IEEE Power Electronics Magazine - September 2020 - 46

The results of these measurements
and simulations are applicable to
practicing power systems designers
in a variety of fields, especially those
investigating SiC implementation.

Seventh Generation Si Technology

The Figure 1 Si module is a
300-A/1700-V dual IGBT power module containing seventh generation silicon CSTBT IGBT technology. Per
Reference 1, the seventh generation
chipset achieves a reduction in turnoff switching losses of 20% over previous IGBT technologies. This reduction in losses is primarily due to the
optimization of the CSTBT structure
and reduced chip thickness. Typically, short circuit capability is a tradeoff with chip thickness. However,
per Reference 2, the short circuit
capability was maintained by reducing maximum short circuit current
without significantly influencing the VCEsat . Thus, the seventh generation IGBT chip achieves an improved tradeoff
relationship between VCEsat and E off with sufficient short
circuit capability.

Second Generation SiC Technology
The Figure 1 SiC module is a 300-A/1700-V dual MOSFET
module containing the Figure 3 SiC MOSFETs fabricated
using a 6-inch wafer process. Per Reference 3, the VDS(on)
and total switching losses of these SiC MOSFETs are among
the lowest compared to similarly rated modules with publically available data. The MOSFET capacitances were optimized for high frequency use. An n-type JFET doping structure was used to reduce on-resistance, which works especially well for high blocking voltage MOSFETs (>1200 V).

For high voltage SiC MOSFETs,
body diode degradation is a challenge for long-ter m module reliability. Continuous conduction of
current in the SiC body diode has
been shown to cause degradation
of R ds(on) over time due to growth
of defects in the SiC crystal. Mitigation techniques and raw material improvements may ultimately
allow reliable use of the body diode
and elimination of the SBD once they
have been fully vetted. An existing
solution to this problem is incorporating separate SiC Schottky Barrier diodes (SBD) to prevent use of
the body diode. The module tested
herein includes these SBD to ensure
long-term reliability.

Experimental Results

Static Characteristics: Each
module's static characteristics
(VCE /VDS and VEC /VSD(off) /VSD(on)) were measured on a
Keysight B1506A power curve tracer up to 550 A at
125 °C as shown in Figure 4 and Figure 5. A gate bias
of 15 V was used for VCE /VDS /VSD(on) and −15 V for
VEC /VSD(off ) . When measuring freewheeling diode characteristics, negative gate bias is used to ensure the
IGBT/MOSFET remains off and only diode characteristics are measured.
Figure 6 shows the results of the IGBT/MOSFET static
testing. The SiC MOSFET module achieves superior forward characteristics for VCE /VDS up to 265 A after which
the Si IGBT module is advantageous. At rated current of
300 A, VCE for the Si module is 2.41 V while the SiC module
has a VDS(on) of 2.59 V. The SiC VDS(on) is among the lowest
values ever reported for similar modules.

Source
Gate

n-Source
p-Well
JFET
Doping

JD
n-Drift

4H-SiC Substrate
Drain
FIG 3 Cross sectional structure of planar second generation
1700 V SiC MOSFET.

IEEE POWER ELECTRONICS MAGAZINE

z September 2020

FIG 4 Curve tracer test setup.

IEEE Power Electronics Magazine - September 2020

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