Driven by the markets of electric vehicle (EV), charger, photovoltaic (PV) inverter and power supply, silicon carbide (SiC) power devices have attracted much attention due to the inherent material properties of wide bandgap, high critical electric field, and high thermal conductivity. Edge termination is an indispensable part of SiC power device to relieve electric field crowding and hence improve the breakdown voltage. Edge termination is expected to have the properties of short edge width, high termination efficiency, good surface charge immunity and high dV/dt capability, considering the device cost, fabrication yield and device overall performances. In this thesis, novel edge termination structures are proposed to achieve the aforementioned properties, and the detailed design and ch...[ Read more ]

Driven by the markets of electric vehicle (EV), charger, photovoltaic (PV) inverter and power supply, silicon carbide (SiC) power devices have attracted much attention due to the inherent material properties of wide bandgap, high critical electric field, and high thermal conductivity. Edge termination is an indispensable part of SiC power device to relieve electric field crowding and hence improve the breakdown voltage. Edge termination is expected to have the properties of short edge width, high termination efficiency, good surface charge immunity and high dV/dt capability, considering the device cost, fabrication yield and device overall performances. In this thesis, novel edge termination structures are proposed to achieve the aforementioned properties, and the detailed design and characterization of the structures will also be given.

First, a novel deep trench, U-shaped field plate (DTUFP) edge termination structure is designed and experimentally demonstrated. The structure features a deep trench with a U-shaped field plate, which is fabricated with a PiN diode on a 4H-SiC wafer. Experimental results show that the DTUFP structure achieves a breakdown voltage of 1380 V with an edge width of 33 μm. Compared with the conventional JTE-based edge termination, the edge width of the proposed structure decreases approximately 75%. The termination efficiency is proved to be 100% via LC thermal measurement, lock-in infrared thermography, and high voltage destructive measurement. Furthermore, the fabricated device can handle a high dV/dt of 92 kV/μs at a bus voltage of 1200 V. Second, a new double trench, buried-P JTE (DTBP-JTE) edge termination structure is proposed to reduce the fabrication complexity and improve process compatibility without sacrificing device performances. The fabricated device is experimentally demonstrated to achieve a breakdown voltage of 1416 V with an ultra-short edge with of only 19 μm. The termination efficiency is calculated to be ~95%. In addition, the DTBP-JTE can pass the high dV/dt test of 88 kV/μs at a bus voltage of 1200 V. Third, the effects of the floating buried-P in the DTBP-JTE structure on the device’s dynamic performances are numerically analyzed and experimentally characterized. The measurement results show that the DTBP-JTE can withstand reverse voltage normally after suffering from multiple voltage pulse stress with bus voltage of 1200 V. Furthermore, the DTBPJTE does not fail in the switching transient given that the holes from the P-base at the device onstate are stored in the floating buried-P. The experimental results demonstrate that the floating design of buried-P layers in the edge termination area will not bring adverse effects on the device’s dynamic performance. Finally, a treble trench, buried-P JTE (TTBP-JTE) edge termination structure with improved JTE dose sensitivity compared with the DTBP-JTE is proposed. The simulation results show that the TTBP-JTE has approximately two times wider process window on the JTE dose. Experimental results show that the TTBP-JTE achieves a breakdown voltage of 1436 V with an edge width of 26 μm, while still keeping a comparable termination efficiency and high dV/dt capability.