Over-current Capability of SiC Devices for Short Power and Heat Pulses

Unsymmetrical faults in the power system typically last for approximately 200 ms until the circuit breakers clear the faults. Hence, it is important to ensure that power semiconductors in converters do not fail due to the associated increased current. This is possible if the heat generated in the SiC device due to over-currents (OCs) is removed as soon as possible. Various materials such as metals (copper, aluminum, nickel, silver and gold), diamond, graphite and phase change materials for removing the heat just below/above the semiconductor have been considered in this paper. The calculations and COMSOL simulations have been performed assuming a heat pulse on one side of the material and adiabatic conditions on the other side. This assumption is valid for short pulses as the components further away would take more time to absorb heat. It has been concluded that the higher thermal conductivity, the faster is the removal of the heat from the semiconductor. Because of this, metals, diamond and graphite have been proven to be more effective in heat removal and keeping the temperature below 250°C during OCs for the heat pulse of 400 W/cm
²
for 200 ms. The concept of sensible height and limitations of the use of the materials is also discussed. There is a limit to the reduction of junction temperature by adding and increasing the amount of material above the chip. After this limit, the further reduction of junction temperature is not possible, even by increasing the amount of material. This limit reached is different for different materials.