Patent ID: 8399907

Claim:
A power transistor device comprising: a substrate of a first conductivity type; a buffer layer of a second conductivity type opposite to the first conductivity type, the buffer layer being disposed on top of the substrate with a first PN junction being formed between the substrate and the buffer layer; a plurality of pillars of semiconductor material, each pillar including: a first region of the second conductivity type; a second region of the first conductivity type disposed adjacent to the first region; a body region of the first conductivity type, the body region adjoining both the first and second regions; a drift region of the second conductivity type that extends in a vertical direction from the body region to the buffer layer, a second PN junction being formed between the body region and the drift region; adjoining pairs of the pillars being separated in a lateral direction by a dielectric region that extends in the vertical direction from at least just near to the second PN junction down at least into the buffer layer, the dielectric region forming a sidewall interface with each drift region of the adjoining pairs of the pillars; a field plate member disposed within the dielectric region, the field plate member having a length that extends in the vertical direction, the field plate member being formed of a conductive material that is fully insulated from the drift region and the buffer layer; a trench gate disposed in the dielectric region adjacent to the body region, the gate being insulated from the body region and the field plate member; wherein when the power transistor device is in an on-state, the first and second PN junctions operate as a bipolar transistor with the substrate comprising an emitter, the second region comprising a collector, and the trench gate functioning as a control input of a field-effect transistor (FET) that controls forward conduction between the emitter and collector, when the power transistor device is in an off-state, the first PN junction being reversed-biased.