Correlation between local segment characteristics and dynamic current redistribution in GTO power thyristors

The peak controllable current of a typical GTO (gate turn-off) thyristor is limited by the redistribution of anode current, occurring during the turn-off transient. This behavior is investigated in practical large-area GTOs (600 A, 1600 V) by comparing the static and dynamic characteristics of the individual device segments with turn-off current density estimates for the complete device. Reverse gate-cathode breakdown voltage, forward on-state voltage, and storage time are mapped using an automatic probing system while the current density estimates are obtained using a magnetic field measurement technique. Good correlation is found between the current density peaks, the segment measurement, and variations in the mesa etching depth across the processed wafer. Conditions are established which relate the distribution of current density peaks and segment characteristics to the realization of a near-perfect GTO technology. The behavior of the current density distribution during the current fall and early tail period is related to the onset of of filamentation and subsequent device failure