Study of short-circuit robustness of SiC MOSFETs, analysis of the failure modes and comparison with BJTs

Abstract

International audienceThis paper presents experimental robustness tests made on Silicon Carbide (SiC) MOSFETs and SiC Bipolar Junction Transistors (BJTs) submitted to short-circuit operations (SC) or current limitation modes. For SiC MOSFETs, a gate leakage current is detected before failure without being responsible for the immediate failure. Nevertheless this gate leakage current is not without effect on the integrity of the SiC MOSFETs. Based on several robustness tests performed on SiC MOSFETs and on the comparison with experimental results obtained with SiC BJTs, the paper points out two main failure modes for SiC MOSFETs. The first one results in a simultaneously short circuit between drain and gate and drain and source and the second one in a degradation of the insulation between gate and source leading to a short circuit between gate and source. For some tested devices, the failure appears in a very interesting open state mode between drain and source after physical short-circuit between gate and source with a mode of failure very similar to those observed for SiC BJT

Investigation on damaged planar-oxide of 1200 V SiC power MOSFETs in non-destructive short-circuit operation

“…Recently, several research efforts demonstrate that ruggedness of SiC power MOSFETs during short-circuit (SC) is, for most of devices, much lower than silicon (Si) devices, with similar rating [1]. Indeed, the weakness may be related to a higher short-circuit current density and a lower die area resulting in a higher temperature rising during SC leading to faster degradations.…”

Extraction of the 4H-SiC/SiO2Barrier Height Over Temperature

“…Indeed, when operating under these conditions, a lot of energy is dissipated in the device over a short period of time, causing a great increase of temperature in the oxide, favouring gate current increase. This is evidenced by Chen et al [29], who observed an increase in the gate-source current before failure happened during a shortcircuit test and relate this with tunneling current. However, a recent study [3] suggests that Schottky emission may be the predominant phenomenon in this gate current increase.…”

Approaching repetitive short circuit tests on MW-scale power modules by means of an automatic testing setup

“…Many efforts have been devoted to the short-circuit testing of power semiconductor devices. The minimum dissipated energy that leads to failure of the specific device after a single short-circuit is referred to the critical energy E C [7]. If the dissipated energy is less than E C , the device is able to survive after Repetitive Short-Circuit (RSC) testing.…”

“…The aim of RSC testing is to study how safe short-circuit operation will affect the electro-thermal parameters and the degradation of power semiconductors, or to benchmark the short-circuit robustness of different devices. Various research activities on RSC testing of Si IGBTs and MOSFETs, and SiC MOSFETs have been presented in [7]- [15]. In [8], the RSC testing of a 600 V customized IGBT module is performed, with a measured saturation current of around 50-60 A.…”

“…In [12], the tested Si MOSFET is observed with no evolution of the above two parameters after 35,000 times of testing, with a relatively lower dissipated energy. In [7], [10], [11], the testing focuses on the discrete 1.2 kV SiC MOSFETs, with the current rating in the range of 20 A to 50 A. In [13], [14], RSC testing is performed for discrete 1.2 kV single-chip normally-on SiC JFET.…”