Theory of a novel voltage-sustaining layer for power devices

TLDR

The CB‑layer structure is applicable to a wide range of power devices. The paper proposes a theory for a novel voltage‑sustaining Composite Buffer (CB) layer for power devices. The CB‑layer consists of alternating high‑doping n‑ and p‑type regions aligned with the electric field; in the off‑state the depletion fields cancel, preserving high breakdown voltage, while in the on‑state the heavy doping yields a low voltage drop and high saturation current density. Simulations confirm the theory, showing that the CB‑layer’s on‑resistance follows Ron = 2.53 × 10⁻⁷ b VB¹·²³ ωcm² and that an RMOST implementation delivers excellent performance.

Abstract

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 Ron and the sustaining voltage VB can be shown to be Ron=2.53 × 10−7bVB1.23 ωcm2, where the breadth b (in μm) 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.