Patent ID: 8049276

Claim:
A semiconductor device, comprising: a semiconductor layer of a first conductivity type having a first surface, a second surface, and a mesa region, the mesa region having a top surface adjacent to the layer's first surface, and a graded net doping concentration of the first conductivity type within a first portion of the mesa region, the graded net doping concentration decreasing in value with distance from the top surface of the mesa region; a trench electrode extending in the semiconductor layer and adjacent to the mesa region, the trench having an electrically insulated electrode disposed therein and extending from the semiconductor layer's first surface toward the semiconductor layer's second surface to a first depth below the layer's first surface; a second electrode disposed at the top surface of the mesa region; and a third electrode electrically coupled to the semiconductor layer; and wherein the first portion of the mesa region is located within a first distance of the top surface of the semiconductor layer, the first distance being the greater one of one-half micron or one-half the first depth, and wherein the maximum net doping concentration of the first conductivity type in the first portion is equal to or less than 2×10 17 cm −3 .