An analytic approach for optimal field ring spacing of a diode under punchthrough operation

The use of floating field limiting ring (FFRL) reduces the surface field due to junction curvature effect, and the breakdown voltage in planar devices can be increased. In this paper, a new analytic method is developed based on the combination of plane junction in the bulk and cylindrical junction at the surface. From these analysis, optimal space between main diffusion and FFLR can be obtained. The influences of concentration and width of lightly doped collector region and base diffusion junction depth are also investigated. The results are in good agreement with the two-dimensional numerical ones.