Onset of current filamentation in GTO devices

The onset of inhomogeneous current distribution at turn-off of fine-structured gate turn-off thyristors was investigated. The investigation has been done using two-dimensional device simulation to describe how a perturbed thyristor cell, located in a surrounding of unperturbed cells, behaves during a turn-off sequence. Criteria for absolute stability and a description of the development of an instability are given. It is found that this onset current filamentation can be avoided if a turn-off gain less than a certain critical value, B/sub crit/, is used, and a homogeneous turn-off can be achieved. B/sub crit/ is always less than 1.0, i.e more current must be extracted from the gate than flows through the device in the on state.<>