Study on the influence of voltage rise rate of the external pulse on the characteristic of ultra-high voltage silicon carbide superfast ionization thyristor

Superfast ionization thyristor (SIT) is a novel solid-state semiconductor switch specifically designed for the pulse power systems. Compared to the traditional pulse power switches, the SIT exhibit advantages in terms of voltage handling, operating frequency, stability, reliability and compact size. Although research on silicon-based SIT (Si SIT) dominates this field for many years, studies focusing on silicon carbide-based (SiC) SIT remain relatively scarce. A voltage rise rate (dV/dt) of the external pulse is critical to the operation of SIT. However, few studies have explored the physical mechanisms linking dV/dt with the switching characteristics of SIT. In this article, the device under the study is traditional SiC thyristor with static breakdown voltage (U_vb) of 13.27 kV. The influence of external pulse’s dV/dt on the switching characteristics of ultra-high voltage silicon carbide superfast ionization thyristor (UHV SiC SIT) was investigated through numerical simulation. Under a DC bias voltage (U₀) of 10 kV, the UHV SiC SIT was triggered by the external pulse with varying dV/dt values. The switching characteristics, including maximum voltage (U_max), switching time (T_on), and delayed time (T_delay) were obtained. The electric field distribution and carrier concentration profiles were compared at the moments when the device anode voltage reached U₀ and U_vb. The results show that the switching characteristics of the UHV SiC SIT improve as the dV/dt value of external pulse increases, these improvements are attributed to the variation in carrier concentration within the N⁻ long base layer of device. The effects of non-equilibrium carrier drift and injection significantly influence carrier concentration variations, the injection effect having a stronger influence on carrier concentration than the drift effect. Our research shows that for the UHV SiC FID, the dV/dt of the external pulse is not the larger the better, it needs to be considered in a compromise in the discharge circuit limitation, the switching time of device and the minimum dV/dt of external pulse.