trench based sic power mosfets an example how to merge ... · 3/6/2018 · extreme high volume...

Trench based SiC power MOSFETs – an example how to merge performance, robustness and further application relevant features

Dr. Peter FriedrichsSenior Director SiC, Infineon Technologies AG

12018-03-06 Copyright © Infineon Technologies AG 2018. All rights reserved. Infineon Proprietary

Outline

SiC transistors – brief introduction and target use cases

SiC MOSFETs – design goals and philosophy for Trench

Driving SiC MOSFETs efficiently

Summary

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Outline




Summary

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Power semiconductors provide new potentials along the whole electrical energy supply chain

Energy generationEnergy

transmissionEnergy

consumption


SiC MOSFET – what differentiates towards the IGBT – less losses, less space in the module

Benchmark in switching lossesIntegrated freewheeling diode

Knee voltage free on state


fsw [Hz]

Pout [W]

1k

1k 10k 100k 1M

1M

10k

100k

10M

10M

Silicon

SiC

GaN

Central PV*

› Remains mainstream technology

* PV = photovoltaic inverter; ** OBC = onboard charger

String PV*

pile

OBC**

Reliability and robustness assurance in SiC strongly linked to silicon mainstream technologies

SiC is excepted to complement silicon in many applications and

to enable new solutions


Industrial grade Automotive grade

1st wave CoolSiC™ MOSFET is designed for certain initial applications

Bare dieDiscreteModule

Infineon offers CoolSiC™ solutions as chips, discretes and modules

Photovoltaic EV charging

UPS/ SMPS1)

xEV (OBC)

1) UPS = uninterrupted power supply; SMPS = Switched-mode power supply

xEV (inverter)

Traction

Drives

2nd

wave


Outline




Summary

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Multiple levers for a SiC MOSFET must match

Static behavior

Short Circuit capability

Gate oxide reliability

Threshold voltage

Dynamic behavior

Ease of use

Performance Robustness&Manufacturing stability

Stable chip process

and more…



Static behavior



Threshold voltage

Dynamic behavior

Ease of use


Stable chip process

and more…


Reliability – Oxide lifetime – Planar MOS vs. Trench MOS

DMOS

Trench

n-

e e e e

High density of defects in the so called channel region

n-

pe

e

One order of magnitude lower defect density in channel region

Plus better outlook regarding cell shrinking as proven in Si technology


SiC MOSFET concepts – options to design a reliable component

DMOS half cell Trench MOS half cell

Channel Resistance(due to µcha)

high low low

GOX Field on-state low high low

GOX Field off-stateuncritical

uncritical if design appropriate

GOX Reliability high low high

pn+

Gate

n- n-

p

n+

GOX: Gate oxide – thin insulating layer for control of the device, most sensitive part of the device


Main conclusion

Oxide reliability topics in SiC are more critical in on state

› This stress is permanently applied and does affect the complete oxide

Reverse mode is of minor importance for the real application

› Only a fraction of the maximum rated voltage is really applied in the application

› Just a small area of the oxide is stressed

› HTRB stress at biases higher than the rated Vdsmax

is misleading and will overestimate the extrapolated lifetime due to cosmic ray overlap


New opportunities by modern Trench-CoolSiC™ Technology from Infineon

Best Rdson at robustness levels equivalent to IGBT based systems

DMOS

Trench

vs.

n-

e e e e

strong trade-off between performance and gate oxide robustness in on-state

n-

pe

e

easier to reach performance without violating gate oxide safe conditions

Perf

orm

ance

Robustness

positioning



Static behavior



Threshold voltage

Dynamic behavior

Ease of use


Stable chip process

and more…


CoolSiC™ MOSFET comes with IGBT compatible gate driving and control

0

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Vendor A Vendor B Vendor C Infineon

Vgs

,th

[V

]

Vgs,maxVgs,typVgs,min 4.5 V

3.5 V

› 1200 V CoolSiC™ MOSFET needs only +15 V for turn-on similar as a conventional IGBT

› High Vgs(th) gives highest robustness against parasitic dv/dt triggered turn-on


SiC MOSFETs need the feature to be externally slowed down – example CoolSiC™ MOSFET

Rg controllable di/dt and dv/dt

I(t)

t

RG

Impact of Rg on dv/dt

MOSFET

IGBT

› Controllability of current and voltage slopes with a simple change of the gate resistor

› Essential pre-condition to cope with EMI aspects


50 pF x 50 kV / 1 µS ≈ 2.5 A

GateDriver

GateDriver

Current will complete loopback to the module

SupplyTransformer

Ease of use – Effects of high dV/dt – EMI and capacitive coupling


Module Layout

& PCB layout

What are the keys for package and interface to the system ?

Low Inductance

& Symmetry

IN BOTH


Low inductance and symmetry in a module design – stripe line based case study

Strip line based DC in and out Symmetric chip positioning

Integrated body diodes allow for more flexibility in module designs while keeping symmetry and low inductance

requirements


Outline




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SiC offers a lot of new design optionsin 1200 V

› SiC MOSFETs are fast switching devices, which can reach 50 V/ns or even above. Timing is crucial.

› SiC MOSFET have a freewheeling body diode without recoveredcharge Qr, but with a high forward voltage VF

› SiC MOSFET might need a negative gate voltage

› SiC MOSFET have only a reduced short circuit capability today

Rds(on)

iRt

Irrm

vR

VRQr


Propagation delay for fast switching –Keep tolerances under control: input filter

Integrated filter leads to lower propagation delay variation

Integrated ramp-based filter External RC filter

VCVC

Increasedspread

t

Vtrig

Vmax

Vmin

tmin ttrig tmax

VC Capacitor charge curve:

tightspread

t

Vtrig

Vmax

Vmin

tmin ttrig tmax

VC Capacitor charge curve:

External filters (with R and C tolerances) increase propagation delay and propagation delay variation

If I can, I decide for integrated filters


High DC-link voltages lead to longer exposureto dv/dt stress

› Isolated gate drivers are used in state-of-the-art in systems with IGBT in half bridge configurations and a DC voltage up to 900 V

› Modern power transistors (e.g. CoolSiC™) allow very high dv/dt

› The intervals with dv/dt are long in systems with high DC voltage

› Noise which is generated by dv/dt mayoverride the isolated signal transfer due to coupling capacitances

› The gate driver ICs are key componentswhich have to be CMTI proof in voltage amplitude and voltage slope

› Other parts, e.g. PCB can also contributeto CMTI noise

VDCIsolated

gate driver

T1 D1

T2 D2

PWM

GND GND

Cpar1

...

Cpar2


Single transistor topologies

› Flyback, buck and boost converters are popular single transistor converters

› Passive dv/dt events do not occur during the off-state

› Strongly reduced threat of parasitic dv/dt triggered turn-on

› Driver ICs with active miller clamp and unipolar gate supply can be sufficient

TFB

VOUT

VIN

LPFC

SiC

iT

C1

GD

Tbuck

VOUT

VIN

LbuckSiC

iT

C1

GDSiCTPFC

VOUT

VIN

LPFC SiC

iTC1

GD


A fast short circuit detection capability is important for SiC MOSFETs

› Its SC capability 3 µs absolute maximum rating (not every vendor !)

› The DESAT-to-shutdown delay of EiceDRIVER™ is max. 430 ns

› The DESAT function of driver ICs should therefore use only a short blanking time of approx. 1 – 2 µs

› A tuning for DESAT trigger at low MOSFET voltages is possible by using‒ a higher value for RDESAT, e.g. 10 kW or‒ a zener diode in series to RDESAT

› SiC MOSFET trigger voltage:

= 9 V − 500 µA 𝑅DESAT − 0.7 V

𝑣T,trig = 9 V − 𝑣RDESAT − 𝑣DDESAT


Outline




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Infineon's 1200 V MOSFET chip –major features

› RDS,on*A=3,5 mΩcm² (typical)

› RDS,on=45 mΩ typ. @Tvj=25°C

– Increase by 50% @ 150°C

› VGS,th=4.5 V (typical) @ID=1 mA, VDS=VGS

› Body diode enabled for commutation

› Avalanche capable device

› IGBT like FIT rates

› Gate control window: 15 V/-5 V

– Gatecharge: typ. 62 nC

Simultaneous achievement of those parameters in one device unique worldwide


Extreme high volume flexibility

and reliability proven by multi

million track record

Most comprehensive power portfolio

in the market ensures always

best-fit

Innovative technology andexpertise in allleading powermaterials(Si, SiC, GaN)

Key ingredients for a successful roll out of SiC in mainstream applications

Extensiveapplicationsystem under-standing andglobal support

Unique power technology portfolio

Benchmark in manufacturing

Extensive system expertise Application-dedicated products

Ensure highest quality, ideally comparable with the established silicon world, cost effective and

scalable production

Optimize the product for its target application, provide a bundle (e.g. package, driver

etc.) enabling easy implementation to speed up

design in

Help our customers in the design in phase of new components by training, demos and

on-site support


trench based sic power mosfets an example how to merge ... · 3/6/2018 · extreme high volume...

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