Theory of 3-D Superjunction MOSFET

The state-of-the-art superjunction (SJ) MOSFETs are based on the p-n pillar structures, arranged in a 2-D stripe geometry. This arrangement uses the superposition of the electric field components at the p-n junctions to create an enhanced depletion volume for higher breakdown capability. In this article, we will discuss structures, which additionally use the component of the electric field in the third dimension, to further enhance the depletion space. This allows higher doping concentrations in the pillars, which result in a better tradeoff between the breakdown voltage and the ON-state resistance, when compared with the 2-D structures. Specifically, we present a core-shell cylindrical SJ structure, and using the radial Poisson equation, we explain the electric field distribution within the SJ. We further discuss which geometry (core or shell) gives the best performance tradeoff. This is followed by the development of an analytical model, for the ON-state resistance in a 3-D SJ. Finally, we derive a specific figure of merit for the 3-D SJs and compare it with that of the equivalent 2-D structures.