiC and GaN)

Devices – Characteristics and

Applications

Wide band-gap power devices

SiC :

GaN :

• MOSFET

• JFET

• Schottky Diodes

Unipolar

• BJT?

Bipolar

• Enhancement mode

• Depletion mode (in cascode) FET

• Schottky diodes Diode

GaN power devices

EPC :30-450 V

E-mode HEMTs (normally-off)

(commercial)

Infineon (IR)

600 V HEMTs

(Cascode ) +

Panasonic (normally-off

GIT)

Transphorm : 600 V HEMTs

(Cascode)

Gan Systems : 100 & 650 V HEMTs

(Cascode)

DC to DC converters for automotive 48 V / 12 V

systems using GaN HEMTs

• Typical power density 1.5

kW/l - 2 kg

• Reduce mass and volume

• Increase efficiency

Low voltage semiconductor

technologies

Si MOSFET GaN FET

Fast switching

efficiency

Temperature

Cost

Easy to use /

Experience

Switching Considerations

Low threshold voltage issue (low-side turn-off)

Negative gate drive in half

bridges may be needed

Increases reverse conduction

voltage drop

Dead time must be kept

extremely short

Limits choice of driver IC

Converter development

August 2013 January 2015

Max power 100 W 420 W

Efficiency 88 % – 90 % 93 % to 94 %

Robustness dV/dt Problems Solved

Active Temperature

monitoring

No Yes

Version 1 3

Key findings to date

• GaN offers benefits for DC-DC converters

• GaN matches silicon losses at 10 to 20 times the

switching speed

• Power density however will be limited by cooling

constraints.

High voltage (ca. 600 V) opportunities for GaN

• Data centres

• Wireless charging

• Electric vehicles

• Drives

• Power factor correction

• Point of load dc-dc converters

• AC voltage regulators

• Solar inverters?

GaN based half-bridge

Transphorm 600 V devices

Design issues with E-mode devices

(low-side turn-off)

• Tight gate threshold margin

• Accurate gate supply voltage

• Stringent dead time requirements

• dv/dt undesired turn-on

• Ringing increases for fr >1MHz

• Parasitic and loop inductances

HEMT Cascode structure

(Infineon,GaN Systems & Transphorm)

Switching waveforms turn-on and turn-off

• Switching node voltage: 400 V

• Gate voltage: 5 V (yellow trace)

• Switching frequency 50 kHz

• Output rise time: 3 ns, fall time: 4 ns

(standard gate drive with tighter

layout & forced commutation )

First design rise time : 31ns and fall time : 25ns

16

Commercial SiC devices

Schottky Diodes:

Rohm

Cree

GeneSiC

STMicroelectronics

United SiC

Infineon

Transistors:

Rohm

Cree

GeneSiC

STMicroelectronics

United SiC

Power Modules:

Cree

Mitsubishi

Semikron

Rohm

SiC applications

Distribution networks

Drives for automotive

Aerospace

High temperatures

Power converters for wind, solar etc.

HVDC

Breakdown Voltage

On State

Switching – Dependence of Turn off

Energy loss with temperature

Switching current = 20 A

High temperature tests - 110ºC

heatsink/hotplate

Half-bridge inverter (2 kW)

Step-up converter

Measurements on a boost converter with a

SiC JFET and a Si CoolMOS.

800 W and100 kHz switching frequency

SiC JFET

Si CoolMos

SiC Cascode

SiC MOSFET and JFET

SiC MOSFET

Cascode

SiC MOSFET Cascode

Challenges

Circuit layout

EMC

Thermal design

Packaging

Device reliability

Device availability

29

Conclusions

• GaN & SiC devices are emerging

• GaN looks good up to 600 V

• SiC offers advantages at high voltage

• Both are relatively expensive – cost must be justified

• Silicon design techniques are not necessarily

transferable

• Reliability and supply remain concerns

GaN based half-bridge

(Transphorm 600 V devices)

Switching waveforms(turn-on&off)

Switching node voltage: 400 V

Gate Voltage: 5 V

Switching frequency 50 kHz

Rise time: 31 ns, fall time: 25 ns

Transfer characteristic of EPC 100 V GaN FET

EPC 2022 E-GaN (100 V)

HEMT Cascode structure

(Infineon,GaN Systems &Transphorm)

GaN power devices

EPC :30-450 V

HEMTs (commercial)

Infineon (IR) :

600 V HEMTs

Panasonic :

650 V GITs

Transphorm : 600 V HEMTs

and SBDs

Gan Systems : 100 V HEMTs

Gan Systems : 650 V HEMTs

GaN HEMTs are lateral devices

E-GaN HEMT (EPC)

Cascode characteristics

Courtesy : Transphorm TPH3002LD 600 V

Issues with cascodes

• Overshoot during turn-on

• Upper side gate ringing

• Voltage mismatch

• Parasitic inductances