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Separate MOSFET and Bond-wire Resistance

Monitoring for SiC MOSFETs

Nick Baker

CORPE

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VDS is commonly used for condition monitoring

How to know when VDS signals end-of-life?

- VDS is influenced by junction temperature, gate driver condition,

bond-wire health, threshold voltage... Etc. Same for IGBTs

- Hard to know what causes increase without post-failure analysis.

Therefore difficult to predict end-of-life.

MOSFET

D

S

G

VVVDS

Bond-wire

Typical VDS measurement includes both

MOSFET (or IGBT) and bond-wire voltage

What is the cause of increase in on-resistance (calculated

using VDS), since VDS includes both die and bond-wire. At

which point is end-of-life signified?

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VDS in a 4-terminal device

2 on-state voltage measurements: VDS and VSS

- Use of Kelvin-source (or emitter) becoming more common

- VDS covers MOSFET die (could also be IGBT)

- VSS covers bond-wires

- MOSFET die resistance and bond-wire resistance can be

calculated separately

VSS

MOSFET

D

S

G

Bond-w

ire

Aux. S

VDS

VDS Measurement Circuit [17] Instrumentation Amplifier

Schematic for online VSS and VDS measurements Prototype Measurement Board

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First Proof-of-Concept

Faulty gate driver

- Emulate MOSFET/gate driver

related failure

- Single phase inverter with gate

driver positive voltage at 15V

and a ‘faulty’ condition of 12V

- MOSFET die resistance

increases by 10mΩ

- Bond-wire resistance shows no

change

- Fault in MOSFET side

detected

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First Proof-of-Concept

Power Cycling Test of 20A SiC MOSFETs

- 3 MOSFETs - 50k Temperature cycles

- Opposite trends in MOSFET and bond-wire resistance

- MOSFET resistance decreases slightly or no change

- Bond-wire resistance increases up to 2mΩ

Bond-wire resistance increases up to 2mΩ MOSFET Resistance decreases slightly – maximum 1mΩ

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Conclusion

Online measurements of die and bondwire resistance

- Possible in devices with a kelvin-source or kelvin-emitter

- Can separate die and bond-wire degradation

- Can provide more information to help predict why and when a

device will fail – reduce chance of false positives

- Full accelerated aging tests will be carried out on IGBTs and

MOSFETs

VSS

MOSFET

D

S

G

Bond-w

ire

Aux. S

VDS

VDS Measurement Circuit [17] Instrumentation Amplifier