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Bipolar degradation continues to be a key issue that should be taken into account in 4H-SiC devices using bipolar operation modes. The generation and expansion of recombination-induced stacking faults (SFs) in 4H-SiC devices results in a forward-voltage drift, which has been widely discussed in the literature. In this work, 1.2 kV SiC MOSFET body diodes were stressed at different current densities to investigate the influence of crystal-induced voltage drifts like bipolar degradation caused by stacking faults (SFs), expansion from pre-existing basal plane dislocations (BPDs) or conversion points. Additionally, thermomechanical failures (gate-oxide damage, front-side metallization degradation, bond-wire heel crack and lift-off) inevitably occurred due to high surge-current stress. The measurement results illustrate the spectrum of degradation by applying different current densities to the body diode of SiC MOSFETs.

In this work, thermomechanical failures during single and repetitive surge current events of 40 mΩ class, 1.2 kV SiC MOSFET inverse diodes were investigated. The single event surge current was performed under different pulse length in channel-off mode. It was observed that the body diode survived 10 ms surge currents more than 11 times the application-near nominal current of 20 A. After surge current destruction a failure analysis was performed. At a high surge current event (232 A) the device failed due to the very high temperature, the aluminium metallization was melted around the bond foot and the melted metallization shorted gate and source (GS) metal. In addition to that, repetitive surge current tests, high temperature reverse bias (HTRB) tests under negative gate bias and high temperature gate bias test (HTGB) with samples exposed to repetitive surge current were performed to investigate different aging mechanisms to determine reliability aspects of the inverse diode in SiC MOSFETs.

The surge current ruggedness is an important factor for a diode in power electronic applications. The diodes will face very high temperatures during a surge current event. In this work, the temperature was determined during surge current event of SiC MPS diodes under different pulse lengths using measurement and numerical simulation. Even though SiC itself can withstand very high temperatures, the maximum operating temperature of the diode is limited by the anode metallization in TO-247 during the surge current event. The temperature distribution during the surge current event was analysed and explained in detail with help of numerical simulation of the diode model in ANSYS.

The reliability of power diodes under surge current is an important factor that has to be taken into account for power electronic applications. In this work, latest generation SiC MPS (Merged Pin Schottky) diodes (650V, 1200V, 1700V) with different current classes from Infineon are exposed to repetitive high surge current stress. Furthermore, the temperature was estimated using different methods including direct measurement, Sentaurus TCAD simulation, Cauer network and an analytical model using temperature dependent mobility. It was found that the diodes could withstand a high number of high-current pulses. However, before reaching final destruction, different ageing phenomenon were observed at the unipolar and bipolar regime of the MPS diode. A detailed investigation on the aging mechanisms including failure analysis was performed.

State of the art freewheeling diodes are connected antiparallel with a switch like IGBT or MOSFET and for latter also with the internal body diode. The diodes have to be rugged enough to overcome temporary overvoltage and overcurrent conditions during transient operation. SiC merged pin Schottky (MPS) diodes are one of the superior contenders and thus it is essential to make investigations under high avalanche energy. In this work, an avalanche ruggedness of 20 A/1.2 kV SiC MPS diodes was investigated far beyond the specified maximum ratings of the device under unclamped inductive switching (UIS) measurement. The function of avalanche energy versus applied inductance was investigated under single event avalanche stress. The reliability under high repetitive avalanche energy was studied in detail. A forward voltage drift, change in the Schottky junction voltage and increase in the leakage current was observed after the high repetitive avalanche stress far beyond the safe operating area. Detailed failure analysis was made, focusing on the degradation of the metallization and possible stacking faults (SFs) in the SiC bulk. Furthermore, the temperature was determined as a function of the blocking voltage during avalanche stress.

In this work, the surge current behavior of 1200V SiC MPS diodes is analyzed using electro-thermal simulations. The results are compared to measurements for calibration. The isothermal surge current simulations are performed with a simplified model of the real diode structure with various sizes of pin-regions and various total model widths. The simulation result shows that smaller pin-regions trigger minority carrier injection at higher voltage drop and current density than the larger pinregions. The negative differential resistance (NDR) regime, seen in the measurement, is modeled successfully. Both, simulations and measurements show a similar behavior during a surge current event. Furthermore, the influence of the model geometry during the surge current event is investigated.