Breakdown voltage of elliptic PN junctions

2D simulations of diffused profiles reveal that the shapes of curvature regions of PN junctions fit closer to elliptical than cylindrical ones. In this article the investigation into breakdown voltages of diffused PN junctions with different lateral to vertical diffusion depths is presented. Metallurgical junctions of real 2D diffused PN structures were approximated by elliptic junction curvature. It is shown that breakdown voltages of planar junctions are underestimated if they are calculated as breakdown voltage of a cylindrical junction with junction depth equal to lateral junction depth. The difference between the breakdown voltage of an elliptic and a cylindrical junction curvature at lateral to vertical diffusion depth ratio 0.5 can be as large as 25%. Breakdown voltages are more sensitive to junction curvature at larger junction depths and lower substrate concentrations. A set of design curves is given that allows accurate and simple determination of breakdown voltages for substrate dopings from 10 ¹³ cm^-3 to 10¹⁶ cm^-3 and junction curvature ratios from 0.5 to 1