ANALOG FEEDBACK
SiC Technology Enables Discrete Revolutions
By Mark Valentine, Technical Editor,
Power Electronics Technology
W
hile silicon carbide (SiC) was once well
known as the technology used to implement the first blue light-emitting diodes
(LEDs), and is now used as a substrate
for high-power LEDs, the technology
is also enabling performance advances in discrete power
components.
For example, SiC versions of the diode, the simplest
semiconductor device, have been available for several years.
Another relatively mature device, the SiC enhancement JFET,
functions as a power switch. The characteristics of this device
can reduce the switching losses generated by conventional
MOSFETs in switching power supplies. There is also the SiC
MESFET, a fairly exotic component that has found a niche
in radio-frequency transmitters. All of these applications
illustrate how SiC technology is providing viable alternatives
to well-established silicon devices.
In keeping with this trend, Cree Semiconductor has recently announced the availability of a power-device combination pack (co-pack), which combines IGBT devices from
International Rectifier with SiC Schottky diodes from Cree.
In this module, the SiC device serves as the freewheeling
diode and is connected in reverse parallel across the emitter
and collector contacts of the IGBT.
The first part released in this product family is the
CID150660 (Fig. 1). This
is a 15-A IGBT co-packaged with a 6-A SiC diode in a TO-220 case.
The SiC device replaces
a 15-A silicon rectifier.
Michael O’Neill, an applications engineer with
Cree, explained that the
SiC device is rated for 6 A
at 150°C case temperature,
but at a case temperature
of 100°C (which is where
the silicon device is rated),
it is capable of supporting
a steady-state current of
13 A.
Because the SiC diode is
Fig. 1. Cree’s CID150660 contains a a unipolar device, reverse15-A IGBT and an antiparallel 6-A recovery currents associated with minority carrier
SiC diode in a TO-220 case.
Power Electronics Technology November 2006
recombination in conventional
silicon devices are eliminated; the only recovery
mechanism is the charge
associated with the junction capacitance of the
device. According to
O’Neill, for the SiC
devices in the coFig. 2. Infineon’s
pack this is roughly
ThinQ!2G
series
1 A sustained for
with
a
TO-220
packaging
20 ns, or approxioption incorporates a
mately 1% of the
merged structure that
switching loss
combines the benefits of SiC
of a convenSchottky and silicon diodes.
tional silicon diode.
It translates into the elimination of diode switching losses
and a significant reduction in IGBT turn-on loss when used
in a half-bridge configuration.
Cree’s co-pack is rated for 600 V. This is the first device in
a family that will support this same voltage for a variety of
current ratings. However, Cree’s main focus is with 300-V,
600-V and 1200-V SiC Schottky diodes, the main application for these devices being PFC converters. Cree has field
reliability data showing more than 31 billion device hours of
reliable operation for these components. For more information, see www.cree.com.
Infineon, another major developer of SiC technology, is
now in production with its second-generation SiC diodes,
the ThinQ!2G series. This technology employs a structure
referred to as the merged junction. This is a configuration where small p-n junctions are interleaved within the
rectifying Schottky metal-SiC interface. The p-n structures
contribute to the surge robustness of the device as well as
the reduction of reverse-bias leakage currents. Beyond a
certain forward voltage, the operation of the device transitions from Schottky mode to bipolar mode, which provides
surge-current capabilities comparable to silicon diodes.
For Infineon’s ThinQ!2G 4-A SiC device, this threshold is
4 V, beyond which the current slope is approximately linear
and temperature independent. The application of an 8-V
forward voltage across this part produces a current on the
order of 45 A.
All second-generation SiC diodes from Infineon are
rated for 600 V. The device family includes the IDT04S60C,
IDT05S60C, IDT06S60C, IDT08S60C, IDT10S60C,
38
www.powerelectronics.com
IDT12S60C and IDT16S60C, all packaged in the TO-220 case style (Fig. 2), and
the IDD04S60C, which uses the DPAK
package.
Infineon’s philosophy in the use of SiC
devices in power design is to offset higher
component costs with system-level gains
enabled by SiC technology. In a PFC stage,
for example, the elimination of reverserecovery current in a SiC boost diode and
the resulting increase in switching speed
enables the use of a smaller switching
device and inductor, respectively. For more
information, see www.infineon.com.
SiC FETs
SiC can contribute indirectly to power
savings in switching devices by eliminating reverse-recovery current. It also can
contribute directly in the form of SiC JFETs.
Infineon has chosen to develop the SiC JFET
because it promises device ruggedness and
high performance at a reasonable cost.
Another company, SemiSouth, has
fully developed SiC JFETs as well as cir-
Fig. 3. This SiC vertical junction FET
(VJFET) from SemiSouth is housed
in high-reliability packaging for
military, aerospace and harshenvironment applications.
cuit designs for driving the gate of these
devices. SemiSouth’s focus is on devices
with vertical channels and corresponding
very high-channel packing density (Fig. 3).
This feature produces very low, specific onresistance, which is one factor in the race to
reduce cost. One consideration for these SiC
JFETs is that an enhancement-mode option
is available, which means a slight forward
bias must be applied to the gate of the device. While this may be a radical departure
from conventional wisdom with respect to
the JFET, the voltage swing is lower than it
would be for a MOSFET (6 V wide versus
15 V for a MOSFET). For more information,
visit www.semisouth.com.
The future of SiC technology is promising. Especially bright is the potential of SiC
FETs once the various technical challenges
to developing a cost-effective device have
been overcome. However, another challenge
of equal significance will be changing established power-design practices to accommodate the electrical and thermal advantages of
SiC devices as they continue to evolve. PETech
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Power Electronics Technology November 2006