Semiconductor-on-insulator device having a laterally-graded channel region and method of making

A method for fabricating a semiconductor device, comprising the steps of:

• providing a semiconductor-on-insulator substrate having a layer of semiconductor material disposed on a layer of insulator material, the layer of semiconductor material having a major surface;
• forming an active area in a portion of the layer of semiconductor material;
• forming a gate structure having first and second edges over a portion of the active area;
• forming a first doped region of a first conductivity type in a first portion of the active area aligned to the first edge of the gate structure;
• forming a second doped region of the first conductivity type in a portion of the active area aligned to the second edge of the gate structure;
• forming a third doped region of a second conductivity type in a second portion of the active area aligned to the first edge of the gate structure;
• forming a lightly doped region of a first conductivity type in a portion of the active area adjacent a first side of the gate structure by activating the first doped region, the lightly doped region formed below the gate structure;
• forming a laterally-graded channel region of a second conductivity type in a portion of the active area below the gate structure and abutting the lightly doped region by activating the third doped region, the laterally-graded channel region abutting the lightly doped region, adjacent the layer of insulator material and spaced apart from the major surface;
• forming a source region in a portion of the lightly doped region, the source region extending to underlie the gate structure;
• and
• forming a drain region in a portion of the active area adjacent a second side of the gate structure, the drain region extending to underlie the gate structure.