Modeling of terminal ring structures for high-voltage power MOSFETs

To achieve a high blocking voltage, a power MOSFET is often guarded with multiple floating field limiting rings (MFFLRs) to re-distribute the electric field for extending the breakdown voltage. However, this high-voltage protecting structure occupies a significant silicon area of the power MOSFET. The breakdown field of a floating ring depends on the junction curvature, sizes of the rings and the spacing between the rings. A good design can reduce the total silicon area of the MOSFET transistor by optimizing the floating ring design through modeling. The conventional approach was based on the classical breakdown field model originally developed for the low-voltage p–n junction which has limited precision in the medium to high electric field range. In this work, a precise fitting model for the MFFLR structure with high junction breakdown voltage is proposed. Measurement results of the breakdown voltage of the MOSFETs for the MFFLR structure are presented.