A proposal for early warning indicators to detect impending metallization failure of DMOS transistors in cyclic operation

DMOS transistors in integrated smart power technologies are often subject to cyclic power dissipation with substantial self-heating. This leads to repetitive thermo-mechanical stress, causing fatigue of the on-chip metallization and limiting the lifetime. Hence, most designs use large devices for lower peak temperatures and thus reduced stress to avoid premature failures. However, significantly smaller DMOS transistors are acceptable if the system reverts to a safer operating condition with lower stress when a failure is expected to occur in the near future. Hence, suitable early-warning sensors are required. This paper proposes a floating metal meander embedded between DMOS source and drain to detect an impending metallization failure. Measurement results of several variants will be presented and discussed, investigating their suitability as early warning indicators.