Optimum design of power MOSFET's

Abstract

We present a model for the on-state resistance of power vertical, double-diffused MOS (VDMOS) transistors with emphasis on cell layout optimization and supporting experimental data. Essentially the same minimum R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</inf> can be achieved using any of six different cellular cell geometries including square and hexagonal cells. Specifically, the on-resistances of all cellular designs are essentially identical if they have the same p-well width and the same ratio of well area to cell area. Cellular designs yield lower on-resistance than linear-cell designs unless the latter, through clever layout perhaps, allows at least 1.6 times smaller well width than the former. Design examples and experiments illustrate a simple optimization procedure, which starts with choosing the minimum p-well width and depth compatible with production technology and then finding the optimum spacing between the p-wells.