Wide Band-Gap (SiC and GaN) Devices Characteristics and Applications Richard McMahon University of Cambridge
Wide band-gap power devices SiC : MOSFET JFET Schottky Diodes Unipolar BJT? Bipolar GaN : FET Diode Enhancement mode Depletion mode (in cascode) Schottky diodes
GaN power devices EPC :30-450 V E-mode HEMTs (normally-off) (commercial) Transphorm : 600 V HEMTs (Cascode) Infineon (IR) 600 V HEMTs (Cascode ) + Panasonic (normally-off GIT) 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 Version 1 3 Yes
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
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 16
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
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 29
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
Overshoot during turn-on Upper side gate ringing Voltage mismatch Parasitic inductances Issues with cascodes