ELECTRONICS

Dynamic Characteristics Analysis of 3,300 V
Full SiC Power Module by New Equivalent Circuit
Satoshi HATSUKAWA*, Shigenori TOYOSHIMA, Takashi TSUNOand Yasuki MIKAMURA---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Silicon Carbide (SiC) devices are promising candidates for high power, high speed, and high temperature switches owing to theirsuperior properties. We have been developing SiC based 3,300 V class metal-oxide-semiconductor field-effect transistors(MOSFETs) and schottky-barrier diodes (SBDs). Stray inductance in the module and the great current changing rate with highspeed switching may cause excessive voltage overshooting. Although equivalent circuits are effective for stray inductanceanalysis, previous equivalent circuit studies covered only a partial area of the entire module. This paper proposes a new method
for the dynamic characteristics analysis using the precise equivalent circuit of the entire module.

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Keywords: SiC MOSFET, SiC SBD, SiC power module, low inductance, equivalent circuit

1. Introduction
Reflecting significantly growing international concern
regarding global warming, the need to reduce CO2 emissions has been widely recognized. In parallel with this, thedevelopment of energy-saving technology is regarded as animportant measure for coping with the approaching depletion of oil and other fossil fuel resources. Electric energy isa very convenient form of energy and is increasing its
proportion of total energy year by year. Therefore, thedevelopment of technology that will enable efficient use ofelectric energy is positioned as an important pillar toward
effective energy conservation. Electric power energy isconverted to various forms before it is consumed by end
users. Semiconductor devices or power devices used inelectric power equipment play a key role in converting
electric energy to other forms. User demand for the development of power devices with high energy-saving performance has been increasing recently.
Similarly to ordinary semiconductors, most currently
available high voltage, high current, high speed/highfrequency power devices are formed on silicon (Si)substrates. Regarding Si-based power devices, metal-oxidesemiconductor field-effect transistors, insulated gate
bipolar transistors, and other devices have been developed
and their uses for power conversion are expanding.
However, these devices are reaching their performance
limits, which are determined theoretically by their dielectric breakdown field, electron saturation velocity, and otherphysical properties. The development of high performance
power devices made from a new semiconductor material
other than Si is desirable.
One of the new promising semiconductor materials issilicon carbide (SiC), which is a wide band gap semiconductor material. SiC has been previously used as an abrasiveor heat dissipation material. However, the success in developing a high quality single crystal SiC has intensified
research on the use of SiC as a semiconductor. SiC is apromising power device material as it has a higher dielectric
breakdown field, electron saturation velocity, and thermal
conductivity than Si. Research and development ofSiC-based high blocking voltage, high speed, low on resistance power devices has been energetically carried out.(1)-(3)Following the commercialization of a SiC Schottky
diode, the development of other types of switching devices,a vertical metal-oxide-semiconductor field-effect transistors (MOSFET) in particular, has been energeticallypursued. A vertical MOSFET is highly expected as a highcurrent, high voltage device. The vertical MOSFET has thesame structure as that of Si MOSFETs and it can be madeby the same process as that for Si MOSFETs.
The authors have developed a SiC power module
having a withstand voltage of 3,300 V and a current
capacity of 400 A, and confirmed that it has a superior
switching characteristic.(4) Stray inductance in the moduleand an increase in current change rate attributed to fastswitching may cause excessive voltage overshooting.
As a device that can prevent such voltage overshooting, we have also developed a 1,200 V, 100 A lowinductance SiC power module.(5) To reduce the stray inductance of the newly developed 3,300 V, 400 A SiC power
module, we analyzed the stray inductance of this module.
Although it is effective to analyze stray inductance byrepresenting the power module by its equivalent circuit,previously known analysis method used an equivalentcircuit that was expressed by only the representative valueof the elements and inductance of the power module. We
have developed a new method for creating an equivalentcircuit that can express every element of the module, andconfirmed that the new method reproduces actual measured
values at high accuracy. This paper describes and discusses
the newly developed analysis method and the results
obtained by the method.

2. New Model of SiC Power Module
A photo of the newly developed 3,300 V, 400 A SiC
power module is shown in Fig. 1. For inverter application,
this power module is made as a 2 in 1 module consisting ofa high voltage arm (D1-S1) and low voltage arm (D2-S2).

SEI TECHNICAL REVIEW · NUMBER 83 · OCTOBER 2016 · 55

The forward ON characteristic of one arm is shown inFig. 2. This figure shows that the rated current of 400 A
flows when the gate voltage (VGS) is 20 V and the drain
voltage (VDS) is 2 V. The internal structure of the power
module is shown in Fig. 3. Six SiC MOSFET chips and six
SiC schottky-barrier diode (SBD) chips are mounted on asingle substrate so that two substrates constitute one armand two arms constitute a 2 in 1 module. Twelve SiC
MOSFETs and twelve SiC SBDs are arranged in parallelfor each arm.
The equivalent circuit of a previous module is shownin Fig. 4. The SiC MOSFET, SiC SBD, and stray inductance are each illustrated integrally by their respective

representative models.
When we developed the new equivalent circuit, wefirst determined the simulation program with integrated
circuit emphasis (SPICE)*1 model of each of the SiC
MOSFET and SiC SBD chips. Using an NMOS model for
the SiC MOSFET and a D model for the SBD, we manually adjusted the parameters of these models so that thecalculation would agree well with the actual measurement.
The calculated values and actual measured values of theforward characteristics of a single chip of the SiC
MOSFET and SBD were compared. The results are shownin Fig. 5. The figure verifies that the calculation can accurately simulate the actual measurement. To express theS2S1

D2

D2D1

D1S1S2Fig. 1. 3,300 V, 400 A 2 in 1 SiC power module (130 x 140 mm2)

Fig. 3. Internal structure of 3,300 V, 400 A SiC power module

S2StrayInductance

D2504030
20

VGS=20V
Measurement
VGS=15V
Spice Model

1000.0

1.0
2.0
3.0
VDS Drain Source Voltage (V)(a) 3,300 V SiC MOSFET (1 chip)

S1Fig. 4. Equivalent circuit of a previous module

IF Forward Current (A)ID Drain Current (A)Fig. 2. ID-VDS forward characteristics of 3,300 V, 400 A SiC
power module

D1504030

Spice Model

20Measurement

1000.01.0
2.0
VF Forward Voltage (V)

3.0(b) 3,300 V SiC SBD (1 chip)Fig. 5. Comparison between calculation and actual measurement of forward characteristics

56 · Dynamic Characteristics Analysis of 3,300 V Full SiC Power Module by New Equivalent Circuit

stray inductance of terminals, circuits on the substrate,bonded wires, and other conductors by an equivalentcircuit, we used the ANSYS Q3D Extractor.
We created an equivalent circuit of the inner portionof the module by combining the equivalent circuits of theSiC MOSFET model, SiC SBD model, and stray inductance. Part of the equivalent circuit is shown in Fig. 6.
Figure 6 shows six SiC MOSFET chips, six SBD
chips, and their inductance circuits on a single substrate.
The mutual inductance between the inductance circuits isnot shown in this figure. When the equivalent circuit
created above was calculated on the LTspice IV, the calculated values contained large errors or the calculation
required a considerably long period of time. The reason forsuch large errors was that the equivalent circuit of theinductance was complex and made the calculations
cumbersome and complicated. To enhance the calculation
efficiency, we developed a new program that can efficiently
create the equivalent circuit of inductance by omitting lessinfluential inductance.

3. Evaluation of SiC Power Module Model
The circuit that we used to evaluate the dynamic characteristics of SiC power modules is shown in Fig. 7. For
the evaluation, we applied a 100 μH reactance load to thespecimen at room temperature. The dynamic characteristics
waveforms at a voltage of 1,650 V are shown in Fig. 8.

L=100 μH-5V15V-5V50ID

RG=2.2 Ω

VDD = 1,650 VVDS

VGS

Pulse
Generator

ModuleFig. 7. Dynamic characteristics evaluation circuit
GT1

T2

T3T4T5

D1 D2 D3 D4 D5 D6T6SFig. 6. Equivalent circuit of module (for a single substrate)

5002000
1500
1000
5000-500

VGSVDSID

0102030Time (μs)

4012001000
800
600
4002000-200ID (A)VDS (V) VGS (V)Combined use of a new equivalent inductance circuitwith the equivalent circuits of the SiC MOSFET and SBD
chips has enabled the elimination of calculation errors andanalysis of the characteristics of power devices within ashort period of time.
An electromagnetic field analysis was previously
required to simulate the dynamic characteristics of a powermodule. The newly developed analysis method enables thesame simulation within about one-tenth time.

50(a) Actually measured waveforms

Figure 8 (a) shows the actual measured waveforms,
while Fig. 8 (b) shows the waveforms of a SiC power
module that were calculated using LTspice IV. The actually
measured rise time tr and fall time tf were 404 ns and 238
ns, respectively, while the calculated tr and tf were 402 ns
and 226 ns, respectively. Thus the calculation agreed quite
well with the actual measurement. The calculated resonancefrequency of VDS, which was 23.2 kHz, also agreed wellwith the actual measured value, which was 22.5 kHz.
We also calculated the voltage and current of each SiC
chip that constituted the power module. As shown in Fig. 9,
the arm on the operation side of this module comprised
near side and far side substrates when viewed from the subterminals. Calculation results of the turn-on time and turnoff time dynamic characteristics are shown in Fig. 10 (a)and (b), respectively. These figures show that voltage VDS
was the same between individual chips, while current ID
was larger on the near side than the far side. In particular,
turn-on time current overshooting occurred on the nearside. The maximum overshooting current of nearly 90 A
was measured in the N4 chip.

5002000
1500
10005000-500VGSVDSID0102030Time (μs)

40120010008006004002000-200ID (A)DVDS (V) VGS (V)S50(b) Waveforms calculated using modelFig. 8. Comparison of dynamic characteristics waveforms (switching of inductance load at power source voltage of 1,650 V)

SEI TECHNICAL REVIEW · NUMBER 83 · OCTOBER 2016 · 57

Near side substrate

Sub terminals

N6N5

Technical Term

Far side substrate
F6SiC MOSFETs

F5N4F4N3F3N2N1＊1 Simulation program with integrated circuit emphasis(SPICE): An analog electronic circuit simulation
program developed in 1973 by the University ofCalifornia, Berkeley.

F2
Drain
terminal

References

F1

Sourceterminal(1)(2)

Fig. 9. Chip layout for one arm

(3)
(4)
(5)

We concluded that the current was larger on the nearside than on the far side because the gate voltage VGS waslarger on the near side than on the far side as shown inFig. 10, and this difference in gate voltage created a difference in the on resistance of the MOSFET, leading to adifference in current. We also concluded that current overshooting occurred on the near side because the inductanceof the gate circuit on the far side delayed signals andconcentrated the current on only the near side.
Based on the above analytical study results, we will
modify the substrate wiring so that the gate signal willreach each chip at the same time.

M. Bhatnagar, B.J. Baliga, IEEE Trans. Electron Devices, 40 (1993)
645-655
Z. Stum, A.V. Bolotnikov, et al., Mater. Sci. Forum., 679-680 (2011)637-640
A. Bolotnikov, P. Losee, et al., in Proc. ISPSD (2012) 389-392
Y. Saitoh, T. Hiyoshi, K. Wada, T. Masuda, T. Tsuno and Y. Mikamura,
SEI Technical Review, No. 80, pp. 75-80 (2015)
S. Toyoshima, S. Hatsukawa, N. Hirakata, T. Tsuno, Y. Mikamura, SEI
Technical Review, No. 80, pp. 81-84 (2015)

Contributors The lead author is indicated by an asterisk (*).

S. HATSUKAWA*• Senior Assistant Manager, Power Device Development
Division

S. TOYOSHIMA
4. Conclusion• Transmission Devices Laboratory

The authors have developed an equivalent circuit of
the 3,300 V, 400 A SiC power module, and confirmed thatthe new equivalent circuit can simulate the actual waveforms of the module.
In the future, we will use this new equivalent circuit
model to optimize the current distribution in the moduleand thereby design a low inductance module that will not
produce current overshooting or any other abnormal waveform.

T. TSUNO• Doctor of Science
Group Manager, Power Device Development Division

Y. MIKAMURA• Department Manager, Power Device DevelopmentDivision• Q3D Extractor is a trademark of ANSYS Corp.
• LTspice is a trademark of Linear Technology Corp.

2kVVDS

1kV
200ns080A
60A
40A
20A020V
10V0-10VVDS200nsOvershoot

N1~N6ID

F1~F6
N1~N6Difference

F1~F6(a) Turn-on timeID

F1~F6Delay

N1~N6VGSVGSDelay

F1~F6

N1~N6(b) Turn-off time

Fig. 10. Calculated switching waveform of each chip current (power source voltage: 1,650 V)

58 · Dynamic Characteristics Analysis of 3,300 V Full SiC Power Module by New Equivalent Circuit