Integrated mos power transistor with body extension region for poly field plate depletion assist

Abstract

A split gate power transistor includes a doped substrate, a gate oxide layer on the substrate, and a split polysilicon layer over the gate oxide layer, which forms a polysilicon gate positioned over a channel region and a first portion of a transition region and a polysilicon field plate positioned over a second portion of the transition region and a shallow trench isolation region. The two polysilicon portions are separated by a gap. The field plate is electrically coupled to a source of the split gate power transistor. One or more body extension regions, each having the same doping type as the body substrate, extend at least underneath the edge of the field plate adjacent to the gap. The body extension regions force the portion of the transition region underneath the field plate into deep-depletion, thereby preventing the formation of a hole inversion layer in this region.