Electro — Thermal analysis of relationship between boundary thermal resistance and hot spot temperature of power Si MOSFET

This paper describes the relationship between the boundary thermal resistance and the hot spot temperature in power Si MOSFET. Power Si MOSFET is widely used semiconductor device in various area, for example car electronics. Since high voltage is applied to power Si MOSFET, high electric field (more than 10 V/m) is generated. Under such high electric field, electron thermal energy becomes much higher than lattice thermal energy. To consider this non-equilibrium state between electron energy and lattice energy, electro-thermal analysis is employed in this work. Conventionally, constant temperature boundary is applied at the bottom surface (cooling surface) of power Si MOSFET, and adiabatic boundary is applied at other surface in electro-thermal analysis. However, constant temperature means zero thermal resistance of the surface on power Si MOSFET. This is not real case since any cooling technique has thermal resistance. And temperature of cooling surface is dependent on thermal resistance (cooling performance) of the surface. In this paper, the relationship between boundary thermal resistance and hot spot temperature of power Si MOSFET is discussed. The calculation results show that the adiabatic boundary condition is appropriate for the boundaries except for the cooling surface, but the constant temperature boundary is not suitable in almost all cases.