Hydrogen-silicon carbide power switching devices for extreme environment applications

Most traditional integrated circuit technologies using silicon (Si) devices are not able to operate in extreme environments such as high power, high temperature (above 250°C) and high-radiation. Much attention has been given to Silicon Carbide (SiC), currently the most mature of the wide-bandgap (2.0 eV < EG < 7.0 eV) semiconductors, as a material that is potentially well-suited for many extreme environment operation. Of the over 200 polytypes, 4H-SiC is the most attractive polytype for power devices due to its wide band gap (3.2eV), excellent thermal conductivity (4.9 W/cmK at room temperature), and high critical field strength (2 x 10 6 V/cm). Particularly important for power devices, the 10x increase in critical field strength of SiC allows high voltage blocking layers to be fabricated significantly thinner than for comparable Si devices. For power rectifiers, this reduces device on-resistance, while maintaining the same high voltage blocking capability. This would also increase the radiation hardness of SiC devices.; In this research, both optimization of edge termination structures for 4H-SiC devices and characterization of 4H-SiC devices under high radiation environments were implemented. Chapter 1 presents an introduction on SiC material and devices, including the fundamental material properties, device physics, radiation fundamentals and experimental setup. Chapter 2 reports on 4H-SiC diodes with different edge termination designs that were optimized with respect of breakdown efficiency, area consumption, resistance to interface charge and fabrication practicality. Termination structures simulated were focused on various optimized junction termination extensions (JTE), including single zone JTE, Graded JTE (GJTE), and optimized GJTE.; Chapter 3 and 4 report on studies of Schottky diodes with various HE structures that were fabricated using graded carbon masks with process elements developed at the Alabama Microelectronics Science and Technology Center facility. Simulation results were verified and compared with experimental characterizations of these diodes. After optimizing the fabrication process, these rectifiers exhibited good forward characteristics with blocking voltages in excess of 1000kV for 10 mum drift region thickness and 1 x 1016 cm-3 doping. Yields of working devices for optimized GJTE and GJTE devices are much higher than those of JTE devices. Results suggest that Optimized GJTE has much higher resistance to interface charge and fabrication errors than GJTE and single zone JTE.; Chapter 5 presents results on proton radiation effects on 4H-SiC Junction Barrier Schottky (JBS) switching diodes. Both DC and AC responses of these diodes to proton irradiation were characterized and analyzed. Chapter 6 reports on the effects of proton radiation on 4H-SiC Schottky Barrier Diodes (SBD) compared with that of JBS diodes described in chapter 5. The difference between these two sets of results was analyzed and attributed to p-type SiC process induced defects in JBS diodes. In Chapter 7, gamma radiation and proton radiation effects on 4H-SiC nMOS capacitors were investigated. Interface state changes due to radiation effects were quantified and related to breakdown voltage increases for SiC diodes.; Finally, Chapter 8 presents the conclusions of this work, and makes suggestions for future work.