Eliminating antiparallel silicon carbide Schottky barrier diode (SiC SBD) and making use of the intrinsic body diode of SiC metal–oxide–semiconductor-field-effect transistor (SiC MOSFET) offer a cost-effectiveness solution without obviously sacrificing the conversion efficiency in some power converter applications. Although the body diode of commercial SiC MOSFET has been qualified by several manufacturers, the reliability of SiC MOSFET under repetitive surge current stress of body diode has not been sufficiently studied. In this article, the new degradation phenomena of SiC MOSFET’s gate oxide are observed, and the degradation mechanism is discussed when the intrinsic body diode of the 1200-V SiC planar gate MOSFETs was subjected to surge current stress. TCAD simulation and experimental measurements indicate that the generation and accumulation of electrons or holes within the gate oxide under surge current stress are the main reasons for the degradation of SiC MOSFET. Finally, a mitigation technique with optimal gate turn-off voltage is suggested to suppress the gate oxide degradation of the SiC MOSFET under surge current stress of its body diode.

Investigation on Degradation of SiC MOSFET Under Surge Current Stress of Body Diode

Recent advancements in silicon carbide (SiC) power semiconductor technology enable developments in the high-power sector, e.g., high-voltage-direct-current (HVdc) converters for transmission, where today silicon (Si) devices are state-of-the-art. New submodule (SM) topologies for modular multilevel converters offer benefits in combination with these new SiC semiconductors. This article reviews developments in both fields, SiC power semiconductor devices and SM topologies, and evaluates their combined performance in relation to core requirements for HVdc converters: grid code compliance, reliability, and cost. A detailed comparison of SM topologies regarding their structural properties, design and control complexity, voltage capability, losses, and fault handling is given. Alternatives to state-of-the-art SMs with Si insulated-gate bipolar transistors (IGBTs) are proposed, and several promising design approaches are discussed. Most advantages can be gained from three technology features. First, SM bipolar capability enables dc fault handling and reduced the energy storage requirements. Second, SM topologies with parallel conduction paths in combination with SiC metal–oxide–semiconductor field-effect transistors offer reduced losses. Third, a higher SM voltage enabled by a higher blocking voltage of SiC devices results in a reduced converter complexity. For the latter, ultrahigh-voltage bipolar devices, such as SiC IGBTs and SiC gate turn- off thyristors, are envisioned.

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Comparative Evaluation of Voltage Source Converters With Silicon Carbide Semiconductor Devices for High-Voltage Direct Current Transmission

Accelerated lifetime tests (ALTs) play a critical role in long-term reliability studies of SiC MOSFETs, including lifetime estimation, failure analysis, and condition monitoring. This article presents a comprehensive review of state-of-the-art ALTs circuits, operating principles, and induced failure modes for SiC MOSFETs. First, the weak spots and corresponding aging mechanisms in both device chip and package are summarized. Next, based on the system operating conditions, ALT configurations and working principles are discussed. Specifically, SiC MOSFET ALTs under normal operation, third-quadrant conduction, and extreme conditions are comprehensively described and compared. Requirements and future trends on ALTs selection and development are comprehensively discussed corresponding to various reliability research directions. Finally, suitable ALTs, corresponding failure locations, and mechanisms are tabulated as the conclusion. This review intends to provide insight on SiC MOSFET reliability test selection, platform development, and test parameter adjustments depending on application requirements. 

Aging Mechanisms and Accelerated Lifetime Tests for SiC MOSFETs: An Overview

In this work, the surge reliability of 1200 V SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) from various manufactures has been investigated in the reverse conduction mode. The surge current tests have been carried out in the channel conduction and non-conduction modes. The experimental results show that the maximum surge currents that the devices can withstand are similar for both cases. It is found that short circuits occurred between the gate and the source in the failed devices. The characteristics of the body diode have also changed after the tests. By measuring the device characteristics after each surge current is applied, it can be concluded that the damages to the gate oxide layer and the body diode occurred only when the maximum surge current is applied. By decapping the failed devices and observing the cross section of the damaged cell, it is found that high temperature caused by excessive current flow through the devices during the surge tests is the main reason for the device failure. Finally, the TCAD simulation of the devices has been carried out to bring insight into the operation of the devices during the surge events.

Investigation of 1200 V SiC MOSFETs' Surge Reliability.

In this work, third-quadrant $I$ – $V$ characterization and surge current tests are carried out on SiC asymmetric-trench MOSFET (DUT A) and SiC double-trench MOSFET (DUT B) under various gate–source biases ( $V_{\mathrm {GS}}$ ). The surge capability is found to be uninfluenced by $V_{\mathrm {GS}}$ for DUT A. However, it has a 71.4% increase when $V_{\mathrm {GS}}$ changes from 0 to −5 V for DUT B. The $I$ – $V$ characteristics in the third quadrant are measured under various $V_{\mathrm {GS}}$ . It is found that the channel is open when the source–drain voltage is >2.5 V for DUT A and >1.5 V for DUT B at $V_{\mathrm {GS}} =0$ V. High-temperature measurements are also conducted from 298 K to 448 K. When $V_{\mathrm {GS}} =0$ V, the channel current takes up to 50% at 10-A source-to-drain current for DUT B, whereas only 10% for DUT A. This could lead to high current/heat density in the channel of DUT B. The transient resistance is also extracted from the surge $I$ – $V$ trajectories, and it is higher for DUT B tested under $V_{\mathrm {GS}} =0$ V, which will increase the dissipated surge energy. Finally, the failure mechanism is analyzed. For DUT A, aluminum melting contributes to the failure at $V_{\mathrm {GS}}= -5$ V and $V_{\mathrm {GS}} =0$ V. For DUT B tested at $V_{\mathrm {GS}} =0$ V, the earlier breakdown happens due to gate oxide failure.

Investigation on Surge Current Capability of 4H-SiC Trench-Gate MOSFETs in Third Quadrant Under Various V GS Biases

The superior performance of the SiC MOSFETs operating in synchronous mode converter without external antiparallel SiC Schottky diodes have been demonstrated recently. However, there are few studies of the surge current capability of the SiC MOSFET's body diode, leading severe concern for its ruggedness in practical power converter applications. The purpose of this paper is to experimentally compare the non-repetitive surge current capability of the SiC MOSFET's intrinsic body diode and SiC Schottky diode, and analyze the physical mechanisms of their degradation after surge current stress. Their surge current capability and electrical characteristics before and after surge current stress are measured and analyzed. Experimental study shows that the non-repetitive peak surge current of the SiC MOSFET's body diode is slightly larger than that of the SiC Schottky diodes. The degradation of the SiC Schottky diode after surge current stress is accompanied with the increase of drain leakage current, while the degradation of the SiC MOSFET after the body diode's surge current stress is accompanied with the variation of the threshold voltage and input capacitance of the SiC MOSFET. The analysis shows that the degradation of the SiC MOSFET after the surge current stress may be correlated with the interface traps of SiC/SiO 2 interface.

Dongyuan Zhai

Papers

Investigation on Degradation of SiC MOSFET Under Surge Current Stress of Body Diode

Comparison Study of Surge Current Capability of Body Diode of SiC MOSFET and SiC Schottky Diode