A novel combined charge balance termination structure insensitive to ionizing radiation effect

Ionizing radiation effects on termination structures employing field limiting rings (FLR) and/or equipotential field plates have been actively studied to achieve radiation tolerance for more than two decades. However, ionizing radiation effects on charge balance termination structure have not been investigated and reported. In this paper, sensitivity of charge balance termination structure to ionizing radiation was experimentally identified for the first time and is attributed to the radiation-induced oxide trapped charges in the field oxide. It was demonstrated that these charges alter the potential at the surface and affects the breakdown voltage of charge balance termination using 3-D simulations. Based on the 3-D simulations results, a novel rad-hardened combined charge balance termination structure was proposed and optimized. The new termination structure is combined by normal charge balance termination, surface FLRs and field plates, which can improve the insensitivity of surface charge induced by ionizing radiation effect. A 300V super junction MOSFET employing novel insensitive charge balance termination structures were fabricated and exposed to Co-60 y-rays at room temperature with a total dose of 150krad(Si). The test results show that the degradation of breakdown voltage of this termination structure is less than 1V with a total dose up to 150krad(Si).