IEEE Power Electronics Magazine - September 2014 - 28

from the mean time between failure (MTBF) of the power
converter under extreme field operating conditions. However, current power converter design approaches only consider in an ad hoc manner the maximum junction temperature (T j max) of the power semiconductor switch within the
PEM in assessing the MTBF of the power converter in the
OEM application. This conventional design approach needs
to be revisited, especially since most power semiconductor failures occur during transient switching conditions,
and the semiconductor chip is unlikely to be in the isothermal condition [2]. This feature requires serious consideration, as PEMs based on WBG power switching devices are

*N-Enhancement Layer

Emitter

High-Power Modules

*Short Channel

*Low Gate-Collector
Capacitance
*N-Base
*SPT Buffer
*P+
*Collector
(a)

6,500-V SPT + HiPak Modules
Rated at 750 A

3.5
3.0
2.5
2.0
1.5

SPT
6,500 V

2,500 V

4.5
1,200 V
1,700 V

Vce,on (V)

5 0.

3,300 V

5.5

4,500 V

(b)

6.0

SPT+

1,000 2,000 3,000 4,000 5,000 6,000 7,000

Voltage Class (V)
(c)
fig 1 (a) The cell design, (b) a 6.5-kV/750-A HV-HiPak power
module, and (c) the loss reduction achieved with SPT-IGBT and
diode technology. [Image (b) courtesy of Dr. Arnost Kopra, ABB
Switzerland.]

IEEE PowEr ElEctronIcs MagazInE

expected to operate at much higher T jmax than their silicon
counterparts.
This article provides a status report on advanced silicon
and WBG PEMs and discusses the key challenges that must
be addressed when developing future compact power electronics systems targeted for deployment in the emerging
energy economy. For silicon, the focus is on HV and highpower insulated-gate bipolar transistor (IGBT) power modules, as they represent the most advanced PEM technology
in the market today. For WBG technology, the discussion
is limited to converter-level package optimization of lowvoltage point-of-load (POL) power converters that employ
gallium nitride (GaN) power transistors.

z September 2014

In the past ten years or so, dramatic improvements in HV
and high-power silicon IGBT module technology have been
achieved in terms of energy efficiency, cost, and reliability.
Figure 1(a) shows the typical planar IGBT cell design
employed, where improved on-state conduction and low
Miller capacitance are obtained by increasing the minority
carrier injection efficiency and decreasing the gate-collector
overlap capacitance [3]. The planar soft punch-through
(SPT) design approach provides for increased carrier concentration at the collector and reduces both conduction and
turn-off losses. The planar cell design facilitates an easy integration of low Miller capacitance, good turn-on controllability, and fast voltage decay at turn-on, without adversely
affecting other important device parameters. As shown in
Figure 1(b), 6.5-kV IGBT power modules rated at 750 A are
commercially available in industry-standard housing with a
190 # 140 -mm footprint. These power modules are optimized for high-reliability traction applications and consist of
aluminum silicon carbide base plates and aluminum nitride
substrates with excellent thermal capability and high turn-off
ruggedness and can sustain an isolation voltage of
10.2 kVrms . Figure 1(c) shows a systematic reduction in
power loss achieved using the SPT-IGBT technology.
A more recent development in HV-HiPak technology pertains to the development of a reverse conducting IGBT (RCIGBT) concept integrated with a free-wheeling diode, as shown
in Figure 2(a) [4]. The bimode insulated gate transistor (BIGT)
provides a potential solution for future high-voltage applications that demand compact systems with increased power levels. The new device can operate in both free-wheeling diode
and IGBT modes by utilizing the same available silicon volume. Therefore, the BIGT is targeted to fully replace the stateof-the-art two-chip IGBT/diode approach with a single BIGT
chip [Figure 2(b)]. This is achieved while also improving the
overall performance, especially under hard-switching conditions with low losses, soft-switching characteristics, and high
SOA, as shown in Figure 2(c).
Further improvement in IGBT power module performance
can be achieved using a silicon carbide (SiC) Schottky barrier
diode (SBD) as the free-wheeling diode. One such commercial rendering of this hybrid technology is shown in Figure 3;

Table of Contents for the Digital Edition of IEEE Power Electronics Magazine - September 2014