Thyristors for pulsed power applications

Among solid state switches, thyristors are best suited for pulsed power applications. An important rating for thyristors operated in the pulse mode is the action of the current, the integral of the square of the current over time, which can be related to the heating of the wafer. The action ratings of the 125 mm thyristors having a involuted gate structure were determined. Changing the gate structure to a highly interdigitated pattern resulted in thyristors with improved action ratings. This change in the gate structure decreased the switching time and the forward voltage drop of the switch, but the thyristors failed when the action of the current was less than expected. As an example, one thyristor with a highly interdigitated gate structure was degraded by a damped current waveform with a peak current of 270 kA, an initial di/dt of 4.7 kA//spl mu/s and an action of 6.6/spl times/10/sup 6/ A/sup 2/s. The expected ratings for the peak current and action were 410 kA and 1.5/spl times/10/sup 7/ A/sup 2/s respectively. It is speculated that the thyristors failed due to dynamic avalanche which is caused by a critical combination of peak recovery current and reverse voltage. The details of this phenomenon, the circuit configurations, device processing and gate structures and gating techniques are described.