A Study of a 5.2-kV/100-mm Thyristor Triggered in Impact-Ionization Mode Toward Fast High-Current Applications

Microsecond-range high-current pulses (hundreds of kA) with high $dI/dt$ (100 $\textrm {kA/$\mu $s}$ ) are used to generate megagauss-range magnetic fields. Industrial applications of such technology require high average power, repeatability, and a reliable high-current pulse generator with a long lifespan. Hence, the development of a fast solid-state switch operating in the range of several hundred kA is of great interest. The switching characteristics of semiconductor devices have been substantially enhanced due to an effect of the delayed impact-ionization breakdown of the high-voltage p-n junction. This leads to the subnanosecond switching time of high-voltage semiconductor devices and an increase in their rate of current rise $dI/dt$ capability. Nevertheless, the maximum current amplitude and $dI/dt$ are limited by the area of the semiconductor device. Therefore, to increase current switching parameters, one can use a large-area structure. However, a trigger generator becomes the main challenge, in this case, due to the increased capacitance of the switch. In this article, we study the possibility of triggering large-area thyristors in impact-ionization wave mode using a Marx generator equipped with a peaking module. An experimental setup has been developed to investigate a switching process of the thyristors with a wafer diameter of $\textrm {100}~\textrm {mm}$ and a blocking voltage of $\textrm {5.2}~\textrm {kV}$ . A trigger circuit based on the Marx generator with the peaking module was developed. It can deliver pulses with $dV/dt$ of several kV/ns into a few nF capacitive loads which correspond to the equivalent thyristor capacitance. Next, the transition of the thyristor from the blocking state to the conducting state in impact-ionization mode without energy switching is presented. Finally, by adding an energy discharge circuit, the thyristor switching in impact-ionization mode is analyzed. By applying a trigger pulse with $dV/dt$ of 1.7 kV/ns to the thyristor, the voltage across it reaches 10.7 kV that leads to the following switching parameters: thyristor switching time 420 ps, $dI/dt~\sim 15~\textrm {kA/$\mu $s}$ , current amplitude $\sim 20$ kA, and current full width at half maximum (FWHM) $\sim 3~\mu \text{s}$ . To the best of our knowledge, impact-ionization switching of the standard thyristor (5.2 kV, 100 mm) was demonstrated for the first time.