APEC 2013 Industry Session: Key Components for EV
GaN Offers Advantages to Future HEV
Yifeng Wu
ywu@transphoromusa.com
Transphorm Inc.
115 Castilian Dr.
Goleta, CA 93117, USA
Table of Contents
1. GaN’s potential as an efficient kV-class
devices
2. GaN-on-Si HEMT Performance and
robustness
3. High temperature operation
4. Device paralleling for extended power
5 . GaN diode-free hard-switched bridges
6. Motor drive system benefits from GaN
7. Summary
2
Key Considerations For HEV
1. Resistance-capacitance figure of merit
at high voltages
2. Over-voltage, dV/dt & dI/dt capabilities
3. High temperature tolerance
4. Extended power capability
5. Hard-switched H-bridge simplicity & performance
6. System benefit
GaN Is Inherently a Highly Reliable Material
• GaN is inherently reliable
Wurtzite Crystal: high biding energy
GaN Crystal Structure
• Dislocations in GaN is benign
Lasers stable with 100x more dislocation
than other semiconductors
• Intrinsic device reliability has been proven in RF
applications
• Learn from experience in RF devices
Epi quality for high m & low leakage
Passivation guidelines for low trapping
Principle of electric field management
Basic fabrication process
• Challenges:
High voltage epi / device designs &
process realization
New operation space exceeding
traditional package schemes
Stringent qualification requirement
4
GaN RF Device Reliability
GaN HEMT Spike Tolerance Test at Vdc=600V
Using Artificially-High Parasitic Inductance
Vdc =600V, Inductor current =16A
Normal layout
4cm2 loop inserted to induce spike
• GaN HEMTs successfully turned on and off 16A current at 600V bus with
parasite inductor loop of 4cm2 (90nH with current probe on).
• Voltage transient up to 380V/ns and spikes up to 850V.
• Device has no functionality change after 100,000 shots of 850V spikes.
• Datasheet spike rating 750V for safety margin.
5
5
600V Converter Operation at 100kHz
300:600V Converter w/ GaN at 100kHz
50
99
45
98.5
40
98
35
97.5
30
97
25
96.5
20
96
15
95.5
Loss (W)
Efficiency (%)
99.5
10
Eff
95
Loss
94.5
0
500
1000
1500
2000
2500
5
0
3000
POUT (W)
• GaN-on-Si HEMT achieves 99% 1:2 boost efficiency at 100kHz
• Low on-resistance, low charge and high speed are key in obtaining high
efficiency for compact systems running at high PWM.
600V GaN-on-Si HEMT Voltage Blocking Capability at 175oC
1000
0.15-ohm device
ID (uA)
TC=175oC
100
CoolMOS
GaN-on-Si HEMT
10
0
200
400
600
800
1000
VDS (V)
• kV capability at 175oC.
7
1200
High Temperature Converter Operation Compared with Si CoolMOS
200:400V, 400W, TJ=175oC
CoolMOS 60R385
Loss (W)
Dloss=2.1W
GaN 310mW HEMT
Dloss=1.4W
T (hr)
• GaN devices show lower increase of loss at high T.
• Due to less heating & lower temperature sensitivity.
8
GaN-on-Si Hybrid HEMT High Temperature Operation
up to 1.5kW at TC=187oC (Tj=215oC)
Eff. (%)
Air gap
Hot plate
TC point
99.2
40
99
36
98.8
Eff_23C
32
98.6
Eff_100C
28
98.4
Eff_187C
24
Loss_23C
98.2
20
Loss_100C
98
16
Loss_187C
97.8
12
97.6
8
97.4
4
97.2
0
200
400
600
800
1000
1200
1400
POUT (W)
• GaN-on-Si can operate at high volt & high current
at Tj=215C with ease
• HT performance lends support for inherent
robustness
9
0
1600
Loss (W)
230V:400V boost Converter
f=100kHz
Hi-Temp operation of GaN HEMT
Preliminary Life Time Indication
Tj=215oC
Efficiency (%)
99
98
1.00E+00
1.00E+02
1.00E+04
1.00E+06
1.00E+08
T (hr)
106 hr for Eff. to degrade by 0.2%
(By no means device life time prediction)
Device Paralleling for Extended Power
Without Reducing Speed and Efficiency
C1
L1
C1
VIN
b1
(A)
D1
PWM/
Driver
Q1
VIN
a
(B)
PWM/
Driver
Q1
Q2
a
c
c
b1 D2
11
VOUT
a1
C4
d
C2
L1
b2
C2
C3
Q1a
Q2a
a2
PWM/
Driver
a2
Q2b
d
Q1b
a1
C2a
c
e
C3a
c
b1/2
VOUT
C4
b2
L1
(C)
b1 D1 b2
C1
VIN
b2
b1 D1a
D2a/1b
c
C4
C3b
e
c
b1 D1b b
2
• Scalable unit cell
• Equal-length fan-in
• Low-impedance diode termination
• Equal-length inductive fan-out
VOUT
C2b
Parallel GaN HEMT Boost Converter Performance (4x)
99.5
60
99
50
98.5
40
98
30
Eff_1Device
Eff_2device
97.5
20
Eff_4device
Loss_1device
97
Loss_2device
Loss (W)
Eff. (%)
Vin/Vout =220V/400V, f=100kHz
10
Loss_4device
96.5
0
1000
2000
3000
4000
0
5000
POUT (W)
• Roughly 4x increase in output power
• No loss in efficiency
12
12
Table of Contents
1. GaN’s potential as a efficient kV class
devices
2. GaN-on-Si HEMT Performance and
robustness
3. High temperature operation
4. Device paralleling for extended power
5 . GaN diode-free hard-switched bridges
6. Motor drive system benefits from GaN
7. Summary
13
GaN HEMT Offers Low Qrr in Reverse Conduction Mode,
Enables Simple Hard-switched Bridge Operation
Qrr=1000nC at 9A, 400V
Qrr=54nC at 9A, 400V
• Both measured in the same test board
• Transphorm GaN HEMT was tested at 450A/ms with little ringing
• CoolMOS was not stable at 450A/ms. dI/dt reduced to 100A/ms for stability.
• GaN HEMT has Qrr of ~20x less than CFD-type CoolMOS (Low Qrr design).
14
14
Device Suitability for Hard-switched Bridge Applications
IGBT
GaN HEMT
Bridge configurations
Bridge operation
properties:
Si MOSFET
Si IGBT
GaN
Initial forward drop (Vf)
No
Yes
No
Ron Resistance (RON)
Low
Extremely Low
Very Low
Reverse conduction
Yes
No (Need FW-Diode) Yes
Reverse Qrr (body
diode)
High (hard switch bridge
impractical)
NA
Low
Operation speed*
Fast
Slow to Medium
Very fast
Overall bridge
performance
Poor
Good
Superior
15
15
Performance Benchmarking Between IGBT and GaN Bridges
Si IGBT Bridge Converter
GaN Bridge Converter
VDD
Driver
L
VOAC
VODC
Driver
VDD
L
VODC
VOAC
RL
RL
• Buck converter is configured from a half bridge
• 2 state-of-the-art HF IGBTs + 2 state-of-the-art SiC SBDs were used in IGBT bridge
• 2 Transphorm GaN HEMTs were used in GaN bridge
Spec comparison:
Vbd
Imax at 25oC
Imax at 100C
Vce (Ron)
16
IGBT
600 V
23 A
12 A
2.1 V at 12A
GaN
600 V
19A
14A
(0.15 W)
Output Waveforms Between IGBT and GaN Bridges
Turn on
Rise time:
GaN
= 2.8 nS (1.5-2ns)
Si IGBT = 7 nS
Turn off
@
400V
4.5A
Fall time:
GaN
= 8 nS
Si IGBT = 42 nS
• GaN has 3-5x less rise time: Reduced commutation loss
• GaN has 5x less fall time: Much less output charging loss
17
25
100
20
99
15
98
10
97
Eff. (%)
Loss (W)
400-200V Buck Performance as a Function of Frequency
Loss_IGBT
Loss_GaN
5
Eff_IGBT
96
Eff_GaN
0
0.0E+00
1.0E+05
2.0E+05
3.0E+05
4.0E+05
95
5.0E+05
Freq. (Hz)
• Si IGBT loss escalates as frequency increases (breaking down at 400kHz)
• GaN bridge converter maintains >98% at 300kHz
High PWM frequencies enable inductor/capacitor size reduction
18
GaN Diode-freeTM 3-Phase Bridge Modules
Module Package
Module Schematics
GUH
GVH
GWH
KUH
KVH
KWH
U
V
GUL
GVL
GWL
KUL
KVL
KWL
W
P
Module spec:
• 6 in 1 switches
• 600V, 14A capability
at TC = 100oC
19
(a)
(b)
Transphorm’s High-Frequency 3-Phase GaN Motor Drive Inverter
LU
UO
CU
LV
DSP
CV
VO
LW
CW
WO
Available as Demo kit from Transphorm
• High frequency design enables compact filter
• Pure Sine-wave output eliminates un-wanted PWM stresses on motor
20
Project supported by ARPA-E
Output Current Waveform Comparison
IGBT Inverter: PWM Power
GaN Inverter: Sine-wave Power
• GaN inverter operating at 100 kHz with compact filter & pure Sine-Wave
output
• IGBT inverter operating at only 15kHz with PWM output
• GaN inverter output current is spike-free, ideal for motor drive
21
99
Efficiency (%)
98
97
96
95
94
93
Eff_EE_GaN
92
E_Loss_GaN
91
0
500
1000
1500
80
75
70
65
60
55
50
45
40
35
30
25
20
15
Eff_EE_IGBT
10
E_Loss_IGBT
5
0
2000
2500
POUT (W)
• GaN Inverter efficiency exceeded IGBT:
GaN: 100kHz, include filter loss
IGBT: 15kHz, w/o filter loss
• Superior efficiency margin of GaN allows
high PWM and filter losses
22
Loss (W)
GaN Motor-drive at 100kHz with Filter Vs.
State-of-the-art IGBT at 15 kHz w/o Filter
Motor Drive System Efficiency: GaN Vs. State-of-the-art IGBT
Motor Efficiency
System Efficiency
System Efficiency (%)
90
Efficiency (%)
80
70
60
Eff_M_GaN
50
Eff_M_IGBT
40
30
0
500
1000
1500
POUT, Mechanical (W)
2000
90
80
70
60
50
Eff_EM_GaN
Eff_EM_IGBT
40
30
0
500
1000
1500
POUT, Mechanical (W)
• Pure Sine-Wave output from GaN inverter significantly improved motor
efficiency
• Overall system benefit is compelling:
2.5% at full load, ~4% at mid load and ~8% at low load
23
2000
10kW GaN Converter At 600V Bus
600V:420V Converter
f=100kHz
200
99.5
180
99
160
98.5
140
98
120
97.5
100
Eff
97
80
Loss
96.5
60
96
40
95.5
20
95
Loss (W)
Eff. (%)
100
0
0
2000
4000
6000
8000
10000
POUT (W)
• GaN can push power conversion to
new power/frequency space
Summary
1) GaN-on-Si have shown superior performance including low Ron,
kV-level breakdown voltages, high spike tolerance and high
temperature robustness at >200 C.
2) Device paralleling at high speed demonstrated with 4x increase in
power and no loss in efficiency at 100 kHz.
2) GaN enables diode-free bridge hard-switched at 5-10x higher
PWM than conventional IGBT, yet offering high efficiency.
3) Compact on-board filtering realized with high PWM, boosting
motor system efficiency by 2-5%.
4) 10-kW GaN-based converter demonstrated with a single H-bridge,
further scaling will enable HEV level applications.
25