Asad Fayyaz

Transient robustness testing of silicon carbide (SiC) power MOSFETs

This paper presents the development of a unified test set-up and experimental results of the robustness characterisation of new generation of silicon carbide (SiC) power MOSFETs. In particular, unclamped inductive switching (UIS) and short-circuit withstand capability (SC) are investigated, with the aim of assessing the actual limits of operation of the devices and highlighting the underlying physical mechanisms. An electro-thermal device model is used to support the experimental analysis and interpret the observations.

SiC power MOSFETs performance, robustness and technology maturity

Relatively recently, SiC power MOSFETs have transitioned from being a research exercise to becoming an industrial reality. The potential benefits that can be drawn from this technology in the electrical energy conversion domain have been amply discussed and partly demonstrated. Before their widespread use in the field, the transistors need to be thoroughly investigated and later validated for robustness and longer term stability and reliability. This paper proposes a review of commercial SiC power MOSFETs state-of-the-art characteristics and discusses trends and needs for further technology improvements, as well as device design and engineering advancements to meet the increasing demands of power electronics.

Short-circuit robustness of SiC Power MOSFETs: Experimental analysis

This paper proposes a thorough experimental characterization of the performance of commercially available SiC Power MOSFETs under short-circuit conditions. The purpose is to assess and understand the degradation process and the failure mechanisms that limit device reliability to identify optimal routes for subsequent technology development. This paper complements electro-thermal functional tests with structural characterization offering deeper insight into device technology related aspects.

Short-circuit failure mechanism of SiC power MOSFETs

Failure mechanisms during short-circuit conditions of Silicon Carbide Power MOSFETs are analysed in this work, and a possible theoretical explanation is provided. Insight into the physics involved in such processes was inferred through experimental and numerical analyses. The TCAD structure used for electro-thermal simulations was calibrated to fit the ID-VGS characteristics of a commercial device. Adequate physical effects were considered, such as the presence of charges and traps at the oxide-SiC interface and their effect on threshold voltage and carrier mobility. Experimental evidences were explained by analyzing the numerical results. The high temperature reached during these operating conditions was addressed as the main cause of the device failure. The effect on the leakage current and the activation of a parasitic bipolar transistor are also shown.

Single pulse avalanche robustness and repetitive stress ageing of SiC power MOSFETs

This paper presents an extensive electro-thermal characterisation of latest generation silicon carbide (SiC) Power MOSFETs under unclamped inductive switching (UIS) conditions. Tests are carried out to thoroughly understand the single pulse avalanche ruggedness limits of commercial SiC MOSFETs and assess their aging under repetitive stress conditions. Both a functional and a structural characterisation of the transistors is presented, with the aim of informing future device technology development for robust and reliable power system development.

Influence of design parameters on the short-circuit ruggedness of SiC power MOSFETs

This work aims to present an investigation on short-circuit (SC) failure behaviour of SiC Power MOSFETs due to the onset of thermal runaway. As inferable from experimental outcomes, it is related to the formation of hotspot, whose exact location is mainly unpredictable and dictated by device structure and design parameters non-uniformities. TCAD simulations were performed to examine the impact of some parameters mismatch on hotspot formation and failure occurrence.

High temperature pulsed-gate robustness testing of SiC power MOSFETs

Silicon Carbide (SiC) gate oxide reliability still remains a crucial issue and is amongst the important consideration factors when it comes to the implementation of SiC MOS-based devices within industrial power electronic applications. Recent studies have emerged assessing the gate oxide reliability of SiC MOSFETs. Such studies are needed in order to fully understand the properties of SiC/SiO2 interface which is currently holding back the industry from fully utilising the superior features that SiC may offer. This paper aims to present experimental results showing the threshold voltage (VTH) and gate leakage current (IGSS) behaviour of SiC MOSFETs when subjected to pulsed-gate switching bias and drain-source bias stress at high temperature over time. The results obtained are then used to investigate the gate-oxide reliability of SiC MOSFETs. 2D TCAD static simulation results showing electric field distribution near the SiC/SiO2 interface are also presented in this paper.

Transient out-of-SOA robustness of SiC power MOSFETs

Beyond their main function of high-frequency switches in modulated power converters, solid-state power devices are required in many application domains to also ensure robustness against a number of overload operational conditions. This paper considers the specific case of 1200 V SiC power MOSFETs and analyses their performance under three main transient regimes at the edge of and out of their Safe Operating Area: unclamped inductive switching led avalanche breakdown; short-circuit; operation as current limiting and regulating devices. The results presented highlight both inherent major strengths of SiC over Si and areas for improvement by tailored device design. The paper aims to contribute useful indications for technology development in future device generations to better match widespread and varied application requirements.

Body diode reliability investigation of SiC power MOSFETs

A special feature of vertical power MOSFETs, in general, is the inbuilt body diode which could eliminate the need of having to use additional anti-parallel diodes for current freewheeling in industrial inverter applications: this, clearly, subject to their demonstration of an acceptable level of reliability. Recent improvements in Silicon Carbide (SiC) power MOSFET device manufacturing technology has resulted in their wider commercial availability with different voltage and current ratings and from various manufacturers. Hence, it is essential to perform characterisation of its intrinsic body diode. This paper presents the reliability assessment of body diodes of latest generation discrete SiC power MOSFETs within a 3-phase 2-level DC-to-AC inverter representing realistic operating conditions for power electronic applications.

Robustness investigation of SiC power MOSFETs under negative temperature

Recent material technological advances for silicon carbide (SiC) have led to a wide selection of commercial SiC power transistors, especially MOSFETs, from various manufacturers and hence it is vital to have these devices thoroughly characterized under different test conditions representative of power electronics applications. This paper aims to present an experimental characterization under negative temperature of commercially available SiC Power MOSFETs in order to assess their robustness. Devices were tested during short circuit (SC) and unclamped inductive switching (UIS) conditions.