Theory and breakdown voltage for planar devices with a single field limiting ring

The use of one or more floating field limiting rings reduces the adverse effect of junction curvature on the breakdown voltage in planar devices. Although this has been known for some time, there has not been a way of accurately predicting the amount of improvement that can be achieved using field rings. In this paper, a computer algorithm is presented which makes it possible to perform field calculations on devices with floating field rings. In addition, a normalized curve is presented which shows the relative improvement that a single optimally placed field ring has on the breakdown voltage for any planar device. The basis of the construction of this curve is the use of a normalized radius of curvature which is a precise measure of the effect of curvature for any device. The theoretical predictions are compared with experiments for over 640 devices encompassing 16 different field ring locations. Good agreement is achieved between theory and experiment.