Surface breakdown and stability of high-voltage planar junctions

The authors introduce a one-dimensional model allowing evaluation of the surface electric field of planar resurf diodes or variation in lateral doping structures with an n⁺-channel stop ring. Based on this model the surface electric field of a resurf diode including a passivation layer with finite sheet resistance (e.g., thermal oxide) is calculated. In a series of self-consistent calculations, where the surface charge density depends on the surface electric field, it is shown that the gradient of the surface electric field causes charge buildup on top of the passivation layer due to its finite sheet resistance. It is shown that these induced surface charges can lead to surface breakdown of the underlying p-n junction. The calculations were confirmed by transient reverse current measurements, performed at a resurf diode with an n⁺-channel stop ring