Verification of Single-Pulse Avalanche Failure Mechanism for Double-Trench SiC Power MOSFETs

The failure mechanism of double-trench silicon carbide (SiC) power metal-oxide-semiconductor field-effect transistors (MOSFETs) under single-pulse avalanche stress is verified. Instead of the widely reported burning out failure mechanism for planar-gate devices, double-trench SiC power MOSFETs suffer from a totally different failure mechanism, as they can only endure a much lower maximum single-pulse avalanche energy (E
_as
). It is found that during the avalanche process, obvious gate leakage current (I
_g
) appears, which is resulted from the high impact ionization rate and high electric field along the gate trench bottom oxide interface, especially the trench corners. The I
_g
continuously grows along with the increase in the peak load current (I
_peak
), eventually leading to the breakdown of the trench bottom gate oxide under avalanche status. By increasing the value of gate resistor (R
_g
), the I
_g
raises the gate-source voltage (V
_gs
) during the avalanche process, forcing the channel region in an inversion state. Part of the avalanche current is then diverted into the forward conductive current, changing the failure mode from breakdown of the gate oxide to burning out of the entire device. Moreover, the influence of different avalanche stress conditions, including the di/dt and the ambient temperature (T
_a
), on the single-pulse avalanche endurance capability of double-trench SiC power MOSFETs is investigated. All the samples express a similar failure phenomenon. The higher the di/dt is, the shorter the avalanche time the device can endure. This is because the higher I
_peak
results in a higher I
_g
during the avalanche process, leading to early failure of the gate oxide. However, the T
_a
rarely influences the E
_as
of the device, indicating that the single-pulse avalanche-induced failure of double-trench SiC power MOSFETs has little business with the melting of the lattice or package, demonstrating the correctness of the failure mechanism proposed in this article.