Design of Superjunction Power MOSFET Devices using the Gradient Oxide-Bypassed Structure

Superjunction (SJ) and other concepts have been proposed to overcome ideal silicon MOSFET limit and to lower the on-state resistance without sacrificing the breakdown rating. The gradient oxide-bypassed structure (GOB) is one such novel structure, in which a slanted oxide layer along with a poly contact is used to replace the p-column of conventional superjuntion structure. This provides modulation of the drift-region electric field and minimises the process complexity in precise charge matching as faced by the SJ structure. In this paper, the principle of operation, theoretical analysis and fabrication issues of GOB devices are discussed. The closed-form derivations of GOB on-state and breakdown performance are also presented. The derivations were verified by 2D numerical device simulator MEDICI. The performance sensitivity on the slope of sidewall oxide is also discussed in this paper. Based on the overall analyses, a design for the GOB device is proposed for the first time. Using this design, one can achieve desirable breakdown voltage and specific on state resistance characteristics with good process tolerance.