The future of power conversion at low-to-medium voltages (around 650V) poses a very interesting debate. At low voltages (below 100V), the silicon MOSFET reigns supreme and at the higher end of the automotive medium voltage application spectrum (approximately 1 kV and above) the SiC power MOSFET looks set to topple the dominance of the silicon IGBT. At very high voltages (4.5 kV, 6.5 kV and above) used for grid applications, the press-pack thyristor remains undisputed for current source converters and the press-pack IGBTs for voltage source converters. However, around 650 V, there does not seem to be a clear choice with all the major device manufacturers releasing different technology variants ranging from SiC Trench MOSFETs, SiC Planar MOSFETs, cascode-driven WBG FETs, silicon NPT and Field-stop IGBTs, silicon super-junction MOSFETs, standard silicon MOSFETs and enhancement mode GaN HEMTs. Each technology comes with its unique selling point with GaN being well known for ultra-high speed and compact integration, SiC is well known for high temperature, electro-thermal ruggedness and fast switching while silicon remains clearly dominant in cost and proven reliability. This review comparatively assesses the performance of some of these technologies, investigates their body diodes, discusses device reliability and avalanche ruggedness.

The temperature and dV/dt dependence of crosstalk has been analyzed for Si-IGBT and SiC-MOSFET power modules. Due to a smaller Miller capacitance resulting from a smaller die area, the SiC module exhibits smaller shoot-through currents compared with similarly rated Si-IGBT modules in spite of switching with a higher dV/dt and with a lower threshold voltage. However, due to high voltage overshoots and ringing from the SiC Schottky diode, SiC modules exhibit higher shoot-through energy density and induce voltage oscillations in the dc link. Measurements show that the shoot-through current exhibits a positive temperature coefficient for both technologies, the magnitude of which is higher for the Si-IGBT, i.e., the shoot-through current and energy show better temperature stability in the SiC power module. The effectiveness of common techniques of mitigating shoot-through, including bipolar gate drives, multiple gate resistance switching paths, and external gate-source and snubber capacitors, has been evaluated for both technologies at different temperatures and switching rates. The results show that solutions are less effective for SiC-MOSFETs because of lower threshold voltages and smaller margins for negative gate bias on the SiC-MOSFET gate. Models for evaluating the parasitic voltage have also been developed for diagnostic and predictive purposes. These results are important for converter designers seeking to use SiC technology.

The tradeoff between the switching energy and electro-thermal robustness is explored for 1.2-kV SiC MOSFET, silicon power MOSFET, and 900-V CoolMOS body diodes at different temperatures. The maximum forward current for dynamic avalanche breakdown is decreased with increasing supply voltage and temperature for all technologies. The CoolMOS exhibited the largest latch-up current followed by the SiC MOSFET and silicon power MOSFET; however, when expressed as current density, the SiC MOSFET comes first followed by the CoolMOS and silicon power MOSFET. For the CoolMOS, the alternating p and n pillars of the superjunctions in the drift region suppress BJT latch-up during reverse recovery by minimizing lateral currents and providing low-resistance paths for carriers. Hence, the temperature dependence of the latch-up current for CoolMOS was the lowest. The switching energy of the CoolMOS body diode is the largest because of its superjunction architecture which means the drift region have higher doping, hence more reverse charge. In spite of having a higher thermal resistance, the SiC MOSFET has approximately the same latch-up current while exhibiting the lowest switching energy because of the least reverse charge. The silicon power MOSFET exhibits intermediate performance on switching energy with lowest dynamic latching current.

Silicon carbide Schottky barrier diodes (SiC-SBDs) are prone to electromagnetic oscillations in the output characteristics. The oscillation frequency, peak voltage overshoot, and damping are shown to depend on the ambient temperature and the metal-oxide- semiconductor field-effect transistor (MOSFET) switching rate (dI _DS /dt). In this paper, it is shown experimentally and theoretically that dI _DS /dt increases with temperature for a given gate resistance during MOSFET turn-on and reduces with increasing temperature during turn-off. As a result, the oscillation frequency and peak voltage overshoot of the SiC-SBD increases with temperature during diode turn-off. This temperature dependence of the diode ringing reduces at higher dI _DS /dt and increases at lower dI _DS /dt. It is also shown that the rate of change of dIDS/dt with temperature (d ² I _DS /dtdT) is strongly dependent on R _G and using fundamental device physics equations, this behavior is predictable. The dependence of the switching energy on dI _DS /dt and temperature in 1.2-kV SiC-SBDs is measured over a wide temperature range (-75 °C to 200 °C). The diode switching energy analysis shows that the losses at low dI _DS /dt are dominated by the transient duration and losses at high dI _DS /dt are dominated by electromagnetic oscillations. The model developed and results obtained are important for predicting electromagnetic interference, reliability, and losses in SiC MOSFET/SBDs.

A 1.2-kV/24-A SiC-MOSFET and a 1.2-kV/30-A Si-Insulated gate bipolar transistor (IGBT) have been electrothermally stressed in unclamped inductive switching conditions at different ambient temperatures ranging from -25 °C to 125 °C. The devices have been stressed with avalanche currents at their rated currents and 40% higher. The activation of the parasitic bipolar junction transistor (BJT) during avalanche mode conduction results from the increased body resistance causing a voltage drop between the source and body, greater than the emitter-base voltage of the parasitic BJT. Because the BJT current and temperature relate through a positive feedback mechanism, thermal runaway results in the destruction of the device. It is shown that the avalanche power sustained before the destruction of the device increases as the ambient temperature decreases. SiC MOSFETs are shown to be able to withstand avalanche currents equal to the rated forward current at 25 °C, whereas IGBTs cannot sustain the same electrothermal stress. SiC MOSFETs are also shown to be capable of withstanding avalanche currents 40% above the rated forward current though only at reduced temperatures. An electrothermal model has been developed to explain the temperature dependency of the BJT latchup, and the results are supported by finite-element models.

Voltage sourced converters (VSCs) in electric vehicle (EV) drive-trains are conventionally implemented by silicon Insulated Gate Bipolar Transistors (IGBTs) and p-i-n diodes. The emergence of SiC unipolar technologies opens up new avenues for power integration and energy conversion efficiency. This paper presents a comparative analysis between 1.2-kV SiC MOSFET/Schottky diodes and silicon IGBT/p-i-n diode technologies for EV drive-train performance. The switching performances of devices have been tested between -75 °C and 175 °C at different switching speeds modulated by a range of gate resistances. The temperature impact on the electromagnetic oscillations in SiC technologies and reverse recovery in silicon bipolar technologies is analyzed, showing improvements with increasing temperature in SiC unipolar devices whereas those of the silicon-bipolar technologies deteriorate. The measurements are used in an EV drive-train model as a three-level neutral point clamped VSC connected to an electric machine where the temperature performance, conversion efficiency and the total harmonic distortion is studied. At a given switching frequency, the SiC unipolar technologies outperform silicon bipolar technologies showing an average of 80% reduction in switching losses, 70% reduction in operating temperature and enhanced conversion efficiency. These performance enhancements can enable lighter cooling and more compact vehicle systems.