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7/29/2019 809pet Silicon Carbide Mosfets Igbt
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In light o recent silicon carbide (SiC) technology advances, commercial production o
1200-V 4H-SiC[1]power MOSFEs is now easible. Tere have been improvementsin 4H-SiC substrate quality and epitaxy, optimized device designs and abricationprocesses, plus increased channel mobility with nitridation annealing.[2] SiC is abetter power semiconductor than Si, because o a 10-times higher electric-eldbreakdown capability, higher thermal conductivity and higher temperature opera-
tion capability due to a wide electronic bandgap.SiC excels over Si as a semiconductor material in 600-V and higher-rated breakdown
voltage devices. SiC Schottky diodes at 600-V and 1200-V ratings are commercially avail-able today and are already accepted as the best solution or eciency improvement in boost
converter topologies. In addition, these diodes nd use in solar inverters, because they have lowerswitching losses than the Si PIN reewheeling diodes now used in that application.
At 600-V and 1200-V ratings, IGBs have been the switch o choice or power conversion. Previously,Si MOSFEs were handicapped in those applications by their high on-resistance (RDSON). At high breakdownvoltages, RDSON increases approximately with the square o the drain-source breakdown voltage VDSMAX.
[3]Te RDSON o a MOSFE consists o the sum o the channel resistance, the inherent JFE resistance
and the dri resistance (Fig. 1). Te dri resistance (RDRIF
) is the dominant portion o the overallresistance, where d equals dri-layer thickness, q equals electron charge, n equals channel
mobility and ND
equals doping actor.Te new generation o SiC MOSFEs cuts dri-layer thickness by nearly a ac-
tor o 10 while simultaneously enabling the doping actor to increase by the same order omagnitude. Te overall eect results in a reduction o the dri resistance to 1/100th o its Si
MOSFE equivalent.he improved SiC MOSFE
discussed here is an engineeringsample o a 1200-V, 20-A devicewith a 100-mV RDSON at a 15-Vgate-source voltage. Besides its in-herent reduction in on-resistance,SiC also oers a substantiallyreduced on-resistance variationover its operating temperature.From 25C to 150C, SiC varia-tions are in the range o 20%,compared with 200% to 300% orSi. Te SiC MOSFE die is capableo operation at junction tempera-tures greater than 200C, but theengineering sample is limited in
By Michael ONeill,Applications Engineering Manager, CREE, Durham, N.C.
SiC technoog has undergone signifcantimprovements that now aow abricationo MOSFETs capabe o outperormingtheir Si IGBT cousins, particuar at highpower and high temperatures.
SiliconCarbide
Challenge
14
Fig. 1. Cross-section o DMOSFET power transistor shows its
resistive components: the channel resistance, the inherent
JFET resistance and the drit resistance that combine to
produce a relatively high on-resistance.
Ni
Ni
N+
Source
P-well
N type substrate
Gate metal
Gate oxide
RCHANNEL
RJFET
RDRIFT
P+
Ni
N+
Source
P-well
P+
RDRIFT =d
qnND
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temperature to150C by its O-247 plastic package.Compared with a Si IGB, a SiC MOSFE has a substan-
tial advantage in conduction losses, particularly at lowerpower outputs. By virtue o its unipolar nature, it has no tailcurrents at turn-o, thereby leading to greatly reduced turn-o losses. able 1 shows the switching loss dierence whencompared with a standard o-the-shel 1200-V IGB.
Te switching losses o a SiC MOSFE are less than halthose o a Si IGB (1.14 mJ versus 2.6 mJ, respectively). Com-bining this switching-loss reduction with the lower overallconduction losses, it is clear that the SiC switch is a muchmore ecient device or high-power-conversion systems.
Three-Phase Solar Invertero demonstrate its application as a solar inverter, a 7-kW,
16.6-kHz three-phase grid-connected system was imple-mented. Tis B6 topology, developed by the FraunhoerInstitute ISE, uses a split-link dc capacitor with a connectiono the neutral conductor to the center point o both capaci-
tors. Te unit connects to a 400-V grid, using 1200-V IGBsas the standard power-conversion devices. Tese IGBswere replaced by 1200-V SiC MOSFEs, and the signicantperormance dierence is clearly visible in Fig. 2. able 2shows the maximum eciency and European-eciencyimprovements that were achieved.
As seen by the Fig. 2 curves, the SiC devices oer a peror-mance advantage over their Si IGB counterparts. Maximumeciency increased by 1.92%, and the overall Euro-eciencyrating improved by 2.36%. Tis equates to a 50% reductionin overall losses in the system.
Another perormance-parameter improvement o notewas the systems reduction in heatsink temperature at ull-rated power output. At a 25C ambient, the nal steady-stateheatsink temperature with the IGBs was 93C versus 50Cwith the SiC MOSFEs.[3]
Tere are several dierent ways o looking at the systembenets obtainable by using a ull SiC-based solution in aphotovoltaic (PV) power converter:
lCost o inductive components. Te volume o an induc-tive component depends most signicantly on the systemswitching requency. A good approximation is a reduction
Fig. 2. Comparison o 1200-V SiC DMOSFET and 1200-V Si IGBT
eciencies in a three-phase inverter shows that at the same
voltage rating, the higher-eciency SiC DMOSFETs provide a
perormance advantage over their Si IGBT counterparts.[3]
Table 1. Switching loss comparison.[2] Table 2. Measured eciencies (single-phase inverter).[2]
Max. eiciency (h) Euro eiciency*
Fairchild IGBT hMAX
= 95.89% hEURO
= 95.07%
CREEs SiCDMOSFET
hMAX
= 97.81% hEURO
= 97.43%
Efficiency gain DhMAX
= 1.92% DhEURO
= 2.36%
*hEURO
= 0.03 h5%
+ 0.06 h10%
% + 0.13 h20%
+ 0.1 h30%
+ 0.48 h50%
+ 0.2 h100%
.
EIGBT, 1200-V
Infneon BSM 15GD120 DN2
ID
(max.) = 15 A at 80C
SiC DMOSFET,1200-V
CREE engineeringsample
ID
(max.) = 10 A at25C to 150C
VDS
600 V 800 V
Load Inductive Inductive(L
L= 500 H )
VGE
15 V 0 V/15 V
RG
82 V 10V
EON
at ID
= 10 A 1.6 mJ 0.8 mJ
EOFF
at ID
= 10 A 1.0 mJ 0.34 mJ
close to the reciprocal o the times actor increase in switch-ing requency, taking into account lling actor and windingtechnique. Te cost o inductive components decreases byabout 50% or a two to three times increase in switchingrequency (which is entirely possible with this technology).o keep the third harmonic beneath the lower conductedemission foor o 150 kHz, the practical limit or hardswitching is just below 50 kHz in these systems.
l Reduced cooling requirements. Reductions o up to50% or more in heatsink temperature are possible withthis technology. A comparable reduction in heatsink siz-
ing is possible while still maintaining the higher-eciencyadvantage that this technology enables. Tis solar inverterexample o reduction in heatsink sizing should allow areduction in production cost o around 5%, while stilldelivering increased annual benet through eed-in tarisrom the grid. A eed-in tari is an incentive structureto encourage the adoption o renewable energy throughgovernment legislation.
lAnnual eed-in beneft. A common PV system with7 kW in Germany produces approximately 7000 kWh peryear with a eed-in tari o 0.49 euro/kWh. (In June 2008, theeuro approximately was worth US$1.60.) Te annual benet
is approximately 3430 euros. Te three-phase inverter givenin the previous example showed an increase in Euro eciencyo 2.36%. Tis equates to an annual gain o 81 euros per yearwith this particular system. Tis is the estimation or centralEurope. However, i looking at southern Europe, where the
0 1000 2000 3000 4000 5000 6000 7000
AC power (W)
Efficiencyfactor(%)
98
97
96
95
94
93
92
91
90
1200-V SiC-DMOS
1200-V IGBT module
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SiC TECHNOlOGy
achieve the same goal with only two switches. When switchesS1 and S2 are turned on, the stored energy in C1 to C3 isquickly moved to the secondary-side resonant capacitor(C
D) through the transormer (
R) and resonant inductor
(LR). Te discharging time is designed to be approximately
equal to one-hal o the resonant period (O). For an optimal
design, O
should be relatively shorter than the switchingperiod (
S) to achieve a low total harmonic distortion.
Fig. 3. Three-phase 3-kW, HPF, two-switch orward converter
initially employed 1200-V IGBTs, which were replaced by 1200-V
SiC DMOSFETs that improved system eciency.[5]
Fig. 4. Eciency prole comparison at 67 kHz shows a higher
SiC eciency at 3-kW output and throughout the entire
load curve, as well as a case-temperature reduction with the
MOSFETs relative to the IGBTs.[5]irradiation level is about twice that in Germany, the annual
benet can be even greater, as shown in a table in the onlineversion o this article.[4]
Three-Phase High-Power-Factor RectiferA three-phase six-switch rectier ollowed by an isolated
dc-dc converter is typically used in three-phase applicationsthat require high power actor (HPF) and galvanic isolationbetween input and output. Te rectier shown in Fig. 3(a 3-kW zero current switching resonant topology) can
LA
LF
LR
N2
TR
N1
VAN
VBN
VCN
LB
C1CD
DD
+
CFR
D1
DF
VO
D2 D3
DC1
DC2
S2
S1
D4 D5 D6
C2
C3
LC
Tape Wound Cores
Bobbin Cores
Cut Cores
Kool Mu Cores
Molypermalloy Cores
High Flux Cores
XFLUX
Power Materials
High Permeability MaterialsSpecial Materials
Strip Wound Cores
Powder Cores
Ferrite Cores
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0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0
Output power (kW)
fSMAX= 67 kHz
2.2%
Efficiencyfactor(%)
92
90
88
86
84
82
80
CREE SiC MOSFET2x10 A, 1200 V
FGA25N120
25-A IGBT
FGL40N120
40-A IGBT
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17www.powerelectronics.com Power Electronics Technology September 2008
SiC TECHNOlOGy
Te system was run initially at ull load with a pair o
standard 1200-V, 25-A-rated IGBs. Tese devices were thenreplaced by a pair o standard 1200-V, 40-A IGBs, and thesystem was re-run at ull load. Te eciency versus outputpower curves were recorded.
he IGBs were then replaced by a pair o 1200-V,20-A-rated SiC MOSFEs and the exercise repeated. Asseen in Fig. 4, the SiC devices resulted in a 2.2% increasein eciency at a 3-kW output and substantial eciencyimprovement throughout the entire load curve. Also o notewas a 25C case-temperature reduction with the MOSFEsversus the 40-A-rated IGBs and a 36C dierence when
compared with the 25-A-rated devices.[5]
10-kV, 10-A SiC MOSFET in a Boost ConverterSiC technology shows signicant improvements in the
1200-V MOSFE arena, as revealed in the two previousexamples. Te perormance improvement becomes evengreater when compared to Si power switches rated at6.5 kV and above.
Recently developed was a 10-kV, 10-A SiC MOSFE.Te 10-kV device exhibits a drain-source orward voltagedrop o only 4.1 V, while conducting ull-rated 10-A draincurrent with a 20-V gate-source voltage. Tis is equivalent
to a specic on-resistance characteristic o only 127 mV/cm2. Te drain-source leakage current measured 124 nAat a 10-kV blocking voltage. In a direct comparison with astandard 6.5-kV Si IGB in a clamped inductive switchingtest xture, a SiC MOSFE exhibited 1/200th o the totalswitching energy o the IGB. Tis unipolar SiC MOSFEsturn-on delay time was only 94 ns compared with 1.4 sor the IGB and the turn-o time was only 50 ns insteado the IGBs 540 ns.
o analyze in-circuit perormance, a 10-kV SiC MOSFEwas combined with a 10-kV SiC Schottky diode and anair-core inductor in a standard boost-circuit topology(Fig. 5). Te circuit was designed to boost a 500-Vdc inputto a 5-kVdc output at a switching requency o 20 kHz. Tesystem ran at 91% eciency throughout the power band up
Fig. 5. Result o a 10-kV SiC MOSFET combined with a 10-kV
SiC Schottky diode and an air-core inductor in a boost
circuit that accepts a 500-Vdc input and produces a 5-kVdc
output, at 20-kHz switching requency.[6]
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10-A, 10-kV SiC Schottky diode 10-A, 10-kV SiC MOSFET
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to 600 W. Considering that this same circuit with standardSi MOSFE switches would only be capable o running ata ew hundred Hertz switching requency, there is an evengreater perormance advantage with SiC material at thesevoltage levels. Te waveorm shown in Fig. 6 exhibits theexceptionally ast turn-o transient o this system.[6]
With the most recent advancements in SiC materialsprocessing and device design, it will soon be possible toproduce reliable MOSFE switches or the commercialmarketplace. Considering the recent surge in interest in
alternative energy systems, SiC technology is now ready tourther improve their benets. Te reduction in power lossesthat this technology will provide in a PV systems powerconversion section will enable more ecient usage o PVpanel energy, in turn providing more power to the grid andallowing a reduction in uture ossil-uel generation. PETech
Reerences1. 4H reers to the SiC crystalline structure used in powersemiconductors.2. Hull, Brett, et al. Status o 1200 V 4H-SiC Power DMOS-FEs, International Semiconductor Device Research Sym-
posium, December 2007.3. Burger, B.; Kranzer, D.; Stalter, O.; and Lehrmann, S.Silicon Carbide (SiC) D-MOS or Grid-Feeding Solar-In-verters, Fraunhoer Institute, EPE 2007, September 2007.4. Burger, B.; Kranzer, D.; and Stalter, O. Cost Reduction oPV Inverters with SiC DMOSFEs, Fraunhoer Institute, 5thInternational Conerence on Integrated Power ElectronicsSystems, March 2008.5. Yang, Yungtaek; Dillman, David L.; and Jovanovic, MilanM. Perormance Evaluation o Silicon Carbide MOSFE inTree-Phase High-Power-Factor Rectier, Power Electron-ics Laboratory, Delta Products, www.deltartp.com.6. Das, Mrinal K., et al. State-o-the-Art 10-kV NMOSransistors, 20th Annual International Symposium onPower Semiconductor Devices and ICs, May 2008.
Fig. 6.A 10-kV SiC MOSFET running at 20 kHz and dissipating
600 W exhibited about 1.5-s drain current turn-of transient.[6]
SiC TECHNOlOGy
11 11.1 11.2 11.3 11.4
Time (s)tDOFF
= 50 ns tFALL = 94 ns
VDS
(kV)
ID(
A)
VGS
(V)
6
5
4
3
2
1
0
1
30
25
20
15
10
5
0
5
VDS
ID
VGS
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