Analytical expression for the potential of guard rings of diodes operating in the punchthrough mode

An analytical modeling is given to prove that the potential of the floating guard ring varies linearly versus the reverse applied bias in planar punch through diodes with one ring. The result is valid for multiple guard-ring structures. From this modeling and using the criterion of simultaneous breakdown on the main junction and on the rings for a given structure, an approximate and quick determination of the optimized ring spacings is obtained.