Patent ID: 8587054

Claim:
A trench MOSFET comprising: a substrate of a first conductivity type; an epitaxial layer of said first conductivity type onto said substrate, said epitaxial layer having a lower doping concentration than said substrate; a plurality of gate trenches formed from a top surface of said epitaxial layer and extending downward into said epitaxial layer in an active area; a first gate insulation layer formed along trench sidewalls of a lower portion of each of said gate trenches; a source electrode formed within each of said gate trenches and surrounded by said first gate insulation layer in said lower portion of each of said gate trenches; a second gate insulation layer formed at least along trench sidewalls of an upper portion of each of said gate trenches and upper sidewalls of said source electrode above said first gate insulation layer, said second gate insulation layer having a thinner thickness than said first gate insulation layer; a pair of split gate electrodes of said first conductivity type disposed adjacent to said second gate insulation layer and above said first gate insulation layer in said upper portion of each of said gate trenches, wherein each of said split gate electrodes disposed in the middle between said source electrode and adjacent trench sidewall in said gate trenches; a diffused drift region of said first conductivity and having a higher doping concentration than said epitaxial layer, disposed in a mesa between two adjacent said gate trenches; said diffused drift region having a higher doping concentration near trench sidewalls of said gate trenches than in the center of said mesa; a body region of a second conductivity type formed in said mesa, above a top surface of said diffused drift region; and a source region of said first conductivity type formed near a top surface of said body region and adjacent to said split gate electrodes.