From the beginning, the FREEDM System was built on the premise of using wide bandgap semiconductors. SiC MOSFETs were selected to achieve the necessary performance for the solid state transformer (SST). To further increase SST efficiency, researchers selected GaN devices to operate at medium voltage (600V) and high current (100A) on the secondary side. SiC ETOs and JFETs were also selected and optimized for the fault isolation device to include bidirectional voltage-blocking capability. But more breakthroughs were needed to achieve the FREEDM vision.
The Principal Investigator for this project is Dr. Jay Baliga.
To reduce switching losses in the 10 kV SiC P-i-N fly-back diodes initially used in the SST, Dr. Baliga’s team developed a novel 10 kV SiC Merged-PiN-Schottky (MPS) rectifier able to withstand high operating temperatures with resultant savings in heat sink size and weight. This team also characterized 10kV SiC MOSFET operation at high temperatures.
Dr. Misra’s team fabricated vertical GaN devices to overcome inherent limitations in lateral device structure. This required evaluating a variety of edge termination techniques to support high voltage blocking capability. And to further knowledge of GaN device development, they evaluated high temperature device reliability and stability with various gate dielectric materials.
The 10 kV SiC MPS devices are ready for commercialization. This research also produced advances in edge termination methods. One contribution was the development of a unique multiple-floating-zone junction-termination-extension (MFZ-JTE) edge termination that is highly tolerant to process variations. In addition, researchers proposed and demonstrated a novel orthogonal bevel-edge termination to achieve high-voltage bidirectional blocking capability, the first and only known method for creating bidirectional blocking SiC power devices.
- “A Novel Edge Termination Technique for High Voltage Devices in 4H-SiC – Multiple Floating Zone Junction Termination Extension (MFZ-JTE)”, IEEE Electron Device Letters, Vol. 32, pp. 880-882, 2011.
- “10-kV SiC MPS Diodes for High Temperature Applications, IEEE Int. Symp. On Power Semiconductor Devices and ICs, pp. 43-46, 2016.
- “Performance Improvement of 10-kV 4H-SiC MPS Rectifiers with High Schottky Barrier Height”, Electronic Materials Conference, 2017.
- “Electrical Characteristics of 10-kV 4H-SiC MPS Rectifiers with High Schottky Barrier Height”, Journal of Electronic Materials, Vol. 47, pp. 927-931, 2017.
- “Physics understanding of high temperature behavior of Gallium Nitride power transistor.” Wide Bandgap Power Devices and Applications (WiPDA), 2016 IEEE 4th Workshop on, pp. 324-327. IEEE, 2016.
- “Advanced Power Rectifier Concepts” Springer, 2009.
- “Development of Optimal 4H-SiC Bipolar Power Diodes for High Voltage High-Frequency Applications” Edward Van Brunt PhD Thesis, North Carolina State University, 2013.
- “Explanation of the linear correlation between barrier heights and ideality factors of real metal semiconductor contacts by laterally nonuniform Schottky barriers” J. Vac. Sci. Techno. B 15,(1997), p. 1221.
- “10kV SiC MPS Diodes for High Temperature Applications”, Proceedings of 28th ISPSD, Prague, Czech Republic, 2016.
- “Ultrahigh–Voltage SiC MPS Diodes with Hybrid Unipolar/Bipolar operation”, IEEE Transaction on Electron Devices, pp 99, 2016.
- “Understanding high temperature static and dynamic characteristics of 1.2kV SiC MOSFET”, ECSCRM 2016.