IEEE Power Electronics Magazine - March 2023 - 36

FIG 14 Key components of an ac solid-state circuit breaker
(SSCB) realized with an MBDS and comparison of the reaction
times between an SSCB and a conventional mechanical circuit
breaker, see also [29].
require multi-step commutation sequences to ensure that
there is always a path for the inductor current while never
short-circuiting any of the capacitors. Typically, four-step
commutation sequences that depend on the current direction
[Figure 13(c) and (d)] [25] or on the voltage polarity
[26] are employed; but also variants with fewer steps
have been described. Clearly, the availability of MBDSs
renders the DMC topology a highly attractive realization
option for ac-ac VSDs due to the minimal switch count.
Thus, for example, a GaN MBDS-based DMC achieving
extreme compactness by massive on-chip/in-PCB integration
has been demonstrated in [27], and [28] describes a
Monolithic Bidirectional Switch Concepts
It is beyond the scope of this article to provide a comprehensive
history of the MBDS development. Thus, suffice to say that
early activities regarding MBDS semiconductor realizations can
be traced back to the turn of the millennium, where not only
reverse-blocking IGBTs (RB-IGBTs) [33] have been demonstrated,
but also early MBDS concepts [34]. A few years later, various
companies started to investigate MBDSs based on GaN HEMTs
featuring two individual gates and especially a shared drain
region that is used for blocking either voltage polarity [35], [36],
[37], [38]. Thus, GaN MBDSs can be considered the most mature
MBDS technology, with ±600 V, 140 mΩ samples being available
[7], [38]. Figure 15(a) shows a schematic device cross section
of such a normally-off dual-gate GaN MBDS (gate-injection
transistor, GIT); alternative realizations feature normally-on gates
or cascode configurations with LV MOSFETs connected in series
with either source terminal [39].
SiC-based MBDSs have been demonstrated recently, too,
which would allow for increased blocking voltages above
the ±650 V typically achieved with GaN-based lateral device
concepts. Figure 15(b) shows a BiDFET [40], a monolithic (in
the sense of on-chip) arrangement of two SiC transistors
with integrated JBS diodes. Whereas the BiDFET provides a
blocking voltage of ±1200 V, it is essentially a common-drain
arrangement of two transistors and hence there are two drift
regions, one for supporting each blocking voltage polarity.
Thus, whereas there are benefits from the on-chip inverseseries
connection, e.g., regarding handling and packaging,
the factor-of-four penalty in chip area usage [see Figure 2(g)]
still applies. The same is true for a vertical back-to-back
configuration of two MOSFET dies with a metal interposer layer
in-between [41], see Figure 15(c). This is in contrast to the true
monolithic bidirectional 4H-SiC IGBT device [42] shown in Figure 15(d), where the shared drain region is clearly visible; initial prototype devices
achieved measured blocking voltages of up to ±7 kV. Such vertical SiC MBDS concepts, however, require non-standard double-sided lithography
processes and are more challenging to cool as both sides of the wafer feature intricate structures (gates, etc.). Finally, Figure 15(e) shows a recently
demonstrated true monolithic bidirectional Si bipolar junction transistor (BJT) with a shared collector region (B-TRAN) [43]. The devices achieve a
blocking voltage of ±1200 V and support pulsed currents of up to ±100 A, but, being BJTs with a typical current gain of three to four, require
relatively complex gate drive circuitry providing the corresponding base currents.
FIG 15 Conceptual (more details are given in the references)
device cross sections of various MBDSs. (a) Monolithic bidirectional
dual-gate GaN HEMT [35], [36], [37], [38] with a single
drift region for both blocking voltage polarities, and test board
with a CSC commutation cell [see Figure 12(b)] realized with
first-generation ±600 V, 140 mΩ samples [38]. (b) SiC BiDFET [40]
and (c) similar vertical back-to-back connection of two SiC MOSFETs
[41]. (d) Monolithic bidirectional 4H-SiC IGBT with a single
drift region [42] and (e) B-TRAN [43], a monolithic bidirectional
Si bipolar junction transistor, also with a single drift region.
36 IEEE POWER ELECTRONICS MAGAZINE z March 2023
IEEE Power Electronics Magazine - March 2023

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