Investigation on Single Pulse Failure of Avalanche Transistors Triggered by Voltage Ramps in Marx Bank Circuits

Although the Marx bank circuit (MBC) based on the avalanche bipolar junction transistor (ABJT) is widely used in the field of pulse power generators, the main trouble that ABJT triggered by voltage ramp is prone to failure still exists. To explain the obvious reliability differences of ABJTs triggered by voltage ramps of different dV/dt in MBC, the degradation and failure features under a single switching event are analyzed. The normal current path and the leakage current path of the failed device are compared by optical visualization to determine the failure point. A three-dimensional model is established to summarize the voltage ramp triggering conditions and the influence factors. The variations of the current path and the temperature distributions are analyzed by corresponding physical models. The results show that the current path triggered by the slow voltage ramp is easily confined to the device edge due to the insufficient displacement current. The formation of the current filament is related to the way of electron injection and causes the local overheating to damage the main junction. The degraded device completely fails during turning off due to the repeated formations of current filament leading to thermal runaway. The consistency between experimental results and simulations verifies the validity of the explanations. A reference is provided for the optimization of MBC based on ABJT.