Mounira Berkani

Ageing and Failure Modes of IGBT Modules in High-Temperature Power Cycling

This paper presents an experimental study on the ageing of insulated-gate bipolar transistor (IGBT) power modules. The aim is to identify the effects of power cycling on these devices with high baseplate temperatures (60 °C to 90 °C) and wide temperature swings (60 °C to 100 °C). These values for thermal stresses have been defined according to automotive applications. The test conditions are provided by two types of test benches that will be described in this paper. The changes in electrical and thermal indicators are observed regularly by a monitoring system. At the end of the test (reaching damage criterion or failure), different analyses are performed (acoustic scanning and SEM imaging), and the damage is listed systematically. Nineteen samples of 600-V 200-A IGBT modules were thus aged using five different power-cycling protocols. The final summary of results shows that ageing mechanisms mainly concern wire bonds and emitter metallization, with gradual impact depending on protocol severity.

Comparison study on performances and robustness between SiC MOSFET & JFET devices – Abilities for aeronautics application

Abstract This paper deals with performances and reliability aspects of MOSFET and JFET power transistors devices based on silicon carbide technology. The purpose of this article is to evaluate the abilities and effects of each technology on the conception of power converter for avionic applications. Experimental measurements of steady-on-state resistance dependence and transient performances with temperature are presented and discussed. The second section focuses mainly on robustness aspects of the two types of power transistors in order to analyze their capability to withstand with aeronautic harsh environmental constrains.

Robustness of 1.2 kV SiC MOSFET devices

This paper provides an evaluation of robustness and performances of two types of 1.2 kV SiC MOSFETs in order to investigate these power devices for aircraft applications in medium power range. The paper focuses on robustness results showing the weakness of the gate under short-circuit tests. Observed failures appear at the gate level with effects on the mode of failure depending of the short-circuit duration.

Investigation of 1.2 kV investigation of SiC MOSFETs for aeronautics applications

This paper evaluates robustness and performances of two types of 1.2 kV SiC MOSFETs in order to investigate these power devices for medium power aeronautics applications. The first part focuses on switching performances with effects of gate resistance and load current level. The second part focuses on robustness results showing the weakness of the gate under short-circuit test.

Reliability of power MOSFET-based smart switches under normal and extreme conditions for 24 V battery system applications

This study aims to assess the reliability of smart converters for applications using 24 V batteries. It compares degradation effects and lifetime durations for similar dissipated energies when these smart power switches are subjected to normal and extreme protection test conditions. Three experimental ageing tests have been performed: (i) ageing tests under normal protection mode, (ii) ageing tests under repetitive inductive avalanche switching and (iii) ageing tests under repetitive short-circuit. Evolution of several electrical parameters such as on-state resistance; threshold voltage and saturation current have been monitored. Tested devices under normal condition and under repetitive inductive avalanche have failed after about the same number of cycles with the same dissipated energy. However, several results show a significant decrease of the lifetime under repetitive short-circuit tests for a similar dissipated energy.

Estimation of SiC JFET temperature during short-circuit operations

This paper presents results showing the robustness of different SiC JFET transistors from SiCED in current limitation regime or short-circuit operation. Crystal temperature during failure was estimated after different electrical characterizations and using appropriate models of saturation current which is used as a thermal indicator. This work shows the exceptional robustness of SiC JFET transistors in current limitation mode compared to Si devices (MOSFETS and IGBTs).

Mechanisms of power module source metal degradation during electro-thermal aging

The long-term reliability of power devices for applications in the automotive industry is limited by the electro-thermal and/or thermo-mechanical aging of the metallic parts. In the present work, we characterize the bonding wire and source metallization degradation of power MOSFETs-based devices under accelerated aging conditions, through electron and ion microscopy. The metal degradation is driven by an enhanced self-diffusion of aluminium (Al) atoms along the grain boundaries and a generalized fatigue crack propagation from the surface down to the silicon (Si) bulk. The metallization under the wire bonds is a critical location because it is initially plastically deformed during the bonding process. In addition, the wire-metal interface presents several imperfections, such as small cavities and Al oxide residues. During the electro-thermal cycles, they could be the starting point for harmful cracks that run along the interface (and eventually cause the wire lift-off or the cracking of the substrate). Whichever the propagation direction, the generation of these cracks locally increases the device resistance and temperature, and accelerates the aging process until failure. Mechanisms of power module source metal degradation during electro-thermal aging.

In-depth investigation of metallization aging in power MOSFETs ☆

The long-term reliability of modern power MOSFETs is assessed through accelerated electro-thermal aging tests. Previous studies have shown that the source metallization (top metal and wires) is a failure-prone location of the component. To study how the top aluminum metallization microstructure ages, we have performed ion and electron microscopy and mapped the grain structure before and after avalanche and short-circuit aging tests. The situation under the bond wires is significantly different as the bonding process induces plastic deformation prior to aging. Ion microscopy seems to show two inverse tendencies: grain growth under the wires and grain refinement elsewhere in the metallization. Transmission electron microscopy shows that the situation is more complex. Rearrangement of the initial defect and grain structure happen below and away from the wire. The most harmful fatigue cracks propagate parallel to the wire/metal bonding interface.

3-D electrothermal simulation of active cycling on smart power MOSFETs during short-circuit and UIS conditions

Abstract Active cycling of power devices operated in harsh conditions causes high power dissipation, resulting in critical electrothermal and thermo-mechanical effects that may lead to catastrophic failures. This paper analyzes the ageing-induced degradation of the chip metallization of a power MOSFET and its impact on the device robustness during short-circuit and unclamped inductive switching tests. A 3-D electrothermal simulator relying on a full circuit representation of the whole device is used to predict the influence of various ageing levels. It is found that ageing can jeopardize the robustness of the transistor when subject to short-circuit conditions due to the exacerbated de-biasing effect on the gate-source voltage distribution; conversely, this mechanism does not arise under unclamped inductive switching conditions. This allows explaining the difference in time-to-failure experimentally observed for the transistors subject to these tests and dissipating the same energy.

Surface analysis of smart power top metal: IR thermal measurement and source potential mapping

Reliability of modern power MOSFETs is assessed through accelerated electro-thermal aging tests. Top metallization layer reconstruction is one of the most observed degradation mechanisms in power devices operating under short circuit conditions. Experimental analysis results focused on temperature measurement and source potential mapping during ageing will be presented to corroborate previous results on electrical parameters evolution and to give new tools for health monitoring.