Repetitive Short-circuit Tests Research Articles

Adaptive Level-Shift Gate Driver With Indirect Gate Oxide Health Monitoring for Suppressing Crosstalk of SiC MOSFETs

An adaptive level-shift gate driver with indirect gate oxide health monitoring for suppressing crosstalk of bridge-leg configured SiC MOSFETs is proposed. This paper firstly presents a holistic assessment of the changes in major intrinsic parameters before and after aging SiC MOSFETs with repetitive short-circuit tests. Gate leakage is found to be an appropriate precursor to reflect gate oxide degradation. Then, the structure, operation, and design of the proposed gate driver are given. The working principle is based on using a digitally controlled variable resistor in a resistor-capacitor-based voltage divider network to adjust the off-state gate-source voltage. Then, the peak off-state gate-source voltage caused by the spurious voltage is regulated at a level that can avoid shoot-through and reduce off-state voltage stress on the gate. Besides suppressing crosstalk, an optimal off-state gate-source voltage can also improve the life expectancy of SiC MOSFET. By utilizing the loading effect of gate leakage current on the proposed gate driver output, the gate oxide degradation is indirectly monitored by observing the change in the value of the variable resistor. The proposed gate driver has been evaluated on a 1kW inverter prototype under various intrinsic parameter variations. Performance comparisons between proposed and traditional gate drivers are given.

Short Circuit Capability Characterization and Analysis of p-GaN Gate High-Electron-Mobility Transistors Under Single and Repetitive Tests

Short circuit (SC) capability of 650-V Schottky-type p-GaN gate high-electron-mobility transistors (HEMTs) under single and repetitive tests is characterized in this article. The investigated devices exhibit strong capability under a single SC test, but weak capability under repetitive SC tests with a bus voltage of 400 V and a gate drive voltage of 6 V. The failure mechanism under repetitive SC tests is revealed through electrothermal simulation and microscale failure spot analysis. Thermal fatigue cracks are formed due to the high temperature spike and local temperature fluctuations in the narrow GaN channel and buffer layers, leading to weak repetitive SC capability. The unique heat confinement effect in the GaN layer plays an important role in the formation of high temperature spike and fatigue cracks. The withstand time in a single SC test is several hundred microseconds due to fast drain current drop that results from high temperature and, to a lesser degree, the dynamic threshold voltage shift during the SC transient. The device failure in a single-event SC test is related to heat diffusion to a wider region. Some guidelines are proposed for handling and improving the repetitive SC capability.

Impact of Repetitive Short-Circuit Tests on the Normal Operation of SiC MOSFETs Considering Case Temperature Influence

This article presents the impact of repetitive short-circuit (SC) tests on the normal operation of a commercial silicon carbide (SiC) MOSFET and the influence of different case temperatures on the SC degradation process. To ensure repeatable SC test conditions, the maximum SC withstanding time is studied at three different case temperatures and the critical energy is identified. To investigate the effect of SC stress on the normal operation, the static and dynamic characteristics are periodically measured along with the repetitive SC activity. The turn-on switching loss increases gradually with the increasing number of repetitive SC tests. This is associated with the increase in the gate leakage current during the SC tests, which shows a reduction in the ON-state gate voltage because of the gate oxide degradation. Then, since the case temperature of the device is subject to the operating condition in the application, the degradation process of repetitive SC tests with respect to different case temperatures is investigated, and the relationship between the number of repetitions to failure and the initial case temperature is established. Finally, the case temperature influence is explained by a 1-D transient thermal model based on the SC condition.

Short Circuit Capability and Short Circuit Induced $V_{\mathrm{TH}}$ Instability of a 1.2-kV SiC Power MOSFET

The withstand capability and threshold voltage ( $V_{\mathrm {TH}}$ ) instability of 1.2-kV silicon carbide (SiC) MOSFETs under repetitive short circuit (SC) tests are investigated. An SC test system is constructed to apply repetitive SC stress to SiC MOSFETs and measure the transfer $I$ – $V$ characteristics and gate-to-source leakage current ( $I_{\mathrm {GSS}}$ ) after each set of SC tests. To evaluate the SC capability, repetitive SC tests with different SC durations ( $t_{p}$ ) are conducted until device failure. The SC withstand time (SCWT) at 1000 SC cycles is found to be $\sim 3.3~\mu \text{s}$ . $V_{\mathrm {TH}}$ instability under repetitive SC tests prior to the device failure is characterized. A bidirectional $V_{\mathrm {TH}}$ shift behavior, i.e., negative shift at shorter $t_{p}$ and positive shift at longer $t_{p}$ , was revealed. The $V_{\mathrm {TH}}$ shifts under repetitive SC tests are attributed to the SC pulse process according to the results of high-temperature reverse bias (HTRB) and dynamic high-temperature gate bias (HTGB) tests. The underlying mechanisms of the complex $V_{\mathrm {TH}}$ shift behavior are explained in a unified framework by taking into account the junction temperature ( $T_{j}$ ) increase with longer $t_{p}$ . TCAD device simulation is used to help analyze the mechanisms.

Radiated EMI evolution of power SiC MOSFET in a boost converter after short-circuit aging tests

Increasing power density, faster switching speed and higher switching frequency force designers to spend more time both considering the effect of Electromagnetic Interferences (EMI) and debugging a design that has EMI problems but studying the reliability and robustness of some components, silicon carbide (SiC) power switching devices in particular, under severe conditions such as short-circuit. In this paper we present a comparison of the EMI generated by a dc-dc boost converter, using SiC MOSFETs before and after repetitive short-circuit aging tests. The compared parameter is the Near H-Field. This paper shows that the repetitive short-circuit aging tests of SiC MOSFET has great influence on the radiated EMI. Experimental results are presented and analysed.

Investigation of repetitive short-circuit operation of 1200 V IGBTs in the IC-VCE phase space

This work shows an investigation of repetitive Short-Circuit (SC) operation of 1200 V–15 A IGBT far above the Short-Circuit Safe Operating Area (SC-SOA). The goal behind this work was to perform repetitive SC tests with test conditions provoking the formation of current filaments in the short-circuit pulse, which leads to a non-homogeneous heating but not to a destruction. The target was to investigate unknown physical effects that lead to device degradation during the repetitive SC test. The IGBT device shows strong deterioration in its blocking characteristic after it was subjected to several 1000 SC pulses at extremely high SC levels.

Robustness of 650-V Enhancement-Mode GaN HEMTs Under Various Short-Circuit Conditions

This paper presents the short-circuit behavior and degradation of 650-V/60-A enhancement-mode Gallium nitride (GaN) high electron mobility transistors (HEMTs) under various test conditions. First, this paper introduces the basic information of device, test method, and platform. Subsequently, single pulse, 10-μs short-circuit tests are performed from 50 to 400 V to extract the typical behavior of devices. Both short-circuit current self-regulation phenomenon and quick failure have been observed. Simultaneously, the short-circuit behavior of the device at various gate drive voltages and temperatures has been explored to identify the protection condition. Then, repetitive short-circuit tests have been performed to reveal device degradation trends. As a result, their output current reduction and gate-to-source threshold voltage shift have occurred. This paper shows the critical need to improve the robustness of this type of GaN HEMT from the device and circuit perspectives.

Evolution of C-V and I-V characteristics for a commercial 600 V GaN GIT power device under repetitive short-circuit tests

In this article, a repetitive and non-destructive short-circuit aging test is developed to characterize the electrical parameters evolutions of a 600 V GaN Gate Injection Transistor (GIT). The evolutions of C-V and I-V characteristics during the repetitive short-circuit tests with a relatively low bias voltage and long pulse duration are presented and summarized. The capacitance CGD at on-state mode and the gate current at relative high gate voltage show significant degradations before and after test.

Effect of short circuit aging on safe operating area of SiC MOSFET

In this paper, we study the effect of aging of SIC MOSFETs on Short Circuit Safe Operating Area and Reverse Bias Safe Operating Area of SiC MOSFETs. SCSOA and RBSOA are determined using short circuit and unclamped inductive switching tests, respectively. Aging of SiC MOSFETs are performed with repetitive short circuit tests at low dissipated energies, which allows to validate the relevance of evolution of different aging indicators measured during the aging process. The decrease in the dissipated energy leading to failure in short circuit and unclamped inductive switching tests allows to clearly link the evolution of these Safe Operating Areas to the degradation of electrical performances (drain and gate leakage currents and on-state resistance). Obtained results show that a strong increase in the drain and/or gate leakage currents after aging has a great effect on the decrease of Safe Operating Area especially on RBSOA and that on-state resistance increase due to aging process represents less impacts in the evolution of RBSOA than in the case of SCSOA. It is also clear from the obtained results that without any apparent evolution of these leakage currents, the decrease of SCSOA after aging is related to the increase in the on-state resistance.

Experimental investigation of the reliability of Printed Circuit Board (PCB)-embedded power dies with pressed contact made of metal foam

A Printed Circuit Board (PCB)-embedding process using pressed metal foam to connect the top-side pads of power dies is considered. The manufacturing process, simple and highly cost-effective, is described in detail; samples are manufactured and their reliability and robustness are characterised. It is shown that thermally cycled prototypes exhibit reliability close to that of Direct Bounded Copper (DBC) substrates. Samples submitted to 150 A-surges have highly scattered reliability. SiC MOSFETs submitted to destructive current limiting tests and repetitive short-circuit tests performed similarly to dies reported in TO247 packages. A discussion on the development of reliability-assessment-methods, especially suited for PCB-embedding processes, is proposed.

Investigations on the Degradation of 1.2-kV 4H-SiC MOSFETs Under Repetitive Short-Circuit Tests

The long-term operational reliability of silicon carbide (SiC) MOSFETs needs to be further verified before they could replace silicon counterparts in power applications. In this paper, the failure mechanism of commercial 1.2-kV SiC MOFSETs under repetitive short-circuit (SC) tests has been investigated. Relatively low stress defined as low bias voltage and short SC duration is imposed on the devices, eliminating the effect of gate oxide degradation and metal deterioration. The generation of hot holes in the oxide is confirmed by the charge pumping experiments and measurements on the transfer characteristics of the stressed devices during the tests. Electrothermal simulation results demonstrate that the trapped holes are located above the channel region due to the high local impact ionization generation rate and electric field. Besides, the additional positive electric field to the channel makes $V_{\mathrm {th}}$ decrease and $I_{\mathrm {dss}}$ increase, which are consistent with the experimental results. What is more, the trapped holes get indeed released, as the ambient temperature increases when the stress is removed.

Repetitive Short-Circuit Tests on SiC VMOS Devices

SiC MOSFET are now commercially available and show promising performances when considering static losses, commutations and long term reliability. The devices may face short-circuit conditions and knowing their capibility in terms of critical time and repetitive fault is mandatory before integration in commercial systems. This paper presents the short-circuit performances for two families of commercial devices in terms of critical energy, time and repetitve SC stress. It shows that both devices show similar critical time but very different behavior when stressed under repetitive SC pulses. These results demonstrate that SiC MOSFET reliability under repetitive short-circuit pulses strongly depends on the pulse length and device provider. This information will be crucial to design the system in order to limit the SC length depending on the application requirements.

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 24V 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.