Dynamic Degradation in SiC Trench MOSFET With a Floating p-Shield Revealed With Numerical Simulations

A p-type shield region (p-shield) under the gate trench is typically adopted in a SiC trench MOSFET for achieving a lower oxide field and reverse transfer capacitance (Cᵣₛₛ). This paper comparatively studies the effects of a grounded p-shield and a floating p-shield. Device simulations using Sentaurus TCAD are carried out in this paper to reveal the devices’ internal dynamics. The floating p-shield can effectively reduce the OFF-state oxide field as a grounded p-shield does, without degrading its static performance. However, after being switched from the OFF-state, the ON-state oxide field in the trench MOSFET with a floating p-shield (FS-MOS) is dramatically elevated. Compared with the trench MOSFET with a grounded p-shield, the FS-MOS also exhibits a higherC_rssand a consequently slower switching speed. Furthermore, the FS-MOS exhibits a degradation of dynamicR_ ONduring switching operation. A charge storage mechanism is then presented to explain the dynamics in FS-MOS. Upon a highV_DS, holes are emitted from the floating p-shield when the parasitic p-n-p structure consisting of p-shield, p-body, and n-region between them is punched through, leaving negative charges in the floating p-shield even when the highV_DSis removed. Based on this mechanism, the behaviors of the FS-MOS are well explained.