Understanding Short-Circuit Failure Mechanism of Double-Trench SiC Power MOSFETs

The short-circuit (SC) failure mechanism of double-trench silicon carbide (SiC) power metal-oxide- semiconductor field-effect transistors (MOSFETs) is comprehensively studied and analyzed. Unlike traditional planar-gate devices which die from thermal runaway, the double-trench ones exhibit a different SC failure phenomenon. After enduring an ultimate SC stress cycle, the gate of the double-trench device breaks down while the conducting and blocking characteristics of the body diode remain stable. During the SC process, a substantial negative gate current from the semiconductor side to the poly gate side is observed. Silvaco TCAD simulations demonstrate that ultrahigh current density and impact ionization appear at the gate trench corners simultaneously, driving the generated hot holes through the oxide, forming the negative gate current. The sustained action of this gate current component on the oxide finally results in the failure. Moreover, the influence that bias voltages have on the SC endurance capability of the device is analyzed. In general, the higher the V _ds and V _gs are the shorter the SC endurance time will be. It is also found that the double-trench device fails with a higher junction temperature when stressed under a lower V _ds condition, implying that the temperature rarely affects the failure, proving the correctness of the proposed SC failure mechanism.