Estimate of increase of planar junction breakdown voltage with field limiting ring

The increase in breakdown voltage of a planar junction with field limiting rings is estimated with a one-dimensional analysis that is based on the premise that the placement of a floating diffused ring at the side of the junction increases the effective radius of curvature of the junction of interest. The floating ring assumes a potential less than the applied voltage and thus is stressed with a lower electric field at the far end where the radius curvature is small. The floating potential is estimated by a one-dimensional analysis of Poisson's equation. The breakdown voltage of this floating diffusion is calculated using published curves of the avalanche breakdown voltage versus impurity concentration for one-sided cylindrical or spherical step junctions. The analysis can be used to determine the optimum spacing between the diffusions and the number of rings required. Experimental results are in good agreement with the analysis.<>