True Material Limit of Power Devices—Applied to 2-D Superjunction MOSFET

Abstract

Predictions on limits of silicon in power devices have failed spectacularly in the past, but in spite of that, the theory that generated them is still used today and adapted for wide bandgap materials to justify their superior standing against silicon. The superjunction (SJ) MOSFET was the first device to break by more than one order of magnitude the so-called “limit of silicon” above 600 V. The current theory of SJ seems, however, to define a new technology-based limit rather than a material-based only limit. This implies that by scaling down the dimensions, in particular the cell pitch, the on-state resistances can continually decrease by several orders of magnitude, without a boundary. This paper shows that the downscaling of the cell dimensions cannot happen indefinitely and there is a material-dependent intrinsic limit for any power device, which no longer is limited by the geometry or the technology available. Using an analytical approach, and backed up by advanced numerical simulations, we show that the minimum cell pitch is $0.18~\mu \text{m}$ for silicon and $0.05~\mu \text{m}$ for 4H silicon carbide, and further reduction in the cell pitch would result in an increase in the specific resistance. Finally, a new figure of merit for an SJ MOSFET based on a rigorous 2-D analysis is defined.