Physics of the Negative Resistance in the Avalanche $I{-}V$ Curve of Field Stop IGBTs: Collector Design Rules for Improved Ruggedness

In this paper, we investigate the avalanche behavior of field-stop insulated gate bipolar transistors (IGBTs) by means of analytical and theoretical considerations, supported by ad hoc numerical simulations. A physical explanation of the presence of negative differential resistance branches in the avalanche I-V curve of the IGBT is presented and design criteria are derived to reduce and eventually eliminate this effect.