Reliability Evaluation of Power Devices for High Performance Power Conversion

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2021-06-23

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Abstract

The reliability of power devices becomes significantly important due to the extensive deployment of power electronic systems, especially in industries associated with mission and safety critical products, such as photovoltaic power stations, electric transportation systems. The failure of devices causes unexpected power outages and catastrophic faults. The increasing demand for high power density and high efficiency drives the adoption of wide bandgap (WBG) devices and power integration. Gallium Nitride (GaN) devices, as one type of WBG devices, is favorable due to the lower specific on-state resistance and smaller capacitance, which reduce both the conduction and switching loss and achieve high efficiency. However, as a newly developed device, GaN devices’ reliability still requires comprehensive assessments. To fully understand GaN devices’ robustness, one of the commonly used methods, the DC power cycling test, is conducted to detect the weak points of the devices and identify aging precursors for lifetime estimation. Besides, due to the unique structure and material property, GaN devices suffer dynamic on-state resistance and threshold voltage shift under high voltage stress and hard switching transient, which requires an extended stress profile for thorough reliability evaluation. Therefore, an AC power cycling test covering both high voltage stress and various switching transients is developed to mimic real operations for the comprehensive study of GaN devices’ reliability. Besides, power integration is quite attractive at low power levels using processes that are compatible with the standard (Complementary Metal-Oxide-Semiconductor) CMOS process. With the increase in power rating and faster switching speed, the voltage overshoot on the drain-source terminals during the turn-off transient may push the devices into the avalanche region, which may damage the device and cause power converter malfunctions. Hence, it is necessary to investigate the devices’ robustness against such repetitive strikes. For this purpose, a high-resolution and cost-effective nanosecond current pulse generator (CPG) is designed to inject a current with adjustable magnitude and duration into the device, which can charge the drain-source voltage up to the avalanche voltage under different stress conditions. By using this test setup, a commercial (Metal–Oxide–Semiconductor FieldEffect Transistor) MOSFET is firstly stressed under both long and short pulse durations. The results reveal different degradation and failure mechanisms under different stress conditions. Due to the importance of a large dataset in reliability studies and validation of power devices, a fully modular and scalable test bench is designed based on the proposed CPG, which allows easy maintenance and seamless capacity expansion. Finally, customized (Laterally-Diffused MetalOxide Semiconductor) LDMOS devices are designed to investigate the effect of different chip layouts over the robustness under avalanche conditions.

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Reliability (Engineering), Gallium nitride, Power electronics, Failure analysis (Engineering)

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