Investigation of the relationship between current filament movement and local heat generation in IGBTs by using modified avalanche model of TCAD

For development of high voltage power devices, it is very important to understand local heat generation phenomena of current filaments especially for reliability designs. Current filaments mean high density currents flow only in some parts of active cells and induce large heat generation locally. They appear when excessive current flows for some reasons during device switching. The aim of this paper is to clarify the following by using a modified avalanche model: The local lattice temperature dependence of impact ionization coefficients is a main factor in current filament movements, and the movements significantly suppress local heat generation. In particular, this tendency becomes even stronger when the ambient temperature is low and after the depletion layer reaches the buffer layer on the back surface side of IGBTs.