Theory of a novel voltage-sustaining layer for power devices

The theory of a novel voltage-sustaining layer for power devices, called a Composite Buffer layer (CB-layer for short) is proposed. The CB-layer can be implemented in several ways, one particular implementation is used here, which consists of alternating n- and p-type regions, that are parallel to the direction of the applied electric field. In the off-state, the fields induced by the depletion charges of both region types compensate each other to allowing the doping in both n-regions and p-regions to be very high without causing a reduction of the breakdown voltage. In the onstate the heavy doping ensures the voltage drop is very low and that the saturation current density high. A simple relationship between the specific on-resistance and R-on and the sustaining voltage V-B can be shown to be R-on = 2.53 x 10(-7) bV(B)(1.23) Omega Cm-2, where the breadth b (in mu m) of each region is much smaller than the thickness W. The design method of the CB-layer is discussed in some detail. The simulation results are shown to be in perfect agreement with the theory. The structure has application to a wide variety of different power devices, An RMOST structure has been used to demonstrate the benefits of the technique in the paper, for which excellent performance is demonstrated. (C) 1998 Elsevier Science Ltd. All rights reserved.