Oxide-bypassed VDMOS (OBVDMOS): An alternative to superjunction high voltage MOS power devices

Abstract

Superjunction concept had been proposed to overcome ideal silicon MOSFET limit, but its fabrication was handicapped by the precise charge balance requirement and inter-diffusion problem. We report a novel device structure termed oxide-bypassed VDMOS (OBVDMOS) that requires the well-established oxide thickness control instead of the difficult doping control in translating the limit to a higher blocking voltage. This is done by using metal-thick-oxide (MTO) at the sidewalls of drift region. One can choose to have a higher blocking voltage or increase the background doping. A PiN structure, essentially identical to MOSFET during off state, was fabricated to demonstrate the proposed concept. Its measured BV dss of 170 V is 2.5 times higher than measured conventional device BV dss of 67 V on the same silicon wafer.