Two-dimensional off-state modelling of high-voltage semiconductor devices with floating guard rings

The authors present novel algorithms for the off-state modelling of high-voltage devices with floating guard rings. The computation is based on quadratic isoparametric finite elements which improved accuracy in the determination of electric fields and ionisation integrals. The special boundary conditions for floating rings are considered together with an approach that automatically selects which ones to include in the calculations at a given bias. In addition, an efficient voltage-stepping technique is described for determining the breakdown voltage. Comparisons are made with measured values of floating ring potential and breakdown voltage on a variety of test devices with excellent agreement being found