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Home > Knowledge > 5.Silicon Carbide Technology > 5.3.2 High-Power Device Operation
5.3.2 High-Power Device Operation

5.3 Applications and Benefits of SiC Electronics

5.3.2 High-Power Device Operation

The high breakdown field and high thermal conductivity of SiC coupled with high operational junction
temperatures theoretically permit extremely high-power densities and efficiencies to be realized in SiC
devices. The high breakdown field of SiC relative to silicon enables the blocking voltage region of a
power device to be roughly 10×thinner and 10×heavier doped, permitting a roughly 100-fold
beneficial decrease in the blocking region resistance at the same voltage rating. Significant energy
losses in many silicon high-power system circuits, particularly hard-switching motor drive and power
conversion circuits, arise from semiconductor switching energy loss . While the physics of
semiconductor device switching loss are discussed in detail elsewhere, switching energy loss is
often a function of the turn-off time of the semiconductor switching device, generally defined as the
time lapse between application of a turn-off bias and the time when the device actually cuts off most
of the current flow. In general, the faster a device turns off, the smaller its energy loss in a switched
power conversion circuit. For device-topology reasons discussed in References 3,8, and 19–21, SiC’s
high breakdown field and wide energy bandgap enable much faster power switching than is possible
in comparably volt–ampere-rated silicon power-switching devices. The fact that high-voltage operation
is achieved with much thinner blocking regions using SiC enables much faster switching (for comparable
voltage rating) in both unipolar and bipolar power device structures. Therefore, SiC-based power
converters could operate at higher switching frequencies with much greater efficiency (i.e., less switching
energy loss). Higher switching frequency in power converters is highly desirable because it
permits use of smaller capacitors, inductors, and transformers, which in turn can greatly reduce overall
power converter size, weight, and cost.
While SiC’s smaller on-resistance and faster switching helps minimize energy loss and heat generation,
SiC’s higher thermal conductivity enables more efficient removal of waste heat energy from the active
device. Because heat energy radiation efficiency increases greatly with increasing temperature difference
between the device and the cooling ambient, SiC’s ability to operate at high junction temperatures permits
much more efficient cooling to take place, so that heat sinks and other device-cooling hardware (i.e., fan
cooling, liquid cooling, air conditioning, heat radiators, etc.) typically needed to keep high-power devices
from overheating can be made much smaller or even eliminated.
While the preceding discussion focused on high-power switching for power conversion, many of the
same arguments can be applied to devices used to generate and amplify RF signals used in radar and
communications applications. In particular, the high breakdown voltage and high thermal conductivity
coupled with high carrier saturation velocity allow SiC microwave devices to handle much higher power
densities than their silicon or GaAs RF counterparts, despite SiC’s disadvantage in low-field carrier
mobility.