Characterization of silicon carbide power semiconductor Schottky diodes and JFETs for high-switching frequency applications.

摘要

The published data on Silicon Carbide (SiC) power devices (FETs and diodes) show that these devices promise to achieve performance superior to available Silicon (Si) devices. However, nearly all of the reported data on SiC FETs has been static characterization data taken at the wafer level using wafer probes rather than the device's performance in a real application. The goal of this dissertation is to predict the performance of experimental SiC JFETs and Schottky diodes and then characterize, evaluate, and test them as individual devices and in circuits. Further, this research is intended to identify the limitations of present SiC JFETs and to determine if present experimental devices achieve the expected switching time of 10ns or less needed for high frequency DC/DC converters.; The framework of this thesis has three dimensions. The first dimension is the theoretical estimation of the benefits of using SiC power semiconductor devices in high-switching frequency power electronics applications and in particular in high frequency DC/DC converters. The second dimension is the measured single device characteristics. These characteristics include break-down voltage, pinch-off voltage, internal gate resistance, internal capacitances, maximum and minimum allowable gate voltage, ON resistance, thermal resistance, and leakage current. The last dimension is the performance of SiC power semiconductors in a selected application circuit. A 1MHz hard-switched DC/DC converter has been chosen for this application circuit.; This thesis presents research results that demonstrate the higher frequency DC/DC converter operation that is enabled by SiC power JFETs and Schottky diodes. Design and experimental results for a hard-switched DC/DC converter operating at 1 MHz are presented. During this research, experimental SiC JFETs from three different device research groups were studied. Each group has developed a different device design and fabrication process. This research has identified various problems and limitations of the SiC JFETs from each of the SiC research groups related to their use in high-switching frequency applications. Depending on the source of the JFETs, these problems and limitations include high internal gate resistance, high Miller capacitance, and most commonly problems related to the packaging process such as high thermal resistance and poor wire bonds. None of the problems or limitations identified is inherent to SiC devices but rather is related to the various device designs, their device fabrication process, and the fabrication workmanship.