2-kV Thyristor Triggered in Impact-Ionization Wave Mode by a Solid-State Spiral Generator

Impact-ionization wave triggering of a thyristor enables it to switch significantly higher currents with much faster rise times ( $\text{d}I / \text{d}t$ ) than through conventional triggering; indeed tests on commercial components demonstrate that both current and $\text{d}I / \text{d}t$ can be increased an order of magnitude over their specified datasheet values by utilizing impact ionization. However, creating an impact ionization wave places stringent requirements on the generator used to trigger the thyristor—particularly the trigger pulse must have a voltage rise rate ( $\text{d}V / \text{d}t$ ) of more than 1 kV/ns and an amplitude over twice the thyristors static breakdown voltage. Given the capacitance of a thyristor is relatively large, often hundreds of pF, this is difficult to achieve with many common triggering methods. In this study, we present a bespoke, cost-effective, trigger generator that has been developed based on spiral/vector inversion techniques coupled to an optimized sharpening circuit. Using this generator, both a 2-kV single thyristor and a 4-kV stack of two thyristors in series were triggered in the impact-ionization mode. The thyristors had a wafer diameter of 32 mm and capacitances of 370 pF. With a single thyristor 100 shots were performed with it switching a peak current of 1.25 kA and an associated $\text{d}I / \text{d}t$ of 12 kA/ $\mu \text{s}$ . With two thyristors, peak currents of 2.6 kA and with $\text{d}I / \text{d}t$ of 25 kA/ $\mu \text{s}$ were achieved. In all experiments no degradation of the semiconductor structure was observed. The work opens the way for developing very powerful, but still compact, solid-state trigger generators and larger pulsers for a wide range of pulsed power applications.