Design, Simulation and Analysis of Novel Types of Unipolar Diodes

Abstract

With the growing demand of low and medium voltage switch-mode power supplies (SMPS) for use in the state-of-the-art integrated circuits, the development of output rectifiers with low forward voltage drop and low reverse leakage current becomes essential. In low voltage SMPS applications (1 to 5 V), the on-state loss of the fast recovery p-i-n diode or the Schottky diode contributes greatly to the total power loss in power supplies. This is due to their forward threshold voltage. One possible way to achieve low on-state losses is to reduce or remove the forward threshold voltage. The first part of this thesis is mainly devoted to a novel Regenerative diode structure based on Silicon material. Its main advantages are reduction or removal of forward threshold voltage and much improved reverse characteristics without the necessity of a gate control like in synchronous rectifiers. The silicon unipolar device application is, however, restricted to relatively low voltages because of on-state and blocking problems at device blocking capabilities above 200 V. For high voltage applications (> 200 V), SiC Schottky or JBS rectifiers have demonstrated a good differential on state resistance and reasonable blocking behavior. In principle, one could try to construct a Regenerative diode like device based on SiC material, but poor hole mobility and much less developed integrated device technology seem to discourage such efforts. However, the second part of this thesis work presents a simulation study on a Si/6H-SiC heterojunction. The p-Si/N-6H-SiC heterojunction diode behaves like a Schottky diode but with much lower threshold voltage than that of the 6H-SiC SBD. Therefore, the heterojunction diode has better on state characteristics than 6H-SiC SBD without sacrificing in blocking.