Design and Application of SiC Power MOSFET

Abstract

This thesis focuses on the design of high voltage MOSFET on SiC and its application in power electronic systems. Parameters extraction for 4H SiC MOS devices is the main focus of the first topic developed in this thesis. Calibration of two-dimensional (2-D) device and circuit simulators (MEDICI and SPICE) with state-of-the-art 4H SiC MOSFETs data are performed, which includes the mobility parameter extraction. The experimental data were obtained from lateral N-channel 4H SiC MOSFETs with nitrided oxide-semiconductor interfaces, exhibiting normal mobility behavior. The presence of increasing interface-trap density (Dit) toward the edge of the conduction band is included during the 2-D device simulation. Using measured distribution of interface-trap density for simulation of the transfer characteristics leads to good agreement with the experimental transfer characteristic. The results demonstrate that both MEDICI and SPICE simulators can be used for design and optimization of 4H SiC MOSFETs and the circuits utilizing these MOSFETs. Based on critical review of SiC power MOSFETs, a new structure of SiC accumulation-mode MOSFET (ACCUFET) designed to address most of the open issues related to MOS interface is proposed. Detailed analysis of the important design parameters of the novel structure is performed using MEDICI with the parameter set used in the calibration process. The novel structure was also compared to alternative ACCUFET approaches, specifically planar and trench-gate ACCUFETs. The comparison shows that the novel structure provides the highest figure of merit for power devices. The analysis of circuit advantages enabled by the novel SiC ACCUFET is given in the final part of this thesis. The results from circuit simulation show that by utilizing the novel SiC ACCUFET the operating frequency of the circuit can be increased 10 times for the same power efficiency of the system. This leads to dramatic improvements in size, weight, cost and thermal management of power electronic systems.