evaluation of sic diodes for smps applications€¦ · · 2001-10-06evaluation of sic diodes for...

Electrical Engineering and Computer ScienceUniversity of Illinois at Chicago

Evaluation of SiC Diodesfor

SMPS Applications

Prof. K Shenai


Commercial Power Converters

TRACTION

UTILITY

WASHINGCOOLING

AUTOMOTIVE

LIGHTING

FREQUENCY (Hz)

1

100

10k

1M

10 1k 100k 10M

UPS

ON-CHIP SUPPLIES

PORTABLE-POWER SUPPLIESLAPTOPDESKTOP

POW

ER R

ATIN

G (V

A)

Low-Power(<100 W)

Medium-Power(100 W-50 kW)

High-Power(>50 kW)

MAINFRAMES

TELECOM

SiC POWERELECTRONICSMOTOR CONTROL


250V/ 0.1A SiC Schottky Diode

0 0.5 1 1.5 2VOLTAGE (V)

MEASUREDMODELED

10-8

10-6

10-7

10-5

10-4

10-3

10-2

10-1

Defect-free

Excess current

n>1

Defect

Defect-free

Defect

RND

RD

A K

• Anomalies in forward conduction• Material parameters vary at defect sites• Ideality factor (n) represents quality of the diode• A good diode has n ~1

Static Characteristics Ideality Factor

1

1.5

2

2.5

3

3.5

275 300 325 350 375 400 425

TEMPERATURE (K)

MEASURED

MODELED

Non-defect, To = 80 K

Defect, To = 650 K

SurfaceLeakage

Ideal Diode


Forward I-V Characteristics

0 0.2 0.4 0.6 0.8 1 1.2VOLTAGE (V)

10-3

10-2

10-1

100

101

MODELEDMEASURED

T = 290 KT = 373 K

Schottky

PiN

CU

RR

ENT

(A)

Si Diode 4H-SiC Diode

100 V/1 A

200 V/1 A

0 1 2 3VOLTAGE (V

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

MODELEDMEASURED

Schottky

PNT = 290 KT = 423 K

CU

RR

ENT

(A)

200 V/1 A

200 V/0.1 A

Si diodes have much lower on-state voltage than SiC diodesDefect-induced excess current in SiC Schottky and PN diodes at low forward bias


Reverse Recovery Test Circuit

• Forward current adjusted with pulse width of Q1 gate pulse• Gate pulse is applied to Q1 to intiate reverse recovery of diode• Turn-off dI/dt is controlled by RG• Reverse recovery performance under various conditions of VDD, ION, diR/dt

Test Circuit Reverse RecoveryVDD

DUT

RG

VGG

CGD

CGS

Q1

S

L

R

ION: Forward CurrentdiR/dt: Turn-off di/dtdv/dt: Recovery dv/dtIrr : Peak Reverse Recovery Currenttrr : Reverse Recovery Time

ION

diR/dt

Irr

trr

dv/dt

VDD

+

-


Reverse Recovery Performance

-60

-40

-20

0

20

40

60

80

100

0 50 100 150 200 250

TIME (ns)-60

-40

-20

0

20

40

60

80

100

RG = 56 Ω

RG = 5.6 Ω

MEASUREDMODELED

CU

RR

ENT

(mA

)

VO

LTA

GE

(V)

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0 100 200 300 400 500

TIME ( ns )

MEASUREDMODELED

CU

RR

ENT

(A)

200 V/0.1 A4H-SiC Schottky Diode

VBUS = 50 V, ION = 60 mA

200 V/1 A4H-SiC PN Diode

VBUS = 40 V, RG = 10 Ω

Tail in turn-off current appears because of junction capacitanceSchottky diode reverse recovery independent of temperature

PN diode reverse recovery weakly dependent on on-state current

C (0V) = 25 pF C (0V) = 1 nF


DC-DC Buck Converter for Diode Testing

Hard Switching

Zero Voltage Switching

`

ControlCircuit

L f

C fR

VBUS

VGS DUT

ControlCircuit

L f

C fR

VBUS

VGS

Lr

Cr

DUT

time

timevD

iD

time

timevD

iD

iD+

-vD

iD+

-vD


DC-DC Buck Converter PerformanceSiC Schottky, SiC PN and Si PiN diodes

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

-0.1 0.2TIME (µs)

250V/0.1A SiCSchottky100V/1A SiCPiN100V/1A Si PiN

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

-5 0 5 10 15 20TIME (µsec)

250V/0.1A SiCSchottky

100V/1A SiCPiN

100V/1A SiPiN

Hard Switching Zero Voltage Switching

• Comparable switching performance of low-voltage SiC and Si PiN Diodes• Negligible switching transient in zero voltage switching configuration• Low voltage SiC devices only offer advantage of high-temperature operation


Hard-Switching Buck ConverterPerformance

-400

-300

-200

-100

0

100

200

300

0 5 10 15

TIME (µs)

VDIODE

VOUTPUT

Converter ParametersSwitch : 600 V/ 5 A Si MOSFETInductor : 5 mHCapacitor : 1 µFFrequency : 90 kHzI/O Voltage : 400 V/ 250 VOutput Power : 150 W

Si diode converter failed at 90 W, 30 kHz, 290 K


Simulation of Diode PerformanceHard-Switching of PiN Diodes

-25

-20

-15

-10

-5

0

5

0 0.05 0.1 0.15 0.2TIME (µs)

290 K

373 K

MEASUREDSIMULATED

CU

RR

ENT

(A)

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

0 0.02 0.04 0.06 0.08 0.1

TIME (µs)

SIMULATED

MEASURED

373 K

290 K

CU

RR

ENT

(A)

1.5 kV/10 A Si 3 kV/1 A 4H-SiC

Reasonable match between static and switching simulations and measurement4H-SiC material parameters from recent published reports


ZVS Buck Converter PerformancePiN Diodes

-0.10

0.00

0.10

0.20

0.30

0.40

17 19 21 23 25 27 29

TIME (µs)-150

0

150

300

450

600

MEASUREDSIMULATED

290 K

373 K

CU

RR

ENT

(A)

VO

LTA

GE

(V)

-0.05

0.00

0.05

0.10

0.15

0.20

18 20 22 24 26 28

TIME (µs)-90

0

90

180

270

360

MEASUREDSIMULATED

CU

RR

ENT

(A)

VO

LTA

GE

(V)


Reasonable match between static and switching simulations and measurement4H-SiC material parameters from recent published reports

VBUS = 200 V, IMAX = 0.6 A


Comparison of Si and 4H-SiCHigh-Voltage PiN Diodes

-14

-12

-10

-8

-6

-4

-2

0

2

0 0.05 0.1 0.15 0.2

TIME (µs)

290 K373 K

4H-SiC

Si

a

b

c

d

CU

RR

ENT

(A)

-0.15

0

0.15

0.3

0.45

0.6

14 16 18 20 22 24 26

TIME (µs)

290 K373 K

Si

4H-SiCCU

RR

ENT

(A)

Hard-SwitchingVBUS = 300 V, JF = 100 A/cm2

Soft-SwitchingVBUS = 200 V, JF = 100 A/cm2

SiC has negligible reverse recovery compared to Si under identical switching conditionsConsiderable performance improvement in Si diode with soft-switching (lower di/dt)


Charge Decay During Reverse Recovery(PiN Diode 2-D Simulations)

0 10 20 30 40 50

DISTANCE FROM SURFACE (µm)

a

b

cd

Net Doping

1013

1014

1015

1016

1017

1018

1019

CO

NC

ENTR

ATI

ON

(cm

-3)

0 50 100DISTANCE FROM SURFACE (µm)

a

bc

d

1013

1014

1015

1016

1017

1018

1019

Net DopingCO

NC

ENTR

ATI

ON

(cm

-3)


Si diode has very high excess charge in drift regionRapid charge decay in SiC diode because of low carrier lifetime

Current tail because of excess charge trapped in quasi-neutral drift region


Simulated PiN Diode Buck ConverterPerformance Trend

• Total power loss in Si diode isvery sensitive to switchingfrequency

• Frequency dependence of SiCdiode above 300 kHz

• Total loss in SiC diodedominated by conduction loss

• Switching loss in Si diodeappears because of excesscharge removal

• Switching loss in SiC diodeappears because of junctioncapacitance

300 V/150 V, 90 W, 373 K

PD = DVON ION + Esw fsw

0.1

1

10

FREQUENCY (Hz)

JF = 100 A/cm2

JF = 30 A/cm2

JF = 6 A/cm2

Si

4H-SiC

103 104 105 106

TOTA

L PO

WER

LO

SS (W

)

1.5 kV/1 A

3 kV/1 A

Electrical Engineering and Computer ScienceUniversity of Illinois at ChicagoReliability Testing of Diodes

• Performance evaluationwas conducted at voltageand current levels muchlower than rated values

• Fragile SiC devices

• Assessment of devicereliability is crucial

• Dynamic stress testing todetermine avalancherating of SiC diodes

TEST CIRCUIT

TYPICAL WAVEFORMS


High-TemperatureControl

High-Density SiC Power Converters

Robust SiCPower Converter

Choice ofCircuit Topologies

Packaging(High temp., modular)

Optimal Edge Termination

New Device Structures

Magnetics, Passives


NASA Schottky Diodes

• Performance evaluation of 4H-SiC schottky diodes was conducted

• Comparative study of diodes with different perimeters and areas was conducted

• Tests were conducted to evaluate the dv/dt withstanding capability of the diodes

• 5 identical samples of each device were tested for consistency in results

• All devices were rated at I kV


Breakdown Performance

0

100

200

300

400

500

600

700

800

0 50 100 150 200 250DIAMETER (µm)

MaximumAverageMinimum

T = 298 K

VO

LTA

GE

(V)

• Strong area dependence of breakdown voltage was observed

• Highest breakdown voltage of 750 V was measured on a 50 µm device

• Lowest breakdown voltage of 100 V was measured on a 200 µm device

MEASURED RESULTS

• High temperature breakdown measurements were not performed


Forward I-V Characteristics

VOLTAGE (V)

CU

RR

ENT

(A)

0 0.5 1 1.5 2

200 u

100

10-3

10-9

10-6

10-12

VOLTAGE (V)

200 µ

NON - DEFECTIVE DIODE I-V DEFECTIVE DIODE I-V

• Leakage current increases with temperature

• Defective diode current starts rising rapidly at very low bias voltages

0 0.5 1 1.5 2

25 C50 C100 C150 C

10-3

100

10-6

10-9

10-12

CU

RR

ENT

(A)

200 µ


Forward J-V Characteristics

0 0.5 1 1.5 2

200 µ150 µ100 µ70 µ50 µ30 µ

102

10-2

10-4

10-6

10-8

10-10

10-0

CU

RR

ENT

DEN

SITY

(A/c

m2 )

VOLTAGE (V)

T = 290 K

0 0.5 1 1.5 2

200 µ150 µ100 µ70 µ50 µ30 µ

102

100

10-2

10-4

10-6

10-8

10-10

VOLTAGE (V)

CU

RR

ENT

DEN

SITY

(A/c

m2 ) T = 373 K

• Influence of perimeter on leakage current density is negligible

MEASURED WAVEFORMS


Perimeter/Area Dependence

0 500 1000 1500

25 C50 C100 C150 C

10-10

10-12

10-14

10-16

10-8

PERIMETER/AREA (cm-1)

SA

TUR

ATI

ON

CU

RR

ENT

DEN

SITY

(A/c

m2 )

• Saturation current densities were extracted from the J-V characteristics• Saturation current density is independent of P/A ratio• No perimeter recombination current along the periphery because of absence of a junction


Ideality Factor Extraction

• Ideality factor was extracted from forward I-V characteristics

• Room temperature ideality factor ranged from 1.22 - 1.33

• Ideality factor decreases with temperature

1.16

1.2

1.24

1.28

1.32

1.36

0 50 100 150 200TEMPERATURE (oC)

200 µ150 µ100 µ70 µ50 µ30 µ

IDEA

LITY

FA

CTO

R n =1

∂(ln IF )∂VF

VT

• Thermionic emission current contribution is more at higher temperatures.

• Therefore the ideality factor approaches unity

Electrical Engineering and Computer ScienceUniversity of Illinois at ChicagoReliability Testing of Diodes

• Performance evaluationwas conducted at voltageand current levels muchlower than rated values

• Fragile SiC devices

• Assessment of devicereliability is crucial

• Dynamic stress testing todetermine dv/dt rating ofSiC diodes

TEST CIRCUIT

TYPICAL WAVEFORMS


dv/dt Characterization

• Diode current increased at higher dv/dt • dv/dt varied from 4V/ns to 30 V/ns• With a 250 V switch the DUT survived the highest applied dv/dt• With a 500 V switch the device failed even for the lowest dv/dt• Failure was voltage dependent rather than dv/dt

DIODE WAVEFORMS

0

50

100

150

200

250

300

350

400

-

0 pF80 pF220 pF330 pF

20 20 60 100

TIME (nS)V

OLT

AG

E (V

)

200 µ

CS

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06

-

0 pF80 pF220 pF330 pF

20 60 100-20TIME (nS)

DIO

DE

CU

RR

ENT

(A)

200 µ

CS


SiC Diodes for

SMPS applications


Forward I-V CharacteristicsC

UR

REN

T (A

)

VOLTAGE (V)

0 0.2 0.4 0.6 0.8 1

25 C75 C125 C175 C

101

10-1

10-3

10-5

10-7

10-9

10-11

10-13

Device D1

0 0.2 0.4 0.6 0.8 1

25 C75 C125 C175 C

10-0

10-2

10-4

10-6

10-8

10-10

10-12

10-14

CU

RR

ENT

(A)

VOLTAGE (V)

Device D2

• 5 samples of each device were tested for consistency• Leakage current increases with temperature

MEASURED WAVEFORMS



0 200 400 600 800

25 C75 C100 C125 C150 C175 C

0

50

100

150

200

250

CU

RR

ENT

(µA

)

VOLTAGE (V)

Device D2Sample # 1

0 100 200 300 400 500 600

25 C75 C100 C125 C150 C175 C

0

50

100

150

200

250

CU

RR

ENT

(µA

)

VOLTAGE (V)

Device D1Sample # 1

MEASURED WAVEFORMS

• Breakdown voltage decreases with increase in temperature



480

490

500

510

520

530

540

550

560

570

0 50 100 150 200

#1#2#3#4#5

VO

LTA

GE

(V)

TEMPERATURE (･C)

• 5 samples of device D1 were characterized

• Sample # 2 failed during testing

• For every 1････C rise in temperature the voltage drops by 0.5 V approximately

Device D1



640

660

680

700

720

740

760

0 50 100 150 200

#1#2#3#4#5

VO

LTA

GE

(V)

TEMPERATURE (･C)

Device D2

• 5 samples of device D2 were characterized.

• Sample # 2 and 5 failed during testing.

• For every 1････C rise in temperature the voltage drops by 0.6 V approximately.


Ideality Factor Extraction

TEMPERATURE (･C)

IDEA

LITY

FA

CTO

R

0.99

1

1.01

1.02

1.03

1.04

1.05

1.06

0 50 100 150 200

Device D1Device D2

Ideality factor was extractedfrom the expression for diodeforward current

Ideality factor approaches unitywith increase in temperature.

n =1

∂(ln IF )∂VF

VT

• Thermionic emission current contribution is more at higher temperatures


Barrier Height from forward IV

TEMPERATURE (･C)

BA

RR

IER

HEI

GH

T (e

V)

1.23

1.24

1.25

1.26

1.27

1.28

1.29

0 50 100 150 200

Device D1Device D2

Where A** is Richardson’s constant VT is the Thermal Voltage

Since n ≡≡≡≡ 1 the barrier height was extracted using the simplified expression for JS

φB = VT ln(A**T 2

JS

)


Barrier Height from C-V Characteristics

1.25

1.29

1.33

1.37

1.41

1.45

0 50 100 150 200

Device D2Device D1

TEMPERATURE (･C)

BA

RR

IER

HEI

GH

T (e

V)

• Doping concentration and device Area were provided.

• Using the device area and the slope of the (1/C2)-V plot the doping was extracted from the expression for Capacitance.

• Extracted value of doping was then used to estimate the barrier height

C = A qεS ND

2(VR + Vbi − kTq

)

φB°=Vi +

kTq

+EG

2q−

kTq

ln(ND

ni

)

Vi is voltage intercept (1/C2)-V plotVbi is the built in voltage


Reverse RecoveryMeasurement Procedure

• Devices Under Test (DUT)• D1• D2

• Measurements were performed at:– Three different forward currents (2A, 4A and 6A)– Three different temperatures ( 25 ･C, 75 ･C, 125 ･C )– Three different bus voltages ( 200V, 250V,300V )

IF

Irr

trr

di/dt


Test Circuit

Device D2

CU

RR

ENT

(A)

VO

LTA

GE

(V)

TIME (µs)

-12

-8

-4

0

4

8

12

-300

-200

-100

0

100

200

300

0 0.05 0.1 0.15 0.2

di/dt = 315 A/µsVBUS = 200 VT = 125°CIF = 10 A


Measured Results

Device D1

I RR

M (A

)

E off (

µJ )

IF (A)

00.20.40.60.8

11.21.41.61.8

2

0 2 4 6 80

1

2

3

4

5

T= 25 °C

VBUS = 300 Vdi/dt = 230 A/µs

I RR

M(A

)

E off (

µJ )

di/dt (A/µs)

00.20.40.60.8

11.21.41.61.8

2

0 100 200 300 4000

1

2

3

4

5

VBUS = 300 V

IF = 6 A

25 ･C125 ･C


Measured ResultsI R

RM

(A)

E off (

µJ )

0.5

1.5

2.5

3.5

di/dt (A/µs)

E off (

µJ )

TEMPERATURE ( ･C )

I RR

M(A

)

0.5

1.5

2.5

3.5

00.20.40.60.8

11.21.41.61.8

2

0 100 200 300 4000

1

2

3

4

5

IF = 4 AVBUS = 300 V

T= 125°C

00.20.40.60.8

11.21.41.61.8

2

0 50 100 1500

1

2

3

4

5


di/dt = 350 A/µs

Device D1


Measured ResultsI R

RM

(A)

E off (

µJ )

IF (A)

I RR

M (A

)

E off (

µJ )

di/dt (A/µs)

00.20.40.60.8

11.21.41.61.8

2

0 2 4 6 80

1

2

3

4

5

T= 25 °C

VBUS = 300 Vdi/dt = 200 A/µs

00.20.4

0.60.8

11.21.4

1.61.8

2

0 100 200 300 4000

1

2

3

4

5

VBUS = 300 V

IF = 6 A

25 ･C125 ･C

Device D2


Measured ResultsI R

RM

(A)

E off( µ

J )

di/dt (A/µs)

E off (

µJ )

I RR

M (A

)

TEMPERATURE ( ･C )

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 100 200 3000

1

2

3

4

5

T= 125 °C


00.20.40.60.8

1

1.21.41.61.8

2

0 50 100 1500

1

2

3

4

5


di/dt = 315 A/µs

Device D2


Conclusion

• SiC Schottky diodes show promise for SMPS applications.

• Needs further investigation in key SMPS circuits

• SiC device reliability needs to be investigated in detail.

evaluation of sic diodes for smps applications€¦ · · 2001-10-06evaluation of sic diodes for...

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