2.2.2 High Power Device Operation

SiC has been projected to have tremendous potential for high voltage solid state power devices with very high voltage and current ratings because of its high electric breakdown field of $1.5-4\times 10^{6}$ V/cm and high thermal conductivity of $2.3-4$W/cmK, depending on the doping level [43].

$$V_\mathrm{B}=\displaystyle\frac{E_\mathrm{B}\cdot W}{2}=\displaystyle\frac {\varepsilon_{s}\cdot E^2_\mathrm{B}}{2{\mathrm{q}}\cdot N_\mathrm{B}}$$ (2.3)

The high breakdown field allows the use of much higher doping and thinner layers for a given voltage than required in Si devices, resulting in specific on-resistances for SiC unipolar devices that can be 1/300$^{th}$ that of the equivalent Si devices.

$$R_\mathrm{on,sp}=\displaystyle\frac{V^2_\mathrm{B}}{\mu_{n}\cdot\varepsilon_{s}}\cdot\left(\frac{3}{2E_\mathrm{B}}\right)^{3}$$ (2.4)

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 [44,13]. Switching energy loss is often a function of the turn-off time of the semiconductor device. The faster a device turns off, the smaller its energy loss in a switched power conversion circuit. 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.

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 the use of proportionally smaller capacitors, inductors, and transformers, which in turn can greatly reduce overall system size and weight [10]. While SiC's smaller on-resistance and faster switching helps minimize energy loss and heat generation [45], SiC's higher thermal conductivity enables more efficient removal of heat from the active device region. 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, etc.) typically needed to keep high-power devices from overheating can be made much smaller or even eliminated. T. Ayalew: SiC Semiconductor Devices Technology, Modeling, and Simulation