Page 28 - NEW Armstrong Book - 2

14
ASPENCORE GUIDE TO SILICON CARBIDE
rating addresses the problem by introducing a partial degradation of performance to avoid compromising the component at high temperatures.
SiC characteristics
SiC-based power devices are driv-
ing a radical transformation of power
electronics, thanks to a combination
of excellent physical and electronic
properties. Semiconductors based on
SiC offer higher thermal conductivity,
higher electron mobility, and lower
power losses. SiC diodes and transis-
tors can also operate at higher fre-
quencies and temperatures without
compromising reliability. The main
applications of SiC devices, such as
Schottky diodes and FET/MOSFET
transistors, include converters,
inverters, power supplies, battery chargers, and motor con- trol systems.
A relevant factor in these applications is the bandgap, or energy gap, offered by the semiconductor. When the band- gap is high, the electronics it uses can be smaller and run faster and more reliably. Because the dielectric breakdown intensity of the electric field is about 10× higher for SiC than for silicon, SiC can reach a very high breakdown voltage, from 600 V to a few thousand volts. SiC can use higher dop- ing concentrations than silicon, and the drift layers can be made very thin. Traditionally, IGBTs and bipolar transistors have been the devices of choice in high-power applications, with the aim of reducing the turn-on resistance that occurs at high breakdown voltages. These devices, however, offer sig- nificant switching losses, resulting in heat-generation issues
FIGURE 2: REVERSE-RECOVERY TIME COMPARISON (SOURCE: ROHM SEMICONDUCTOR)
that limit their use at high frequencies. Using SiC, it is pos- sible to make devices such as Schottky barrier diodes and MOSFETs that achieve high voltages, low turn-on resistance, and fast operation.
If a semiconductor is not able to dissipate heat effectively, a limitation is introduced on the maximum operating volt- age and temperature that the device can withstand. This is another area where SiC outperforms silicon: The thermal conductivity of SiC is 3.3–4.9 W/cm⋅K, compared with the 1.4–1.5 W/cm⋅K offered by silicon.
SiC MOSFETs, like their silicon counterparts, have an inter- nal body diode. One of the main limitations offered by the body diode is the undesired reverse-recovery behavior, which occurs when the diode switches off while carrying a