High voltage MOS transistor

Claim 1

A metal oxide semiconductor device of a high voltage type which prevents field concentration near the edge of a gate electrode, eliminates a reverse field plate effect and provides for stable driving operation of said device comprising in cross section: a semiconductor substrate comprising an upper surface having a conductivity of a first type; a source region having a conductivity of a second type opposite to that of said semiconductor substrate formed in the surface of said substrate; a drain region having a conductivity of said second type opposite to that of said semiconductor substrate formed in the surface of said substrate apart from said source region; a gate channel region having the same conductivity type as said semiconductor substrate connected to said source region within said substrate; a field dope region positioned adjacent and outside said gate channel region at the surface of said substrate having a conductivity the same as said first type; a high resistance region of said second type conductivity disposed substantially at the surface of said substrate between said source and drain regions connected to said drain region and separated by a portion of said substrate from said gate channel region; a continuous insulating layer overlying a portion of said source region, a portion of said gate channel region, said high resistance region and a portion of said drain region; a drain electrode connected to said drain region having a field plate layer portion extending radially inwardly from said drain electrode; a source electrode connected to said source region, said gate channel region and said field dope region, having a field plate layer portion extending radially inwardly from said source electrode; a gate electrode formed above said gate channel region within said continuous insulating layer having a portion of said continuous insulating layer interpositioned between said gate electrode and said substrate; and a high resistance covering layer substantially overlying said high resistance region so as to provide said high resistance region with a constant electric field and to eliminate influence by external charges, said continuous insulating layer being interposed between said high resistance covering layer and said high resistance region, said high resistance covering layer having first and second terminal end portions of low resistance connecting said high resistance covering layer by said first end to said drain electrode and by said second end to said source electrode through said respective radially extending field plate layer portion extension or directly to said gate electrode.