Demonstrations of high voltage SiC materials, devices and applications in the solid state transformer

High voltage SiC power devices have been proven as the potential candidates in replacing the Si counterparts to improve the overall power converting efficiency of the power grids and power systems. In this paper, the demonstrations of high voltage materials and devices along with the applications in the power electronic transformer are presented. Through optimizing the temperature and pressure fields, the grown wafer is totally 4H-SiC and no foreign type exists. The FWHM (Full Width at Half Maximum) of the X-ray rocking curve is 23 arcsec, which indicates a high crystalline quality. Moreover, a thick epitaxial layer is then grown on the wafer. The BPD (Basal Plane Dislocation) density of the epitaxial layer is eliminated by converting the BPD to TED (Threading Edge Dislocation) through a proposed doping-induced defect evolution technology. Furthermore, the high voltage SiC MOSFETs with a blocking voltage of over 6.5 kV are fabricated by optimizing the cell and termination structures. The channel region and JFET region are optimized to further improve the device performance. The typical current conducting capability of a single MOSFET is up to 25 A and the breakdown voltage reaches 7.8 kV at a leakage current of 10 μA. The devices are then packaged to form the 6.5 kV/400 A power modules. The current balancing and thermal designs are taken into consideration to improve the reliability of power modules. Finally, the developed SiC modules are applied in a solid state transformer to demonstrate the advantages of SiC devices. The work presented in this article provides an important guide in developing high voltage and high current SiC power devices.