Edge Termination With Enhanced Field-Limiting Rings Insensitive to Surface Charge for High-Voltage SiC Power Devices

An edge termination structure with enhanced field-limiting rings (enhanced FLRs) is proposed to stabilize the breakdown voltage against the surface charge. The pitches of the enhanced rings are designed to mitigate the electric field and expand the depletion layer, which leads to an improvement of the breakdown voltage. In addition, the enhanced FLR is insensitive to surface charge because the field plates completely cover the n
^-
layer. Simulation results indicated that the enhanced FLR did not have any fluctuation of breakdown voltage against surface charge density from 0 to 1×10
¹³
cm
^-2
, whereas conventional structures did have fluctuation. To examine the validity of the concept, we fabricated a silicon carbide (SiC) merged p-i-n Schottky diode with the proposed structure. DC bias stress tests at 150 °C over 1000 h demonstrated the breakdown voltage stability of the enhanced FLR.