Design strategy and working principle of GaN vertical trench gate MOSFETs with p-type shielding rings

Shielding ring (SR) structures are widely employed beneath the gate trench of vertical trench gate MOSFETs for the purpose of enhancing the gate oxide reliability and avoiding premature breakdown. To facilitate an in-depth understanding of the vertical power MOSFETs with p-type SRs (SR-MOSFETs), we numerically investigated the influence of the key parameters on the static characteristics of GaN-based vertical power SR-MOSFETs by TCAD simulation. We comprehensively elucidated the reach-through and non-reach through behaviors in the SR structures with different thicknesses, widths, and p-doping concentrations. We also illustrated the quasi-saturation effect by analyzing the 2D electron distribution and current density at the pinch-off point. With the same off-state voltage levels as conventional vertical MOSFETs, the SR-MOSFETs feature reduced on-state resistance and improved switching performance, which can provide theoretical guidance towards the development of high performance vertical gallium nitride power MOSFETs.