(A) new analytical design method for optimum field limiting ring systems in semiconductor power devices

Abstract

The behavior of field limiting ring (FLR) which is the most widely used mothod among the several junction termination techinques in power devices is fully analyzed. Analytical expressions for the voltage relations between the floating rings are derived using the equi-potential line approach both the non-punchthrough structrue and for the punchthrough structrue, and they are confirmed by the numerical simulations for various junction depths and various substrate doping concentrations. Avalanche breakdown voltage of a floating ring is calculated using the ionization integral model and a simple expression for the breakdown volatge is dreived using the critical field model. A new analytical design method for the optimum FLR systems is developed based on the analytical voltage realtions and the avalanche breakdown models. FLR experiments show that the newly developed design method can achieve the breakdown volatge over 85% of the ideal breakdown voltage. One or two additive rings in the optimally designed FLR system compensate the effect of the three-dimensional structure, the effect of surface charge and the effect of process deviations. Experimental results on the optimum FLR system with the additive rings show that the breakdown voltage which is up to 95% of the ideal breakdown voltage can easily be obtained with the proposed design method.