Wide Band Gap Power Device Evaluation Challenges and Technologies
Ryo Takeda
Solution Architect
Keysight Technologies
November 2016
Page
Application Requirements from Modern Power Electronics
Motor drive system
Presented by
Yaskawa Electric
Corp. SiC
Si
Improved conversion efficiency
Volume and weight reduction Use in harsh environments
2
Page
Why Use Wide Band Gap (WBG) Semiconductors
Higher frequency operation Smaller passive circuit components
Lower power loss Better conversion efficiency =
Smaller / Lighter cooling system
Higher temperature operation Smaller / Lighter / Sealed cooling system for
harsh environment use, (e.g. excavator use)
WBG properties Benefits
3
Page
Expected Application Map for SiC/GaN
0
5
10Breakdown voltage
Operation speedOn-resistance
GaN
SiC
• SiC: Suitable for very high power (high current / high voltage) application
• GaN: Suitable for middle range power application
Gate
Drainn+ Substrate
n-
p-
Source
n+
Gate
Substrate
Buffer layern-GaN
AlGaN
Source Drain
SiC: Vertical
GaN: Lateral
4
Page
Expected Application Map for SiC/GaN
On-board
power supply
General
purpose
inverter
Industrial
equipment
Electrical
train
Backbone
electricity
Switching
power
supply
New
energy/
Distributed
PS
Hybrid /
Electric
vehicle
HDD
Automotive
electronics
Home
appliances
Voltage rating (V)
Cu
rre
nt ra
tin
g (
A)
2000
10 1000020 50 100 200 500 1000 2000 5000
1000
500
200
100
50
20
10
5
2
1
Communic
ation
equipment
GaN
SiC
5
Page
Critical Evaluation Items for SiC/GaN
6
• High Current
• High current is often used in actual operation in many applications
• Ron becomes smaller and therefore high current is mandatory for accurate Ron
evaluation. Ron is important to calculate conduction loss.
• High Voltage
• Basic parameter but one of the most important parameters from reliability perspective
• Temperature dependency
• Various power electronics products are used in harsh environment
• Capacitance (Ciss, Coss, Crss, Rg, Normally-on device)
• Critical parameters for switching performance
• Important to estimate power losses such as output capacitance loss, etc.
• Gate Charge
• Critical parameter for switching performance and gate drive circuit design
• Important to estimate switching loss
• Reliability
• Long term reliability is one of the main concerns when adopting new/emerging devices
Especially important for SiC
Especially important for SiC
Especially important for GaN
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Challenges in SiC/GaN Device Evaluation
7
• Lack of Standard Solution• How many hours have you invested in isolating your test problems?
• Device manufacturers also suffer the lack of reference measurement equipment
• Device users have no easy way to make accurate device evaluation
• High Voltage / High Current• Accuracy is questionable without having a well thought test circuit and NIST traceable
standard
• Temperature dependency• Long cable extension from test equipment to thermostatic chamber results in:
• 1) current reduction, 2) oscillation, and 3) deteriorated accuracy
• Capacitance (Ciss, Coss, Crss, Rg & Normally-on)• Complicated connections and special techniques result in many measurement
problems
• Gate Charge• Difficult to construct a test system with good accuracy and safety
• Intuitive and Standard User Interface• Anybody should be able to conduct device evaluation without training
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High Current / High Voltage
8
Many factors to take into account for accurate high power test
Standard solution with NIST traceability is required in all aspects of the power
electronics industry.
Fast pulse to avoid self heatingAppropriate test circuitry
A
V
Low
High
Both voltage & current sources
Short, low L and low R cables for
high current & fast rise time Guarding for low leakage at high
voltage test
Traceability to international
standard
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Issues with Temperature Dependency Test using Thermostatic Chamber
Thermostatic chamber Measurement equipment
• Time consuming set up / measurement
• Extremely slow test throughput. Only a few tests performed a day
• Long cable causes several issues
• Lowered maximum current
• Deteriorated accuracy
• High risk of oscillation
9
Although the temperature dependent test is important most people don’t perform it
due to problematic measurement and long test time. Fast and accurate thermal test
equipment is necessary across the entire power electronics industry.
Page
Issues Associated with Capacitance Measurement (1)Measuring Crss?
Ciss = Cgd + Cgs
Coss = Cgd + Cds
Cgd
(=Crss)
Cds
Cgs
D
S
High
G
LCR meter
Low
V
Cgd
Lc
Lp
Hp
~
A
Hc
Cds
Cgs
Igd
Ids
Ids
IgdIgd
Drain
Gate
Source
+Igd
~
10
Page
Issues Associated with Capacitance Measurement (2)Measuring Ciss with high voltage bias?
Ciss = Cgd + Cgs
Cgd
(=Crss)
Cds
Cgs
D
S
High
G
LCR meter
Low
Drain – Source
shorting cable
AC Blocking Resistor (e.g.
100kΩ >> ZAC short)
Cgd
(=Crss)
Cds
Cgs
D
S
LCR
meter
Low
A
High Voltage Bias-T
G
DC Blocking & AC
Short Capacitor
(>>Cds)
High
11
Complicated test circuit with manual connection changes make the capacitance test
challenging and result in human errors, an industrial solution is required for users of
power devices.
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Issues with Gate Charge Measurement
Courtesy of International Rectifier
1. Difficult to prepare a power source at drain that has enough simultaneous current and
voltage capacity. Using a capacitor is a solution. However, it has safety issues.
2. Difficult to prepare a constant current source which has small enough current to allow slow
gate charge accumulation for accurate sampling.
3. Device is likely to be destroyed by measuring at up to rated current with high voltage bias.
12
Designing a safe and accurate test system is difficult, an industrial solution is
required for users of power devices.
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Standard Solution Example
13
Keysight B1506A Power Device Analyzer
B1506A
Critical power device test technologies
NIST traceabilityDatasheet format Software I/F
Datasheet format report
A
V
Low
High
Full automation through IV, CV switches
G
D
S
Ma
infr
am
e
DC switches
Sw
itch
es
Device
capacitan
ce
selector
GuardingKelvin connection
Low L, R cables
SMU technology
Fast pulses
key points
• To cover critical power device test technologies when building test system or test instrument
• To make the instrument NIST traceable in order to deploy the test system to different locations.
Calibration standard must be built first to make it happen.
• Switching matrix that change the test resources connected to DUT is necessary to make the
automated and reliable test system. For FET capacitance test, the matrix should include DC
blocking capacitor and AC blocking resistor.
• User interface should be easy enough. One example is to simulate datasheet, which is friendly
to device manufacturer and device users.
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3 Terminal FET Capacitance Measurement
14
Circuit Diagrams
A
SMU
~
V
LCR meter
D
S
GACMH
CML
Cds
Cgd
SMU
A
Coss
A
SMU
~
V
LCR meter
D
S
GA CMH
CML
Cgs
Cgd
SMU
A
Ciss
A
SMU
~
V
LCR meter
D
S
GACMH
CML
Cgd
SMU
A
Crss
G
D
S
Ma
infr
am
e
DC switches
Sw
itch
es
Device
capacitan
ce
selector
DC blocking C
(>> Cgd,Cds)
Necessary for
normally-on
device
AC blocking RAC blocking R
(e.g. 100 kΩ)
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Fully Automatic Temperature Dependency Test Example
15
With Thermostream
(-50°C to +220°C)
With hot plate
(Room temp to +250°C)
key points
• To bring test resource (i.e. current amplifier in a test fixture) near
DUT in order to reduce cable inductance and therefore maximize
current and reduce the chance of oscillation
• To use thermal equipment that can be controlled via computer.
• To avoid condensation in the fixture when cooling DUT
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Novel Qg Measurement Method
G
D
S
AV
Constant Ig DUT
Gate drive SMU
A
High Voltage SMU
CLK
G
D
S
AV
AV
ARout
V
Lout
+
-
Constant Ig
Current
regulation FET
DUTUltra high current unit
Gate drive SMU
Floating SMU
to control Id
CLK
16
key points
• To separate Qg measurement into two, 1) high voltage low current
measurement and 2) low voltage high current measurement
• To regulate maximum current with another FET
• To use SMU in order to apply precise current to the gate
• Fast sampling to monitor gate voltage and drain current changes
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Reliability Test System Concept
17
• Choose instrument that has enough voltage or current range for reliability testing
• Use multiple instruments in order to give stress to multiple devices simultaneously
Page
Summary
18
• Wide Band Gap devices brings about new measurement challenges
• High voltage
• High current (Accurate Ron)
• Temperature dependency
• Capacitances & Rg
• Gate charge
• A standard solution is necessary across the entire power electronics industry
• Consistent test results in any location every time
• Everyone should make evaluation without having product training
• Keysight provides a product that fills the gap