IEEE Power Electronics Magazine - September 2020 - 24

Sidebar #2: Reverse-Voltage-Blocking WBG Switches
As noted in the main article, one of the key practical obstacles to
the future success of the WBG-based CSI is the current unavailability
of commercially-produced monolithic SiC or GaN switches with
reverse-voltage-blocking (RVB) capability. The baseline approach
of placing a discrete diode (junction or Schottky) in series with the
WBG switch is generally acknowledged to be unacceptable because
of the diode's cost and additional forward voltage drop. The good
news is that multiple researchers in academia and industry have
designed, fabricated, and tested monolithic RVB-WBG switches,
convincingly demonstrating their technical feasibility.
The most appealing technical approach being pursued today is to
use lateral GaN epitaxial device technology to design bi-directional
(BD) switches that make it possible to gate-control the current in both
directions while also providing bipolar voltage-blocking capabilities.
While controllable reverse current may at first seem unnecessary since
current flow in CSI switches is unidirectional, there are two powerful
motivating factors that may not be apparent initially. First, BD
switches are critical to a variety of other power electronics applications
including matrix inverters [20] and fast-acting ac switches in solid-state
circuit breakers, providing a much more potent combined market
opportunity to incentivize power semiconductor manufacturers to
launch production. Second, BD switches turn out to be valuable
in CSIs during phase-leg switching events for meeting the dual
requirements of preventing the current in the dc link inductor from
ever encountering an open-circuit condition, as well as preventing the
output filter capacitors from ever experiencing short circuits [21].
Panasonic has successfully developed a lateral GaN BD switch with
preliminary specifications of 42 mX on-state resistance (+ 50 A)
with a breakdown voltage exceeding 1300 V in both polarities [22].
This device uses a dual-gate structure (Figure S2) that can be modeled
as two normally-off Gate Injection Transistors (GITs) connected in anti-

series with a common drain. Other researchers are developing lateral
GaN BD switches that adopt a complementary anti-series switch
configuration with a common-source connection, requiring only a
single gate [23]. Both configurations have their respective advantages
and disadvantages, but the common-drain configuration provides the
highest control flexibility during CSI switching events and the lowest
on-state voltage drop.
For researchers who do not yet have access to monolithic BD switch
devices, high-quality substitutes can be fabricated as hybrid switches
consisting of two discrete GaN or SiC switches connected in either of
the anti-series connections noted above [24].

Source 1
(S1)

Gate 1
(G1)

Gate 2
(G2)

p-AlGaN

p-AlGaN
i-AlGaN
i-GaN

Vg1

S1

G1

G2

S D

D S

Vg2

S2

FIG S2 Cross-section of Panasonic GaN-based monolithic
bidirectional (BD) switch device and equivalent circuit highlighting common-drain configuration with two gates. (Source:
[20]; © 2014 IEEE)

Current (A)

10

Ia
Ib
Ic

5
0
-5
-10

0

5

10

15
Time (ms)

20

Current
THD: <2%
at 100 kHz

400
Voltage (V)

Source 2
(S2)

Vab
Vbc
Vca

200
0
-200
-400

0

5

10

15
Time (ms)

20

25

30

FIG 7 Prototype version of 3 kW Integrated Motor Drive developed at UW-Madison as part of the ARPA-E CIRCUITS program using
CSI with wide-bandgap SiC switches, showing current and voltage output waveforms without any external filters.

24

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