Optimization of Specific On-Resistance of Balanced Symmetric Superjunction MOSFETs Based on a Better Approximation of Ionization Integral

A breakdown voltage model based on the 2-D analytical model of the electric field distributions for the balanced and symmetric superjunction (SJ) MOSFET is presented and used to explain the different breakdown mechanisms as a function of column doping concentrations and widths. It is observed that breakdowns simultaneously occur along different electric field lines across some special symmetric points when the drift region is not fully depleted. Moreover, the minimum specific on-resistance can be obtained when the ionization integrals along these electric field lines are both in unity. For a breakdown voltage larger than 600 V, the minimum specific on-resistance R_on of the SJ structure can be reduced by larger than 13 % compared with the “suboptimum” case in the previous literature. Comparisons of results from the proposed model and simulation data show that the approximation solution exhibits excellent accuracy. The dependence values of the breakdown voltages on charge imbalance and the transient characteristics are also discussed.