Turn-Off Time as an Early Indicator of Insulated Gate Bipolar Transistor Latch-up

In this paper, effects preceding a latch-up fault in insulated gate bipolar transistors (IGBTs) are studied. Primary failure modes associated with IGBT latch-up faults are reviewed. Precursors to latch-up, primarily an increase in turn-off time as a consequence of elevated junction temperature, are examined for an IGBT. The relationship between junction temperature and turn-off time is explained by modeling the parasitic properties of an IGBT. A metric is derived from the model to standardize the relative estimates in junction temperature from measurements of turn-off time. To evaluate the effects preceding latch-up in-situ, seeded fault testing is conducted on a three-phase power inverter using aged transistors induced with a fault located in the die-attach solder layer. Experimental results demonstrated the feasibility of using the proposed metric as a precursor to transistor latch-up.

I. Introduction

Next generation integrated power systems (NGIPS) aims to increase “fight through” capability and survivability by enabling near instantaneous reconfiguration of power resources and graceful degradation following damage or equipment failure [1]. Of particular interest are propulsion motor modules (PMM) which consist of electric propulsion motors and electric motor drives. Propulsion motors include permanent magnet motors (radial air gap, axial air gap, or transverse flux) and induction motors (wound rotor or squirrel cage). Corresponding electric motor drives include cyclo-converter (with variations in control and power device types), pulse width modulated converter/inverter (with many variations in topology) and switching (hard switched, soft switched) [2]. Critical components of a PMM include switching elements (transistors and diodes), DC filter capacitors and machine windings [3]. In the case of the switching elements, the insulated gate bipolar transistor (IGBT) is frequently used in medium to high-power applications such as switched-mode power supply, traction motor control, and induction heating.