Edge termination impact on clamped inductive turn-off failure in high-voltage IGBTs under overcurrent conditions

Abstract

This work provides a physical insight into the failure of high-voltage IGBT modules for railway traction when an overload current event occurs during a clamped inductive turnoff. The inspection of failed IGBTs in power modules coming from the field reveals burnt-out points in the vicinity of the device edge termination. This physical signature has been also verified by experimental tests. To explore this result, physical TCAD simulations have been carried out considering, for the first time, the electro-thermal mismatch introduced by the edge termination. From simulation and experimental results, a destructive dynamic avalanche phenomenon at the last IGBT cell is identified as responsible for the observed failure.

Unclamped repetitive stress on 1200V normally-off SiC JFETs

“…The other 50% did not show any appreciable surface damage. The above observation suggests a consideration: the weakness of the analyzed devices is strongly related to the termination behavior during unclamped operations, very similarly to what evidenced in past works that refer to silicon traditional devices [8][9][10].…”

“…It is worth to note that many results have been reported in the literature on the weaknesses of the terminations during unclamped operations, but all of them about conventional silicon devices [7][8][9][10], except for two very recent papers, that face the termination weakness problem on silicon carbide devices for Schottky diodes [11,12].…”

Study of layout influence on ruggedness of NPT-IGBT devices by physical modelling

“…To account for the electrothermal mismatch in the die, they have been connected in a mixed mode approach by means of sharing resistors, as detailed further on. This approach contrasts to those followed up to now [6,[8][9][10].…”

“…But, all cells of a single die cannot be considered in our simulation. As a consequence, R Sh,Core and R Sh,Periphery are tuned with the purpose of: Certainly, these resistances are a simulation strategy to attenuate the current diverted through the StrA and StrB structures which could lead to an overestimated enhancement of the electric field and a premature breakdown of the device termination [6]. In addition, capacitive effects among the several structures can lead to a non-realistic current redistribution as reported in [9], since a full die is simulated by means of a simple paralleled IGBT cell distribution and the intercell capacitive effects (negative differential capacitive effects [13]) are not properly taken into account.…”

“…Experimental ruggedness tests previously performed on several IGBT power modules (3.3 kV/1200 A, 24 IGBT devices) in a clamped inductive turn-off have shown a not so good avalanche capability [1,6]. The failure sequence of an overcurrent turn-off process during a clamped inductive turn-off is extensively depicted in [1].…”