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

Page

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

Page

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

Page

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.

Page

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.

Page

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.

Page

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)

Page

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

Page

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

Page

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