Physical Origin of the Gate Current Surge During Short-Circuit Operation of SiC MOSFET

Abstract

During short-circuit of a vertical 4H-SiC power MOSFET, a high gate current starts to flow through the gate dielectric. We demonstrate that the Schottky emission is the main physical mechanisms.

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

“…4. As introduced in section I, it is expected that FN tunnel injection will be the governor mechanism [4,3] because of the oxide thickness and temperature range of this experiment.…”

“…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.…”

“…1: with sufficient thermal energy, electrons can overcome the energy barrier between the semiconductor and the dielectric conduction bands. Boige et al showed (in SiC power MOSFETs) that this carrier transport phenomenon only becomes predominant for temperatures above 700 K [3].…”

Circuit-type modelling of SiC power Mosfet in short-circuit operation including selective fail-to-open and fail-to-short modes competition

“…Such a stress dynamic can reveal specific drift mechanisms or even degradation mechanisms of weak region which are not visible in nominal operation [2]. For example, the strong gate-source leakage-current is caused by a hot electron injection through the thin gate oxide [4] and the high drain-source peak current decreases as the channel mobility decreases at high temperature [12]. As a matter of fact, in order to model and fit the thermal-dependant physical mechanisms involved during the short circuit operation, an extended electrothermal modelling is needed.…”

“…The very thin gate-oxide (typically 50nm against 100nm for silicone-planar device) under a high gate field (4MV/cm compared to 10MV/cm breakdown field of the SiO2) is highly stressed in short-circuit operation. Indeed, the junction temperature can reach at least 1300K, leading to hot carrier injection in the oxide that could explain the possible weakness of the gate region and its variability in extreme operation [3], [4].…”