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

The peak commutatable current of a typical GTO thyristor is limited by the redistribution of anode current occurring during the turnoff transient. This behavior is investigated in practical, large area GTO's (600 A, 1600 V) by comparing the static and dynamic characteristics of the individual device segments with turnoff current density estimates for the complete device. Critical quantities (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 recently developed magnetic field measurement technique. Good correlation is found between the current density peaks, the segment measurements and variations in the mesa etching depth across the processed wafer. In addition, conditions are established which relate the distribution of current density peaks and segment characteristics to the realization of a near-perfect GTO technology. Finally, the behavior of the current density distribution during the current fall and early tail period is related to the onset of filamentation and subsequent device failure