Characterization and Analysis of a Power Transistor for Reverse Second Breakdown When Subjected to Neutron Fluence

It is shown, using extensive experimental data, that the dominant mode of reverse-biased second breakdown (RBSB) in a typical fast-switching radiation hardened power transistor is that of avalanche injection. This is an electronic mechanism rather than a thermal mechanism; therefore, the use of the second breakdown energy parameter, ESB, to characterize the RBSB performance is incorrect. The RBSB characteristics of a large sample of devices were measured over a wide range of conditions in sophisticated test circuits before and after neutron irradiation. The observed behavior is explained using computer models for current pinching and avalanche injection.