(ultra-) wide-bandgap materials and devices: reshaping the
TRANSCRIPT
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The Bradley Department of Electrical and Computer Engineering
College of Engineering
Blacksburg, Virginia, USA
(Ultra-) Wide-Bandgap Materials and Devices: Reshaping the Power Electronics Landscape
Dr. Yuhao Zhang
Assistant Professor
Center for Power Electronics Systems, Virginia Tech
Email: [email protected]
IEEE-EDS Santa Clara
Valley/San Francisco
Chapter June Seminar
June 16, 2019, online
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• Power electronics: conversion of electric energy with solid-state electronics
Power Electronics
Center for Power Electronics Systems 1
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Basic Idea of Power Electronics: Non-linear Switches
Center for Power Electronics Systems 2
• Non-linear switch: no I and V simultaneously (no loss)
• Energy storage/filtering: add lossless element
$25 billion/year market
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Power Devices are Ubiquitous in Electric Vehicles
Center for Power Electronics Systems 3
Proceedings of the IEEE, vol. 95, no. 4, April 2007
Market Projection (US $Bn)
100
200
2011 20192015
Year
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Efficient Data Center Enabled by Power Device Innovations
Center for Power Electronics Systems 4
Market Projection (US $Bn)
100
200
2012 20222017Year
• Data center will reach 10% of the total electrical power consumption in 2020
• Power device innovation allows for the architecture innovation
• 1% efficiency improvement: 160 TWH ≈ 5 nuclear power plant
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WBG Semiconductor: Superior Power Semiconductor Over Si
Center for Power Electronics Systems 5
MV/cm4
2
2
2
43.0
1.5
1000
0
0
0 Si
SiC
GaN
eV
W/cm·K107 cm/s
0
4
High Voltage
High TemperatureHigh Voltage
High Current
High Frequency
Heat Dissipation
Source: Proceedings of the IEEE, vol. 105, no. 11, Nov. 2017 .
cm2/Vs
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WBG: Lower Power Loss, Higher Efficiency, Higher Frequency
Center for Power Electronics Systems 6
n/p type 𝑅on,𝑠𝑝 =4𝐵𝑉2
𝜀𝜇𝐸𝐵3
𝑅on,𝑠𝑝 = 𝑅on ∙ 𝐴
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WBG Benefits: System Simplification & Miniaturization
Center for Power Electronics Systems 7
Source: Cambridge Electronics Inc.
Source: Rohm
Frequency scaling-up allows
for significant reduction in
system size and weight
Source: Anker
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Revolutionize the Power Electronics Manufacturing Paradigm
Center for Power Electronics Systems 8
LTCC integrated
inductor structures Integrated PoL Converter
F. C. Lee, Q. Li, T-PE, 28 (9), 2013
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WBG Devices Reduce System-level Cost
Center for Power Electronics Systems 9
• System-level cost reduction due to reduced size, weight of magnetics and reduced system cooling;
• Reduced system loses provide savings throughout life of the system
Courtesy: Dr. V. Veliadis, PowerAmerica
Dr. Levett, Infineon
SiC
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WBG Power Semiconductor Wafer Diameter & Cost
Center for Power Electronics Systems 10
Source: Proceedings of the IEEE, vol. 105, no. 11, Nov. 2017 . Source: Journal of Physics D: Applied Physics, 51 (2018) 273001
6 inch == 150 mm 8 inch == 200mm
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WBG Power Devices: GaN HEMTs and SiC MOSFETs
15 V 650 V 1200 V 1700 V 10000 V
× large chip size (cost) for high-voltage devices
√ 2DEG channel: high mobility (>1500 cm2/Vs)
√ easy for integration with driver/control IC× MOS channel: low mobility (~100 cm2/Vs)
× Difficult for integration
× Substrate resistance
√ high current capability
√ small chip size for high-voltage devices
3300 V
GaN SiC
√ high-speed switching
× more challenging thermal and E-field
management√ easier thermal management
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Adoption of WBG Power Devices at a Unprecedented Speed
Center for Power Electronics Systems 12
Significant loss reduction
Less Conversion stages
• Google’s New 48V Architecture
Tesla Model 3 Inverter with SiC Modules
(Source: Tesla & STMicroelectronics)
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WBG/UWBG Power Device Research in My Group
June 12, 2020 Center for Power Electronics Systems 13
Physics
& Material
Proof-of-
concept
Device Demo
Large-area
Device &
Packaging
Robustness
& ReliabilityConverter
ApplicationDevice
Design
Processing
Technologies
Medium-voltage Vertical
GaN Devices
Ultra-wide Bandgap
Materials & DevicesApplication-oriented Device
Robustness & Prognosis
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WBG/UWBG Power Device Research in My Group
June 10, 2020 Center for Power Electronics Systems 14
Physics
& Material
Proof-of-
concept
Device Demo
Large-area
Device &
Packaging
Robustness
& ReliabilityConverter
ApplicationDevice
Design
Processing
Technologies
Medium-voltage Vertical
GaN Devices
Ultra-wide Bandgap
Materials & DevicesApplication-oriented Device
Robustness & Prognosis
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Reliability & Robustness Test Conditions
Center for Power Electronics Systems 15
Time ~
Reliability
Stress ~
Robustness
Specified
lifetime (e.g., 15 years)
Operation Conditions (e.g., f, V, I)
Acceptable
Test Time(e.g., 1000
hours)
Single Event
Field Test
(by device
users)
Qualification
(by device
manufactures)
< Device
RatingWorst Case Destruction
Limit
Thermal
Aging
Thermal
Cycling
Power
Cycling
Short
Circuit Avalanche
High Temp
Reverse Bias
High Temp
Gate BiasPackage
Failure
Device
Failure
Stress Events
Dynamic Ron
robustness
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A New Switching-based Robustness Test Methodology
June 10, 2020 Center for Power Electronics Systems 16
V & I overstress
Switching Cycling = Overstressed Stimuli + Hard Switching
• Robustness: withstand capability of out-of-SOA event
• Surge V & I in any switching due to di/dt, dv/dt, parasitics
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“Switching Cycling” test on 1.2 kV SiC Power MOSFETs
June 10, 2020 Center for Power Electronics Systems 17
Test Circuit and Hotplate
Auxiliary Equipment
• V overshoot of 1500 V, 94% of
avalanche breakdown voltage
• I overshoot of 23 A
• 250 μs period, 150 ns on time
• Characterization after every 6
hours (86.4 million cycles)
𝑬𝒙𝒑𝒆𝒓𝒊𝒎𝒆𝒏𝒕𝒂𝒍𝑻𝒆𝒔𝒕𝒃𝒆𝒅
𝑬𝒙𝒑𝒆𝒓𝒊𝒎𝒆𝒏𝒕𝒂𝒍𝑾𝒂𝒗𝒆𝒇𝒐𝒓𝒎𝒔
J. Kozak…..Y. Zhang, Applied Power Electronics Conference (APEC 2020)
Cree C2M0280120D
TO-247, 1200 V, 10 A
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SiC MOSFET Degradation Mechanism #1 – Gate Oxide
June 11, 2020 Center for Power Electronics Systems 18
Minimal change in Ron
Gate Leakage Current @ 25 oC
(Degradation and induce device failure)
J. Kozak…..Y. Zhang, Applied Power Electronics Conference (APEC 2020)
Accelerated gate degradation @ 100 oC
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• A new degradation mechanism independent of gate bias
• Drain leakage increase by 100-fold, avalanche BV unchanged
• Non-reversible, no further change with increased switching cycles
• For the first time reported, not report in HTRB tests
Degradation Mechanism #2 – Semiconductor Degradation
June 12, 2020 Center for Power Electronics Systems 19
J. Kozak…..Y. Zhang, Applied Power Electronics Conference (APEC 2020)
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SiC MOSFET Degradation Mechanisms
June 11, 2020 Center for Power Electronics Systems 20
- Increased leakage at higher temperature (1,000-fold higher leakage at 100 oC)
- I-V-T relations: electron hopping through defect states
Degraded Device
Good Device
J. Kozak…..Y. Zhang, International Reliability Physics Symposium (IRPS 2020)
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SiC MOSFET Degradation Mechanisms (cont.)
June 11, 2020 Center for Power Electronics Systems 21
- No degradation in body diode forward conduction -> degradation in edge termination
- Relate to the turn-off process: capacitive current discharges the depletion region in the edge
termination + overvoltage during turn-off -> higher E-field at the edge termination
- New switching-based stress profile generates new degradation in devices
J. Kozak…..Y. Zhang, under review, IEEE Trans. Power Electron.
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GaN HEMTs: still open questions in conventional robustness
Center for Power Electronics Systems 22
- Power device surge energy robustness is essential in many applications (EVs, power grids, etc.)
- Usually characterized by unclamped inductive switching (UIS) test
- Often referred to as “avalanche robustness”
DUT
V & I overstress
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How do GaN HEMTs withstand surge energy (w/o avalanche)?
Center for Power Electronics Systems 23
• No or minimal avalanche capability
Open questions
• How to withstand/dissipate surge energy?
• What determines the withstand capability?
• What is the failure/degradation mechanism
under surge energy condition?
• Surge energy is dissipated by avalanching
in device.
• Impact ionization process to accommodate
high current at breakdown voltage
• Avalanche energy (thermal-limited) is an
important JEDEC metric for power devices.
Si / SiC power MOSFETs GaN HEMTs
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• Tested 4 mainstream 600/650 V E-mode GaN HEMTs (in collaboration with companies)
• A unified mother board and three daughter boards
UIS Test of GaN HEMTs – Withstand Process
Center for Power Electronics Systems 24
R. Zhang…..Y. Zhang, International Reliability Physics Symposium (IRPS 2020)
• I: DUT on, inductor charging.
• II: DUT turn-off.
• III: Resonance between
inductor & device Coss, little
resistive energy dissipation.
• IV: Device 3rd-quad
conduction, resistive energy
dissipation via device,
inductor is dis-charged by
the power supply.
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UIS Test of GaN HEMTs – Failure Waveform and Boundaries
Center for Power Electronics Systems 25
Linear relationship between IL and
peak transient VDS (Vm):
• Drain-to-source leakage
• Gate is still functional
Company A
Device failure solely determined by
the transient peak voltage, not
surge energy, surge time, etc.
R. Zhang…..Y. Zhang, International Reliability Physics Symposium (IRPS 2020)
𝑽𝒎 = 𝑳𝑰𝑳𝟐/𝑪𝑶𝑺𝑺
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UIS Test of GaN HEMTs – Failure Analysis
Center for Power Electronics Systems 26
Company A Company B
• Emission microscopy +
cross-sectional SEM +
mix-mode TCAD
simulation
• Failure locations
consistent with peak E-
field locations
• Confirms the failure is
E-field inducted rather
than thermal limited
R. Zhang…..Y. Zhang, IEEE Trans.
Power Electron., early access, May. 2020
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Surge-energy Robustness: Si/SiC MOSFETs v.s. GaN HEMTs
Center for Power Electronics Systems 27
Si & SiC MOSFET: GaN HEMT:
Withstand process avalanching LC resonance & reverse conduction
Energy pathdissipation in device in
avalanching
little/no dissipation in withstand;
dissipation in reverse conduction
Limiting factor avalanche energy overvoltage capability
Failure mechanism thermal run-away E-field induced breakdown
R. Zhang…..Y. Zhang, IEEE Trans. Power Electron., early access, May. 2020
Is EAVA still the
best meaningful
metric for the
surge-energy
robustness of
GaN HEMTs?
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What is the implementation for converter-like switching?
Center for Power Electronics Systems 28
• In converters, the device typically undergoes
a clamped inductive switching, and the surge
energy is produced by circuit parasitics
• Designed a clamped inductive switching test
with controllable parasitic inductance
R. Zhang…..Y. Zhang, IEEE Trans. Power Electron.,
early access, May. 2020
Company A
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Surge-energy failure under clamped inductive switching
Center for Power Electronics Systems 29
• Test the device to failure
under different turn-off
current and parasitic
inductance
• Consistent failure
boundary with UIS (peak
transient voltage)
• The gate is still
functional, oscillation
continues, but due to
large drain-to-source
leakage under high
voltage, the device
ultimately fails thermally
R. Zhang…..Y. Zhang, IEEE Trans. Power Electron.,
early access, May. 2020
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Summary
June 10, 2020 Center for Power Electronics Systems 30
Physics
& Material
Proof-of-
concept Device
Demo
Large-area
Device
Manufacturing
Robustness &
ReliabilityConverter
ApplicationDevice
Design
Processing
Technologies
SiC (650-1700 V) & Lateral GaN (15-650 V)
(application at an unprecedented speed)Application-oriented
Reliability/Robustness
Vertical GaN:
New medium-voltage device beyond SiC
limit & new device designs and physics
(e.g. power FinFETs)
• Device manufacturing
• Reliability & robustness
• Fundamental material issues
• Converter applications
UWBG: fast progress, still not
competitive with SiC/GaN, far
from theoretical limit
• Distinct capabilities for PE applications?
• New processing and device technologies
• material-device-packaging co-optimization
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Center for Power Electronics Systems (CPES)
• 10 Tenure-track Faculty
- Founder (Director Emeritus): Fred C. Lee
- Director: Dushan Boroyevich
- 2 NAE members, 4 IEEE fellows
• 40 Ph. D. students & 20 master students
• 15 visiting scholars (academia & industry)
• 2 campus (Blacksburg & Arlington)
• New to devices and semiconductors
31
Statistics (1978-2017)
• 26 Startup companies founded by CPES alumni
• 19 CPES alumni in academia
• $158M Research expenditures
• 185 Masters degrees awarded
• 175 Ph. D. degrees awarded
• 298 Invention disclosure & 126 patents awarded
• 275 Visiting professors and industry members
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CPES Research Today
Technology Areas
Application Areas
Sustainable & Distributed
Electronic Energy
Systems
Vehicular
Power Converter
Systems
Point-of-Load
Conversion
Power Management
for Computers &
Telecommunications
watts to megawatts
Point of Load ConvertersTraction Converters Medium Voltage Converters
High Density
Integration
Modeling and
Control
EMI and
Power Quality
Power Devices &
Semiconductors
Power Conversion
Topologies and
Architectures
High-Power
High-Voltage
Converters
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CPES Industry Consortium and Funding Growth
Center for Power Electronics Systems 33