Failure mechanism of GTO devices and optimization for minimum current crowding during turn-off

Abstract

The maximum controllable anode current is influenced by the current crowding phenomenon observed in GTO thyristors during turn-ofT. This phenomenon initiates (1) the formation of the current filament with a density much higher than its surrounding the leads to localized thermal instability; and (2) the conductivity modulation at the conduction channel causing a non-uniform electric field distribution within the depletion layer, and a resulting an early punch-through breakdown. In this paper, the failure mechanism is discussed. Internal parameters are optimized qualitatively through detailed two-dimensional device simulations to minimize the current crowding and, at the same time, to maintain a low forward voltage drop and short turn-off time for a GTO model-cell. It is found that a lower localized thermal stress and a more uniform electric field distribution can be obtained.