Abstract :
A simple equivalent circuit and iteration procedure are introduced that enable the separation of the on-resistance of a VDMOS into three physically meaningful components. These components can be obtained by a novel forward-bias I-V measurement of the parasitic p-n junction without regard for the structural details of the device. The method has been applied to devices with various blocking voltages between 40 and 500 V. With increasing values of the drain-to-source blocking voltage, the epidrain component of resistance was found to increase dramatically, whereas the other two resistance components remained fairly constant. Thus, to appreciably reduce the on-resistance, one must optimize the epi-drain resistance for a given blocking voltage. Several new parameters of the nonuniformly doped channel are defined and evaluated, i.e., an effective channel resistance, an effective mobility, an effective threshold voltage, and the ratio of the average to maximum channel doping. The significance of these quantities are discussed.
