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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.

The high-voltage sub-nanosecond pulses with high repetition rate are widely used. The Marx-bank circuit (MBC) based on the avalanche bipolar junction transistor (ABJT) is an important and efficient choice to meet the above pulse requirements. However, in traditional MBC, the ABJTs triggered by voltage ramps at the first few stages have obvious reliability differences. The pulse repetition frequency (PRF) of MBC is commonly limited to the kHz level due to the failure of ABJT at the most vulnerable stage. By analyzing the switching transients of ABJT, this work shows that the device reliability is closely related to the slope of voltage ramp. The current paths of devices are experimentally observed and their formation processes and reliability differences are analyzed by simulation under different slope voltage ramp triggering conditions. The results show that the device triggered by slow voltage ramp is most vulnerable to damage due to its limited conductive width. Therefore, an improved MBC with triggering acceleration (MBC-TA) is proposed. The device reliability at the most failure-prone stage is improved by increasing the triggering speed. A $1\times 15$ -stage MBC-TA is developed to verify the capability of high PRF and high reliability. It achieves an output amplitude of 1.15 kV, a rise time of 250 ps, a pulsewidth of 500 ps, and a PRF of 1 MHz. This investigation of device reliability and the improvement of MBC-TA provide a reference for the applications of MBCs based on ABJTs under high-frequency pulse conditions.