MOS transistor with semi-insulating field plate and surface-adjoining top layer

Claim 1

An MOS transistor comprising a semiconductor body of a first conductivity type and having a major surface, a surface-adjoining source region of said first conductivity type in said body, a surface-adjoining channel region of a second conductivity type opposite to that of said first type in said body and adjacent said source region, a surface-adjoining drain region of said first conductivity type in said body and spaced apart from said channel region, a drift region formed from a portion of said body between said channel region and said drain region, an insulating layer on said surface and covering at least that portion of the channel region located between said source region and said drain region, a gate electrode on said insulating layer and over said portion of the channel region, source and drain electrodes connected respectively to the source and drain regions of said transistor, and a semi-insulating field plate adjacent said surface, over said drift region and extending laterally in a first direction from said drain electrode toward said gate and source electrodes, said field plate being connected at a first end to said drain electrode and at a second opposite end to only one of said gate and source electrodes, characterized in that a surface-adjoining top layer of said second conductivity type is provided in said drift region between said channel region and said drain region, and in that said top layer is spaced apart from said drain region and is connected only at selected locations to said channel region, said selected locations being spaced apart in a second direction perpendicular to said first direction.