Patent ID: 7557409

Claim:
A trench-gate MOSFET comprising: a semiconductor substrate having first and second trenches formed at a first surface thereof, said first and second trenches forming a mesa therebetween, said mesa comprising: a source region of a first conductivity type located adjacent said first and second trenches at said first surface; a body region of a second conductivity type opposite to said first conductivity type adjacent said first and second trenches and forming a junction with said source region; and a drift region of said first conductivity type located adjacent said first and second trenches and forming a junction with said body region, wherein said drift region has a substantially uniform doping concentration Nconst in a central portion of said drift region; a drain region of said first conductivity type adjacent a second surface of said substrate opposite to said first surface, said drain region having a doping concentration greater than Nconst; and a metal layer overlying said first surface of said substrate and being in electrical contact with said source region; each of said first and second trenches comprising an upper portion comprising a gate electrode, said gate electrode being separated from said body region by a gate oxide layer; and a lower portion comprising a buried source electrode, said buried source electrode being electrically isolated from said drift region by a second oxide layer and from said gate electrode by a third oxide layer, said buried source electrode being electrically connected to said source region; wherein a width of said mesa, a width of said trench, and said doping concentration Nconst in said drift region are established such that said drift region is fully depleted at a drain-to-source voltage equal to Vds but is not fully depleted at a drain-to-source voltage of less than Vds; wherein a thickness of said second oxide layer in cm is approximately equal to 10 −7 times said voltage Vds in volts; and wherein Vds equals 200 volts, Nconst equals 7.5×10 16 cm −3 , said mesa width equals 3.1 μm, said trench width equals 3.4 μm, and said thickness of said second oxide layer equals 1.6 μm.