Analysis of the various SiC power MOSFETs

Recently, the climate extreme and global warming have become serious so that the carbon emission needs to be reduced. Therefore, the renewable energy and electric vehicles have rapidly developed to alleviate the carbon emission. Generally, in the process of power conversion for the renewable energy and electric vehicles, the power loss (switching loss, off-state loss and conduction loss) of the inverter is partly from the power devices. This is because that the overlaps of the current and voltage during the switching transients cause the switching loss; the specific onresistance during the on-state causes the conduction loss and the reverse leakage current during the off-state causes the off-state loss. Because silicon carbide (SiC) material has the advantages of the higher electric field, better thermal conductivity and lower leakage current, the power system with SiC power devices can have higher power density, higher efficiency, smaller size and lighter weight. Therefore, SiC power devices seem to be the best solution. In order to reduce the power loss further, the structures of SiC diodes and metal-oxide-semiconductor electric effect transistors (MOSFET) must be well designed to have lower reverse recovery time, smaller gate charges, lower leakage current and higher breakdown voltage so that it can be operated at higher frequency and voltage with the very low power loss. For example, if the channel length of a planar MOSFET is reduced, the specific on-resistance and cell pitch will be reduced. But, the short channel effect and lower threshold voltage may occur; if a trench MOSFET is designed to reduce the specific on-resistance, the breakdown voltage may be affected; if a superjunction MOSFET is designed, the process time and cost will be higher. These trade-off relationships between MOSFET structures and performance will be discussed in this presentation.