High voltage transistor structure

A transistor, comprising:

• a gate structure having a gate dielectric layer and an overlying gate electrode layer;
• a source structure disposed on a first side of the gate structure;
• a drain structure disposed on a second side of the gate structure opposite the first side;
• an insulating layer disposed between the drain structure and the gate structure;
• a first buried layer under the drain structure wherein the first buried layer does not extend under the source structure or the gate structure, wherein the first buried layer has a dopant of a first type of conductivity at a first concentration;
• and
• a second buried layer under the gate structure and the source structure, wherein the second buried layer has a dopant of the first type of conductivity at a second concentration, the second concentration less than the first concentration.

A transistor, comprising:

• a semiconductor substrate having a first type of conductivity;
• a first well region having a second type of conductivity and formed over the semiconductor substrate;
• a second well region in the first well region and having the first type of conductivity, the second well region having a U-shape in a cross section and extending from a source region to a first insulating structure disposed on the semiconductor substrate adjacent a drain region, and the cross section is taken in a direction perpendicular to a top surface of the semiconductor substrate;
• a second insulating structure over the first well region and at least a portion of the U-shape of the second well region and not contacting the second well region;
• a gate structure between the source region and the drain region;
• the drain region across the second insulating structure from the gate structure, the drain region comprising a first drain portion between the first insulating structure and the second insulating structure and a second drain portion across the first insulating structure from the first drain portion;
• and
• the source region disposed on a side of the gate structure opposite from the drain region.