The safe-operating-area (SOA) of automotive DMOS transistors, which are operated repeatedly under high power pulses (power cycling), is lower than the classical singlepulse SOA and it is dependent on the geometry of the transistor. In this paper, we present a test system for reliability characterization of power devices, of various geometries, which operate under power cycling conditions.
INTRODUCTIONAutomotive smart-power switches are used in powertrain applications (e.g. engine management) to drive actuators which have an inductive behavior (relays, valves) or a capacitive behavior (light bulbs). Often, the switching element is a DMOS (double-diffused MOS) transistor. These devices are subject to elevated junction temperatures, caused by self-heating, during high power transients generated while driving inductive or capacitive loads. While operated repetitively under high power events (power cycling), the reliability of the whole chip can be affected by cracks in the DMOS metallization system due to thermo-mechanical effects [1]. Mechanical stresses accumulate with each power cycle, until fracture of inter-metal dielectric (IMD) occurs, which is followed by short-circuit of nearby metal lines [2].