CORRELATION BETWEEN LOCAL SEGMENT CHARACTERISTICS AND DYNAMIC CURRENTREDISTRIBUTION 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 tran sient. This behavior is investigated in practical, large area GTO's (6 00 A, 1600 V) by comparing the static and dynamic characteristics of t he individual device segments with turnoff current density estimates f or the complete device. Critical quantities (reverse gate-cathode brea kdown voltage, forward on-state voltage and storage time) are mapped u sing an automatic probing system while the current density estimates a re obtained using a recently developed magnetic field measurement tech nique. Good correlation is found between the current density peaks, th e segment measurements and variations in the mesa etching depth across the processed wafer. In addition, conditions are established which re late the distribution of current density peaks and segment characteris tics 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 sub sequent device failure.